Category Archives: Aircraft

Lockheed-1249-R7V-2-in-flight-no-wing-tanks

Lockheed Model 1249 Turboprop Super Constellation

By William Pearce

In 1938, the Lockheed Corporation in Burbank, California began design work on a large commercial airliner intended to outperform other transports then in service. Initially known as the Model 44 Excalibur, the aircraft’s design changed as feedback provided by Pan American Airways was evaluated. In 1939, Transcontinental and Western Air (TWA) approached Lockheed in search of an aircraft with performance superior to that of the planned Model 44. Lockheed decided to redesign its airliner based on TWA’s requirements, and the new design became the Model 049 Constellation (originally Model 49 and known as Excalibur A).

Lockheed-1249-R7V-2-Super-Constellation

The Lockheed Model 1249 was a turboprop-powered Super Constellation originally ordered by the US Navy as the R7V-2. The aircraft was the fastest of the Constellation series by far, but other turboprop and jet aircraft were favored by all parties.

The Model 049 Constellation was an all-metal, low-wing aircraft with tricycle landing gear. The airliner was powered by four 2,200 hp (1,641 kW) Wright R-3350 engines and carried 60 passengers in its pressurized cabin. The Model 049 had a 123 ft (37.5 m) wingspan and was 95 ft 2 in (29.0 m) long and 23 ft 8 in (7.2 m) tall. The aircraft’s tail had three vertical stabilizers with rudders to keep the aircraft’s overall height down so that it would fit in TWA’s existing hangars. The Model 049 had a top speed of 329 mph (529 km/h) at sea level, a cruising speed of 275 mph (443 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,620 fpm (8.2 m/s), and a range of 2,290 miles (3,685 km) with a maximum payload of 18,400 lb (8,346 kg). The aircraft had an empty weight of 55,345 lb (25,104 kg) and a maximum weight of 86,250 lb (39,122 kg).

In 1940, the design of the Model 049 was mostly finalized, and three airlines had placed orders for a total of 84 aircraft (30 of these were long-range Model 349s). In May 1941, the United States Army Air Corps ordered 180 Model 349s to be used as transports. Lockheed tooled-up for aircraft production, and construction of the first Model 049 was underway when the United States entered World War II after the bombing of Pearl Harbor on 7 December 1941. With the United States at war, production priorities shifted, and all of the aircraft intended for the airlines would be completed as C-69s, the military designation for the Model 049/349.

Lockheed-1249-R7V-2-under-wing

Installation of the Pratt & Whitney T34 turboprop engines onto the Super Constellation airframe was well-executed. The tight-fitting cowling was much smaller than those needed to cover the larger-diameter R-3350 piston engine. The aircraft’s main gear was unchanged, which resulted in an awkward hump under the No. 2 and 3 engines. Note the wide cord of the three-blade propeller.

The C-69 received a low priority compared to Lockheed’s other commitments, and the prototype made its first flight on 9 January 1943. Only 15 C-69s were completed by the end of the war. After the war, Lockheed again focused on the Constellation for airline use, and new orders were received. In May 1945, Lockheed made use of new 2,500 hp (1,864 kW) R-3350 engines and designed the Model 649 and the Model 749, which had increased range. The United States Air Force also used the Model 749 as the C-121A. The Model 749 had a top speed of 358 mph (576 km/h) at 19,200 ft (5,852 m), a cruising speed of 304 mph (489 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,280 fpm (6.5 m/s), and a range of 1,760 miles (2,834 km) with a payload of 16,300 lb (7,394 kg). The aircraft had an empty weight of 58,970 lb (26,748 kg) and a maximum weight of 107,000 lb (48,534 kg).

In late 1949, Lockheed investigated ways to improve the Constellation’s performance and keep the aircraft on the frontline of airline service. The result was the Model 1049 Super Constellation, which had two new fuselage sections added that increased the aircraft’s length by 18 ft 5 in (5.6 m). In addition, 2,700 hp (2,013 kW) R-3350 engines were installed, and the height of the vertical stabilizers was increased by 1 ft 3 in (.38 m). The aircraft could accommodate up to 92 passengers. The Model 1049 was 113 ft 7 in (34.6 m) long, 24 ft 9 in (7.6 m) tall, had a top speed of 338 mph (544 km/h) at sea level, a cruising speed of 302 mph (485 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,100 fpm (5.6 m/s), and a range of 2,880 miles (4,635 km) with a payload of 18,800 lb (8,528 kg). The aircraft had an empty weight of 69,210 lb (31,393 kg) and a maximum weight of 120,000 lb (54,431 kg). The Model 1049 made its first flight on 13 October 1950. The Model 1049B was a military transport version of the Super Constellation, designated R7V-1 (originally R7O-1) for the US Navy and C-121C for the US Air Force.

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The first R7V-2 (BuNo 131630) seen on a test flight without the wingtip fuel tanks. The Constellation-series of aircraft is known as one of the more graceful airframes, and the turboprop engines made the aircraft that much more impressive.

From the start of the Model 1049’s design, Lockheed had envisioned using 3,250 hp (2,424 kW) R-3350 Turbo Compound (TC) engines, which used three power recovery turbines to harness energy from the exhaust and feed it back to the crankshaft via fluid couplings. However, Wright’s development of the engine lagged behind that of the aircraft. The R-3350 TC engines were first incorporated into the Model 1049C, which made its first flight on 17 February 1953. The pinnacle of the Super Constellations was the Model 1049G, powered by 3,400 hp (2,535 kW) R-3350 TC engines. The aircraft made its first flight on 7 December 1954. The Model 1049G had a top speed of 370 mph (595 km/h) at 20,000 (6,096 m), a cruising speed of 310 mph (499 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,165 fpm (5.9 m/s), and a range of 4,165 miles (6,704 km) with a payload of 18,300 lb (8,301 kg). The aircraft had an empty weight of 73,016 lb (33,120 kg) and a maximum weight of 137,500 lb (62,369 kg).

The US Navy had been instrumental in supporting Wright’s development of the turbo compound engine, but in the early 1950s, the turboprop engine was making its way onto the aviation scene. In June 1950, Lockheed considered a turboprop-powered Super Constellation airliner as the Model 1149, but the design did not procced. In November 1951, Lockheed proposed to the Navy a turboprop R7V-1 (Model 1049B) powered by Pratt & Whitney T34 turboprop engines. The Navy was interested, and Lockheed proceeded with design work on the turboprop Super Constellation as the Model 1249. The Navy ultimately amended its R7V-1 order to include two airframes converted to turboprop-power. These aircraft were designated R7V-2 by the Navy and carried the Lockheed serial numbers 4131 and 4132 and the Navy BuNos 131630 and 131631.

Lockheed-1249-R7V-2-no-wing-tanks

Side view of the R7V-2 shows the reinforcements on the rear fuselage above and below the large cargo door, which hinged up. The turboprop aircraft used standard Super Constellation fuselages, and most were reused on piston-powered aircraft once their days of testing were over.

Two additional airframes were ordered in May 1953. They carried the Lockheed serial numbers 4161 and 4162 and Navy BuNos 131660 and 131661. In October 1953, BuNos 131660 and 131661 were slated to be completed as YC-121Fs for the Air Force and were also assigned Air Force serial numbers 53-8157 and 53-8158. The YC-121F was the Lockheed Model 1249A. Since the order originated with the Navy, all four turboprop Super Constellations carried the Navy designation R7V-2, with the last two also assigned the Air Force designation. All four aircraft were purely intended to test the serviceability of the turboprop engine.

The Model 1249 was based on the Model 1049B, with a modified wing and new engines. The R-3350-powered Constellations had the engine nacelle’s centerline mounted below the wing. The Model 1249 had the engine nacelle’s centerline mounted above the wing, and the nacelle extended back to the wing’s trailing edge. Exhaust from the turboprop engine was expelled from the back of the nacelle and generated thrust. The Model 1249 could also accommodate removable 600 US gallon (500 Imp gal / 2,271 L) wingtip tanks that were first installed on Navy Super Constellations and later used by airlines. Additional fuselage fuel tanks were fitted, and the landing gear was strengthened.

Lockheed-1249-YC-121F-131660-over-Pacific-Palisades

The first YC-121F, still with Navy BuNo 131660 painted on the tail, seen on a test flight over Pacific Palisades, just north of Santa Monica, California. Note the large, removable wingtip fuel tanks.

The T34 turboprop was an axial-flow engine that consisted of a 13-stage compressor powered by a three-stage turbine. Sources indicate that the R7V-2s for the Navy used T34-P-12 engines, while the YC-121Fs for the Air Force used T34-P-6 engines. The T34-P-12 produced 5,005 shp (3,732 kW) and 1,360 lbf (6.05 kN) of thrust, for a total of 5,550 eshp (4,139 kW) at 11,000 rpm for takeoff power. Continuous power for the T34-P-12 was 4,210 shp (3,139 kW) and 1,165 lbf (5.18 kN) of thrust, for a total of 4,675 eshp (3,486 kW) at 10,500 rpm.

The T34-P-6 produced 5,500 shp (4,101 kW) and 1,250 lbf (5.56 kN) of thrust, for a total of 6,000 eshp (4,474 kW) at 11,000 rpm for takeoff power. Continuous power for the T34-P-6 was 4,750 shp (3,542 kW) and 1,125 lbf (5.57 kN) of thrust, for a total of 5,200 eshp (3,878 kW) at 10,750 rpm. Each engine turned a three-blade Hamilton Standard A-3470 propeller at .0909 engine speed. The propeller was 15 ft in (4.57 m) diameter, and each blade was 24 in (610 mm) wide.

The Model 1249 had a 117 ft (35.7 m) wingspan without wingtip fuel tanks and a 119 ft (36.3 m) wingspan with wingtip fuel tanks. The aircraft was 116 ft 2 in (35.4 m) long and 25 ft 6 in tall (7.8 m). The Model 1249 had a top speed of 444 mph (715 km/h) at 15,000 ft (4,572 m) and could maintain 420 mph (676 km/h) at 25,000 ft (7,620 m). The aircraft had an initial climb rate of 4,600 fpm (23.4 m/s) at maximum power and 2,310 fpm (11.7 m/s) at normal power. The Model 1249’s ceiling was 32,900 ft (10,028 m) at maximum power and 26,400 ft (8,047 m) at normal power. The aircraft’s range was 2,230 miles (3,589 km) with a payload of 24,210 lb (10,981 kg), and it had an empty weight of 72,387 lb (32,834 kg) and a maximum weight of 148,540 lb (67,377 kg). The Model 1249 could accommodate 106 passengers and four crew members for short flights, 87 passengers and 15 crew members for long flights, or 35,500 lb (16,103 kg) of cargo. For medical evacuations, the aircraft could accommodate 73 litters, four attendants, and four crew members.

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The second YC-121F, Air Force serial number 53-8158, seen with flaps and gear extended. Note the exhaust outlet at the rear of the engine nacelles.

The Model 1249 / R7V-2, BuNo 131630, made its first flight on 1 September 1954. The aircraft was not initially fitted with the wingtip tanks, and it was accepted by the Navy on 10 September 1954. The second R7V-2 soon followed and was accepted by the Navy on 30 November 1954. The Navy put the R7V-2 aircraft through various tests. A top speed of 479 mph (771 km/h) was achieved in a slight dive, and the aircraft took off overweight at 166,400 lb (75,478 kg). However, the R7V-2’s career was short. In December 1956, and with just 109 total hours, BuNo 131630 was put into storage at Naval Air Station (NAS) Litchfield Park in Arizona. The aircraft was struck off charge in April 1959 and provided spare parts for other Constellations.

In late 1956, BuNo 131631 was loaned back to Lockheed as an engine testbed for the L-188 Electra airliner and later the P-3 Orion maritime patrol aircraft. At the time, BuNo 131631 had accumulated 120 hours of operation. Rohr Aircraft in Chula Vista, California removed the T34 engines and replaced them with Allison 501-D (T56) engines in new nacelles intended for the Electra. The 501-D produced 3,460 shp (2,580 kW) and 726 lbf (3.23 kN) of thrust, for a total of 3,750 eshp (2,796 kW) for takeoff power. The engines turned four-blade Aeroproducts 606 propellers that were 13 ft 6 in (4.11 m) in diameter. The modified aircraft was nicknamed ‘Elation,’ a combination of Electra and Constellation. Elation made its first flight in July 1957 and was used until July 1959 when it was damaged at Palmdale, California. With 882 hours, BuNo 131631 was delivered to NAS Litchfield Park. In May 1960, the aircraft was sold to California Airmotive. The fuselage and some other parts were used to rebuild 1049G Super Constellation N7121C, and the remainder was scrapped. N7121C went through various air cargo owners until it was scrapped in March 1968.

Lockheed-1249-131631-4132-Elation

Lockheed serial 4132, the second R7V-2 (BuNo 131631), fitted with Allison 501-D engines to test their installation for the L-1888 Electra. Known as the Elation, the aircraft flew more with the Allisons than it did with its original Pratt & Whitney engines. Note the four-blade propellers.

The Model 1249A / YC-121F, serial no 53-8157, made its first flight on 5 April 1955 and was accepted by the Air Force in July. The second aircraft, serial number 53-8158, took to the air in August 1955. Both YC-121Fs were assigned to the 1700th Test Squadron of the Military Air Transport Service, based at Kelly Air Force Base in San Antonio, Texas. In April 1956, a YC-121F set a point-to-point speed record, traveling the 1,445 miles (2,326 km) between Kelly, Texas and Andrews Air Force Base, Maryland in 2 hours 53 minutes, an average of 501.16 mph (806.54 km/h). Between 25 and 26 January 1957, another record was set flying from Long Beach, California to Andrews Air Force Base, Maryland. The 2,340-mile (3,766-km) route was covered in 4 hours 43 minutes at an average speed of 496.11 mph (798.41 km/h). Both record flights were most likely made by 53-8157.

In June 1957, 53-8158 was assigned to McClellan Air Force Base in Sacramento, California; 53-8157 followed a year later. In February 1959, the two YC-121Fs were placed in storage at Davis Montham Air Force Base in Tucson, Arizona. Both aircraft were sold to the Flying Tiger Line 1963. The fuselages of the two YC-121Fs were used with wings, engines, and tails from two 1049Gs and pressed into cargo transport service in 1963. In 1966, both aircraft were sold to North Slope Aviation Company in Alaska. Serial number 53-8158 (N174W) was written off in May 1970. Serial number 53-8157 (N173W) was sold to Aviation Specialties and written off in June 1973.

Along with the military versions, Lockheed had designed a turboprop Super Constellation airliner in 1952 designated as the Model 1249B. The aircraft was planned to have a maximum speed of 451 mph (726 km/h) and a maximum range of 4,125 miles (6,639 km). However, the 1249B was not pursued, and the L-188 Electra eventually took its place.

Lockheed-1249-Super-Constellation-ad

An ad for the turboprop Super Constellation as Lockheed made a light push to interest airlines in the concept. There were no takers, and Lockheed developed the L-188 Electra instead.

Sources:
The Lockheed Constellation by Peter J. Marson (2007)
Lockheed Constellation by Curtiss K. Stringfellow and Peter M. Bowers (1992)
Lockheed Aircraft since 1913 by René J. Francillon (1987)
Lockheed C-121 Constellation by Steve Ginter (1983)
Characteristics Summary YC-121F by US Air Force (1 April 1957)
Lockheed Constellation by Dominique Breffort (2006)
https://www.thisdayinaviation.com/tag/lockheed-yc-121f/
http://www.conniesurvivors.com/1-QandA.htm

Blackburn-B20-front-water

Blackburn B-20 Experimental Flying Boat

By William Pearce

On 13 February 1935, John Douglas Rennie submitted a patent application for “Improvements in and relating to Seaplanes.” Rennie was the Chief Seaplane Designer for the Blackburn Aeroplane and Motor Company, which was renamed in 1936 as Blackburn Aircraft Ltd. Rennie’s design idea was for the lower portion of the flying boat’s hull to be sealed and extend for takeoff and landing. The extendable hull would essentially act as the aircraft’s main float.

Blackburn-B20-left-front-beached

An excellent view of the Blackburn B-20 highlighting the aircraft’s extended hull, retracted wingtip floats, and well-engineered cowlings for the Vulture engine.

In order to provide clearance for the propellers, traditional flying boats have some combination of a parasol or strut-mounted wing positioned above the fuselage, a gull wing, and a tall hull. In addition, the hull and wing are designed for the essential task of lifting the aircraft from the water, but they are far from optimized for cruise flight. All of these compromises add significant drag to the aircraft. With Rennie’s hydraulically-operated extendable hull, the flying boat’s cross section with the hull retracted was much more like that of a conventional aircraft, and drag was significantly reduced. In addition, when the hull was extended, the aircraft assumed the ideal angle for takeoff and landing, which allowed the aircraft’s wing to have an angle of incidence optimized for cruise flight when the hull was retracted. Rennie’s patent also included retractable wingtip floats.

Rennie was granted Great Britain patent 433,925 on 22 August 1935. In 1936 the British Air Ministry issued Specification R.1/36 for a small, general purpose flying boat capable of cruising at 230 mph (370 km/h). Rennie and Blackburn responded with a twin-engine flying boat that featured a retractable hull. Blackburn’s design carried the company designation B-20. The Air Ministry ordered the Saunders-Roe A.36 Lerwick for Specification R.1/36, but they were sufficiently intrigued by the Blackburn B-20 to order a prototype, which was later assigned serial number V8914.

Technically, the B-20 was more of a floatplane with a retractable center main float than a flying boat. However, when the float was retracted, the aircraft took on the appearance and configuration of a flying boat. The B-20 had a high wing and was of all-metal, stressed-skin construction. All of the control surfaces were fabric covered. With the exception of the extending hull, the aircraft had a conventional layout. The B-20 had a standard crew of six. The fuselage housed a bombardier’s compartment in the nose. The fight deck was located well forward of the wing attachment and provided the pilot and copilot a good view. Behind and slightly below the cockpit was the flight engineer, navigator, and observer’s compartment. Under the wing was a wardroom with sleeping accommodations for two, followed by the crew’s quarters with accommodations for four, a galley, and a lavatory.

Blackburn-B20-left-side-beached

This side view of the B-20 illustrates how the hull moved forward as it was extended. The rear member of each of the four hull mounts was a hydraulic cylinder that actuated the extension and retraction of the hull.

The one-piece wing had three main spars, a straight leading edge, and a tapered trailing edge. Mounted in a nicely streamlined nacelle on each wing was a Rolls-Royce Vulture II X-24 engine capable of 1,800 hp (1,342 kW) for takeoff. The engine had an international rating of 1,780 hp (1,327 kW) at 4,000 ft (1,219 m) and 1,660 hp (1,237 kW) at 13,500 ft (4,115 m). A scoop under the engine nacelle housed the engine’s coolant radiator and oil cooler. Each engine turned a three-blade, constant-speed, de Havilland propeller. Unlike the patent design, which featured wing floats that retracted into the engine nacelles, the wing floats of the B-20 retracted outward to be flush with the wing and form the wingtip.

The extendable hull had five watertight compartments. The center compartment housed four fuel tanks with a total capacity of 1,172 US gallons (976 Imp gal / 4,437 L). The hull also housed most of the mooring equipment. Four hydraulic cylinders mounted in the fuselage controlled the extension and retraction of the 48 ft 9 in (14.86 m) hull. The hydraulic cylinders extended the hull approximately 5 ft 8.25 in (1.73 m) down from the fuselage for operating on the water’s surface. Forward of each hydraulic cylinder was a hinged triangular frame mounted to one point on the fuselage and two points on the hull. As the hull extended down, it also traversed forward. This movement of the hull gave the aircraft the proper angle for landing and taking off. Entry to the fuselage was achieved with the hull extended. Hatches under the fuselage led to the bombardier’s station, the wardroom, and the galley. A ladder that hinged down from the hatch under the bombardier’s station was the main access point.

Although the prototype was unarmed, the B-20’s planned armament consisted of two .303 machine guns in the nose, a dorsal turret with two .303 machine guns, and a tail turret with four .303 machine guns. In each wing, two compartments between the engine nacelle and the fuselage could each house a 500 lb (227 kg) bomb or two 250 lb (113 kg) bombs.

Blackburn-B20-front-water

The B-20 on the water looked a little ungainly with its hull extended. Note the access ladder between the hull and the fuselage.

The Blackburn B-20 had a wingspan of 82 ft 2 in (25.04 m) with the floats retracted and 76 ft (23.16 m) with the floats extended. The aircraft was 69 ft 7.5 in (21.22 m) long, and was 25 ft 2 in (7.67 m) tall on its beaching gear with the hull extended. Without the turrets, the B-20 had a top speed of 322 mph (518 km/h) at 15,000 ft (4,572 m), 302 mph (486 km/h) at 5,750 ft (1,753 m), and 280 mph (451 km/h) at sea level. With the proposed turrets, the aircraft’s performance fell to a maximum speed of 306 mph (492 km/h) at 15,000 ft (4,572 m), 288 mph (464 km/h) at 5,750 ft (1,753 m), and 268 mph (431 km/h) at sea level. Cruising speed was 200 mph (322 km/h), and the B-20’s range was 1,500 miles (2,414 km). The aircraft had a normal weight of 35,000 lb (15,876 kg).

The B-20 was completed at Blackburn’s factory in Dumbarton, Scotland, near the River Clyde. The aircraft made its first flight on 27 March 1940, piloted by Blackburn’s test pilot Harry Bailey. Another four or five flights were made with some aileron trouble, but otherwise there were no issues. The extending hull worked well, although its extension and retraction in flight were not entirely smooth. Once extended, the hull offered an open platform from which to conduct mooring operations, and the aircraft was well-behaved on the water.

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The B-20 providing a good view of the wing float design. Note the Short Sunderland and what appears to be a Short Empire framed nicely between the B-20’s hull and fuselage.

On 7 April 1940, Bailey was joined by Blackburn test engineer Fred Weeks, Blackburn aircraft riggers Sam McMillan and Duncan Roberts, and Rolls Royce flight engineer Ivan Waller. The task of the day was to complete high-speed tests in the B-20. During the fight, the aircraft reached an unofficial speed of 345 mph (555 km/h). On the next run, an aileron experienced flutter and failed, sending the B-20 out of control. The aircraft crashed in the Firth of Clyde off Garroch Head. Weeks and Waller were able to successful bail out and were picked up by the HMS Transylvania, a merchant ship converted to an auxiliary cruiser. Bailey also bailed out but was too low for his parachute to fully open. His body was recovered from the sea. However, the bodies of McMillan and Roberts were never found.

Even though its flight career was very short, the B-20 had given every indication that its hull design significantly improved performance. Based on the B-20 design, the Blackburn B-40 and B-44 were proposed. The B-40 was in response to Specification R.13/40. The aircraft was a twin-engine flying boat transport powered by two Bristol Centaurus radial engines and intended as a possible replacement for the Short Sunderland. The B-40 was larger and heavier than the B-20 and had twice the range. Two B-40 prototypes were ordered on 9 September 1941, but the aircraft’s poor single engine performance and other priorities led to its cancellation on 6 January 1942. The B-44 was a single-engine floatplane fighter designed to Specification N.2/43. The aircraft was armed with four 20 mm cannons and powered by a Napier Sabre H-24 engine turning contra-rotating propellers. Two B-44 prototypes were ordered in October 1942, but the project was cancelled shortly after a mockup was built. An analysis of the design indicated that the B-44 would be difficult to handle on the water.

In August 1998, one of the B-20’s Vulture engines was recovered after becoming tangled in the nets of a trawler. The B-20’s crash site was subsequently classified as a war grave. What remains of the Vulture engine is now on display at the Dumfries and Galloway Aviation Museum in Scotland.

Blackburn-B20-rear-water

Rear view of the B-20 helps visualize the defense the four .303 machine guns in the turret would have provided.

Sources:
Aircraft of the Fighting Powers Volume 6 by Owen Theyford (1945/1980)
Blackburn Aircraft since 1909 by A. J. Jackson (1989)
British Experimental Combat Aircraft of World War II by Tony Buttler (2012)
British Prototype Aircraft by Ray Sturtivant (1990)
Jane’s All the World’s Aircraft 1945/46 By Leonard Bridgman (1946)
– “Improvements in and relating to Seaplanes” GB patent 433,925 by John Douglas Rennie (applied 13 February 1935).
https://aviation-safety.net/wikibase/204426
http://helensburgh-heritage.co.uk/index.php/heritage/military/1608-three-died-in-prototype-crash

Hawker-Tornado-P5224-front

Hawker Tornado Fighter

By William Pearce

In early 1937, Hawker Aircraft Limited and the company’s chief designer, Sydney Camm, began to consider the next generation of fighter aircraft for the Royal Air Force. The British Air Ministry was also considering the future of fighter airframes as well as the incorporation of powerful, new engines under development—specifically the Napier Sabre H-24, the Rolls-Royce Vulture X-24, and the Bristol Centaurus 18-cylinder radial.

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The first Hawker Tornado prototype P5219 in its original form with the belly radiator. The Vulture’s two rows of exhaust stacks are evident. The aircraft’s resemblance to the Hurricane is apparent.

In July 1937, Hawker proposed two Camm-designed aircraft—the N-type and the R-type, named for their respective Napier and Rolls-Royce powerplants. The Air Ministry told Hawker to wait until an official request was issued, which came in March 1938 in the form of Specification F.18/37 seeking a fighter capable of 400 mph (644 km/h) at 20,000 ft (6,096 m). Hawker was notified in August 1938 that they had won the design contest for Specification F.18/37, and two prototypes of each N-type and R-type were ordered. However, an official contract was not issued until December 1938. The N-type went on to become the Sabre-powered Hawker Typhoon, while the R-type became the Vulture-powered Hawker Tornado. The two Tornado prototypes were assigned serial numbers P5219 and P5224.

The Tornado was a single-engine fighter of all-metal construction with a conventional taildragger layout. The aircraft somewhat resembled an enlarged Hawker Hurricane. From the engine to just behind the cockpit, the fuselage consisted of a tubular frame covered with aluminum panels. The rear fuselage and tail were of monocoque construction. The pilot sat in an enclosed cockpit that was accessible via side entry doors. A fairing extended behind the cockpit and limited the pilot’s rearward vision.

The Tornado’s wing was mounted to the tubular frame of the center fuselage. Because of the Vulture’s installation, the wing was mounted to the fuselage about 3 in (76 mm) lower than on the Typhoon. The wing had two main spars and consisted of an inner and outer section. The inner section had a 1.0-degree anhedral and housed the inward-retracting main landing gear. The landing gear had a wide track of 13 ft 8 in (4.17 m). A 48 US gal (40 Imp gal / 182 L) fuel tank was located in each wing between the main gear leg well and the rear spar, and a 42 US gal (35 Imp gal / 159 L) fuel tank was located in the leading edge of each inner wing section. The Tornado’s total fuel capacity was 180 US gal (150 Imp gal / 682 L). Each outer wing section had a 5.5-degree dihedral and housed six Browning .303 machine guns with 500 rpg. The thick wing was originally designed for the possible installation of six 20 mm cannons, but this configuration was never tried. Each wing had a two-section, hydraulically actuated split flap and featured a large aileron. Except for the fabric-covered rudder, all control surfaces were covered with metal.

Hawker-Tornado-P5219-rear

Another shot of the newly completed P5219 displays the aircraft’s original short tail. Note the opaque fairing behind the cockpit that blocked the pilot’s vision.

The Tornado’s Rolls-Royce Vulture II engine had 24 cylinders arranged in an X configuration. The engine was mounted to the forward part of the tubular fuselage frame and produced 1,760 hp (1,312 kW). Two rows of exhaust stacks protruded from each side of the engine’s cowling. A belly scoop between the main gear wells housed the engine’s coolant radiator and oil cooler. A door in the aft section of the scoop regulated temperatures. Two intakes between the belly scoop and the underside of the fuselage fed air to the engine’s carburetor. The engine turned a three-blade, constant-speed Rotol propeller that was 14 ft (4.27 m) in diameter.

The Hawker Tornado had a wingspan of 41 ft 11 in (12.78 m), a length of 32 ft 10 in (10.01 m), and a height of 14 ft 8 in (4.47 m). The aircraft had a top speed of 398 mph (641 km/h) at 23,000 ft (7,010 m) and stalling speeds of 82 mph (132 km/h) clean and 61 mph (98 km/h) with flaps and gear extended. The Tornado had an empty weight of 8,377 lb (3,800 kg) and a loaded weight of 10,668 lb (4,839 kg). The aircraft’s initial rate of climb was around 3,500 fpm (17.8 m/s), and its ceiling was 34,900 ft (10,638 m).

Hawker-Tornado-P5224-front

The second Tornado prototype P5224 with the chin radiator and windows behind the pilot to help improve vision. The aircraft now resembles a Typhoon, with which it shared many components.

The Tornado prototype P5219 was built at the experimental shop in Hawker’s Canbury Park Road facility in Kingston, but it was sent to Hawker’s new facility in Langley for final assembly in July 1939. The Vulture II engine was delivered in September 1939, and ground tests were started later that month. Piloted by Philip Lucas, P5219 made its first flight on 6 October 1939. During the preliminary flight tests in October and November, the aircraft achieved a speed of 370 mph (595 km/h) at 15,000 ft (4,572 m). However, the Tornado’s tail was lacking in surface area, and the rudder did not have sufficient authority to hold a straight course during takeoff and proved ineffective at speeds under 150 mph (241 km/h). Engine cooling was a constant issue, especially during ground operations. While in flight at higher speeds, turbulence from the wings disrupted airflow into the radiator, which impaired engine cooling. A new radiator was designed that would relocate the cooling system from its ventral position to a chin location under the engine. Metal was also found in the engine oil, indicating a possible issue with the Vulture’s bearings.

While the Vulture engine was undergoing maintenance, the Tornado airframe was modified with the new chin radiator and oil cooler, which shifted the aircraft’s appearance away from that of the Hurricane. In November 1939, an order for Hawker to produce 1,000 Tornados was placed. The contract was later changed to Typhoons, but then amended for 800 Typhoons and 200 Tornados, with the Tornados to be built by Avro due to Hawker’s production commitments of other aircraft, namely the Hurricane. Other Tornado production contracts were later issued, including 200 aircraft to be built by Cuncliffe-Owen and another 760 aircraft to be built by Avro. The revised Tornado took to the air on 6 December 1939, but Lucas reported that the aircraft was even more directionally unstable with the chin radiator. Performance tests in March 1940 indicated a top speed of 384 mph (618 km/h) at 20,500 ft (6,248 m), but the engine was not making full power. Various modifications were made to improve the aircraft’s stability. The exit of the radiator was extended 3 in (76 mm); the vertical stabilizer and rudder were enlarged in May 1940; and tailwheel doors were added in June 1940.

Hawker-Tornado-P5224-in-flight

P5224 in flight displaying the aircraft’s aggressive appearance and enlarged tail. Note the carburetor intake atop the engine cowling.

With stability improved, P5219 was sent to Rolls-Royce’s flight-testing facility at Hucknall to improve the engine’s performance. The aircraft was returned to Langley in mid-July 1940 with a new engine and a new Rotol propeller that was 13 ft 2.5 in (4.02 m) in diameter. Performance flight testing continued, and on 27 July, the Tornado climbed to 20,000 ft (6,096 m) in 6 minutes and 36 seconds and achieved a speed of 396.5 mph (638.1 km/h) at 20,800 ft (6,340 m). On 31 July, the Vulture engine failed in flight, and the aircraft was damaged in the subsequent forced landing.

While P5219 was being repaired, the second Tornado prototype, P5224, was flown on 7 December 1940. Construction of the second prototype was delayed by other priority war work. P5224 was built from the start with the chin radiator and an enlarged tail. The aircraft also had the carburetor intake atop the engine cowling, inner gear doors to completely enclose the main gear, and side windows behind the cockpit to improve the pilot’s vision (which was still restricted). However, engine cooling was still an issue, as were excessive vibrations with the Vulture engine.

The repaired P5219 returned to active flight testing with a 1,980 hp (1,476 kW) Vulture V engine installed by March 1941, but the future of the Vulture engine was in doubt. P5224 suffered an engine failure on 21 March 1941, and its Vulture II was subsequently replaced by a Vulture V. P5224 first flew with the Vulture V on 11 June 1941. Around June 1941, Avro was instructed to halt work on producing the Tornado fighter, and the Tornado contracts were cancelled. The Vulture engine was stalled by Rolls-Royce so they could focus on the Merlin, and the Vulture was officially cancelled in October 1941. The Sabre-powered Typhoon fighter would be produced and take over resources previously allocated to the Tornado.

Hawker-Tornado-CR-props

The first and only production Tornado, R7936, was used as a propeller testbed after its initial flight testing. The aircraft is seen here with Rotol contra-rotating propellers, which had a smaller diameter than the standard, single-rotation propellers used on the Tornado and Typhoon. Note that the aircraft did not have the windows behind the pilot like the second prototype.

P5219 continued flight testing with Hawker until at least April 1943, and the aircraft was scrapped in August 1943. P5224 was tested by the Aeroplane & Armament Experimental Establishment at Boscombe Down starting in October 1941. The aircraft was then delivered to the Royal Aircraft Establishment at Farnborough in December 1941. P5224 was scrapped in late 1944.

After the Tornado contracts were cancelled, construction of the first production Tornado, serial number R7936, was allowed to continue as well as components for two other examples that were nearing completion. R7936 was powered by a Vulture V engine and made its first flight on 29 August 1941, piloted by Lucas. In general, pilots that flew R7936 were impressed by its handling and performance. The aircraft recorded a speed of 402 mph (647 km) at 21,800 ft (6,645 m) and climbed to 20,000 ft (6,096 m) in 6 minutes and 54 seconds. With the Tornado program dead, R7936 was used as a testbed for Rotol and de Havilland contra-rotating propellers. Little information has been found on these tests, but the aircraft was delivered to Rolls-Royce in March 1942 for the installation of a Vulture engine with a contra-rotating gear reduction. The six-blade Rotol contra-rotating propeller was 11 ft (3.35 m) in diameter, and the aircraft was flown with the unit in September 1942. The de Havilland contra-rotating propellers were installed as early as December 1942. It appears R7936 continued with propeller tests until April 1944, when it was scrapped.

Hawker-Tempest-HG641-side-org

Typhoon HG641 was built to serve as a testbed for the Bristol Centaurus engine. Seen here with its original three-blade propeller, cowling, and single large exhaust manifold. The silhouette of the oil cooler can just be seen between the main landing gear.

From the first discussion with the Air Ministry before Specification F.18/37 was issued, Camm and Hawker had given some consideration to a Centaurus-powered Tornado, but little progress was undertaken beyond the preliminary design. With the Vulture and Sabre engines running into development issues by late 1940, more-serious consideration was given to installing a 2,210 hp (1,678 kW) Centaurus engine in a Tornado airframe. In September 1940, Hawker was given permission to proceed with the Centaurus-powered Tornado prototype, but the official contract was not issued until February 1941. Some work was also done on using a Wright R-3350 engine, but this design was dropped in June 1941.

The Centaurus Tornado was assigned serial number HG641. The aircraft was built by Hawker at Langley using components from uncompleted Tornado production airframes and a new center fuselage. The Centaurus engine turned a 12 ft 9 in (3.89 m) diameter, three-blade, Rotol propeller and was covered by a conventional cowling. Exhaust from the engine was expelled via a single manifold protruding from the cowling under the left side of the engine. An oil cooler was mounted between the wells for the main landing gear. The air-cooled radial reduced the aircraft’s weight by about 350 lb (159 kg). Lucas took the Centaurus Tornado up for its first flight on 23 October 1941.

Hawker-Tempest-HG641-side-mod

HG641 with the new four-blade propeller and revised cowling. The oil cooler was located in the large duct under the engine.

Initial flight tests of HG641 indicated that airflow through the oil cooler was not efficient and led to the engine running near its upper temperature limit. Even so, a speed of 378 mph (608 km/h) was recorded at 20,000 ft (6,096 m). The oil cooler was modified, and testing continued until December 1941. At that time, the aircraft was modified to improve the installation of the engine package, including exhaust and oil cooler. The cowling was revised, and a new oil cooler duct was faired into the lower cowling. Two exhaust stacks were incorporated into the left and right sides of the fairing. A four-blade propeller, also 12 ft 9 in (3.89 m) diameter, was installed, and the modified Centaurus Tornado took its first flight on 23 December 1942, piloted by Lucas. Cooling was improved, and the aircraft achieved 403 mph (649 km/h) at 22,000 ft (6,706 m) and had a ceiling of 32,800 ft (9,997 m). In February 1943, the aircraft was transferred to Bristol’s facility in Filton, where a speed of 412 mph (663 km/h) at 18,000 ft (5,486 m) was reportedly recorded. The Centaurus Tornado continued engine testing until August 1944, when the aircraft was scrapped.

The testing of Tornado aircraft provided information for developing the Typhoon fighter, contra-rotating propellers, and the Bristol Centaurus engine, which was particularly helpful when applied to the Centaurus-powered Hawker Tempest II fighter. Although the Tornado has been mostly forgotten, both the Typhoon and the Tempest served with distinction during World War II.

Hawker-Tempest-HG641-rear-mod

Side view of HG641 with the new cowling. The aircraft did not have the windows behind the pilot and used hinged doors on the landing gear to completely conceal the main wheels. This was also tried on the prototypes before switching to a separate inner door.

Sources:
The Hawker Typhoon and Tempest by Francis K. Mason (1988)
Hawker Typhoon, Tempest and Sea Fury by Kev Darling (2003)
British Experimental Combat Aircraft of World War II by Tony Buttler (2012)
Fighters Volume Two by William Green (1964)
Hawker Typhoon and Tempest: A Formidable Pair by Philip Birtles (2018)
Aircraft of the Fighting Powers Volume V by H. J. Cooper and O. G. Thetford (1944)
The Secret Years: Flight Testing at Boscombe Down 1939 – 1945 by Tim Mason (1998)
Hawker Aircraft since 1920 by Francis K. Mason (1991)

Beardmore-Inflexible-nose

Beardmore Inflexible / Rohrbach Ro VI Transport

By William Pearce

In 1914, Adolf Karl Rohrbach started working for Luftschiffbau Zeppelin GmbH as the company began to diversify from airship construction into building heavier-than-air aircraft. Claude Dornier was also employed by Zeppelin and was tasked with designing airframes out of metal, rather than wood. Rohrbach worked with Dornier on the design of several aircraft before Rohrbach was reassigned in 1917 to the Zeppelin plant in Staaken, near Berlin, Germany. At Staaken, Rohrbach worked with Alexander Baumann and was involved in the design of large R-Plane (Riesenflugzeuge, or giant aircraft) bombers.

Beardmore-Inflexible-rear

The duralumin fuselage skin of the Beardmore Inflexible exhibited significant wrinkling. The staining above the wings was caused by engine exhaust and oil. Note the cable running from the wing to the lower fuselage.

Immediately following World War I, Rohrbach designed the Zeppelin-Staaken E.4/20. Like Dornier and Hugo Junkers, Rohrbach was pioneering the construction of aircraft using metal and stressed skin. The E.4/20 was an all-metal, four-engine airliner that made its first flight on 30 September 1920. However, the Treaty of Versailles prevented Germany’s possession of large aircraft, and the E.4/20 was scrapped in 1922. That same year, Rohrbach founded Rohrbach Metall-Flugzeugbau GmbH (Rohrbach Metal Aircraft, Ltd) in Berlin. To work around the Treaty of Versailles, aircraft designed at Rohrbach in Berlin were built at an assembly plant in Copenhagen, Denmark or licensed to be constructed elsewhere.

Following World War I, the British Air Ministry became increasingly interested in all-metal aircraft. In 1923, the Air Ministry issued specification No. 18/23 for a large, all-metal, experimental transport, and order No. 445337/23 was awarded to William Beardmore & Company, Ltd in Dalmuir, Scotland for the construction of such an aircraft. At the time, Beardmore was involved in building ships, locomotives, aircraft engines, and airships. In addition, the company had built aircraft under license during World War I. Beardmore was to collaborate with Rohrbach on the design of the transport aircraft. Beardmore outlined the aircraft’s basic specifications, Rohrbach supplied some of the detailed drawings, and Beardmore built the transport. The aircraft was known as the Beardmore AV 1 Inflexible, or the Rohrbach Ro VI, or the BeRo 1—a combination of Beardmore and Rohrbach. Most commonly, the aircraft is referred to as the Beardmore Inflexible. It was not until 1924 that Beardmore obtained the license from Rohrbach and construction of the aircraft began.

Beardmore-Inflexible-top

The Inflexible at Martlesham Heath. In the lower right of the image are the wheel trollies used to move the aircraft sideways into the hangar.

At Beardmore, the design of the Inflexible was initially laid out and modified by William. S. Shackleton. The project was later taken over by Rollo A. de Haga Haig. The aircraft’s design was tested in the Royal Aircraft Establishment’s wind tunnel at Farnborough. Except for its size, the aircraft possessed a fairly conventional layout. The monoplane trimotor had shoulder-mounted wings and taildragger landing gear. One engine was mounted in the nose, and an engine was mounted on each wing. Each engine was a water-cooled Rolls-Royce Condor II that produced 650 hp (485 kW) and turned a wooden, fixed-pitch, two-blade propeller. The radiator for the nose-mounted engine was directly below the fuselage, and the radiator for each wing-mounted engine was located under the wing between the engine nacelle and the fuselage. The two-place, side-by-side, open cockpit was positioned just forward of where the wings mounted to the fuselage. Below the cockpit on the left side of the fuselage was a small propeller for a wind-driven pump. The pump supplied oil to a servo system that boosted movement of the ailerons and elevator.

Beardmore-Inflexible-nose

The group posing in front of the Inflexible gives scale to the aircraft’s immense size. The radiator for the fuselage-mounted engine can be seen under the nose. Exhaust manifolds carried the gasses from the center engine away from the cockpit. Just under the cockpit is the windmill for the servo system pump.

The Inflexible was made of duralumin, an aluminum alloy that incorporates copper, manganese, and magnesium for increased strength. The fuselage had a rectangular cross section and consisted of front and rear sections that were bolted together. Both sections were made of duralumin sheets riveted to a duralumin frame. Mounted to the rear of the fuselage were the horizontal and vertical stabilizers. The elevator spanned the entire length of the horizontal stabilizer. A Flettner servo tab trailed behind the rudder and controlled its movement.

The wings were formed by a wing box that bolted to the fuselage and made up the center wing section. An outer wing section bolted to each side of the wing box and was supported by two spars. Like the fuselage, the wing was covered with sheets of duralumin. A cable that kept each wing in tension while in flight connected the rear spar, at about two-thirds the span of the wing, to the lower fuselage. This cable was tensioned to about 3,000 lb (1,361 kg). The wings had a six-degree dihedral. Sections of the leading and trailing edges of the wings were hinged for access and inspection of the inner wing. The aircraft’s 656 US gal (546 Imp gal / 2,482 L) of fuel was carried in four wing tanks. The Inflexible did not have any flaps, but its large ailerons spanned the outer half of each wing’s trailing edge. Extending from each of the aircraft’s control surfaces was an aerodynamic balance horn.

The Inflexible was on hand at the Royal Air Force Display at Hendon in late June 1928. The aircraft now has “9” painted on the fuselage. In a size comparison, the Inflexible was displayed with a de Havilland DH.71 Tiger Moth (far left). The Tiger Moth’s 22 ft 6 in (6.59 m) wingspan was about one-eighth that of the Inflexible.

The aircraft’s immense weight was supported by two large main wheels and a steerable tailwheel. During component testing, wire wheels collapsed under the expected weight of the Inflexible. New wheels were designed and made from steel and aluminum. Mounted to the wheels were 90-in (2.29-m) tall tires, specially developed by the Dunlop Rubber Company. The weight of the large tires increased by 70 lb (32 kg) when they were filled with air. Each main wheel was supported by a shock-absorbing strut that extended from just inside the engine nacelle. An A-frame mounted to the lower fuselage secured each main wheel. The main gear had a track of 25 ft 7 in (7.80 m). For landing, the main wheels had a hydraulic braking system that could be automatically applied when the tail wheel connected with the ground. This system was designed by Rohrbach engineer Kurt Tank.

The Beardmore Inflexible had a wingspan of 157 ft 6 in (48.01 m), a length of 75 ft 6 in (23.01 m), and a height of 21 ft 2 in (6.45 m). The aircraft had a top speed of 110 mph (177 km/h) at sea level and 101 mph (163 km/h) at 6,500 ft (1,981 m). Its landing speed was 65 mph (105 km/h). The Inflexible had a climb rate of 359 fpm (1.8 m/s) and took 18 minutes and 06 seconds to reach 6,500 ft (1,981 m). The aircraft’s service ceiling was 9,350 ft (2,850 m). The Inflexible had an empty weight of 24,923 lb (11,305 kg), a gross weight of 31,400 lb (14,243 kg), and a maximum weight of 37,000 lb (16,783 kg). Reportedly, the aircraft could seat 20 passengers, but it does not appear that such accommodations were ever installed.

Beardmore-Inflexible-bottom

Underside of the Inflexible as it overflies the Royal Air Force Display at Hendon. The radiators for the wing-mounted engines are visible by the fuselage. Note the aerodynamic balance horns extending from all of the control surfaces.

Construction of the Inflexible progressed slowly and was often delayed by various material shortages. The aircraft was initially given civil registration G-EBNG on 29 December 1925. This registration was cancelled on 12 July 1927, and military serial number J7557 was assigned. The aircraft was completed at Dalmuir, near Glasgow, Scotland, in mid-1927. It was then broken down into various sections and transported by sea from Glasgow to Ipswich, England. However, the Aeroplane and Armament Experimental Establishment had no way to transport the large components from the Ipswich docks to the nearby Martlesham Heath Airfield. Disassembled, the two fuselage sections were 41 ft (12.50 m) long, and the outer wing sections were 61 ft (18.59 m) long. Moving the large sections of the Inflexible to Martlesham Heath required the construction of a special transport with steerable axles. Once assembled, the Inflexible’s wingspan was larger than any hanger opening at Martlesham Heath. Special trollies were built that supported each of the aircraft’s wheels and enabled movement in all directions. With the trollies, the aircraft could be moved sideways into the hanger.

Initial ground tests were started in January 1928, and the Inflexible was soon ready for flight tests when the weather was clear. The aircraft’s first flight occurred on 5 March 1928 and was flown by Jack Noakes. A Beardmore mechanic was also on the flight. The Inflexible took off in about 1,014 ft (309 m) and flew for 15 minutes; at the time, it was the world’s largest aircraft to fly. The Inflexible was stable in flight and exhibited good controls. Further flight testing revealed the aircraft to be underpowered, and its pitch and roll control was lacking in rough weather and at slow speeds. Wake turbulence from the fuselage-mounted engine also caused vibration issues with the aircraft’s tail.

Beardmore-Inflexible-flight

The Inflexible makes a pass during the Royal Air Force Display. The pilot, Jack Noakes, is just visible in the open cockpit.

The Inflexible was displayed for the public on at least three different occasions. On 27–30 June 1928, the aircraft was flown during the Royal Air Force Display at Hendon, near London. On 18–20 May 1929, it appeared at the Norwich Aero Club Air Display at the Mousehold Aerodrome. On 10 June 1929, the Inflexible was at the Cambridge Aero Club Display in Conington.

Beardmore struggled financially after World War I, and the aircraft department closed in February 1929. Rohrbach also suffered financial difficulties, and the company merged with a Deschimag subsidiary to form Weser Flugzeugbau GmbH in 1934. Although the Inflexible had demonstrated the feasibility of all-metal, stressed-skin construction, it would be a few years before the technique was fully adopted by the British aircraft industry. In January 1930, the Inflexible was disassembled for static tests at Martlesham Heath. The aircraft had accumulated 47 hours and 55 minutes of flight time. The engines were removed and placed into storage. After the static tests, the wings, fuselage, and other components were left exposed to the elements for corrosion tests. Occasionally, parts of the duralumin skin were removed and repurposed, and the fuselage served as a space for guards to get out of the weather. The remains of the Inflexible were eventually scrapped in 1931. The only surviving component of the aircraft is one main wheel, which is on display in the Science Museum, London.

Beardmore-Inflexible-side

Aerodynamic wheel covers were added to the aircraft sometime in early 1929. The Flettner tab controlling the rudder extended some distance behind the aircraft. The aerodynamic balance horns of the rudder and aileron are clearly visible.

Sources:
Beardmore Aviation 1913-1930 by Charles Mac Kay (2012)
British Prototype Aircraft by Ray Sturtivant (1990)
Jane’s All the World’s Aircraft 1928 by C. G. Grey and Leonard Bridgman (1928)
British Flight Testing: Martlesham Heath 1920-1939 by Tim Mason (1993)
– “Die Monster von Beardmore” by Philip Jarrett, Flugzeug Classic (May 2002)
https://earlyflightera.com/dr-adolf-rohrbach-chronicles-2/
https://en.wikipedia.org/wiki/Beardmore_Inflexible
https://en.wikipedia.org/wiki/Rohrbach_Metall-Flugzeugbau

Martin-XB-51-flight-top

Martin XB-51 Attack Bomber

By William Pearce

In February 1946, the United States Army Air Force (AAF) sought design proposals for an attack aircraft to replace the Douglas A-26 Invader. The Glenn L. Martin Company (Martin) responded with its Model 234, a straight-wing aircraft of a rather conventional layout, except that the engine nacelle on each wing housed a turboprop and a turbojet engine. The Model 234 had a crew of six and was forecasted to carry 8,000 lb (3,629 kg) of ordinance over 800 miles (1,287 km).

Martin-XB-51-flight-top

The Martin XB-51 was a unique attack bomber designed at the dawn of the jet age. The first prototype is seen here with its original tail. Note the inlet for the fuselage-mounted engine. The dark square behind the canopy is a window over the radio operator. (Martin/USAF image)

Martin was awarded a contract to develop the Model 234 on 23 May 1946, and the aircraft was designated XA-45. A few weeks later, the AAF decided to discard the “Attack” category, and the XA-45 was subsequently redesignated XB-51. The AAF then requested new requirements for the XB-51 with an emphasis on speed. The AAF’s new desired specifications for the A-26 replacement was a top speed of 640 mph (1,030 km/h) and the ability to carry 4,000 lb (1,814 kg) of ordinance over 600 miles (966 km). The new requirements necessitated a complete redesign of the XB-51, which Martin completed and submitted to the AAF in February 1947. After slight modifications, the design was somewhat finalized by July 1947. The AAF ordered two prototypes, which were assigned serial numbers 46-685 and 46-686.

The Martin XB-51 was a radical departure from the firm’s previous aircraft designs. The XB-51 was an all-metal aircraft that featured a relatively large fuselage supported by relatively small swept wings. The aircraft had a crew of two and was powered by three General Electric J47-GE-13 engines, each developing 5,200 lbf (23.13 kN) of thrust. Two of the engines were mounted on short pylons attached to the lower sides of the aircraft in front of the wings. The third engine was buried in the extreme rear of the fuselage.

Martin-XB-51-rollout

The XB-51 with its flaps up and its wing at an incidence of three degrees as the aircraft is rolled out on 4 September 1949. The circle on the side of the fuselage just behind the cockpit is a side window for the radio operator. There is no window mirrored on the left side of the aircraft. Note that the intake for the fuselage-mounted engine has its cover rotated closed. (Martin/USAF image)

The pilot sat in the front of the aircraft under what appeared to be a small canopy in contrast to the large fuselage. Behind the pilot and completely within the fuselage was the radio operator, who was also in charge of the short range navigation and bombing (SHORAN) system. The crew compartment was pressurized, and access was provided by a door on the left underside of the fuselage, between the pilot and radio operator’s stations. In case of an emergency, both crew were provided with upward firing ejection seats.

The engine housed in the rear fuselage was fed by an inlet duct located atop the fuselage. A rotating assembly was installed forward of the inlet to either cover the inlet with an aerodynamic fairing when the engine was not in use, or rotate to provide a duct to feed air to the engine. The rear engine could be shut down in flight to extend the aircraft’s range. When not in use, a door in the intake duct prevented the back flow of air through the rear engine. Large doors swung open beneath the fuselage to access the rear engine.

Martin-XB-51-color

The first XB-51 with flaps down and its wing at an incidence of 7.5 degrees. Note that only one of the wingtip outrigger gears is touching the ground. (Martin/USAF image)

Mounted above the rear engine was the vertical stabilizer, with the horizontal stabilizer mounted to its top. Originally, the XB-51’s design had the horizontal stabilizer mounted midway up the vertical stabilizer, but the aircraft was not built with this configuration. The horizontal stabilizer was swept back 35 degrees, and its incidence could be changed for trimming. Two rocket assisted takeoff (RATO) bottles could be fitted to each side of the rear fuselage. The RATO packs would be ignited to shorten the XB-51’s takeoff distance, then discarded once the aircraft was in flight. Each bottle provided 1,000 lbf (4.44 kN) of thrust. Hydraulically operated air brakes were located on each side of the fuselage, under the intake for the rear engine. A braking parachute was housed in the left side of a fairing located below the rudder.

The XB-51 used tandem (bicycle) main gear that consisted of front and aft trucks, and outrigger wheels that deployed from the aircraft’s wingtips for support. Martin had used a similar gear arrangement for the straight-wing XB-48 jet medium bomber and had initially tested the setup using the Martin XB-26H, a B-26 Marauder specially modified for to test the tandem landing gear. The main trucks could swivel to counteract the aircraft’s yaw while taking off or landing with a crosswind.

Martin-XB-51-ordinance

Ordinance for the XB-51 that would fit in the bomb bay. From left to right, four 1,600 lb (726 kg) bombs, eight 5 in (127 mm) High Velocity Aircraft Rockets (HAVR), one 4,000 lb (1,814 kg) bomb, four 2,000 lb (907 kg) bombs, four 1,000 lb (454 kg) bombs, and nine 500 lb (227 kg) bombs. The 4,000 lb (1,814 kg) bomb required an enlarged bomb bay door. (Martin/USAF image)

The aircraft’s bomb bay was located in the fuselage between the main wheels. The bomb bay had a single rotating door to which the bomb load was attached. Opening the rotating door did not create any buffeting or require any speed restriction normally required by two conventional doors. In addition, the rotating door was removable and could be quickly replaced with another door already loaded with ordinance. The standard door could accommodate nine 500 lb (227 kg) bombs, four 1,000 lb (454 kg) bombs; four 1,600 lb (726 kg) bombs; or two 2,000 lb (907 kg) bombs. Two additional 2,000 lb (907 kg) bombs could be accommodated on exterior bomb racks mounted on the bottom of the door. A special enlarged door could be fitted to carry a single 4,000 lb (1,814 kg) bomb or a Mk 5 or Mk 7 nuclear bomb. The XB-51’s maximum bomb load was 10,400 lb (4,717 kg). Eight 5 in (127 mm) High Velocity Aircraft Rockets (HAVR) could be carried in the bomb bay in place of internal bombs.

Three fuel tanks were installed in the aircraft’s fuselage. The forward tank was located above the front main gear and held 640 US gal (2,426 L). The center and aft tanks were both located above the bomb bay and held 745 US gal (2,820 L) and 1,450 US gal (5,489 L) respectively. All the standard fuel tanks could be filled via a single fueling receptacle. A 160.5 US gal (607.6 L) water/alcohol tank to boost engine performance during takeoff was mounted between the front and center fuel tanks. Two 350 US gal (1,325 L) tanks could be carried in the bomb bay for ferrying the aircraft over long distances. The XB-51 had a total normal fuel capacity of 2,835 US gal (10,732 L), and 3,535 US gal (13,381 L) with the bomb bay tanks.

Martin-XB-51-takeoff

The XB-51 executing a high-performance takeoff provides a good view of the aircraft’s leading-edge slats and large flaps. No RATO bottles are fitted. (Martin/USAF image)

In the nose of the XB-51 were eight fixed 20 mm cannons with 160 rpg and a forward strike camera. The nose of the second XB-51 was detachable, and different noses could be fitted depending on the aircraft’s mission. In addition to the standard gun nose, other noses featured equipment for precision bombing and equipment for photo-reconnaissance. As standard, the XB-51 had a reconnaissance camera installed under the cockpit and a strike assessment camera installed in the lower rear fuselage.

With fuel, engines, and the main landing gear all housed in the fuselage, the XB-51’s mid-mounted wings were very thin. The wings were swept back 35 degrees and had six degrees of anhedral. Outrigger wheels deployed from the wingtips to steady the aircraft on the tandem main gear. Slats extended along the outer 70 percent of the wing’s leading edge. Large, slotted flaps covered 75 percent of the wings trailing edge, with small ailerons taking up 15 percent of the trailing edge. While the ailerons contributed to aircraft’s roll control, their main purpose was to provide feedback for the pilot. The majority of roll control was provided by spoilers positioned on the wing’s upper surface, just forward of the flaps. The spoilers extended about 40 percent of the wing’s span. The incidence of the entire wing could vary from 2 to 7.5 degrees and would automatically change with deployment of the flaps. The wing incidence increased at lower speeds to decrease the aircraft’s stall speed and make the aircraft assume the correct attitude for landing, which was with the nose high approximately six degrees. The tandem landing gear required the simultaneous touchdown of both the forward and aft trucks. To prevent the accumulation of ice, hot air was bled off from the engines, directed through a passageway in the wing’s leading edge, and exhausted out the wingtip.

The Martin XB-51 had a 53 ft 1 in (16.18 m) wingspan, was 85 ft 1 in (25.93 m) long, and was 17 ft 4 in (5.28 m) tall. The track between the outrigger landing gear was 49 ft 5 in (15.06 m). The aircraft had a top speed of 645 mph (1,038 km/h) at sea level and 580 mph (933 km/h) at 35,000 ft (10,668 m). Cruising speed was 532 mph (856 mph) at 35,000 ft (10,668 m), and the aircraft’s landing speed was around 140 mph (225 km/h). The XB-51’s initial rate of climb was 6,980 ft (35.5 m/s) at maximum power and 3,600 ft (18.3 m/s) at normal power. The service ceiling was 40,500 ft (12,344 m); normal range was 980 miles (1,577 km), and ferry range was 1,445 miles (2,326 km). The XB-51 had an empty weight of 30,906 lb (14,019 kg), a combat weight of 44,000 (19,958 kg), and a gross weight of 55,930 lb (25,369 kg).

Martin-XB-51-ground

The first XB-51 undergoing an engine run. The bullet fairing has been added to the tail. Note the covered ports in the nose for the 20 mm cannons. (Martin/USAF image)

On 24 February 1948, a mockup of the XB-51 was inspected by the United States Air Force (USAF), which had become a separate branch of the US Armed Forces on 18 September 1947. Construction of the first prototype (46-685) proceeded swiftly at the Martin plant in Middle River, Maryland, and the completed aircraft was rolled out on 4 September 1949. After completing ground tests, aircraft 46-685 made is first flight on 28 October 1949, piloted by Orville Edward ‘Pat’ Tibbs. Initial flight testing went well until the rear main gear collapsed after landing on 28 December. The aircraft was repaired and returned to flight status in early 1950. High-speed testing had revealed some vibrations with the tail and a tendency to Dutch roll. A bullet faring was added at the intersection of the horizontal and vertical stabilizers in March 1950 to mitigate the issues.

The second prototype (46-686) made its first flight on 17 April 1950, piloted by Frank Earl ‘Chris’ Christofferson. Although 46-686 was initially flown with the original tail, bullet fairings were soon added. Both aircraft were involved in numerous landing accidents, mostly attributed to the tandem landing gear and the pilot’s lack of familiarity with its nuances. Nose high landings resulted in tail strikes that damaged the aft fuselage. Nose low and hard landings resulted in the collapse or shearing of the front main gear. Despite the landing difficulties, pilots seemed to like the aircraft and its performance. While the XB-51 could perform rolls and outpace some fighters, the aircraft was not stressed for aggressive maneuvers.

Martin-XB-51-flight

Another image of the first XB-51 with its bullet tail fairing. Note the RATO bottles attached to the rear fuselage. The shield painted under the cockpit says “Air Force Flight Test Center.” (Martin/USAF image)

The USAF considered putting the XB-51 into production, but the role for which the aircraft was intended had changed again with the outbreak of the Korean War. Speed was no longer the main focus, and the USAF now desired an aircraft that could loiter in an area until needed by ground forces. The USAF compared the XB-51 against the North American AJ-1 Savage and B-45 Tornado, the Avro Canada CF-100 Canuck, and the English Electric Canberra. Under the new criteria, the USAF selected the Canberra as the winner in February 1951, and the XB-51 program was essentially cancelled. The Canberra had more than twice the range and loiter time of the XB-51. The following month, Martin was awarded a contract to build the Canberra as the B-57, and the rotary-style bomb bay pioneered on the XB-51 was installed on the B-57. Ultimately, 403 B-57 aircraft would be produced. Both XB-51 aircraft continued to be evaluated and tested. The two XB-51s underwent performance and armament tests at Edwards Air Force Base (AFB) in California and Elgin AFB in Florida.

On 9 May 1952, the second prototype XB-51 was destroyed at Edwards AFB when Major Neal Lathrop executed a roll at low altitude and collided with the ground. Lathrop was the sole occupant on board. At the time of the accident, 46-686 had accumulated 151 hours of flight time and had made 193 flights.

Martin-XB-51-two-ship-plant

The second (left) and first (right) XB-51 aircraft at the Martin plant in Middle River. Both aircraft have the bullet tail fairings, and the second prototype (left) has RATO bottles attached. The Martin plant in the background still has the camouflage paint scheme applied during World War II. Compare the different flap and wing positions between the two aircraft. (Martin/USAF image)

The first prototype played the role of the “Gilbert XF-120” fighter in the 1956 movie “Toward the Unknown.” The movie was shot mostly at Edwards AFB in 1955. On 25 March 1956 the 46-685 was destroyed while taking off from El Paso Municipal (now International) Airport in Texas. The stop in El Paso was to refuel as the aircraft traveled from Edwards AFB to Eglin AFB. The accident occurred due to a premature rotation and subsequent stall. The radio operator, Staff Sergeant Wilbur R. Savage, was killed in the crash, and the pilot, Major James O. Rudolph, died of his injuries on 16 April 1956. The first XB-51 prototype had accumulated 432 hours and made 453 flights.

Performance of the Martin XB-51 had exceeded the manufacturer’s guarantees. However, the aircraft was designed and built at a time when USAF’s desires and priorities were rapidly shifting, and it turned out that the service did not really want the aircraft they had originally asked for. Pilots held the XB-51 in a high regard despite its demanding landing characteristics. Ultimately, the XB-51 faded into history as a short-lived experimental aircraft investigating a new direction at the dawn of the jet age.

Martin-XB-51-two-ship-pass

The second (right) and first (left) XB-51 aircraft make a low pass over Martin Field on 11 October 1950. Note the shadows of the aircraft on the runway. (Martin/USAF image)

Sources:
The Martin XB-51 by Scott Libis (1998)
“Martin XB-51” by Clive Richards, Wings of Fame Volume 14 (1999)
Martin Aircraft 1909–1950 by John R. Breihan, Stan Piet, and Roger S. Mason (1995)
Standard Aircraft Characteristics XB-51 by U.S. Air Force (11 July 1952)
Jane’s All the World’s Aircraft 1951-1952 by Leonard Bridgman (1951)
U.S. Bombers 1928 to 1980s by Lloyd S. Jones (1980)
https://www.avgeekery.com/the-xb-51-martins-movie-star-bomber-smashed-the-bomber-mold/
https://www.thisdayinaviation.com/tag/martin-xb-51/

Hawker-Tempest-I-front-side

Hawker Tempest I Fighter

By William Pearce

On 24 February 1940, the Hawker Typhoon fighter prototype (P5212) made its first flight, piloted by Philip G. Lucas. The Typhoon was designed by Sydney Camm of Hawker Aircraft Limited and was intended as a high-altitude interceptor capable of 400 mph (644 km/h) at 20,000 ft (6,069 m). The British Ministry of Aircraft Production placed an order for 250 Typhoons on 8 October 1939, months before the prototype’s first flight. Flight testing revealed a number of design deficiencies and that the aircraft was not quite suited for its intended role. A major issue was that the compressibility of the Typhoon’s thick wing while diving at high speed caused some instability which made it very difficult to accurately fire the aircraft’s cannons. However, the Typhoon did show promise as a low-altitude interceptor and fighter-bomber.

Hawker-Tempest-I-front-side

An excellent view of the recently completed Hawker Tempest I at Langley. Note the wing radiators, the large propeller, and the wide track of the main landing gear. The cannons are installed in the wings. A number of newly-built Hawker Hurricanes are in the background.

In March 1941, Camm proposed an updated Typhoon design with a new wing and a more powerful Napier Sabre IV engine to improve the aircraft’s performance over that of the original Typhoon, powered by a Sabre II. This new design was initially forecasted to have a top speed of 430 mph (644 km/h) at 20,000 ft (6,096 m) but was later revised up to 455 mph (732 km/h) at 26,000 ft (7,925 m). The anticipated development time of the new fighter was decreased by utilizing many existing Typhoon components, and the aircraft had an anticipated in-service date of December 1943. Discussions continued with the Ministry of Aircraft Production, and Specification F.10/41 was issued to cover the new aircraft. On 18 November 1941, two prototypes were ordered and issued serial numbers HM595 and HM599. The aircraft was designated as the Typhoon II. An order for 100 production aircraft was placed on 24 February 1942. With detailed design work underway, it was realized that few existing Typhoon components could be used in the Typhoon II. Camm proposed that a new name should be selected for the aircraft. Eventually, in August 1942, the Typhoon II was officially renamed Tempest to reflect that is was essentially a new aircraft.

The Sabre IV engine for the Tempest was expected in December 1941, and the aircraft was to make its first flight in late March 1942. However, complications with the aircraft’s design and delays with its engine resulted in a slip of the project’s entire timeline. In March 1942, Hawker decided to finish the first prototype, HM595, with a Sabre II engine and a chin radiator as used on the Typhoon. This would allow time for the airframe to be developed while Napier finished work on the Sabre IV engine, which would be installed in the second Tempest prototype, HM599.

Hawker-Tempest-I-side-high

Side view of the Tempest I with its original framed canopy and cockpit entry door on the side of the aircraft. The tail was very similar to that of the Typhoon, and unlike the Tempest V, its area was not increased. Note the tail wheel doors.

In June 1942, the Tempest project was redefined. As previously specified, HM599 would be finished with the Sabre IV engine as the Tempest I, and HM595 would be finished with the Sabre II and chin radiator as the Tempest V. Four additional prototypes were ordered: two (LA602 and LA607) would be powered by the Bristol Centaurus radial engine as the Tempest II, and two (LA610 and LA614) would be powered by the Rolls-Royce Griffon IIB as the Tempest III. The Griffon IIB would later be replaced by the Griffon 61, at which time the aircraft would become the Tempest IV. An order for 400 production Tempest Is followed in August 1942.

The Hawker Tempest I was a single-engine fighter of all-metal construction with a conventional taildragger layout. The fuselage was made up of four sections: engine and engine mount, center fuselage, rear fuselage, and tail. The center fuselage consisted of the cockpit and forward fuselage and was comprised of a tubular frame covered with aluminum panels. The rear fuselage was of monocoque construction. The Tempest I’s tail section, which included the vertical and horizontal stabilizers, was basically the same as that used on production Typhoons. The tail’s attachment was reinforced with “fish plates,” just like those on mid-war Typhoons. One difference from the Typhoon was that the Tempest I’s tailwheel was fully retractable and concealed by gear doors. The fuselage of the Tempest I was 21 in (533 mm) longer than that of the Typhoon because the engine was moved forward to accommodate a 91 US gal (76 Imp gal / 345 L) fuel tank installed in the fuselage ahead of the cockpit. The cockpit was accessible via a side entry door, and the pilot sat under a framed canopy.

Hawker-Tempest-I-rear

Rear view of the Tempest I with its original canopy. Even though the Tempest I shared many components with the Tempest V, it looks like a different aircraft.

The Tempest I’s new semi-elliptical wing was mounted to the tubular frame of the center fuselage. The wing had two main spars and consisted of an inner and outer section. The inner section had no dihedral and housed the inward-retracting main landing gear that had been redesigned from that of the Typhoon. The landing gear had a wide track of 14 ft 11 in (4.53 m). A 34 US gal (28 Imp gal / 127 L) fuel tank was located in each wing between the main gear leg well and rear spar. Engine coolant radiators and the oil cooler were installed in the leading edge of the wing’s center section. Adjustable flaps on the underside of the wing just aft of the heat exchangers regulated coolant and oil temperatures. Each outer wing section had a 5.5-degree dihedral and housed two 20 mm Hispano Mk II cannons with 150 rpg. Each wing had a two-section, hydraulically actuated split flap and featured a large aileron. The Tempest I’s wing was approximately 5 in (127 mm) thinner at the root and 7 in (178 mm) shorter in span than that of the Typhoon and could not house all the needed fuel, which is why the fuselage tank was added. Provisions were included for the installation of a 54 US gal (45 Imp gal / 205 L) drop tank under each wing. Except for the fabric-covered rudder, all control surfaces were covered with metal.

The Tempest I’s sleeve-valve, H-24 Napier Sabre IV engine was mounted to the forward part of the tubular fuselage frame. The engine produced 2,240 hp (1,670kW) at 4,000 rpm at 8,000 ft (2,438 m) with 9 psi (.62 bar) of boost. This was some 200 hp (149 kW) more than the Sabre II used on the Typhoon. A small scoop under the engine fed air into the carburetor. The Sabre IV turned a metal, four-blade, constant-speed de Havilland propeller that was 14 ft (4.27 m) in diameter. Omitting the Typhoon’s chin radiator and relocating the cooling system in the wings gave the Tempest I a much more refined and aerodynamic look compared to the earlier aircraft.

Hawker-Tempest-I-in-flight

The Tempest I in flight with Bill Humble at the controls. The aircraft now has the one-piece bubble canopy, and its armament has been removed. Note the carburetor intake under the engine.

The Hawker Tempest I had a 41 ft (12.40 m) wingspan, was 33 ft 7 in (10.24 m) long, and was 15 ft 10 in (4.83 m) tall. The aircraft’s top speed was 466 mph (750 km/h) at 24,500 ft (7,468 m) and 441 mph (710 km/h) at 13,600 ft (4,145 m). It could climb to 15,000 ft (4,572 m) in 4 minutes and 15 seconds and had a ceiling of 37,000 ft (11,278 m). The Tempest I weighed 8,950 lb (4,060 kg) empty and 11,300 lb (5,126 kg) loaded. The aircraft’s range was 500 miles (805 km) on internal fuel and 800 miles (1,287 km) with drop tanks.

Construction of the Tempest I prototype at Hawker’s new facility in Langley, England was delayed by other war work and by the wing radiators. As previously mentioned, delivery of the Sabre IV was delayed by Napier. The Sabre II-powered Tempest V was first flown on 2 September 1942 by Lucas and gave some indication of what to expect with the Tempest I. The Sabre IV engine was delivered in November 1942, and the Tempest I underwent ground trials in February 1943. Tempest I HM599 was first flown on 24 February 1943, piloted by Lucas. Lucas found the Tempest I to have improved stability over that of the Tempest V, although pitch authority became non-existent under 110 mph (177 km/h).

A new engine was installed in early March 1943, and the aircraft returned to the air on 26 March. Two days later, Bill Humble made his first flight in the Tempest I. In late April and through May, a more developed Sabre IV engine was installed, and the Tempest I was modified with a conventional, one-piece, rearward-sliding bubble canopy. It also appears that the cannons were removed, at least temporarily, at this time. The updated Tempest I flew on 4 June, piloted by Humble. Some performance testing was done during the remainder of June. The Sabre IV engine exhibited a drastic increase in oil consumption at speeds over 3,750 rpm, and the hand-built engines seldom reached 50 hours before needing to be replaced. Despite the engine difficulties, the Tempest I was praised for its performance and handling, especially at higher altitudes.

Hawker-Tempest-I-Napier-Sabre-IV

Another image of Humble in the Tempest I. This angle illustrates the aircraft’s clean lines. The air exit gap aft of the wing radiator is somewhat visible, as are the fish plates to reinforce the tail.

Another Sabre IV engine was installed in late July 1943, and a thinner horizontal stabilizer may have been installed at this time. The Tempest I resumed flight testing in August, at which time speeds of 460 mph (740 km/h) at 25,300 ft (7,711 m) and 443 mph (713 km/h) at 13,300 ft (4,054 m) were recorded. Humble achieved higher speeds in September, which included the aircraft’s official 466 mph (750 km/h) at 24,500 ft (7,468 m) and 441 mph (710 km/h) at 13,600 ft (4,145 m). The highest recorded level speed was 472 mph (760 km/h) at 18,000 ft (5,486 m). Testing continued, but development issues with the Sabre IV engine led to further work on the Tempest I project not being covered by government contract beyond December 1943. The Tempest V with its Sabre II engine required less development, and the type took over the original order for the Tempest I.

There was still life for the Tempest I. The aircraft was fitted with a 2,420 hp (1,805 kW) Sabre V engine, and the combination was first flown on 8 February 1944 by Humble. On 12 February, an order for 700 Sabre V-powered Tempest Is was received. On 9 March, the Tempest I was damaged in a ground accident involving a Hawker Hurricane. The Tempest I was quickly repaired and resumed flying on 28 March. The Tempest I order was cut to 300 aircraft in April and then converted to the Sabre V-powered Tempest VI in May.

The Tempest I continued to serve as a Sabre V engine testbed until at least March 1945. With the Sabre V, the Tempest I recorded a speed of 462 mph (743 km/h) at 17,600 ft (5,364 m) and 444 mph (715 km/h) at 7,200 ft (2,195 m). The Tempest I’s last flight appears to have been made on 31 August 1945. On 11 September 1947, the Tempest I was struck off charge, and the aircraft was scrapped on or shortly after 27 October 1947. At least six pilots made at least 91 flights in the Tempest I, but a full account of its flight time has not been found.

Hawker-Tempest-I-in-flight-top

The Tempest I was an elegant aircraft that demonstrated excellent performance. Engine trouble and the more straightforward development of the Tempest V led to the Tempest I ultimately not being produced.

Sources:
Hawker Typhoon, Tempest and Sea Fury by Kev Darling (2003)
Tempest: Hawker’s Outstanding Piston-Engined Fighter by Tony Buttler (2011)
The Hawker Typhoon and Tempest by Francis K. Mason (1988)
Fighters Volume Two by William Green (1964)
Hawker Typhoon and Tempest: A Formidable Pair by Philip Birtles (2018)
Hawker Aircraft since 1920 by Francis K. Mason (1991)

piaggio-pegna_pc7

Piaggio P.7 / Piaggio-Pegna Pc 7 Schneider Racer

By William Pearce

Giovanni Pegna was an Italian aeronautical engineer who started to design racing seaplanes and other aircraft in the early 1920s. Partnering with Count Giovanni Bonmartini, the pair formed Pegna-Bonmartini in 1922 to bring some of Pegna’s aircraft designs to life. Pegna was particularly interested in designing a racing seaplane for the Schneider Trophy Contest. Pegna-Bonmartini was short lived, as it was bought out by Piaggio & C. SpA (Piaggio) in 1923, when the latter company decided to start designing its own aircraft. Pegna was appointed head aircraft designer for Piaggio.

Pegna-Pc-racing-seaplanes-2

Giovanni Pegna’s previous racing seaplane designs. The engine and propeller of the Pc 1 pivoted up to clear the water for takeoff, landing, and while operating on the water’s surface. The Pc 2 and Pc 3 were fairly conventional designs but were advanced for their 1923 time period. The Pc 4 had tandem engines in a push/pull configuration and a single, central float. Wing floats would have been incorporated into the design. The Pc 5 and Pc 6 both used a retractable hull that was extended for takeoff and landing. The Pc 6 also had tandem engines in a push/pull configuration.

Pegna’s racing seaplane designs focused on minimizing the aircraft’s frontal area. Some of the designs used floats, while others incorporated a flying boat hull. Construction of the Pc 3 was started by Piaggio in 1923. The “Pc” in the aircraft’s designation stood for Pegna Corsa (Race), and this aircraft most likely carried the Piaggio designation P.5. The Pc 3 was a fairly conventional, single-engine monoplane utilizing two floats, but the aircraft was never finished.

Pegna-Pc-7-Drawing

The Schneider Trophy Contest inspired a number of extraordinary designs, but the Piaggio P.7 / Pegna-Piaggio Pc.7 was the most radical to be built. Its hydrovanes were much smaller and lighter than floats, offering the aircraft a distinct advantage if it could get airborne. Note the water rudder behind the water propeller.

In 1927, Pegna was asked by the Ministero dell’Aeronautica (Italian Air Ministry) to design a racing seaplane for the 1929 Schneider Trophy Contest. After studying three designs (Pc 4 through Pc 6), Pegna became increasingly focused on utilizing a central float that would be extended to support the aircraft on water and retracted while the aircraft was in the air. However, the complexity and estimated weight of the float and its retraction mechanism, combined with the unknown aerodynamic forces during retraction and extension, made the design impractical. Pegna returned to the drawing board and, aided by Giuseppe Gabrielli, designed the Pc 7, which was also known as the Piaggio P.7. On 24 March 1928, the Italian Air Ministry ordered two examples of the P.7 and assigned them serial numbers (Matricola Militare) MM126 and MM127.

After experiments in a water tank, Pegna finalized the aircraft’s design. The Piaggio P.7 (Piaggio-Pegna Pc 7) had a watertight fuselage that sat in the water up to the shoulder-mounted wings when the aircraft was at rest. A two-blade propeller at the front of the aircraft was just above the waterline. The engine was located just forward of the wing and drove the propeller via a shaft. A second shaft extended behind the engine to a water propeller positioned in a skeg under the tail. Clutches on both shafts allowed the front propeller or the water propeller to be decoupled from the engine. When the front propeller was decoupled, it would come to rest in a horizontal position. For takeoff, the engine would power the water propeller with the front propeller stationary. As the aircraft gained speed, the front would rise about 10 degrees out of the water by the hydrodynamic forces imparted on two hydrovanes extending below the fuselage and by a third hydrovane located in front of the water propeller. With the front propeller clear of the water, engine power was diverted from the water propeller to the front air propeller. The front propeller would continue the aircraft’s acceleration until enough speed was gained to lift off from the water’s surface.

Piaggio-Penga-Pc-7-drawing

A view of the P.7’s internal layout. A and B are the drive shaft clutches. C is the lever that engages and disengages the air propeller; when disengaged, it locks the propeller in a horizontal position and closes the main carburetor inlets. D is the lever that engages and disengages the water propeller; when disengaged, it feathers the water propeller. E is not recorded, but it appears to be a bulkhead and support for the propeller shaft. F is a rubber diaphragm operated by the air propeller lever that seals the propeller shaft when the air propeller was disengaged.

The P.7’s airframe was made mostly of wood with some metal components. The aircraft was skinned with two layers of plywood with a waterproof fabric sandwiched between the layers. Two watertight compartments were sealed into the fuselage, and the vertical and horizontal stabilizers were watertight. A single fuel tank was positioned in the fuselage under the wing and between the engine and cockpit. The one-piece wing had three main spars and was mounted atop the fuselage. Two legs extended below the fuselage, and each supported a planing surface. The planing surfaces, including the one on the tail, were inclined approximately three degrees compared to the aircraft while in level flight. The relative angle would increase as the aircraft was landed with a slight tail-down configuration. A water rudder extended below the fuselage directly under the aircraft’s tail. The movement of the water rudder and normal rudder were linked.

Piaggio-Penga-Pc-7-construction

The nearly complete P.7 without its engine or hydrovanes. The original carburetor inlets are visible on the side of the aircraft. Note the pipes for the surface radiators on the wings.

Originally, the P.7 was to be powered by a 1,000 hp (746 kW) FIAT AS.5 V-12 engine. For reasons that have not been found, the engine was switched to an Isotta Fraschini Asso 500 V-12 that produced 800 hp (597 kW) at 2,600 rpm. Isotta Fraschini fully supported the P.7 project, and Giustino Cattaneo, the Asso 500’s designer, redesigned the engine with a rear drive for the water propeller. In addition, new cylinder heads were designed with the exhaust ports on the inner, Vee side of the engine. As originally designed, the Asso 500 had intake and exhaust ports on the outer sides of the engine. Having the open exhaust ports on the side of the fuselage would lead to water intrusion when the aircraft was at rest on the surface. Relocating the exhaust ports to vent out the top of the fuselage resolved this issue. The cylinder heads were most likely the same or very similar to those that Cattaneo had designed for the Savoia-Marchetti S.65 Schneider racer. Cattaneo and Isotta Fraschini also designed at least some of the P.7’s drive systems. Surface radiators on the wings cooled the engine’s water coolant, and engine oil was cooled by a surface radiator on the sides and bottom of the aircraft’s nose.

The cockpit was situated low in the aircraft’s fuselage and between the wing’s trailing edge and the tail. Two levers on the left side of the cockpit controlled the engine’s output to the air and water propellers. One lever engaged and disengaged the air propeller. When engaged, the main carburetor inlets at the front of the aircraft were automatically opened. When disengaged, the carburetor inlets were closed, a rubber seal was pressed against the front of the propeller shaft, and the propeller was slowed and subsequently locked in a horizontal position. The carburetor inlets were originally located on the sides of the aircraft by the engine but were moved to above the nose. When the carburetor inlets were closed, the engine drew in air from the cockpit. When the water propeller’s lever was disengaged, the blades were feathered to offer as little aerodynamic resistance as possible.

piaggio-pegna_pc7

The completed P.7 supported by a hoist illustrates the aircraft’s sleek design. The pilot sat quite far aft, and landings would have been a challenge.

Six air propellers were ordered for testing on the P.7. They varied in diameter and profile. Three were made from steel with a ground-adjustable pitch, and the other three were made from duralumin, and each had a different fixed pitch. One of the steel air propellers was designed by Pegna. Originally, the adjustable-pitch water propeller was made from duralumin components, but testing resulted in a switch to a steel hub with duralumin blades. The Piaggio P.7 had a 22 ft 2 in (6.76 m) wingspan, was 29 ft 1 in (8.86 m) long, and was 8 ft (2.45 m) tall. It had a maximum speed of 373 mph (600 km/h) and a landing speed of 103 mph (165 km/h). The aircraft weighed 3,122 lb (1,416 kg) empty and 3,717 lb (1,686 kg) fully loaded.

The design of the complex and unique aircraft delayed its completion. It appears that the first aircraft, MM126, was completed and sent to Desenzano before the Schneider Trophy Contest was held in September 1929, but there was not enough time to test the P.7 before the race. Both P.7 aircraft were finished by late October 1929, which is when testing began. Most pilots of the Italian Reparto Alta Velocità (High Speed Unit) were not interested in testing the radical machine. However, Tommaso Dal Molin was up to the task. Testing occurred on Lake Garda, just off from Desenzano, home of the Reparto Alta Velocità.

Piaggio-Penga-Pc-7-rest-water

The P.7 on Lake Garda for tests. A simple structure connected to hardpoints above the wing was used to raise and lower the aircraft out of the water. More so that most Schneider Trophy racers, the P.7 could only be operated on calm waters.

Using the water propeller, Dal Molin in MM126 was able to raise the nose of the aircraft to a sufficient height to engage the air propeller, but this was not done. The P.7 was unstable planing on the water, and issues were experienced with the clutch for the water propeller. Oil on the clutch caused it to slip, resulting in a loss of power to the water propeller. In addition, the sudden cavitation of the main hydrovanes while planing caused a loss of buoyancy, which resulted in the P.7 suddenly and violently settling back on the water’s surface. Because of the issues, it seems that tests were conducted over only a few days.

There was no cover to easily access the clutch. The needed repairs would require substantial disassembly of the aircraft. By this time, the Air Ministry and Piaggio showed little interested in the P.7, but Pegna wanted to continue its development. Some of the changes Pegna had in mind were adjustable hydrovanes and cooling the engine oil with water rather than using a surface radiator. However, it appears that the repairs were never made. MM126 was stored at Desenzano for a time but was destroyed after a few years. MM127 was taken to Guidonia Montecelio, near Rome, for testing in a water tank to improve the aircraft’s hydrovanes. The aircraft was eventually abandoned, and it is not clear if any tests were ever conducted. MM127, along with other aircraft, was destroyed in 1944—a casualty of World War II.

Piaggio_Pegna_P7_in_hangar

The P.7 surrounded by contemporaries at Desenzano. At left is the Macchi M.39. At right is the Savoia-Marchetti S.65. The Macchi M.52’s wing is in the foreground. Note the P.7’s exhaust stacks protruding above the engine.

Sources:
Some Ideas on Racing Seaplanes (Technical Memorandums National Advisory Committee for Aeronautics No. 691) by Giovanni Pegna (November 1932) 31.4 MB
Schneider Trophy Seaplanes and Flying Boats by Ralph Pegram (2012)
MC 72 & Coppa Schneider Vol. 2 by Igino Coggi (1984)
Schneider Trophy Aircraft 1913–1931 by Derek N. James (1981)
Volare Avanti by Paolo Gavazzi (2000)
Jane’s All the World’s Aircraft 1932 by C. G. Grey (1932)

Kyushu-J7W1-Shinden-left-rear

Kyushu J7W1 Shinden Interceptor Fighter

By William Pearce

Masayoshi Tsuruno (also spelled Masaoki) was a member of the Imperial Japanese Navy’s (IJN) Aviation Research Department. Around 1940, Tsuruno first began to investigate designs of a pusher aircraft with a canard layout. Tsuruno’s research led him to believe that such a configuration would enable an aircraft to achieve a very high level of performance. In addition, the basic configuration could be easily adapted to turbojet power if such an engine became available.

Kyushu-J7W1-Shinden-left-rear

Kyushu J7W1 Shinden was an unorthodox fighter designed to intercept US bombers at high speed and high altitude. Although just two were completed, it was the only canard aircraft ordered into production during World War II. Exhaust from two cylinders flowed out the two ejector slits atop the engine cowling.

In early 1943, the IJN issued 18-Shi Otsu specification calling for a land-based fighter capable of intercepting enemy bombers. The aircraft should achieve 460 mph (740 km/h) at 28,543 ft (8,700 m), reach 26,247 ft (8,000 m) in 10.5 minutes, have a service ceiling of 39,370 ft (12,000 m), and carry four 30 mm cannons. Tsuruno worked up a design for such an aircraft and submitted it to the IJN. The IJN liked the design but was hesitant to move forward with the radical, untested configuration. Tsuruno was able to work with the First Naval Air Technical Depot (Dai-Ichi Kaigun Koku Gijitsusho) at Yokosuka to develop a proof of concept, designated MXY6.

The Yokosuka MXY6 was a glider of all wooden construction possessing a canard layout with fixed tricycle landing gear. The aircraft featured a foreplane with elevators mounted to its nose for pitch control. The swept wings were mounted to the rear fuselage, and each wing had a vertical stabilizer with a rudder mounted near its mid-point. Three of the gliders were built by Chigasaki Industry Ltd (Chigasaki Seizo KK). Piloted by Tsuruno, the MXY6’s first flight was made in January 1944. Later, one of the gliders was fitted with a 22 hp (16 kW) Nippon Hainenki Semi 11 [Ha-90] engine turning a wooden, fixed-pitch, two-blade propeller. The engine was not intended make the MXY6 fully operational under its own power, but it would enable the aircraft to sustain flight and prolong its glide. The MXY6’s flight tests indicated that Tsuruno’s design was sound. The aircraft handled well at low speeds and resisted stalling. Based on the positive preliminary tests of the MXY6, the IJN decided to proceed with Tsuruno’s 18-Shi Otsu design in February 1944. The aircraft would be built by the Kyushu Airplane Company (Kyushu Hikoki KK), and it was designated J7W1 Shinden (Magnificent Lightning).

Yokosuka_MXY6_Glider

One of the Yokosuka MXY6 gliders that survived to the end of the war and was found by US forces. The glider validated the basic configuration that was later applied to the J7W1.

Kyushu Airplane Company was founded in October 1943 as a subsidiary of the Watanabe Iron Works Ltd (Watanabe Tekkosho KK). Kyushu was selected as the manufacturer because it had both workers and production facilities that were available. Kyushu had no experience designing high-performance fighter aircraft, but the company would be aided by Tsuruno and the First Naval Air Technical Depot. An official order for the J7W1 was issued in June 1944, with the prototype’s first flight expected in January 1945.

The Kyushu J7W1 Shinden used the same layout as the MXY6, having a canard configuration with a swept, rear-mounted wing and tricycle undercarriage. The aircraft consisted of an aluminum airframe covered by aluminum panels, forming a monocoque structure. Depending on location, the panels were either flush riveted or spot welded in place. The control surfaces were skinned with aluminum. The foreplane had two spars and was mounted to the extreme nose of the aircraft at a one-degree angle of incidence. A leading-edge slat was deployed with the flaps. On the foreplane’s trailing edge was a two-section flap. The first section acted as a traditional flap that extended 26 degrees. The second section on the trailing edge acted as an elevator.

Mounted in the fuselage between the foreplanes were four 30 mm Type 5 cannons, each with 60 rounds per gun. Each cannon was 7 ft 2 in (2.19 m) long and weighed 154 lb (70 kg). The cannons were slightly staggered to allow for clearance of their respective feed belts and keep the fuselage as narrow as possible. A compartment under the cannons collected the spent shell casings because of concerns that they would strike the propeller if they were ejected from the aircraft. Two 7.9 mm machine guns with 75 rounds per gun were planned for the very front of the nose and could be used for either training or target ranging. As ranging guns, they would help ensure that the cannon shells hit the intended target and not waste the limited ammunition supply. No armament was fitted to the prototype, and ballast weight was used to simulate the cannons.

Kyushu-J7W1-Shinden-left

The wheels under the vertical stabilizers were added after the aircraft’s first flight attempt ended with bent propeller blades. Note the long landing gear’s relatively short wheel base.

Behind the cannons was the single-seat cockpit, which was covered by a rearward-sliding glazed canopy. The pilot was protected by 2.76 in (70 mm) of armored glass in the front windscreen and a .63 in (16 mm) bulkhead by the cannons. Passageways ran on both sides of the aircraft between the cockpit and outer skin. Flight controls, hydraulic lines, and wiring ran in these passageways, which were accessible via removable outer skin panels. Under and slightly behind the cockpit was a 106-gallon (400-L) self-sealing fuel tank made of .87 in (22 mm) thick rubber.

Directly behind the cockpit was a 44-gallon (165-L) oil tank, followed by a Mitsubishi [Ha-43] 42 (IJN designation MK9D) engine. The [Ha-43] was a two-row, 18-cylinder, air-cooled engine. The [Ha-43] 42 had two-stage supercharging, with the first stage made up by a pair of transversely-mounted centrifugal impellers, one on each side of the engine. The shaft of these impellers was joined to the engine by a continuously variable coupling. The output from each of the first stage impellers joined together as they fed the second stage, two-speed supercharger mounted to the rear of the engine and geared to the crankshaft. As installed in the J7W1, the engine produced 2,030 hp (1,514 kW) at 2,900 rpm with 9.7 psi (.67 bar) of boost for takeoff. Military power at 2,800 rpm and 5.8 psi (.40 bar) of boost was 1,850 hp (1,380 kW) at 6,562 ft (2,000 m) in low gear and 1,660 hp (1,238 kW) at 27,559 ft (8,400 m) in high gear.

Kyushu-J7W1-Shinden-front

The prototype was unarmed, but four 30 mm cannons, each capable of firing 500 rounds per minute, were to be mounted in the nose. The projectile from each 30 mm shell weighed 12.3 oz / 5,401 grains (350 g).

The engine was mounted in the center of the fuselage and atop the wingbox. An extension shaft approximately 29.5 in (750 mm) long extended back from the engine to a remote propeller reduction gear box. The extension shaft passed through an extended housing that was mounted between the engine and the propeller gear reduction. The gear reduction turned the propeller at .412 times crankshaft speed and also drove a 12-blade cooling fan that was 2 ft 11 in (900 mm) in diameter. A screen was placed in front of the fan to prevent any debris from exiting the rear of the aircraft and hitting either the fan or propeller. Mounted to the propeller shaft was a 11 ft 2 in (3.40 m) diameter, metal, six-blade, constant-speed, VDM (Vereinigte Deutsche Metallwerke)-type propeller built by Sumitomo Metal Industries Ltd, Propeller Division (Sumitomo Kinzoku Kogyo KK, Puropera Seizosho). The propeller had approximately 29 in (740 mm) of ground clearance with the aircraft resting on all of its landing gear. If bailing out of the aircraft was needed, the pilot could detonate an explosive cord that would sever the propeller and gear reduction.

Cooling air for the [Ha-43] engine was taken in via an oblique inlet mounted on each side of the fuselage just behind the cockpit. Flaps at the inlet’s opening were raised to decrease the flow of cooling air to the engine. Cooling air entered the inlets, passed through the fins on the engine’s cylinders, traveled along the outside of the extension shaft housing, passed through the cooling fan, and exited around the spinner or an outlet under the rear of the aircraft. Two intakes, one on each side of the aircraft, were mounted to the cooling inlet. These intakes ducted induction air through the cooling air duct and directly into the transversely mounted superchargers.

Kyushu-J7W1-Shinden-Ha-43-42-engine

The Mitsubishi [Ha-43] 42 engine installed in the J7W1 as seen post-war. The front of the aircraft is on the left. One of the two transversely-mounted, first-stage superchargers can be seen left of the engine. The oil cooler duct is in place and blocking the view of the extension shaft to the right of the engine. On the wing is the middle panel of the supercharger’s inlet scoop.

On each side of the fuselage directly behind the induction scoop was an inlet for an oil cooler. For each of the two oil coolers, after air passed through the cooler, it was mixed with the exhaust of four cylinders and ejected out a slit on the side of the fuselage just before the spinner. The ejector exhaust was used to help draw air through the oil coolers. The same philosophy applied to the exhaust from six cylinders on the bottom of the engine. These were ducted into an augmenter that helped draw cooling air through the cowling and out an outlet under the spinner. The exhaust from the remaining four cylinders, which were located on the top of the engine, exited via two outlets arranged atop the cowling to generate thrust.

The leading edge of the J7W1’s wing was swept back 20 degrees, and the trailing edge was swept back six degrees. The wings were mounted with no incidence angle. The inner wing from the wingbox to the rudder had 2.5 degrees of dihedral, and the outer wing from the rudder to the tip had zero dihedral. The structure of each wing was formed with three spars. The front spar ran along the wing’s leading edge. The center, main spar was swept back 14.5 degrees and ran in front of the main landing gear wells. A rear spar was swept forward 3.5 degrees and ran from the wingbox to just behind the main gear mount. A vertical stabilizer extended above and below the rear spar. The vertical stabilizer was mounted at approximately the midpoint of each wing and extended past the wing’s trailing edge. Initially, nothing was mounted under the vertical stabilizers, but a wheel was later added under each stabilizer to prevent propeller ground strikes. A rudder ran the entire 7 ft 3 in (2.20 m) height of each vertical stabilizer. Each wing housed a 53-gallon (200-L) fuel tank and a 20-gallon (75-L) anti-detonation fluid (water/methanol) tank for injection into the engine. Split flaps were positioned along the trailing edge of the wing between the vertical stabilizer and the fuselage. The flaps on the main wing extended 20 degrees. Two hardpoints under each outer wing could accommodate 66 or 132 lb (30 or 60 kg) bombs.

Kyushu-J7W1-Shinden-rear

Rear view of the J7W1 showing its six-blade propeller and the engine’s 12-blade cooling fan in the rear of the cowling. The exhaust augmenter outlet can be seen on the bottom of the cowling. Note the rudders extending the entire height of the vertical stabilizers.

When deployed, the legs of the main gear were angled forward more than the nose gear. This effectively extended the nose gear and caused the aircraft to sit five-degrees nose-high while on the ground. This stance minimized the rotation needed to achieve liftoff, which is very important in the pusher aircraft. The main gear was mounted forward of the vertical stabilizers. The swiveling but non-steerable nose gear retracted forward, and the main gear retracted inward. Gear retraction and extension were powered hydraulically. At approximately 5 ft 11 in (1.8 m) long, the landing gear was quite tall to allow clearance for the propeller. The gear had a fairly wide track of 15 ft (4.56 m), but the wheelbase was short at only 10 ft 2 in (3.11 m). The short wheelbase combined with the tall gear legs and the aircraft’s high center of gravity could have given the J7W1 undesirable ground handling characteristics.

The J7W1 had a 36 ft 5 in (11.11 m) wingspan, was 32 ft (9.76 m) long, and was 12 ft 10 in (3.92 m) tall. The aircraft had a top speed of 466 mph (750 km/h) at 28,543 ft (8,700 m), a cruising speed of 276 mph (444 km/h), and a stalling speed of 107 mph (172 km/h). The J7W1 could climb to 26,247 ft (8,000 m) in 10 minutes and 40 seconds and had a 39,370 ft (12,000 m) service ceiling. The aircraft had an empty weight of 7,639 lb (3,465 kg), a normal weight of 10,864 lb (4,928 kg), and a maximum weight of 11,526 lb (5,228 kg). Cruising at 9,843 ft (3,000 m) gave the J7W1 a 528-mile (850-km) range. The aircraft was stressed for a maximum speed of 575 mph (926 km/h) and 7 Gs.

Kyushu-J7W1-Shinden-front-left

The various ducts on the side of the J7W1 are illustrated in this image. The flaps to reduce cooling air can be seen just before the oblique inlet on the side of the aircraft. The smaller scoop that fed air into the supercharger is mounted to the outside of the cooling air inlet. The oil cooler inlet can be seen just behind the tapered fairing for the induction scoop.

While the prototype was still under construction, the IJN ordered the J7W1 into production in May 1944 to counter the imminent threat of American bombing raids with the Boeing B-29 Superfortress. Ultimately, the production schedule called for Kyushu to produce 30 aircraft per month, and the Nakajima Aircraft Company, Ltd (Nakajima Hikoki KK) would build 120 units per month. In June 1944, the United States Army Air Force began conducting bombing raids against Japan using the B-29. To intercept these bombers and disrupt these raids were the exact purposes for which the J7W1 was designed. In September 1944, a mockup of the J7W1 was inspected by the IJN, and wind tunnel tests of a scale model had yielded positive results.

The J7W1 was built at Kyushu’s Zasshonokuma Plant, near Fukuoka city. The airframe was nearing completion in January 1945, when the first flight was originally scheduled to be conducted. Bombing raids delayed delivery of the [Ha-43] 42 engine, which finally arrived in April. The J7W1 was finally completed on 10 June and was subsequently disassembled and moved to Mushiroda Airfield (now Fukuoka Airport) in Fukuoka city on 15 June. Reassembled, the aircraft was inspected on 19 June, but bombing raids caused some delays. Ground tests were soon conducted and indicated a tendency for the engine to overheat due to a lack of cooling airflow. Tsuruno attempted the first flight in July, but as the J7W1 began to take flight, the engine’s torque induced a roll to the right. The aircraft’s nose went high and caused the propeller tips to strike the ground, bending the tips back.

Kyushu-J7W1-Shinden-repair-right-side

Following World War II, the J7W1 was repaired and then painted before the aircraft was shipped to the United States. The new panels are easily seen in this image prior to the aircraft being repainted. Note that there is no cockpit glass.

The J7W1 was repaired, and the second prototype’s propeller was installed. A tailwheel from a Kyushu K11W Shiragiku (White Chrysanthemum) trainer was added under each vertical stabilizer so that during an over-rotation, a propeller strike would not occur again. Yoshitaka Miyaishi took over the flight tests and started over with ground runs to assess the aircraft’s handling. The J7W1 made its first flight on 3 August 1945. Liftoff occurred at 126 mph (204 km/h), and the aircraft was not flown above 1,312 ft (400 m). The speed did not exceed 161 mph (259 km/h), and the flight lasted under 15 minutes, with the aircraft landing at 115 mph (185 km/h). The J7W1’s tendency to roll to the right persisted and needed much left aileron input to correct, but the aircraft behaved reasonably well otherwise. Two further flights were made on 6 and 8 August, each about 15 minutes in length. The aircraft’s basic handling was evaluated, and the landing gear was never retracted during the tests. The roll to the right was made worse with the flaps deployed and the engine producing more torque to maintain airspeed. The J7W1 exhibited a tendency for its nose to pitch down, which was countered by a steady pull on the control stick. The engine, extension shaft, and remote gear reduction caused some vibration issues.

Modifications were contemplated to neutralize the engine’s torque reaction and correct the aircraft’s handling. A proposition was made to increase the foreplane’s angle of incidence to three degrees and change the main wing’s flap deployment to 30 degrees. In addition, the oil cooler needed to be improved. It was decided that speed tests would be initiated on the aircraft’s next flight, scheduled for 17 August. However, all work was stopped with the Japanese surrender on 15 August, and much of the aircraft’s documentation was burned on 16 August.

Kyushu-J7W1-Shinden-display

The J7W1 on display in Japan after it was repaired and painted. The inlet for the right oil cooler can be seen just behind the induction scoop, and the oil cooler’s exit can be seen right before the propeller. Note that the flaps are partially deployed.

At the end of the war, the second J7W1 was nearly complete and waiting on its [Ha-43] 42 engine, and the third aircraft was under construction. No other examples were completed to any meaningful level. The third J7W1 was planned to have the three-degree foreplane angle of incidence and a [Ha-43] 43 engine that produced an additional 130 hp (97 kW) for takeoff. This engine would have a single impeller for its first-stage, continuously-variable supercharger. The intake for the engine was moved to the inside of the J7W1’s cooling air inlets. The fourth and later aircraft would incorporate the changes from the third and also have a four-blade propeller 11 ft 6 in or 11 ft 10 in (3.5 m or 3.6 m) in diameter. The four-blade propeller had wider blades, was easier to manufacture, and was intended to cure some of the J7W1’s tendency to roll to the right. Beginning with the eighth aircraft, a 2,250 hp (1678 kW) [Ha-43] 51 engine would be installed. The [Ha-43] 51 had a single-stage, three-speed, mechanical supercharger instead of two-stage supercharging with a continuously-variable first stage.

The second and third J7W1 were both destroyed following the Japanese surrender. The first prototype, with around 45 minutes of flight time, was captured by US Marines and found to have all of the cockpit glass removed and some body panels damaged, possibly from a typhoon. For many years, it was thought that the first prototype was destroyed and that the second aircraft was captured by US forces, but this was later found to be incorrect. Under US orders, the aircraft was repaired and repainted while still in Japan. Most pictures of the J7W1 are immediately after the repairs have been made or shortly after it was painted. In almost all of the pictures, the cockpit glass is missing. In October 1945, the J7W1 was disassembled and shipped to the United States.

Kyushu-J7W1-Shinden-Tsuruno

Six US Servicemen and four Japanese dignitaries pose next to the J7W1. Masayoshi Tsuruno, the aircraft’s designer, is the fourth from the left. The men give a good indication of the aircraft’s tall stance and overall size.

The surviving J7W1 was assigned ‘Foreign Evaluation’ FE-326 (later T2-326), and attempts were made to bring the aircraft to a flightworthy status. It is believed that most of this work, including new cockpit glass and installing several American flight instruments, was conducted in mid-1946 at Middletown Air Depot (now Harrisburg International Airport) in Pennsylvania. In September 1946, the aircraft was moved to the Orchard Field Airport (now O’Hare Airport) Special Depot in Park Ridge, Illinois. Instructions indicated that the J7W1 could be made airworthy if an overhauled engine was found, but this never occurred and the aircraft was not flown in the United States. The J7W1 was transferred to the Smithsonian National Air and Space Museum in 1960. The aircraft is preserved in a disassembled and unrestored state, with the [Ha-43] 42 engine still installed in the fuselage. Amazingly, video of the aircraft’s aborted first flight attempt and eventual first flight can be found on YouTube.

Around 2016, a full-size model of the J7W1 was built by Hitoshi Sakamoto. The model was on special display at the Yoichi Space Museum in Hokkaido, but it is not known if it is still there.

A turbojet version of the aircraft had been considered from the start, but a suitable powerplant had not been built in Japan by the close of the war. Designated J7W2 Shinden-Kai, the jet aircraft most likely would have had shorter landing gear, with additional fuel tanks in the wings occupying the space formerly used by the longer gear. There is no indication that the J7W2 had progressed beyond the preliminary design phase before the war’s end.

Kyushu-J7W1-Shinden-NASM

Today, J7W1 is disassembled but fairly complete. However, the years of storage have led to many bent and dented parts. The aircraft was long stored in the Smithsonian National Air and Space Museum’s Paul E. Garber facility, but the cockpit and foreplanes are on display at the Steven F. Udvar-Hazy Center in Chantilly, Virginia. (NASM image)

Sources:
Zoukei-mura Concept Note SWS No. 1 J7W1 Imperial Japanese Navy Fighter Aircraft Shin Den by Hideyuki Shigete (2010)
Japanese Secret Projects by Edwin M. Dyer III (2009)
Japanese Aircraft of the Pacific War by René J. Francillon (1979/2000)
– “Kyushu Airplane Company” The United States Strategic Bombing Survey, Corporation Report No. XV (February 1947)
Encyclopedia of Japanese Aircraft 1900–1945 Vol. 4: Kawasaki by Tadashi Nozawa (1966)
The XPlanes of Imperial Japanese Army & Navy 1924–45 by Shigeru Nohara (1999)
War Prizes by Phil Butler (1994/1998)
https://www.secretprojects.co.uk/threads/kyushu-J7W1-shinden-J7W2-shinden-kai.16914/
https://airandspace.si.edu/collection-objects/kyushu-j7w1-shinden-magnificent-lightning

McDonnell-XP-67-top

McDonnell Aircraft Corporation XP-67 Fighter

By William Pearce

On 20 February 1940, the Army Air Corps (AAC) issued Request for Data R40-C that sought designs of new fighter aircraft capable of 450 mph (724 km/h), with 525 mph (845 km/h) listed as desirable. The AAC encouraged aircraft manufacturers to propose unconventional designs. The McDonnell Aircraft Corporation proposed four variants of its highly-streamlined Model 1 (often called Model I), the company’s first design. Each of the four Model 1 variants were powered by a different engine, and all the engines produced over 2,000 hp (1,491 kW). The Model 1’s engine was buried in the fuselage and drove wing-mounted pusher propellers via extensions shafts and right-angle gear boxes. Although not selected for R40-C, the AAC did purchase engineering data and a wind tunnel model of the design powered by an Allison V-4320 engine.

McDonnell-Model-2-original

The McDonnell Model 2 as originally proposed was similar to the Model 1 but with Continental XI-1430 engines mounted under the wings. This configuration was found to create excessive drag.

McDonnell worked with the AAC to refine the Model 1 design and submitted the Model 2 (often called Model II) on 30 June 1940. The Model 2 had a crew of two, and two wing-mounted Continental XI-1430 engines replaced the single engine in the fuselage. The aircraft retained the basic shape of the Model 1’s fuselage and wings, but the engines were initially mounted directly under the wings in a tractor configuration. The engine mounting was changed as a result of wind tunnel tests. The new configuration was to mount the engine forward of the wing with a nacelle that housed a turbosupercharger extending back past the wing’s trailing edge. The nacelle was mounted mid-wing, and this design minimized drag. To further reduce drag, the Model 2 design was modified to incorporate fairings that blended the fuselage and engine nacelles to the wings. In addition, the design had the pilot as the sole occupant. The single-seat, blended design was called the Model 2A (often called Model IIA), and it was submitted to the AAC on 24 April 1941.

On 5 May 1941, McDonnell submitted preliminary specifications of the Model 2A to the AAC. Under these specifications, the aircraft had a wingspan of 55 ft (16.8 m), a length of 42 ft 3 in (12.9 m), and a height of 14 ft 9 in (4.5 m). The Model 2A had a calculated speed of 500 mph (805 km/h) at 35,000 ft (10,668 km), 472 mph (760 km/h) at 25,000 ft (7,620 m), and 384 mph (618 km) at 5,000 ft (1,524 m). The aircraft would climb to 25,000 ft (7,620 m) in 9 minutes and have a service ceiling of 41,500 ft (12,649 m). At a cruising speed of 316 mph (509 km/h), maximum range was 2,400 miles (3,862 km) with 760 gallons (2,877 L) of internal fuel. The Model 2A had an empty weight of 13,953 lb (6,329 kg), a gross weight of 18,600 lb (8,437 kg), and a maximum weight of 21,480 lb (9,743 kg).

McDonnell-Model-2-revised

The Model 2 was revised with the engines mounted forward of the wings with streamlined nacelles mounted mid-wing. This produced a more attractive aircraft, very similar to the Model 1. However, the relation to the XP-67 is clear.

McDonnell continued to work with the AAC to refine the design of the Model 2A. On 30 September 1941, the Army Air Force (AAF—the AAC was renamed in June 1941) issued a contract to McDonnell to build two prototypes of the Model 2A interceptor pursuit fighter as the XP-67. The aircraft was assigned Materiel Experimental code MX-127. The first aircraft was scheduled to be delivered on 29 April 1943, with the second example delivered six months later on 29 October 1943. The XP-67 had a fairly conventional layout for a single-seat, twin-engine aircraft with tricycle undercarriage. What was not conventional was the extensive blending of the fuselage and engines nacelles to the aircraft’s wings to maintain true airfoil sections throughout the entire aircraft. The end result was a streamlined appearance.

The XP-67 was constructed of an aluminum frame with aluminum skin that formed a monocoque structure. All control surfaces consisted of a fabric covered aluminum frame, although aluminum skinning was later proposed for production aircraft. Effort was expended to keep the XP-67’s surface smooth and make everything flush. Initially, a door on the left side of the pressurized cockpit was to allow access. However, pressurization was dropped on the prototype, and a glazed, rearward-sliding canopy was used.

The wings had two spars, a dihedral of five degrees, and consisted of inner and outer wing sections. The outer wing section extended from the engine nacelle and was removable. Split flaps were located between the nacelle and fuselage. A small split flap existed on the outer side of the engine nacelle. The outer wing section’s trailing edge was occupied by an aileron. The ailerons drooped 15 degrees with deployment of the flaps, which had a maximum deployment of 45 degrees. However, it does not appear that the drooping ailerons were ever installed on the prototype. No hardpoints existed under the wings for bombs or drop tanks.

McDonnell-Model-2A-drawing

The Model 2A as originally proposed in May 1941 was essentially the latest Model 2 design but with large fairings that blended the fuselage and engine nacelles to the wing. This design was contracted as the XP-67.

Mounted to each wing was a liquid-cooled, Continental XI-1430 inverted V-12 engine. Initially, clockwise-rotating (right-handed) XI-1430-1 engines were to be used. In June 1942, the engines were switched to an XI-1430-17 installed on the right wing (clockwise, right-handed rotation) and an XI-1430-19 installed on the left wing (counterclockwise, left-handed rotation). Each engine of the first prototype turned a cuffed, four-blade Curtiss Electric constant-speed propeller that was 10 ft 6 in (3.2 m) in diameter. However, the cuffs were installed after the first aircraft was completed. In April 1943, McDonnell proposed installing Curtiss Electric contra-rotating propellers on the second XP-67 prototype, noting that such a change would increase the aircraft’s speed by 7–10 mph (11–16 km/h) and climb rate by 400 fpm (2.0 m/s).

The engine nacelle extended back from each engine and housed a General Electric D-23 turbosupercharger. Engine exhaust was directed straight back from the nacelle to gain some thrust. Initially, it was proposed that each engine would have a coolant radiator located in the fuselage. This was changed to each engine having two coolant radiators housed in the engine nacelle and located directly under the rear of the engine. The engine nacelles were blended into the wing, and several intakes were incorporated into the wing’s leading edge. For both engine nacelles, the intakes closest to the nacelle passed air to a cooling jacket around the exhaust manifold. The center intake directed air through the two coolant radiators per engine and to the turbosupercharger. The intakes farthest from the engine each led to an oil cooler.

An oil tank in each wing held 26 gallons (98 L) for each engine. The aircraft’s normal fuel load was 282 gallons (1,067 L), but 478 gallons (1,809 L) of additional fuel could be housed in the aircraft’s four fuel tanks located in the fuselage and wing. This brought the XP-67’s total fuel capacity to 760 gallons (2,877 L). The aircraft’s tricycle landing gear was hydraulically-powered and fully retractable. The nose wheel was swiveled, but was not steerable, and folded back into the fuselage. The main gear was mounted just inboard of the engine nacelles and folded inward. In early 1942, the AAF requested that the main gear fold into the engine nacelle, necessitating a complete redesign of the nacelles to accommodate the rearward retracting main wheels. The horizontal stabilizer had 9.55 degrees of dihedral and was mid-mounted to the aircraft’s vertical stabilizer. Like the outer wing panels, the tail was detachable for transporting the aircraft by ground. The XP-67 airframe was stressed for +8 and -4 Gs and had a diving limit of 604 mph (972 km/h) indicated.

McDonnell-XP-67-nacelle-LMAL

An XI-1430-17 with a GE D-23 turbosupercharger installed in the McDonnell XP-67 wing section for tests at the Langley Memorial Aeronautical Laboratory in September 1943. The tests were conducted to evaluate the cooling ducts of the XP-67’s radical blended design. The top image illustrates the unusual ducting of the XP-67’s nacelles, which were duplicated on the opposite side. Closest to the spinner is the exhaust manifold cooling air duct. The large middle duct was for the coolant radiator and engine intake. The outer duct was for the oil cooler. The bottom image shows the turbosupercharger, which was installed so that the exhaust provided additional thrust. Note the radiator cooling air exit duct on the landing gear door and the cuffed propellers. (LMAL images)

The XP-67’s armament changed as the aircraft was developed. Initially, the aircraft would have four 20 mm cannons with 166 rounds per gun and six .50-cal machine guns with 500 rounds per gun. The cannons would be installed on the sides of the cockpit, just behind the pilot. The machine guns were to be installed just behind the cannons. On 5 August 1941, the AAF requested that two 37 mm cannons be installed in place of two 20 mm cannons. By 16 August, the armament was revised again to six 37 mm cannons with 45 rounds per gun and no other guns. The 37 mm cannons were installed in the blended-wing’s leading edge between the cockpit and engine nacelle. The three cannons on each side of the fuselage were outside of the propeller arc. On 20 October, it was suggested that the aircraft’s design should incorporate provisions to replace four of the 37 mm cannons with four 20 mm cannons. On 8 November, it was decided that the first aircraft would have six 37 mm cannons, and the second aircraft would have two 37 mm and four 20 mm cannons.

Extensive wind tunnel tests were conducted on various XP-67 models throughout 1942 and 1943. These tests led to many minor changes in the aircraft. Much of this testing was focused on the extensive fairing used to blend the wing and fuselage. The cooling system was also carefully scrutinized with many minor changes taking place to the cooling ducts. A full-size mockup of the XP-67 was inspected in mid-April 1942, which led to more changes. The most significant changes were lengthening the aircraft’s nose by 15 in (381 mm) and changing the flight control actuation system from push-pull rods to cables. In May, a fuselage section was built to test fire the 37 mm cannons. The tests proved satisfactory, but McDonnell redesigned the 37 mm cannon installation in October, necessitating another mockup and more tests. The new 37mm cannon installation mockup successfully passed its tests in March 1944, but the armament was never installed in the prototype. On 17 June 1942, the decision was made to finish the prototype without a pressurized cockpit. In April 1943, there were discussions of cancelling the XP-67, but the aircraft was seen as a good way to test the experimental wing blending, cannon armament, and XI-1430 engines.

McDonnell-XP-67-construction

The McDonnell XP-67 nearly complete in mid-November 1943. Even though the nacelle’s duct design was found to be insufficient in the wind tunnel tests, the aircraft was not modified with a new design until later. Note the covered ports for 37 mm cannons on each side of the cockpit and that the propellers do not have their cuffs installed.

McDonnell had built a full-scale XP-67 engine nacelle for testing the XI-1430 engine installation. Tests were conducted by McDonnell starting in May 1943. After accumulating almost 27 hours of operation, the rig was sent to the National Advisory Committee for Aeronautics (NACA) at the Langley Memorial Aeronautical Laboratory (LMAL, now Langley Research Center) in Virginia. The NACA added about 17.5 hours to the engine conducting tests in August and September to analyze the installation’s effectiveness for cooling the coolant, oil, and intercooler. The tests indicated that the cooling system was insufficient. The nacelle with revised ducts was then shipped to Wright Field in Dayton, Ohio in October 1943. Wright field added another 6.5 hours to the engine, bringing the total to 51 hours. The new ducts proved satisfactory, reducing the drag of the ducts by 25 percent and improving cooling by 200 percent. However, excessive vibrations occurred between the engine and its mounting structure, necessitating a more rigid mount. McDonnell was allowed to proceeded with testing the first XP-67, although the prototype would not be changed until after its first flight when additional changes beyond the cooling system would most likely need to take place. Wind tunnel tests had indicated that the horizontal stabilizer would need to be raised by 12 in (305 mm) to improve stability. McDonnell was instructed to stop work on the second prototype until successful flight tests of the first aircraft had been conducted.

Serial number 42-11677 was given to the first XP-67, and serial number 42-11678 was given to the second prototype. Unofficially, the XP-67 was given the name ‘Moonbat’ or just ‘Bat,’ but it does not appear that an official name was ever bestowed upon the aircraft. With all the design changes since the XP-67 was initially contracted, the aircraft’s specifications had changed. The wingspan remained at 55 ft (16.8 m), but the length increased 2 ft 6 in (.8 m) to 44 ft 9 in (13.6 m), and the height increased 1 ft (.3 m) to 15 ft 9 in (4.8 m). The standard fuel load remained at 280 gallons (1,060 L), but the additional fuel load decreased by 25 gallons (95 L) to 455 gallons (1,722 L), giving a total maximum internal fuel load of 735 gallons (2,782 L). The XP-67’s weight had increased by 3,792 lb (1,720 kg), resulting in an empty weight of 17,745 lb (8,049 kg), a gross weight of 22,114 lb (10,031 kg), and a maximum weight of 24,836 lb (11,265 kg). A reduction in performance accompanied the weight increase, resulting in an estimated speed of 448 mph (720 km/h) at 25,000 ft (7,620 m), which was a 24 mph (39 km/h) reduction, and 367 mph (591 km/h) at sea level. The time to climb to 25,000 ft (7,620 m) was increased by nearly five minutes to 14.8 minutes, and the service ceiling decreased 4,100 ft (1,250 m) to 37,400 ft (11,400 m). The XP-67’s cruising speed decreased 46 mph (74 km/h) to 270 mph (435 km/h), but maximum range was little changed at 2,385 miles (3,838 km) with 735 gallons (2,782 L) of fuel.

McDonnell-XP-67-right-front

The completed XP-67 with revised nacelle cooling ducts and after the horizontal stabilizer was raised 12 in (305 mm). The most noticeable duct modification was to the exhaust manifold cooling intake, which was changed to a scoop. Note that the propellers rotated in opposite directions.

On 1 December 1943, the XP-67 had its XI-1430 engines installed and was ready for ground tests. However, both engines caught fire and damaged the aircraft on 8 December. The fires were caused by issues with the exhaust manifolds. The XP-67 was repaired and made its first flight on 6 January 1944, taking off from Scott Field in Belleville, Illinois. The flight was nearly two years later than the anticipated first flight when the XP-67 contract was originally issued. Test pilot Ed E. Elliott had to cut the flight to just six minutes due to both turbosuperchargers overheating, which resulted in small fires. During the short flight, the XP-67 exhibited good handling characteristics.

The aircraft was again repaired, with the second and third flights occurring on 26 and 28 January 1944. On 1 February, the aircraft’s fourth flight was cut short due to a main bearing failure on the left engine caused by an unintentional overspeed of the engine. The cockpit canopy also detached during the flight. While the XP-67 was down for repairs and new XI-1430 engines, the horizontal stabilizer was raised 12 in (305 mm). The cooling ducts in the engine nacelles were also modified, with the most noticeable being the exhaust shroud inlet, which was changed to more of a scoop. The updated aircraft flew again on 23 March 1944 and demonstrated improved stability, but one turbosupercharger failed at 10,000 ft (3,048 m).

In April 1944, it was reported that the engines were running too cool. The closed main gear door formed part of the air duct aft of the radiator. However, the gear doors did not seal tightly and caused an excessive amount of air to exit the duct. This resulted in too much air passing through the radiator and reducing the engine temperature below ideal levels. McDonnell was allowed to install a thermostat on the prototype to help control coolant temperatures but was also told that such issues would not be acceptable on production aircraft. Around this same time, construction of the second prototype was allowed to proceed with the exception of parts that would be affected by an engine change.

McDonnell-XP-67-top

The unusual planform of the XP-67 is illustrated in this view. The two ports in the middle of each nacelle were the forward exit for the exhaust manifold cooling air. The rear exit is denoted by the white staining at the end of the nacelle. The outer wing section was detachable just outside of the nacelle.

In May 1944, three AAF pilots flew the XP-67 and reported that the XI-1430 engines ran rough and seemed underpowered. Tests indicated that at normal power, the engines were only delivering 1,060 hp (790 kW), well below the expected 1,350 hp (1,007 kW). The XP-67 was noted for having high control forces at high speeds, exhibiting a Dutch roll indicating some directional instability, and not making a good gun platform. The maximum speed with the engines delivering 1,600 hp (1,193 kW) at 3,200 rpm was 357 mph (574 km/h) at 10,000 ft (3,048 m) and 393 mph (632 km/h) at 20,000 ft (6,096 m). From these values and other tests, McDonnell calculated that the XP-67 could attain 405 mph (652 km/h) at 25,000 ft (7,620 m) at the same power setting. Takeoff speed was 130 mph (209 km/h); the clean stall speed was 118 mph (190 km/h) with buffeting starting at 140 mph (225 km/h); and the aircraft had a high landing speed of 120 mph (193 km/h). In general, the XP-67 was found to be inferior to other fighters currently in production.

McDonnell got permission to install contra-rotating propellers on the first prototype when the engines were ready, and they were expected in June 1944. No information has been found indicating that the contra-rotating versions of the XI-1430 were delivered. In June, it was decided to install 11 ft (3.4 m) diameter four-blade Aeroproducts propellers rather than contra-rotating propellers. However, tests would continue with the Curtiss propellers until the Aeroproducts were ready. It was also noted that the XP-67 had experienced no engine fires since its fourth flight, and the aircraft had completed about 50 flights without any serious issues.

McDonnell-XP-67-in-flight

The limited flight trials of the XP-67 indicated the aircraft handled fairly well. It was noted as underpowered and slightly unstable. Overall, visibility was said to be poor, with the engine and fairing blocking most of the view to the side and rear. Formation flying would have been difficult, as the pilot was unable to see their wingtips.

In July 1944, some in the AAF felt that the XP-67 program was expensive and served no purpose. However, others felt that the aircraft was a unique platform that would allow the testing of the six 37 mm cannons. In addition, the possibility existed to install 12 .50-cal machine guns or eight 20 mm cannons. The aircraft was seen as a good test machine, even if its performance fell below what was originally specified. It was decided to complete tests on the current aircraft to assess the blended design and then consider the possibility of armament trials.

McDonnell had long sought to change the aircraft’s engines. On 19 January 1944, McDonnell proposed discarding the XI-1430s for the second prototype and using either two-stage Allison V-1710 or Rolls-Royce Merlin RM 14SM (100-series prototype) piston engines. In addition, each engine nacelle would house a Westinghouse 9.5 (J32) turbojet behind the piston engine. The mixed-power proposal was brought up again on 16 March 1944, now using an Allison V-1710-199 (F32R) piston engine and either a Rolls-Royce W2B/37 turbojet or a GE I-20 (J39) turbojet in the nacelle. With mixed power plants, the aircraft had an estimated top speed at sea level of 500 mph (805 km/h). The engine issue was discussed again in July 1944, with McDonnell now suggesting a Rolls-Royce Merlin RM 14SM piston engine paired with a GE I-20 (J39) turbojet in each nacelle. However, AAF felt that the aircraft would need a complete redesign to incorporate different piston engines with turbojets.

Since its initial design in May 1941, there were suggestions of using a modified version of the XP-67 for photo reconnaissance. In April 1942, McDonnell suggested that the aircraft’s range could be extended to 4,000 miles (6,437 km) at a cruise speed of 200 mph (322 km/h), which would be a 20-hour flight. For this, two of the 37 mm cannons would need to be omitted and six additional fuel tanks installed along with 280 lb (127 kg) of ballast in the nose. With the extra tanks, the aircraft’s internal fuel capacity was 1,290 gallons (4,883 L). This concept was not pursued at the time, but the range extension was considered later for a photo-recon role.

McDonnell-XP-67E-model

A model of the XP-67E with its bubble canopy and mixed piston / turbojet power plants. It is not clear what engines (if any) are intended to be depicted by the model, but the nacelles were extended back to house the jet engine (LMAL image).

By July 1944, it was believed that a photo-recon version of the XP-67 would have inferior performance compared to the Lockheed F-5 (P-38). However, a mixed-power version of the aircraft was seen as a possible candidate as a photo-recon aircraft. The XP-67E was designed for the photo-recon role, and it incorporated mixed power, additional internal fuel tanks, and provisions for two 150-gallon (568-L) drop tanks mounted under the aircraft’s center section. In the XP-67E design, the engine nacelles were extended back to house the GE I-20 (J39) turbojet engine. Cameras were installed in the aft fuselage, and the XP-67E was unarmed. The fuselage was mostly unchanged, but the cockpit was enclosed in a rearward-sliding bubble canopy.

The XP-67 prototype had been undergoing modifications and repairs through August 1944. Perhaps the most major change was alerting the wing dihedral from 5 degrees to 7 degrees in an attempt to increase stability. The aircraft was ready to resume flight tests in early September. On 6 September 1944, the exhaust valve rocker of the No. 1 cylinder in the XP-67’s right engine broke while the aircraft was in flight at 10,000 ft (3,048 m). Exhaust gases unable to escape the cylinder backed up into the intake manifold and caused it to fail, resulting in a fire. The fire was first noticed at 3,000 ft (914 m) as the aircraft was preparing to land. Test pilot Elliott was able to land the XP-67 and stopped it to limit the flames from spreading. However, the brake failed after Elliott exited the aircraft, and wind turned the XP-67 so that the flames blew toward the fuselage. The XP-67 was nearly burned in half and damaged beyond repair. The aircraft had a total flight time of 43 hours. This event effectively killed the XP-67 project and the XP-67E photo-recon proposal. The entire program was suspended seven days later on 13 September, and on 24 October, McDonnell was notified that the XP-67 contract was cancelled. A formal Notice of Cancellation followed on 27 October 1944. The second prototype was about 15 percent complete and was subsequently scrapped. The total cost of the XP-67 program was approximately $4,733,476.92.

McDonnell-XP-67-fire-front

The XP-67 after the fire on 6 September 1944. Once on the ground, the fire from the right engine spread to the rear fuselage and left nacelle. The rear fuselage was nearly burned through and collapsed to the ground. An inglorious end to both the XP-67 and XI-1430 programs.

Sources:
Interceptor Pursuit Airplane Twin Engine Type XP Preliminary Specifications by McDonnell Aircraft Corporation (5 May 1941)
Memorandum Report on XP-67 Airplane, AAF No, 42-11677 by Osmond J. Ritland (19 May 1944)
Final Report on the XP-67 Airplane by John F Aldridge Jr. (31 January 1946)
Case History of XP-67 Airplane by Historical Division, Air Materiel Command (23 July 1946)
USAF Fighters of World War Two Volume Three by Michael O’Leary (1986)
U.S. Experimental & Prototype Aircraft Projects: Fighters 1939-1945 by Bill Norton (2008)

Curtiss-XF14C-2-front-left

Curtiss XF14C Carrier-Based Fighter

By William Pearce

On 30 June 1941, the United States Navy, in preparation for the future of aerial combat, ordered prototypes of the Grumman F6F Hellcat carrier fighter and the F7F Tigercat heavy fighter. The Hellcat was intended to replace the F4F Wildcat and counter the Japanese Mitsubishi A6M Zero. The Tigercat was intended to out-perform and out-gun all other fighters. The Hellcat and Tigercat went on to serve with distinction for many years. Also on 30 June 1941, the Navy ordered two prototypes of the Curtiss XF14C.

Curtiss-XF14C-2-front-left

The Curtiss XF14C-2 with its contra-rotating propellers and four 20 mm cannons appears as an imposing aircraft. However, its performance did not meet expectations. Note the stagger of the cannons and the glazed, rearward-sliding canopy.

Since 1939, the Navy had been supporting the development of the 2,300 hp (1,715 kW) Lycoming XH-2470 engine. The XH-2470 was a liquid-cooled, 24-cylinder engine in a vertical H configuration. The Navy’s support for the XH-2470 was unusual, as it had a long history of exclusively using air-cooled radial engines. In addition, the Navy had no applications for the engine until the XF14C was proposed as a high-performance fighter.

The Curtiss-Wright XF14C was designed at the company’s main facility in Buffalo, New York. The two XF14C-1 prototypes ordered were assigned Navy Bureau of Aeronautics numbers (BuNo) 03183 and 03184. Most sources state that the XF14C-1 was to be powered by the XH-2470-4 engine. Lycoming documents indicate that the -4 featured contra-rotating propellers. However, some sources state the XF14C-1 had a single rotation propeller that was 14 ft 2 in (4.32 m) in diameter. The XH-2470-2 used a single rotation propeller, but no sources have been found specifically stating that this was the engine for XF14C-1.

Regardless of the exact engine model and propellers, the XF14C-1 was an all-metal, low-wing aircraft with standard landing gear and a conventional layout. The gear was fully retractable, including the tail-wheel, and the main legs had a wide track. The arrestor tail hook extended from the extreme rear of the fuselage. The outer panels of the wings had around 7.5 degrees of dihedral and folded up for aircraft storage on an aircraft carrier. The fixed wing section had a flap along its trailing edge, and the folding section had a small flap on its inner trailing edge. The rest of the folding section had an aileron along its trailing edge. Just inboard of the wing-fold was the aircraft’s armament. Initially, each wing would house three .50-cal machine guns, but this was revised to two 20 mm cannons with 166 rounds per gun.

Curtiss-XF14C-2-right-side

Side profile of the XF14C-2 illustrates the large exhaust pipe from the turbosupercharger under the aircraft. The inscription under the diving figure on the cowling reads “Coral Princess.” Note the large wheel covers and the retracted tail hook.

The XF14C-1 had a 46 ft (14.02 m) wingspan, was 38 ft 4 in (11.68 m) long, and was 14 ft 6 in (4.42 m) tall. With the wings folded, the aircraft’s span was 22 ft 6 in (6.89 m). The XF14C-1 had an estimated speed of 344 mph (554 km/h) at 3,500 ft (1,067 m) and 374 mph (602 km/h) at 17,000 ft (5,182 m). Its initial rate of climb was 2,810 fpm (14.3 m/s), and it had a service ceiling of 30,500 ft (9,296 m). The aircraft had an empty weight of 9,868 lb (4,476 kg), a gross weight of 12,691 lb (5,757 kg), and a maximum weight of 13,868 lb (6,290 kg). The XF14C-1 had a range of 1,080 miles (1,738 km) at 176 mph (283 km/h) on 230 US gallons (192 Imp gal / 871 L) of internal fuel. With two 75-US gallon (62 Imp gal / 284 L) drop tanks, range increased to 1,520 miles (2,446 km) at 164 mph (264 km).

Wind tunnel tests conducted by the Navy in October 1942 indicated that the Curtiss-provided performance specifications for the XF14C-1 were optimistic, but the program moved forward. The first airframe (BuNo 03183) was mostly complete by September 1943. However, delays with the XH-2470 left the XF14C-1 without an engine. The engine delay gives some credence to a contra-rotating version of the XH-2470 being used in the XF14C-1. A single rotation XH-2470 had passed a Navy acceptance test in April 1941, and a single rotation XH-2470 that was delivered to the Army Air Force had made its first flight in the Vultee XP-54 on 15 January 1943. With the availability of the single-rotation XH-2470 for the Army Air Force, it seems that such an engine could have been supplied to Curtiss for the XF14C-1 if that is what the aircraft needed. The Navy subsequently dropped its participation in the XH-2470 engine program, and the XF14C-1 was cancelled in December 1943.

Curtiss and the Navy negotiated to proceed with the XF14C program by changing the engine to the experimental Wright XR-3350-16. The -16 was turbosupercharged and used contra-rotating propellers. Rated at 2,250 hp (1,678 kW) at 32,000 ft (9,754 m), the 18-cylinder, air-cooled, radial engine offered a higher service ceiling than the XH-2470. This interested the Navy, as they were looking toward developing a high-altitude interceptor. With the new engine, the Curtiss aircraft became the XF14C-2 and was pushed into a high-altitude fighter role. The cancellation of the XF14C-1 terminated all work on the second prototype, BuNo 03184, which was never built.

Curtiss-XF14C-2-wings-folded

The XF14C-2’s outer wing section folded up just outside of the cannons. Note the gap around the spinner for cooling the two-row, 18-cylinder R-3350 engine and that the second set of propeller blades have cuffs to aid cooling.

BuNo 03183 became the XF14C-2 and was modified to accept the new engine. A six-blade, contra-rotating Curtiss Electric propeller with a diameter of approximately 12 ft 10 in (3.91 m) was installed on the XR-3350-16 engine. The cowling incorporated an intake scoop under the engine. Oil coolers were placed in extensions of the XF14C-2 wing roots. The turbosupercharger was installed directly behind the engine in a housing that extended back from the lower cowling. A large exhaust pipe from the turbosupercharger extended below the aircraft behind the main wheels.

The Curtiss XF14C-2 had the same 46 ft (14.02 m) wingspan as the XF14C-1 but was shorter at 37 ft 9 in (37.75 m) long and 12 ft 4 in (3.76 m) tall. The aircraft had an estimated speed of 317 mph (510 km/h) at sea level and 424 mph (682 km/h) at 32,000 ft (9,754 m). The XF14C-2’s initial rate of climb was 2,700 fpm (13.7 m/s), and it had a service ceiling of 39,500 ft (12,040 m). The aircraft had an empty weight of 10,582 lb (4,800 kg), a gross weight of 13,405 lb (6,080 kg), and a maximum weight of 14,950 lb (6,781 kg). At a cruising speed of 172 mph (277 km/h), the XF14C-2 had a range of 950 miles (1,529 km) on 230 US gallons (192 Imp gal / 871 L) of internal fuel and 1,355 miles (2,181 km) with two 75-US gallon (62 Imp gal / 284 L) drop tanks.

The XF14C-2 was first flown in July 1944 and delivered to the Navy on 2 September 1944. Testing quickly revealed that the aircraft did not meet the expected performance and offered no advantage over fighters already in service. Top speeds of only 300 mph (483 km/h) at sea level and 398 mph (641 km/h) at 32,000 ft (9,754 m) were achieved. The aircraft’s engine and propeller combination also caused a bad vibration throughout the airframe. With the XF14C-2 underperforming, no urgent need for a high-altitude fighter, and all the R-3350 production dedicated for the Boeing B-29 Superfortress and Convair B-32 Dominator bombers, the Navy cancelled the XF14C-2. The airframe was eventually scrapped. The XF14C-2 was the last piston-engine fighter built by Curtiss.

Curtiss proposed the XF14C-3 to truly fulfill the role of a high-altitude fighter. It had a pressurized cockpit and could operate at 40,000 ft. Studies of the XF14C-3 were conducted at Navy expense until early 1945, but no aircraft was built.

Curtiss-XF14C-2-front-right

The XF14C-2 had oil-coolers in the wing roots. Note the dihedral angle of the outer wing sections. The engine and propeller combination caused an unacceptable level of vibration.

Sources:
Curtiss Fighter Aircraft by Francis H. Dean and Dan Hegedorn (2007)
US Experimental & Prototype Aircraft Projects: Fighters 1939-1945 by Bill Norton (2008)
American Secret Projects 1 by Tony Buttler and Alan Griffith (2015)
To Join with the Eagles by Murry Rubenstein and Richard M. Goldman (1974)
The American Fighter by Enzo Angelucci and Peter Bowers (1987)