Category Archives: World War II

Hughes XF-11 no1 taxi

Hughes XF-11 Photo-Reconnaissance Aircraft

By William Pearce

In the early World War II years, the Hughes Aircraft Company (HAC) worked to design and build its D-2 aircraft intended for a variety of roles. However, the United States Army Air Force (AAF) was not truly interested in the twin-engine wooded aircraft. To cure design deficiencies and make the aircraft more appealing to the AAF, HAC proposed a redesign of the D-2, designated D-5.

Hughes XF-11 no1 front

The Hughes XF-11 was an impressive and powerful aircraft intended for the photo-reconnaissance role. The eight-blade, contra-rotating propellers were over 15 ft (4.6 m) in diameter. Note the deployed flaps between the tail booms. (UNLV Libraries image)

The initial D-5 design was an enlarged D-2 and employed Duramold construction using resin-impregnated layers of wood, molded to shape under pressure and heat. The proposed aircraft had a 92 ft (28.0 m) wingspan, was 58 ft (17.7 m) in length, and weighed 36,400 lb (16,511 kg). The D-5 was powered by Pratt & Whitney (P&W) R-2800 engines and had a forecasted top speed of 488 mph (785 km/h) at 30,000 ft (9,144 m) and 451 mph (726 km/h) at 36,000 ft (10,973 m). A 4,000 lb (1,814 kg) bomb load could be carried in an internal bay. The AAF was still not interested in the aircraft and felt that HAC did not have the capability to manufacture such an aircraft in large numbers.

In early August 1943, Col. Elliot Roosevelt, President Franklin Roosevelt’s son, was in the Los Angeles inquiring with various aircraft manufacturers to find a photo-reconnaissance aircraft. Col. Roosevelt, who had previously commanded a reconnaissance unit, was hosted by Hughes and taken on a personal tour of the D-2. At the time, the aircraft was undergoing modification to become the D-5 and was not available for flight, but Col. Roosevelt was sufficiently impressed.

Hughes XF-11 no1 taxi

Howard Hughes taxies the first XF-11 out for its first and last flight. The nose of the aircraft accommodated a variety of camera equipment. Note the cowl flaps and the large scoops under the engine nacelles. (UNLV Libraries image)

General Henry “Hap” Arnold of the AAF was put under pressure from the White House to order the D-5 reconnaissance aircraft into production. To ease the AAF’s concerns about the D-5’s Duramold construction, the design was changed to metal wings and tail booms and only the fuselage built from Durmold. Arnold made the decision to order the D-5 aircraft “much against [his] better judgment and the advice of [his] staff.” The AAF issued a letter of intent on 6 October 1943 for the purchase of 100 examples of the D-5 reconnaissance aircraft. An official contract for the aircraft, designated F-11, was issued on 5 May 1944. Two aircraft would serve as prototypes with the remaining 98 aircraft as production versions.

As contracted, the Hughes XF-11 prototypes were of an all-metal construction and powered by two P&W R-4360 engines. The aircraft had the same layout as the Lockheed P-38 Lightning but was much larger. The fuselage consisted of a streamlined nacelle mounted to the center of the wing. At the front of the fuselage were provisions for photographic equipment. The cockpit was positioned just before the wing’s leading edge, and the cockpit was covered by a large, fixed bubble canopy. The pressurized cockpit could maintain an altitude of 10,500 ft (3,200 m) up an aircraft altitude of 33,500 ft (10,211 m). Entry to the cockpit was via a hatch and extendable ladder just behind the nose wheel landing gear well. The pilot’s seat was offset slightly to the left. Behind and to the right of the pilot sat a second crew member, who would fulfill the role of a navigator/photographer. The second crew member could crawl past the pilot and into the aircraft’s nose to service the cameras while in flight. The nose landing gear retracted to the rear and was stowed under the cockpit.

Hughes XF-11 no1 first flight

One of the very few images of the first XF-11 in flight as it takes off from Hughes Airport in Culver City, California on 7 July 1946. Note the rural background that is now completely developed. (UNLV Libraries image)

The XF-11’s wings had a straight leading and trailing edges, with the leading edge swept back approximately 6 degrees and the trailing edge swept forward around 3.5 degrees. Mounted to each wing about a third of the distance from the fuselage to the wing tip was the engine. The engine nacelle was slung under the wing and extended back to the aircraft’s tail. A large flap was located on the wing’s trailing edge between the tail booms. Each wing had an addition flap that extended from outside of the tail boom to near the wing tip. Relatively small ailerons spanned the approximate 66 in (1.68 m) distance from the flap to the wing tip. The aircraft’s main source of roll control were spoilers positioned on the upper surface of the outer wing and in front of the flap. Each wing incorporated a hardpoint outside of the tail boom for a 700 gallon (2,650 L) drop tank, and 600 gallon (2,271 L) jettisonable tip tanks were proposed but not included on the prototype aircraft.

Each 3,000 hp (2,237 kW), 28-cylinder R-4360 engine was installed in the front of the wing and was housed in a streamlined cowling. Cowl flaps for engine cooling circled the sides and top of the cowling. Under the engine nacelle was a scoop that housed the oil cooler and provided air to the intercooler and the two General Electric BH-1 turbosuperchargers installed in each tail boom. Air that flowed through the oil cooler exited at the back of the scoop. Air that flowed through the intercooler was routed to an exit door on top of the engine nacelle, just above the wing’s leading edge. Exhaust from the superchargers was expelled from the sides of the engine nacelle, just under the wing. The turbosupercharger on the inner side of each tail boom could be shut down during cruise flight to take full advantage of the remaining turbosupercharger operating at its maximum performance. The main landing gear was positioned behind the engine and retracted to the rear into the tail boom. Attached to the end of each tail boom was a large, 11 ft 8 in (3.56 m) tall vertical stabilizer. Mounted in the 25 ft 8 in (7.82 m) space between the vertical stabilizers was the horizontal stabilizer. The left tail boom housed additional camera equipment behind the main landing gear well.

Hughes XF-11 no1 cockpit crash

The cockpit of the crashed XF-11 illustrates how lucky Hughes was to have survived. Hughes crawled out through the melted Plexiglas and was aided by residents who had witnessed the crash. Note the armored seat. The XF-11 had 350 lb (159 kg) of cockpit armor and self-sealing fuel tanks. (UNLV Libraries image)

The XF-11 had a wingspan of 101 ft 4 in (30.9 m), a length of 65 ft 5 in (19.9 m), and a height of 23 ft 3 (7.09 m). The aircraft had a top speed of 450 mph (725 km/h) at 33,000 ft (10,058 m) and 295 mph (475 km/h) at sea level. The XF-11 had a service ceiling of 42,000 ft (12,802 m), an initial climb rate of 2,025 fpm (10.3 m/s) and could climb to 33,000 ft (10,058 m) in 17.4 minutes. The aircraft had an empty weight of 39,278 lb (17,816 kg) and a maximum weight of 58,315 lb (26,451 kg). With its 2,105 gallon (7,968 L) internal fuel load, the XF-11 had a 5,000 mile (8,047 km) maximum range.

Delivery of the first XF-11 (44-70155) was originally scheduled for November 1944 with peak production of 10 aircraft per month being reached in March 1945—an ambitions timeline for any aircraft manufacturer. Delays were encountered almost immediately and gave credence to the AAF’s belief that HAC was not up to the task of designing and manufacturing aircraft for series production. By mid-1945, the XF-11 had still not flown, and the war was winding down. It was clear that the XF-11 would not be involved in World War II, and there was much doubt as to the usefulness of the aircraft post-war. As a result, the order for 98 production examples was cancelled on 26 May 1945, but the construction of the two prototypes was to proceed.

Hughes XF-11 no2 front

With the exception of its propellers, the second XF-11 was essentially the same as the first aircraft. The bulges on the nacelles under the wings were the exhaust outlets for the inner turbosuperchargers. (UNLV Libraries image)

The first XF-11 prototype was fitted with Hamilton-Standard Superhydromatic contra-rotating propellers. The front four-blade propeller was 15 ft 1 in (4.60 m) in diameter, and the rear four-blade propeller was 2 in (51 mm) longer at 15 ft and 3 in (4.65 m) in diameter. The impressive aircraft was finally finished by April 1946 and began taxi test. With Howard Hughes at the controls, an aborted high-speed taxi test on 15 April resulted in some minor damage and the need to rework some of the aircraft’s systems.

Once repaired, Hughes decided to make the XF-11’s first flight on 7 July 1946. The AAF had stipulated that the XF-11’s first flight should be no more that 45 minutes, the landing gear should not be retracted, the aircraft should stay near the airport and away from populated areas, communication should be established with the chase plane, and the flight should follow the plan discussed beforehand. While the flight was discussed with some, many involved with the aircraft were unaware of Hughes’ plans. Had his intentions been better known, someone may have reminded him about the propeller seal leak on the right engine. Hughes request 1,200 gallons (4,542 L) of fuel to be on board, which was twice as much as should be needed for the scheduled 45-minute flight. HAC’s Douglas A-20 Havoc would serve as a chase plane for the flight, but radio issues prevented communication between the two aircraft.

Hughes XF-11 no2 top

Top view of the second XF-11 illustrates the aircraft’s layout, which was similar to that of a Lockheed P-38. However, the XF-11 was a massive aircraft. Note that the rear of the fixed canopy has been removed. (UNLV Libraries image)

At around 5:20 PM, Hughes took the XF-11 off from Hughes Airport in Culver City, California on its maiden flight. Shortly after takeoff, Hughes retracted the gar, and the right main light remined illuminated, indicating a possible issue with the retraction. Hughes and the XF-11 flew out over the Pacific Ocean and turned back toward land. The landing gear was cycled several times during the flight in an attempt to resolve the perceived issue on account of the illuminated light.

After about an hour and 15 minutes, the oil supply in the right propeller was exhausted and the rear set of blades moved into a flat or reversed pitch. Had Hughes stuck to the 45-minute flight as the AAF ordered, the oil supply would not have been depleted. The reversed pitch propeller created a massive amount of drag on the right side of the aircraft. To the A-20 chase plane, it appeared that Hughes was maneuvering to land back at Culver City, some distance away. The chase plane broke formation to return to the airfield on its own. Had the two aircraft been in communication, the situation could have been discussed.

Hughes XF-11 no2 top rear

The trailing edge of the XF-11’s wing had a flap between the tail booms. Long flaps extended from the outer side of the tail booms almost to the wing tips. Note the relatively small ailerons at the wing tips. The wing spoilers are visible just in front of the outer flaps. (UNLV Libraries image)

Hughes, now alone, believed that the right main gear had deployed on its own and was causing the drag. Had Hughes left the gear down, he would have known the drag was a result of some other issue with the aircraft. Trying to keep the XF-11 straight resulted in the deployment of the left-wing spoilers, which further slowed the aircraft. Low, slow, and over a populated area, Hughes tried to make it to the open space of the Los Angles Country Club golf course in Beverly Hills. Landing short, the XF-11 crashed into four houses, broke apart, and caught fire. Hughes managed to pull himself from the wreckage, where he was helped further by neighborhood residents and arriving paramedics. Hughes suffers major injuries, including severe burns, at least 11 broken ribs, a punctured lung, and a displaced heart. Remarkably, he made a near-full recovery, but the incident started an addiction to codine, which would cause Hughes problems throughout the rest of his life.

Construction of the second XF-11 prototype (44-70156) continued after the accident. The second prototype used single rotation, four-blade propellers that were 14 ft 8 in (4.47 m) in diameter and made by Curtis Electric. Despite all of the new rules implemented because of his crash, Hughes was adamant that he pilot the first flight of the second XF-11 prototype. The AAF initially refused, but Hughes pressed the issue and made personal appeals to Lt.Gen. Ira Eaker and Gen. Carl Spaatz. Hughes also offered to put up a $5 million bond payable to the AAF if he crashed. With the posting of the bond, the AAF gave in. On 4 April 1947, Hughes flew the second XF-11 on its first flight, taking off from Hughes Airport. The flight was a personal victory for Hughes.

Hughes XF-11 no2 flight

The second XF-11 on an early test flight. The aircraft was later fitted with spinners. Note the turbosupercharger’s exhaust just under the wing and the oil cooler’s air exit at the end of the scoop. (UNLV Libraries image)

The second XF-11 was later delivered to the AAF at Wright Field, Ohio in November 1947. After further flight tests, the aircraft went to Eglin Air Force Base in Florida. The XF-11 was noted for having good flight characteristics, but in-flight access of the camera equipment was extremely difficult and some of the aircraft’s systems were unreliable. In 1948, the aircraft was redesignated XR-11 in accordance to the new Air Force designation system. The XF-11 was tested at Eglin from December 1947 through July 1949.

Other, existing aircraft, mainly Boeing RB-29s and RB-50s, were serving in the reconnaissance role intended for the XF-11. These aircraft proved much less expensive than the XF-11, making the impressive and powerful XF-11 irrelevant. While the XF-11 probably could have done the reconnaissance job better, money was tight in the post-war years and there were other, more-promising projects to fund. The XF-11 was transferred to Sheppard Air Force Base in Wichita Falls, Texas on 26 July 1949 and subsequently served as a ground training aid, never flying again. The aircraft was struck from the Air Force’s inventory in November 1949 and was eventually scrapped.

Hughes XF-11 no2 1948

The second XF-11 sometime in 1948 with the revised (red stripe) Air Force insignia. The aircraft has recently taken off and the very large nose gear doors are just closing. Note the underwing pylons. (UNLV Libraries image)

Sources:
World’s Fastest Four-Engined Piston-Powered Aircraft by Mike Machat (2011)
R-4360: Pratt & Whitney’s Major Miracle by Graham White (2006)
Howard Hughes: An Airman, His Aircraft, and His Great Flights by Thomas Wildenberg and R.E.G. Davies (2006)
McDonnell Douglas Aircraft since 1920: Volume II by René J. Francillon (1990)
“A Visionary Ahead of His Time: Howard Hughes and the U.S. Air Force—Part II” by Thomas Wildenberg, Air Power History (Spring 2008)
https://en.wikipedia.org/wiki/Hughes_XF-11

Vickers Type 432 in flight

Vickers Type 432 High-Altitude Fighter

By William Pearce

In March 1939, The British Air Ministry issued Specification F.6/39 for a 400 mph (644 km/h) two-seat fighter. The aircraft was to carry four 20-mm cannons, with the possibility of later mounting two 40-mm cannons. Under a design team led by Rex Pierson, Vickers-Armstrongs Ltd. (Vickers) had been working on a fighter with a single flexibly-mounted 40-mm cannon installed in the aircraft’s nose. The twin-engine aircraft was powered by Rolls-Royce Griffon engines and met the requirements of F.6/39, aside from its armament. Vickers met with the Air Ministry in April 1939 to discuss the aircraft’s potential. The Air Ministry was sufficiently impressed and issued Specification F.22/39 that covered the Vickers fighter, which carried the internal designation Type 414. Specification F.6/39 was subsequently cancelled in November 1939.

Vickers Type 432 front right

The Vickers Type 432 prototype DZ217 appears shortly after its completion at Foxwarren. The bystander gives some indication to the aircraft’s size. Note the bubble canopy.

Two Type 414 prototypes were ordered on 30 August 1939, and they were assigned serial numbers R2436 and R2437. After inspection of the Type 414 mockup in early February, the Air Ministry inquired about the possibility of installing several 20-mm cannons in place of the single 40-mm cannon. Vickers responded with aircraft proposals incorporating eight 20-mm cannons or two 40-mm cannons.

Vickers designated the fighter with 20-mm cannons as the Type 420. Two cannons were positioned in the aircraft’s nose, and three were on each side of the cockpit. Vickers and the Air Ministry discussed the Type 420 in June 1940, and Specification F.16/40 was issued for the aircraft’s development. The Type 420 was given a high priority, and an order for two prototypes was expected. The order for two Type 414 prototypes was still in place. However, the Type 420 took precedence, and work on the Type 414 slowed substantially.

In early January 1941, the Air Ministry requested a design change to reduce the number of 20-mm cannons to six. At the same time, Vickers had designed a high-altitude fighter that used many components from the Type 420. The high-altitude aircraft was armed with four 20-mm cannons and powered by two Rolls-Royce Merlin engines. The Air Ministry was interested in Vickers’ proposal, as they felt there was an urgent need for a heavily armed, high-altitude fighter aircraft to intercept high-altitude German bombers that were expected in the skies over Britain. However, high-altitude German bombing raids were never undertaken en masse and did not present a significant threat to Britain during World War II.

Vickers Type 432 rear right

Rear view of the Type 432 displays the aircraft’s long engine nacelles and ventral pod for the six 20-mm cannons. Note how the aircraft’s tail resembles that of a de Havilland Mosquito. The completed aircraft was disassembled at Foxwarren and taken to Farnborough for flight testing.

In March 1941, work on the Type 414 was stopped completely, and discussions with Rolls Royce commenced regarding the acquisition of Merlin engines. In May 1941, Vickers detailed the specifics of the high-altitude aircraft, which it had designated as Type 432. Specification F.22/39 was cancelled, thus halting work on the Type 420. Design work on the Type 432 continued, resulting in the switch to a single-seat cockpit placed in the nose of the aircraft and six 20-mm cannons installed in a ventral fairing. Each cannon had 120 rounds of ammunition. The Air Ministry ordered two Type 432 prototypes on 9 September 1941, and the aircraft would be built to the new Specification F.7/41. The two Type 432 prototypes were issued serial numbers DZ217 and DZ223.

The fuselage of the Vickers Type 432 was made of stressed-skin aluminum panels that were flush-riveted to the closely-spaced circular structures that made up the airframe. The forward part of each wing was made of a similar stressed-skin construction. The thick skins and their supports created a torsion box of sufficient strength so that conventional wing spars and ribs were omitted. Fabric covered the aft section of the wings and the aircraft’s control surfaces. The wings had a unique elliptical planform with a slight forward-sweep outside of the engines. The wing leading edges between the engines and fuselage housed the coolant radiators.

The aircraft was powered by two-stage, two-speed Merlin 61 engines capable of 1,580 hp (1,178 kW) at 23,500 ft (7,163 m). The engines were housed in long, streamlined nacelles mounted to each wing. The main landing gear retracted rearward into the nacelle behind the engine. The cockpit consisted of a pressure cabin topped by a small canopy that hinged to the side for entry.

The Type 432 was a rather large aircraft with a wingspan of 56 ft 10 in (17.3 m), a length of 40 ft 7 in (12.4 m), and a height of 13 ft 9 in (4.9 m). Forecasted top speeds were estimated at 320 mph (515 km/h) at sea level, 435 mph (700 km/h) at 28,000 ft (8,534 m), and 400 mph (644 km/h) at 40,000 ft (12,192 m). Cruise speed was estimated at 400 mph (644 km/h) at 29,500 mph (8,992 m). The aircraft had a 2,750 fpm (14.0 m/s) initial climb rate and a service ceiling of 43,500 ft (13,259 m). The Type 432 weighed 16,373 lb (7,427 kg) empty and had a maximum takeoff weight of 20,168 lb (9,148 kg). With 506 gallons (421 Imp gal / 1,914 L) of fuel, the aircraft had a 1,500 mi (2,414 km) range.

Vickers Type 432 left side

During its initial taxiing tests at Farnborough, the Type 432 exhibited tracking issues and snaked from side-to-side. The landing gear was moved aft 3 in (76 mm) to improve handling. Flight tests revealed other undesirable characteristics, and modifications were made to the aircraft’s ailerons and tail to improve its handling.

The Type 432 mockup was inspected in late December 1941, and the first prototype, DZ217, was built throughout 1942. The aircraft was built at Foxwarren, a special Vickers dispersal site for experimental work near Brooklands in Surrey, England. The site did not have an airfield, so the Type 432 was disassembled and transported to Royal Aircraft Establishment Farnborough for its first flight. The Type 432 was first flown on 24 December 1942, piloted by Tommy Lucke. On 29 December, the Ministry of Aircraft Production cancelled the partially-built second prototype. This decision was not made official until 1 May 1943. The entire Type 432 program was cancelled at the end of 1943.

The sole Type 432 aircraft continued to fly occasionally until November 1944. Some efforts were made throughout the aircraft’s existence to improve its handling and flight qualities, as the Type 432 was noted as having heavy controls. Only 28 flights were made, and the aircraft was never submitted for official trials or tested to its maximum performance. Additionally, the 20-mm armament and the pressurized cabin were never installed. Although the Type 432 exceeded 400 mph (644 km/h) in a slight dive, the highest speed obtained in level flight was 380 mph (612 km/h), recorded on 14 May 1943. One of the factors that limited flight testing was that the Merlin engines installed in the Type 432 did not run well above 23,000 ft (7,010 m). Since the Type 432 had no future as a production aircraft, the performance issues of its Merlins were never fully investigated.

Aircraft observers were a regular fixture during World War II, keeping an eye out for any enemy action in the skies over Britain. The rarely-seen and oddly-shaped Type 432 was only listed as “AP1480” in the recognition handbooks. This non-descript designation led the spotters to dub the Type 432 as the “Tin Mossie” on account of the aircraft’s resemblance to the wooden de Haviland Mosquito. Some source list the aircraft as being referred to as “Mayfly,” but the origin of this name has not been found.

Vickers Type 432 in flight

The Type 432 made only 28 flights in its two-year life. The aircraft was noted as having some handling deficiencies that were never completely resolved, because the project was a dead end. Note the slight forward sweep of the Type 432’s outer wing panels.

Sources:
British Secret Projects: Fighters & Bombers 1935-1950 by Tony Buttler (2004)
Vickers Aircraft since 1908 by C. F. Andrews and E. B. Morgan (1988)
RAF Fighters Part 3 by William Green and Gordon Swanborough (1981)
The British Fighter since 1912 by Francis K. Mason (1992)
Aircraft of the Fighting Powers Volume VII by Owen Thetford (1946)

VEF I-16 Front right

VEF I-16 Light Fighter Aircraft

By William Pearce

VEF (Valsts Elektrotehniskā Fabrika or State Electro-Technical Factory, often spelled Valsts Elektrotechniskā Fabrika) was a large industrial manufacturer founded in Latvia in 1919. Kārlis Irbītis was an engineer at VEF during the 1930s and 1940s. Irbītis had designed aircraft since the 1920s and continued the practice in his spare time while employed at VEF. In 1935, Irbītis suggested that VEF should enter the aircraft manufacturing business, and VEF management was responsive.

VEF I-12 International Expo 1938

The VEF I-12 was a light sport plane and a follow-on to the I-11 aircraft. Powered by a 90 hp (67 kW), air-cooled, four-cylinder Cirrus Minor engine, the I-12 had a top speed of 143 mph (230 km/h).

VEF solicited a manufacturing contract from the Latvian government, but the request was denied. Frustrated, VEF decided to build Irbītis’ latest aircraft design, the I-11, as a private venture. The I-11 was the first in a series of fixed-gear, low-wing aircraft designed by Irbītis and built by VEF. The I-11 was a two-seat sport plane that first flew in late June 1936. Some aspects of the I-11 design were less than ideal, as aircraft components had to be made to fit out the workshop’s small door. After the I-11’s successful flight tests, an improved model was designed and designated I-12.

The I-12 was seen as a stepping stone to the design and construction of future military aircraft. VEF approved of Irbītis’ plan to build a military trainer after the I-12, and a light fighter would follow after construction of the trainer. The I-12 was first flown on 26 June 1937 and demonstrated good performance and handling. Ultimately, around 12 I-12 aircraft were built. Construction of the I-14 military trainer started in April 1937, and the aircraft made its first flight on 19 November 1937. The I-14 prototype was damaged beyond repair during an emergency landing on 23 April 1938. Undeterred, VEF authorized the design and construction of two new aircraft types: the I-15 trainer and the I-16 fighter.

VEF I-14

The VEF I-14 was developed as a military trainer and was powered by a 200 hp (149 kW), air-cooled, six-cylinder Menasco B6S Buccaneer engine. The I-14 had an estimated top speed of 186 mph (300 km/h), but a crash prevented the completion of flight tests.

Irbītis continued to improve his aircraft designs. The I-15 and I-16 shared a very similar layout and employed the same construction techniques. Manufacture of the I-15 started in the summer of 1938, and two aircraft were built. The I-15a had a wooden, fixed-pitch propeller and gun camera, but it had no armament. The I-15a was powered by an air-cooled, 200 hp (149 kW) de Havilland Gipsy Six series I engine. The I-15b was powered by a 210 hp (157 kW) Gipsy Six series II engine and used a metal, constant-speed propeller. The I-15b could accommodate a single 7.7 mm machine gun, and its cockpit was moved forward slightly to improve pilot visibility.

The I-15a first flew in April 1939. The first flight of the I-15b was delayed because of the late delivery of its constant-speed propeller but finally occurred around November 1939. The Latvian Aviation Regiment decided to purchase the I-15a and I-15b aircraft based on the favorable experience with four I-12 aircraft given to the Aizsargu Aviācija (Aviation Guard) by VEF in late 1938. The I-15a had a top speed of 186 mph (300 km/h), and the I-15b had a top speed of 205 mph (330 km/h). Both I-15 aircraft had successfully completed flight testing by the time Latvia was invaded by Soviet forces in June 1940; the invasion stopped further development.

VEF I-15a

The VEF I-15a on skis to enable flight testing during the Latvian winter. The I-15A carried the Latvian military serial number 190, while the I-15b carried 191.

Design work on the VEF I-16 light fighter began in late 1938. The aircraft was a single-seat, low-wing monoplane with fixed undercarriage. The landing gear was covered in streamlined fairings, and a retractable gear design was to be incorporated on a later model. The I-16 was comprised of a wooden structure covered in plywood and had fabric-covered control surfaces. Each wing accommodated a 10.6 gallon (40 L) fuel tank, and a single fuel tank in the fuselage held 58.1 gallons (220 L). The I-16 had two 7.7 mm machine guns mounted in the upper cowling in front of the cockpit. Provisions were made for an additional 7.7 mm machine gun to be mounted under each wing.

The I-16 was powered by a Sagitta I-SR engine built by Walter in Czechoslovakia. The Sagitta was an air-cooled, inverted V-12 engine that had a 4.65 in (118 mm) bore and a 5.51 in (140 mm) stroke. The supercharged engine displaced 1,121 cu in (18.4 L) and produced 520 hp (388 kW) at 12,467 ft (3,800 m). Air was fed into the supercharger via two scoops on the upper cowling. Engine exhaust was discharged through ejector stacks positioned at the bottom of the cowling. The shroud around the exhaust stacks also allowed cooling air to exit the cowling after passing through the cylinders’ fins. Additional cooling air exited via a vertical slit at the rear of the cowling. The engine turned a two-blade, wooden, fixed-pitch propeller, but a three-blade, metal, constant-speed propeller was planned for future use.

VEF I-16 construction

The VEF I-16 was a continuation of Kārlis Irbītis’ light, sleek monoplane design. The aircraft was the only monoplane fighter designed and built in Latvia. The wooden, fixed-pitch propeller was considered temporary. The cockpit canopy hinged open toward the right.

The I-16’s wingspan was 26 ft 11 in (8.2 m); its length was 23 ft 11 in (7.3 m); and its height was 8 ft 10 in (2.7 m). With the three-blade propeller, the aircraft had an estimated maximum speed of 286 mph (460 km/h) at 13,123 ft (4,000 m) and 249 mph (400 km/h) at sea level. The I-16 had an initial rate of climb of 2,187 fpm (11.1 m/s), and its ceiling was 26,247 ft (8,000 m). The aircraft had an empty weight of 2,425 lb (1,100 kg) and a loaded weight of 3,417 lb (1,550 kg). The I-16’s range was around 497 miles (800 km).

Construction on the I-16 continued through 1939, and the aircraft made its first flight in the spring of 1940 at Riga, Latvia. The pilot for the first flight was Konstantīns Reichmanis, and the I-16’s engine quit after about 20 minutes of flight time. Reichmanis managed to get the aircraft back on the ground without any damage. Poor fuel distribution was thought to have caused the engine trouble, as similar issues had been encountered during ground runs. Reichmanis praised the aircraft’s handling during his short flight. Changes were made to the I-16’s fuel system, and a few more flights were accomplished before testing was halted by the Soviet invasion.

VEF I-16 rear left

The completed I-16 with German markings during an engine runup in 1941. The two intake scoops for the engine are visible on the top of the cowling, with the left gun port immediately below. Armament was never installed in the aircraft, but VEF did have possession of the Browning machine guns until they were removed by Soviet occupying forces.

The Soviets expressed some interest in the VEF aircraft, and the I-15a, I-15b, and other aircraft were shipped to the Soviet Union in March 1941. The I-16 remained in Latvia to resolve the fuel distribution issues. Before the I-16 could be sent to Russia, the Germans attacked the Soviets and took over Latvia in June 1941. Irbītis escaped deportation, but many of his colleagues, including Reichmanis, were not so fortunate and disappeared into the work camps in Siberia. Under German occupation, the I-16 was returned to an airworthy status and carried the identification code AW+10. The aircraft made two test flights before it was taken over by the Luftwaffe. Some accounts list the aircraft as being part of a training school in Toruń (in occupied Poland) until 1942, but its final disposition is not known.

In late 1939, Irbītis began designing a new fighter, the I-19. With a wingspan of 36 ft 1 in (11 m) and a length of 29 ft 6 in (9 m), the I-19 was larger than the I-16. The I-19 also featured retractable gear, two machine guns in each wing, and a top speed of 404 mph (650 km/h). Irbītis persisted with the wooden construction, but the lack of a suitable power plant led him to consider building his own engine comprised of three V-12 engine sections, with each engine section based on a Ranger V-770. The cylinder banks of each engine section were spaced at 120 degrees. The resulting 36-cylinder engine employed three crankshafts and three superchargers. Irbītis estimated that the engine would displace around 2,200 cu in (36 L) and produce 1,450 hp (1,081 kW) at 3,250 rpm. However, Irbītis switched to an Allison V-1710 engine when more serious design work was undertaken. The I-19 never proceeded beyond the preliminary design phase. After World War II, Irbītis immigrated to Canada and helped develop the tiltwing Canadair CL-84 Dynavert.

VEF I-16 Front right

The sleek I-16 aircraft resembled similar light fighters developed in France (Caudron) and Italy (Ambrosini) during the same period. Note the streamlined fairings covering the gear.

Sources:
Of Struggle and Flight: The History of Latvian Aviation by Kārlis Irbītis (1986)
Latvian Air Force 1918–1940 by Richard Humberstone (2000)
http://latvianaviation.com/VEF_I-16.html
http://airwar.ru/enc/fww2/i16l.html

Republic XP-72 No 2 front

Republic XP-72 Super Thunderbolt / Ultrabolt Fighter

By William Pearce

In 1941, the Republic P-47 Thunderbolt had just entered production, and hundreds of the aircraft had been ordered. However, led by Alexander Kartveli, the design team at Republic stayed at the forefront of fighter development by incorporating new engines into new airframe designs. In July 1941, Republic submitted two new designs to the United States Army Air Force (AAF), the AP-18 and the AP-19. The AP-18 was a unique interceptor fighter powered by the Wright R-2160 Tornado engine. The AP-19 design was more conventional and was powered by the Pratt & Whitney (P&W) Wasp X (R-4360). Both engines were under development, but the R-2160 was anticipated first and received much interest from the AAF. As a result, the AP-18 design was ordered on December 1941 as the Republic XP-69.

Republic XP-72 No 1 roll out

The first Republic XP-72 prototype soon after being completed. The 14 ft 2 in (4.23 m) diameter Curtiss propeller was one of the largest used during World War II.

By 1943, the R-2160 engine had encountered major issues, but development of the R-4360 engine was steadily progressing. Republic felt the AP-19 design held more potential and wanted to end work on the XP-69. The AAF agreed, and the XP-69 project was cancelled on 11 May 1943. Two prototypes of the AP-19 design were ordered on 18 June 1943, and the aircraft was designated XP-72 (it also carried the “Materiel, Experimental” project designation MX-189). In addition, Republic felt the XP-72 was superior to the XP-47J, an interceptor derivative of the P-47, and asked that the second XP-47J prototype be cancelled. The AAF approved this request, and Republic focused on the XP-72.

The XP-72 was often called the Super Thunderbolt, or Superbolt, or Ultrabolt, and it benefitted from everything Republic had learned with the P-47 series, including the XP-47J. The XP-72 was essentially the wings, fuselage, and tail of a bubble-canopied P-47D combined with the close-fitting cowling used on the XP-47J. Of course, numerous internal changes made the XP-72’s resemblance to the P-47 a superficial oversimplification of the new aircraft’s design. Under the close-fitting cowling was a 28-cylinder P&W R-4360 engine. The engine drove a fan at the front of the cowling to assist cooling. A small cowl flap was positioned on each side of the cowling. The cowl flaps were automatic but could be manually controlled. At the cowl flaps, air exiting the cowling was combined with exhaust gases being expelled through ejector stacks and provided a small amount of thrust.

PW R-4360 remote supercharger

The Pratt & Whitney R-4360-13 and -19 engines had a remote, variable-speed, first-stage supercharger. This large supercharger was installed behind the XP-72’s cockpit and was connected to the engine via a fluid coupling.

The XP-72’s R-4360 engine used two-stage supercharging. The first stage was a mechanically-driven, variable-speed, remote supercharger positioned behind the cockpit, where the turbosupercharger was located on the P-47. To power the remote supercharger, a covered shaft extended from the unit, through the lower cockpit, and connected to the engine via a fluid coupling. The remote supercharger’s impeller was around 3 ft (.9 m) in diameter. The second stage was the standard supercharger that was integral with the engine.

A scoop positioned under the fuselage and in line with the wings leading edge split air into three ducts. The left and right ducts delivered air to oil coolers positioned on the bottom sides of the scoop. The outlet for each oil cooler was on the lower side of the scoop and about at the midpoint of its length. The larger, center duct fed air to the intake on the back of the remote supercharger and to the intercooler. The intercooler was positioned behind the remote supercharger. After being compressed in the supercharger, the air exited via two outlets and passed through the intercooler. After leaving the intercooler, the cooled induction air was split into two ducts and delivered to the R-4360’s downdraft intake, which is where the two ducts merged. The air then passed through the engine’s integral supercharger and into the engine’s cylinders. Cooling air that passed through the intercooler was discharged via an outlet in front of the tailwheel. No exhaust-driven turbosupercharger was installed on or planned for the XP-72 prototypes or the P-72 production aircraft.

Republic XP-72 No 1 left side

This side view of the first XP-72 illustrates the aircraft’s resemblance to the P-47 Thunderbolt. The notch just before the tailwheel is the air outlet from the intercooler. The serial number painted on the tail should actually be “336598” to conform to AAF guidelines. Neither XP-72 had the “correct” serial number painted on their tails.

Some sources state the XP-72 had strengthened landing gear compared to the P-47, while other sources say it was the same landing gear used on the P-47. The wings incorporated six .50-cal machine guns (three in each wing) with 267 rpg. However, the gun package could be changed to four 37-mm cannons (two in each wing). A hardpoint under each wing could carry a 150-gallon (568 L) drop tank or up to a 1,000 lb (454 kg) bomb. Just like on the P-47, an inlet for cabin air was located on the leading edge of the right wing. Dive recovery flaps were fitted under the wings, just behind the main gear wells.

The XP-72 was roughly the same size and weight as the P-47D but was more aerodynamic and possessed about 50% more power. The XP-72 aircraft had a 40 ft 11 in (12.47 m) wingspan, was 36 ft 8 in (11.18 m) long, and was 16 ft (4.88 m) tall. The aircraft had an empty weight of 11,375 lb (5,160 kg), a normal weight of 14,760 lb (6,695 kg), and a maximum takeoff weight of 17,492 lb (7,934 kg). The XP-72 had a top speed of 490 mph (789 km/h) at 25,000 ft (7,620 m) and an initial rate of climb of 5,280 fpm (26.8 m/s), decreasing to 3,550 fpm (18.0 m/s) at 25,000 ft (7,620 m). The aircraft could reach 20,000 ft (6,096 m) in under five minutes. The XP-72’s service ceiling was 42,000 ft (12,802 m). With 370 gallons (1,401 L) of internal fuel and two 150-gallon (568 L) drop tanks, the aircraft had a range of 1,200 miles (1,931 km) at a 300 mph (483 km/h) cruise speed.

Republic XP-72 No 1 right front

The XP-72 was a formidable aircraft with amazing performance. The scoop under the fuselage brought air to the oil coolers, intercooler, and supercharger. The duct in the wing was for cabin air. The close-fitting engine cowling was one of the best installations of an R-4360 and used an engine-driven fan to assist cooling.

The first XP-72 prototype (serial number 43-36598) was completed with a single-rotation propeller and a P&W R-4360-13 engine. The Curtiss Electric four-blade propeller was 14 ft 2 in (4.23 m) in diameter, which was one of the largest propellers used during World War II and was probably the largest propeller fitted to a fighter. The propeller left only 5 in (127 mm) of ground clearance, and the pilots employed three-point takeoffs and landings to make sure there were no propeller ground strikes. The R-4360-13 engine could accommodate the remote, variable-speed supercharger, but sources disagree regarding whether or not the remote supercharger was installed in the XP-72. The -13 engine produced 3,450 hp (2,573 kW) with the remote supercharger and 3,000 hp (2,237 kW) without it. The first XP-72 was finished on 29 January 1944. The aircraft’s first flight was made from Republic Field in Farmingdale, New York on 2 February 1944.

The second XP-72 prototype (serial number 43-36599) used a 13 ft 6 in (4.11 m) diameter, six-blade, contra-rotating Aeroproducts propeller. This propeller gave 9 in (229 mm) of ground clearance, and three-point takeoffs and landings were still the standard practice. Sources disagree on which dash number engine was used in the second prototype. Some sources claim a 3,000 hp (2,237 kW) R-4360-3 engine was used on the second XP-72. The -3 had a single-speed, single-stage (non-remote) supercharger and accommodated contra-rotating propellers, but the -3 engine used SAE #60-80 spline shafts. The Aeroproducts propeller used SAE #50-70 spline shafts, so it seems unlikely that the -3 engine was used. Many sources state the second XP-72 used a R-4360-13 engine, the same type fitted to the first prototype. The -13 engine was single-rotation with a SAE #60 spline shaft and could not accommodate contra-rotating propellers. However, it is possible that a contra-rotating gear case from another engine could have been fitted to the -13. The -8 (Douglas XTB2D) and -10 (Boeing XF8B) engines built for the Navy both used SAE #50-70 spline shafts. It is odd that another dash number was not assigned for such a change, but the -13 engine seems like the most likely candidate to have powered the second XP-72. Other sources propose that the engine was a R-4360-19 (see below), but there is no indication that any -19 engines were built.

Republic XP-72 No 2 front

With its six-blade, contra-rotating propellers, the second XP-72 is an impressive sight. Even with its hollow blades, the propeller still weighed around 765 lb (347 kg). Note the installed underwing pylons.

Regardless of the exact dash number, the second XP-72 was first flown on 26 June 1944. The contra-rotating propellers had a slight destabilizing effect on the aircraft, but the effect was manageable, and the aircraft still exhibited excellent flight characteristics. It is often reported that the second XP-72 was damaged beyond repair because of an emergency landing following an inflight fire. However, Ken Jernstedt, the pilot on that flight, has stated the incident never happened. In Jernstedt’s account, he was making a high-performance takeoff from Caldwell, New Jersey when an oil seal on the supercharger failed and caused a massive oil leak. Hot oil sprayed into the cockpit, on Jernstedt’s legs, and on the outside of the canopy. When Jernstedt brought the aircraft around for a quick landing, a Vought F4U Corsair suffering from an inflight fire crossed his path. Jernstedt had to veer around the Corsair to land the XP-72, which was damaged in the incident. While the aircraft could have been repaired, the XP-72 program ended soon after.

The Republic XP-72 was noted as exceptionally fast with amazing performance and for being a beautifully flying airplane. It is often reported that test pilot Carl Bellinger attained a speed of 480 mph (772 km/h) at sea level, but this speed was most likely recorded at altitude. Almost all sources indicate that both XP-72 prototypes achieved 490 mph (789 km/h) at 25,000 ft (7,620 m).

Republic XP-72 no 2 right side

The second XP-72 shortly after an engine run. Note that the tail of the aircraft is tied down. The air outlet from the oil cooler is visible on the lower fuselage, just under the wing’s trailing edge. Another outlet was positioned in the same spot on the opposite side of the aircraft.

An order for 100 P-72 aircraft was placed in late 1944. Production P-72s were to be powered by the P&W R-4360-19 engine, which used the Aeroproducts contra-rotating propeller and had an engine-driven, variable-speed, remote supercharger similar to the one used on the -13. The -19 engine was planned to provide 3,650 hp (2,722 kW) at sea level and 3,000 hp (2,237 kW) at 25,000 ft (7,620 m), allowing the P-72 to attain an estimated speed of 504 mph (811 km/h) at 25,000 ft (7,620 m). Further engine development resulting in 4,000 hp (2,983 kW) would reportedly enable the P-72 to reach a speed of 540 mph (869 km/h) at 25,000 ft (7,620 m). The 540 mph (869 km/h) speed seems a little optimistic. An upgraded wing, similar to that used on the P-47N, was to be applied to production P-72s. The P-47N wing held more fuel and increased the aircraft’s span by about 2 ft (.61 m). The speeds mentioned above were most likely estimated with the original, smaller wing.

As excellent as the P-72 may have been, the war situation indicated the aircraft was not needed, and the emergence of jet aircraft indicated that the P-72’s speed would soon be outclassed. The order for 100 P-72 aircraft was cancelled on 4 January 1945 so that Republic could focus on the P-84 Thunderjet fighter. On the day the P-72 was cancelled, the AAF ordered 100 P-84 jet aircraft (25 pre-production YP-84As and 75 production P-84Bs). The two XP-72 aircraft survived the war but did not last much longer. One airframe, without its engine, was given to a local (on Long Island, NY) chapter of the Air Scouts in August 1946. The other airframe was eventually scrapped.

Republic XP-72 No 2 right rear

With the war winding down and jet aircraft on the horizon, the XP-72 never entered production, despite the aircraft’s impressive performance. Production P-72 aircraft could have been the ultimate piston-engine fighter.

Sources:
Correspondence with Tom Fey
U.S. Experimental and Prototype Aircraft Projects: Fighters 1939–1945 by Bill Norton (2008)
R-4360: Pratt & Whitney’s Major Miracle by Graham White (2006)
Republic’s P-47 Thunderbolt by Warren M. Bodie (1994)
American Secret Projects: Fighters, Bombers, and Attack Aircraft, 1937-1945 by Tony Buttler and Alan Griffith (2015)
US Army Air Force Fighters Part 2 by William Green and Gordon Swanborough (1978)
http://www.seabee.info/seabee_history_racac.htm
http://www.joebaugher.com/usaf_fighters/p72.html

Douglas XB-42 no1 in flight

Douglas XB-42 Mixmaster Attack Bomber

By William Pearce

In the early 1940s, Edward F. Burton began to investigate ways to simplify bomber aircraft. Burton was the Chief of Engineering at the Douglas Aircraft Company (Douglas), and he had noted that each subsequent generation of bomber aircraft was substantially larger, more complex, and more expensive than the preceding generation. Burton and his team started with a clean sheet of paper and designed what would become the XB-42.

Douglas XB-42 no1 in flight

The Douglas XB-42 Mixmaster had a unique design that provided very good performance. However, it was too late for World War II and too slow compared to jet aircraft. The first prototype (43-50224) is seen with its short tail on an early test flight.

Acting on their own, with no official United States Army Air Force (AAF) requirement, Burton and his team worked to design a two-engine tactical bomber with a top speed of over 400 mph (644 km/h) and that was capable of carrying 2,000 lb (907 kg) of bombs to a target 2,500 miles (4,023 km) away. The aircraft’s high speed would eliminate the need for extensive defensive armament, which would minimize the bomber’s crew and save weight. Burton’s team placed the wings, tail, and propellers in their optimal positions; the designers then filled in the rest of the aircraft with the needed equipment. What emerged from the drafting table was the Douglas Model 459: a mid-wing aircraft operated by a crew of three. At the rear of the aircraft were a set of coaxial contra-rotating pusher propellers driven by engines buried in the fuselage. In May 1943, Douglas proposed the aircraft to the AAF, and they were sufficiently impressed to order two prototypes and a static test airframe on 25 June 1943.

The AAF originally gave the aircraft the Attack designation XA-42. Douglas had presented the aircraft in a variety of roles that suited the Attack aircraft profile. However, the aircraft was reclassified as a bomber and redesignated XB-42 on 25 November 1943. Unofficially, the XB-42 was given the name Mixmaster, on account of its eight contra-rotating propeller blades loosely resembling a popular kitchen mixer.

The Douglas XB-42 Mixmaster was a unique aircraft. It was an all-metal aircraft with a tricycle landing gear arrangement, which was novel at the time. A plexiglass nose covered the bombardier’s position. Atop the fuselage were two separate bubble canopies for the pilot and copilot. At the rear of the aircraft was a cruciform tail; its ventral fin contained an oleo-pneumatic bumper to protect the propellers from potential ground strikes during takeoff and landing.

Douglas XB-42 no1 nose

Nose view of the first prototype shows the twin bubble canopies to advantage. Both XB-42 aircraft were originally built with the canopies, but they were disliked. The second aircraft was later modified with a more conventional canopy.

The aircraft’s long wing used a laminar flow airfoil and was fitted with double-slotted flaps. An inlet in the wing’s leading edge led to the engine oil cooler and radiator, both fitted with electric fans for ground operation. After air flowed through the coolers, it was expelled out the top of the wing. The main landing gear retracted back into the sides of the fuselage, below and behind the wings. The complex retraction required the gear legs and wheels to rotate 180 degrees. Fuel tanks in each wing carried 330 gallons (1,249 L) of fuel. Four additional 275 gallon (1,041 L) fuel tanks could be installed in the bomb bay to extend the aircraft’s range. In addition, a 300 gallon (1,136 L) drop tank could be installed under each wing.

Housed in the fuselage behind the cockpit were two Allison V-1710 engines. Each engine was installed with its vertical axis tilted 20 degrees out from center, and the engines were angled toward the tail. Ducts flush with the aircraft’s skin and positioned below the cockpit on both sides of the aircraft brought induction air to the engines. A row of exhaust stacks was located above the leading edge of each wing, and two rows of exhaust stacks were positioned along the aircraft’s spine. The engines of the first XB-42 prototype produced 1,325 hp (988 kW) at takeoff and 1,820 hp (1,357 kW) at war emergency power. The second prototype had engines that produced 1,675 hp (1,249 kW) for takeoff and 1,900 hp (1,417 kW) for war emergency power.

Douglas XB-42 no2 gear retract

An unusual view of the second prototype (43-50225) that displays the aircraft’s slotted flaps and uncommon main gear retraction that required the legs and wheels to rotate 180 degrees into the fuselage sides. Also visible are the wing guns and revised leading edge inlets, both features exclusive to the second prototype.

Extending from each engine was an extension shaft made up of six sections. The shaft sections were like those used in the Bell P-39 Airacobra (which used two sections). The shafts extended around 29 ft (8.8 m) and connected the engines to a remote, contra-rotating gear reduction box from an Allison V-3420-B engine. The gearbox had been slightly modified for the XB-42 and used a .361 gear ratio that was unique to the aircraft. Each engine turned a three-blade Curtiss Electric propeller. The left engine drove the forward propeller, which was 13 ft 2 in (4.01 m) in diameter. The right engine drove the rear propeller, which was 13 ft (3.96 m) in diameter. The engines and propellers were operated independently—if needed, one engine could be shut down and its propeller feathered while in flight.

To eliminate the danger the propellers presented to the crew during a bail out, a cord of explosives (cordite) was threaded through holes carefully drilled around the gearbox mount. Before bailing out, the crew could detonate the explosives, which would separate the gearbox and propellers from the aircraft.

Douglas XB-42 Allison engine test

Two Allison V-1710 engines connected to the V-3420 remote gear reduction for the contra-rotating propellers as used on the XB-42. The power system accumulated over 600 hours on the test stand and never caused serious issues during the XB-42 program.

The XB-42’s bomb bay was covered by two-piece, snap-action doors. The bay accommodated 8,000 lb (3,629 kg) of bombs, or a single 10,000 lb (4,536 kg) bomb could be carried if the doors were kept open six inches. The bay was long enough to carry two 13 ft 9 in (4.2 m) Mk 13 torpedoes. Two fixed .50-cal machine guns with 500 rpg were installed in the aircraft’s nose. Housed in the trailing edge of each wing, between the aileron and flap, were a pair of rearward-firing .50-cal machine guns, each with 350 rpg. The guns were concealed behind snap-action doors. Once exposed, the guns could be angled through a range of 30 degrees up, 15 degrees down, and 25 degrees to the left or right. Their minimum convergence was 75 ft behind the aircraft. The rear-firing guns were operated by the copilot, who rotated his seat 180 degrees to use the gun’s sighting system.

Douglas designers envisioned that the B-42 aircraft could be fitted with a solid nose containing different weapons for different roles. This is the same concept that was applied to the Douglas A-20 Havoc and A-26 Invader. Three of the possible B-42 nose configurations were as follows: eight .50-cal machine guns; two 37 mm cannons and two .50-cal machine guns; or a 75 mm cannon and two .50-cal machine guns. Douglas also thought the aircraft’s speed and range would make it very useful in a reconnaissance role. None of these plans made it off the drawing board.

The XB-42 had a 70 ft 6 in (21.49 m) wingspan and was 53 ft 8 in (16.4 m) long. Originally, the aircraft was 18 ft 10 in (5.7m) tall, but the tail and rudder were extended to cure some instability. The extension increased the XB-42’s height to 20 ft 7 in (6.3 m). A brochure published by Douglas in April 1944 predicted the B-42 would be able to carry 2,000 lb (907 kg) of bombs over 5,333 miles (8,583 km) and have a top speed of 470 mph (756 km/h). These numbers proved very optimistic. Perhaps the speed was a misprint, because some sources indicate the anticipated top speed was 440 mph (708 km/h). Regardless, the aircraft only achieved 410 mph (660 km/h) at 23,440 ft (7,145 m), and its cruising speed was 312 mph (502 km/h). The XB-42 had an empty weight of 20,888 lb (9,475 kg) and a maximum weight of 35,702 lb (16,194 kg). The aircraft’s service ceiling was 29,400 ft (8,961 m). Its combat range was 1,800 miles (2,897 km), but additional fuel tanks in the bomb bay could extend the XB-42’s range to a maximum of 5,400 miles (8,690 km).

Douglas XB-42 no2 rear

Rear view of the second prototype shows the ventral tail and rudder. Note the oleo-pneumatic bumper on the tail and its minimal ground clearance. The wing guns and new canopy are just barely visible.

Construction of the XB-42 proceeded rapidly. The AAF inspected and approved an aircraft mockup in September 1943, and the first prototype (43-50224) was completed in May 1944—one year after the aircraft was proposed and 10 months after the contract was awarded. The XB-42 flew for the first time on 6 May 1944, flown by Bob Brush and taking off from the Palm Springs Army Airfield in California. The second prototype (43-50225) flew for the first time on 1 August 1944, taking off from Santa Monica Airport in California.

Both XB-42s were originally fitted with separate bubble canopies. This cockpit layout was not very popular with the pilots. Although they could communicate via intercom, the pilots often found themselves leaning forward to speak with one another face to face under the canopies. The second aircraft was modified with a more conventional single canopy that encompassed both pilot and copilot. While the bubble canopies reduced drag, the single canopy was preferred. Another issue facing the aircraft was that cracks formed in the plexiglass nose. After the plexiglass was replaced several times, the nose was eventually covered with plywood.

Both prototypes were heavier than expected, which reduced performance. Some work went into lightening the second aircraft, like the use of hollow propeller blades. However, issues with vibrations occurred when disturbed air encountered the propellers, and this phenomenon was exacerbated by the hollow blades. No issues were encountered when the aircraft was clean, but when the bomb bay doors were open or when the gear or flaps were deployed, the vibration issue occurred. Some pilots lived with the vibrations and dismissed the issue, but other pilots found it very disconcerting. An improved propeller was designed that featured reversible blades to decrease landing roll and to slow the aircraft in flight. However, it was cancelled in March 1945 and was never built.

Douglas XB-42 no2 with canopy

Front view of the second prototype illustrates the aircraft’s revised canopy. The canopy on production aircraft would have been similar but more refined. Again, note the tail clearance and wing guns.

Some cooling issues were encountered, and modifications to the air intakes were made to improve airflow. The main gear was also modified a few times to improve its retraction and performance. Overall, the aircraft flew well, but the controls were not well harmonized. In addition, the XB-42 aircraft would encounter a slow dutch roll oscillation if not counteracted by the pilot. As previously mentioned, the tail of the aircraft was enlarged to resolve the issue, but it was never entirely solved. The XB-42 required a very long takeoff run of some 6,415 ft (1,955 m). Because there was only about 9 in (.23 m) of clearance between the ventral tail and the ground, the aircraft needed to build up a substantial amount of speed before it was carefully rotated for liftoff.

The second XB-42 prototype was the only aircraft to have revised wing inlets and to be fitted with its machine gun armament, although the guns were never tested. The second aircraft was flown around 70 hours before it was turned over to the AAF. On 8 December 1945, Lieutenant Colonel Henry E. Warden and Captain Glen W. Edwards flew the second XB-42 from Long Beach, California to Bolling Field in Washington, D.C. The record-setting, point-to-point flight covered 2,295 miles (3,693 km) in a time of 5:17:34—an average of 433.6 mph (697.8 km/h). The XB-42 had benefited from a favorable tailwind, and the aircraft’s average true airspeed was around 375 mph (604 km/h).

Douglas XB-42 wing guns

The guns in the left wing are seen aimed 30 degrees up and 25 degrees inboard. Only the second aircraft was fitted with the guns, and they were never tested. Note the snap-action doors that covered the guns. When open, the doors increased the XB-42’s directional stability, resulting in additional rudder force to give the desired yaw.

On 16 December 1945, the second XB-42 was lost during a test flight near Bolling Field. The aircraft was in a landing configuration when there was an issue with extending the landing gear. While the crew was troubleshooting the problem, the left engine began to overheat and then died. The right engine was taken to full power and began to overheat. The decision was made to bail out, and two of the crew safely jumped free before the pilot remembered to jettison the propellers. The propellers and their gearbox were successfully severed from the XB-42, and the pilot bailed out. All three crew members survived the ordeal without any injuries, but the aircraft was completely destroyed.

An exact cause of the crash was never determined, but it was speculated that the coolant doors were inadvertently left in their nearly-closed landing configuration while the crew investigated the gear issue. This resulted in the engines overheating. At the same time, a fuel tank switch was made a bit late and probably led to fuel starvation of the left engine. The second XB-42 had accumulated a little over 118 hours of flight time when it crashed.

The first XB-42 prototype had made 42 flights and accumulated over 34 flight hours by 30 September 1944. A year later, that number rose to around 150 flights, with the aircraft accumulating around 125 flight hours. Before the XB-42 had even flown, Douglas contemplated adding jet engines to the aircraft. An official proposal for the modification was submitted on 23 February 1945. The proposal was approved on 8 March 1946, and modifications to the aircraft began on 26 June 1946. At the time, the first XB-42 had made 168 flights and had flown around 144.5 hours. The two Westinghouse 19XB-2A (J30) jet engines were finally delivered in October 1946 and were installed on the aircraft.

Douglas XB-42A rear

Rear view of the XB-42A illustrates the notches in the new flaps to avoid the jet exhaust. The rest of the aircraft remained relatively unchanged from the XB-42 configuration. The cooling air exit can be seen on the right wing. Note the various Douglas aircraft in the background.

With the jet engines added to the first prototype, the aircraft was redesignated as the Douglas XB-42A. The 1,600 lbf (7.12 kN) thrust jet engines were mounted under the aircraft’s wings. New flaps were installed that were notched behind the jet engines. The notches allowed the flaps to avoid the jet exhaust when they were deployed. The fuel tanks in the wings were modified because of the jet engine mounts. Total wing tankage was decreased by 154 gallons (583 L), but two additional 74 gallon (280 L) tanks were installed in the fuselage. The jets themselves burned the same fuel as the piston engines. The aircraft’s instrumentation was also modified to accommodate the jet engines.

The XB-42A is listed as having a 70 ft 7 in (21.51 m) wingspan and a length of 53 ft 10 in (16.4 m). In reality, the wingspan was probably the same as the XB-42, and the length was slightly longer due to a different spinner. The aircraft’s height was 20 ft 7 in (6.3 m). The XB-42A had a predicted maximum speed of 488 mph (785 km/h) but only achieved 473 mph (761 km/h) at 14,000 ft (4,267 m); cruising speed was 442 mph (711 km/h). The XB-42A had an empty weight of 24,775 lb (11,238 kg) and a maximum weight of 44,900 lb (20,366 kg). The aircraft’s service ceiling was 34,500 ft (10,516 m). The XB-42A had a normal range of around 1,200 miles (1,931 km), but a maximum range of 4,750 miles (7,644 km) could be achieved with additional fuel tanks in the bomb bay.

Douglas XB-42A

The XB-42A makes a low pass over Muroc Air Base during an early test flight. Note the exhaust stains above the wing and the oil stains below the wing. The aircraft was outclassed by other jet aircraft, including its XB-43 cousin.

The first flight of the XB-42A (still 43-50224) occurred on 27 May 1947 at Muroc (now Edwards) Air Base in California. The aircraft required a lot of maintenance and did not prove remarkable in any category to justify further development. Despite the increased performance, the XB-42A was perched on the awkward dividing line between piston-powered aircraft of the past and jet-powered aircraft of the future. There is no better indicator of this than the fact that Douglas had already moved forward with an all-jet XB-42 aircraft, designated XB-43. The Douglas XB-43 Jetmaster had its jet engines buried in the fuselage, near were the Allison engines were installed on the XB-42. The first XB-43 was built using the XB-42 static test airframe. The jet-powered XB-43 made its first flight on 17 May 1946—little more than a year before the jet/piston-powered XB-42A first flew. The XB-42A made only 23 flights, accounting for a little under 18.5 hours of flight time.

With technological progress outpacing the XB-42A, the aircraft was donated to the Air Force Museum on 30 June 1949. It was later moved to the National Air and Space Museum’s Paul Gerber Facility in Silver Hill, Maryland, where it was stored for a number of years. In 2010, the XB-42A was transferred to the National Museum of the United States Air Force in Dayton, Ohio. The aircraft, along with second XB-43 prototype, will eventually be restored for static display.

Douglas persisted with the pusher configuration and designed a number of other military and commercial aircraft. The most developed design was that of the Model 1004, which was actually designated DC-8. Known as the Skybus, the aircraft was similar to an XB-42, but with an extended fuselage for airline service. The aircraft could seat a maximum of 48 passengers, and the extension shafts from the Allison engines traveled under the passenger compartment. First proposed in October 1945, the Skybus was never built, and the DC-8 designation was reapplied to Douglas’s first jet airliner.

Douglas DC-8 Skybus

Although visually similar to the XB-42, the Douglas DC-8 Skybus was an entirely new design. The aircraft’s excellent performance and great single-engine handling was not enough to justify its expense over more conventional designs.

Sources:
American Bomber Development in World War 2 by Bill Norton (2012)
Vee’s for Victory! The Story of the Allison V-1710 Aircraft Engine 1929-1948 by Daniel D. Whitney (1998)
McDonnell Douglas Aircraft since 1920: Volume I by René J Francillon (1979/1988)
The Allison Engine Catalog 1915–2007 by John M. Leonard (2008)
“The First, The Last, and the Only” by Walt Boyne, Airpower Vol. 3 No. 5 (September 1973)
“The Douglas DC-8 Skybus” by R. E. Williams, Douglas Service Vol. 41 (second quarter 1984)
http://www.enginehistory.org/Propellers/Curtiss/XB-42Prop.shtml