Category Archives: World War II

Martin-Baker MB3 runup

Martin-Baker MB3 Fighter

By William Pearce

By 1939, it was clear that the British Air Ministry would not order the Martin-Baker MB2 into production. James Martin (main designer) and Captain Valentine H. Baker had already been at work designing a new fighter aircraft—the MB3. Since the MB2 had proved to be a well-designed fighter, the British Air Ministry ordered three prototypes of the MB3 fighter on 16 June 1939. The new aircraft would be built under Specification F.18/39, issued to Martin-Baker in May 1939. The minimum requirements of Specification F.18/39 were a speed of 400 mph (644 km/h) at 15,000 ft (4,572 m), a ceiling of 35,000 ft (10,668 m), an endurance of 2.5 hours, and an armament of four 20 mm cannons. With the contract issued, Martin worked to finalize the MB3’s design.

Martin-Baker MB3 Denham guns

The nearly complete Martin-Baker MB3 in the summer of 1942 at Martin-Baker’s factory in Denham. The aircraft is not painted, and its six 20 mm cannons are installed. The cannons were removed before flight testing.

The timetable for completing the aircraft was rather optimistic for the relatively small Martin-Baker company. The original contract stated the first MB3 prototype was to be ready by 15 December 1939, with the two remaining aircraft completed by 15 February 1940. At this early stage, the aircraft was to be powered by a Rolls-Royce Griffon engine. By September 1939, it was apparent that the Griffon engine would not be available to Martin-Baker for some time. At the insistence of the Air Ministry, the Napier Sabre replaced the Griffon, and the entire aircraft was redesigned for the new engine. This resulted in a new contract that was somewhat delayed but ultimately signed on 11 August 1940. Britain was now fully involved in World War II, and Martin-Baker was inundated with other work of a higher priority. Therefore, completing the first MB3 took longer than anticipated. By the end of 1941, Martin-Baker was informed that there would be no production orders for the MB3, but the first prototype was so far along that it made sense to finish it.

Construction of the Martin-Baker MB3 followed the established company practice of using a tubular steel frame to make up the fuselage structure. The main wing spar was made of laminated steel, with the number of laminations decreasing near the wingtips. The rest of the wing structure formed a torsion box of extreme rigidity. The entire aircraft was covered with stressed aluminum skin, but many panels could be opened or removed for quick access to equipment and armament. The rudder was fabric-covered, but the rest of the control surfaces were skinned with aluminum.

Martin-Baker MB3 left

The MB3 during its brief flight testing career at RAF Wing. Note the retractable stirrup and fold-down door for cockpit entry.

The aircraft used pneumatically controlled split flaps and had spring loaded aileron gap seals to increase its roll rate and improve aerodynamics. The elevator also had gap seals. Fuel was carried in a fuselage tank in front of the cockpit. The aircraft’s fully retractable main landing gear had a wide track of 15 ft 5 in (4.7 m). The tailwheel retracted into an open well under the tail. The landing gear was lowered by gravity and raised by a pneumatic system, which was separate from the system that controlled the flaps.

Each wing housed three 20 mm cannons with 200 rpg, all installed outside of the aircraft’s main gear. The ammunition belts were installed parallel to the cannons; each bullet had to turn 90 degrees before being fed into the breach. This “flat-feed” ammunition system was patented by Martin. The cannon and ammunition arrangement made for a compact package that could be easily accessed and quickly serviced. With its six 20 mm cannons, the MB3 was one of the most heavily armed fighters of World War II.

Martin-Baker MB3 runup

This image of the MB3 running up gives a good view of the aircraft’s wide-track landing gear and the close-fitting cowling that covered the Sabre engine. Also visible are the under-wing scoops for the radiator and oil cooler.

The Rolls-Royce Vulture X-24 engine was also considered to power the MB3. The V-12 Griffon was initially selected because it was a far less complex power plant than the Vulture or Sabre. However, because the Sabre was more readily available than the Griffon and was favored by the Air Ministry, it was ultimately selected to power the MB3. The 2,020 hp (1,506 kW) Sabre II engine had 24 cylinders arranged in a horizontal H configuration and used sleeve valves. The engine drove a three-blade de Havilland propeller that was 14 ft (4.27 m) in diameter. Engine cooling was provided by a radiator installed in the right wing and an oil cooler installed in the left wing. The radiator ran from the wing root to the main gear, and the oil cooler was about half the size of the radiator. The scoops for the radiator and oil cooler extended about 5 in (127 mm) under the wings and were positioned between the gear wells and the flaps.

The MB3 had a 35 ft (10.7 m) wingspan and was 35 ft 4 in (10.8 m) long. The aircraft had a gross weight of 11,497 lb (5,215 kg). The MB3 had a top speed of 418 mph (673 km/h) at 20,000 ft (6,096 m). However, Martin claimed that Captain Baker had achieved 430 mph (632 km/h) at the same altitude, albeit without the drag that the six cannons would produce. At sea level, the aircraft was capable of 372 mph (599 km/h), and maximum cruising speed was 370 mph (595 km/h) at 15,000 ft (4,572 m). The MB3’s landing speed was 88 mph (142 km/h). The aircraft had a service ceiling of 35,000 ft (10,668 m) and a range of approximately 420 miles (676 km).

Martin-Baker MB3 rear

This rear view of the MB3 illustrates the aircraft’s fine fit and finish. The aileron and elevator gap seals can just be seen.

The first MB3 was given the serial number R2492. The aircraft was expected in March 1942 but was not completed until early August. The aircraft was trucked to Royal Air Force Station Wing (RAF Wing) in Buckinghamshire for flight testing. Surrounded by small fields and many trees, the small airbase of RAF Wing was not an ideal location for flight testing. Martin had objected to using RAF Wing, but the Air Ministry insisted.

Captain Baker was at the controls when the MB3 flew for the first time on 31 August 1942. The six wing cannons had been installed when the aircraft was built at Denham (near London) but were removed before the aircraft flew and were never reinstalled. Ballast had been added to simulate the weight of the cannons and their ammunition. Flight testing revealed that the aircraft had excellent maneuverability and handling characteristics. However, difficulty was experienced with the Sabre engine, and engine overheating issues troubled the MB3.

Martin-Baker MB3 right rear

Many sources claimed that the MB3 was fitted with a bubble canopy after its first flight. This belief stems from a doctored image of the MB3 with a bubble canopy meant to illustrate what the production version of the aircraft would look like. A bubble canopy was never installed on the MB3.

On 12 September 1942, the aircraft made its 10th flight. Captain Baker had just taken off when the engine seized, a result of a sleeve drive crank failure. Low to the ground and without any options, Captain Baker put the MB3 down in one of the many small fields lined with hedgerows and other obstacles surrounding RAF Wing. The aircraft clipped a pile of straw and crashed through a hedgerow at high speed. The MB3 cartwheeled, broke apart, and caught fire. Captain Baker was killed instantly.

The death of Captain Baker was a bitter blow for the Martin-Baker company. Martin took it especially hard; he had lost his friend in an aircraft powered by an engine he did not want to use and at a test site that he thought was inadequate. It was not long before Martin and the Martin-Baker company began work to improve aircrew safety and developed a series of ejection seats, which the company still manufactures today.

Martin-Baker MB3 with Captain V H Baker

Captain Valentine H. Baker posses with the MB3 shortly before a test flight. The engine seized on the MB3’s 10th flight, and Captain Baker was killed during the subsequent crash landing.

With the first MB3 prototype destroyed, Martin’s attention turned to the partially completed second prototype (R2496). Construction of the third prototype (R2499, or possibly R2500) was probably never started. Martin had already designed the MB3A, which was the production version of the MB3. The MB3A had a bubble canopy (that was never fitted to the prototype), and its cockpit was moved slightly forward to improve the pilot’s view over the wing. The MB4 had also been designed; it used a Bristol Centaurs engine in the same basic MB3 airframe. However, since the Air Ministry was finally willing to provide Martin-Baker with a Griffon engine and with the MB3’s performance now on par with existing aircraft, Martin sought to redesign the entire aircraft as the improved MB5 fighter. The Air Ministry was agreeable, and serial R2496 was reallocated to the MB5 aircraft in late 1943. The MB5 flew in 1944 and was another outstanding aircraft. However, the MB5 never went into production, and it was the last aircraft built by Martin-Baker.

Sources:
“Martin-Baker Fighters,” by Bill Gunston, Wings of Fame Volume 9 (1997)
British Experimental Combat Aircraft of World War II by Tony Buttler (2012)
RAF Fighters Part 2 by William Green and Gordon Swanborough (1979)
The British Fighter since 1912 by Francis K. Mason (1992)
Interceptor Fighters of the Royal Air Force 1935–45 by Michael J. F. Bowyer (1984)
https://picasaweb.google.com/109207897425941419378/MartinBakerAircraft

Republic XP-69 side

Republic XP-69 Fighter

By William Pearce

In February 1940, the United States Army Air Corps (AAC) issued Request for Data R40-C to various engine and aircraft manufacturers. R40-C encouraged aircraft manufacturers to propose unorthodox aircraft capable of at least 450 mph (724 km/h), but preferably 525 mph (845 km/h), and to meet other requirements outlined in Type Specification XC-622. R40-C also asked aircraft engine manufacturers to develop new power plants. Initially, a total of 26 aircraft designs were submitted by six selected aircraft companies and included a mix of eight different engines from four engine companies. Republic Aviation’s entry carried the company designation AP-12.

Republic AP-12 Rocket

The AP-12 Rocket was Republic’s entry into the R40-C fighter competition. Note the mid-fuselage-mounted Wright R-2160 Tornado engine.

Like almost all of the other R40-C entries, the Republic AP-12 ‘Rocket’ was not a conventional aircraft. The AP-12 had a streamlined, cigar-shaped fuselage and utilized a tricycle undercarriage. The aircraft’s Wright R-2160 Tornado engine was placed behind the pilot. The engine’s extension shaft ran under the cockpit and drove a six-blade, contra-rotating airscrew at the front of the aircraft. Four machine guns were installed in the AP-12’s nose and fired through the propellers, and an additional machine gun was installed in each wing, outside of the propeller arc. A 20 mm cannon was installed in the nose of the aircraft and fired through the propeller hub.

After the AP-12 placed 13th out of the R40-C entries, Republic literally went back to the drawing board and created a new design, designated AP-18. The AP-18 possessed some of the same lines and used the same engine as the AP-12; however, the R-2160 engine was now installed in the nose of the aircraft. Republic submitted its AP-18 design to the AAC in July 1941 and was awarded a contract in December 1941 to produce two prototypes of the aircraft, designated XP-69 (it also carried the “Materiel, Experimental” project designation MX-162).

Republic XP-69 15-Sept-1941 inboard drawing

This XP-69 drawing dated 15 September 1941 clearly shows the Wright Tornado installed in the nose of the aircraft, with the turbosupercharger and its ancillary equipment mounted behind the cockpit. While the leading edge is distorted, the trailing edge shows the inner wing section perpendicular to the fuselage, then tapering toward the wing tip. This drawing was discovered in the National Archives by Kimble McCutcheon of the Aircraft Engine Historical Society.

The Republic XP-69 was an all-metal, high-altitude interceptor fighter with a conventional layout. The aircraft was powered by a 42-cylinder R-2160 engine that produced 2,500 hp (1,864 kW) at 4,600 rpm and was installed in a normal manner, without an extension shaft. The engine drove a 13 ft 8 in (4.17 m) diameter, six-blade, contra-rotating propeller built by Hamilton Standard. The turbosupercharger, intercoolers, radiator, and oil coolers were all positioned behind the cockpit. The scoop mounted under the cockpit brought in air for the radiator, oil coolers, intercoolers, and turbosupercharger via a complex series of ducts. The scoop also incorporated a boundary layer air bleed duct. Initially, four air exit doors were located under the fuselage, but the exits were later relocated, with two on each side of the XP-69 (the oil cooler was the lower exit and the intercooler the upper). However, radiator and boundary layer air as well as exhaust from the turbosupercharger exited from the bottom of the aircraft.

Most sources contend that the R-2160 engine was installed behind the XP-69’s cockpit. However, all of the equipment and associated ducting that was installed behind the cockpit left no room for anything else. In addition, a drawing dated 15 September 1941 found in the U.S. National Archives by Kimble McCutcheon clearly shows the Wright Tornado installed in the nose of the aircraft.

Republic XP-69 side

The Republic XP-69 model undergoing wind tunnel tests. Note the revised belly scoop and the air exits on the rear fuselage. The man pictured at the bottom of the photo gives some scale to the large size of the model, which was 3/4-scale. (image via Langley Memorial Aeronautical Laboratory / NASA)

The XP-69 utilized a pressurized cockpit in a fairly narrow fuselage, and its standard taildragger landing gear was fully retractable. The aircraft’s armament consisted of two .50 cal machine guns and one 37 mm cannon installed in each wing, outboard of the main landing gear. The machine guns had 320 rpg, and the cannons had 40 rpg. Some sources state an alternative armament installation consisted of six .50 cal machine guns in the wings and no cannons. Initially, the leading and trailing edges of the inboard wing sections were exactly perpendicular to the fuselage. This was later revised so that the wing’s taper was unchanged throughout its leading and trailing edges. Slotted flaps extended across about 50 percent of the wing’s trailing edge to help lower the heavy aircraft’s landing speed.

The XP-69 was a large aircraft with a wingspan of 52 ft (15.85 m), a length of 51 ft 8 in (15.75 m), and a height of 17 ft 3 in (5.26 m). The aircraft had a top speed of 450 mph (724 km/h) at 35,000 ft (10,668 m), an initial climb rate of 2,750 fpm (13.97 m/s), and a ceiling of 48,900 ft (14,905 m). Eight wing fuel tanks provided a total capacity of 386 gal (1,461 L), and a 114 gal (432 L) fuselage tank brought the aircraft’s total fuel capacity to 500 gal (1,893 L), which provided a maximum range of 1,800 miles (2,897 km). Wind tunnel tests were conducted with a 75 gal (284 L) drop tank under each wing of the aircraft. The XP-69 had an empty weight of 15,595 lb (7,074 kg), a gross weight of 18,655 lb (8,462 kg), and a maximum weight of 26,164 lb (11,868 kg).

Republic XP-69 top

Top view of the XP-69 model illustrates the aircraft’s relatively narrow fuselage and that its wings had a continuous taper. Note the 75 gallon drop tank mockups on the left of the image and the Douglas XB-19 model on the right. (image via Langley Memorial Aeronautical Laboratory / NASA)

A 1/20-scale XP-69 model was used for spin recovery tests, the results of which were generally satisfactory—although, recovery was problematic at 30,000 ft (9,144 m). A 3/4-scale model of the XP-69 was completed around June 1942 and began wind tunnel tests in August. The extensive tests were to analyze and evaluate the aircraft’s stability, controls, and cooling system and included fitting the model with 10 ft (3.0 m) diameter, contra-rotating propellers driven by two 25 hp (19 kW) electric motors in the fuselage. The tests indicated some longitudinal instability; the forecasted rate of roll was inadequate, and the estimated control forces for full aileron deflection were excessive. The XP-69 would utilize a control yoke, which would provide a certain degree of mechanical advantage over a control stick. Tests also revealed that the cooling system was not as efficient as expected and required some revision.

Construction of the first prototype began in November 1942 and incorporated changes shown necessary from the various wind tunnel experiments. While development of the XP-69 continued, the R-2160 engine was delayed with design issues that, in turn, would delay the aircraft. Also, a miscommunication had occurred: Republic thought the first engines would be capable of 2,500 hp (1,864 kW) at 4,600 rpm. In reality, the R-2160 would produce only 2,350 hp (1,752 kW) at 4,150 rpm; 2,500 hp (1,864 kW) was the engine’s developmental goal. The reduced power would inhibit the XP-69’s performance, and its 450 (724 km/h) mph top speed was already seen as optimistic.

Republic XP-69 flaps

The XP-69 model with its flaps fully deployed at 40 degrees. The slotted flaps extended aft and down. Note the air exits on the side of the fuselage. (image via Langley Memorial Aeronautical Laboratory / NASA)

Republic wanted to end work on the XP-69 and focus their resources on an alternative project. The company believed their AP-19 design (in a way, a Pratt & Whitney R-4360-powered P-47) held more potential and could fly sooner than the XP-69. The AP-19 (designated XP-72) was designed for and proposed to the AAC at the same time as the AP-18/XP-69. Since the AAC wanted an R-2160-powered fighter as soon as possible, Republic’s AP-18/XP-69 design was contracted, as it was the most appealing candidate. But now, with the engine issues affecting the XP-69, the XP-72 could no longer be overlooked as the superior aircraft. The XP-69 was cancelled on 11 May 1943, and two prototypes of Republic’s XP-72 were ordered on 18 June 1943. The Wright R-2160 Tornado was cancelled on 12 February 1944.

Note: Most sources list the XP-69’s wingspan as 51 ft 8 in (15.75 m) and its length as 51 ft 6 in (15.70 m). The dimensions given in this article, a 52 ft (15.85 m) wingspan and a 51 ft 8 in (15.75 m) length, come from two NACA reports from the 1940s.

Republic XP-69 nose

This image of the XP-69’s nose displays the propellers that were powered by two 25 hp motors for the wind tunnel tests. Also note the complex segmentation of the belly scoop inlet. (image via Langley Memorial Aeronautical Laboratory / NASA)

Sources:
Tornado: Wright Aero’s Last Liquid-Cooled Piston Engine by Kimble D. McCutcheon (2001)
U.S. Experimental & Prototype Aircraft Projects: Fighters by Bill Norton (2008)
American Secret Projects 1937–1945 by Tony Buttler and Alan Griffith (2015)
American Secret Pusher Fighters of World War II by Gerald H. Balzer (2008)
Stability and Control Tests of a 3/4-Scale Model of the XP-69 Airplane in the NACA Full-Scale Tunnel by Harold H. Sweberg (7 January 1943)
Compilation of Test Data on 111 Free-Spinning Airplane Models Tested in the Langley 15-Foot and 20-Foot Free-Spinning Tunnels by Malvestuto, Gale, and Wood (1947)
http://www.weakforcepress.com/tornado_errata.shtml
http://www.weakforcepress.com/XP-69/index.html
http://crgis.ndc.nasa.gov/historic/Test_139:_XP-69_3/4%E2%80%93scale_Model_%28Stability_and_Cooling%29

CAC CA-14A front

Commonwealth Aircraft Corporation CA-14/A Fighter

By William Pearce

In late 1941, the Australian aviation industry took stock of its resources and worked to create an indigenous fighter aircraft to defend against the Japanese. The result of this effort was the Commonwealth Aircraft Corporation (CAC) CA-12, CA-13, and CA-19 Boomerang fighters. In many respects, the Boomerang was an outgrowth of the CAC Wirraway general use aircraft. The Wirraway itself was a modified, licensed production version of the North American NA-16 (also referred to as NA-33) trainer. With a low top speed and poor altitude performance, the very maneuverable and rugged Boomerang found itself excelling in the ground attack role. In late 1942, The Australian War Cabinet and CAC sought to improve the Boomerang’s altitude performance by adding a turbosupercharger. This new aircraft was designated CA-14.

CAC CA-14 front

At first glance, the CAC CA-14 looks like a standard Boomerang fighter, but the aircraft’s unique turbosupercharger scoop can be seen on the side of the fuselage. Less noticeable modifications from a standard Boomerang include a new wing root fairing and a slightly enlarged tail.

The CA-14 was a standard CA-13 Boomerang that had been heavily modified to accommodate a turbosupercharger. Like all CA-13 Boomerangs, the CA-14 had a 1,200 hp (895 kW) Pratt & Whitney (P&W) R-1830 engine. The fuselage was built with a steel tube frame, and the wings and tail were built up from aluminum components. The wings housed four .303 machine guns and two 20 mm cannons. The tail, cowling, lower part of the fuselage, and in front of the cockpit were skinned with aluminum. All tail control surfaces were fabric-covered, and the ailerons were aluminum-skinned.

Unlike a normal Boomerang, the CA-14 had a new cowling that omitted the air intake scoop positioned above the engine on a standard Boomerang. A large scoop was added on the left side of the fuselage, next to the cockpit, and provided intake air for the engine and air for the turbosupercharger’s intercooler. Air exited the intercooler via an adjustable flap located on the right side of the upper fuselage, just behind the cockpit. The engine’s exhaust pipe was extended back along the right side of the fuselage to the turbosupercharger installed behind the cockpit. The General Electric (GE) B-2 turbosupercharger was from a Consolidated B-24 Liberator, and the Harrison intercooler was from a Boeing B-17 Flying Fortress; these parts were chosen because they were available, not because they were ideal. The fuselage was skinned with aluminum to just behind the turbosupercharger. Farther aft, the fuselage was wood-covered. A new, more streamlined fairing was installed on the wing’s leading edge. The fairing ran from the wing root to the fuselage, over the main gear wheel bays. The CA-14’s vertical stabilizer was slightly enlarged, and it used an 11 ft (3.35 m), three-blade, Curtiss propeller.

CAC CA-14 left side

The CA-14’s large scoop can be seen in this view. The scoop created turbulence that interfered with the aircraft’s tail. Pilot visibility was improved over the standard Boomerang by removing the engine intake scoop on the upper cowling.

The CA-14 was assigned serial number A46-1001 and first flew on 13 January 1943 piloted by Flt. Lt. John Holden. Its performance was on par with a standard Boomerang below 10,000 ft (3,048 m) but was superior above that altitude. At 28,000 ft (8,534 m), the CA-14 had a top speed of 354 mph (570 km/h) and a 1,400 fpm (7.1 m/s) rate of climb, while the standard Boomerang was 76 mph (122 km/h) slower at 278 mph (447 km/h) and could only climb at 450 fpm (2.3 m/s). The CA-14 had a 2,150 fpm (10.9 m/s) initial rate of climb and a ceiling of 36,000 ft (10,973 m), which was 2,000 ft (610 m) higher than a standard Boomerang’s ceiling. The CA-14 had the same 36 ft (10.97 m) wingspan and 25.5 ft (7.77 m) length as the Boomerang; however, it was some 400 lb (180 kg) heavier, at 8,095 lb (3,672 kg). The aircraft had a range of 930 miles (1,497 km).

Flight testing revealed directional instability and cooling issues with engine and turbosupercharger. The large scoop mounted on the side of the fuselage created turbulent air which interfered with the aircraft’s tail and caused some instability and buffeting. Starting in May 1943, the CA-14 was reworked to solve its issues and was redesignated CA-14A. Changes included adding a new, larger vertical stabilizer with an aluminum-skinned rudder and deleting the scoop from the aircraft’s fuselage. The engine cowling was reworked to provide better cooling, and a geared (3 to 1), 10-blade cooling fan was added behind the spinner. Air for the engine and intercooler was taken from the high-pressure area behind the cooling fan and internally ducted in the left side of the fuselage back to the turbosupercharger. A GE B-13 turbosupercharger and an AiResearch intercooler replaced the original units. The CA-14A was fitted with a three-blade Hamilton Standard or de Havilland propeller (sources disagree on which, but perhaps both propellers were tested), and its guns were removed. First flown around 26 July 1943, the CA-14A most likely achieved better performance than the CA-14; however, specifics have not been found. Sources indicate the CA-14A’s ceiling was in excess of 40,000 ft (12,192 m).

CAC CA-14 and CA-14A

A comparison of the CA-14 (top) and CA-14A (bottom), with its revised tail and cowling. The exit flap for the intercooler can bee seen in the upper fuselage, just behind the cockpit. The installation of the supercharger and its required accessories in the Boomerang’s small airframe was an impressive feat of engineering.

The ultimate goal of improving the Boomerang was to install a 1,450 hp (1,081 kW) P&W R-2000 engine and GE B-9 turbosupercharger in the aircraft. Originally, these changes were to be incorporated when the aircraft was rebuilt as the CA-14A. However, the United States was very reluctant to provide a license for supercharger production, and CAC’s production of licensed R-2000 engines encountered technical setbacks. The estimated speed of an R-2000-powered Boomerang was 286 mph (460 km/h) at sea level and 372 mph (599 km/h) at 27,000 ft (8,230 m). The aircraft’s rate of climb at sea level was 2,100 fpm (10.7 m/s) and 1,770 fpm (9.0 m/s) at 30,000 ft (9,144 m).

Based on the known performance of the CA-14 and the estimated performance of the R-2000-powered Boomerang, the Minister for Aircraft Production recommended that 120 R-2000-powered fighters be ordered. However, the Australian War Cabinet approved only 50 aircraft. With such a short production run, it was not worth the inevitable delays and required resources to upgrade Boomerang production to a new standard, especially with better performing fighters from the United States and Britain already arriving in Australia. As a result, the 50 aircraft were completed as CA-19 Boomerangs, which differed little from the CA-13s and CA-12s.

CAC CA-14A front

This view of the CA-14A displays its 10-blade engine cooling fan as well as its lack of armament. Undoubtedly, the aircraft’s performance was much improved, but its usefulness was in question since superior British and American aircraft were available in Australia. Note the Republic P-47 Thunderbolts in the background.

While the A46-1001 airframe was being designed and tested with its turbosupercharger, CAC looked to take the next step to enhance performance by fitting a 1,700 hp (1,268 kW) Wright R-2600 engine to an even more modified Boomerang. However, the availability of R-2600 engines to Australia was in question, and modifications to the Boomerang airframe would be substantial. It was deemed more practical to start development of a new aircraft with a 2,000 hp (1,491 kW) P&W R-2800 engine. Designated CA-15, this new aircraft would eventually fly, but with a Rolls-Royce Griffon V-12 engine and little resemblance to its initial design heritage.

The obsolete CA-14A continued to undergo flight testing and was used for high altitude weather observations, regularly flying at 40,000 ft (12,192 m). It was removed from service in 1946 and scrapped in 1947 (some sources say March 1949).

Note: The B-13 turbosupercharger was interchangeable with the B-2. Several sources state that CAC intended to install a B-9 turbosupercharger in the CA-14/A aircraft, but no GE references to a B-9 turbosupercharger have been found. Perhaps “B-9” was a typo or was a designation given to a licensed production or export model (like “B-10” for turbosuperchargers supplied to Britain).

CAC CA-14A left side

For the CA-14A, the large fuselage scoop was removed, and air to the turbosupercharger was delivered via an internal duct. The location of that duct can be discerned by the bulge running along the side of the fuselage

Sources:
Wirraway, Boomerang & CA-15 in Australian Service by Stewart Wilson (1991)
Wirraway to Hornet by Brian L Hill (1998)
Australia’s Lost Fighter: The CA-15 and its Demise by David Clark (2010)
http://www.australianflying.com.au/news/warbirds-the-turbo-interceptor-boomerang

Sud-Est SE 580 cowling

Sud-Est (SNCASE) SE 580 Fighter

By William Pearce

The state-owned French aircraft manufacturer SNCAM (Société nationale des constructions aéronautiques du Midi or National Society of Aircraft Constructors South) was formed in March 1937 when the Dewoitine firm was nationalized. Many Dewoitine personnel, including the company’s founder, Émile Dewoitine, continued to work for SNCAM. As a result, aircraft designed and built at SNCAM continued to bear the Dewoitine name.

Sud-Est SE 580 model

Wind tunnel model of the Sud-Est SE 580 complete with contra-rotating propellers.

In 1940, SNCAM began studies of a new fighter aircraft. The aircraft was based on a continuing design evolution that started with the Dewoitine D.520 production fighter and progressed through the D.551/552 pre-production fighters. SNCAM’s new fighter design was designated M 580.

The M 580 aircraft was a tractor design with conventional undercarriage. However, the power plant was unusual in that it utilized two Hispano-Suiza 12Z engines coupled in tandem and driving a coaxial contra-rotating propeller (similar to the Arsenal VB 10). The M 580 was designed by Robert Castello and Jacques Henrat, who had been very involved with previous Dewoitine fighter designs. Before much design work was completed, SNCAM was absorbed into SNCASE (Société nationale des constructions aéronautiques du Sud-Est or National Society of Aircraft Constructors Southeast) in late 1940.

With the SNCASE (often referred to as Sud-Est) takeover and the German occupation of France, the M 580 design languished during the war. Under Sud-Est, the aircraft was redesignated SE 580. Wind-tunnel tests were conducted in 1943, and the SE 580 design was changed to incorporate a new engine then under development. Gone was the tandem V-12 engine configuration, and in its place was a single 24-cylinder Hispano-Suiza 24Z engine. With much of France liberated in 1944, two SE 580 prototypes were ordered by the Ministère de l’Air (French Air Ministry). The Marine Nationale (French Navy) was interested in a navalized version designated SE 582 and ordered two prototypes in early 1945.

Sud-Est SE 580 HS 24Z

The SE 580 with open cowling revealing the 24-cylinder, 3,600 hp (2,685 kW) Hispano-Suiza 24Z engine.

Work on the SE 580 prototype was started first. The aircraft was of all-metal construction with fabric-covered control surfaces. The aircraft’s structure, especially the wings, followed basic Dewoitine design principals used in their earlier fighter aircraft. The SE 580 featured dive recovery flaps positioned under the wing and outside of the fully retractable main landing gear. Another unusual feature was that the incidence of the aircraft’s horizontal stabilizer was adjustable.

The smooth flow of the aircraft’s fuselage was interrupted by a large hump behind the cockpit. This structure housed the scoop that directed air through a radiator positioned horizontally in the aircraft’s rear fuselage. Cooling air entered a large opening just behind the cockpit, traveled down through the radiator, and exited the fuselage via a ventral flap. The intake also incorporated a slot for boundary layer air bleed. The radiator’s location in the center of the aircraft offered some inherent protection that was further enhanced by rear armor plating to protect against enemy fire.

Three fuselage fuel tanks and one fuel tank in each wing held a total of 660 gallons (2,500 L). A drop tank under the fuselage held an additional 79 gallons (300 L) of fuel. The SE 580’s Hispano-Suiza 24Z engine was an H-24 that was forecasted to produce 3,600 hp (2,685 kW). The 24Z would turn an 11.5 ft (3.50 m) diameter, six-blade, contra-rotating propeller.

Sud-Est SE 580 front

The supercharger intakes and numerous exhaust stacks interrupt the otherwise clean lines of the SE 580’s fuselage. The dorsal radiator scoop created a large blind spot for the pilot. One must wonder how cleanly air would flow into the scoop after being disrupted by the canopy.

The SE 580’s armament was quite substantial and consisted of a 30 mm cannon mounted between the engine’s upper cylinder banks and firing through the propeller hub. Each wing housed two 20 mm cannons and four 7.5 mm (or three 12.7 mm) machine guns. A hardpoint under each wing could accommodate a 1,102 lb (500 kg) bomb. A photo reconnaissance version would accommodate a vertical camera in the central fuselage.

The SE 580 had a 52.0 ft (15.86 m) wingspan and was 42.7 ft (13.0 m) long. The aircraft had an empty weight of 11,228 lb (5,093 kg) and a gross weight of 17,919 lb (8,128 kg). The SE 580 had a top speed of 373 mph (600 km/h) at sea level and 465 mph (749 km/h) at 30,512 ft (9,300 m). Its landing speed was 88 mph (141 km/h). The SE 580 could climb to 19,685 ft (6,000 m) in just over six minutes and had a theoretical ceiling of 44,619 ft (13,600 m). The aircraft’s maximum range was 1,709 miles (2,750 km).

By 1946, construction of the first SE 580 prototype was well underway, and a Hispano-Suiza 24Z engine was installed in the airframe. Unfortunately, problems with the 24Z engine resulted in its cancellation. The Arsenal 24H was selected as the replacement engine. The 4,000 hp (2,983 kW) 24H was also a 24-cylinder engine in an “H” configuration but had many differences when compared to the 24Z. The 24H was heavier and had a different propeller location; it used a single rotation, 12.1 ft (3.70 m) diameter, five-blade propeller. These differences required numerous, complex changes to the SE 580. The longer propeller was located 5.12 in (130 mm) lower on the engine and required changes to the aircraft’s landing gear and wings to maintain acceptable ground clearance. Wind-tunnel tests indicated further wing changes would be needed and that the engine had to be moved forward. In light of all the required changes, budgetary cutbacks, Sud-Est’s preoccupation with other projects, and the emergence of jet aircraft, the SE 580 was cancelled in 1947.

Sud-Est 580 rear

This rear view of the SE 580 shows the large radiator housing behind the cockpit. Note the cooling air exit flap under the fuselage.

SE 582 development trailed behind that of the SE 580; the French Navy was more interested in the Sud-Ost SO.8000, and Sud-Est was more focused on the SE 580. Changes needed to navalize the aircraft included incorporating an arrestor hook and folding wings. Construction of the SE 582 was limited to components that were shared with the SE 580, but it does not appear that any substantial part of the SE 582 was ever completed. The SE 582 had the same basic specification as the SE 582, except it was 712 lb (323 kg) heavier, at a gross weight of 18,631 lb (8,451 kg).

When Sud-Est abandoned the SE 580/582, the possibility of SNCAC (Société nationale des constructions aéronautiques du Centre or National Society of Aircraft Constructors Center) taking over the projects was discussed. However, the status of aviation could not be changed—the SE 580 and 582 were outdated, and existing aircraft already matched their performance. The first SE 580 prototype was never completed.

Sud-Est SE 580 cowling

SE 580 was a large aircraft, and its predicted performance equaled, but not bettered, existing aircraft then in service. Lack of available information about the aircraft, combined with its unique configuration and engine have made the SE 580 a curiosity for many aviation enthusiasts.

Sources:
Les Avions de Combat Francais 1944-1960 I – Chasse-Assaut by Jean Cuny (1988)
Les Avions Dewoitine by Raymond Danel and Jean Cuny (1982)
http://www.secretprojects.co.uk/forum/index.php/topic,4110.0.html
http://www.aviationbanter.com/showthread.php?t=76826

de Havilland DH91 Forbisher front

De Havilland DH.91 Albatross Transport

by William Pearce

In the mid-1930s, the de Havilland Aircraft Company (de Havilland ) sought financial support from the British Air Ministry to develop a new transport aircraft. De Havilland felt that Britain was not developing transport aircraft of the same performance level as those from the United States. On 21 January 1936, the Air Ministry ordered two of the new de Havilland transports as transatlantic mailplanes under Specification 36/35. Five additional aircraft were ordered by Imperial Airways Ltd. and would be completed as passenger transports. The mailplane and airliner versions had only minor differences, and both aircraft were designated DH.91 Albatross.

de Havilland DH91 Forbisher flight

The flagship of Imperial Airways F class: the de Havilland DH.91 Albatross ‘Frobisher.’ Its clean lines can be seen in the image above.

Designed by Arthur E. Hagg, the Albatross was an exceptionally clean, four-engine monoplane constructed almost entirely of wood. The long, circular fuselage had a steady taper toward the tail and was made of balsa wood sandwiched between thin layers of either cedar or birch, depending on location. The wood layers were cemented together and formed under pressure. Cabin construction allowed for pressurization, but such a system was never designed for the aircraft. The wing of the Albatross was constructed as one piece from a spruce structure covered with two layers of diagonal spruce planking. The thin wing was virtually sealed and would provide some level of buoyancy in the event of a water landing. The aircraft’s control surfaces were fabric-covered.

The Albatross had twin tails. Originally, the vertical stabilizers were positioned near the fuselage, about a third of the way along the horizontal stabilizer. Due to control issues, the tails were redesigned and positioned at the ends of the horizontal stabilizer. The aircraft used a conventional taildragger landing gear arrangement. The main wheels retracted inward and were fully enclosed in the wing’s center section. The tailwheel did not retract.

de Havilland DH91 Faraday early

The first Albatross prototype. Note its original tail and how close the vertical stabilizers are to the fuselage. This mailplane version would later be named ‘Faraday.’

Four de Havilland Gipsy Twelve (King I) engines powered the Albatross. The Gipsy Twelve was an air-cooled, supercharged, inverted, V-12 engine. The engine had a 4.65 in (118 mm) bore, a 5.51 in (140 mm) stroke, and a total displacement of 1,121 cu in (18.4 L). The Gipsy Twelve produced 525 hp (391 kW) at 2,600 rpm for takeoff power, 425 hp (317 kW) at 2,400 rpm for maximum climbing power, and 320 hp (239 kW) at 2,200 rpm for maximum economical cruse power. Each engine was housed in a very tight-fitting, streamlined cowling. Cooling air was brought in via pressure-ducts in the wing’s leading edge. The ducts were located in the propeller’s slipstream on both sides of each engine nacelle. The cooling air flowed forward along the outer side of the cylinders, from the back of the engine to the front. The air was forced through the cylinders’ cooling fins and into the Vee of the engine, where an exit flap on the bottom of the cowling allowed the air to escape. The opening of the exit flap controlled the engine temperature. Each engine turned a two-blade, constant-speed, 10 ft 6 in (3.2 m) diameter de Havilland propeller via a .66 gear reduction.

The basic structure of the mailplane and airliner versions of the Albatross were the same, but the aircraft did have their differences. The mailplane was designed to carry 1,000 lb (454 kg) of mail 2,500 mi (4,023 km) against a 40 mph (64 km/h) headwind, while the airliner was designed to carry 22 passengers and four crew 1,000 mi (1,609 km). The mailplane had four cabin windows on each side of its fuselage, compared to six for the airliner version. The mailplane utilized split flaps, while the airliner used slotted flaps. The mailplane Albatross had four 330 gal (1,250 L) fuel tanks mounted in the cabin, while the airliner had one 270 gal (1,022 L) and one 170 gal (644 L) fuel tank mounted under the cabin floor. The mailplane had two 9 gal (7.5 L) oil tanks per engine; the airliner had just one oil tank per engine.

de Havilland DH91 Forbisher front

The cooling-air ducts in the wing’s leading edge can be seen in this view of ‘Frobisher.’ Each duct brought in air to the nearest cylinder bank. Note the landing gear wheel wells and the hinged cover on the main wheels.

The Albatross had a wingspan of 105 ft (32.0 m) and was 71 ft 6 in (21.8 m) long. The mailplane had a top speed of 222 mph (357 km/h) at 8,700 ft (2,652 m) and a maximum economical cruse speed of 204 mph (328 km/h) at 11,000 ft (3,353 m). Its maximum range was 3,300 mi (5,311 km), and its gross weight was 32,500 lb (14,742 kg). The aircraft had a 550 fpm (2.8 m/s) climb rate and a ceiling of 15,100 ft (4,602 m).

The airliner version had a top speed of 225 mph (362 km/h) at 8,700 ft (2,652 m) and a maximum economical cruse speed of 210 mph (378 km/h) at 11,000 ft (3,353 m). Its maximum range was 1,040 mi (1,634 km), and its gross weight was 29,500 lb (13,381 kg). The aircraft had a 710 fpm (3.6 m/s) climb rate and a ceiling of 17,900 ft (5,456 m).

de Havilland DH91 Forbisher rear

This view of ‘Frobisher’ shows the additional windows incorporated into the airliner version of the Albatross. The revised tail is also apparent.

The Albatross mailplanes were built first, and the initial prototype flew for the first time on 20 May 1937. Robert John Waight was the pilot for the first flight. By October, the need to redesign the tails was evident, and the new tail fins were installed on the ends of the horizontal stabilizer. After the modification, the aircraft was registered as G-AEVV on 3 January 1938. On 31 March 1938, the Albatross suffered a belly landing due to a landing gear issue. Once repaired, G-AEVV became part of Imperial Airways in August 1939. All DH.91s were part of Imperial Airways F (Frobisher) class of aircraft and were given names starting with the letter “F.” G-AEVV was named Faraday. When Imperial Airways was merged with British Airways Ltd. in 1940 to form the British Overseas Airways Corporation (BOAC), the ownership of all DH.91s was eventually transferred to BOAC. Faraday was transferred to BOAC on 17 June 1940. On 1 September 1940, Faraday was impressed into service (as AX903) during World War II as a transport shuttle flying between Great Britain and Iceland. While landing at Reykjavik, Iceland on 11 August 1941, the aircraft collided with a Fairey Battle and was damaged beyond repair. Fortunately, the five people onboard the Albatross escaped unharmed. Some records claim the accident occurred on 11 August 1940, but this does not fit the timeline, especially since the date of impressment is recorded as 1 September 1940.

The second mailplane was registered as G-AEVW and named Franklin. On 27 August 1938, the aircraft’s rear fuselage broke in two during overload landing tests, revealing a structural weakness. The aircraft was repaired, and the changes were incorporated into the other Albatross aircraft. G-AEVW was transferred to BOAC on 8 July 1940. Like Faraday, Franklin was impressed into service (as AX904) on 1 September 1940 and was damaged beyond repair in a landing accident at Reykjavik. The mishap occurred on 7 April 1942 when the aircraft’s landing gear collapsed. The four people onboard were not injured.

de Havilland DH91 Forbisher side

The DH.91 was a very graceful and aerodynamic aircraft. Note the sleek engine installation and the cooling-air exit flaps under the engine nacelles.

The first Albatross airliner was registered as G-AFDI and given the name Frobisher. It was delivered in October 1938 and served as the flagship for Imperial Airways. The aircraft started experimental service in December and averaged 219 mph on its first service flight from Croydon, England to Cairo, Egypt. The aircraft was transferred to BOAC on 22 August 1940. Frobisher was destroyed during a German air raid at the Bristol (Whitchurch) Airport on 20 December 1940.

The second airliner was registered as G-AFDJ and named Falcon. It was delivered to Imperial Airways in November 1938 and entered service in January 1939. The aircraft was transferred to BOAC on 27 August 1940. Falcon was scrapped in August 1943 after the loss of Fortuna (see below) and because the spare parts supply for the Albatross aircraft had been depleted.

The third airliner was registered as G-AFDK and named Fortuna. It was in service by mid-1939 and was transferred to BOAC on 27 August 1940. Fortuna crashed on approach to Shannon Airport in Ireland on 16 July 1943. The aircraft’s wing started to break up, and Fortuna crash landed short of the runway. All fourteen people on the aircraft survived the crash. This accident precipitated the last two surviving DH.91s, Falcon and Fiona (see below), to be removed from service.

de Havilland DH91 Franklin

The two Albatross mailplanes served as transports during World War II, and both were lost in separate landing accidents at Reykjavik, Iceland. ‘Franklin,’ the second mailplane  is seen above in its wartime camouflage.

The fourth airliner was registered as G-AFDL and named Fingal. It entered service for Imperial Airways in 1939 and was transferred to BOAC on 29 August 1940. The aircraft was lost on 6 October 1940 while making an emergency landing near Pucklechurch, England because of a fractured fuel line. Fingal hit a farmhouse during the forced landing and was damaged beyond repair, but none of the three people onboard were injured.

The last airliner was registered as G-AFDM and named Fiona. The aircraft entered service with Imperial Airways in 1939. The aircraft was transferred to BOAC on 22 August 1940 and continued in service until being withdrawn after the Fortuna crash. Fiona was scrapped along with Falcon in August 1943.

The de Havilland DH.91 Albatross was a beautiful aircraft that performed well in service. Part of its downfall can be attributed to its production right before World War II. It is rather remarkable to consider that four of the aircraft crashed during the landing phase of flight but that no one was killed in any of the accidents. While the Albatross cannot be considered a success, the techniques used in the Albatross’ wooden construction were applied directly to the incredibly successful World War II-era DH.98 Mosquito. Hagg went on to design the Napier-Heston Racer, and some of the Albatross’ streamlining traits can be seen in that aircraft.

de Havilland DH91 Fortuna

While landing in Shannon, Ireland, the wing of ‘Fortuna’ (seen above) began to break apart. The aircraft crashed short of the runway, but no lives were lost. Due to the crash and lack of spare parts, the two remaining DH.91s were withdrawn from service. Note the Bristol Beaufighter in the distance.

Sources:
“The Albatross in Detail” Flight (17 November 1938)
De Havilland Aircraft since 1909 by A. J. Jackson (1987)
Shannon Airport: A Unique Story of Survival by Valerie Sweeney (2004/2015)
“Cooling the Gipsy Twelve” Flight (31 March 1938)
http://aviation-safety.net/database/record.php?id=19400811-0
http://aviation-safety.net/database/record.php?id=19420407-0
http://aviation-safety.net/database/record.php?id=19401220-0
http://aviation-safety.net/database/record.php?id=19401006-0