By William Pearce

In early 1942, Austrian engineer Otto Kauba had interested the RLM (Reichsluftfahrtministerium or German Ministry of Aviation) in the design of a flying bomb. The RLM founded the Škoda-Kauba Flugzeugbau in German-occupied Prague, Czechoslovakia to produce the aircraft. Kauba was assigned to work out of the Škoda Auto Works, and the aircraft were to be built by the Czech company Avia. Although the flying bomb project was unsuccessful, Škoda-Kauba continued to design a series of small aircraft for the RLM, all of which were built by Avia. His next two designs yielded small and strangely shaped aircraft, but Kauba’s fourth design was a much more refined and sleek aircraft: the V4.

The Argus As 10C-3-powered Škoda-Kauba V4 was a sleek and attractive aircraft. Note the cut-out in the vertical stabilizer that allowed the variable incidence horizontal stabilizer to move.

The Škoda-Kauba V4 was designed to be a single-seat advanced trainer. It was an exceptionally clean low wing aircraft with retractable, wide-track main gear. The V4 employed simple construction and used non-strategic materials, such as steel, wood, and canvas. The wing’s leading edge was swept back and its tubular main spar tapered toward the rounded wingtip. Ribs were welded onto the main spar to form the basic frame of the wing, which was then covered with plywood. The fuselage had a welded steel-tube frame skinned with plywood. The V4 had a variable incidence horizontal stabilizer that was adjusted by the pilot via an electric motor for trim control. The V4 was powered by a 240 hp (179 kW) Argus As 10C-3 inverted, air-cooled, V-8 engine. Provisions were made to mount a single 7.9 mm machine gun.

The V4 had a wingspan of 24 ft 11 in (7.6 m) and a length of 18 ft 4 in (5.6 m). The aircraft’s maximum speed was 261 mph (420 km/h) at altitude and 236 mph (380 km/h) at sea level. Cruising speed was 196 mph (315 km/h). The SK 257’s initial rate of climb was 2,008 ft/min (10.2 m/sec). Its service ceiling was 24,600 ft (7,500 m), and it had a range of 578 miles (930 km). The aircraft weighed 2,249 lb (1,020 kg) empty and 2,756 lb (1,250 kg) loaded.

This image gives a good view of the differences between the V4 and the SK 257 prototype. Note the different wing shape and longer Argus As 410 engine and rear fuselage of the SK 257.

The V4, carrying the registration D-EZWA, exhibited good flying characteristics and performance. Since it was constructed from non-strategic materials, the RLM saw the makings of a good aircraft. However, the desire for more power could not be overlooked. The RLM awarded Škoda-Kauba a contract for the development of a more powerful advanced trainer, designated SK 257. The RLM believed the SK 257 would prepare new pilots for the challenging Messerschmitt Bf 109. Four SK 257 prototypes were ordered.

The SK 257 was very similar to the V4, although slightly longer and powered by a larger engine. The SK 257’s engine was an air-cooled, inverted, V-12 Argus As 410 that produced 485 hp (362 kW). Reportedly, the SK 257 had the same 24 ft 11 in (7.6 m) wingspan as the V4, but its wing had square tips and less sweep. At 23 ft 4 in (7.1 m), the SK 257 was 5 ft (1.5 m) longer than the V4. The aircraft had a maximum speed of 217 mph (350 km/h).

Two production Škoda-Kauba SK 257 come to grief. Note the different tail and canopy when compared to the prototype and the absence of gear doors.

The four (some say two) SK 257 prototypes were completed and the first flew in 1943. The aircraft displayed excellent handling and performance. Subsequently, The RLM ordered 1,000 SK 257 trainers for the Luftwaffe. This order was quickly reduced to 100 aircraft. The production aircraft were built at Trenčin on the Biskupice airfield in Slovakia. The production SK 257 aircraft had a simplified square tail, whereas the prototypes had a curved tail. After five examples had been built, their construction was judged to be so poor that they did not pass the Luftwaffe quality control inspections, and the entire order was cancelled.

Undeterred, Kauba designed a fighter based on the V4/SK 257 aircraft. This fighter was designated V5 and was to be powered by a 1,750 hp (1,305 kW) Daimler-Benz DB 603 liquid-cooled inverted V-12 engine. The V5 was intended to out-perform the Focke-Wulf Fw 190 with a maximum speed of 475 mph (765 km/h). It would have a 40 ft (12.2 m) wingspan with two 20 mm cannons in each wing, be 32.8 ft (10 m) long, and weigh 9,920 lb (4,500 kg). However, the V5 progressed no further than a series of wind tunnel models and a full-scale mockup. The RLM was focused on other projects and felt the development of an entirely new piston-engine fighter was a waste of time, resources, and effort.

The full scale mockup of the Škoda-Kauba V5 fighter. Note the Škoda-Kauba emblem that was also worn by all the prototypes and derived from the Škoda Auto Works emblem.

The only surviving piece of Škoda-Kauba’s efforts is the left wing, including landing gear, from a SK 257. This artifact is on display at the Vojenský Historický Ústav (Military History Institute) in Prague.

Preserved wing of a Škoda-Kauba SK 257 at Vojenský Historický Ústav in Prague. Note the tapered, tubular main spar protruding from the wing. (Vojenský Historický Ústav image)

Sources:
– German Aircraft of the Second World War by J. R. Smith and Antony L. Kay (1972/1992)
– Československá Letadla [1] 1918-1945 by Václav Němeček (1983)
– http://www.histaviation.com/Skoda-Kauba.html and subpages
– http://www.vhu.cz/exhibit/kridlo-z-nemeckeho-cvicneho-letounu-sk-257/

By William Pearce

In mid-1942, Republic Aviation Corporation initiated a design study to lighten their P-47 Thunderbolt fighter for improved performance. The Thunderbolt had been steadily gaining weight as the design matured, while comparative enemy aircraft, like the Focke-Wulf FW 190A, were much lighter. Republic officially proposed a light-P-47 to the Army Air Force (AAF) on 22 November 1942. On 1 April 1943, the AAF gave Republic a letter of intent to purchase two light-weight P-47s, and the contract was officially approved on 18 June 1943. This new aircraft was designated the XP-47J.

An early image of the Republic XP-47J before the Superman nose art was applied. Note the cooling fan vanes around the spinner inside the cowling.

As with all P-47s, Alexander Kartveli was the main designer of the XP-47J, and he was assisted by Murray Burkow. The XP-47J was similar in appearance to a P-47B, but it was a completely new aircraft. The XP-47J had a close-fitting cowl installed around its Pratt & Whitney (P&W) R-2800 engine of increased power output. A large spinner was added, along with a fan to aid engine cooling. The turbosupercharger’s intake had been refined, and the flow of its exhaust was directed to provide additional thrust. Two of the .50-cal machine guns were deleted (leaving six) in the XP-47J’s lightened wing, and the rounds per gun were reduced to 267. Other weight-saving measures were the omission of radio equipment and the aft fuel tank. To keep the aerodynamics clean, the XP-47J had no provisions for external stores under the wings or fuselage.

Originally, the AAF wanted the XP-47J to have contra-rotating propellers and a bubble canopy, like a late P-47D. To expedite the XP-47J, the decision was made for the first prototype to be a razorback version and the second prototype would include a bubble canopy. The six-blade contra-rotating propeller was test-flown on a P-47B but showed no increase in performance. This, combined with delays at P&W on the R-2800-61 engine with a contra-rotating gear reduction, resulted in the substitution of a R-2800-57 engine with a standard gear reduction. Both the -57 and -61 engines were rated at 2,100 hp (1,566 kW) and had a War Emergency Power (WEP) rating of 2,800 hp (2,088 kW). The -61 engine would be supplied later, when it was available. The engine, cowling, and cooling fan were installed and test flown on a P-47D-15.

This side view of the XP-47J reveals its distinct intercooler air and exhaust exits under the rear fuselage.

The XP-47J had a wingspan of 40 ft 10 in (12.4 m) and a length of 33 ft 3 in (10.1 m). The aircraft had an empty weight of 9,663 lb (4,383 kg) and a design gross weight of 12,400 lb (5,625kg). Its service ceiling was 45,000 feet (13,716 m). The XP-47J had a range of 765 mi (1,231 km) at a cruising speed of 400 mph (644 km/h) and a range of 1,070 mi (1,722 km) at optimum cruising speed. Fuel capacity was 287 US gal (1,086 L).

On 31 July 1943, Republic issued a report comparing the estimated performance of the XP-47J with the P&W R-4360-powered XP-72 that was under development. The report concluded that the Republic XP-72 had more potential and recommended resources be focused on that aircraft. In addition, 70% of the P-47 production line needed to be re-tooled in order to produce the P-47J. Republic called for the cancellation of the second XP-47J prototype but encouraged the completion and testing of the first prototype. The AAF approved Republic’s plan and cancelled the second XP-47J.

The sole XP-47J prototype (serial number 43-46952) was completed in mid-November 1943 and made its first flight on the 26th of that month. The aircraft was quickly dubbed Superbolt and wore nose art on both sides of the cowling of Superman holding a lightning bolt. After about 10 hours of flying time, the R-2800-57 engine was making metal and was replaced by another engine of the same type in February 1944.

The factory-fresh Superbolt is being run-up outside of Republic’s plant in Farmingdale, New York. Unlike a standard P-47, the intake under the engine was separate and pushed back from the front of the cowling.

A short time later, P&W informed the AAF and Republic that the R-2800-57 engine was not compatible with the 2,800 hp (2,088 kW) WEP rating. A water-injected R-2800-14W was substituted in the XP-47J in April. Water injection is a system that sprays anti-detonation fluid (a mixture of alcohol and water) into the induction system to lower the charge temperature and prevent detonation in the cylinders. This allowed the -14W to produce 2,800 hp (2,088 kW). In March, P&W informed Republic that it was still having difficulty with the R-2800-61’s contra-rotating gear reduction and did not know when the engine would be available. This effectively put an end to the possibility that the XP-47J would have contra-rotating propellers anytime in the near future.

On 11 July 1944 and equipped with a General Electric CH-3 turbosupercharger, the XP-47J achieved 493 mph (793 km/h) at 33,350 feet (10,165 m). Although the engine was producing 2,800 hp (2,088 kW), Republic believed the aircraft had more potential. At its own expense, Republic installed a CH-5 turbosupercharger and a larger 13 ft (3.96 m) Curtiss propeller. The propeller was an experimental unit with 2 in (51 mm) added to its trailing edge to increase its width. With the changes, the engine producing 2,730 hp (2,036 kW), and 400 lb (1.78 kN) of jet thrust from the exhaust, Mike Ritchie flew the XP-47J over a calibrated course at 34,450 (10,500 m) feet on 4 August 1944* and achieved 505 mph (813 km/h). This is the highest speed recorded in level flight by any propeller-driven aircraft during World War II.

The Republic XP-47J, now with the Superman nose art. Some differences from a standard P-47 are the additional plexiglass panel behind the pilot and the lack of intercooler exhaust doors on the sides of the rear fuselage.

The XP-47J was handed over to AAF and arrived at Wright Field, Ohio on 9 December 1944. During flight tests, the AAF was unable to get maximum power from the R-2800 engine. The AAF recorded a speed of only 484 mph (779 km/h) at 25,350 feet (7,727 m) and with the engine producing 2,770 hp (2,066 kW). Near the end of flight testing, the exhaust manifold system had a serious failure while the aircraft was at 36,000 ft (10,943 m). The cause of the failure was the increase in pressure and temperature from the CH-5 turbosupercharger acting upon the unstrengthened exhaust system. The Official Performance Summary report states the XP-47J had a max speed of 507 mph (816 km/h) and a 4,900 fpm (24.9 m/s) initial rate of climb. Republic’s Test Report No. 51 (27 January 1945) lists the max speed as 502 mph (808 km/h).

While the XP-47J Superbolt had remarkable performance, it was overshadowed by other aircraft, like the XP-72, that were under development. Work on the XP-72, which first flew on 2 February 1944, was not far behind that of the XP-47J, but as the war progressed and with the advent of jet fighters, neither aircraft were needed.

*Mike Ritchie’s report recording the 505 mph (813 km/h) speed was dated 5 August 1944, but it is believed the flight actually occurred on 4 August 1944.

The six wing guns are evident in this image of the 500+ mph Republic XP-47J Superbolt.

Sources:
– Republic’s P-47 Thunderbolt by Warren M. Bodie (1994)
– US Army Air Force Fighters Part 2 by William Green and Gordon Swanborough (1978)
– R-2800: Pratt & Whitney’s Dependable Masterpiece by Graham White (2001)
– The American Fighter by Enzo Angelucci and Peter Bowers (1985/1987)
– “500-Mph. P-47 Disclosed by AAF” Aviation News (29 October 1945)
– http://www.joebaugher.com/usaf_fighters/p47_9.html

By William Pearce

In May 1943, the Japanese Army Air Force issued a specification for a high altitude, long range heavy fighter. Led by Tomio Kubo, a team at Mitsubishi began to design the single-engine Ki-73 (Allied codename: Steve) to meet this specification. However, the aircraft’s power plant, a 2,600 hp (1,939 kW) Mitsubishi Ha-203-II 24-cylinder “H” engine, suffered from severe developmental delays and was ultimately abandoned. As a result, the Ki-73 was abandoned as well.

The Mitsubishi Ki-83 on a test flight with US markings on the fuselage. The brace from the horizontal stabilizer to the fuselage can barely be seen. The notch in the underside of the fuselage should be the access hatch for the second crew member. Apparently the hatch was missing on this flight, as a hatch made mostly of acrylic glass should be visible in other images.

Kubo went back to the drawing board and created another designed based on his experience with twin-engine aircraft, including the Mitsubishi Ki-46 (Allied codename: Dinah). What Kubo designed was perhaps the most advanced Japanese aircraft built during World War II: Mitsubishi Ki-83.

The Ki-83 was an aerodynamically clean, all metal aircraft with two crew stations. Its mid-fuselage mounted wings were equipped with Fowler-style flaps. The pilot had a 360-degree view, and the radio operator/navigator was positioned in the aircraft’s fuselage behind the wings. The second crew member had very cramped accommodations with small windows. However, the second crew member was not intended to be on every mission.

The aircraft featured fully retractable gear including the tailwheel. The main wheels retracted back into the engine nacelles. The Ki-83’s armament consisted of two 30 mm Ho-105 and two 20 mm Ho-105 cannons, all housed in the lower nose. In addition, two 110 lb (50 kg) bombs could be carried on under-wing hardpoints. Some sources say the bombs were carried internally, but this appears unlikely unless the bombs replaced the second crew member.

The Ki-83 still in Japanese markings. The windows for the second crewman can be seen just above the tip of the horizontal stabilizer. Presumably, this is an early photo of the Ki-83, because the brace for the horizontal stabilizer appears to be absent.

The Ki-83 was powered by two Mitsubishi Ha-211-IRu (joint designation [Ha-43] 12) air-cooled radial engines, each driving an 11.5 ft (3.5 m), four-blade propeller. The 18-cylinder engines had a bore of 5.51 in (140 mm), a stroke of 5.90 in (150 mm), and a total displacement of 2,536 cu in (41.6 L). The engine was turbosupercharged and produced 2,200 hp (1,640 kW) for takeoff and 1,750 hp (1,305 kW) at 31,170 ft (9,500 m). The turbocharger was placed in the rear of the engine nacelle. Fresh air would enter the turbocharger near the rear of the nacelle on the outboard side, be compressed, and then flow to the engine through an air box in the upper nacelle. The engine’s exhaust was expelled from the turbocharger on the inboard side of the nacelle, and a wastegate was positioned at the end of the nacelle. The exhaust arrangement provided some additional thrust. An engine oil cooler was positioned under the nacelle.

The Ki-83 had a 50.85 ft (15.5 m) wingspan, was 41.0 ft (12.5) long, and weighed 13,184 lb (5,980 kg) empty and 20,790 lb (9,430 kg) maximum. A speed of 426 mph (686 km/h) was recorded at 26,250 ft (8,000 m), but top speed rose to 438 mph (705 km/h) at 29,530 ft (9,000 m). Cruise speed was 280 mph (450 km/h) at 13,125 ft (4,000 m). The Ki-83 could climb to 32,810 ft (10,000 m) in 10 minutes and had a ceiling of 41,535 ft (12,660 m). Normal range was 1,214 mi (1,953 km), and maximum range was 2,175 mi (3,500 km).

Another early image of the Mitsubishi Ki-83 in Japanese markings. Curiously, there seem to be no oil coolers under the engine nacelles.

The first Ki-83 prototype was completed in October 1944 and flew the following month on 18 November. Test flights were often interrupted by Allied bombing raids, but the Ki-83 demonstrated excellent maneuverability and performance. However, the prototype did experience tail and engine vibration issues and failures of the turbochargers. To cure the issues with the tail, an angled brace was added from the horizontal stabilizer down to the fuselage, and balance weights were added to the elevators. Based on the Ki-83’s performance, the Japanese Navy expressed interest in the aircraft, and the Army agreed to give the Navy some examples after production had started. Reportedly, 39 Ki-83 aircraft had been ordered.

Three additional prototypes were built that incorporated changes to fix the first Ki-83’s deficiencies. The second Ki-83 was completed in April 1945 and flew on 9 March 1945. The third and fourth prototypes had their first flights in the summer of 1945. However, the three additional prototypes were damaged (most likely destroyed) in Allied bombing raids. A fifth prototype was under construction at the end of the war.

The captured Ki-83 while still in Japan. The wastegate exhaust is visible at the rear of the nacelle, and the air intake can be seen on the outboard side of the nacelle just below the trailing edge of the wing.

With the war situation deteriorating for Japan, their limited resources were dedicated to the production of interceptor fighters, and the Ki-83 never entered production. At the end of the war, US forces were surprised to find the Ki-83 because it was an aircraft they knew nothing about. In addition, an advanced high-altitude interceptor version, the Ki-103, and a reconnaissance version, the Ki-95, were under development. The original and sole remaining Ki-83 was flight tested by the Allies at the Matsumotu Army Air Base in Japan. On one of those flights and with the aid of high-performance US aviation fuel, the Ki-83 reportedly achieved a top speed of 473 mph (762 km/h) at 22,965 ft (7,000 m) and could climb to 32,810 ft (10,000 m) in 9 minutes, but a definitive source reporting this impressive performance has not been found.

After flight testing, the Allies came to the conclusion that the Ki-83 was a very maneuverable and high-performance aircraft. In December 1945, the Ki-83 was shipped to the Alameda Air Station near San Francisco, California aboard the USS Tulagi escort carrier. The Ki-83 was given the Foreign Evaluation number FE-151 and flown some in the US. By February 1946, it was at the Middletown Air Depot (now Harrisburg International Airport) at Middletown, Pennsylvania and available for examination by the US aircraft industry. In September 1946, the Ki-83 was allotted to the Air Force Museum, but evidently these plans fell through. The Ki-83’s last known whereabouts were at Orchard Field Airport (now O’Hare Airport) Special Depot in Park Ridge, Illinois in 1949. There are no further details of its fate and it is presumed to have been scrapped at Park Ridge in 1950.

Mitsubishi Ki-83 under guard by US forces in Japan. The 30 mm cannons are in the lower nose with the 20 mm cannons above. The turbocharger exhaust can just be seen at the rear of the nacelle in the center of the image.

Sources:
– Japanese Aircraft of the Pacific War by Rene J. Francillon (1970/2000)
– Japanese Army Fighters Part 1 by William Green and Gordon Swanborough (1977)
– Japanese Aircraft: Performance and Characteristics by Edward T. Maloney (2000)
– War Prizes by Phil Butler (1994/1998)
– http://www.secretprojects.co.uk/forum/index.php/topic,14960.0/all.html
– http://www.secretprojects.co.uk/forum/index.php/topic,8898.0/all.html
– http://forums.ubi.com/showthread.php/101463-Mitsubishi-Ki-83/page2

By William Pearce

With the intention of creating a high speed light bomber, Viktor Bolkhovitinov designed what is commonly referred to as the Bolkhovitinov S or Sparka. During flight trials the Soviet Air Force (VVS) referred to the aircraft as S-2M-103, for skorostnoy (high speed) with two M-103 engines; however, a number of other designations have been applied over the years. The common “Sparka” designation means twin—because the aircraft had two engines mounted in tandem. Other designations are BBS-1 for blizhniy bombardirovshchik skorostnoy (short range bomber, high-speed), BB for blizhniy bombardovshchik (short range bomber), and LB-S for lyohkiy bombardirovshchik-sparka (light bomber-paired).

A good view of the twin-engine Bolkhovitinov Sparka. Note the plexiglass glazing for the bombardier’s downward view.

The Sparka was a low-wing aircraft of all-aluminum construction with stressed skin. The aircraft had a twin fin tail to increase the rear gunner’s field of fire. The undercarriage was fully retractable; the main gear retracted toward the rear, and the wheels rotated 90 degrees to lie flat within the wings. The pilot and navigator/bombardier/gunner sat in tandem under a long canopy. Between the pilot and second crew member was a small bomb bay for 882 lb (400 kg) of bombs. A plexiglass section on the bottom of the aircraft just aft of the bomb bay provided the bombardier a view of the ground. The aircraft was 43 ft 4 in (13.2 m) long and had a relatively short wingspan of 37 ft 4 in (11.38 m). The Sparka weighed 12,460 lb (5,652 kg).

The Sparka was powered by two Klimov M-103A engines positioned in tandem in the aircraft’s nose. This coupled engine package was designated M-103SP. Each engine drove half of the aircraft’s six-blade, coaxial contra-rotating propeller unit. This engine and propeller arrangement was similar to the FIAT AS.6 installed in the Italian MC.72 and the Hispano-Suiza 12Y installed in the French Arsenal VB 10. With this engine arrangement, the front engine drove the rear propeller, and the rear engine drove the front propeller via a drive shaft that ran through the Vee of the front engine.

Schematic of the paired Klimov M-103 engines installed in the Bolkhovitinov Sparka with the rear engine’s drive shaft passing through the Vee of the front engine.

The Klimov M-103 engine was derived from the M-100, which was a licensed copy of the Hispano-Suiza 12Ybrs. The M-103SP had a 5.83 in (148 mm) bore and a 6.69 in (170 mm) stroke. Total displacement was 2,142 cu in (35.09 L). The engine produced 960 hp (716 kW). A radiator was installed in a large duct just below the rear engine, and it cooled both of the Sparka’s engines.

Bolkhovitinov started design work on the Sparka in 1937, and prototype construction began in July 1938. The aircraft made its first flight in January 1940 (some say late 1939) with B. N. Kudrin at the controls. VVS testing took place from March through July 1940. The Sparka showed good speed, reaching 354 mph (570 km/h). However, the takeoff run was excessive, landing speeds were high, and visibility over the nose was impaired. In addition, some trouble was encountered with the rear engine’s propeller drive shaft breaking due to excessive vibrations. Even so, the aircraft received a positive assessment, noting that the installation of the tandem engines eliminated a considerable amount of drag over two separate nacelles.

Engine bay view of the two Klimov M-103 engines.

A new wing was designed with a NACA-230 airfoil section to improve takeoff and landing performance. The aircraft was tested with this new wing from September to December 1940, and it did improve the aircraft’s takeoff and landing characteristics.

The Sparka was reconfigured for a single 1,050 hp (783 kW) Klimov M-105P (some say 103P) engine, which was installed in the forward engine bay. The M-105P was a development of the M-103P and could be fitted with a cannon in the engine’s Vee to fire through the propeller hub. The M-105P retained the bore and stroke of the earlier M-103P (and M-103SP) engine. The aircraft was tested on skis in early 1942 but was underpowered with the single M-105P, attaining a top speed of only 249 mph (400 km/h).

In this side view, the glazing on the bottom of the Sparka can clearly be seen.

Some say the single engine version was really a separate aircraft (known as S-1) that flew in January 1940 to test the airframe configuration. This seems unlikely because of the time frame involved. The twin-engine Sparka (S-2) would have been nearly complete by the time the single engine airframe test ship first took to the air, making major changes impossible and minor changes difficult. If the airframe test ship had issues, there would not have been enough time for any changes to be made before the official trials took place in March 1940. Not to mention that adding the power and weight of another engine would change the aircraft’s flight dynamics considerably.

The single-engined Bolkhovitinov S on skis.

Regardless, development on the Sparka was abandoned in mid-1941, partially a result of the German invasion. However, further studies were made on the feasibility of the tandem engine arrangement powering a fighter, but these studies did not lead to the production of any aircraft. In addition, the factory where the Sparka was built was needed to produce the Petlyakov Pe-2 attack bomber.

Rear view of the Sparka showing the defensive machine gun installation.

Sources:
– Soviet X-Planes by Gordon and Gunston (2000)
– Soviet Air Power in World War 2 by Yefim Gordon (2008)
– Soviet Combat Aircraft of the Second World War, Vol. 2 by Gordon and Khazanov (1999)
– Aircraft of the Soviet Union by Bill Gunston (1983)
– Russian Piston Aero Engines by Vladimir Kotelnikov (2005)
– http://www.secretprojects.co.uk/forum/index.php/topic,4532.msg152239.html#msg152239
– http://en.wikipedia.org/wiki/Bolkhovitinov_S

By William Pearce

In March 1942, the Beech Aircraft Company began design work on a two-seat heavy fighter to destroy enemy bombers. Since the Curtiss XP-71 had already been delegated this task, the Beech developed the design into an attack aircraft to replace the Douglas A-20 Havoc. Beech gave this aircraft the in-house designation Model 28 and submitted its proposal to the US Army Air Force on 23 September 1942. On 2 December 1942, the AAF ordered two prototypes and designated the aircraft XA-38; this was Beech’s first combat aircraft. Beech originally called the aircraft Destroyer, but the AAF changed the name to Grizzly. The XA-38 was similar in appearance to the Beech 18, but it was an all-new aircraft. The project was led by Bill Cassidy, and the aircraft was to be strong, maneuverable, and well-armed. Its mission was to destroy fortified gun emplacements, armored vehicles, tanks, submarines, and coastal surface vessels.

The second Beech XA-38 Grizzly (serial no 43-11407), with all guns installed.

The XA-38 was a two-place, mid-wing aircraft with a slim fuselage and twin tails. The gunner sat in the rear of the fuselage and operated remote upper and lower turrets, each fitted with two Browning .50 cal guns. The ventral turret could be locked in the forward position and fired by the pilot in strafing attacks. In the nose of the aircraft were another two Browning .50 cal guns and a T15E1 (M10) 75 mm cannon. The nose swung open to service the guns and was even removable so that different armament could be used. The .50 cal guns each had 500 rounds, and the 75 mm cannon had 20 rounds. Each wing supported two hard points that could carry a combined total of 2,650 lb (1,200 kg) of ordinance or 600 gal (2,270 L) of fuel.

The T15E1 75 mm cannon had an 84 in (2.13 m) barrel that extended about 2 ft (.61 m) beyond the aircraft’s nose. The cannon was self-loading, 144 in (3.66 m) long, and originally weighed 1,800 lb (816 kg). However, through further development, the weight was reduced to 1,138 lb (516 kg). It fired a 26 in (.66 m) shell with a 15 lb (6.8 kg) projectile. The cannon consisted of a 75 mm gun (T9E2), 75 mm feed mechanism (T13), and the 75 mm gun mount (T15E1).

Excellent view of the second XA-38, showing the slim fuselage. The aircraft was on a test flight over Kansas.

The Grizzly’s aluminum skin was entirely flush riveted, and the fully retractable gear, including tailwheel, was engineered for operations out of unimproved airstrips. The aircraft was powered by two Wright R-3350-43 engines producing 2,300 hp (1,715 kW) each. Each engine turned a 14.2 ft (4.32 m), three-blade Hamilton Standard propeller. The XA-38 could carry 640 gal (2,423 L) of fuel in its wings and an additional 185 gal (700 L) in the fuselage behind the pilot. The aircraft had a wingspan of 67.3 ft (20.5 m) and was 51.8 ft (15.8 m) long. It weighed 22,480 lb (10,197 kg) empty and had a maximum takeoff weight of 35,265 lb (15,995 kg). The XA-38’s climb rate was 2,170 fpm (661 m/m), and it had a service ceiling of 27,800 ft (8,475 m). Maximum speed at 3,100 ft (945 m) was 376 mph (605 km/h), and cruise speed at 16,000 ft (4,877 m) was 344 mph (554 km/h). The 45-degree flaps allowed the aircraft to land at 97 mph and operate out of a 2,500 ft (762 m) runway.

Both XA-38 aircraft in flight. The dummy turrets can be see on the first XA-38 to fly (furthest from camera).

The aircraft program was met with long delays due to the unavailability of the R-3350 engines, remote turrets, and the 75 mm cannon. The Boeing B-29 had engine priority; the Douglas A-26 had the turrets; and the cannon was still being developed. The first XA-38 (serial no 43-14406) took to the air on 7 May 1944 with Vern Carstens at the controls. The turrets were still not available, so dummy turrets were substituted. In July 1944, the aircraft was flown to Tulsa, Oklahoma, where the 75 mm cannon was fitted and ground fired. Later in July, the Grizzly fired the cannon in-flight over Great Bend, Kansas.

Flight tests continued and minor issues were worked out. The aircraft performed very well, and during one early, low-level test flight, the XA-38 was able to pull away from the P-51B chase plane. Capt. Jack Williams evaluated the aircraft for the AAF and made 38 flights in the XA-38 between 13-24 October 1944. The aircraft was reported to be very maneuverable for an aircraft of its size and easy to fly through most aerobatic maneuvers. The aircraft was transferred to Dayton, Ohio for further evaluation on 7 July 1945. At some point, at least a mockup of the upper turret was added to the aircraft.

What must be a late image of the first Beech XA-38 Grizzly (serial no 43-14406) with what appears to be a mockup of the upper turret installed.

The second aircraft (serial no 43-11407) took to the air on 22 September 1945; Carstens was again at the controls. This aircraft had the correct turrets installed, and all weapons were operational. After initial flight tests, the XA-38 was transferred to Eglin Field, Florida for armament trials. Here, it amassed an additional 38 hours of flight tests, but there was little interest since the war was over.

The Grizzly’s main problem was that its engines were needed elsewhere. B-29 production left no spare R-3350s available for any type of A-38 production until mid-1945. By that time, the war was winding down, and there was no foreseeable need for the A-38. One of the XA-38s reportedly went to Davis-Monthan AFB, Arizona, but its ultimate fate is not recorded. The other aircraft was believed to be scrapped. The only remnant of the XA-38 Grizzly is the T15E1 cannon on display at the United States Air Force Armament Museum in Eglin AFB, Florida.

The T15E1 (M10) 75 mm cannon from the XA-38 as displayed in the United States Air Force Armament Museum. (Tom Fey image)

Sources:
– Beech Aircraft and their Predecessors by A.J. Pelleteir (1995)
– U.S. Experimental & Prototype Aircraft Projects by Bill Noton (2008)
– American Attack Aircraft Since 1926 by E.R. Johnson (2008)
– U.S. Aerial Armament in World War II, Vol. 1 by William Wolf (2009)
– American Combat Planes of the 20th Century by Ray Wagner (2004)
– 75MM Cannon M10 display in the United States Air Force Armament Museum in Eglin AFB, Florida

By William Pearce

Late in 1938, the Heinkel He 119 experimental high-speed reconnaissance aircraft was shown to a Japanese Naval delegation visiting Germany. The Japanese liked the speed and range of the He 119, and overall, were impressed by the aircraft. Based on the positive initial interest, the Japanese sent a group of technicians from the Yokosuka Naval Air Technical Arsenal (Yokosuka, also known as Kaigun Koku Gijutsusho or Kugisho) to Germany for a closer examination of the He 119. Eventually, Commander Hideo Tsukada was able to purchase two He 119 prototypes and a license to manufacture the aircraft in Japan.

The standard image of the Yokosuka R2Y1 Keiun. Speculation suggests the first scoop on the side of the aircraft provided cooling air for the engine’s internal exhaust baffling, the second, larger scoop provided induction air for the normally aspirated Aichi [Ha-70] engine installed in the prototype, and the final two ports were for the engine’s exhaust.

The two He 119 prototypes were delivered via ship to Japan in 1941 (some say 1940). The aircraft were reassembled at Kasumigaura Air Field, and flight tests occurred at Yokosuka Naval Base. During an early test flight, one of the He 119s was badly damaged in a landing accident, and it is believed the other He 119 suffered a similar fate. Plans to produce the He 119 never moved forward, but the Japanese were still interested in a high-speed reconnaissance aircraft and felt the general configuration of the He 119 held promise.

Inspired by the Heinkel He 119, Yokosuka began to design an aircraft of a similar layout, known as the Y-40, in 1943. Headed by Commander Shiro Otsuki, the aircraft project was a pressurized, two-seat, unarmed, high-speed, reconnaissance aircraft of all-metal construction that featured tricycle retractable gear. The design was approved, and the Y-40 officially became known as the R2Y1 Keiun (Beautiful Cloud). The construction of two prototypes was ordered.

A good view of the R2Y1 where a radiator inlet can be seen under the wing and in front of the main gear. The ventral scoop was an intake for the turbocharger and intercooler but these were not installed on the prototype.

The R2Y1 had a 45.93 ft (14 m) wingspan and was 42.81 ft (13.05 m) long. The aircraft stood 13.91 ft (4.24 m) high, weighed 13,260 lb (6,015 kg) empty, and had a maximum weight of 20,725 lb (9,400 kg). The Keiun had an estimated top speed of 447 mph (720 km/h) at 32,810 ft (10,000 m) and a cruise speed of 288 mph (463 km/h) at 13,125 ft (4,000 m). Maximum range was an estimated at 2,240 mi (3,610 km). The pilot sat under a raised bubble-style canopy that was toward the extreme front of the aircraft. The radio operator/navigator occupied an area in the fuselage just behind and a little below the pilot.

The Keiun was powered by two 60-degree, inverted V-12 Aichi Atsuta 30 series engines, licensed-built versions of the Daimler-Benz DB 601. The engines were coupled together by a common gear reduction in a similar fashion as the DB 606. The resulting 24-cylinder power unit was known as the Aichi [Ha-70]. With a 5.91 in (150 mm) bore and 6.30 in (160 mm) stroke, the engine displaced 4,141 cu in (67.8 L) and was installed behind the cockpit and above the wings. The Aichi [Ha-70] engine was to be turbocharged and rated at 3,400 hp (2,535 kW) for takeoff and 3,000 hp (2,237 kW) at 26,247 ft (8,000 m). Without the turbocharger, the engine was rated at 3,100 hp (2,312 kW) for takeoff and 3,060 hp (2,282 kW) at 9,843 ft (3,000 m). The engine drove a 12.47 ft (3.8 m), six-blade propeller via a 12.8 ft (3.9 m) long extension shaft that ran under the cockpit. Engine cooling was achieved by radiators under the fuselage and inlets for oil coolers in the wing roots. A ventral air scoop was located behind the engine to provide induction air for the turbocharger and air for the intercooler.

The R2Y1 Keiun undergoing taxi tests in May 1945.

By the fall of 1944, the direction of the war had changed, and Japan no longer needed a high-speed reconnaissance aircraft. The R2Y1 Keiun was all but cancelled when the design team suggested the aircraft could easily be made into a fast attack bomber. In addition, the Aichi [Ha-70] power plant would be discarded, and one 2,910 lb (1,320 kg) thrust Mitsubishi Ne 330 jet engine would be installed under each wing. A fuel tank would be installed in the space made available by the removal of the piston engine. This jet-powered attack bomber had an estimated top speed of 495 mph (797 km/h). The project was approved, and the new aircraft was designated R2Y2.

The decision was made to finish the nearly completed R2Y1 airframe and use it as a flight demonstrator to assess the flying characteristics of the aircraft. With pressurization, the turbocharger, and the intercooler omitted, the R2Y1 prototype was completed in April 1945 and transferred to Kisarazu Air Field for tests. Ground tests revealed that the aircraft suffered from nose-wheel shimmy and engine overheating.

Yokosuka R2Y1 Keiun taking off from Kisarazu Air Field for its first an only flight.

Adjustments were made to overcome the issues, and the Keiun took to the air on 29 May 1945 (date varies by source and is often cited as 8 May 1945), piloted by Lt. Commander Kitajima. The flight proved to be very short because the engine quickly overheated, and a fire broke out in the engine bay. Lt. Commander Kitajima quickly returned to the field, and the R2Y1 suffered surprisingly little damage. On 31 May during a ground run to test revised cooling, the engine was mistakenly run at high power for too long and overheated. The engine was removed from the aircraft to repair the damage. The R2Y1 sat awaiting repair for some time before it was destroyed by Japanese Naval personnel to prevent its capture by American forces (some say it was destroyed in an Allied bombing raid). Because of the end of the War, the second R2Y1 prototype was never completed nor was the design work for the R2Y2.

The unfinished second R2Y1 prototype as seen at the end of WWII. Note the wing root and ventral intakes. The hole in the center of the bulkhead in the nose was for the propeller’s drive shaft.

Sources:
– “Yokosuka R2Y1 Keiun: Japan’s mid-engined twin” Wings of Fame, Volume 12 (1998)
– Japanese Secret Projects by Edwin Dyer (2009)
– Japanese Aircraft of the Pacific War by Rene Francillon (1970/2000)
– Japanese Aero-Engines 1910–1945 by Mike Goodwin and Peter Starkings (2017)
– General View of Japanese Military Aircraft in the Pacific War by Airview (1956)
– Japanese Aircraft Performance & Characteristics TAIC Manual by Edward Maloney (2000)
– http://www.secretprojects.co.uk/forum/index.php/topic,15633.0/all.html