Category Archives: World War II


Mitsubishi [Ha-43] (A20 / Ha-211 / MK9) Aircraft Engine

By William Pearce

In 1916, the Internal Combustion Engine Section, Machinery Works (Nainenki-ka Zokisho) of the Mitsubishi Shipbuilding Company Ltd (Mitsubishi Zosen KK) was formed to build aircraft engines. A number of licenses to build engines in Japan were acquired from various European engine manufacturers. Initially, the engines were of the Vee type. The aircraft engine works was renamed Mitsubishi Aircraft Company Ltd (Mitsubishi Hokuki KK) in 1928. In the late 1920s, licenses were acquired to produce the five-cylinder Armstrong Siddeley Mongoose and the nine-cylinder Pratt & Whitney R-1690 Hornet air-cooled radial engines.


Front and side views of the Mitsubishi [Ha-43] (A/20 / Ha-211 / MK9). The engine performed well but was underdeveloped. Its development and production were slowed by bombing raids and materiel shortages. The engine powered two of Japan’s best next-generation fighters, the A7M2 and Ki-83. While the aircraft were excellent, the war was already lost.

In 1929, Mitsubishi built the first aircraft engine of its own design. Carrying the Mitsubishi designation A1, the engine was a two-row, 14-cylinder, air-cooled radial of 700 hp (522 kW). This engine was followed in 1930 by the A2, a 320 hp (237 kW) nine-cylinder radial. A larger 600 hp (477 kW) nine-cylinder engine, the A3, was also built the same year. None of these early engines were particularly successful, and only a small number were built: one A1, 14 A2s, and one A3. However, Mitsubishi learned many valuable lessons that it applied to its next engine, the A4 Kinsei.

The two-row, 14-cylinder A4 was developed in 1932 and was initially rated at 650 hp (485 kW). The A4 had a 5.51 in (140 mm) bore, a 5.91 in (150 mm) stroke, and a total displacement of 1,973 cu in (32.33 L). In 1934, Mitsubishi consolidated its subsidiaries and became Mitsubishi Heavy Industries Ltd (Mitsubishi Jukogyo KK). Also in 1934, an upgraded version of the A4 engine was developed as the 830 hp (619 kW) A8 Kinsei. The Kinsei was under continual development through World War II, and numerous versions of the engine were produced. Ultimately, the last variants were capable of 1,500 hp (1,119 kW), and production of all Kinsei engines totaled approximately 15,325 units.

In mid-1941, Mitsubishi began work on an 18-cylinder engine that carried the company designation A20. The engine was intended to be lightweight and produce 2,200 hp (1,641 kW). The A20 design was developed from the Kinsei, although the 18-cylinder A20 really only shared its bore and stroke with the 14-cylinder engine—it is not even clear if the pistons were interchangeable. The team at Mitsubishi designing the A20 engine were Kazuo Sasaki—main engine section; Kazuo Inoue, Ding Kakuda, and Mitsukuni Kada—supercharger and auxiliary equipment; Katsukawa Kurokawa—propeller gear reduction; Shigeta Aso—engine cooling; Shuichi Sugihara—fuel injection system, and Shin Nakano—turbosupercharger. The A20 eventually carried the Imperial Japanese Army (IJA) designation Ha-211, the Imperial Japanese Navy (IJN) designation MK9, and the joint designation [Ha-43]. For simplicity, the joint designation will primarily be used. However, few sources agree on the engine’s various sub-type designations, and there is some doubt regarding their accuracy.


The mockup of the Tachikawa Ki-94-I illustrated the aircraft unorthodox configuration. With its two [Ha-43] engines, the fighter had an estimated top speed of 485 mph (781 km/h). However, its complexity led to its cancellation and the pursuit of a more conventional design.

The Mitsubishi [Ha-43] had two rows of nine cylinders mounted to an aluminum crankcase. The crankcase was formed by three sections. Each section was split vertically through the centerline of a cylinder row, with the middle section split between both the front and rear cylinder rows. Each crankshaft section contained a main bearing to support the built-up, three-piece crankshaft. An additional main bearing was contained in the front accessory drive. The cylinders were made up of a steel barrel screwed and shrunk into a cast aluminum head. Each cylinder had one intake valve and one sodium-cooled exhaust valve. The valves were actuated by separate rockers and pushrods. Unlike the Kinsei engine, the [Ha-43] did not have all of its pushrods at the front of the engine. The [Ha-43] had a front cam ring that drove the pushrods for the front cylinders, and a rear cam ring that did the same for the rear cylinders. When viewed from the rear, the cylinder’s intake port was on the right side, and the exhaust port was on the left. Sheet metal baffles attached to the cylinder head helped direct the flow of cooling air through the cylinder’s fins. Cylinder numbering proceeded clockwise around the engine when viewed from the rear. The vertical cylinder atop the second row was No. 1 Rear, and the inverted cylinder under the front row was No. 1 Front.

At the front of the engine was the propeller gear reduction and the magneto drive. Planetary gear reduction turned the propeller shaft clockwise at .472 times crankshaft speed. Each of the two magnetos mounted atop the gear reduction fired one of the two spark plugs mounted in each cylinder. One spark plug was located on the front side of the cylinder and the other was on the rear side. A 14-blade cooling fan was driven by the propeller shaft and mounted in front of the gear reduction. Not all [Ha-43] engines had a cooling fan. At the rear of the engine was an accessory and supercharger section. The single-stage, two-speed, centrifugal supercharger was mechanically driven by the crankshaft. Individual intake runners extended from the supercharger housing to each cylinder. The intake and exhaust from the front cylinders passed between the rear cylinders, with the exhaust running above the intake runners. The supercharger’s inlet was directly behind the second row of cylinder. Behind the inlet was a fuel distribution pump that directed fuel to an injector installed by the inlet port of each cylinder.

The 18-cylinder [Ha-43] had a 5.51 in (140 mm) bore a 5.91 in (150 mm) stroke, and displaced 2,536 cu in (41.56 L). The basic engine with its 7.0 to 1 compression ratio and single-stage, two-speed supercharger produced 2,200 hp (1,641 kW) at 2,900 rpm and 10.1 psi (.69 bar) of boost for takeoff. Military power was 2,050 hp (1,527 kW) at 3,281 ft (1,000 m) in low gear and 1,820 hp (1,357 kW) at 21,654 ft (6,600 m) in high gear. Both power ratings were produced at 2,800 rpm and 8.1 psi (.56 bar) of boost. Anti-detonation (water) injection was available, but it is not clear at what point it was used—most likely for military power and above. The engine was 48 in (1.23 m) in diameter, 82 in (2.09 m) long, and weighed 2,161 lb (980 kg).


The high-altitude Tachikawa Ki-74 was built around a pressure cabin for high-altitude flight. The aircraft most likely has [Ha-43] engines with a 14-blade cooling fan. The [Ha-42] engine had a 10-blade cooling fan. The exhaust from the turbosupercharger can be seen on the right side of the image.

[Ha-43] design work was completed in October 1941. The first engine was built at the Mitsubishi No. 2 Engine Works (Mitsubishi Dai Ni Hatsudoki Seisakusho), which was located in Nagoya and developed experimental engines, and was finished in February 1942. As the [Ha-43] was being tested, Mitsubishi proposed in April 1942 to use the engine for its new A7M fighter. The first [Ha-43] engine for the IJA was completed in August 1942. In September 1942, the IJN selected the 2,000 hp (1,491 kW) Nakajima [Ha-45] engine for the A7M1 and many of its other high-powered fighter projects under development. This setback inevitably slowed development of the [Ha-43]. At the time, there were no applications for the engine, with the IJA feeling it was too powerful and the IJN selecting the Nakajima engine. Two more [Ha-43] engines, one each for the IJA and IJN were completed in November 1942.

Mitsubishi continued development at a slow pace, hampered in part by difficulties with designing turbine wheels for the engine’s remote turbosupercharger. It was not until June 1943 that the [Ha-43] passed operational tests and began to be selected for installation on several aircraft types and not just projects. The first [Ha-43]-powered aircraft to fly was the third prototype of the Tachikawa Ki-70. The Ki-70 was a twin-engine reconnaissance aircraft with a glazed nose and twin tails. Originally powered by two 1,900 hp (1,417 kW) Mitsubishi [Ha-42] engines, the aircraft’s performance was lacking, and the third prototype was built with two turbosupercharged [Ha-43] 12 (IJA Ha-211-IRu) engines. The [Ha-43] 12 produced 2,200 hp (1,641 kW) for takeoff; 1,930 hp (1,439 kW) at 16,404 ft (5,000 m); and 1,750 hp (1,305 kW) at 31,170 ft (9,500 m). First flying in late 1943, the [Ha-43] 12-powered aircraft still underperformed, and the engines were unreliable. Development of the Ki-70 was abandoned.


The Mitsubishi A7M2 Reppu (Strong Gale) with its [Ha-43] 11 engine did not have a cooling fan like the A7M1. As a result, the cowling was redesigned with a larger opening and scoops for the engine intake (top) and oil cooler (lower). Note that the individual exhaust stacks were grouped together, mostly in pairs.

In 1943, Tachikawa designed the tandem-engine, twin-boom Ki-94-I (originally Ki-94) fighter powered by two [Ha-43] 12 (IJA Ha-211-IRu) engines. The cockpit was positioned between the two engines, which were mounted in a push-pull configuration in the short fuselage that sat atop the aircraft’s wing. The front and rear engines both turned four-blade propellers. The front propeller was 10 ft 10 in (3.3 m) in diameter, and the rear was 11 ft 2 in (3.4 m) in diameter. After a mockup was inspected in October 1943, the design was judged to be too unorthodox and complex. This resulted in a complete redesign to a more conventional single engine aircraft, the Ki-84-II, which was powered by a 2,400 hp (1,790 kW) Nakajima [Ha-44] engine.

In early 1944, two [Ha-43] 12 (IJA Ha-211-I) engines were installed in the Tachikawa Ki-74, a pressurized, high-altitude, long-range reconnaissance bomber with a conventional taildragger layout. With only the mechanical two-speed supercharger, the [Ha-43] 12 produced 2,200 hp (1,641 kW) for takeoff; 2,020 hp (1,506 kW) at 3,281 ft (1,000 m) in low gear; and 1,800 hp (1,342 kW) at 16,404 ft (5,000 m) in high gear. The Ki-74 made its first flight in March 1944, and turbosupercharged [Ha-43] 12 (IJA Ha-211-IRu) engines were installed in the second and third prototypes. The turbosupercharger was located behind the engine on the outer side of the nacelle and improved the aircraft’s performance at altitude. However, the [Ha-43] engines were still under development and suffered from reliability and vibration issues. Subsequent Ki-74 aircraft used larger and less-powerful Mitsubishi [Ha-42] engines.


Like the A7M2, the Mitsubishi Ki-83 also did not use a cooling fan on its [Ha-43] engine. However, the Ki-83 did have a turbosupercharger which helped it achieve its very impressive performance of at least 438 mph (705 km/h) at 29,530 ft (9,000 m). Note the sheet-metal baffles on the cylinder heads.

In the summer of 1944, Mitsubishi was given permission to install a [Ha-43] 11 (IJN MK9A, similar to the [Ha-43] 12) engine in an A7M1 airframe, creating the A7M2. The Mitsubishi A7M Reppu (Strong Gale) was a carrier-based fighter intended to replace the A6M Zero. The A7M1 prototypes had underperformed with the 2,000 hp (1,491 kW) Nakajima [Ha-45] engine selected by the IJN. The [Ha-43]’s installation in the A7M2 was conventional, and the aircraft made its first flight on 13 October 1944. Performance met expectations, and the A7M2 was ordered into production. Subsequently, manufacturing of the [Ha-43] started to ramp up, with 13 engines being built in March 1945. The following month, [Ha-43] 11 production was sanctioned at the Mitsubishi No. 4 Engine Works (Mitsubishi Yon Hatsudoki Seisakusho) in Nagoya. On 1 May 1945, Mitsubishi No. 18 Engine Works (Mitsubishi Dai Juhachi Hatsudoki Seisakusho) was established in Fukui city to build [Ha-43] 11 engines for the IJN, while the No. 4 Engine Works would build engines for the IJA. As events played out, only seven or eight A7M2s were built by the end of the war, the No. 18 Engine Works never produced a complete engine, and bombing raids prevented the March 1945 [Ha-43] production numbers from ever being eclipsed.

Further developments of the A7M were planned, such as the A7M3 powered by a [Ha-43] 31 (IJN MK9C) engine with a single-stage, three-speed mechanical supercharger. The [Ha-43] 31 produced 2,250 hp (1,678 kW) for takeoff; 2,000 hp (1,491 kW) at 5,906 ft (1,800 m) in low gear; 1,800 hp (1,342 kW) at 16,404 ft (5,000 m) in medium gear; and 1,660 hp (1,238 kW) at 28,543 ft (8,700 m) in high gear. The three-speed supercharger added about 5.4 in (138 mm) to the engine’s length and 88 lb (40 kg) to the engine’s weight, increasing the respective totals to 87 in (2.22 m) and 2,249 lb (1,020 kg). The A7M3-J would incorporate the [Ha-43] 11 engine with a turbosupercharger installed under the cockpit to produce 2,200 hp (1,641 kW) for takeoff; 2,130 hp (1,588 kW) at 22,310 ft (6,800 m); and 1,920 hp (1,432 kW) at 33,793 ft (10,300 m). While the A7M2 did not have a cooling fan, one was used in the A7M3 and A7M3-J designs.


The turbosupercharger installed in the Ki-83’s left engine nacelle. The large duct on the right was for the exhaust after it passed through the turbosupercharger. The outlet at the end of the nacelle was from the wastegate. Both were positioned to provided additional thrust. The Ki-83 had a ceiling of 41,535 ft (12,660 m).

In the fall of 1944, two [Ha-43] 12 (IJA Ha-211-IRu) engines were installed in the Mitsubishi Ki-83. The Ki-83 was a twin-engine heavy fighter with a conventional taildragger layout. A turbosupercharger was placed in the rear of each 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. Each engine turned an 11 ft 6 in (3.5 m) diameter, four-blade propeller. The Ki-83 made its first flight on 18 November 1944, but with the main focus on single-engine interceptors, only one was built before the Japanese surrender.

In April 1945, a [Ha-43] 42 (IJN MK9D) was installed in the Kyushu J7W1 Shinden (Magnificent Lightning), an unconventional pusher fighter with a canard layout. The [Ha-43] 42 had two-stage supercharging, with the first stage made up by a pair of transversely-mounted centrifugal impellers, one on each side of the engine. The shaft of these impellers was joined to the engine by a continuously variable coupling. The output from each of the first stage impellers joined together as they fed the normal, two-speed supercharger mounted to the rear of the engine and geared to the crankshaft. The [Ha-43] 42 produced 2,030 hp (1,514 kW) at 2,900 rpm with 9.7 psi (.67 bar) of boost for takeoff. Military power at 2,800 rpm and 5.8 psi (.40 bar) of boost was 1,850 hp (1,380 kW) at 6,562 ft (2,000 m) in low gear and 1,660 hp (1,238 kW) at 27,559 ft (8,400 m) in high gear. An extension shaft approximately 29.5 in (750 mm) long extended back from the engine to a remote propeller reduction gear box. The gear reduction turned the 11 ft 2 in (3.40 m), six-blade propeller at .412 times crankshaft speed and also drove a 12-blade cooling fan that was 2 ft 11 in (900 mm) in diameter.


The [Ha-43] 42 (IJN MK9D) installed in the Kyushu J7W1 Shinden, pictured while the aircraft was in storage at the Smithsonian National Air and Space Museum’s Paul E. Garber facility. The front of the aircraft is on the left. One of the two transversely-mounted, first-stage superchargers can be seen left of the engine, and the ducts from both superchargers can be seen joining together as they feed the mechanically-driven supercharger at the rear of the engine. Note that the exhaust stacks are flowing toward the front of the engine (rear of the aircraft).

Since the engine was mounted with the propeller shaft toward the rear of the aircraft, it incorporated new cylinders with the exhaust port on the side opposite of the intake port. The intake port faced toward the supercharger (front of the aircraft), and the exhaust port faced toward the propeller (rear of the aircraft). The engine’s individual exhaust pipes were used to help the flow of air through the cowling and oil coolers. After flowing through the oil cooler on each side of the aircraft, air was mixed with the exhaust from four cylinders and ejected out a slit on the side of the fuselage just before the spinner. The ejector exhaust helped draw air through the oil coolers. The same was true for the exhaust from the lower six cylinders, which was ducted into an augmenter that helped draw cooling air through the engine cowling and out an outlet under the spinner. The exhaust from the remaining four cylinders, which were located on the top of the engine, exited via two outlets arranged atop the cowling to generate thrust.

The J7W1 made its first flight on 3 August 1945. The third J7W1 was planned to have a [Ha-43] 43 engine that used a single impeller for its first-stage, continuously variable supercharger and produced an additional 130 hp (97 kW) for takeoff. Production J7W1 aircraft would be powered by a 2,250 hp (1,678 kW) [Ha-43] 51 engine with a single-stage, three-speed, mechanical supercharger replacing the two-stage setup with the continuously variable first stage. The engine would turn a four-blade propeller, 11 ft 6 in or 11 ft 10 in (3.5 m or 3.6 m) in diameter. However, only the first J7W1 was completed by war’s end.


The [Ha-43] 11 engine with cooling fan in storage as part of the Smithsonian National Air and Space Museum’s collection. Note the rust on the steel cylinder barrels. The spark plug wires are disconnected and desiccant plugs have been installed to help preserve the engine. (Tom Fey image)

In January 1945, construction commenced on the Mansyu Ki-98 (or Manshu Ki-98), a twin-boom pusher fighter with tricycle undercarriage. A single, turbosupercharged [Ha-43] 12 (IJA Ha-211-IRu) engine turning an 11 ft 10 in (3.6 m) four-blade propeller would power the aircraft. With the exception of the turbosupercharger, the installation was similar to that of the J7W1 with an extension shaft and remote propeller gear reduction. The prototype was ready for assembly when it was destroyed in August 1945 to prevent its capture by Soviet forces.

In addition to the aircraft listed above, the [Ha-43] was selected to power a number of aircraft projects that were not built. Plans were initiated to use the [Ha-43] to repower a number of different production aircraft that used the 2,000 hp (1,491 kW) Nakajima [Ha-45]. However, none of these retrofit redesigns were carried out before the end of the war. From 1942 to 1945, the production run of the [Ha-43] amounted to only 77 engines, and it was not fully developed by the end of the war.

At least three [Ha-43] engine survive, and all three are held by the Smithsonian National Air and Space Museum. One engine does not have a cooling fan and is probably a [Ha-43] 11 for a A7M2. The second engine is a [Ha-43] 11 with a cooling fan. The third engine is a [Ha-43] 42 still installed in the J7W1 prototype. All of the engines are in storage and not on display.


The fanless [Ha-43] 11 engine held by the Smithsonian National Air and Space Museum. The fuel distribution pump with its 18 lines can be seen atop the rear of the engine. The small-diameter lines appear to be made of copper.

Japanese Aero-Engines 1910 – 1945 by Mike Goodwin and Peter Starkings (2017)
Japanese Secret Projects by Edwin M. Dyer III (2009)
Japanese Secret Projects 2 by Edwin M. Dyer III (2014)
Japanese Aircraft of the Pacific War by René J. Francillon (1979/2000)
The History of Mitsubishi Aero-Engines 1915–1945 by Matsuoka Hisamitsu and Nakanishi Masayoshi (2005)
– “Mitsubishi Heavy Industries, LTD” The United States Strategic Bombing Survey, Corporation Report No. I (June 1947)
– “Design Details of the Mitsubishi Kinsei Engine” by W. G. Ovens, Aviation (August 1942)


Continental XI-1430 Aircraft Engine

By William Pearce

In 1932, the Army Air Corps (AAC) contracted the Continental Motors Company to develop a high-performance (Hyper) cylinder that would produce 1 hp per cu in (.7 kW per 16 cc). Based on promising test results, an order was placed for a 1,000 hp (746 kW), 12-cylinder O-1430 aircraft engine. The AAC had stipulated that the engine needed to be a horizontally opposed (flat) configuration and use individual cylinders. Lengthy delays were encountered with development of the Hyper No. 2 cylinder, and the situation was made worse by Continental’s financial state. Continental did not fund much of the project, and each change and every purchase was sent to the AAC for contractual approval.


The Continental XI-1430 was a compact, high-performance aircraft engine capable of producing an impressive amount of power but also suffered from reliability issues. The mounting pads on the front accessory case, below the nose case, were for the starter and generator.

The O-1430 was finally completed and run in 1938. While it did meet the 1,000 hp (746 kW) goal, the six years of development rendered the engine obsolete. The Allison V-1710 and the Rolls-Royce Merlin had already passed the 1,000 hp (746 kW) mark years previously. However, the AAC and Continental believed that the engine could be reworked to produce 1,600 hp (1,193 kW). In 1939, the AAC requested that Continental use the O-1430 as the basis for an inverted Vee engine designated XI-1430. Especially early on, the engine was also referred to as the XIV-1430 or IV-1430. The XI-1430 would keep the basic individual cylinders of the O-1430, but the cooling requirement was changed from 300° F (149° C) to 250° F (121° C). The Vee configuration (even if inverted) and 250° F (121° C) coolant were preferred by Continental from the start. To speed development of the engine, Continental agreed to put at least $250,000 of its own money toward the project and was willing to proceed based on verbal agreements with the AAC rather than waiting for changes to be specified in writing.

In 1940, Continental Motors Company created a subsidiary known as Continental Aviation and Engineering Corporation to develop aircraft engines of over 500 hp (373 kW). Most of the XI-1430 development was done under the Continental Aviation and Engineering Corporation. The XI-1430 was essentially a new engine with perhaps just the pistons, connecting rods, and a few other parts being interchangeable with the earlier O-1430.

The XI-1430 had a one-piece aluminum crankcase. The crankshaft was supported by seven main bearings and secured to the crankcase by bearing caps. A cover plate sealed the top of the inverted crankcase. Two banks of six individual cylinders were secured to the crankcase via studs. The cylinder banks had an included angle of 60 degrees. The pistons were attached to the crankshaft via fork-and-blade connecting rods. When viewed from the rear, the blade rods served the left bank, and the fork rods served the right bank.


The gear train of a clockwise-turning (right-handed) XI-1430-9. Unlike with the O-1430 in which a few gears could be swapped for clockwise vs counterclockwise rotation, the XI-1430 had a different gear train that incorporated various idler gears for counterclockwise rotation.

The cylinders used the same bore and stroke as the Hyper No. 2 test cylinder and the O-1430. While their design was similar to the previous applications, the XI-1430’s cylinders had been further refined. Each cylinder was made up of a forged steel barrel screwed and shrunk into a forged aluminum cylinder head. The new cylinder head was more compact than that used previously. A steel water jacket surrounded the cylinder barrel and was secured to the cylinder head. Two spark plugs were installed in each cylinder, with one by the intake port and the other by the exhaust port. The cylinder had a single intake valve and a single sodium-cooled exhaust valve. Both valves were actuated by a single overhead camshaft located in a housing that bolted atop all the cylinders of a given bank. Each camshaft was driven through bevel gears by a nearly-horizontal shaft at the front of the engine. Various accessories were driven from the rear of the camshaft.

An updraft Stromberg injection carburetor was positioned at the extreme rear of the XI-1430 engine. It fed air and fuel into the single-speed, single-stage supercharger, which was mounted to the rear of the engine. The supercharger impeller was 10.5 in (267 mm) in diameter and turned at 5.928 times crankshaft speed. The supercharger drive case also powered various pumps: oil, water, vacuum, and hydraulic. An intake manifold led from the bottom of the supercharger and extended through the inverted Vee of the engine. Short individual runners branched off the manifold and supplied the air and fuel mixture to each cylinder.

An accessory drive case was mounted to the front of the engine. Driven from the accessory case were the starter, generator, an oil pump, and a single dual-magneto. The magneto was mounted on the upper front of the accessory drive case and fired the two spark plugs in each cylinder. The accessory drive case also housed the spur gears that made up part of the XI-1430’s propeller gear reduction. Mounted to the front of the accessory drive was a nose case that contained a bevel planetary gear reduction that drove the propeller shaft. The speed of the crankshaft was partly reduced via the spur gears in the accessory drive case, then further reduced via the planetary gears in the nose case. This two-stage gear reduction was probably adopted to keep the XI-1430’s frontal area to a minimum and possibly to extended the nose of the engine for a more streamlined installation. Depending on the engine model, the final speed of the propeller shaft was .360, .385, or .439 crankshaft speed.


Front and rear views of the XI-1430 illustrate the engine’s rather compact configuration. On the front of the engine, the housings for the camshaft drives can just be seen between the accessory drive and the circular covers on the cylinder banks. Note the size of the supercharger housing on the rear view.

The Continental XI-1430 had a 5.5 in (140 mm) bore and a 5.0 in (127 mm) stroke. The engine displaced 1,425 cu in (23.4 L) and had a compression ratio of 6.5 to 1. XI-1430 installations included a General Electric (GE) turbosupercharger and air-to-air intercooler. The engine initially had a takeoff rating of 1,350 hp (1,007 kW) at 3,300 rpm and a military rating of 1,600 hp (1,193 kW) at 3,200 rpm up to 25,000 ft (7,620 m). Development ultimately increased takeoff power to 1,600 hp (1,193 kW) at 3,300 rpm and 15.3 psi (1.05 bar) of boost. The XI-1430 maintained this power as its normal rating up to 25,000 ft (7,620 m), but at 3,000 rpm. Emergency power was 2,100 hp (1,566 kW) at 3,400 rpm with 28.5 psi (1.97 bar) of boost at 25,000 ft (7,620 m). The XI-1430 was 112.5 in (2.86 m) long, 30.9 in (.78 m) wide, and 33.5 in (.85 m) tall. The engine weighed 1,615 lb (733 kg).

On 20 February 1940, the AAC issued Request for Data R40-C that sought designs of new fighter aircraft capable of 450 mph (724 km/h), with 525 mph (845 km/h) listed as desirable. With a new generation of high-power aircraft engines under development, manufacturers saw it as an opportunity be creative. Five of the 26 submitted designs (some of which only offered slight variations) used the XI-1430 as the selected engine. Bell offered two XI-1430-powered variants of what was similar to a P-39 Airacobra, and two Curtiss-Wright XI-1430-powered submissions were similar to reengined examples of their CW-21 and XP-46. The later design was contracted mid-1940 as the XP-53. However, due to delays with the XI-1430 engine, the AAC requested the substitution of a Packard V-1650 (Merlin) in October 1940, and the XP-53 was subsequently redesignated as the XP-60.

A third XI-1430-powered R40-C proposal from Curtiss-Wright was a pusher aircraft designated P-249C. A design contract for the P-249C was issued on 22 June 1940, but the decision was made not to proceed with a prototype. Curtiss-Wright continued to refine the design and substituted an Allison V-1710 engine (this aircraft design was also an R40-C submission). The V-1710-powered aircraft was eventually built as the XP-55 Ascender. None of XI-1430-powered R40-C aircraft were built.


The induction pipe can be seen extended from the bottom of the supercharger housing and to the inverted Vee between the cylinder banks. Note how the camshaft housing was attached to each individual cylinder.

In March 1940, the engines for the Lockheed XP-49 design were switched to the XI-1430 with a GE B-33 turbosupercharger. The XP-49 was not part of R40-C and was essentially an advancement of the P-38 Lightning. The Pratt & Whitney X-1800 / XH-2600 originally selected for the XP-49 was cancelled, necessitating a power plant switch. Lockheed began to modify the XP-49 for the XI-1430 engines.

In mid-1940, the AAC expressed interest in the XI-1430-powered Bell XP-52. The XP-52 was a twin-boom pusher fighter that never progressed beyond the initial design phase. The project ended in October 1940, before a contract was formalized.

For R40-C, McDonnell Aircraft Corporation proposed four variants of its Model 1 with different engines. None of the variants used the IX-1430. The Model 1 had its engine buried in the fuselage and drove wing-mounted pusher propellers via extensions shafts and right-angle gear boxes. Although radical, the AAC purchased engineering data and a wind tunnel model of the design. McDonnell worked with the AAC to refine the design, which eventually became the Model 2a. The Model 2a was powered by two XI-1430 engines, each with a GE D-23 turbosupercharger. On 30 September 1941, the Army Air Force (AAF—the AAC was renamed in June 1941) contracted McDonnell to build two prototypes of the aircraft as the XP-67.

Meanwhile, the XI-1430 was first run in late 1940 and underwent its first tests in January 1941. Plans were initiated to install the XI-1430 in a few P-39D aircraft, but the concept was ultimately dropped due to a lack of available engines. In July 1941, the AAF and the Defense Plant Corporation funded a new aircraft engine plant for Continental on Getty Street in Muskegon, Michigan that cost $5 million. It appeared as if the AAF truly believed that the XI-1430 would be a successful engine.


The Lockheed XP-49 was obviously a development of the P-38, with the airframes sharing many common parts. However, the XP-49 as built offered no advantage over the P-38, and the aircraft was used mostly as an XI-1430 test bed.

On 22 April 1942, XI-1430 engines that were not fully developed were delivered to Lockheed in Burbank, California for installation in the XP-49. In May, the engine passed a preliminary test at 1,600 hp (1,193 kW). The XP-49 made its first flight on 11 November 1942, piloted by Joe Towle. That same month, the AAF ordered 100 I-1430 engines but required a type test to be passed before delivery. At the end of November, the XP-49 had more powerful engines installed capable of 1,350 hp (1,006 kW) for takeoff and 1,600 hp (1,193 kW) at 25,000 ft (7,620 m). The engines in the XP-49 proved to be troublesome and required constant maintenance, and the aircraft itself had numerous issues. The I-1430 was also having trouble passing the type test. Around August 1943, the AAF cut its order to 50 engines and later reduced the quantity again to 25. By September 1943, the XP-49 became essentially a testbed for the XI-1430, as the aircraft offered no advantage over the P-38. It was clear that the XP-49 would not go into production.

McDonnell had built a full-scale XP-67 engine nacelle for testing the XI-1430 engine installation. Tests were conducted by McDonnell starting in May 1943. After accumulating almost 27 hours of operation, the rig was sent to the National Advisory Committee for Aeronautics (NACA) at the Langley Memorial Aeronautical Laboratory (now Langley Research Center) in Virginia. The NACA added about 17.5 hours to the engine conducting tests to analyze the installation’s effectiveness for cooling the coolant, oil, and intercooler. The tests indicated that the cooling was insufficient. The nacelle with revised ducts was then shipped to Wright Field in Dayton, Ohio in October 1943. Wright field added another 6.5 hours to the engine, bringing the total to 51 hours. The new ducts proved satisfactory, and McDonnell was allowed to proceeded with XP-67 testing. However, excessive vibrations were noted between the engine and its mounting structure, and a more rigid mount was required to resolve the issue.

On 1 December 1943, the XP-67 had its XI-1430 engines installed and was ready for ground tests. However, both engines caught fire and damaged the aircraft on 8 December. The fire was caused by issues with the exhaust manifolds. By the end of 1943, the AAF had reduced the I-1430 order to just eight engines, signaling that the engine would not enter quantity production. The XP-67 was repaired and made its first flight on 6 January 1944, taking off from Scott Field in Belleville, Illinois. Test pilot Ed E. Elliott had to cut the flight to just six minutes due to both turbosuperchargers overheating, which resulted in small fires. The aircraft was again repaired, but engine and turbosupercharger issues continued to plague the program. The engines were only delivering 1,060 hp (790 kW), well below the expected output of 1,350 hp (1,007 kW).


Underside of an XI-1430-17 installed in the McDonnell XP-67 wing section for tests at the Langley Memorial Aeronautical Laboratory in September 1943. The tests were conducted to evaluate the cooling ducts of the XP-67’s radical blended design. Illustrated is the engine’s intake manifold and two coolant radiators. Note the generator and starter installed on the front accessory drive. The air-cooled jackets surrounding the engine’s exhaust manifolds are also visible. (LMAL image)

In March 1944, the I-1430 type test was partially completed, and the eight engines ordered by the AAF were delivered. At the time, the engine achieved an emergency power rating of 2,000 hp (1,491 kW) with water injection. Continental continued its efforts, and in August 1944, the I-1430 earned a rating of 2,100 hp (1,566 kW) with 150 PN fuel and no water injection.

On 6 September 1944, the exhaust valve rocker of the No. 1 cylinder in the XP-67’s right engine broke while the aircraft was in flight. Exhaust gases unable to escape the cylinder backed up into the induction manifold and caused it to fail, resulting in a fire. Test pilot Elliott was able to land the aircraft, but it was subsequently damaged beyond repair by the fire. This event effectively killed the XP-67, and the project was suspended seven days later on 13 September. All XI-1430 development was halted around this time.

The XP-49 had continued to fly when it could, but engine and airframe issues caused the aircraft to be grounded in December 1944. No longer of any useful service, the XP-49 was subsequently scrapped.


The XP-67 had an impressive appearance with its nacelles and fuselage blended into the wings. However, the XI-1430 engines did not deliver their expected power, and the XP-67’s top speed was 405 mph (652 km/h), well below the expected 448 mph (721 km/h). The XP-67 originally had a guaranteed speed of 472 mph (760 km/h) at 25,000 ft (7,620 m) with a gross weight of 18,600 lb (8,437 kg). Once its weight had increased to 22,500 lb (10,206 kg), the expected speed was reduced to 448 mph (721 km/h).

Continental had investigated designs for XI-1430 engines with a two-speed supercharger, a two-stage and two-speed supercharger, contra-rotating propellers, a spur-gear-only propeller reduction, and turbocompounding with a turbine feeding power back to the crankshaft. Continental was to supply XI-1430 engines with a contra-rotating propeller shaft for the second XP-67. The engines were expected in June 1944, but no further information has been found.

Continental did work with General Electric on a turbocompound XI-1430 in 1943, and it appears detailed design work was undertaken. The XP-67 was used for performance calculations with a turbocompounded XI-1430 engine. The turbocompound engines decreased the time of a climb to 25,000 ft (7,620 m) by approximately 38 percent and increased range by 25 percent. The turbocompound XI-1430’s output was an additional 580 hp (395 kW). The engine with its power recovery turbine weighed an additional 235 lb (107 kg), but the total installation weight was only 30 lb (14 kg) additional because a turbosupercharger and its ducting was not needed. In February 1944, Materiel Command’s Engineering Division encouraged the completion of a turbocompound XI-1430 engine to test against the calculated performance estimates, but it does not appear that a complete engine was ever built.

Although the XI-1430 was lighter and more powerful than comparatively sized engines in production, it required additional development to become reliable. It was obvious that the engine would not see combat in World War II, and there was little point in continuing the program. A total of 23 XI-1430 engines were built, and at least four engines are known to survive. A -11 and a -15, are held by the Smithsonian Air and Space Museum, a -9 is on display at the National Museum of the U.S. Air Force, and a running -11 is part of a private collection.


The two XI-1430 engines held by the Smithsonian Air and Space Museum, with the -11 at top and the -15 at bottom. Both examples rotate counterclockwise (left-handed). The engines are currently in storage and not on display. (NASM images)

Development of Aircraft Engines and Aviation Fuels by Robert Schlaifer and S. D. Heron (1950)
Continental! Its Motors and its People by William Wagner (1983)
Aircraft Engines of the World 1946 by Paul H. Wilkinson (1946)
Service Instructions for Aircraft Engines Army Models I-1430-9 and -11 By (20 May 1943)
Performance of the McDonnell XP-67 Airplane with XI-1430 Compound Engines and with Present XI-1430 Engines Using Continental Turbo Chargers by J. H. Gilmore, E. P. Kiefer, and H. D. Delameter (25 February 1944)
U.S. Experimental & Prototype Aircraft Projects: Fighters 1939-1945 by Bill Norton (2008)
American Secret Pusher Fighters of World War II by Gerald H. Balzer (2008)
Final Report on the XP-67 Airplane by John F. Aldridge, Jr. (31 January 1946)
Tornado: Wright Aero’s Last Liquid-Cooled Piston Engine by Kimble D. McCutcheon (2001)
– “Fabricated Crankcase Structure” U.S. patent 2,340,885 by James W. Kinnucan (filed 7 December 1940)
– “Cylinder Head” U.S. patent 2,395,712 by Carl F. Bachle (filed 12 January 1942)
– Accessory Mechanism and Drive for Aircraft Engines” U.S. patent 2,410,167 by James W. Kinnucan (filed 20 March 1942)

Yokosuka YE2H front

Yokosuka YE2H (W-18) and YE3B (X-24) Aircraft Engines

By William Pearce

After World War I, the Japanese Navy established the Aircraft Department of the Hiro Branch Arsenal, which was part of the Kure Naval Arsenal. These arsenals were located near Hiroshima, in the southern part of Japan. The Aircraft Department was the Japanese Navy’s first aircraft maintenance and construction facility. In April 1923, the Hiro Branch Arsenal became independent from the Kure Naval Arsenal and was renamed the Hiro Naval Arsenal (Hiro).

Kawanishi E7K1 floatplane

The Kawanishi E7K1 floatplane served into the 1940s and was powered by the Hiro Type 91 W-12 engine. The Type 91 was based on the Lorraine 12Fa Courlis.

In 1924, the Japanese Navy purchased licenses from Lorraine-Dietrich in France to manufacture the company’s 450 hp (336 kW) 12E aircraft engine. The Lorraine 12E was a liquid-cooled, W-12 aircraft engine, and Hiro was one of the factories chosen to produce the engine. Hiro manufactured three different versions of the Lorraine engine, appropriately called the Hiro-Lorraine 1, 2, and 3. In the late 1920s, Hiro started designing its own engines derived from the Lorraine architecture. Hiro also produced engines based on the updated Lorraine 12Fa Courlis W-12. It is not clear if Hiro obtained a license to produce the 12Fa or if the production was unlicensed. The most successful of the Hiro W-12 engines was the 500–600 hp (373–447 kW) Type 91, which was in service until the early 1940s. Modeled after the 12Fa Courlis, the Type 91 had a bank angle of 60-degrees and four valves per cylinder. The engine had a 5.71 in (145 mm) bore, a 6.30 in (160 mm) stroke, and displaced 1,935 cu in (31.7 L).

Like Lorraine, Hiro also produced W-18 engines. Hiro’s first W-18 engine was built in the early 1930s and used individual cylinders derived from the type used on the 12Fa Courlis / Type 91. While Hiro’s W-18 engine may have been inspired by the Lorraine 18K, the engine was not a copy of any Lorraine engine. Reportedly, Hiro’s first W-18 had a 60-degree bank angle between its cylinders. The engine did not enter production and was superseded in 1934 by the Type 94. The Type 94 replaced the earlier engine’s individual cylinders with monobloc cylinder banks and used a 40-degree angle between the banks. The W-18 engine had a 5.71 in (145 mm) bore and a 6.30 in (160 mm) stroke. The Type 94 displaced 2,902 cu in (47.6 L) and produced 900 hp (671 kW) at 2,000 rpm. The engine was 86 in (2.18 m) long, 44 in (1.11 m) wide, 43 in (1.10 m) tall, and weighed 1,631 lb (740 kg). Only a small number of Type 94 engines were produced, and its main application was the Hiro G2H long-range bomber, of which eight were built. The engine was found to be temperamental and unreliable in service.

Hiro G2H1 bomber

The Hiro G2H1 bomber was the only application for the company’s Type 94 W-18 engine. The engine was problematic, and only eight G2H1s were built. Note the exhaust manifold for the center cylinder bank.

By the mid-1930s, the Navy’s aircraft engine development had been transferred from Hiro to the Yokosuka Naval Air Arsenal (Yokosuka). For a few years, the Navy and Yokosuka let aircraft engine manufacturers develop and produce engines rather than undertaking development on its own. However, around 1940, Yokosuka began development of a new W-18 aircraft engine, the YE2.

The Yokosuka YE2 was based on the Hiro Type 94 but incorporated many changes. The liquid-cooled YE2 had an aluminum, barrel-type crankcase, and its three aluminum, monobloc cylinder banks were attached by studs. The cylinder banks had an included angle of 40 degrees and used crossflow cylinder heads with the intake and exhaust ports on opposite sides of the head. All of the cylinder banks had the intake and exhaust ports on common sides and were interchangeable.

Each cylinder had two intake and two exhaust valves, all actuated by a single overhead camshaft. The camshaft for each cylinder bank was driven via a vertical shaft from an accessory section attached to the drive-end of the engine. The YE2 had a 5.71 in (145 mm) bore, 6.30 in (160 mm) stroke, and displaced 2,902 cu in (47.6 L). The YE2A, B, and C variants had a rated output of 1,600 hp. However, very little is known about these engines, and it is not clear if they were all built.

Yokosuka YE2H front

The Yokosuka YE2-series was developed from the Hiro Type 94. The YE2H was built in the early 1940s, but no applications for the engine have been found. Note the output shaft on the front of the engine that is bare of its extension shaft. The vertical fuel injection pump is just above the horizontally-mounted magnetos. (Smithsonian Air and Space Museum image)

The Yokosuka YE2H variant was developed around 1942 and given the Army-Navy designation [Ha-73]01. It is not clear how the YE2H differed from the earlier YE2 engine. The YE2H was intended for installation in an aircraft’s fuselage (or wing) in a pusher configuration. The rear-facing intake brought in air to the engine’s supercharger. Air from the supercharger was supplied to the cylinders at 12.6 psi (.87 bar) via three intake manifolds—one for each cylinder bank. A common pipe at the drive-end of the engine connected the three intake manifolds to equalize pressure. Fuel was then injected into the cylinders via the fuel injection pump driven at the drive-end of the engine. The two spark plugs per cylinder were fired by magnetos, located under the fuel injection pump. An extension shaft linked the engine to a remote gear reduction unit that turned the propeller at .60 times crankshaft speed.

The YE2H had a maximum output of 2,500 hp (1,864 kW) at 3,000 rpm. The engine had power ratings of 2,000 hp (1,491 kW) at 2,800 rpm at 4,921 ft (1,500 m) and 1,650 hp (1,230 kW) at 2,800 rpm at 26,247 ft (8,000 m). The YE2H was approximately 83 in (2.10 m) long, 37 in (.95 m) wide, and 39 in (1.00 m) tall. The engine weighed around 2,634 lb (1,195 kg). The YE2H was completed and run around March 1944, but development of the engine had tapered off in mid-1943. At that time, Yokosuka refocused on the YE3 engine, which was derived from the YE2H.

Yokosuka YE2H side

The YE2H’s rear-facing intake scoop (far left) indicates the engine was to be installed in a pusher configuration. Note the intake manifolds extending from the supercharger housing. (Smithsonian Air and Space Museum image)

Development of the Yokosuka YE3 started in the early 1940s. The engine possessed the same bore and stroke as the YE2, but the rest of the engine was redesigned. The YE3 was an X-24 engine with four banks of six cylinders. The left and right engine Vees had a 60-degree included angle between the cylinder banks, which gave the upper and lower Vees a 120-degree angle. The YE3’s single crankshaft was at the center of its large aluminum crankcase.

Each cylinder bank had dual overhead camshafts actuating the four valves in each cylinder. The camshafts were driven off the supercharger drive at the non-drive end of the engine. The supercharger delivered air to the cylinders via two loop manifolds—one located in each of the left and right engine Vees. Two fuel injection pumps provided fuel to the cylinders where it was fired by two spark plugs in each cylinder. The fuel injection pumps and magnetos were driven from the drive end of the engine. Exhaust was expelled from the upper and lower engine Vees. Like the YE2, the YE3 was designed for installation in an aircraft’s fuselage or wing, with an extension shaft connecting the engine to the remote propeller gear reduction.

Yokosuka YE3B front

The drive end of the Yoskosuka YE3B gives a good view of the engine’s X configuration. The fuel injection pumps are below the output shaft. (Larry Rinek image via the Aircraft Engine Historical Society)

The YE3A preceded the YE3B, but it is not clear if the YE3A was actually built. The Yokosuka YE3B was given the joint Army-Navy designation [Ha-74]01. The YE3B had a 5.71 in (145 mm) bore and a 6.30 in (160 mm) stroke. The engine displaced 3,870 cu in (63.4 L) and produced 2,500 hp (1,864 kW). The YE3B was rated at 2,150 hp (1,603 kW) at 6,562 ft (2,000 m) and 1,950 hp (1,454 kW) at 16,404 ft (5,000 m). The engine was approximately 79 in (2.00 m) long, 43 in (1.10 m) wide, and 28 in (.70 m) tall.

The YE3B was run by October 1943. The engine used a two-speed remote gear reduction that drove contra-rotating propellers. No real applications for the YE3B are known. However, the engine is often listed as the powerplant for the S-31 Kurowashi (Black Eagle), which was a purely speculative propaganda aircraft. The S-31 was designed as a heavy bomber, and its four YE3B engines were buried in its fuselage.


Side view of the YE3B illustrates the engine’s loop intake manifold. Spark plug leads and fuel injector lines can be seen in the Vee between the cylinder banks. Note the camshaft-driven water pump mounted on the end of the lower cylinder bank. (Tom Fey image)

A further development of the YE3-series was the YE3E. The YE3E was given the joint Army-Navy designation [Ha-74]11. The engine was similar to the earlier YE3-series except that it had two crankshafts. Some sources indicate the engine essentially consisted of two V-12s laid on their sides in a common crankcase with their crankshafts coupled to a common output shaft. The YE3E produced 3,200 hp (2,386 kW) and had power ratings of 2,650 hp (1,976 kW) at 4,921 ft (1,500 m) and 2,200 hp (1,641 kW) at 26,247 ft (8,000 m). The YE3E was approximately 79 in (2.00 m) long, 51 in (1.30 m) wide, and 39 in (1.00 m) tall. The engine was scheduled for completion in spring 1944, but no records have been found indicating it was finished.

A YE2H [Ha-73]01 W-18 engine and a YE3B [Ha-74]01 X-24 engine were captured by US forces after World War II. The engines were sent to Wright Field in Dayton Ohio for further examination. The United States Air Force eventually gave the YE2H and YE3B engines to the Smithsonian National Air and Space Museum, where they are currently in storage.


Detail view of the supercharger mounted to the end of the YE3B. Note the updraft inlet for the supercharger. Camshaft drives can be seen extending from the supercharger housing to the cylinder banks. (Tom Fey image)

Japanese Aero-Engines 1910–1945 by Mike Goodwin and Peter Starkings (2017)
Japanese Secret Projects 1 by Edwin M. Dyer III (2009)

Mathis Vega 42 front

Mathis Vega 42-Cylinder Aircraft Engine

By William Pearce

Émile E. C. Mathis was a French automobile dealer who began manufacturing cars under his own name in 1910. Mathis was based in Strasbourg, which was part of Germany at the time. The Mathis automobile began to achieve success just before World War I. After the start of the war, Émile was conscripted into the German Army. Because of his knowledge of automobiles, the Germans sent Émile on a mission to Switzerland to purchase trucks and other supplies. Émile was given a substantial amount of money for the transaction, and he took the opportunity to desert the Germany Army and keep the funds. When Germany was defeated, Émile returned to his automobile company in Strasbourg, which was then in French territory near the German border, and resumed production.

Mathis Vega 42 front

The high-performance, 42-cylinder Mathis Vega aircraft engine. Note the camshaft-driven distributors attached to the front of each cylinder bank.

In 1937, the Mathis company began designing aircraft engines. A new company division, the Société Mathis Aviation (Mathis Aviation Company), was founded with offices in Paris and factories in Strasbourg and Gennevilliers. These were mostly the same facilities as the automobile business, with auto development out of Strasbourg and aircraft engine development centered in Gennevilliers, near Paris. Raymond Georges was the technical director in charge of the aircraft engines. The Mathis company started their involvement in aircraft engines with the rather ambitious Vega.

The origins of the Mathis Vega can be traced back to 1935, when the Ministère de l’Air (French Air Ministry) sought a high-power aircraft engine with cylinder bores of 4.92 in (125 mm) or less. The Vega was a 42-cylinder inline radial aircraft engine. The liquid-cooled engine had seven cylinder banks, each with six cylinders. The cylinder banks had an integral cylinder head and were made from aluminum. Steel cylinder barrels were screwed into the cylinder bank. Each cylinder had one intake valve and one sodium-cooled exhaust valve. A single overhead camshaft actuated the valves for each cylinder bank. The camshafts were driven from the front of the engine. Camshaft-driven distributors mounted to the front of each cylinder bank fired the two spark plugs in each cylinder. The spark plugs were positioned on opposite sides of the cylinder. The two-piece crankcase was made from aluminum.

At the front of the engine was a planetary gear reduction that turned the propeller shaft at .42 times crankshaft speed. At the rear of the engine was a single-speed and single-stage supercharger that turned at 5.53 times crankshaft speed. A single, two-barrel, downdraft carburetor fed fuel into the supercharger. Seven intake manifolds extended from the supercharger housing to feed the air/fuel mixture to the left side of each cylinder bank. Individual exhaust stacks were mounted to the right side of each cylinder bank. Attached to the back of the supercharger housing was a coolant water pump with seven outlets, one for each cylinder bank.

Mathis Vega 42 side

The Vega was a relatively compact engine. Note the exhaust port spacing on the cylinder banks. Presumably, different exhaust manifolds would be designed based on how the engine was installed in an aircraft.

The Vega had a 4.92 in (125 mm) bore and a 4.53 in (115 mm) stroke. The 42-cylinder engine displaced 3,617 cu in (59.3 L) and had a compression ratio of 6.5. The Vega was 42.1 in (1.07 m) in diameter and 59.8 in (1.52 m) long. The French Air Ministry was very enthusiastic about the Vega and paid for its development and the construction of two prototypes. The first Vega was known as the 42A, and the engine was first run in 1938. The 42A produced 2,300 hp (1,715 kW) at 3,000 rpm and 3,000 hp (2,237 kW) at 3,500 rpm. The engine weighed 2,756 lb (1,250 kg). Reportedly, two examples were built as well as a full-scale model. It is not clear how much testing was undertaken, but some sources indicate the engine was flown 100 hours in a test bed during 1939. Unfortunately, details of the engine’s testing and the aircraft in which it was fitted have not been found.

An improved version, the 42B, was under development when the Germans invaded in May 1940. The Vega engine program was evacuated from Gennevilliers and hidden in the Pyrenees mountains in southern France for the duration of the war. Believing that the Germans would not have forgotten his desertion and miss-appropriation of funds during World War I, Émile fled to the United States in 1940.

In 1941, Émile founded the Matam Corporation in New York, and Matam manufactured ammunition for the US Navy. In October 1942 Émile offered the Vega engine to the US Army Air Force (AAF) and indicated that he was in possession of the engine’s blueprints and that the prototype engine had been hidden in Lyon, France. Émile also stated that an unsupercharged version could equip speed boats for the US Navy. However, the AAF felt that attempting to obtain the engine or any of its components from France was impossible and that, with mass production of other engine types well underway, resources could be better allocated than undertaking the time-consuming process of converting the Vega to English measurements and planning production.

Mathis Vega 42 rear

Rear view of the Vega displays the intake manifolds, single carburetor, and the seven-outlet water pump. On paper, the Vega was a light and powerful engine, but no details have been found regarding its reliability.

After World War II, Émile returned to France, and work resumed on the Vega engine. The 42B was updated as the 42E (42E00). In all likelihood, the 42B and the 42E were the same engine; an example was exhibited in Paris, France in 1945. The Vega 42E produced 2,800 hp (2,088 kW) at 3,200 rpm with 8.5 psi (.59 bar) of boost for takeoff. The engine was rated for 2,300 hp (1,715 kW) at 3,000 rpm at 6,562 ft (2,000 m) and 1,700 hp (1,268 kW) at 2,500 rpm at 13,123 ft (4,000 m). The engine weighed 2,601 lb (1,180 kg).

The design of an enlarged Vega engine was initiated in 1942. Originally designated 42D, the larger engine was later renamed Vesta. The 42-cylinder Vesta was equipped with a two-speed supercharger that rotated 3.6 times crankshaft speed in low gear and 5.7 times crankshaft speed in high gear. The engine had a .44 gear reduction and utilized direct fuel injection. The Vesta had a 6.22 in (158 mm) bore, a 5.71 in (145 mm) stroke, and a displacement of 7,287 cu in (119.4 L). The engine had a takeoff rating of 5,000 hp (3,728 kW) at 2,800 rpm with 8.5 psi (.59 bar) of boost and a normal rating of over 4,000 hp (2,983 kW). The Vesta was 52.0 in (1.32 m) in diameter and weighed 4,519 lb (2,050 kg).

Like many other large engines built toward the end of World War II, the Vega failed to find an application, and the Vesta was never built. Mathis continued work on aircraft engines and produced a number of different air-cooled engines for general aviation. The design of these smaller engines was initiated during the war, and every attempt was made to maximize the number of interchangeable parts between the smaller engines. Some of the material for the smaller engines was liberated “scrap” provided by the Germans and intended for German projects. However, the general aviation engines were not made in great numbers, and production ceased in the early 1950s. No parts of the Vega engines are known to have survived.

Mathis Vega 42 R Georges

Raymond Georges overlooks the Vega engine mounted on a test stand in 1939. The pipes above the Vega are taking hot water from the engine.

Les Moteurs a Pistons Aeronautiques Francais Tome 2 by Alfred Bodemer and Robert Laugier (1987)
Aircraft Engines of the World 1946 by Paul H. Wilkinson (1946)
L’aviation Francaise de Bombardement et de Renseignement (1918/1940) by Raymond Danel and Jean Cuny (1980)
– “The Mathis 42E 00” Flight (6 September 1945)

Studebaker’s XH-9350 and Their Involvement with Other Aircraft Engines

By William Pearce

Before the United States entered World War II, the Army Air Corps conceptualized a large aircraft engine for which fuel efficiency was the paramount concern. It was believed that such an engine could power bombers from North America to attack targets in Europe, a tactic that would be needed if the United Kingdom were to fall. This engine project was known as MX-232, and Studebaker was tasked with its development. After years of testing and development, the MX-232 program produced the Studebaker XH-9350 engine design.

Although a complete XH-9350 engine was not built, Studebaker’s XH-9350 and Their Involvement with Other Aircraft Engines details the development of the MX-232 program and the XH-9350 design. In addition, the book covers Studebaker’s work with other aircraft engines: the power plant for the Waterman Arrowbile, their licensed production of the Wright R-1820 radial engine during World War II, and their licensed production of the General Electric J47 jet engine during the Korean War.


1. Studebaker History
2. Waldo Waterman and the Arrowbile
3. Studebaker-Built Wright R-1820 Cyclone
4. XH-9350 in Context
5. XH-9350 in Development
6. XH-9350 in Perspective
7. Studebaker-Built GE J47 Turbojet
Appendix: MX-232 / XH-9350 Documents

$19.99 USD
8.5 in x 11 in
214 pages (222 total page count)
Over 185 images, drawings, and tables, and over 75,000 words
ISBN 978-0-9850353-1-0

Studebaker’s XH-9350 and Their Involvement with Other Aircraft Engines is available at If you wish to purchase the book with a check, please contact us for arrangements.

Sample Pages:

Hitachi Nakajima Ha-51 side

Hitachi/Nakajima [Ha-51] 22-Cylinder Aircraft Engine

By William Pearce

In December 1942, the Imperial Japanese Army (IJA) sought a new radial aircraft engine capable of more than 2,500 hp (1,864 kW). At the time, the most powerful Japanese production engines produced around 1,900 hp (1,417 kW). The new engine was given the IJA designation Ha-51 and was later assigned the joint Japanese Army and Navy designation [Ha-51]. However, the Imperial Japanese Navy did not show any interest in the engine.

Hitachi Nakajima Ha-51 side

The 22-cylinder Hitachi/Nakajima [Ha-51] engine had a general similarity to the Nakajima [Ha-45]. Note the cooling fan on the front of the engine and the dense nature of the cylinder positioning.

Some sources state that Nakajima was tasked to develop the new [Ha-51] engine, while other sources contend that Hitachi was in charge of the engine from the start. Both Nakajima and Hitachi had produced previous engines with the same bore and stroke as the [Ha-51]. However, the [Ha-51] shares some characteristics, such as fan-assisted air cooling, with other Nakajima engines. Regardless, development of the [Ha-51] was eventually centered at the Hitachi Aircraft Company (Hitachi Kikuki KK) plant in Tachikawa, near Tokyo, Japan. The Hitachi Aircraft Company was formed in 1939 when the Tokyo Gas & Electric Industry Company (Tokyo Gasu Denki Kogyo KK, or Gasuden for short) merged with the Hitachi Manufacturing Company.

The [Ha-51] was a 22-cylinder, two-row radial engine. Its configuration of 11-cylinders in each of two rows was only common with two other engines: the Mitsubishi A21 / Ha-50 and the Wright R-4090. Although the three engines were developed around the same time, it is not believed that any one influenced the others. Moving from nine cylinders in each row to 11 was a logical step for producing more power without increasing a radial engine’s length. The tradeoff was accepting the increased frontal area of the engine and additional strain on the crankpins.

The engine’s three-piece crankcase was made of steel and split vertically along the cylinder center line. The crankcase bolted together via internal fasteners located between the cylinder mounting pads. The cylinders consisted of an aluminum head screwed and shrunk onto a steel barrel. Each cylinder had one intake valve and one exhaust valve. The valves were inclined at a relatively narrow angle of around 62 degrees. The intake and exhaust ports for each cylinder faced the rear of the engine. The cylinders had a compression ratio of 6.8. The second row of cylinders was staggered behind the first row. Only a very narrow gap existed between the front cylinders to enable cooling air to the rear cylinders. Baffles were used to direct the flow of cooling air.

Hitachi Nakajima Ha-51 drawing

Drawing of the [Ha-51] with details of the cylinder intake and exhaust valves. The angle between the intake and exhaust valves was fairly narrow for a radial engine, a necessity to fit 11 cylinders around the engine while keeping its diameter as small as possible.

A single-stage, two-speed supercharger was mounted to the rear of the [Ha-51]. The supercharger’s impeller was 13 in (330 mm) in diameter and turned at 6.67 times crankshaft speed in low gear and 10.0 times crankshaft speed in high gear. Fuel was fed into the supercharger by a carburetor. At the front of the engine was a planetary gear reduction that used spur gears to turn the propeller at .42 times crankshaft speed. A cooling fan driven from the front of the gear reduction was intended to keep engine temperatures within limits once the [Ha-51] was installed in a close-fitting cowling.

The [Ha-51]’s fan-assisted cooling system was originally developed for the 1,900 hp (1,417 kW) Nakajima [Ha-45] Homare engine, which gives some credence to Nakajima being involved with the [Ha-51]. The [Ha-45] and the [Ha-51] also had the same bore and stroke. Nearly all Gasuden/Hitachi radial engines had a single row of nine-cylinders and produced no more than 500 hp (373 kW). Developing a two-row, 22-cylinder, 2,500 hp (1,864 kW) engine would be a significant jump for Hitachi, but much less so for Nakajima.

The [Ha-51] had a 5.12 in (130 mm) bore and a 5.91 in (150 mm) stroke. Its total displacement was 2,673 cu in (43.8 L). The engine had an initial rating of 2,450 hp (1,827 kW) at 3,000 rpm and 8.7 psi (.60 bar) of boost for takeoff, and 1,950 hp (1,454 kW) at 3,000 rpm with 7.7 psi (.53 bar) of boost at 26,247 ft (8,000 m). However, planned development would increase the [Ha-51]’s output up to 3,000 hp (2,237 kW). The engine was 49.4 in (1.26 m) in diameter, 78.7 in (2.00 m) long, and weighed 2,205 lb (1,000 kg).

Construction of the first [Ha-51] prototype was started in March 1944. Testing of the completed engine revealed high oil consumption and issues with bearing seizures between the crankpins and master rods. The gear reduction and cooling fan drive experienced failures, and difficulty with the supercharger led to broken impellers. Due to these issues, the engine was unable to pass a 100-hour endurance test. Three [Ha-51] engines and parts for a fourth had been built when the prototypes were damaged during a US bombing raid on the factory at Tachikawa in April 1945. Combined with the current state of the war, the setback caused by the air raid signaled the end of the [Ha-51] project. When US troops inspected the Tachikawa plant in late 1945, they found the three damaged and partially constructed [Ha-51] engines. One engine was mostly complete but lacked its supercharger section. Reportedly, this engine was reassembled by order of the US military, but no further information regarding its disposition has been found. All [Ha-51] engines were later scrapped, and no parts for them are known to exist.

Hitachi Nakajima Ha-51 rear

Rear view of a [Ha-51] engine as found by US troops at Hitachi’s Tachikawa plant. The engine was fairly complete, with the exception of the supercharger and accessory section. This engine was reportedly reassembled at the request of the US military.

Japanese Aero-Engines 1910–1945 by Mike Goodwin and Peter Starkings (2017)
– “The Radial 22 Cylinder Engine “HA51” and Genealogic Survey of the Gas-Den Aero-Engine” by Takashi Suzuki, Kenichi Kaki, Toyohiro Takahashi, and Masayoshi Nakanishi Transactions of the Japan Society of Mechanical Engineers (Part C) Vol. 74, No. 746 (October 2008)
– “Hitachi Aircraft Company” The United States Strategic Bombing Survey, Corporation Report No. VII (February 1947)ハ51_(エンジン)

Mitsubishi Ha-50 campns

Mitsubishi A21 / Ha-50 22-Cylinder Aircraft Engine

By William Pearce

Mitsubishi Heavy Industries was Japan’s largest aircraft engine producer and had developed a number of reliable and powerful engines. During 1942, Mitsubishi investigated a 3,000 hp (2,237 kW) engine design. Given the designation A19, the radial engine design had four rows of seven cylinders. The A19 had a 5.51 in (140 mm) bore and a 6.30 in (160 mm) stroke. This gave the 28-cylinder engine a displacement of 4,208 cu in (69.0 L). However, in the spring of 1943, Mitsubishi engineers concluded after extensive testing that the rear rows of the engine would not have enough airflow for sufficient cooling. The A19 was never built.

Mitsubishi Ha-50 campns

Although in a sorry state, the Mitsubishi A21 / Ha-50 preserved at the Museum of Aviation Science in Narita, Japan gives valuable insight into a lost generation of Japanese aircraft engines and 22-cylinder aircraft engines. Nearly all of the non-steel components have rotted away. ( image)

To solve the cooling issues, Mitsubishi turned to a two-row radial engine design with 11-cylinders per row. The new engine carried the Mitsubishi designation A21. The Imperial Japanese Army (IJA) approved of the engine design and instructed Mitsubishi to proceed with construction. The A21 was given the IJA designation Ha-50. Many sources state the engine was later assigned the joint Japanese Army and Navy designation [Ha-50]. However, [Ha-52] would have been more fitting for the engine’s configuration, and the [Ha-50] designation may be the result of confusion with the IJA’s Ha-50 designation. The Imperial Japanese Navy (IJN) was not involved with the engine’s development.

At the time, Mitsubishi was already developing an 18-cylinder radial based on their 14-cylinder [Ha-32] Kasei engine. To speed development of the Ha-50, Mitsubishi decided to continue the practice of adding additional Kasei-type cylinders to a new crankcase. The resulting air-cooled, 22-cylinder, two-row, radial configuration was common with only two other engines: the Hitachi/Nakajima [Ha-51] and the Wright R-4090. Using two rows of 11 cylinders kept the engine short and relatively simple compared to a four-row configuration. The two-row configuration also enabled a rather straightforward engine cooling operation without resorting to complex baffles. However, the large number of cylinders in each row increased the engine’s frontal area and caused greater stresses on the crankshaft’s crankpins.

Mitsubishi Ha-50 side

The Ha-50 had a substantial amount of space between the first and second cylinder rows. Note the pistons frozen in their cylinders. (Rob Mawhinney image via the Aircraft Engine Historical Society)

The Ha-50 used a three-piece, steel crankcase that was split vertically along the cylinder center line and secured via internal fasteners. Aluminum alloy housings were used for the gear reduction and the supercharger. Each cylinder was secured to the crankcase by 16 studs. The cylinders were formed with a cast aluminum head screwed and shrunk onto a steel barrel. Relatively thin fins were cut into the steel cylinder barrels to aid cooling. Each cylinder had one intake valve and one exhaust valve. The intake and exhaust ports for each cylinder faced toward the rear of the engine. The cylinders had a compression ratio of 6.7. Following the typical two-row radial configuration, the second row of cylinders was staggered behind the first row. Ample space existed between the cylinders in the front row for cooling air to reach the cylinders in the rear row. A fairly large space existed between the front and rear cylinder rows, perhaps signifying a rather robust center crankshaft support.

Two-stage supercharging was used in the form of a remote turbosupercharger for the first stage and a gear-driven, two-speed supercharger for the second stage. However, the test engines had only the gear-driven supercharger, which turned at 7.36 times crankshaft speed in low gear and 10.22 times crankshaft speed in high gear. The Ha-50 used fuel injection, and water-injection was available to further boost power. At the front of the engine was a planetary gear reduction that turned the propeller at .412 times crankshaft speed. Some sources state that contra-rotating propellers were to be used, but only a single propeller shaft was provided on the initial engines. A cooling fan was driven from the front of the gear reduction.

Mitsubishi Ha-50 cylinders

Left—An Ha-50 aluminum cylinder head still attached to the cylinder barrel. Note the valve in the intake port. Right—Detailed view of a cylinder barrel illustrates the cooling fins cut into its middle and the threaded portion at the top for cylinder head attachment. (Rob Mawhinney images via the Aircraft Engine Historical Society)

The Ha-50 had a 5.91 in (150 mm) bore and a 6.69 in (170 mm) stroke. Its total displacement was 4,033 cu in (66.1 L). The engine had a takeoff rating of 3,100 hp (2,312 kW) at 2,600 rpm and 8.7 psi (.60 bar) of boost. Normal ratings for the engine were 2,700 hp (2,013 kW) at 4,921 ft (1,500 m) and 2,240 hp (1,670 kW) at 32,808 ft (10,000 m). The normal ratings were achieved at an engine speed of 2,500 rpm and with 5.8 psi (.40 bar) of boost. The Ha-50 was 56.9 in (1.45 m) in diameter, 94.5 in (2.40 m) long, and weighed 3,395 lb (1,540 kg).

Mitsubishi Ha-50 front

Front view of the Ha-50 illustrates the ample space between the front-row cylinders, enabling air to reach the rear-row cylinders. Note the single rotation propeller shaft. (Rob Mawhinney image via the Aircraft Engine Historical Society)

Construction of the Ha-50 started in April 1943, and the first engine was completed in 1944. Engine testing began immediately, and severe vibrations were encountered that reportedly shook one engine apart on the test stand. Some sources indicate the Ha-50 was an optional power plant for the Kawanishi TB, a four-engine transoceanic bomber ordered by the IJA. The Kawanishi TB was a smaller and lighter competitor to the Nakajima Fugaku, which had become exclusively an IJN project. Six Ha-50 engines were ordered for the Kawanishi TB, but the bomber project was cancelled before any aircraft were built. Three of the Ha-50 engines were finished, but their operational issues and the cancelling of the Kawanishi TB resulted in the Ha-50 engine project being abandoned. Two of the engines were damaged in a bombing raid, but the surviving Ha-50 reportedly achieved 3,200 hp (2,386 kW) in July 1945.

The three Ha-50 engines were thought to have been destroyed at the end of World War II and before the arrival of US forces. However, one Ha-50 engine was discovered in November 1984 during expansion work at the Haneda Airport (Tokyo International Airport). Some sources indicate the surviving engine was found by US forces shortly after the war and delivered to Haneda Airport for later shipment to the United States. Apparently, plans changed, and the engine was subsequently bulldozed into a pit and covered with dirt. The discovered Ha-50 was in an advanced state of decay, but it was recovered, and efforts were made to preserve the engine and prevent its continued deterioration. The engine’s condition was stabilized, and it was put on display at the Museum of Aviation Science in Narita, Japan. The surviving Ha-50 is the sole example of any 22-cylinder aircraft engine.

Mitsubishi Ha-50 rear

The supercharger and accessory case completely rotted off the Ha-50 during its near 40-year interment. Note the threads cut into the top of the steel cylinder barrels. (Rob Mawhinney image via the Aircraft Engine Historical Society)

Japanese Aero-Engines 1910–1945 by Mike Goodwin and Peter Starkings (2017)
The History of Mitsubishi Aero-Engines 1915–1945 by Hisamitsu Matsuoka (2005)ハ50_(エンジン)

Daimler-Benz DB 604

Daimler-Benz DB 604 X-24 Aircraft Engine

By William Pearce

In July 1939, the RLM (Reichsluftfahrtministerium, or Germany Air Ministry) issued specifications for a new medium bomber capable of high-speeds. Originally known as Kampfflugzeug B (Warplane B), the aircraft proposal was eventually renamed Bomber B. The Bomber B specification requested an aircraft that could carry a 2,000 kg (4,410 lb) bomb load 3,600 km (2,237 mi) and have a top speed of 600 km/h (373 mph). To power the Bomber B aircraft, the RLM requested engine designs from BMW, Junkers, and Daimler-Benz. The respective companies responded with the BMW 802, the Junkers Jumo 222, and the Daimler-Benz DB 604.

Daimler-Benz DB 604

The Daimler-Benz DB 604 was designed in 1939 to power the next generation of German fast bombers under the Bomber B program. However, the engine was not selected for production.

The DB 604 was an all-new, liquid-cooled, 24-cylinder engine. Four banks of six cylinders were arranged in an “X” configuration with each cylinder bank spaced at 90 degrees. The X-24 engine consisted of a two-piece aluminum alloy crankcase split horizontally at its center. The engine’s single crankshaft had six crankpins that were spaced at 0 degrees, 120 degrees, 240 degrees, 240 degrees, 120 degrees, and 0 degrees. This arrangement resulted in cylinders firing evenly at every 30 degrees of crankshaft rotation. Attached to each crankpin was a master connecting rod that accommodated three articulated connecting rods. A gear reduction at the front of the engine turned the propeller at .334 crankshaft speed. A supercharger mounted to the rear of the engine had an upper and a lower outlet. Each outlet was connected to two intake manifolds that ran along the inner Vee side of the cylinder banks.

The DB 604’s fuel system was located in the upper and lower Vees of the engine and consisted of fuel injection pumps and individual fuel injectors for each cylinder. Each cylinder had two intake and two exhaust valves, all of which were actuated by a single overhead camshaft. The camshaft for each cylinder bank was driven via a vertical shaft from the rear of the engine. The exhaust ports were positioned in the left and right Vees, as were the two spark plugs per cylinder. The spark plugs were fired by two magnetos positioned in the left and right Vees and mounted to the propeller gear reduction housing.

Daimler-Benz DB 604 side

The DB 604 was a rather compact design. A magneto can be seen at the front of the engine between the exhaust ports of the upper and lower cylinder banks. Note the supercharger at the rear of the engine. (Evžen Všetečka image via

The DB 604 had a 5.31 in (135 mm) bore and stroke and displaced 2,830 cu in (46.4 L). The engine had a 7.0 to 1 compression ratio and weighed 2,381 lb (1,080 kg). The DB 604 prototype was first run in late 1939. The first engine produced 2,313 hp (1,725 kW) at 3,200 rpm. This engine may have had a single-speed supercharger. The DB 604 A and DB 604 B engines were produced quickly after the first prototype. These engines had a two-stage supercharger that provided 6.17 psi (.43 bar) of boost. The difference between A and B versions was the rotation of the engine’s crankshaft. The DB 604 A/B had a maximum output at 3,200 rpm of 2,660 hp (1,984 kW) at sea level and 2,410 hp (1,797 kW) at 20,600 ft (6,279 m). The engine’s maximum continuous output was 2,270 hp (1,693 kW) at sea level and 2,120 hp (1,581 kW) at 21,000 ft (6,401 m), both figures at 3,000 rpm. Maximum cruise power was at 2,800 rpm, with the engine producing 1,830 hp (1,365 kW) at sea level and 1,860 hp (1,387 kW) at 20,000 ft (6,096 m). The DB 604 was flight tested in a Junkers Ju 52 trimotor transport, but it is not clear which version of the engine was tested. At least five DB 604 engines were made.

The Bomber B proposals that moved forward as prototypes were the Dornier Do 317, Focke-Wulf Fw 191, and Junkers Ju 288. Despite the DB 604 showing some promise, the RLM chose the Jumo 222, and work on the DB 604 was stopped in September 1942. No records have been found that detail the DB 604’s reliability, and many other X-24 aircraft engine designs were prone to failure. The sole surviving Daimler-Benz DB 604 engine is on display at the Flugausstellung L.+ P. Junior museum in Hermeskeil, Germany.

Daimler-Benz DB 604 right

Some of the fuel injection equipment is just visible in the engine’s upper Vee. The sole surviving DB 604 engine is on display at the Flugausstellung L.+ P. Junior museum in Hermeskeil, Germany. (Evžen Všetečka image via

Ultimately, the Ju 288 was selected as the winner of the Bomber B program. Delays with the 2,500 hp (1,964 kW) Jumo 222 led to it being substituted with the 2,700 hp (2,013 kW) Daimler-Benz DB 606, and that engine was later replaced by the 2,950 hp (2,200 kW) DB 610. The DB 606 consisted of two DB 601 inverted V-12 engines coupled side-by-side, while the DB 610 was the same arrangement but with two DB 605 engines. The Ju 288 aircraft and the Jumo 222 engine never entered large-scale production.

An enlarged version of the DB 604 was contemplated, with the engine’s bore increased .2 in (5 mm) to 5.51 in (140 mm). This gave the engine a displacement of 3,044 cu in (49.9 L). The larger 90-degree, X-24 engine was very similar to the DB 604 but incorporated a three-speed, three-stage supercharger. The engine was forecasted to produce 3,450 hp (2,575 kW) at 36,089 ft (11,000 m). Development of the larger engine did not progress beyond the initial design phase.

Daimler-Benz DB 604 left

Despite a number of X-24 aircraft engines being made, none truly were produced beyond the prototype phase, and the DB 604 was no exception. Note that the two intake manifolds between the upper (and lower) cylinder banks were connected at the front of the engine to equalize pressure. (Evžen Všetečka image via

Flugmotoren und Strahltriebwerke by Kyrill von Gersdorff, et. al. (2007)
German Aero-Engine Development A.I.2.(g) Report No. 2360 by G. E. R. Proctor (22 June 1945)
Luftwaffe: Secret Bombers of the Third Reich by Dan Sharp (2016)
Jane’s All the World’s Aircraft 1945–46 by Leonard Bridgman (1946)

Lycoming XR-7755-3 side

Lycoming XR-7755 36-Cylinder Aircraft Engine

By William Pearce

Since 1933, the Lycoming Division of the Aviation Manufacturing Corporation had worked to create a high-power engine for the United States Armed Forces. Its first attempt was the 1,200 hp (895 kW), 12-cylinder O-1230, which was outclassed by the time it first flew in 1940. Lycoming’s second attempt was the 2,300 hp (1,715 kW), 24-cylinder XH-2470. The engine had shown some promise, but its performance was eclipsed by other engines when the XH-2470 was first flown in 1943. Lycoming set out to design an engine that was more powerful than any other and that would meet the power needs of future large aircraft.

Lycoming XR-7755-3 side

The Lycoming XR-7755 was the most powerful aircraft engine in the world when it was built. The XR-7755 was the culmination of Lycoming’s experience with radial and liquid-cooled engines. Conceived in 1943, such a large engine was not needed by the time it first ran in 1946.

In mid-1943, Lycoming engaged in talks with personnel from the US Army Air Force (AAF) at Wright Field, Ohio. Different sources list the involvement of the Air Materiel Command, Air Technical Service Command, and the Power Plant Lab. By December 1943, the engine concept had been solidified as a very large displacement, high-compression, liquid-cooled engine designed for optimum fuel economy and intended to power the next generation of very large aircraft. Lycoming’s experimental engine was designated XR-7755 and given the “Materiel, Experimental” code MX-434.

Clarence Wiegman headed the Lycoming XR-7755 design team. The engine consisted of nine banks of four inline cylinders positioned radially with 40-degrees of separation around a forged steel crankcase. This formed a 36-cylinder inline radial engine. The crankcase was made up of five sections, each split vertically through the cylinders. The crankcase sections were secured together by nine bolts that extended the length of the case. The individual steel cylinders each had their own water jacket. Each bank of four cylinders shared a common cast aluminum cylinder head. Each four-cylinder bank was secured to the crankcase by 16 long studs that passed through the cylinder head.

Lycoming XR-7755-3 stand

The worker gives some perspective to the XR-7755’s large size. However, the engine’s three-ton (2.74 t) weight is hard to imagine. The engine’s two magnetos and four distributors are visible on the front of the cylinder banks.

Each cylinder had one intake and one exhaust valve. Both valves were sodium cooled, with a hollow stem for the intake valve and a hollow stem and head for the exhaust valve. The valves for each bank of cylinders were actuated by a single overhead camshaft, driven via a vertical shaft at the front of the engine. Each camshaft had two sets of lobes for different valve timing—one lobe set was optimized for power and the other set for economic cruise. The camshafts shifted axially to engage the desired set of lobes. When the camshaft was shifted, the spark plug timing was automatically changed. Ignition was provided by two magnetos and four distributors. Each unit was camshaft-driven and mounted to the front of a separate cylinder bank. The spark plug leads passed through the valve covers and to the spark plugs, which were positioned in opposite corners of each cylinder.

Lycoming XR-7755-1 test stand

The XR-7755-1 on the test stand with its single propeller shaft. With each of the 36-cylinders displacing 215 cu in (3.5 L), witnessing the XR-7755 run was most likely a very memorable event. Note the robust upper engine support.

The crankshaft had four crankpins, each spaced at 180 degrees. The crankshaft was made up of five sections and assembled through the four one-piece master connecting rods. The crankshaft sections were joined at the rear of the crankpin via face splines and secured by four bolts. Five roller bearings supported the crankshaft in the crankcase.

At the rear of the engine was a single-stage, single-speed supercharger. The supercharger’s impeller was 14.4 in (366 mm) in diameter and spun at six times crankshaft speed. The supercharger fed air to nine intake manifolds, each mating with the right side of a cylinder bank. Fuel was provided to the cylinder via either a carburetor or fuel injection. Individual exhaust stacks were attached to the left side of each cylinder. Provisions were also made to incorporate two turbosuperchargers.

Although a single rotation engine was tested, the engine accommodated contra-rotating propellers using SAE #60L-80 spline shafts. The inner shaft rotated counterclockwise, and the outer shaft rotated clockwise. A two-speed propeller gear reduction was hydraulically shifted and used planetary gears. A .2460 reduction was available for high engine speeds, and a .3536 reduction was used for cruise operations with low engine rpm.

Lycoming XR-7755-1 Maxwell and Cervinsky

Lycoming workers Red Maxwell (left) and Paul Cervinsky (right) pose next to the completed XR-7755-1. It appears Maxwell is ready for the big engine to be stuffed in an airframe to see what it will do. Note the ring on the nose case and around the propeller shaft. No other image found has that ring.

The XR-7755 had a 6.375 in (162 mm) bore and a 6.75 in (171 mm) stroke. The engine displaced 7,756 cu in (127.1 L) and had a compression ratio of 8.5 to 1. The XR-7755 produced 5,000 hp (3,728 kW) at 2,600 rpm (.2460 propeller gear) for takeoff, 4,000 hp (2,983 kW) at 2,300 rpm (.2460 propeller gear) for normal operation, and 3,000 hp (2,237 kW) at 2,100 rpm (.3536 propeller gear) for cruise power. Specific fuel consumption at normal cruise power was .43 lb/hp/hr (262 g/kW/hr), but the rate dropped to around .38 lb/hp/hr (231 g/kW/hr) at low cruise power of around 1,500 hp (1,119 kW). The engine was 61.0 in (1.55 m) in diameter, 66.25 in (1.68 m) tall, and 121.35 in (3.08 m) long. The XR-7755 weighed 6,050 lb (2,744 kg).

Lycoming XR-7755 ad Dec 1946

Lycoming ad from December 1946 featuring the XR-7755. If the engine was not going to go into production, Lycoming might as well get some press out of it. One can only wonder how those responsible for marketing imagined the huge, liquid-cooled engine would factor into the decision-making process of a person buying a small, air-cooled engine.

The XR-7755 was first run in July 1946. At the time, some 10,000 hours of single-cylinder testing had been completed. The Lycoming factory was located near a residential area. Reportedly, a nearby grocery store’s canned goods would vibrate off the shelves as the XR-7755 underwent high-power tests. A good neighbor, Lycoming went to the store and installed strips on the shelf edges to keep the cans from falling. At takeoff power, the XR-7755’s fuel consumption was 580 gallons (2,196 L) per hour, or 20.62 fl oz (.61 L) per second. The engine’s coolant pump flowed 750 gpm (2,839 l/m) to dissipate 95,600 BTUs (23,956 kcal) per minute. The flow rate was enough to fill a 55 gallon (208 L) drum every 4.4 seconds. The oil pump circulated 71 gpm (269 l/m) at 100 psi (6.89 bar). Lycoming had an optimistic opinion of the engine and believed that an output of 7,000 hp (5,220 kW) was possible.

Most sources indicate that two XR-7755 engines were built: an XR-7755-1 with a single rotation propeller shaft and an XR-7755-3 with a contra-rotating propeller shaft. Both of these engines used carburetors. There is some indication, including the recollections of those who had family members involved with the project, that a third engine was built: an XR-7755-5 with fuel injection. Reportedly, the -1 underwent a 50-hour test run, but the results are not known. The -3 was delivered to the AAF in 1946, but it is unlikely this engine underwent much testing. It is not clear what happened to the -5, if it was completed. By the time the XR-7755 had run, the concept of an aircraft larger than the Convair B-36 Peacemaker had fallen out of favor, as had the idea of modifying the B-36 with larger piston engines. Rather, jets would be used to improve performance of the aircraft. There was no application for the XR-7755 in a post-war world with the performance of jet aircraft quickly being realized. The XR-7755 never flew.

Lycoming XR-7755 AAF Fair Oct 1945

The XR-7755 on display at the Army Air Forces Fair held at Wright Field, Ohio in October 1945. Note what appears to be a mockup of the contra-rotating propeller shafts.

One curious anomaly in the XR-7755’s story is an appearance of the engine at the Army Air Forces Fair held at Wright Field, Ohio in October 1945. This predates the engine’s run date and its supposed delivery to the AAF. However, the engine appears to have a mockup of its contra-rotating propeller shafts installed. It would seem that the engine is not complete and was shipped the 460 miles (740 km) from Lycoming’s factory in Williamsport, Pennsylvania to Dayton, Ohio to be displayed with other unusual treasures from the war. Presumably, the engine was returned to Lycoming after the show and was subsequently completed and tested in 1946.

The sole XR-7755-3 has been preserved by the Smithsonian National Air and Space Museum and is on display in the Steven F. Udvar-Hazy Center in Chantilly, Virginia. Many consider the XR-7755 the largest aircraft engine ever built. However, the Soviet IAM M-44 (8,107 cu in / 132.8 L) of 1933 and Yakovlev M-501 (8,760 cu in / 143.6 L) of 1952 were larger engines. At the time it first ran, the XR-7755 was the world’s most powerful reciprocating aircraft engine.

Lycoming XR-7755-3 NASM

The restored XR-7755-3 on display in the Steven F. Udvar-Hazy Center of the Smithsonian National Air and Space Museum. The bottom of the engine is on the left, marked by the drain tube from the gear reduction housing and the sump built into the valve cover. Note the two spark plug leads for each cylinder passing through opposite sides of the valve covers. (Sanjay Acharya image via Wikimedia Commons)

– “5,000-Hp. Lycoming Revealed” by J. H. Carpenter, Aviation (December 1946)
– “The Evolution of Reciprocating Engines at Lycoming” by A. E. Light, AIAA: Evolution of Aircraft/Aerospace Structures and Materials Symposium (24–25 April 1985)
Aircraft Engines of the World 1948 by Paul Wilkinson (1948)
The History of North American Small Gas Turbine Aircraft Engines by Richard A. Leyes II and William A. Fleming (1999)
Studebaker’s XH-9350 and Their Other Aircraft Engines by William Pearce (2018)

Lycoming XH-2470 side

Lycoming XH-2470 24-Cylinder Aircraft Engine

By William Pearce

The Lycoming Division of the Aviation Manufacturing Corporation was located in Williamsport (Lycoming County), Pennsylvania. The company had started producing aircraft engines in the late 1920s. In 1937, Lycoming became aware that its most powerful engine to date, the 12-cylinder O-1230, would not produce the power needed for future frontline military aircraft. Development of the O-1230 engine started in 1933, but the anticipated power needs of state-of-the-art aircraft were beyond what the 1,200 hp (895 kW) engine could provide. Lycoming moved quickly to apply knowledge gained from the O-1230 to a new aircraft engine.

Lycoming XH-2470 side

The design of the Lycoming XH-2470 started with the concept of mounting two O-1230 engines to a common crankcase. Note that the propeller shaft is raised above the centerline of the engine.

Lycoming started the design of its new engine in 1938, and detailed design work commenced in mid-1939. The 24-cylinder engine had an H-configuration and consisted of components from two O-1230 engines combined with a new crankcase. The new two-piece aluminum crankcase was split horizontally and accommodated a left and right crankshaft. Each crankshaft served two banks of six cylinders, with one bank above the engine and the other bank below. Fork-and-blade connecting rods were used, with the forked rods serving the lower cylinders. The H-24 engine was designated XH-2470 and given the “Materiel, Experimental” code MX-211. The US Army Air Corps (AAC) initially felt that the engine was too small, but the US Navy supported the design. The Navy ordered a single prototype engine on 11 December 1939, and the AAC started to show some interest in the engine in 1940.

The Lycoming XH-2470 utilized individual cylinders that consisted of a steel barrel screwed and shrunk into an aluminum head. The liquid-cooled cylinder was surrounded by a steel water jacket. The aluminum head had a hemispherical combustion chamber with one intake valve and one sodium-cooled exhaust valve. A cam box was mounted to the top of each cylinder bank, and each cam box contained a single camshaft that was shaft-driven from the rear of the engine.

Lycoming XH-2740 top

Top view of the XH-2470 shows the intake manifold positioned between the cylinder banks. The narrow engine could be installed horizontally (on its side) in an aircraft’s wing. Bell and Northrop pursued this installation for project aircraft, but the designs were not built.

A downdraft carburetor fed fuel into the supercharger’s 12 in (305 mm) diameter impeller mounted to the rear of the engine. Lycoming had experimented with direct fuel injection on test cylinders and planned to have fuel injection available for the XH-2470, but it is unlikely that any complete engines ever used fuel injection. The XH-2470-1, -3, and -7 engines had a single-speed, single-stage supercharger that was driven at 6.142 times crankshaft speed. The XH-2470-5 had a two-speed supercharger that was driven at 6.06 and 7.88 times crankshaft speed. Intake manifolds ran between the upper and lower cylinder banks. Depending on the installation, exhaust gases were either expelled from the outer side of the cylinders via individual stacks or collected in a manifold common to each cylinder bank. Provisions were made for the engine to accommodate a turbosupercharger.

The XH-2470-1, -3, and -5 were available with a single-rotation propeller shaft using a SAE #60 spline shaft. The -1 and -3 had a .38 gear reduction. The -5 was listed as having a two-speed reduction, but the ratios have not been found. The XH-2470-7 had contra-rotating propeller shafts and a two-speed gear reduction with speeds of .433 and .321. The contra-rotating shafts were SAE #40-60 splines, with the inner shaft rotating counterclockwise and the outer shaft rotating clockwise. The gear reduction for all engines was achieved through spur gears, and the propeller shaft was positioned above the engine’s centerline. The engine could be installed in either a vertical or horizontal position.

Lycoming XH-2470-2 drawing

The XH-2470-2 and -4 were engines intended for the Navy. The -2 was similar to the AAF’s engine with a single propeller shaft. The -4 had contra-rotating propeller shafts and was similar to the -7.

The H-2470 had a 5.25 in (133 mm) bore and a 4.75 in (121 mm) stroke. The engine’s total displacement was 2,468 cu in (40.4 L), and it had a 6.5 to 1 compression ratio. The H-2470 produced 2,300 hp (1,715 kW) at 3,300 rpm at 1,500 ft (457 m) for takeoff, 2,000 hp (1,491 kW) at 3,100 rpm at 3,500 ft (1,067 kW) for normal operation, and 1,300 hp (969 kW) at 2,400 rpm at 15,000 ft (4,572 m) for cruise operation. In addition, the two-speed supercharged engine could achieve 1,900 hp (1,417 kW) at 3,300 rpm at 15,000 ft (4,572 m) for emergency power and 1,750 hp (1,305 kW) at 3,100 rpm at 15,000 ft (4,572 m) for normal operation. The XH-2470 had a 3,720-rpm overspeed limit for diving operations. The single-rotation engines were 89.9 in (2.28 m) long, 30.5 in (.77 m) wide, 50.3 in (1.28 m) tall, and weighed 2,430 lb (1,102 kg). The contra-rotating XH-2470-7 was approximately 114 in (2.90 m) long and weighed 2,600 lb (1,179 kg).

Before the XH-2470 had even run, Lycoming proposed a variant of the engine to satisfy the AAC’s Request for Data R40-D, which was issued on 6 March 1940. R40-D sought the design of a 4,000 to 5,500 hp (2,983 to 4,101 kW) aircraft engine for use in long-range bombers. Lycoming proposed coupling two H-2470 engines together, creating a 48-cylinder XH-4940. The XH-4940 would produce 4,800 hp (3,579 kW) at 3,100 rpm up to 8,500 ft (2,591 m) with the aid of a single-speed, single-stage supercharger. The engine had a projected maximum speed of 3,400 rpm and would weigh 6,200 lb (2,812 kg). The AAC’s R40-D ended up going nowhere, and the request was cancelled in mid-1940.

Lycoming XH-2470 test stand

An XH-2470 mounted on a test stand with a tractor propeller. Installed in the XP-54 as a pusher; the blades on the XH-2470 had their angle reversed. Note the individual exhaust stacks.

The XH-2470 was first run in July 1940. The engine was proposed for the Curtiss XF14C Naval fighter and the Vultee XP-54 Swoose Goose AAC fighter. The XP-54’s original power plant was the Pratt & Whitney X-1800 (XH-2240 / XH-2600), but development of this engine stopped in October 1940. It was the cancellation of the X-1800 that led to the AAC’s interest in the XH-2470, and the AAC ordered 25 (later increased to 50) engines in October 1940. The AAC was also interested in potentially using the XH-2470 to power the Lockheed XP-58 Chain Lightning. Bell and Northrop also expressed interest in the engine for future projects.

The XH-2470 completed a Navy acceptance test in April 1941. At the time, the XF14C and XP-54 prototypes were in the detailed design stage. However, the Army Air Force (AAF—the AAC had changed its name in June 1941) continued to alter the XP-54 requirements throughout 1941. Added to the Vultee project were Turbosuperchargers, a pressurized cockpit, and the option of the Wright R-2160 Tornado engine. It was not until 1942 when R-2160 development was seriously behind schedule that the engine was dropped from the XP-54 and a more focused installation of the XH-2470 was presented. An XH-2470-7 engine with contra-rotating propellers was intended for the XP-54, but a single rotation engine was substituted because of delays with the contra-rotating gearbox. The AAF specified two Wright TSBB turbosuperchargers for the first XP-54 prototype and a single, experimental General Electric (GE) XCM turbosupercharger for the second aircraft. Reportedly, the Navy ordered 100 XH-2470 engines in May 1942. However, this may have been a total of 100 engines on order with 50 going to the AAF and 50 to the Navy.

The first XP-54 (41-1210) made its first flight on 15 January 1943, taking off from Muroc (now Edwards) Air Force Base, California. With the exception of the first flight, the XH-2470 engine installed in the XP-54 turned a 12 ft 2 in (3.71 m) Hamilton Standard propeller. Although the aircraft handled well, its development had suffered through constant changes in design and intended role. The aircraft underperformed, and the XH-2470 engine had some issues, such as oil foaming at high RPM or at altitudes above 20,000 ft (6,096 m).

Lycoming XH-2470 Vultee XP-54

The Vultee XP-54 was a very large aircraft. Even so, the installation of the XH-2470 appears to be quite cramped. Note the large exhaust manifold linking the engine to the turbosupercharger, which was positioned behind the cockpit.

The first XP-54 was flown to Wright Field, Ohio on 28 October 1943. After the next flight, a close inspection of the XH-2470 revealed some minor issues as well as damage to the supercharger impeller. The engine was removed and sent to Lycoming for repairs. The cost to fix the engine was more than the AAF was willing to pay, which showed the AAF’s lack of interest in the XH-2470 program. The first XP-54 was removed from flight status and used as a source of spare parts for the second XP-54 aircraft. The first XP-54 had completed 86 flights and accumulated 63.2 hours of flight time.

To make matters worse, the Navy cancelled its XH-2470 order in December 1943, deciding to power the XF14C with a turbosupercharged Wright R-3350 instead. Factors that influenced this change were the Navy’s long-standing preference for air-cooled engines, a shift of the XF14C’s role to that of a high-altitude fighter, issues with the XH-2470’s developmental progress, and doubts that the engine would be ready in time to see combat during World War II. At the same time, Lycoming had moved on to another aircraft engine project, the 36-cylinder XR-7755. Lycoming had invested over $1,000,000 of its own money into the XH-2470 engine.

Lycoming XH-2470 Vultee XP-54 top

The two exhaust outlets from the turbosupercharger protrude quite visibly behind the cockpit. The panel behind the exhaust was stainless steel, and hot exhaust burned the paint off the cowling on early flights. The upper cowling was later replaced with an unpainted stainless steel unit, and the rudders were painted around the same time. (Aerospace Legacy Foundation Archive image)

The second XP-54 prototype (42-108994, but incorrectly painted as 41-1211) made its first flight on 24 May 1944, taking off from Vultee Field. After at least three flights, the GE XCM turbosupercharger and the XH-2470 were removed from the aircraft. Some incompatibility between the turbosupercharger and engine had caused damage to both units. A new engine and turbosupercharger were installed, and the XP-54 flew again in December 1944. The second XP-54 made at least 10 flights, the last ending with an engine failure on 2 April 1945. The airframe had accumulated 10.7 hours of flight time.

At least one XH-2470 engine has been preserved. An XH-2470-7 is in storage at the Smithsonian National Air and Space Museum. The engine, which was never installed in any aircraft, has contra-rotating propellers and a two-speed gear reduction. The Smithsonian also lists an XH-2470-1 engine from the XP-54 in its inventory. However, no further evidence of this engine’s existence has been found.

The preserved XH-2470-7 is in storage at the Smithsonian National Air and Space Museum. Although the engine was never installed in any aircraft, at least it may be displayed one day. (NASM image)

The preserved XH-2470-7 is in storage at the Smithsonian National Air and Space Museum. Although the engine was never installed in any aircraft, at least it may be displayed one day. (NASM image)

Aircraft Engines of the World 1947 by Paul Wilkinson (1947)
American Secret Pusher Fighters of World War II by Gerald H. Balzer (2008)
Development of Aircraft Engines and Fuels by Robert Schlaifer and S. D. Heron (1950)
U.S. Experimental & Prototype Aircraft Projects Fighters 1939–1945 by Bill Norton (2008)
Experimental & Prototype U.S. Air Force Jet Fighters by Dennis R. Jenkins and Tony R. Landis (2008)
The History of North American Small Gas Turbine Aircraft Engines by Richard A. Leyes II and William A. Fleming (1999)
Studebaker’s XH-9350 and Their Other Aircraft Engines by William Pearce (2018)
Preliminary Model Specification for Engine Aircraft Model XH-2470-4 for Opposite Rotating Propellers by Aviation Manufacturing Corporation Lycoming Division (18 April 1940)
– “The Evolution of Reciprocating Engines at Lycoming” by A. E. Light, AIAA: Evolution of Aircraft/Aerospace Structures and Materials Symposium (24–25 April 1985)