Category Archives: Aircraft Engines

Thomas X-8 engine

Thomas / Leyland X-8 Aircraft Engine

By William Pearce

John Godfrey Parry Thomas was a British engineer and was widely known as Parry Thomas. During World War I, Thomas was a member of the Munitions Invention Board and was brought on as the chief engineer at Leyland Motors in 1917 to help the firm develop an aircraft engine.

Allan Ferguson had been working at Leyland on the design of the aircraft engine. The engine Ferguson had designed was a 450 hp (336 kW), water-cooled W-18 with banks set at 40 degrees. Each bank consisted of two three-cylinder blocks, and there were plans to make a W-9 engine with just three banks of three cylinders. Long pushrods extended from camshafts in the crankcase between the cylinder banks to the top of the cylinders to actuate the overhead valves. Thomas felt that the W-18 engine would not be successful and proposed his own design, which won the approval of Leyland management.

Thomas X-8 engine

The Thomas (Leyland) X-8 engine was made from aluminum and had many interesting features. At the rear of the engine, the handle is attached to a dynamo for starting. Just above the dynamo is the crankshaft-driven water pump. The engine’s carburetors are mounted on either side of the water pump. Note the integral passageways leading from the carburetor to the cylinders. The oil sump tank is positioned in the lower engine Vee.

Assisted by Fred Sumner and Reid Railton, Thomas’ engine design was an X-8 with cylinder banks spaced at 90 degrees. Each cylinder bank consisted of two paired cylinders. The cylinder banks were cast integral with the aluminum crankcase, and nickel-chrome cylinder wet liners were heat-shrunk into the cylinder banks. An aluminum cylinder head was attached to each cylinder bank via eight bolts. A propeller gear reduction was incorporated into the engine. The gear reduction used bevel gears and reduced the propeller speed to .50 times crankshaft speed. The gear reduction kept the propeller position in line with the crankshaft.

A single overhead camshaft operated the two intake and two exhaust valves for each cylinder. The camshaft was driven via a vertical shaft at the rear of the engine. The valves were closed by leaf springs. Via adjustable screws, one end of a leaf spring was attached to an intake valve while the other end of the spring was attached to an exhaust valve. The springs were allowed to articulate at their mounting point so that as one valve was opened, additional tension was applied to the closed valve for an even tighter seal.

Two carburetors were positioned at the rear of the engine, with each carburetor providing the air/fuel mixture for one side of the engine. Each carburetor was mounted to an integral intake passageway in the crankcase, with four individual ducts branching off from the passageway. Each duct connected one cylinder to the intake passageway. Exhaust was expelled from the upper and lower engine Vees. Each cylinder had two spark plugs fired by either a magneto or battery ignition.

A water pump driven at the rear of the engine by the crankshaft circulated water through the engine at around 48 gpm (182 L). The coolant flowed into the cylinder banks and around the exhaust ports to keep the exhaust valves cool. A pipe system enabled water to flow through the hollow crankshaft at 10 gpm (36 L), cooling the three main bearings and two connecting rod bearings. The water also cooled the oil that flowed through the crankshaft and to the bearings. To further cool the oil, the water and oil flowed into the propeller gear reduction, where the oil passed along the finned outer side of the water-cooled propeller shaft.

Thomas leaf spring valves

While not of the X-8 engine, this drawing does depict the leaf spring valves, similar to the setup used in the X-8 engine. The leaf spring (5) held the valves (3 and 4) closed. Lobes (11) on the camshaft (12) acted on the rockers (9 and 10) to open the valves. The leaf spring mount (8) could move up and down to add tension on the closed valve for a tighter seal. (GB patent 216,607, granted 5 June 1924)

Attached to each of the crankshaft’s two crankpins was a master connecting rod, and three articulated rods were attached to each master rod. The crankshaft had both of its crankpins inline, which meant that the pistons for one cylinder bank would both be at top dead center at the same time. One source states that the crankpins were in the same phase, meaning the two cylinders of the same bank would be on the same stroke, essentially making the X-8 engine operate like two synchronized X-4 engines. This was reportedly done to prevent any rocking motion created by the front X-4 firing followed by a rear X-4-cylinder firing 90 degrees later. However, a different source says the cylinders were phased 360 degrees apart, which would make more sense. While the pistons of one cylinder bank were both at top dead center, one cylinder was starting the intake stroke while the other was starting the power stroke. The 360-degree phasing would create a rather smooth firing order, such as bank 1 front cylinder (1F), bank 2 rear cylinder (2R), 3F, 4R, 1R, 2F, 3R, and 4F. However, the engine’s true firing order is not known.

A dry-sump lubrication system was used. Oil from the engine was collected in a one gallon (4.5 L) tank mounted in the lower engine Vee. The oil was then returned to a main oil tank of approximately eight gallons (32 L) installed in the aircraft. For starting, the X-8 engine used an electric starter motor or a hand-cranked dynamo. The engine incorporated an interrupter gear for firing guns through the propeller arc.

The X-8 engine had a 6.0 in (152 mm) bore and a 4.5 in (114 mm) stroke. The engine displaced 1,018 cu in (16.7 L) and produced 300 hp (224 kW) at 2,500 rpm and 10,000 ft (3,048 m). Maximum engine speed was around 3,500 rpm. The X-8 engine weighed around 500 lb (227 kg). For the time, 500 lb (227 kg) was remarkably light for a 300 hp (224 kW) engine. The X-8 was noted as being very compact, but a list of engine dimensions has not been found.

Thomas X-8 drawing

Patent drawing of the X-8’s crankshaft with its inline crankpins. The water pump (4) housed the crankshaft-driven impeller (9). Water was pumped through an inlet (11), through a passageway (10), and into the pipe built-up in the hollow crankshaft. The water then flowed through the propeller shaft (36) to cool oil in an adjacent passageway (45).

The design of the Thomas X-8 was completed in December 1917 and submitted to the Air Ministry. Thomas initiated an extensive part-testing program that resulted in the creation of numerous test fixtures. In conjunction with the test-fixtures, A single-cylinder test engine was built and tested in 1918. The single-cylinder produced 37 hp (28 kW) at 2,500 rpm and 53 hp (40 kW) at 3,700 rpm. These outputs equated to 296 hp (221 kW) and 424 hp (316 kW) respectively for the complete eight-cylinder engine. However, the piston in the single-cylinder engine failed after five minutes of running between 3,500 and 3,700 rpm.

A complete X-8 engine was built and run for the first time in August 1918. Compression ratios of 5.8 and 6.3 were used on the single-cylinder engine, but the compression ratio of the complete engine has not been found. Reportedly, the engine was hastily assembled because government inspectors wanted the test two weeks earlier than planned. The X-8 engine’s lightly-built crankcase deformed and closed in the crankshaft bearing clearance, resulting in the engine seizing after a few hours of running.

With the end of World War I on 11 November 1918, further work on the Thomas X-8 engine was abandoned. A number of features from the aircraft engine were later used on the Leyland automotive straight-eight engine developed in 1920. Thomas went on to become a legend at the Brooklands Raceway, campaign one of the first aero-engined Land Speed Record (LSR) monster cars, and set a flying-mile (1.6 km) LSR of 170.624 mph (274.593 km/h) on 28 April 1926. Thomas tragically died in a crash attempting another LSR on 3 March 1927. His death marked the first time a driver was killed while in direct pursuit of a LSR.

Parry Thomas at Brooklands Getty

Thomas behind the wheel of his Leyland-Thomas racer at Brooklands on 4 October 1926. (Getty image)

Sources:
“AIR: Parry Thomas’s Aero-Engine” by William Boddy, Motor Sport (February 1995)
“The Life Story of Parry-Thomas” by Fred Sumner, Motor Sport (November 1941)
“Internal Combustion Engine,” US patent 1,346,280 by John Godfrey Parry Thomas (granted 13 July 1920)
Reid Railton: Man of Speed by Karl Ludvigsen (2018)
Parry Thomas by Hugh Tours (1959)

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 Mathis 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.

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.

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.

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 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 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. Émile offered the Vega engine to the US Military in October 1942, but no action was taken.

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.

Sources:
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)
https://sites.google.com/site/moteursmathis/
https://ww2aircraft.net/forum/threads/mathis-vega-42-cylinder-french-aero-engine.49170/

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.

Contents:

Preface
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
Conclusion
Appendix: MX-232 / XH-9350 Documents
Bibliography
Index

$19.99 USD
Softcover
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 Amazon.com. If you wish to purchase the book with a check, please contact us for arrangements.

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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.

Sources:
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)
http://www.enginehistory.org/Piston/Japanese/japanese.shtml
https://ja.wikipedia.org/wiki/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. (campns.jp 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)

Sources:
Japanese Aero-Engines 1910–1945 by Mike Goodwin and Peter Starkings (2017)
The History of Mitsubishi Aero-Engines 1915–1945 by Hisamitsu Matsuoka (2005)
http://www.arawasi.jp/on%20location/narita1.html
https://ja.wikipedia.org/wiki/ハ50_(エンジン)