Category Archives: Aircraft Engines


Daimler-Benz DB 602 (LOF-6) V-16 Diesel Airship Engine

By William Pearce

Around 1930, Daimler-Benz* developed the F-2 engine, initially intended for aviation use. The F-2 was a 60 degree, supercharged, V-12 engine with individual cylinders and overhead camshafts. The engine had a 6.50 in (165 mm) bore and an 8.27 in (210 mm) stroke. The F-2’s total displacement was 3,288 cu in (53.88 L), and it had a compression ratio of 6.0 to 1. The engine produced 800 hp (597 kW) at 1,500 rpm and 1,000 hp (746 kW) at 1,700 rpm. The engine was available with either direct drive or a .51 gear reduction, and weighed around 1,725 lb (782 kg). It is unlikely that the Daimler-Benz F-2 powered any aircraft, but it was used in a few speed boats.

The Daimler-Benz OF-2 diesel engine was very similar to the spark ignition F-2. Note the dual overhead camshafts in the Elektron housing above the individual cylinders. This was one of the OF-2’s features that was not incorporated into the LOF-6.

The Daimler-Benz OF-2 diesel engine was very similar to the spark ignition F-2. Note the dual overhead camshafts in the Elektron housing above the individual cylinders. This was one of the OF-2’s features that was not incorporated into the LOF-6.

In the early 1930s, Daimler-Benz used the F-2 to develop a diesel engine for airships. This diesel engine was designated OF-2, and it maintained the same basic V-12 configuration as the F-2. The individual cylinders were mounted on an Elektron (magnesium alloy) crankcase. Each cylinder had four valves that were actuated by dual overhead camshafts. The OF-2 had the same bore, stroke, and displacement as the F-2, but the OF-2’s compression ratio was increased to 15 to 1.

Fuel was injected into the cylinders at 1,330 psi (91.7 bar) via two, six-plunger injection pumps built by Bosch. The fuel was injected into a pre-combustion chamber located between the four valves in the cylinder head. This design had been used in automotive diesels built by Mercedes-Benz. Sources disagree on the gear reduction ratio, and it is possible that more than one ratio was offered. Listed ratios include .83, .67, and .58.

The Daimler-Benz OF-2 engine had a normal output of 700 hp (522 kW) at 1,675 rpm, a maximum output of 750 hp (559 kW) at 1,720 rpm, and it was capable of 800 hp (597 kW) at 1,790 rpm for very short periods of time. Fuel consumption at normal power was .392 lb/hp/hr (238 g/kW/hr). The engine was 74.0 in (1.88 m) long, 38.6 in (.98 m) wide, and 42.5 in (1.08 m) tall. The OF-2 weighed 2,061 lb (935 kg).


This view of a display-quality DB 602 engine shows the four Bosch fuel injection pumps at the rear of the engine. The individual valve covers for each cylinder can also be seen.

The OF-2 passed its type test in 1932. At the time, Germany was developing its latest line of airships, the LZ 129 Hindenburg and LZ 130 Graf Zeppelin II. These airships were larger than any previously built, and four OF-2 engines would not be able to provide sufficient power for either airship. As a result, Daimler-Benz began developing a new engine to power the airships in 1933. Daimler-Benz designated the new diesel engine LOF-6, but it was soon given the RLM (Reichsluftfahrtministerium or Germany Air Ministry) designation DB 602.

Designed by Arthur Berger, the Daimler-Benz DB 602 was built upon lessons learned from the OF-2, but it was a completely new engine. The simplest way to build a more powerful engine based on the OF-2 design was by adding two additional cylinders to each cylinder bank, which made the DB 602 a V-16 engine. The two banks of eight cylinders were positioned at 50 degrees. The 50 degree angle was selected over the 45 degree angle typically used for a V-16 engine. This gave the DB 602 an uneven firing order which helped avoid periodic vibrations.

The individual steel cylinders were mounted to the aluminum alloy crankcase. About a third of the cylinder was above the crankcase, and the remaining two-thirds protruded into the crankcase. This arrangement helped eliminate lateral movement of the cylinders and decreased vibrations. The crankcase was made of two pieces and split horizontally through the crankshaft plane. The lower part of the crankcase was finned to increase its rigidity and help cool the engine oil.


Originally called the LOF-6, the Daimler-Benz DB 602 was a large 16-cylinder diesel engine built to power the largest German airships. Note the three-pointed star emblems on the front valve covers. Propeller gear reduction was achieved through bevel planetary gears.

A single camshaft was located in the Vee of the engine. The camshaft had two sets of intake and exhaust lobes per cylinder. One set was for normal operation, and the other set was for running the engine in reverse. The fore and aft movement of the camshaft to engage and disengage reverse operation was pneumatically controlled. Separate pushrods for the intake and exhaust valves rode on the camshaft and acted on duplex rocker arms that actuated the valves. Each cylinder had two intake and two exhaust valves. Four Bosch fuel injection pumps were located at the rear of the engine and were geared to the camshaft. Each injection pump provided fuel at 1,600 psi (110.3 bar) to four cylinders. Fuel was injected into the center of the pre-combustion chamber, which was situated between the four valves. For slow idle (as low as 300 rpm), fuel was cut from one cylinder bank.

The DB 602 engine was not supercharged and had a .50 propeller gear reduction that used bevel planetary gears. The engine used fork-and-blade connecting rods that rode on roller bearings fitted to the crankshaft. The camshaft also used roller bearings, but the crankshaft was supported by plain bearings. Two water pumps were driven by a cross shaft at the rear of the engine. Each pump provided cooling water to one cylinder bank. The engine’s compression ratio was 16.0 to 1, and it was started with compressed air.

The DB 602 had a 6.89 in (175 mm) bore and a 9.06 in (230 mm) stroke, both larger than those of the OF-2. The engine displaced 5,401 cu in (88.51 L). Its maximum continuous output was 900 hp (671 kW) at 1,480 rpm, and it could produce 1,320 hp (984 kW) at 1,650 rpm for 5 minutes. The DB 602 was 105.9 in (2.69 m) long, 40.0 in (1.02 m) wide, and 53.0 in (1.35 m) tall. The engine weighed 4,409 lb (2,000 kg). Fuel consumption at cruising power was 0.37 lb/hp/hr (225 g/kW/hr).


The ill-fated LZ 129 Hindenburg on a flight in 1936. The airship used four DB 602 engines housed in separate cars in a pusher configuration. Note the Olympic rings painted on the airship to celebrate the summer games that were held in Berlin.

Development of the DB 602 progressed well, and it completed two non-stop 150-hour endurance test runs. The runs proved the engine could operate for long periods at 900 hp (671 kW). Four engines were installed in both the LZ 129 Hindenburg and the LZ 130 Graf Zeppelin II. Each engine powered a two-stage compressor. Each compressor filled a 3,051 cu in (50 L) air tank to 850 psi (59 bar) that was used to start the engine and to manipulate the camshaft for engine reversing.

Plans for a water vapor recovery system that used the engines’ exhaust were never implemented, because the airships used hydrogen instead of the more expensive helium. The recovery system would have condensed vapor into water, and the collected water would have been used as ballast to help maintain the airship’s weight and enable the retention of helium. Without the system in place, expensive helium would have been vented to compensate for the airship steadily getting lighter as diesel fuel was consumed. With the United States unwilling to provide helium because of Germany’s aggression, the airships used inexpensive and volatile hydrogen, as it was readily available. The Hindenburg was launched on 4 March 1936, and the Graf Zeppelin II was launched on 14 September 1938.

Engines for the Hindenburg were mounted in a pusher configuration. In April 1936, the Hindenburg’s DB 602 engines experienced some mechanical issues on its first commercial passenger flight, which was to Rio de Janeiro, Brazil. The engines were rebuilt following the airship’s return to Germany, and no further issues were encountered. The Hindenburg tragically and famously burst into flames on 6 May 1937 while landing at Lakehurst, New Jersey.


Front view of the DB 602 engine in the Musée de l’Air et de l’Espace, in Le Bourget, France. Above the engine are the cooling water outlet pipes. In the Vee of the engine is the induction manifold, and the pushrod tubes for the front cylinders can be seen. Note the finning on the bottom half of the crankcase. (Stephen Shakland image via

The Graf Zeppelin II was still being built when the Hindenburg disaster occurred. Design changes were made to the Graf Zeppelin II that included mounting the DB 602 engines in a tractor configuration. The inability of Germany to obtain helium, the start of World War II, and the end of the airship era meant the Graf Zeppelin II would not be used for commercial travel. The airship was broken up in April 1940.

The DB 602 engine proved to be an outstanding and reliable power plant. However, its capabilities will forever be overshadowed by the Hindenburg disaster. Two DB 602 engines still exist and are on display; one is in the Zeppelin Museum in Friedrichshafen, Germany, and the other is in the Musée de l’Air et de l’Espace, in Le Bourget, France. Although the DB 602 was not used on a wide scale, it did serve as the basis for the Mercedes-Benz 500 series marine engines that powered a variety of fast attack boats (Schnellboot) during World War II.

*Daimler-Benz was formed in 1926 with the merger of Daimler Motoren Gesellschaft and Benz & Cie. Prior to their merger, both companies produced aircraft engines under the respective names Mercedes and Benz. After the merger, the Daimler-Benz name was used mostly for aircraft engines, and the Mercedes-Benz name was used mostly for automobiles. However, both names were occasionally applied to aircraft engines in the 1930s.


Rear view of the DB 602 engine on display in the Zeppelin Museum in Friedrichshafen, Germany. A water pump on each side of the engine provided cooling water to a bank of cylinders. (Stahlkocher image via Wikimedia Commons)

Aircraft Diesels by Paul H Wilkinson (1940)
Aerosphere 1939 by Glenn D. Angle (1940)
Diesel Engines by B. J. von Bongart (1938)
High Speed Diesel Engines by Arthur W. Judge (1941)
Diesel Aviation Engines by Paul H Wilkinson (1942)
“The Hindenburg’s New Diesels” Flight (26 March 1936)
“The L.Z.129’s Power Units” Flight (2 January 1936)


FIAT A.38, A.40, and A.44 Aircraft Engines

By William Pearce

In the early 1930s, Italy was a world leader in aviation and had developed both liquid-cooled and air-cooled engines. In 1933, the Italian Air Ministry decided to focus on air-cooled radial engines, and the development of liquid-cooled inline engines was essentially abandoned. By 1939, the shortsightedness of this decision became clear as most premiere frontline fighters from Britain, France, Germany, the Soviet Union, and the United States were powered by liquid-cooled engines. As a result, the Ministero dell’Aeronautica (Italian Air Ministry) began to encourage the development of liquid-cooled engines.


The FIAT A.38 RC15-45 was a 2,118 cu in (34.7 L) inverted V-16. The supercharger was mounted between the cylinder banks to decrease the engine’s length. Note the magnetos and contra-rotating propeller shafts.

In 1939, the Italian Air Ministry asked FIAT to design a new aircraft engine to power the next generation of Italian fighter aircraft. FIAT engineers Antonio Fressa and Carlo Bona began designing the new engine, designated A.38. The A.38 was initially an upright V-16 engine closely based on the FIAT AS.8, which was originally designed to set speed records. While the AS.8 had individual cylinders, the A.38 used two cast cylinder blocks.

After the initial upright engine design, the Italian Air Ministry was inspired by the German Daimler-Benz 600 series of inverted V-12s and requested the A.38’s configuration be changed to an inverted engine. Fressa completely redesigned the A.38, leaving very little in common with the AS.8. The AS.8 engine was a 45 degree V-16 with a 5.51 in (140 mm) bore and stroke, and by 1940, the A.38 had become an inverted, 90 degree V-16 with a 5.43 in (138 mm) bore and a 5.71 in (145 mm) stroke.

The A.38’s 16-cylinder arrangement was selected to maximize the engine’s power output while keeping its cylinder size and supercharger boost within known and reliable limits. However, a V-16 engine is very long, and its crankshaft is subject to torsional vibrations. To keep the engine’s length as short as possible, Fressa used a 90 degree cylinder bank arrangement and positioned the supercharger horizontally between the cylinder banks. This resulted in a rather complex supercharger drive.


The AC.38 in a test cell. The supercharger arrangement greatly increased the engine’s otherwise small frontal area. The 1,200 hp (895 kW) engine could have sufficed with a single-rotation propeller, but the contra-rotating unit would eliminate asymmetrical torque.

The A.38 was of all-aluminum construction with two detachable monobloc cylinder blocks. Each cylinder bank had eight cylinders, and each cylinder had two inlet and two exhaust valves. The valves were actuated by dual overhead (underhead in this case) camshafts that were driven by a single vertical shaft from the front of the engine. Two spark plugs were installed in each cylinder, and the spark plugs for each cylinder bank were fired by two magnetos driven at the front of the engine. The A.38 had a compression ratio of 7 to 1.

The engine had contra-rotating propeller shafts that were driven at .514 engine speed. Between the cylinder banks were the carburetor, supercharger, intake manifolds, and water pump. There were plans to use fuel injection, but this was never completed. The single-stage supercharger had two-speeds that gave critical altitudes of 4,931 ft (1,500 m) and 14,764 ft (4,500 m). The supercharger was powered by a shaft driven from the front of the engine and situated in the Vee between the cylinders. This shaft also drove the oil and water pumps. The supercharger’s outlet was at the center of the engine, and the air was fed into four manifolds, each serving four cylinders.

The engine was officially designated A.38 RC15-45: “RC” for Riduttore de giri (gear reduction) and Compressore (supercharged), and 15/45 for the altitudes (in hectometers) at which maximum power was obtained. The A.38 had a 5.43 in (138 mm) bore, a 5.71 in (145 mm) stroke, and a displacement of 2,118 cu in (34.7 L). The engine produced 1,200 hp (895 kW) at 2,800 rpm at 4,931 ft (1,500 m) and 14,764 ft (4,500 m). The 1,200 hp (895 kW) output was not normally enough to justify the use of contra-rotating propellers, but a photo of the engine in a test cell and a drawing of the FIAT G.55 fighter powered by the A.38 show propellers with just two-blades. It would appear that contra-rotating propellers were used more to eliminate asymmetrical torque than to compensate for exceeding the capabilities of a single-rotation propeller. The engine weighed 1,698 lb (770 kg).


The FIAT G.55 fighter was originally designed to use the A.38 engine with contra-rotating propellers (top), but the aircraft was redesigned once the switch to a single-rotation propeller (bottom) was made. Delays with the A.38 led to the Daimler-Benz DB 605 being installed in the G.55.

Three A.38 engines were ordered, but it is not clear if all were built. The A.38 underwent tests in 1941 and was able to achieved 1,300 hp (969 kW), but even more power was desired. Some developmental changes to the engine included switching to a single-rotation propeller shaft. Trouble was experienced with the engine’s crankshaft and supercharger drive, and despite multiple attempts, the engine failed to pass airworthy certification tests. Fressa continued to work on the engine into 1942, but the Italian Air Ministry had already obtained licenses to produce Daimler-Benz engines and was no longer interested in the A.38—FIAT would build the DB 605 as the RA 1050 Tifone (Typhoon). It is interesting to note that the AS.8 had proven itself reliable and probably would have been a faster and better starting point for Fressa than an all-new engine design.

A number of aircraft designs were made to accommodate the A.38 engine. The only design that was actually built was the G.55. The G.55 was originally planned to be powered by the A.38 turning contra-rotating propellers, but the design was later altered for a single-rotation, three-blade propeller. In late 1941, it became obvious that the G.55 airframe would be completed before the A.38 engine was cleared for flight tests. As a result, a change to the DB 605 engine was initiated. First flown on 30 April 1942, the G.55 arguably became the best Italian fighter of World War II. Due to the state of the Italian aircraft industry in wartime, the G.55 was never made in sufficient numbers to have any impact on the conflict.


The FIAT A.40 was a 2,000 hp (1,491 kW) X-24 that had the same bore and stroke as the A.38. Although two A.40 engines were built, they were never tested because of shifting priorities during World War II. Note the cannon installed in the upper Vee on the side view drawing.

In 1940, Fressa tasked Dante Giacosa to create a new engine to compete with the A.38 and produce 2,000 hp (1,491 kW) at 8,202 ft (2,500 m). Instead of the V-16 layout, Giacosa turned to an X-24 configuration with four six-cylinder banks positioned 90 degrees from each other. The X-24 engine was designated A.40 RC20-60, and it used the same 5.43 in (138 mm) bore and 5.71 in (145 mm) stroke as the A.38. The A.40 engine had a single crankshaft and used one master connecting rod with three articulated connecting rods for each row of cylinders. The induction manifold was installed in the Vee between the lower cylinder banks and fed the two-speed supercharger mounted at the rear of the engine. The A.40 used a fuel injection system that Giacosa and his team had designed. The gear reduction unit raised the single-rotation propeller shaft, which enabled a 20 mm or 37 mm cannon to be fitted in the Vee between the upper cylinder banks and to fire through the propeller hub. The A.40 displaced 3,176 cu in (52.1 L), and an output of 2,000 hp (1,491 kW) was expected at 6,562 ft (2,000 m) and 26,247 ft (6,000 m). Reportedly, two A.40 engines were built in 1943, but Italy’s surrender prevented the engines from ever being tested. No information has been found on the disposition of any A.38 or A.40 engines.

While Fressa was working on the A.38, he also designed a more powerful engine. There is some evidence that suggests the engine was originally designated A.42 and used four A.38 cylinder blocks in an H-32 configuration. However, the engine was redesigned and redesignated A.44 RC15-45. The FIAT A.44 was comprised of two V-16 engines stacked together to form an X configuration. The V-16 engine sections were independent of each other, and each section powered half of the A.44’s contra-rotating propeller at a .429 reduction. A.38 cylinder blocks, pistons, and crankshafts were used, but the V-16 engine sections had a wider bank angle of 135 degrees. The X-32 engine displaced 4,235 cu in (69.4 L) and was forecasted to produce 2,400 hp (1,790 kW) at 2,800 rpm and a maximum of 2,800 hp (2,088 kW) at 2,950 rpm. The engine was estimated to weigh 3,307 lb (1,500 kg), and the design progressed through 1942. While FIAT designed a few aircraft to be powered by the A.44, like the CR.44 fighter/bomber and the BR.44 torpedo bomber, the engine failed to gain the support of the Italian Air Ministry and was never built.


The FIAT CR.44 fighter/bomber was planned around the 2,400 hp (1,790 kW) FIAT A.44 engine. The A.44 X-32 engine was essentially two V-16 engines mounted together. The A.44 engine would have shared most parts with the A.38, except the crankcase. Neither the A.44 nor the CR.44 were built.

Aeronuatica Militare Museo Storico Catalogo Motori by Oscar Marchi (1980)
Ali D’Italia Fiat G 55 by Piero Vergnano and Gregory Alegi (1998)
Forty Years of Design with Fiat by Dante Giacosa (1979)
“Fantasmi di aerie e motori Fiat dal 1935 al 1945 (prime parte)” by Giovanni Masino; Ali Antiche 106 (2011)
“Fantasmi di aerie e motori Fiat dal 1935 al 1945 (seconda parte)” by Giovanni Masino; Ali Antiche 108 (2012),6520.0/all.html


Tips Aero Motor Rotary Aircraft Engines

By William Pearce

From a very early age, Maurice A. Tips and his younger brother Earnest Oscar were interested in aviation. By 1908, the Belgian siblings had built their first aircraft: a canard-design, pusher biplane. The first engine installed in the aircraft proved underpowered and was replaced with a Gnome rotary. The engine was geared to two shafts, each driving a two-blade pusher propeller. Although the aircraft made some flights, its handling was unsatisfactory, and the design was not developed further. The aircraft did possess unique concepts, a theme continued in Maurice’s subsequent designs.


Rear view of Maurice and Earnest Oscar Tips’ 1908 biplane pusher. The aircraft was unable to fly with its original Pipe V-8 engine, but the lighter Gnome rotary enabled the aircraft to takeoff. Note the central gearbox that provided power to the shafts that turned the propellers via right-angle drives.

After the 1908 aircraft, Maurice refocused his efforts on aircraft engines. By 1912, Maurice had designed a 25 hp (19 kW), seven-cylinder, “valveless,” rotary engine. The engine had a 2.76 in (70 mm) bore, a 4.33 in (110 mm) stroke, and a displacement of 181 cu in (3.0 L). Hollow “suction tubes” took the air/fuel mixture from the engine’s crankcase and delivered it to the cylinders. Each suction tube was geared to the engine’s fixed crankshaft. The suction tubes would spin at half the speed of the crankcase as it rotated. The top of the suction tube had two passageways. Each passageway would align with a common port near the top of the cylinder once every two revolutions of the crankcase. One passageway aligned to allow the air/fuel mixture to flow from the suction tube and into the cylinder. The second passageway aligned to allow the exhaust gases to flow from the cylinder out into the atmosphere.

Two larger versions of the seven-cylinder engine were planned. One had a 4.33 in (110 mm) bore, a 4.72 in (120 mm) stroke, a displacement of 487 cu in (8.0 L), and produced 50 hp (37 kW). The largest engine had a 4.41 in (112 mm) bore, a 5.12 in (130 mm) stroke, a displacement of 547 cu in (9.0 L), and produced 70 hp (52 kW). It does not appear that either of the larger engines were built.


Drawings of the 25 hp (19 kW) Tips engine of 1912. Air was drawn through the rotating suction tubes (5) which enable the intake port (14) and exhaust port (13) to align with the cylinder. The suction tubes were geared (9 and 10) to the stationary crankshaft (4).

Maurice worked to refine his “valveless” rotary engine throughout 1913 and 1914. The most obvious change was that the suction tube was moved to be parallel with the cylinder, rather than at an angle as seen in the 1912 engine. The newer engine design had an updated drive for the suction tubes, and the air/fuel mixture no longer passed through the crankcase; rather, it was delivered through a hollow extension of the crankshaft to a space under the suction tubes.


A 1912 advertisement for the Tips seven-cylinder engines. The ad is titled “The new rotary engines without valves,” and includes the more powerful 50 hp (37 kW) and 70 hp (52 kW) models.

A 25 hp (19 kW) Tips valveless rotary engine was installed in a monoplane built by Henri Gérard in 1914. However, it is not clear if the engine was the 1912 design or later. In addition, the results of the engine’s and aircraft’s performance have not been found. When World War I broke out, Maurice and Earnest Tips fled Belgium. Earnest made his way to Britain, where he worked with Charles Richard Fairey and helped start the Fairey Aviation Company in 1915. Earnest would return to Belgium in 1931 to start the Fairey subsidiary, Avions Fairey. He also produced the Tipsy series of light aircraft.

Maurice Tips traveled to the United States and continued to design aircraft engines. In 1917, The Tips Aero Motor Company was founded in Woonsocket, Rhode Island. That same year, Maurice applied for patents covering his new engine design, which incorporated many concepts from the earlier engines. The new Tips engine was an 18-cylinder, twin-row, rotary engine housed in a stationary frame. The new engine employed both water and air cooling. The cylinders were arranged in pairs, with one in the front row of the engine and the other in the rear row. The crankshaft had only one throw, and the pistons for both cylinders in a pair were at top dead center on their compression strokes at the same time. The engine’s compression ratio was 5.25 to 1. Each cylinder had one spark plug at the center of its combustion chamber. The spark plugs were fired by two magnetos mounted to the front of the engine and driven from the propeller shaft.


The 1913 (left) and 1914 (right) versions of the Tips rotary engine. The major changes were to the suction tube drive and rotary valves. The small tube (no. 14 on the 1913 engine and no. 40 on the 1914 engine) in the stationary crankshaft extension provided oil to the crankshaft and connecting rod.

Most rotary engines had a fixed crankshaft and a crankcase that rotated. This arrangement created much stress on the crankshaft and crankcase and also imposed severe gyroscopic effects on the aircraft. The Tips engine employed several unique characteristics to resolve the drawbacks of traditional rotary engines. The crankshaft of the Tips engine rotated and was geared to the propeller shaft. The propeller shaft was geared to the crankcase, which allowed it to rotate in the opposite direction from the crankshaft and propeller. The end result was that when the crankshaft was turning at 1,800 rpm, the propeller would turn at 1,080 rpm, and the crankcase would rotate at 60 rpm in the opposite direction. Rotary engines in which the crankshaft and crankcase rotate in opposite directions and at different speeds are often called bi-directional or differential rotary engines.

The propeller shaft of the Tips 18-cylinder engine was geared to the crankshaft at a .600 reduction; the crankshaft gear had 18 teeth, and the propeller shaft’s internal gear had 30 teeth. For crankcase rotation, the 17 teeth on the propeller shaft gear engaged 51 teeth on one side of a countershaft to give a .333 gear reduction. The other side of the countershaft had 11 teeth that meshed with a 66-tooth internal gear attached to the crankcase and resulted in a further .167 reduction. Having the propeller and crankshaft rotating in opposite directions not only eliminated the gyroscopic effect inherent to conventional rotary engines, but it also neutralized the gyroscopic effect created by the propeller attached to a fixed engine.


The 18-cylinder Tips engine of 1917 was far more complex than the earlier engines. Note the paired cylinders separated by the rotary valve (24). The propeller shaft (10) was geared to the crankshaft (7) via reduction gears (8 and 9). The crankcase was geared to the propeller shaft via a countershaft (16).

On the exterior of the cylinder castings were numerous cooling fins. In addition, internal passageways for water cooling were in the cylinder castings. Between each pair of cylinders were a series of air passageways to further augment cooling. The engine did not have a water pump; rather, thermosyphoning and the relatively slow rotation of the crankcase enabled the circulation of cooling water from the internal hot areas of the cylinders out toward the cooling fins on the exterior of the cylinders. The engine’s rotation also aided oil lubrication from the pressure-fed crankshaft to the rest of the engine. The oil pump and carburetor were located on the stationary frame at the rear of the engine.

A flange was positioned on the crankshaft, between the connecting rods of the cylinder pair. Mounted on the flange via ball bearings was an eccentric gear with 124 teeth on its outer edge. Attached (but not fixed) to the crankcase was a master valve gear that had 128 teeth on its inner edge. The gears meshing with an eccentric action resulted in the master valve gear turning four teeth per revolution of the crankshaft. On the outer edge of the master valve gear was a bevel gear with 128 teeth. These teeth engaged a 16-tooth pinion attached to a rotary valve positioned between each cylinder pair. The four teeth per revolution of the master valve gear acting on the 16-tooth rotary valve resulted in the rotary valve turning at a quarter engine speed. Each hollow rotary valve had two intake ports and two exhaust ports.

Air was drawn in through a carburetor at the rear of the engine. The air/fuel mixture flowed through a manifold bolted to the cylinder casting and into a passageway that led to a chamber around the lower part of the rotary valve. Holes in the valve allowed the air to flow up through its hollow middle and into the cylinder when the intake ports aligned. As the valve rotated, the exhaust ports would align with the cylinder, allowing the gases to escape out the top of the valve head and into the atmosphere. Passageways in the lower part of the rotary valve head brought in cooling water from the cylinder’s water jacket. Water flowed up through the rotary valve and back into the cylinder’s water jacket. The rotary valve was lubricated by graphite pads and held in place by a spiral spring and retaining cap around its upper surface.


On the left is the rotary valve shown with the intake ports aligned (Fig 3). The air/fuel mixture entered the valve through ports in its lower end (27a). On the right is the valve with the exhaust ports aligned (Fig 5). Fig 4 shows a cross section of the rotary valve with intake ports (28), exhaust ports (29), and passageways for the flow of cooling water (30). Fig 8 shows the valve gear drive. The crankshaft (7) turned an eccentric gear (44) that meshed (42 and 41) with a gear mounted to the crankcase. The result is that a bevel gear (27) engaged a gear screwed to the bottom of the rotary valve (26 on Fig 3) and turned the valve once for every four revolutions of the crankshaft.

The 18-cylinder Tips engine had a 4.5 in (114 mm) bore and a 6.0 in (152 mm) stroke. The engine displaced 1,718 cu in (28.1 L) and produced 480 hp (358 kW) at 1,800 rpm. The Tips engine weighed 850 lb (386 kg). At speed, the engine consumed 22 gallons (83 L) of fuel and 3 gallons (11 L) of oil per hour. The oil consumption was particularly high, even for a rotary engine, but the Tips engine was larger and more powerful than other rotary engines.

In 1919, the engine was mentioned in a few publications. In 1920, Leo G. Benoit, Technical Manager at Tips Aero Motors, passed away. Benoit was said to be in charge of the engine’s design and construction. No further information regarding the engine and no images of the engine have been found. This lack of information could mean that the 480 hp (358 kW) Tips engine was never built. However, given the detailed description of the engine and that it was worked on from 1917 to at least 1920, the possibility certainly exists that the engine was built and tested.

Sometime before World War II, Maurice Tips returned to Belgium. He continued to design engines and applied for a patent on a rotary piston engine in 1938. This engine was not designed for aircraft use and bore no similarities to his early aircraft engines.


Rear view of the 480 hp (358 kW) Tips engine shows the extensive fining (22) that covered the engine. The fining and air passages (23) combined to turn the whole engine into a radiator to cool the water that flowed through the engine via thermosyphoning and centrifugal force.

“Valveless Rotary Combustion Engine” US Patent 1,051,290 by Maurice Tips (granted 21 January 1913)
“Improvements in Rotary Combustion Engines” GB Patent 191307778 by Maurice Tips (application 15 April 1913)
“Improvements in or relating to Rotary Combustion Engines” GB Patent 191506821 by Maurice Tips (application 8 May 1914)
“Rotary Valve” US Patent 1,286,149 by Maurice A. Tips (granted 26 November 1918)
“Internal Combustion Engine” US Patent 1,306,035 by Maurice A. Tips (granted 10 June 1919)
“Valve-Operating Mechanism” US Patent 1,306,036 by Maurice A. Tips (granted 10 June 1919)
“Internal Combustion Engine” US Patent 2,203,449 by Maurice Tips (granted 4 June 1940)
“The Tips 480 H.P. Aero Motor” Aerial Age Weekly (17 March 1919)
Airplane Engine Encyclopedia by Glenn Angle (1921)

Zvezda M503 Rear

Yakovlev M-501 and Zvezda M503 and M504 Diesel Engines

By William Pearce

Just after World War II, OKB-500 (Opytno-Konstruktorskoye Byuro-500 or Experimental Design Bureau-500) in Tushino (now part of Moscow), Russia was tasked with building the M-224 engine. The M-224 was the Soviet version of the Junkers Jumo 224 diesel aircraft engine. Many German engineers had been extradited to work on the engine, but the head of OKB-500, Vladimir M. Yakovlev, favored another engine project, designated M-501.

Zvezda M503 front

Front view of a 42-cylinder Zvezda M503 on display at the Technik Museum in Speyer, Germany. Unfortunately, no photos of the Yakovlev M-501 have been found, but the M503 was very similar. Note the large, water-jacketed exhaust manifolds. The intake manifold is visible in the engine Vee closest to the camera. (Stahlkocher image via Wikimedia Commons)

Yakovlev and his team had started the M-501 design in 1946. Yakovlev felt the M-224 took resources away from his engine, and he was able to convince Soviet officials that the M-501 had greater potential. All development on the M-224 was stopped in mid-1948, and the resources were reallocated to the M-501 engine.

The Yakovlev M-501 was a large, water-cooled, diesel, four-stroke, aircraft engine. The 42-cylinder engine was an inline radial configuration consisting of seven cylinder banks positioned around an aluminum crankcase. The crankcase was made up of seven sections bolted together: a front section, five intermediate sections, and a rear accessory section. The crankshaft had six throws and was supported in the crankcase by seven main bearings of the roller type.

Each cylinder bank was made up of six cylinders and was attached to the crankcase by studs. The steel cylinder liners were pressed into the aluminum cylinder block. Each cylinder had two intake and two exhaust valves actuated via roller rockers by a single overhead camshaft. The camshaft for each cylinder bank was driven through bevel gears by a vertical shaft at the rear of the bank. All of the vertical shafts were driven by the crankshaft. The pistons for each row of cylinders were connected to the crankshaft by one master rod and six articulating rods.

Zvezda M503 Rear

Rear view of a M503 on display at Flugausstellung L.+P. Junior in Hermeskeil, Germany. The upper cylinder gives a good view of the exhaust (upper) and intake (lower) manifolds, and the engine’s intake screen can just be seen between the manifolds as they join the compounded turbosupercharger. The exhaust gasses exited the top of the turbine housing. (Alf van Beem image via Wikimedia Commons)

Exhaust was taken from the left side of each cylinder bank and fed through a manifold positioned in the upper part of the Vee formed between the cylinder banks. The exhaust flowed through a turbosupercharger positioned at the extreme rear of the engine. Exhaust gases expelled from the turbosupercharger were used to provide 551 lbf (2.45 kN / 250 kg) of jet thrust.

The pressurized intake air from the turbosupercharger was fed into a supercharger positioned between the turbosupercharger and the engine. The single-speed supercharger was geared to the crankshaft via the engine’s accessory section. Air from the supercharger flowed into a separate intake manifold for each cylinder bank. The intake manifold was positioned in the lower part of the Vee, under the exhaust manifold, and connected to the right side of the cylinder bank.

The M-501 had a 6.30 in (160 mm) bore and a 6.69 in (170 mm) stroke. The engine displaced 8,760 cu in (143.6 L) and produced 4,750 hp (3,542 kW) without the turbosupercharger. With the turbosupercharger and the thrust it provided, the engine produced 6,205 hp (4,627 kW). The engine weighed 6,504 lb (2,950 kg) without the turbocharger and 7,496 lb (3,400 kg) with the turbocharger.

Zvezda M503 Bulgaria

This partially disassembled M503 at the Naval Museum in Varna, Bulgaria gives some insight to the inner workings of the engine. The turbine wheel can be seen on the far left. Immediately to the right is the air intake leading to the compressor wheel, which is just barely visible in its housing. From the compressor, the air was sent through the seven outlets to the cylinder banks. The exhaust pipe can just be seen inside the water-jacketed manifold on the upper cylinder bank. Note the studs used to hold the missing cylinder bank. (Михал Орела image via Wikimedia Commons)

By 1952, the M-501 had been completed and had achieved over 6,000 hp (4,474 kW) during tests. The program was cancelled in 1953, as jet and turbine engines were a better solution for large aircraft, and huge piston aircraft engines proved impractical. The M-501 was intended for the four-engine Tupolev 487 and Ilyushin IL-26 and was proposed for the six-engine Tupolev 489. None of these long-range strategic bombers progressed beyond the design phase.

The lack of aeronautical applications did not stop the M-501 engine. A marine version was developed and designated M-501M. The marine engine possessed the same basic characteristics as the aircraft engine, but the crankcase casting were made from steel rather than aluminum. The M-501M was also fitted with a power take off, reversing clutch, and water-jacketed exhaust manifolds.

The exact details of the M-501M’s history have not been found. It appears that Yakovlev was moved to Factory No. 174 (K.E. Voroshilov) to further develop the marine engine design. Factory No. 174 was founded in 1932 and was formerly part of Bolshevik Plant No. 232 (now the GOZ Obukhov Plant) in Leningrad (now St. Petersburg). Factory No. 174 had been involved with diesel marine engines since 1945, and Yakovlev’s move occurred around 1958. Early versions of the marine engine had numerous issues that resulted in frequent breakage. In the 1960s, the engine issues were resolved, and Factory No. 174 was renamed “Zvezda” after the engine’s layout. Many languages refer to radial engines as having a “star” configuration, and “zvezda” is “star” in Russian. Zvezda produced the refined and further developed 42-cylinder marine engine as the M503.

Zvezda M503 cross section

Sectional rear view of a 42-cylinder Zvezda M503. The cylinder banks were numbered clockwise starting with the lower left; bank three had the master connecting rod. Note the angle of the fuel injector in the cylinder and that the injector pumps were driven by the camshaft (as seen on the upper left bank).

The Zvezda M503 retained the M-501’s basic configuration. The engine had a compounded turbosupercharger system with the compressor wheel connected to the crankshaft via three fluid couplings. The compressor wheel shared the same shaft as the exhaust turbine wheel. At low rpm, the exhaust gases did not have the energy needed to power the turbine, so the compressor was powered by the crankshaft. At high rpm, the turbine would power the compressor and create 15.8 psi (1.09 bar) of boost. Excess power was fed back into the engine via the couplings connecting the compressor to the crankshaft. Air was drawn into the turbosupercharger via an inlet positioned between the compressor and turbine.

The M503’s bore, stroke, and displacement were the same as those of the M-501. Its compression ratio was 13 to 1. The M503’s maximum output was 3,943 hp (2,940 kW) at 2,200 rpm, and its maximum continuous output was 3,252 hp (2,425 kW) at the same rpm. The engine was 12.14 ft (3.70 m) long, 5.12 ft (1.56 m) in diameter, and had a dry weight of 12,015 lb (5,450 kg). The M503 had a fuel consumption of .372 lb/hp/h (226 g/kW/h) and a time between overhauls of 1,500 to 3,000 hours.

Zvezda M503 Dragon Fire

Dragon Fire’s heavily modified M503 engine under construction. Each cylinder bank is missing its fuel rail and three six-cylinder magnetos. The turbine wheel has been discarded. The large throttle body on the left has a single butterfly valve and leads to the supercharger compressor. Note that the cylinder barrels and head mounting studs are exposed and that each valve has its own port. (Sascha Mecking image via Building Dragon Fire Google Album Archive)

M503 engines were installed in Soviet Osa-class (Project 205) fast attack missile boats used by a number of countries. Each of these boats had three M503 engines installed. Engines were also installed in other ships. A heavily modified M503 engine is currently used in the German Tractor Pulling Team Dragon Fire. This engine has been converted to spark ignition and uses methanol fuel. Each cylinder has three spark plugs in custom-built cylinder heads. The engine also uses custom-built, exposed, cylinder barrels and a modified supercharger without the turbine. Dragon Fire’s engine produces around 10,000 hp (7,466 kW) at 2,500 rpm and weighs 7,055 lb (3,200 kg).

For more power, Zvezda built the M504 engine, which had seven banks of eight cylinders. Essentially, two additional cylinders were added to each bank of the M503 to create the 56-cylinder M504. The M504 did have a revised compounded turbosupercharging system; air was drawn in through ducts positioned between the engine and compressor. The intake and exhaust manifolds were also modified, and each intake manifold incorporated a built-in aftercooler. At full power, the turbosupercharger generated 20.1 psi (1.39 bar) of boost. The M504 engine displaced 11,681 cu in (191.4 L), produced a maximum output of 5,163 hp (3,850 kW) at 2,000 rpm, and produced a maximum continuous output of 4,928 hp (3,675 kW) at 2,000 rpm. The engine had a length of 14.44 ft (4.40 m), a diameter of 5.48 ft (1.67 m), and a weight of 15,983 lb (7,250 kg). The M504 had a fuel consumption of .368 lb/hp/h (224 g/kW/h) and a time between overhauls of 4,000 hours. The engine was also used in Osa-class missile boats and other ships.

Zvezda M504 56-cyl

The 56-cylinder Zvezda M504 engine’s architecture was very similar to that of the M503, but note the revised turbocharger arrangement. Wood covers have been inserted into the air intakes. Just to the right of the visible intakes are the aftercoolers incorporated into the intake manifolds.

In the 1970s, Zvezda developed a number of different 42- and 56-cylinder engines with the same 6.30 in (160 mm) bore, 6.69 in (170 mm) stroke, and basic configuration as the original Yakovlev M-501. Zvezda’s most powerful single engine was the 56-cylinder M517, which produced 6,370 hp (4,750 kW) at 2,000 rpm. The rest of the M517’s specifications are the same as those of the M504, except for fuel consumption and time between overhauls, which were .378 lb/hp/h (230 g/kW/h) and 2,500 hours.

Zvezda also coupled two 56-cylinder engines together front-to-front with a common gearbox in between to create the M507 (and others) engine. The engine sections could run independently of each other. The 112-cylinder M507 displaced 23,361 cu in (383 L), produced a maximum output of 10,453 hp (7,795 kW) at 2,000 rpm, and produced a maximum continuous output of 9,863 hp (7,355 kW) at the same rpm. The engine was 22.97 ft (7.00 m) long and weighed 37,699 lb (17,100 kg). The M507 had a fuel consumption of .378 lb/hp/h (230 g/kW/h) and a time between overhauls of 3,500 hours for the engines and 6,000 hours for the gearbox.

Zvezda engineer Boris Petrovich felt the 56-cylinder M504 engine could be developed to 7,000 hp (5,220 kW), and the M507 (two coupled M504s) could be developed to over 13,500 hp (10,067 kW). However, gas turbines were overtaking much of the diesel marine engine’s market share. Today, JSC (Joint Stock Company) Zvezda continues to produce, repair, and develop its line of M500 (or ChNSP 16/17) series inline radial engines as well as other engines for marine and industrial use.

Zvezda M507 engine

The M507 was comprised of two M504 engines joined by a common gearbox. The engine sections had separate systems and were independent of each other.

Russian Piston Aero Engines by Vladimir Kotelnikov (2005)
Unflown Wings by Yefim Gordon and Sergey Komissarov (2013)
Ungewöhnliche Motoren by Stefan Zima and Reinhold Ficht (2010)

Paradox side

Deissner ‘Paradox’ Rotary Aircraft Engine

By William Pearce

Deissner Paradox running

Charles (Carl) Deissner stands next to the 30 hp (22 kW) Paradox engine during a test run. The frame around the engine enabled it to be run in such demonstrations and was not needed when the engine was installed in an aircraft (which probably never happened). Note the carburetor at the front of the engine.

As early aviators began to take flight, it quickly became apparent that most engines were not suitable for use in aircraft. A number of engineers and designers worked to create light and powerful engines that were ideal for aircraft use. Some of these designs, such as the Antoinette, lay the foundation for many engines to follow, but other engine designs were quickly abandoned. Like many others, Charles (Carl) Deissner of London, England designed one of the engines destined to go nowhere. Deissner called his engine the Paradox.

The Paradox was an air-cooled, four-cylinder, four-stroke, rotary engine. In this context, “rotary” refers to a radial engine in which the crankcase and cylinders rotate around the crankshaft. This is not to be confused with a Wankel engine, which uses a rotor spinning in a fixed crankcase to produce power. Most rotary aircraft engines had the crankshaft fixed to the airframe, while the propeller was attached to and spun with the crankcase. However, the Paradox was not like other rotary engines.

While the crankcase of the Paradox rotated just like any other rotary engine, inside the Paradox, the crankshaft turned at twice the speed of the crankcase and in the same direction. The engine’s internals were kept in order by eccentric gears on the crankshaft engaging ring gears inside the crankcase. The stroke of the crankshaft represented one quarter of the piston’s stroke. The path of the eccentric gear also represented one quarter of the piston’s stroke. The relative motions of the crankcase and crankshaft enabled the full stroke to be utilized and allowed the unique Paradox engine to function.

Paradox engine sectional

Sectional view of the 30 hp (22 kW) Paradox engine. The valves can be seen on the front of the L-head cylinders. Below the valves are the pushrods actuated by counter-weighted rockers. The rockers are driven by a short camshaft extending on each side of a pinion. The pinon rotates as its teeth mesh with a gear fixed to a stationary shaft at the front of the engine.

The easiest way to visualize the Paradox engine’s operation is to consider the piston at the top of the cylinder when the cylinder is at the 12 o’clock position. Here, the crankshaft and its throw are at top dead center. When the engine has rotated 180 degrees, putting the cylinder at the six o’clock position, the crankshaft has rotated 360 degrees. The crankshaft is again at top dead center, but since the cylinder is now at the bottom of the engine, the piston is now at the bottom of the cylinder. When the engine has rotated another 180 degrees, the cylinder is back at the 12 o’clock position, and the crankshaft, having rotated 360 degrees, is again at top dead center, returning the piston to the top of the cylinder.

The crankshaft had two throws 180 degrees apart, and each throw served a pair of cylinders. The cylinders of each pair were 180 degrees apart, and the two cylinder pairs were 90 degrees apart. A non-articulating, solid connecting rod served each cylinder pair so that when one piston was at the top of the cylinder, the piston in the opposite cylinder was at the bottom of the cylinder. Deissner stated that since the connecting rod did not articulate, Paradox engines could be made with relatively long strokes and achieve high compression ratios.

Paradox side

The 30 hp (22 kW) Paradox engine complete with propeller. Note the skew gear-driven magneto, counter-weighted rocker arms, and the cylinders’ L-head design.

Three versions of the Paradox engine were planned for construction with different outputs: 30 hp (22 kW), 70 hp (52 kW), and 100 hp (75 kW). However, it appears only the 30 hp (22 kW) and 70 hp (52 kW) engines were actually built. While both engines had four cylinders and shared the same rotary and eccentric crankshaft arrangement, each engine also had a number of unique features.

The 30 hp (22 kW) Paradox was a demonstration engine mounted in a metal frame. The engine utilized an L-head cylinder with side valves. The single intake and exhaust valves were positioned on the front side of the cylinder. Each valve was actuated by a pushrod driven by a large, counter-weighted rocker arm. Part of the rocker rode on a camshaft that extended through the axis of a pinion. The cam on one side of the pinion controlled the intake while the cam on the other side controlled the exhaust. The pinion was driven by a skew gear mounted on a stationary shaft that did not rotate with the engine.

Induction air was brought in through a carburetor at the front of the engine. The air/fuel mixture then passed through the crankcase, where it was warmed, and into separate manifolds for each cylinder. Exhaust was taken through a manifold from each cylinder, piped through the crankcase, and vented out the front of the engine’s propeller shaft, which was fixed to the crankcase.

Paradox Induction Exhaust

Schematic view of the induction and exhaust system in the 70 hp (52 kW) Paradox engine. For clarity, the valves are illustrated on the front and rear of the T-head cylinder, rather than its sides. Note the offset crankshaft.

A magneto was driven by a skew gear at the rear of the engine. The magneto fired the one spark plug installed in each cylinder. However, it appears the engine could accommodate two spark plugs per cylinder. Ball bearings were used throughout the engine. The 30 hp (22 kW) Paradox engine had a 2.76 in (70 mm) bore and a 7.17 in (182 mm) stroke. The engine displaced 171 cu in (2.8 L). Its 30 hp (22 kW) output was obtained at 1,200 rpm. Increasing the engine’s rpm to 1,400 resulted in an output of 40 hp (30 kW).

The 70 hp (52 kW) Paradox engine also used side valves but in a T-head arrangement, with the valves on opposite sides of the cylinder. The valves were actuated by the same method used on the 30 hp (22 kW) engine, but a pushrod and rocker was now positioned on each side of the cylinder. One schematic shows the valves on the front and back sides of the cylinder, rather than the left and right sides. This was most likely done for illustrative purposes, to show how the engine’s induction and exhaust systems worked. Induction air was brought in the front of the engine, passed through the crankcase (where it was warmed), and flowed through a fixed shaft at the rear of the engine. Here, it passed through a carburetor, and the air/fuel mixture flowed back through the shaft to manifolds at the rear of the engine; these manifolds led to each cylinder. The 70 hp (52 kW) Paradox engine had a 4.0 in (102 mm) bore and a 7.0 in (178 mm) stroke. The engine displaced 352 cu in (5.8 L). Its 70 hp (52 kW) output was obtained at 1,400 rpm, and it produced 60 hp (45 kW) at 1,200 rpm. The engine weighed 220 lb (100 kg).

Deissner Paradox Ad

1910 advertisement for the Paradox engine expressing its many virtues over other rotary engines. The pricing for the 70 hp (52 kW) engine is given, although the 30 hp (22 kW) engine is illustrated in the photograph. The price of the 70 hp (52 kW) engine was increased to £460 in March 1911. (via

The 30 hp (22 kW) Paradox engine was running by late 1910. It was run both with and without a 7 ft 6 in (2.3 m) Eta propeller. Some of the engine’s noted advantages were that standard lubricating oil could be used—other rotaries typically needed castor oil. The Paradox engine was also said to have good fuel economy, but no specifics were given. In early 1911, the 30 hp (22 kW) engine broke free during a test run, resulting in a destroyed propeller and a damaged engine. The engine was repaired in February, and the 70 hp (52 kW) Paradox engine was to be finished by March 1911. However, no further information has been found regarding any Paradox engine.

The Paradox engines may have offered some improvements in oil consumption, which was always quite high with standard rotaries, but its other unique features did not offer any tangible advantage over more popular engines. Rotary engines would continue to be widely used until after World War I. At that time, conventional engines had out-powered the rotary, and the inherent limitations of its spinning crankcase design could not be overcome.

“The Paradox Rotary Engine” Flight (19 November 1910)
The Art of Aviation by Robert W. A. Brewer (2nd edition, 1911)

Antoinette VII with 100hp V-16 engine paris 1909

Antoinette (Levavasseur) Aircraft Engines

By William Pearce

Léon Levavasseur was one of those rare geniuses of early aviation who designed and built engines as well as aircraft. In the early 1900s, Levavasseur gave up his career as an electrical engineer to focus on aviation. He needed funding to pursue his interests, so in August (some say July) 1902, Levavasseur approached industrialist and fellow Frenchman Jules Gastambide. Levavasseur had impressed and then befriended Gastambide when he repaired generators at one of Gastambide’s power plants. At the July meeting, Levavasseur outlined his plans for an aircraft of his design to be powered by a new engine that he was also designing. Levavasseur suggested the new enterprise should be named Antoinette, after Gastambide’s young daughter. Gastambide was interested but thought the engine should be built first, as no aircraft had yet flown. Levavasseur was agreeable, and with financial backing secured, he set to work on the new engine.

Antoinette IV 50hp V-8 Latham Levavasseur Camp Chalons 5 June 1909

An Antoinette mechanic (left), Hubert Latham (middle), and Léon Levavasseur (right) with an Antoinette IV aircraft powered by a 50 hp (37 kW) Antoinette V-8 at Camp de Châlons in early June 1909. At the event, Latham flew continuously for 1:07:37, setting a French endurance record. Note the condenser under the aircraft’s wing.

Levavasseur quickly returned to Puteaux (near Paris), France, and set up a shop to work on the new engine. On 28 August 1902, Levavasseur applied for a secret patent on his engine, which consisted of eight cylinders laid out in a Vee pattern, forming two banks of four cylinders. This patent application became public on 28 August 1903 and was granted French patent no 399,068 on 30 September 1904.

From 1902 through 1910, Levavasseur produced several different Antoinette engines, but they all used the same basic layout. Technically, the first time the “Antoinette” name was applied during the Levavasseur-Gastambide partnership was in 1905 when a series of boats were so named. It would not be until 1906 that the Société Anonyme Antoinette was officially incorporated.

All of Levavasseur’s engines consisted of individual, water-cooled cylinders arranged in a 90 degree Vee on an aluminum crankcase. The cylinders were staggered on the crankcase to facilitate the use of side-by-side connecting rods. With this arrangement, the connecting rods for each left and right cylinder pair attached to the crankshaft on the same crankpin. This allowed the engine to be much shorter than if each connecting rod had its own crankpin. The connecting rods were of a tubular design, and the pistons were made from cast iron.

Cody Antoinette 50hp V-8 Nulli Secundus 1907

A 1907 image of Samuel Cody with a 50 hp (37 kW) Antoinette V-8 in the framework of the “Nulli Secundus,” Britain’s first airship.

Each cylinder had one intake and one exhaust valve positioned on the Vee side of the cylinder. The intake valve was situated above the exhaust valve, creating an “F-head” or “Intake Over Exhaust” (IOE) cylinder head. The intake valve was atmospheric (automatic)—drawn open by the vacuum created in the cylinder as the piston moved down. The exhaust valve was actuated by a pushrod driven by the camshaft located in the Vee of the engine. The top of the cylinder’s combustion chamber was hemispherical, with a single spark plug positioned at its center.

The Antoinette engines used a primitive type of direct fuel injection. A belt-driven fuel pump at the rear of the engine fed fuel into a small reservoir (injector) located above each intake valve. When the intake valve opened, the suction that drew in air also pulled in fuel from the reservoir via a narrow, capillary passageway .008 in (.2 mm) in diameter. By manipulating the fuel pump, the pilot could exert a certain degree of fuel flow regulation. However, the system had some issues, and Antoinette engines had difficulty running at low rpm. In addition, the small passageways in the “injectors” easily became clogged by impurities in the fuel. These complications led some Antoinette operators to convert the engine to a carbureted induction system.

To cool a normal Antoinette engine, a belt-driven water pump at the rear of the engine provided water to an inlet at the base of each cylinder on the outer side of the engine. The water then passed up through the water jacket and along the cylinder barrel. The water exited the top of the cylinder on the Vee side of the engine, where it flowed into a common manifold for each cylinder bank. The water was then taken to a radiator or to a reservoir tank, as engine cooling was not critical on very short flights.

Antoinette 50hp V-8 London Science Museum

This 50 hp (37 kW) Antoinette V-8 engine is on display at the Science Museum in London and may have been used by Cody in 1908 for the first flight in Britain. Note the aluminum cylinder heads, brass water jackets, and copper water manifolds. The fuel distributor can be seen on each vertical intake pipe. (Warbird Tails image)

For lubrication, oil was taken from the crankcase and pumped through a pipe inside the crankcase, just above the camshaft. The pipe ran the length of the engine and was pierced with numerous small holes. Oil sprayed from the pipe, lubricating all of the engine’s internal components. Any components not in direct contact with an oil spray were lubricated by the oil mist created inside the crankcase.

Some (but not all) of the Antoinette engines had the ability to reverse their running. This was particularly helpful for braking and maneuvering in dirigibles. The camshaft was normally locked into its driving gear at the rear of the engine. With the engine stopped, the camshaft could be unlocked, rotated 90 degrees, and locked into a second position in its driving gear. One position was for normal (counter-clockwise) rotation, and the other was for reverse rotation (clockwise).

Antoinette engine ad V-16

Antoinette engine ad circa 1907 illustrating the lightness of the 220 lb (100 kg), 100 hp (75 kw) V-16 engine.

Each Antoinette engine was made to the highest standards in a shop that boasted of tolerances down to .0004 in (.01 mm). Another feature of all Antoinette engines was that their components were engineered to be just strong enough for their individual tasks. By designing parts with operating stresses in mind, all extra material could be eliminated, resulting in complete engines that were much lighter than their contemporaries. This design philosophy also had a drawback: engine reliability could suffer because parts were more easily overstressed, resulting in a failure. Antoinette engines were relatively specialized, and when one was in need of repair, it had to be shipped back to the factory.

The early Antoinette engines used open cylinder barrels made from cast iron. An aluminum cylinder head was bolted to the barrel. Each cylinder had a spun brass water jacket shrink-fitted to the cylinder head. The engine’s spark plugs were fired by a battery-powered ignition coil distributor.

Levavasseur’s first engine was running by the end of 1902, but efforts to improve the engine were undertaken throughout 1903. The engine was a V-8 with a 5.12 in (130 mm) bore and stroke. The engine’s total displacement was 842 cu in (13.8 L), and it produced 80 hp (60 kW). Initially, the engine weighed 346 lb (157 kg), but refinements brought the weight down to 320 lb (145 kg).

Antoinette V-16 engine display

An Antoinette V-16 engine possibly in storage at the Musée de l’Air et de l’Espace in Le Bourget, France. Note how the V-16 utilized all the same components as the V-8, with the exception of the crankcase, crankshaft, camshaft, and water manifolds. This engine has rather unique exhaust stacks. (image source)

The 80 hp (60 kW) Levavasseur engine underwent a military test in March 1903 in which it produced 63 hp (50 kW). This output was derived by using a alternative power calculation method, and Levavasseur objected to the results. A little later, the engine was tested again, using another power calculation method. During this test, the engine registered an output of 82 hp (61 kW). The engine’s performance and Levavasseur’s ideas sufficiently impressed General Louis André, France’s Minister of War, who then provided 20,000 Francs of secret funds to Levavasseur for the construction of his airplane.

From July to September 1903, Levavasseur built his airplane in Villotran, France, which is why the aircraft became known as the Aéroplane de Villotran. The aircraft was powered by the 80 hp (60 kW) engine. Unfortunately, the aircraft proved incapable of flight. By 15 September 1903, Levavasseur had decided the aircraft was a failure; the engine was removed, and the aircraft was burned.

Antoinette V-24 marine engine

The 360 hp (268 kW) Antoinette V-24 marine engine of 1906. Unlike the V-16 engines, the V-24 appears to be comprised of V-8 engine sections. The engine is labeled as follows: A) air intake pipe; B) exhaust; C) cooling water outlet; D) aluminum cylinder head; E) steel cylinder covered with a brass water jacket sleeve; F and G) ignition distributors; H) spark plug; h) cylinder head bolts; I) fuel distributor to the intake valve; J) cooling water inlet; K) cylinder mounting bolt; P) engine mounting flange; S and T) gears for the ignition distributors; U) crankshaft gear; V) camshaft gear.

The Aéroplane de Villotran’s failure to fly, and the fact that no other aircraft had yet flown, made the concept of an aircraft engine seem futile. However, Levavasseur and Gastambide knew the engine held great potential and turned to motorboat racing as a way for the engine to prove its worth. From 1904 through 1906, Levavasseur’s engines powered a number of motorboats that achieved various distance speed records. It was to some of these motorboats that the “Antoinette” name was first given. In some cases, V-8 engines were coupled in tandem to create a more substantial power unit. By 1908, the Antoinette company had ended its support for motorboat racing and focused on using its engines only for aviation.

In 1904, while his engine was beginning to gain fame, Levavasseur designed other engines. Using the 80 hp (60 kW) V-8 as a foundation and maintaining the 5.12 in (130 mm) bore and stroke, Levavasseur designed V-16, V-24, and V-32 engines. Levavasseur believed that engines with many cylinders created frequent power pulses that smoothed out the engine’s operation and caused less stress on its internal components. The V-16 displaced 1,685 cu in (27.6 L) and produced 155 hp (116 kW). The V-24 displaced 2,527 cu in (41.4 L) and produced 225 hp (168 kW). The V-32 was most likely never built, but it would have displaced 3,370 cu in (55.2 L) and produced around 300 hp (224 kW).

Bleroit IX 50hp V-16 1908

A Bléroit IX aircraft under construction in 1908 with a 50 hp (37 kW) Antoinette V-16 installed in its frame. From left to right, the Bléroit mechanics are Louis Peyret, Louis Paragot, M. Pelletier, Alfred Bertrand, and Julien Mamet.

Levavasseur also varied the bore and stroke to make engines of different sizes and power. In 1905, Levavasseur built a V-8 Antoinette engine with a 3.15 in (80 mm) bore and stroke for aviation pioneers Ferdinand Ferber and Alberto Santos-Dumont. The engine displaced 196 cu in (3.2 L) and produced 24 hp (18 kW). The engine went through some refining and eventually weighed only 79 lb (36 kg). Another V-8 used a 4.13 in (105 mm) bore and stroke to displace 444 cu in (7.3 L). This engine produced 50 hp (37 kW) and weighed 176 lb (80 kg). The engine was approximately 32 in (.81 m) long, 24 in (.62 m) wide, and 22 in (.55 m) tall. A large V-8 was also built with a 7.87 in (200 mm) bore and stroke. Undoubtedly for marine use, this engine displaced 3,067 cu in (50.3 L), produced 200 hp (149 kW), and weighed 838 lb (380 kg).

In 1906, Levavasseur built a large V-24 Antoinette engine for marine use. The V-24 had a 5.91 in (150 mm) bore and stroke and displaced 3,882 cu in (63.6 L). The engine produced 360 hp (268 kW) and weighed some 1,322 lb (600 kg). Some sources say this engine was too heavy for the intended boat, which ended up sinking. The specifics of this incident have not been found.

Antoinette 50hp V-8 engine Krakow

A later model 50 hp (37 kW) Antoinette V-8 with an extended propeller shaft on display at the Muzeum Lotnictwa Polskiego in Krakow, Poland. Note the different lengths of the air intake pipes and that the water jackets are made from copper. (Alan Wilson image)

An Antoinette automobile made its debut in the 1906 Salon de l’Automobile in Paris, and some Antoinette engines were built for automotive use, these being a slightly different design and heavier than the aviation engines. Adams Manufacturing Company in London built a small number of the automotive engines under license for cars they were manufacturing.

By 1907, V-16 versions of the 3.15 in (80 mm) bore/stroke and 4.13 in (105 mm) bore/stroke engines were being built. The 3.15 in (80 mm) bore and stroke V-16 displaced 393 cu in (6.4 L), produced 50 hp (37 kW), and weighed around 143 lb (65 kg). The 4.13 in (105 mm) bore and stroke V-16 displaced 888 cu in (14.5 L), produced 100 hp (75 kW), and weighed 220 lb (100 kg). The 100 hp V-16 engine’s approximate dimensions were 55 in (1.40 m) long, 24 in (.62 m) wide, and 22 in (.55 m) tall.

Antoinette engines circa1907

The basic specifications of various Antoinette engines available circa 1907.

In addition to the V-16 engines listed above, Levavasseur offered Antoinette V-8 engines with five bore/stroke combinations. The V-8 engines had bores/strokes of 3.15, 4.13, 5.12, 5.91, or 7.87 in (80, 105, 130, 150, or 200 mm); the smallest two were mainly used for aviation.

It seems that around 1908 Levavasseur ceased experimenting with different engines and began working to refine the popular types. Levavasseur incorporated many changes to the Antoinette engines, but not all of the changes were applied at the same time. An elongated propeller shaft housing of approximately 12 in (.30 m) was cast integral with the crankcase. This feature made for a very aesthetically pleasing installation when the engine was used in an Antoinette aircraft. The battery-powered coil ignition was replaced by an accumulator and high-frequency distributor. A new one-piece, steel cylinder was used in which the cylinder head was integral with the cylinder barrel. This construction allowed for a higher compression ratio. New one-piece water jackets made of either brass or copper surrounded the new cylinders. The water jacket was unique in that it was made by electrolytically depositing metal onto a wax mold that had been coated with graphite as a conductive material. The wax was then melted out, leaving a formed water jacket as thin as .04 in (1 mm). While this method of construction could yield perfect parts, it was expensive, and there was a high rejection rate because of irregularities in the water jacket wall.

Antoinette VII with 100hp V-16 engine paris 1909

Antoinette VII aircraft with a 100 hp (75 kW) V-16 engine displayed at the Salon de l’Aeronautique in 1909. Most sources indicate the condenser used aluminum tubes and copper side manifolds, details that this image seems to support.

By 1908, Levavasseur had perfected a zero-loss steam-cooling method for the Antoinette engines that were installed in Antoinette aircraft. The system used the same basic routing as the normal cooling system, but the water was allowed to boil in the water jackets. The steam was then collected and sent to a water separating tank. From the tank, the steam was sent though large condensers made of aluminum tubing with copper side manifolds. The condensers were positioned horizontally on each side of the aircraft. The steam condensed back to water and was routed back to the separating tank by a second pump. From the separating tank, the water was pumped back to the engine. The system condensed .26 gallons (1 L) of water per minute, and its capacity was 3.17 gallons (12 L). By reducing the amount of water needed, the steam-cooling method weighed less than conventional water-cooling.

Four Antoinette engines were displayed at the first Paris Salon de l’Aeronautique, starting in December 1908. A V-8 and V-16 were still offered with bores and strokes of 3.15 in (80 mm). However, the engines’ weights had increased to 93 lb (42 kg) for the V-8 and 165 lb (75 kg) for the V-16. The other two engines were a V-8 and V-16 with a bore of 4.33 in (110 mm) and a stroke of 4.13 in (105 mm). The V-8 engine displaced 487 cu in (8.0 L) and weighed 209 lb (95 kg). The V-16 engine displaced 974 cu in (16.0 L) and weighed 264 lb (120 kg). Some sources list the larger bore engines as producing 50 hp (37 kW) and 100 hp (75 kW) respectively. However, other sources give the outputs as 67 hp (50 kW) and 134 hp (100 kW). Note that the kW values (50 and 100) of the second figures match the hp values of the first figures. Possibly a printing error, the higher power figures have been found in fairly early publications and have been repeated a number of times over the years. The weight increases for all four engines were a result of strengthening components to increase Antoinette engine reliability.

Antoinette 50hp V-8 close up

A late model 50 hp (37 kW) Antoinette V-8 on display in the Musée de l’Air et de l’Espace. Note that this engine used brass water jackets; the piping and water manifolds were made from copper. (Aerofossile2012 image)

Alberto Santos-Dumont, Paul Cornu, Louis Blériot, Gabriel and Charles Voisin, Henri Farman, Léon Delagrange, Samuel Cody, and Hubert Latham are just some of the pioneers who used Antoinette engines to power their flying machines and themselves into the record books. Outside of the Wright brothers, almost all early aviation “firsts” were achieved in machines powered by an Antoinette engine. It was a 100 hp (75 kW) V-16-powered Antoinette aircraft that Latham flew during the aviation meet at Reims, France in August 1909 and for the Gordon Bennett Cup at Belmont Park, New York in October 1910.

With the success of the engine, Levavasseur began to focus entirely on building aircraft. From 1908 on, little engine development was undertaken to keep the Antoinette engines at the forefront of aviation. The Antoinette aircraft were built with the same spare-no-expense mentality as the engines, which resulted in them being priced far above the competition. To make matters worse, the aircraft proved to be a challenge to fly. At the same time, other engine manufactures closed the developmental gap, and the expensive Antoinette engines were no longer the coveted power plant they once were. These factors conspired to put the Antoinette company out of business in 1912.

Latham Antoinette VII 100hp V-16 NY 1910

Latham’s 100 hp (75 kW) V-16-powered Antoinette VII aircraft at Belmont Park, New York in October 1910 for the Gordon Bennett Cup. Note the length of the condenser, which extends some 13 ft (4 m) along the side of the aircraft.

While Levavasseur was not the first to build a V-8 engine, it is a near certainty that he was the first to create V-16 and V-24 engines. Very little information can be found regarding the V-24 marine engine. Some sources state that Levavasseur also built a V-32 intended for marine use, while other sources claim the engine did not proceed past the design phase.

Some sources state that Levavasseur also built V-12 and V-20 engines. These engines, especially the V-20, depart from Levavasseur’s known engine layout with a V-8 at its core. While no photographs of Levavasseur’s V-12 (or V-32) engine have been found, the V-20 engine does still exist (albeit as a table). The V-20’s cylinders, valves, and valve train do not match any other engine built by Levavasseur. There was a commonality of components and configuration from Levavasseur’s earliest engine of 1903 to his last of circa 1910. The components that make up the V-20, reportedly built in 1905, are unique to that engine and are not common with any other Levavasseur engine. This component incompatibility would lead some to conclude that the V-20 engine was not built by Levavasseur.

Antoinette VII with 50hp V-8 Musee du Bourge

An Antoinette VII aircraft with a 50 hp (37 kW) V-8 engine on display in the Musée de l’Air et de l’Espace. Note how well the engine fits into the aircraft and that the condensers appear to be made entirely of copper. For cooling, steam flowed from the top of the water jackets into a separation tank. The steam then flowed from the tank into the condenser, where it returned to water. The water was then pumped from the condenser into the bottom of the separation tank and back to the engine. (Pline image)

Levavasseur’s Antoinette engines were essentially the first commercially available aircraft engine and represented the pinnacle of performance in the early days of aviation. Just about every early European aviation pioneer’s first flight was powered by an Antoinette, but the engines’ reliability left much to be desired. While some changes were incorporated over the years, and their reliability did improve, the basic engine did not change much. Just before 1910, other engines (the Gnome rotary in particular) offered similar power for a similar weight but were often more reliable than the Antoinettes.

Note: Many sources give similar but completely different values for Antoinette engine dimensions, bores, strokes, and outputs. Some discrepancies can be attributed to numerous unit conversions being applied, and some of the power discrepancies can be attributed to the engines having different outputs at different rpms. Sadly, it seems that detailed specifics were not recorded in those early days of aviation; therefore, there can be no absolute certainty about the various Antoinette engine models or their histories.

V-20 engine

The V-20 engine as displayed at Le Manoir de l’Automobile et des Vieux Métiers in Lohéac, France. Regardless of the V-20’s origins, it seems rather inglorious for such machinery to be turned into furniture. However, the engine would have probably been scrapped long ago had it not found favor as a conversation piece. Apparently, its conversion to a table consisted of nothing more than bolting on legs to preexisting mounts, something that could easily be reversed for a more befitting display. (ZANTAFIO56 image)

Bléroit: Herald of an Age by Brain A. Elliot (2000)
Les moteurs et aéroplanes Antoinette by Gérard Hartmann (13 August 2007) 7.4 MB pdf in French
The Art of Aviation by Robert W. A. Brewer (1910)
The Passion That Left the Ground by Stephen H. King (2007)
Vingt Cinq Ans d’Aéronautique française: 1907-1932 Tome 1 (1934)
“The First Paris Aeronautical Salon: Engines for Aeroplanes” Flight (16 January 1909)
“How Levavasseur Built his Light Motor” by Ferdinand Ferber The Automobile (28 March 1907)
“Historie du moteur Antoinette” by Ferdinand Ferber l’Aérophile (15 February 1908)
“Moteur à huit cylindres” French patent 339,068 by Léon Levavasseur (applied 28 August 1903)
“Carbureter” US patent 878,297 by Léon Levavasseur (applied 16 may 1907)
“Umsteuerungsvorrichtung für Mehrzylinder-Explosionskraftmaschinen” Austrian patent 25,610 by Léon Levavasseur (applied 14 September 1904)
Airplane Engine Encyclopedia by Glenn Angle (1921)

FKFS Gruppen-Flugmotor A mockup copy

FKFS Gruppen-Flugmotor A, C, and D

By William Pearce

In 1930, German engineer Wunibald Kamm founded the FKFS (Forschungsinstitut für Kraftfahrwesen und Fahrzeugmotoren Stuttgart or Research Institute of Automotive Engineering and Vehicle Engines Stuttgart). The FKFS was an organization that tried and tested new, inventive ideas in the field of automotive technology. However, it was not long before Kamm’s thoughts and some of the FKFS’s resources were directed toward aircraft engines.

FKFS Gruppen-Flugmotor A mockup copy

Crankcase mockup of the FKFS Gruppen-Flugmotor A with Hirth HM 512 cylinders. Visible on the side of the engine is a mockup of the axial supercharger. (Kevin Kemmerer image)

In mid-1938, Kamm was able to persuade Willy Krautter of Hirth Motoren to join the FKFS as head of the FKFS’s Special Engine Group. Krautter’s first project at FKFS was building FKFS’s first aircraft engine. The result was a flat, air-cooled, two-stroke, four-cylinder engine that displaced 31 cu in (.51 L) and produced 25 hp (18 kW). The engine was used in the Hirth Hi-20 MoSe motor glider. Next, Krautter designed an improved and updated version of the four-cylinder engine, but priorities had shifted with the outbreak of World War II. Inspired by an open request from the RLM (Reichsluftfahrtministerium or German Ministry of Aviation), the FKFS focused on designing much larger engines.

The RLM was interested in large, powerful engines for bombers being designed to reach targets in North America. Both Kamm and Krautter believed that air-cooled engines were overall superior for aircraft use, and they designed a 32-cylinder engine intended for the RLM. This radial engine had eight cylinder banks evenly spaced at 45 degree intervals around the crankcase. Each cylinder bank consisted of four inline, air-cooled cylinders and a single overhead camshaft. The cylinder proposed for the engine was designed by Krautter and was undergoing tests at the FKFS.

FKFS Gruppen-Flugmotor A crankcase copy

Two views of the Gruppen-Flugmotor A’s crankcase. In the left image, note the rear accessory drive housing with provisions to power the axial supercharger. Also note the large roller bearing in the nose case. In the right image, note the crankshaft and camshaft position for each engine section. Crankcase finning is also visible in both images. (Kevin Kemmerer images)

Building a new aircraft engine from scratch is a massive undertaking, so Krautter suggested grouping together existing, proven engines to quickly create a larger, more powerful unit. Kamm supported Krautter’s idea of a Gruppen-Flugmotor (Group Aircraft Engine), and the detailed design of such a power unit commenced in 1939. The first engine was known as the Gruppen-Flugmotor A (or just Motor A), and it utilized almost all of the components from four Hirth HM 512 engines (excluding their crankcases) to create a new 48-cylinder engine. Undoubtedly, Krautter’s experience at Hirth Motoren influenced his decision to use HM 512 parts.

The Hirth HM 512 was an inverted, air-cooled, V-12 engine. Its individual cylinders were arranged in two rows spaced at 60 degrees and attached under an elektron (magnesium alloy) crankcase. Four long studs held each cylinder to the crankcase, and the cylinders were staggered to allow the use of side-by-side connecting rods. Each cylinder was made of cast iron and had an aluminum cylinder head. In the Vee of the engine, one intake and one exhaust valve per cylinder were actuated by individual pushrods driven by a single camshaft. Each cylinder had two spark plugs—one on each side of the cylinder. The intake and exhaust manifolds were mounted to the outer sides of the cylinder banks. The HM 512 had a 4.13 in (105 mm) bore, a 4.53 in (115 mm) stroke, and a displacement of 729 cu in (11.9 L). The engine produced 450 hp (336 kW) at 3,100 rpm.

FKFS Gruppen-Flugmotor A complete copy

The complete 48-cylinder Gruppen-Flugmotor A. Note the intake manifolds leading from the axial supercharger to the two adjacent V-12 engine sections. The four Bosch magnetos are visible at the rear of the engine. (Kevin Kemmerer image)

For the Gruppen-Flugmotor A, an HM 512 crankshaft occupied each corner of the engine’s large, square-shaped, aluminum crankcase, and a camshaft was located at the apex of each corner. The cylinder banks for each engine section were on adjacent sides of the Gruppen-Flugmotor A’s crankcase. The two-piece aluminum crankcase was split horizontally and incorporated cooling fins on its exterior.

At the front of the Gruppen-Flugmotor A’s crankcase was a central combining gear that took power from each of the four crankshafts and transmitted it to a single propeller shaft. The crankshaft of each engine section could be decoupled from the combining gear if the engine section were damaged or to conserve fuel and increase an aircraft’s range. It was believed that the Gruppen-Flugmotor A’s economy could be increased up to 56% by decoupling two of the engine sections while cruising during a long-range flight.

FKFS Gruppen-Flugmotor A axial supercharger housing copy

The housing for an axial supercharger used on the Gruppen-Flugmotor A. Visible are the four stator rows. Each blade was inserted into a dovetail groove and held in place by a screw, visible on the outside of the housing. (Kevin Kemmerer image)

Another unique feature of the Gruppen-Flugmotor A was its use of two axial superchargers that provided 11.6 psi (0.8 bar) of boost. The left and right sides of the engine each had one supercharger located between the cylinder banks. The axial superchargers had four stages (although photos appear to show three compressor stages and four stator rows) and were driven from the accessory section at the rear of the engine. Fuel was injected ahead of the superchargers and subsequently mixed with air. The air/fuel mixture was then fed to the cylinders via long induction manifolds. The engine’s four Bosch dual magnetos and other accessories were mounted to the rear of the engine.

The Gruppen-Flugmotor A had 48 cylinders with a 4.13 in (105 mm) bore and a 4.53 in (115 mm) stroke. The engine’s total displacement was 2,917 cu in (47.8 L). Unfortunately, most of the engine’s specifications have been lost, but it was around 6.07 ft (1.85 m) long and 4.27 ft (1.30 m) in diameter. The engine produced 1,970 hp (1,470 kW) at 3,200 rpm with manifold fuel injection. A switch to direct fuel injection was made by changing to Hirth HM 512 D cylinders that had an unused port in the cylinder head. With direct fuel injection, the Gruppen-Flugmotor A’s output was increased by 200 hp (150 kW) to 2,170 hp (1,620 kW). The engine was tested during 1941 and 1942, but test information has not been found. Photos indicate some trouble was encountered with the axial superchargers failing in dramatic ways. After the war, Krautter stated that the engine was capable of 2,400 hp (1,790 kW).

FKFS Gruppen-Flugmotor C

This drawing of the Gruppen-Flugmotor C illustrates how the engine design was a link between the Gruppen-Flugmotor A and D engines. Note the cooling fan and side-by-side connecting rods. (“Wunibald I. E. Kamm – Wegbereiter der modernen Kraftfahrtechnik” image)

As the Gruppen-Flugmotor A was proving the concept of a grouped-engine power unit, Kamm, Krautter, and the FKFS had already designed a larger, more powerful engine in 1941. Called the Gruppen-Flugmotor C (or Motor C), the 48-cylinder engine had the same basic layout as the earlier engine but used new components. An engine-driven cooling fan was employed to help minimize cooling drag, as both Kamm and Krautter felt the Gruppen-Flugmotor A’s cooling drag was excessive. The engine also had contra-rotating propeller shafts and two five-stage axial superchargers that provided 11.6 psi (0.8 bar) of boost.

FKFS Gruppen-Flugmotor D Cylinder copy

The 122 cu in (2.0 L) cylinder used on the Gruppen-Flugmotor D. The triangular cover conceals the camshaft drive for the valves. The baffle around the cylinder helped direct air to maximize cooling efficiency. (Kevin Kemmerer image)

The individual cylinders of the Gruppen-Flugmotor C were of Krautter’s maturing design, each having a capacity of 67 cu in (1.1 L). The cylinder had a hemispherical combustion chamber with two spark plugs and a port for direct fuel injection. The cylinder barrel and head were cast from aluminum as one piece, and the cylinder bore was chrome plated. A flange at the base of the cylinder attached it to the crankcase. Atop the cylinder was a housing for the intake and exhaust valves. The two valves were actuated via roller rockers by a single overhead camshaft, which served all the cylinders of one bank. Each camshaft was driven by a vertical shaft at the front of the engine.

The Gruppen-Flugmotor C had a 4.33 in (110 mm) bore, a 4.53 in (115 mm) stroke, and a total displacement of 3,201 cu in (52.5 L). The engine was 7.17 ft (2.185 m) long and 4.43 ft (1.35 m) in diameter. The Gruppen-Flugmotor C was forecasted to produce 3,500 hp (2,610 kW) at 4,000 rpm with the original 67 cu in (1.1 L) cylinders, but studies of larger 92 cu in (1.5 L) and 122 cu in (2.0 L) cylinders indicated outputs of 4,290 hp (3,200 kW) and 5,920 hp (4,415 kW), respectively. While some components of the Gruppen-Flugmotor C were built for testing, a complete engine was never built.

Seeing the potential of the Gruppen-Flugmotor C with 122 cu in (2.0 L) cylinders inspired Kamm and Krautter to create the Gruppen-Flugmotor D. Designed in 1943, the engine was very similar to the Gruppen-Flugmotor C, with 48 cylinders, a cooling fan, and contra-rotating propellers, but it used fork-and-blade connecting rods. The 122 cu in (2.0 L) cylinder was basically an enlargement of the 67 cu in (1.1 L) cylinder design. The Gruppen-Flugmotor D had four (one on each side of the engine) five-stage axial superchargers that provided 13.8 psi (0.95 bar) of boost.

FKFS Gruppen-Flugmotor D copy

Drawing of the 48-cylinder Gruppen-Flugmotor D. Note the cooling fan, contra-rotating propeller drive, and fork-and-blade connecting rods. One five-stage axial supercharger can be seen on the right side of the drawing. The engine was estimated to produce 5,920 hp (6,000 ps / 4,415 kW). (Kevin Kemmerer image)

The Gruppen-Flugmotor D had a 5.31 in (135 mm) bore and a 5.51 in (140 mm) stroke. The engine’s total displacement was 5,870 cu in (96.2 L), and it was forecasted to produce 5,920 hp (4,415 kW) at 4,000 rpm. Reportedly, a complete engine was ready for tests in April 1944, but the state of the war and the progress of jet engines rendered the Gruppen-Flugmotor D and its further development irrelevant. At the time, Germany was in need of interceptor fighters, not long-range bombers.

At war’s end, Kamm and Krautter were brought to the United States under Operation Paperclip, a program to extradite the best German scientists, engineers, and technicians and apply their skills and knowledge to further industries in the United States. The two men worked at Wright Field in Dayton, Ohio until they were released from their service. In the 1950s, Krautter founded his own engineering firm, the Wilkra Company, where he designed everything from engines for boats and motorcycles to lawn tractors and ski bikes.

Kamm 60-cylinder compound-diesel

The Kamm-designed 60-cylinder compound-diesel engine incorporating five V-12 engine sections around a central turbine. The engine’s concept was similar to that of the Napier Nomad. (“Wunibald I. E. Kamm – Wegbereiter der modernen Kraftfahrtechnik” image)

For a time, Kamm worked with Krautter at Wilkra but returned to Germany in 1955. Kamm revisited the Gruppen-Flugmotor concept when he designed a 60-cylinder compound diesel-turbine engine. This engine consisted of five V-12 engine sections mounted around a central turbine. The V-12 engine sections were based on an extremely-high-output diesel engine Kamm had helped design while at the Stevens Institute of Technology in Hoboken, New Jersey in the early 1950s. The V-12s were air-cooled, two-stroke, loop-scavenged engines with side-by-side connecting rods. The turbine had a nine-stage axial compressor section, a combustion section, and a five-stage exhaust turbine section. High-pressure air from the compressor section would provide the incoming charge for the diesel engine. The diesel’s exhaust would be expelled into the exhaust section of the turbine. The turbine’s combustion section could run independently of the piston engine sections to increase the compound engine’s overall output. The engine’s bore and stroke were around 2.75 in (70 mm) and 4.5 in (114 mm), respectively, giving a total displacement of approximately 1,604 cu in (26.3 L). The 60-cylinder compound engine was designed to produce 2,950 hp (2,200 kW) without additional power from the turbine’s combustion section and 4,025 hp (3,000 kW) with the additional power. The engine would have had a low specific fuel consumption of .296 lb/hp/h (180 g/kW/h) and was forecasted to be 6.56 ft (2.00 m) long and 4.10 ft (1.25 m) in diameter. The 60-cylinder engine was never built.

Note: Kamm and Krautter’s Gruppen-Flugmotoren were not the first time that multiple engine sections were combined to create a large, powerful engine. In the 1920s, the French firm Bréguet created the Bréguet-Bugatti 32-cylinder Quadimoteurs in a similar but less complex fashion.

FKFS Gruppenmotor 48-Zyl copy

This drawing dated October 1943 depicts a 48-cylinder engine and lists its displacement as 37.6 L (2,294 cu in). The engine’s bore and stroke appear to be the same but are not listed on the drawing. A 100 mm (3.94 in) bore and stroke would give a displacement of 37.70 L (2,300 cu in). It is not clear how this engine fits into the overall history of the Gruppen-Flugmotoren, but its design is similar to the C and D engines. (Kevin Kemmerer image)

Correspondence with Kevin Kemmerer, grandson of Willy Krautter
Wunibald I. E. Kamm – Wegbereiter der modernen Kraftfahrtechnik by Jurgen Potthoff and Ingobert C. Schmid (2012)
“Why Multicylinder Motorcycle Engines?” by W. Krautter, Design of Racing and High Performance Engines edited by Joseph Harralson (1995)
Aircraft Engines of the World 1944 by Paul H. Wilkinson (1944)
Engine-Transmission Power Plants for Tactical Vehicles by Emil M. Szten et. al. (1967)