Category Archives: Between the Wars


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 (O standing for Ölmotor, or oil engine), 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.

Daimler-Benz LOF-6 DB602 V-16 diesel engine

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)


Tips Aero Motor Rotary Aircraft Engines

By William Pearce

From a very early age, Maurice A. Tips and his younger brother Ernest Oscar were interested in aviation. By 1909, 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 Ernest Oscar Tips’ 1909 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 1909 aircraft, Maurice refocused his efforts on aircraft engines. By 1911, Maurice had designed the first in a series of “valveless” rotary engines. All of Tips’ engines used a rotary valve system for cylinder intake and exhaust. Unfortunately, documentation on these engines is nearly non-existent; their exact order of development and specifications are not known with certainty.


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).

The first engine was a seven-cylinder rotary that produced 25 hp (19 kW). 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.

The 25 hp (19 kW) Tips “valveless” rotary engine was installed in a monoplane built by Henri Gérard. It appears the aircraft was completed around 1913. However, the performance results of the engine and aircraft have not been found. As history unfolded, this was the only Tips engine installed in an aircraft.

Maurice and EO Tips Gerard monoplane

Henri Gérard and his mechanic by Gérard’s Tips-powered monoplane. The engine was a 25 hp (19 kW) seven-cylinder “valveless” rotary. Note the spark plug protruding from the top of each cylinder. (Tips Family Archive via Vincent Jacobs)

Maurice continuously refined the design of “valveless” rotary engines. In late 1912, two larger versions of the seven-cylinder engine were planned. A 50 hp (37 kW) version had a 4.33 in (110 mm) bore, a 4.72 in (120 mm) stroke, and a displacement of 487 cu in (8.0 L). The largest engine produced 70 hp (52 kW) and had a 4.41 in (112 mm) bore, a 5.12 in (130 mm) stroke, and a displacement of 547 cu in (9.0 L). An advertisement stated that all three engines would be displayed at the Salon de l’Automobile held in Brussels, Belgium in January 1913. In addition, the 25 hp (19 kW) engine was used to power a Tips airboat that was displayed at the show.

Engine development continued 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 earlier engines. 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 nine-cylinder engine of this design was built, but it is not clear if the engine was built in Europe or the United States; it was most likely built in the US.


The 1913 (left) and 1914 (right) versions of the Tips rotary engine. The major changes were to the suction tube drive and rotary valve. 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.

When World War I broke out, Maurice and Ernest Tips fled Belgium. Ernest made his way to Britain, where he worked with Charles Richard Fairey and helped start the Fairey Aviation Company in 1915. Ernest 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 US in October 1915 and continued to design aircraft engines. It is quite possible that the nine-cylinder engine was built once Tips had established himself in the US. The engine had a 4.92 in (125 mm) bore and a 5.91 in (150 mm) stroke. It displaced 1,011 cu in (16.6 L) and produced 110 hp (82 kW). The nine-cylinder engine was approximately 35 in (.89 m) in diameter and weighed 290 lb (132 kg). A smaller nine-cylinder engine was designed, but it is not clear if it was built. The smaller engine had a 4.92 in (125 mm) bore and a 5.51 in (140 mm) stroke. It displaced 944 cu in (15.5 L) and produced 100 hp (75 kW).

Tips 9-cylinder rear

Rear view of the 110 hp (82 kW) nine-cylinder Tips “valveless” rotary engine. Air was drawn in through the hollow extension to the crankshaft where it mixed with fuel. Ports in the crankshaft extension led to a distribution chamber at the back of the engine. The air/fuel mixture was drawn into the suction tube behind each cylinder and then into the combustion chamber. (Tips Family Archive via Vincent Jacobs)

For more power, Maurice had the idea of coupling two 110 hp (82 kW) nine-cylinder engines in tandem to make an 18-cyinder power unit. The two engine sections would be placed front-to-front and rotate in the same direction. The engines would be suspended some 20 in (508 mm) below the propeller shaft. A Renold Silent (inverted tooth) drive chain positioned between the two engines would deliver power to the propeller shaft. By varying the size of the drives, a propeller speed reduction could be achieved. Drawings show a 5 in (127 mm) drive gear and a 7.5 in (191 mm) gear on the propeller shaft, which would give a .667 speed reduction. The tandem 18-cylinder engine had an output of 220 hp (164 kW) and was 606 lb (275 kg). The power unit was 62 in (1.57 m) long and 40 in (1.02 m) in diameter, not including the propeller shaft. It is unlikely that a tandem engine was built.

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. Rather than a tandem engine, the new Tips engine was a single, 18-cylinder power unit. The rotary engine had two rows of nine cylinders and was 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.

Tips Tandem 18-cylinder engine

The Tips Tandem engine consisted of two nine-cylinder engines coupled together. An inverted tooth chain between the engines delivered power to the propeller shaft. (Tips Family Archive via Vincent Jacobs)

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.


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.

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.

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.


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.

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.

Tips 18-cylinder engine crankcase

Maurice Tips stands next to the unfinished crankcase casting for the 18-cylinder differential rotary engine. The holes in the crankcase’s outer diameter were for the rotary valves. The holes in the crankcase’s face were for water radiators, and the holes inside of the crankcase were for the cylinders. It is not known if a complete engine was built. (Tips Family Archive via Vincent Jacobs)

Les Avions Tipsy by Vincent Jacobs (2011)
– “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)

Hispano-Suiza 24Y Type 90 side

Hispano-Suiza 24Y (Type 82 and Type 90) Aircraft Engine

By William Pearce

In 1936, the Ministère de l’Air (French Air Ministry) issued a specification for a 2,000 hp (1,491 kW) engine intended to power a flying boat for transatlantic service. The aircraft was to carry at least 40 passengers and 1,100 lb (500 kg) of cargo 3,725 miles (6,000 km) against a 37 mph (60 km/h) headwind. Hispano-Suiza already had its 12Y engine of 1,000 hp (746 kW) in production and was investigating ways to effectively double that engine. Their design efforts led to the 24-cylinder Hispano-Suiza 24Y aircraft engine.

Hispano-Suiza 24Y Type 82 front 2

The Hispano-Suiza 24Y Type 82 24-cylinder H engine on display in the Polish Aviation Museum in Krakow. The Type 82 was intended for use with contra-rotating propellers; however, its original propeller shaft is missing.

The idea behind the 24Y engine was to utilize as many 12Y engine components as possible. The Hispano-Suiza 12Y engine was a liquid-cooled V-12. Each bank of six cylinders was cast en bloc with an integral cylinder head. The 12Y had a 5.91 in (150 mm) bore, a 6.69 in (170 mm) stroke, and a total displacement of 2,200 cu in (36.05 L). The 12Y-50 was one of the last and most powerful versions of the engine; it produced 1,100 hp (820 kW) at 2,500 rpm.

The 24Y engine’s configuration was a vertical H-24: two cylinder banks were mounted vertically above the crankcase, and two cylinder banks were below. A crankshaft served each upper and lower cylinder bank pair. Four aluminum 12Y-50* cylinder blocks were mounted on the 24Y’s crankcase. Each cylinder block included two valves per cylinder, a single overhead camshaft, and the camshaft’s vertical drive shaft. The 7 to 1 compression pistons were connected to the hollow, one-piece crankshaft via fork-and-blade connecting rods, and all components were from the 12Y engine. Each crankshaft had six throws and was supported by seven main bearings. The two-piece, aluminum crankcase was formed by an upper and lower half and was unique to the 24Y.

Hispano-Suiza 24Y Type 90 rear

Rear view of the Hispano-Suiza 24Y (Type 90) showing the engine’s four magnetos, two superchargers, four fuel pumps, and two coolant pumps.

At the rear of the engine, each crankshaft drove a single-speed supercharger at 10 times crankshaft speed. The superchargers gave the engine 2.3 psi (.16 bar) of boost. Separate intake manifolds led from each supercharger to the upper and lower cylinder banks on one side of the engine. Three carburetors were positioned along each intake manifold. Each of the engine’s 12 carburetors supplied the air/fuel mixture to a pair of cylinders.

The two spark plugs per cylinder were fired by four magnetos driven from the rear of the engine. Two magnetos were located above each supercharger. Four fuel pumps were mounted below and between the superchargers. The left and right sides of the engine had separate coolant systems, and a coolant pump was located below each supercharger.

At the front of the engine, each crankshaft had a 28-tooth gear that engaged a 55-tooth propeller gear. This combination created a .509 to 1 gear reduction for the propeller shaft. Between each crankshaft and its power gear was a Sarazin torsional vibration damper. Two versions of the 24Y were built, and they differed in their propeller drive. The 24Y Type 82 was designed to power contra-rotating propellers. In this engine, one crankshaft drove the inner propeller shaft while the other crankshaft drove the outer propeller shaft. The 24Y Type 90 was designed to power a single-rotation propeller and was available with either a normal length or extended gear reduction nose case. Some sources state the Type 90 had accommodations for a cannon to fire through the propeller shaft, but photos indicate this was unlikely.

Hispano-Suiza 24Y Type 90 side

Hispano-Suiza 24Y Type 90 engine with its extended gear reduction case for a single rotation propeller. This engine was displayed at the 1938 Salon de l’Aéronautique in Paris. Note the three carburetors for each cylinder bank.

The Hispano-Suiza 24Y had a 5.91 in (150 mm) bore and a 6.69 in (170 mm) stroke. The engine’s total displacement was 4,400 cu in (72.10 L). The 24Y produced 2,200 hp (1,641 kW) at 2,500 rpm for takeoff. Max power was 2,000 hp (1,491 kW) at 2,400 rpm at 10,827 ft (3,300 m), and cruising power was 1,500 hp (1,119 kW) at 2,250 rpm at 10,827 ft (3,300 m). The engine had a specific fuel consumption of .50 lb/hp/hr (304 g/kW/hr). The Type 82 was 6.46 ft (1.97 m) long, 3.05 ft (.93 m) wide, and 4.27 ft (1.30 m) tall. The engine weighed 2,204 lb (1,000 kg). The Type 90 had the same width and height as the Type 82 but was 3.38 ft (1.03 m) longer with the extended gear reduction case, for a total length of 9.84 ft (3.00 m). The Type 90’s weight was listed as 2,161 lb (980 kg).

Exactly when the 24Y was first run has been lost to history. The engine made its public debut in November 1938 at the Salon de l’Aéronautique (Air Show) in Paris, France. A Type 90 engine was displayed there, and it attracted a lot of attention. Unfortunately for Hispano-Suiza, that attention did not translate into sales. War in Europe was imminent by 1939, and Hispano-Suiza had turned its attention to developing the new 12Z engine. The 12Z was the next evolutionary step beyond the 12Y for Hispano-Suiza’s V-12 engines. War would interrupt the 12Z’s development, but the 12Z would later inspire another 24-cylinder engine known as the 24Z, which was configured like the 24Y. It is doubtful that the 24Y was ever flown.

Hispano-Suiza 24Y Type 82 side

The preserved 24Y Type 82 engine is missing many components. Note the vertical drive shaft for the camshaft at the end of each cylinder bank. (Polish Aviation Museum image)

Only a small number of 24Y engines were built—probably just one Type 82 and one Type 90 with an extended gear reduction case. Having disappeared during World War II, the disposition of the Type 90 is not known. The Type 82 wound up in Poland at the end of World War II. Most likely, it was part of Herman Goering’s aviation collection that was moved to Poland late in the war to keep it from being damaged during Allied bombing raids. The Hispano-Suiza 24Y Type 82 engine is currently preserved (without its original propeller shaft) and on display in the Polish Aviation Museum in Krakow.

*Some sources state that 12Y-51 cylinder blocks were used on the 24Y. The 12Y-50 and 12Y-51 were basically the same engine, the only difference being the crankshaft rotation. When viewed from the rear, the 12Y-50 rotated counter clockwise; the 12Y-51 rotated clockwise. The cylinder blocks of the 12Y-50 and 12Y-51 engines were the same.

Hispano-Suiza 24Y Type 82 rear

The supercharger impellers can be seen in this view of the 24Y Type 82. Although the magnetos are gone, the fuel pumps and one coolant pump remain. (Polish Aviation Museum image)

Aircraft Engines of the World 1941 by Paul H. Wilkinson (1941)
Hispano Suiza in Aeronautics by Manuel Lage (2004)
Jane’s All the World’s Aircraft 1939 by C. G. Grey and Leonard Bridgman (1939)
– “Some Trends in Engine Design” Flight (8 December 1938)

Armstrong Siddeley Deerhound III

Armstrong Siddeley ‘Dog’ Aircraft Engines

By William Pearce

The British firm Armstrong Siddeley Motors (ASM) was formed in 1919 when Armstrong Whitworth (founded in 1847) purchased Siddeley-Deasy (founded in 1912). Prior to the merger, both Armstrong and Siddeley were active in the automotive and aeronautical fields. Siddeley first began manufacturing aircraft engines in 1915 under a contract to build the Royal Aircraft Factory’s RAF 1A engine. In 1916, Siddeley had built its first aircraft engine—the Puma—which was developed from the B.H.P. (Beardmore-Halford-Pullinger) six-cylinder engine. The Puma was the first in a long line of engines that were produced by ASM into the 1940s and named after cats (felines)—the last being the Cougar of 1945.

Armstrong Siddeley Hyena AW16

Two versions of the cowling used to cover the 15-cylinder Armstrong Siddeley Hyena installed in an Armstrong Whitworth A.W.XVI (A.W.16). The cowling on the right is illustrative of the Hyena’s inline radial cylinder arrangement.

In 1932, ASM worked to develop a new line of air-cooled, radial engines. These engines would be a design departure from their existing cat-engines, so they decided to name the engines after dogs (canines). Unfortunately, none of these engines were successful, and information about them is frustratingly hard to find and occasionally contradictory. To add to the confusion, some of the engine names were used more than once, and the engines possess many of the same characteristics.

The first engine of the new dog-series was the Mastiff (this name was used again later). This engine was built in 1932 and was a large radial engine with two rows of seven cylinders. The specifications of the 14-cylinder engine are currently not known. In reviewing a photo (that is unfortunately not publishable) of the Mastiff, the engine closely resembles a larger version of the 1,996 cu in (32.7 L) ASM Tiger in appearance and construction. The Mastiff was supercharged and had a one-piece crankcase and gear reduction. A cam ring at the front of the engine acted on pushrods that actuated each cylinder’s two valves. One Mastiff was built for Italy, but it is not known if the engine was ever tested.

Armstrong Siddeley Deerhound I side

This photo gives a good view of the 21-cylinder Armstrong Siddeley Deerhound I’s configuration. Note the engine’s inline radial layout and the vertical shaft in front of each cylinder bank to drive the overhead camshaft.

The second dog-engine was the Hyena. The Hyena’s 15 air-cooled cylinders were arranged in three rows of five. Even more unusual than the three-row arrangement was the fact that the cylinder rows were inline rather than staggered. Between each of the engine’s five cylinder banks was a camshaft that acted upon short pushrods to actuate the two valves per cylinder. The camshafts were geared to the crankshaft.

The Hyena had a 5.39 in (137 mm) bore and a 4.92 (125 mm) stroke. The engine’s total displacement was 1,687 cu in (27.64 L), and it produced 620 hp (462 kW) at 2,250 rpm. The Hyena was first run in 1933 and was installed in an Armstrong Whitworth A.W.XVI (A.W.16) biplane fighter later that year. The Hyena-powered A.W.XVI (registered as G-ABKF) first flew on 25 October 1933. The basic engine proved itself to be mechanically sound but rather heavy for its power. Issues were encountered with cooling the rear cylinders. This led to a number of different engine cowlings being tried, but the overheating issues persisted. Eventually, further development of the Hyena was abandoned, and only one or two engines were built. The Hyena was proposed to power the A.W.21 and A.W.28 fighters, but these projects did not proceed past the design stage.

Armstrong Siddeley Deerhound I rear

This rear view of the Deerhound I shows the supercharger housing with intake manifolds leading to each bank of cylinders.

Lessons learned from the Hyena were applied to the next dog-engine: the Deerhound. Led by Lt. Col. F. L. R. Fell, the design of the Deerhound was underway by late 1935, and it retained the inline radial cylinder configuration of the Hyena. However, the Deerhound had two addition cylinders for each row, making three rows of seven cylinders. Each cylinder bank of the Deerhound used a single overhead camshaft to actuate each cylinder’s two valves. The camshafts were driven from the crankshaft by a vertical shaft at the front of the engine. The Deerhound had a single-stage, two-speed supercharger and a propeller reduction gear of .432.

The 21-cylinder Deerhound had a 5.31 in (135 mm) bore and a 5.00 in (127 mm) stroke. The engine displaced 2,330 cu in (38.18 L) and had a forecasted output of 1,500 hp (1,119 kW). The Deerhound was seen as insurance against the potential failure of the Bristol Hercules engine then under development. The designers of the Deerhound would have preferred to create a liquid-cooled engine in the 1,500 hp (1,119 kW) class, but ASM management (John Siddeley) insisted on air-cooling. One of the engine’s designers, W. H. “Pat” Lindsey, stated the engine was “old-fashioned” and did not possess many then-modern refinements.

Armstrong Siddeley Deerhound construction

This photo shows five Deerhound engines in various stages of assembly. Most likely, all of the engines are Deerhound Is, but it is possible one is a Deerhound II. From left to right, the engines appear to be numbered D1, D5, D3, D4, and D2. The engine marked D5 is definitely a Deerhound I.

The Deerhound was first run in 1936, and it was not long before cooling and other problems were encountered. Most likely, five engines were built, and the last achieved 1,370 hp before it failed. In 1937, the ASM board tasked Fell to redesign the engine to cure its ills. The redesign resulted in the Deerhound II, which will be described later. The Deerhound was proposed for the Armstrong Whitworth A.W.42 heavy bomber.

Another engine from 1935 was the Terrier. The Terrier was a two-row radial engine in which each row had seven cylinders. Again, specifics of the engine’s configuration are not available, but most likely the Terrier was effectively a two-row, 14-cylinder Deerhound. Retaining the Deerhound’s 5.31 in (135 mm) bore and a 5.00 in (127 mm) stroke, the engine would have a displacement of 1,553 cu in (24.45 L). The Terrier had a 6.6 to 1 compression ratio.

Armstrong Siddeley Deerhound II side

An Armstrong Siddeley Deerhound II partially assembled. The front of the engine, gear case, and valve covers have all be redesigned from that used on the Deerhound I. Note the overhead camshaft and valve arrangement visible on the upper cylinder bank.

Like the Deerhound, the Terrier had a single-stage, two-speed supercharger. The engine produced a maximum of 550 hp (410 kW) at 2,700 rpm for takeoff, 510 hp (380 kW) at 2,100 rpm at 6,500 ft (1,981 m), and 476 hp (355 kW) at 3,100 rpm at 14,700 ft (4,481 m). Normal outputs were 470 hp (350 kW) at 2,700 rpm at 5,000 ft (1,524 m), and 450 hp (336 kW) at 2,700 rpm at 12,000 ft (3,658 m). The Terrier was proposed for a number of projects including the Armstrong Whitworth F.9/35 turret fighter proposal, the Blackburn M.15/35 torpedo bomber proposal, and the Avro 672 and 675 multi-role aircraft designs. None of those projects were built, and work on the Deerhound prevented the Terrier from being constructed.

Also in 1935, the Whippet was designed. Specifics of the Whippet are not available, but the 250 hp (186 kW) engine may have had two rows of seven cylinders with a bore and stroke of around 4.02 in (102 mm). That cylinder size would give the engine a total displacement of around 712 cu in (11.67 L). The Whippet did not proceed beyond the design phase.

The next engine design was initiated around 1936 and was for the Wolfhound (this name was used again later). The inline radial Wolfhound was an outgrowth of the Deerhound and had four rows of seven cylinders. Specifics of the engine are not available. However, 28 cylinders with the Deerhound’s 5.31 in (135 mm) bore and 5.00 in (127 mm) stroke would displace 3,106 cu in (50.90 L) and produce around 1,800 hp (1,342 kW). The Wolfhound did not make it off the drawing board.

Deerhound II engine Whitley

A Deerhound II engine installed in an Armstrong Whitworth A.W.38 Whitley bomber. Note the relatively small diameter of the engine compared to that of the firewall. The 44 in (1.12 m) diameter Deerhound replaced the 51 in (1.29m) diameter Armstrong Siddeley Tiger that was originally installed in the Whitley II.

In 1937, the Deerhound was redesigned and became the Deerhound II. The engine’s configuration changed little. However, refinements were made, and the cylinder bore was increased from 5.31 in (135 mm) to 5.51 in (140 mm). The stroke was unchanged, but the larger bore increased the engine’s displacement by 175 cu in (2.88 L), bringing the total displacement to 2,505 cu in (41.06 L). The engine’s forecasted output was still 1,500 hp (1,119 kW). The Deerhound II had a 6.75 to 1 compression ratio and was 44 in (1.12 m) in diameter. Extensive baffles were installed around the cylinders to help direct air flow and cool the rear cylinders.

The Deerhound II was first run in 1938, but more issues were encountered, including a broken crankshaft during a type test in October 1938. Fell and his team were under immense pressure from the ASM board to fix the engine’s issues. Two Deerhound II engines were installed in an Armstrong Whitworth A.W.38 Whitley bomber (serial no. K7243) for flight tests, and the aircraft first flew in January 1940. Fell’s contract with ASM was not renewed when it expired on 9 February 1939. Lindsey temporarily took over Deerhound development until Stewart S. Tresilian was brought on staff in mid-1939.

Deerhound engine cowling Whitley

Any aerodynamic advantages achieved by the close-fitting cowling covering the Deerhound engine installed on the Whitley must have been undermined by the bulbous cooling-air intake under and the large induction scoop above the engine. This Whitley was eventually lost, but through no fault of the engines.

Although the date is not recorded, the engine did achieved and output of 1,500 hp (1,119 kW) at 2,975 rpm with 5 psi (.34 bar) of boost. On the Whitley bomber, the engines were housed in special nacelles. Cooling air was taken in under the spinner and directed from the rear of the engine forward through the cylinders. However, engine cooling issues persisted, and the designers believed increasing the cooling fin area of the cylinders would resolve the problem.

Flight testing continued until 6 March 1940 when the Deerhound II-powered Whitley bomber was lost on takeoff, killing all three people on board. The crash was attributed to an improperly set trim tab and had nothing to do with the engines. With the testbed destroyed, ASM decided to curtain development of the Deerhound II and focus on an improved version that would cure the overheating issues. The new engine, the Deerhound III, will be described later. Five Deerhound II engines were built.

Armstrong Siddeley 36-cyl Mastiff

This drawing illustrates a coupled arrangement for two 36-cylinder Armstrong Siddeley Mastiff engines. The engine’s nine banks of four cylinders can be deduced from the drawing. A similar arrangement was purposed with two Deerhound engines.

In 1937, the Boarhound was designed. This engine possessed the larger 5.51 in (140 mm) bore of the Deerhound II and had a longer 6.30 in (160 mm) stroke. The real design change was the engine’s layout—the Boarhound had three inline rows of nine cylinders. With its 27 cylinders, the Boarhound displaced 4,058 cu in (66.50 L). Its initial and rather conservative estimated output was 2,300 hp (1,715 kW) at 2,700 rpm. The Boarhound had a diameter of 51 in (1.30 m). With all resources focused on the Deerhound, the Boarhound was never built.

Around 1938, the Mastiff name was resurrected and given to a further development of the Boarhound. The new Mastiff had four inline rows of nine cylinders. While the cylinder’s bore was still 5.51 in (140 mm), the stroke was lengthened to 6.69 in (170 mm). The 36 cylinders of the Mastiff engine displaced an impressive 5,749 cu in (94.21 L), and output was estimated at 4,000 hp (2,983 kW). Like the Boarhound, the Mastiff was not developed.

In 1940, Tresilian went to work on the Deerhound III to create an engine free from the issues experienced with the original Deerhound and the Deerhound II. The Deerhound III possessed the same bore, stroke, displacement, and 44 in (1.12 m) diameter as the Deerhound II. However, the engine was essentially redesigned, and its output was increased to 1,800 hp (1,342 kW). The engine was first run in late 1940. High-power tests revealed detonation issues with the first row of cylinders, but some sources state the engine did achieve 1,800 hp (1,342 kW) on the dyno. An updated design, the Deerhound IV, was proposed but never built. Only one Deerhound III was built.

Armstrong Siddeley Deerhound III

This picture shows the sole Armstrong Siddeley Deerhound III engine. Again, revisions to the front of the engine, gear reduction, and valve covers can easily be seen. Reportedly, this engine survived into the 1970s.

In mid-1941, the Wolfhound name was reused for a new Tresilian-designed engine. The new Wolfhound had four inline rows of six cylinders in a flattened X configuration. The 24-cylinder engine had a 5.91 in (150 mm) bore and a 5.51 in (140 mm) stroke. Total displacement was 3,623 cu in (59.38 L), and the engine was to produce 2,600–2,800 hp (1,939–2,088 kW) at 2,800 rpm. The engine had a two-stage supercharger and was designed to power contra-rotating propellers.

In October 1940, a bombing raid severely damaged the Armstrong Siddeley Aero Development shop and destroyed several Deerhound engines. Another raid on 8 April 1941 further damaged the shop and set engine development back even more. ASM dog-engine development continued at a slow pace until October 1941, when the British Ministry of Aircraft Production (MAP) cancelled further work. The ASM dog-engines would not be ready in time to be of any use in the war, and the MAP wanted the company to focus on turbine engines (ASM named theirs after snakes). The sole Deerhound III engine was thought to have survived into the 1970s, but there are no known ASM dog-engines currently preserved.

Armstrong Siddeley Deerhound IV

Drawing of the Armstrong Siddeley Deerhound IV engine that was never built. Even if this design from 1941 proved successful, it would not have been developed in time to see much use during World War II.

Armstrong Siddeley — the Parkside Story 1896–1939 by Ray Cook (1988)
Parkside: Armstrong Siddeley to Rolls-Royce 1939–1994 by Roy Lawton (2008)**
Sectioned Drawings of Piston Aero Engines by Lyndon Jones (1995)**
Armstrong Whitworth Aircraft since 1913 by Oliver Tapper (1973)
British Secret Projects: Fighters & Bombers 1935–1950 by Tony Buttler (2004)
British Piston Aero-Engines and Their Aircraft by Alec Lumsden (1994/2003) (and pages therein)

**Rolls-Royce Heritage Trust books that are currently in print and available from the Rolls-Royce Heritage Trust site.

Sunbeam Sikh I

Sunbeam Sikh I, II, and III Aircraft Engines

By William Pearce

Toward the end of World War I, a number of companies were pursuing the concept of a very large engine powering a very large aircraft. Just about every country that had extensive experience in the field of aeronautics expended resources to create the large engine and aircraft combination. As history unfolded, all of these projects came to naught, although the experience gained did pave the way for future projects.

Sunbeam Sikh I

Side view of the 800 hp (597 kW) Sunbeam Sikh I V-12 engine. Carburetors can be seen attached to the first and last cylinders. Note the two water pumps under the engine and the exposed valves.

The Sunbeam Motor Car Company based in Wolverhampton, England had added aircraft engine design and manufacture to its existing automotive business in 1913. Sunbeam’s aircraft engines were designed by Louis Coatalen, their chief engineer, and were sometimes referred to as Sunbeam-Coatalen Aircraft Engines. As with so many other companies, Sunbeam designed a large aircraft engine during the closing days of World War I. This large engine was named Sikh (or Sikh I), and it was intended for use in either large aircraft or airships.

The Sikh was a 60 degree V-12 engine. Its individual cylinders were a departure from the standard Coatalen-designed engines. The cylinders were machined from steel forgings and had welded sheet metal water jackets. Each cylinder had four spark plugs positioned under its six exposed valves. The three intake valves were positioned on the Vee side of the cylinder, and the three exhaust valves were positioned on the outside of the cylinder. The intake and exhaust valves were operated by separate rocker groups positioned above the valves. This configuration allowed all intake (or exhaust) valves to be opened or closed simultaneously. Each rocker group was actuated by a pushrod that was driven by a camshaft mounted in the Vee of the engine and geared to the crankshaft. Four magnetos at the rear of the engine fired the spark plugs.

Sunbeam Sikh I Ad copy

A Sunbeam Sikh ad from 1920 touts the engine as the most powerful in the world but prophetically adds, “at the moment.” The Duesenberg H developed at the same time as the Sikh I had the same output, and the 1,000 hp (746 kW) Napier Cub would eclipse both engines later in 1920.

Two water pumps were positioned under the engine and driven by vertical shafts from an accessory gear. Each pump supplied cooling water to one cylinder bank. The Sikh had four carburetors—one attached to the first and last cylinders of each row. For each cylinder row, the air/fuel mixture flowed through an intake manifold attached to the cylinders inside the Vee of the engine. The engine used aluminum pistons mounted to H section, forked connecting rods attached to the crankshaft. The hollow crankshaft was made of nickel-chromium steel. Via spur reduction gears, the propeller shaft turned at 0.657 engine speed. The crankcase of the Sikh was an aluminum casting.

The Sunbeam Sikh had a 7.09 in (180 mm) bore and 8.27 in (210 mm) stroke. The engine’s total displacement was 3,913 cu in (64.1 L), and it produced 800 hp (597 kW) at 1,400 rpm. The Sikh had a dry weight of 1,952 lb (885 kg).

The engine was first run on 11 May 1919 and was displayed at a number of aviation shows. Although the Sikh passed British Air Ministry tests to prove its airworthiness, Sunbeam did not receive any orders for the engine. Large engines and large aircraft were simply not practical in the early 1920s, and there was little interest in airships in the immediate post-war era.

In addition to the Sikh, Sunbeam co-developed a smaller engine known as the Sikh II (or Semi-Sikh). The inline-six Sikh II was essentially half a Sikh. The cylinders were the same but they were mounted on a new crankcase. The Sikh II was direct drive without any gear reduction, and the camshaft was mounted on the left side of the engine. With the same bore and stroke as the Sikh, the Sikh II had a total displacement of 1,956 cu in (32.1 L) and produced 425 hp (317 kW) at 1,400 rpm. The engine had a dry weight of 1,120 lb (508 kg). Unfortunately for Sunbeam, the Sikh II, like the Sikh, found no applications.

Sunbeam Sikh I Olympia 1920

The Sunbeam Sikh I as displayed at the Olympia Air Show in 1920. Note the two spark plugs positioned under the valves on both sides of the cylinder, the pushrods in the Vee of the engine, and the four magnetos. In the left corner of the picture is the Short Silver Streak. (Stilltime Collection Image)

By 1927, British airship development had been renewed, and the R100 and R101 programs were underway. Sunbeam saw a new opportunity for the Sikh engine and developed the Sikh III strictly for airship use. The Sikh III was again a 60 degree V-12 engine, and most sources say it possessed the same bore, stroke, and displacement as the original Sikh. However, some original sources (Jane’s and Flight) say the bore was increased to 7.28 in (185 mm), which would give a total displacement of 4,134 cu in (67.7 L).

The individual cylinders of the Sikh III were redesigned and refined using a carbon steel barrel and a cast steel head. In addition, the valve train was completely redesigned. Each cylinder still had three exhaust valves, but the number of intake valves was reduced to two. The valves for each cylinder were enclosed in a common rocker cover. The rockers extended though the cover and were actuated by pushrods that ran between the cylinders. On the left cylinder bank, the exhaust rocker arm protruded out the rear of the cover, and the intake rocker arm protruded out the front. This configuration was reversed for the right cylinder bank. The crankshaft was forged from nickel-chromium steel and had six throws. Each cylinder had two spark plugs that were enclosed by the rocker cover. The spark plugs were fired by two magnetos driven at the rear of the engine.

Sunbeam Sikh II

The inline-six Sunbeam Sikh II was essentially half a Sikh I. Note the camshaft and pushrod arrangement in the rear view on the left. The front view image on the right illustrates the engine’s carburetors, valves, and lack of a propeller gear reduction.

The engine used two carburetors, which, along with the intake manifolds, were positioned in the Vee of the engine. Each carburetor supplied the air/fuel mixture to three cylinders of each bank. The propeller shaft of the Sikh III was geared to the crankshaft at a 0.567 reduction. The Sikh III produced 1,000 hp (476 kW) at 1,650 rpm and had a dry weight of 2,760 lb (1,252 kg). The engine was 7 ft 2 in (2.2 m) long, 3 ft 4 in (1.0 m) wide, and 6 ft 2 in (1.9 m) tall.

The Sikh III was first run in 1928 and was displayed at shows in 1929 and 1930. However, engines for the R100 and R101 airships had already been selected. The disastrous crash of the R101 airship in 1930 caused Britain to cease all further airship development, leaving the Sikh III without any possible applications.

Only small numbers of Sikh I, Sikh II, and Sikh III engines were built. Like many large aircraft engines built over the years, the Sunbeam Sikh engines were never installed in any aircraft or airships.

Sunbeam Sikh III

The Sunbeam Sikh III was intended for airship use but never found an application. Note the new cylinder heads. The exhaust valve pushrod can been seen on the rear left cylinder.

Sunbeam Aero-Engines by Alec Brew (1998)
Aerosphere 1939 by Glenn D. Angle (1940)
Jane’s All the World’s Aircraft 1927 by C. G. Grey
Jane’s All the World’s Aircraft 1929 by C. G. Grey
– “The Sunbeam Motor Car Co., Ltd.” The Aeroplane (31 December 1919)
– “Aero Engines at Olympia” The Aeroplane (21 July 1920)
– “The Sunbeam Motor Car Co., Ltd.” Flight (18 July 1929)

Breguet-Bugatti 32A test

Bréguet-Bugatti 32A and 32B Quadimoteurs

By William Pearce

During World War I, Ettore Bugatti designed and built a U-16 aircraft engine. The engine consisted of two inline eight-cylinder sections mounted side-by-side on a common crankcase. Each eight-cylinder engine section had its own crankshaft and was built up of two four-cylinder blocks. The engine’s two crankshafts directly engaged a common propeller shaft. The Bugatti U-16 engine had a 4.33 in (110 mm) bore and a 6.30 in (160 mm) stroke. Total displacement was 1,485 cu in (24.3 L), and the engine produced 400 hp (298 kW) at 2,100 rpm.

Breguet-Bugatti 32A test

Two 16-cylinder engines positioned front-to-front comprised the Bréguet-Bugatti 32A (Quadimoteur Type A). From the gearbox between the two engines, the propeller shaft extended between the cylinder banks of the front (lower) engine. (Musée de l’Air et de l’Espace image via The Bugatti 100P Record Plane)

Each group of four cylinders had one carburetor attached to an intake manifold on the outside of the engine. The exhaust manifolds were between the cylinder banks. Two spark plugs for each cylinder were positioned on the intake side of the engine, and each cylinder had two intake valves and one exhaust valve. The valves were actuated by a single overhead camshaft that was driven via beveled gears by a vertical shaft positioned between the two blocks of four-cylinders that comprised the eight-cylinder engine section. The vertical shaft also drove the engine’s magnetos. Water was circulated through the engine by pumps driven at the rear of each crankshaft. A single housing for the camshaft served both four-cylinder blocks on one side of the engine.

Bugatti did not have the production capacity to manufacture the engine, so licensed production was undertaken in France by a group headed by Peugeot. An additional license was sold to the United States (the engine was built as the King-Bugatti by Duesenberg). Developmental and production issues resulted in few Bugatti-based U-16 engines being built during World War I. After the war, the licensed manufacturers moved on to other projects, and the French aviation firm Bréguet (Société des Ateliers d’Aviation Louis Bréguet) took over development of the Bugatti U-16 engine in 1919.

Breguet Type XXI and 32A

The Bréguet Type XXI Leviathan airframe fitted with the Bréguet-Bugatti 32A engine at the Salon de l’Aviation in Paris in 1921. The 32A installation in the Type XX was essentially the same. Note the U-16 engine to the left.

Bréguet made a few modifications to the Bugatti U-16 engine. Their first U-16 engines had a 4.25 in (108 mm) bore and a 6.30 in (160 mm) stroke. Total displacement was decreased by 54 cu in (.8 L) to 1,431 cu in (23.5 L), and the engine produced 480 hp (358 kW) at 2,150 rpm. A further development of the U-16 engine was the U.24. The U.24 engine had a 4.25 in (108 mm) bore and a 6.42 in (163 mm) stroke. Total displacement was 1,458 cu in (23.9 L), and the engine reportedly achieved 600 hp (447 kW) at 2,800 rpm.

A major change with the U.24 was how the propeller shaft was driven. In the original engine, if one of the two eight-cylinder sections were to fail, it would cause the entire engine to stop because the crankshafts were directly geared to the propeller shaft. In the Bréguet-Bugatti U.24 engine, the crankshafts drove the propeller shaft through freewheeling (or overrunning) clutch mechanisms. If one eight-cylinder engine section were to fail, the clutch would simply disengage the dead section’s crankshaft from driving the propeller shaft and allow the good engine section to continue to produce power. The two engine sections did share a common oil supply, so they were not completely independent.

Breguet Type XX and 32A

The Bréguet Type XX Leviathan powered by the 32A engine. Note the large radiator above the nose of the aircraft. The four exhaust ports (and a fair amount of soot) can be seen below the radiator. Each cylinder bank has its own exhaust manifold, and they all exit on the left side of the aircraft. The pilots can be seen above the “E” of the aircraft’s registration. (Pierre Bregerie image via

Bréguet envisioned grand applications for their engines, and in 1920, they devised the concept of coupling two U.24 engines (although the bore and stroke are given as 4.33 in/110 mm and 6.30 in/160 mm respectively) to power one propeller. The engines were positioned in tandem, front-to-front, with the rear engine slightly higher than the front engine. Each crankshaft was coupled to a gearbox between the two engines. A freewheeling clutch system was again used so that if any of the four eight-cylinder banks were to fail, the dead crankshaft would automatically decouple, and the remaining banks would continue to provide power.

If the dead engine bank was repaired, it could be recoupled to the propeller shaft. In line with each crankshaft was a sleeve that was permanently engaged to the propeller shaft. The sleeve was keyed so that the coupling on the end of the crankshaft could only engage it at a desired orientation. After the uncoupled engine section was started and brought up to the same rpm as the engine, an operator would pull a lever to slide the coupling on the crankshaft and reengage that crankshaft to the propeller shaft. However, even with the keyway, the crankshaft of a four-stroke engine could be coupled 360 degrees out of sync. To prevent this, a lead was attached to various spark plugs and would indicate when the lever should be thrown to recouple the crankshaft of the desired bank. This ensured the coupling would take place at the right time to maintain the desired firing order and power pulses of the engine sections upon the propeller shaft.

Breguet-Bugatti 32B front

This view of the Bréguet-Bugatti 32B (Quadrimoteur Type B) illustrates how two crankcase top haves of a U-16 engine are mounted on a common crankcase center section. This method of construction keeps the engine fairly modular: two four-cylinder blocks make up one bank; two banks on a common crankcase make up a U-16 top half; two U-16 top haves make up the 32B engine. (Aerofosslle2012 image via

The propeller shaft extended from the middle of the gearbox, ran between the cylinder banks of the front engine, and led to the propeller. Helical gears were used, and the gearbox incorporated a .5 to 1 reduction in speed. It is interesting to note that patent drawings show a configuration in which the front engine is higher than the rear engine and the propeller shaft passes below the front engine. However, this configuration was not used.

The engine group was known as the Bréguet-Bugatti 32A (or Quadimoteur Type A), and its output varies by source from 850 to 1,000 hp (634 to 746 kW). It is possible that all outputs were realized at different rpms—the 850 hp (634 kW) figure was achieved at 2,000 rpm. With a 4.33 in (110 mm) bore and 6.30 in (160 mm) stroke, the 32A displaced 2,969 cu in (48.7 L). The engine’s compression ratio was 4.2 to 1, and it weighed 2,482 lb (1,126 kg).

First run in 1921, a 32A engine was installed in the fuselage of the Bréguet Type XX Leviathan. The Type XX was an all-metal, biplane transport designed to carry 20 passengers. Compared to a standard twin-engine arrangement, the engine’s fuselage installation allowed for better aircraft streamlining, eliminated asymmetric thrust, and allowed the engines to be serviced while in flight. The engines turned two 14 ft 9 in (4.5 m) diameter two-blade propellers that were mounted in tandem. The Type XX had an 83 ft 7 in (25.54 m) wingspan and a length of 46 ft (14.02 m). The aircraft’s top speed was 118 mph (190 km/h), and it cruised at 99 mph (160 km/h).

Breguet-Bugatti 32B rear

The rear of the Bréguet-Bugatti 32B engine displayed in the engine mount used on the Type XXI Leviathan. The various levers controlled the manual coupling and decoupling of the crankshafts to the propeller shaft. (John Martin image via the Aircraft Engine Historical Society)

The sole Type XX first flew on 20 June 1922 with Bréguet test pilot Robert Thiéry at the controls. Flight testing went well, and the aircraft competed in the Grand Prix des Avions de Transport in November. On 14 November, the aircraft had the point lead when trouble occurred and it was forced down. There was little damage to the Type XX, but the aircraft could no longer win the Grand Prix. Apparently, the trouble occurred when one engine bank was shut down to replace its spark plugs, and a mechanic inadvertently shut down a second engine bank. The lack of power resulted in the emergency landing. Some sources state the aircraft was later destroyed during testing, but little information has been found regarding this claim. However, In September 1923, the Type XXII Leviathan of very similar construction (but with conventional engines installed between the wings) was destroyed during testing.

By 1924, Bréguet had moved on from the 32A’s cumbersome coupled engine concept and developed the Bréguet-Bugatti 32B (or Quadimoteur Type B) engine. Rather than having two separate engines, the 32B consisted of two U-16 crankcase top halves mounted on a common crankcase. The engine was configured as an H-32 in which one of the 16-cylinder crankcase halves was mounted in the normal vertical position, and the other was inverted. Each of the crankcase halves had two banks of eight cylinders, and each cylinder bank still had its own crankshaft. At the rear of the engine was a gearbox in which the four crankshafts were geared to a common propeller shaft at a .5 to 1 speed reduction. The gearbox employed the same coupling technique used with the 32A engine. Again, if a power section were to fail, that crankshaft would automatically decouple, and the remaining crankshafts would continue to provide power to the propeller shaft. The clutches also served to dampen vibrations between the individual crankshafts and the propeller shaft. The propeller shaft passed through the crankcase to drive the propeller at the front of the engine.

With the exception of the crankcase and propeller shaft, the 32B was very similar to the 32A and U-16 engines. One change was that each end of the camshafts drove a magneto. The cylinders had a 4.25 in (108 mm) bore and a 6.30 in (160 mm) stroke. The 32B had a total displacement of 2,862 cu in (46.9 L) and a compression ratio of 5.5 to 1. The engine produced 950 hp (708 kW) at 2,100 rpm and was tested to 1,015 hp (757 kW) in 1925. However, some sources indicate 1,200 hp (895 kW) was achieved at 2,800 rpm. The engine weighed 2,403 lb (1,090 kg).

Breguet-Bugatti 32B gear drive

The drive gears at the rear of the Bréguet-Bugatti 32B shown while the engine was under restoration. The image on the right shows the four crankshafts with their notched helical gears. The gears could slide on the crankshaft to couple or decouple with the propeller shaft, which is seen at the center of the crankcase. The image on the right shows the notched helical gears on the end of the propeller shaft. (l’Association Des Amis Du Musée Safran image)

Bréguet also built the Type XXI Leviathan, which was a military version (bomber) of the Type XX. In 1921 and 1922, the airframe of this aircraft was exhibited at the Salon de l’Aviation in Paris with the 32A engine installed—the same power plant used in the Type XX. However, the 32A engine in the Type XXI was substituted for a 32B. Unfortunately, little information has been found on the sole Bréguet Type XXI and its flying history. It is not clear when the 32A engine was removed and the 32B engine installed; presumably, it was not before 1925.

A large engine housed in the fuselage was found to take up too much space and did not yield much, if any, benefit. Bréguet subsequently refocused on conventional power plant arrangements. In addition, Bréguet did not see much of a return from its foray into aircraft engine design and manufacturing. The firm exited the aircraft engine business around 1926.

A Bréguet-Bugatti 32A (or Quadimoteur Type A) engine is in storage at the Musée de l’Air et de l’Espace in le Bourget (near Paris), France. This appears to be the engine that was installed in the Type XX aircraft. Probably only one or two of these engines were built. Also at the Musée de l’Air et de l’Espace is the Bréguet-Bugatti 32B (or Quadimoteur Type B), still in the engine mount for the Type XXI Leviathan. The 32B engine may be in storage, but it was displayed in the Hall de l’entre deux guerres. Most likely, only one 32B engine was built.

Breguet Type XXI and 32B

A rare image of the Bréguet Type XXI Leviathan with the Bréguet-Bugatti 32B engine installed. The aircraft was very similar to the Type XX, but with different wing struts. The frame of a gunner’s station is visible just behind the cockpit. (J. P. Mathieu image via Pyperpote)

The Bugatti 100P Record Plane by Jaap Horst (2013)
Bugatti – The Designer by Barry Eaglesfield (2013)
Les Moteurs a Pistons Aeronautiques Francais Tome I by Alfred Bodemer and Robert Laugier (1987)
Jane’s All the World’s Aircraft 1922 by C.G. Grey (1922)
– “Device for the Automatic Coupling and Uncoupling of Engines Operating Upon a Common Propeller” U.S. patent 1,564,516 by Louis Breguet (granted 8 December 1925)
– “Moteur Breguet-Bugatti 32B” l’Association Des Amis Du Musée Safran Bulletin No 15 (May 2012)
– “The Breguet Leviathan Type XX” by E. H. Lemonon Aviation (25 April 1921)

Marchetti MP Cam Action

Marchetti Cam-Action Engines

By William Pearce

Paul J. Marchetti was born in Italy in 1889. In his adolescence, he became interested in machines, engineering, and aircraft. In 1910, when he was 21 years old, Marchetti emigrated from Lucca, Italy to the United States in search of greater opportunities. He worked his way west and supported himself as a logger, all the while dreaming of entering the aviation business.

Marchetti MP Cam Action side

The Marchetti eight-cylinder, cam-action aircraft engine of 1927. Note the stagger of the front and rear cylinders.

Unfortunately, there is little information about Marchetti, his life, and his inventions. By 1922, he was working with Henry A. Nordwick in Stockton, California. Nordwick was working on designing a radial engine in which the crank throw was replaced by a cam with four lobes. A roller on the big end of the connecting rod made contact with the cam, its points creating the piston strokes. Another Nordwick and Marchetti engine design dating from 1923 had the big end of each connecting rod attached to its own crank, which was geared to a main central gear.

By 1924, Marchetti was in San Francisco, California and filed a patent of his own for a broad-arrow engine using either a three- or four-lobe cam in place of the crankshaft. Still working with Nordwick, another patent was filed for an eight-cylinder radial with a two-lobe cam. A lever extended from the big end of each connecting rod and was attached to the crankcase. Also connected to this lever was an auxiliary piston. Fed by pressurized air, the auxiliary piston forced the connecting rod to be in contact with the cam at all times. One auxiliary piston was positioned between each main piston.

Nordwick Marchetti cam engine patents

Drawings from Nordwick and Marchetti cam engine patents. The patent for the four-lobe cam design (left) was filed in 1922, and the patent for the eight-cylinder engine with auxiliary pistons (right) was filed in 1924.

Nordwick and Marchetti focused on inline engines in 1925. They designed a two-lobe cam engine, again using a lever extending from the big end of the connecting rod to the crankcase. That same year, Marchetti patented an inline engine under his business name: Marchetti Motor Patents. For this engine, the crankshaft throws were replaced with disks, offset to the crankshaft’s centerline. A connecting rod ran in a grove in each disk, and the disk’s offset would create the up and down strokes for the piston. The circular disk could also be substituted in favor of a lobed design for increased engine performance.

In 1926, Marchetti took out a patent on an inline engine with a two-lobe cam driving the pistons. The connecting rods were paired together via a rocker so that when one piston was at top dead center the other piston would be at bottom dead center. This configuration was also suggested for a U engine with two separate cam (crank) shafts.

Marchetti Motor Patents

Drawings from the Marchetti cam engine patents. The 1924 broad-arrow engine design is on the left, and the 1925 inline cam disk design is on the right.

1927 saw Marchetti focus on the business side of his dreams. His company, Marchetti Motor Patents, Inc., was officially formed with $2,000,000 of capital and operated out of the newly completed Russ Building, the tallest building in San Francisco until 1964. Marchetti worked on new engines and aircraft. In 1928, ground was broken for the Marchetti Motor Patents factory at Mills Field (now San Francisco International Airport). The factory had an expected output of 100 aircraft and 1,000 engines per year.

With his business established, Marchetti designed and built a new cam engine. While incorporating some aspects of the previous engine designs, this engine also had some unique features that are not found in any of the patents filed by Marchetti. However, the connecting rod arrangement and cam were similar to those found in a patent filed solely by Nordwick in 1926.

Marchetti MP info

Marchetti Motor Patents Inc. advertisement from 1929.

The new engine was an air-cooled, eight-cylinder radial. The cylinders were slightly staggered, making two rows of four cylinders. Twin two-lobe cams replaced the conventional crankshaft. Via roller bearings, the front cam actuated the connecting rods for the front cylinders, and the rear cam actuated the connecting rods for the rear cylinders. One fore and one aft cylinder were paired together by a common bell crank attached to the big end of the connecting rods. The center of this bell crank was the pivot point and was attached to the crankcase. The cams were staggered so that when one of the paired cylinders was at top dead center, the other cylinder was at bottom dead center. Since each cam had two lobes, there would be four piston strokes (or one power stroke) for each revolution. Marchetti referred to this design as a “cam-action” engine.

Each of the engine’s cylinders had one intake and one exhaust valve at the center of its head. The valves were actuated by pushrods driven at the front of the engine. Two spark plugs were located just below the valves of each cylinder and were fired by a magneto driven from the rear of the engine. A carburetor attached to the lower rear of the engine fed the air/fuel charge into a blower (weak supercharger). The blower helped mix the air/fuel charge, which was then distributed to the cylinder via separate manifolds. The engine had a 4.0 in (102 mm) bore, a 4.25 in (108 mm) stroke, and a total displacement of 427 cu in (7.0 L). Initially, 135 hp (101 kW) was expected from the engine, but 160 hp (119 kW) was achieved after testing. The engine weighed 350 lb (159 kg).

Marchetti MP Cam Action

Cutaway view of the Marchetti cam-action engine. The rear cam can barely be seen in the rear of the crankcase. Note how each cam actuates one “row” of cylinders. The bell crank for the upper right cylinder pair can be seen clearly. The bell crank attached to the connecting rods and pivoted in the middle, where it was mounted to the crankcase.

The eight-cylinder engine was first run in 1927. Most sources say only one engine was built, but some claim more were built. The engine passed a 400 hour maximum load test, and 2,200 hours were accumulated with no apparent signs of wear. Marchetti modified a Cessna AW for flight testing the eight-cylinder radial, but it is not known if the engine was ever installed. This aircraft was designated Marchetti M-I

Marchetti MP M-II Arrow advert

Advertisement from September 1929 for the Marchetti M-II Arrow and its four-cylinder engine cam-action engine.

Another Marchetti aircraft was the M-II Arrow—a two-place monoplane to be powered by a Marchetti inline, four-cylinder, air-cooled, cam-action engine of 100 hp (75 kW). The M-II was constructed of wood covered by fabric. On the drawing board was the Marchetti M-III—an eight passenger, all metal aircraft intended for passenger service. It was to be powered by two Marchetti eight-cylinder cam-action radials.

With his aircraft and aircraft engine manufacturing plans underway, Marchetti continued to chase his dream of becoming a pilot. On 31 August 1929, one week before the plant opened, Marchetti took off from Mills Field to look over his nearly finished factory and log some of the two hours remaining before he could get his pilot’s license. He flew into a fog bank, and what happened next is not known. A short time later, Marchetti’s aircraft was seen falling from under the fog bank in an inverted flat spin. The aircraft crashed half a mile (.8 km) from shore into San Francisco Bay. Rescue boats reached the scene as fast as possible, but it was too late. Marchetti’s body was found in the submerged fuselage.

The Marchetti M-II Arrow was completed and flown, but it is not known which engine powered it. While it is possible that it flew with a Marchetti inline cam engine, it is more likely that another four-cylinder engine was installed. Marchetti’s grand aviation plans drifted into oblivion after his death. Marchetti Engine Patents Inc. was sold to William Rider and then resold to United Aircraft Sales where it faded to obscurity. What happened to the M-I, M-II Arrow, or any of the cam-action test engines is not known. It is believed that the M-III transport never progressed beyond the design phase.

Marchetti MP M-II Arrow

The complete Marchetti M-II Arrow with its unidentified engine. The aircraft carried the registration X-98M. (Frank Rezich image via

– “Falls to Death: Paul Marchetti” Oakland Tribune (1 September 1929)
– “Marchetti Motor to Revolutionize Airplane Industry” Ukiah Dispatch Democrat (12 May 1928)
– “The Business of Building Aircraft” San Francisco Business (11 September 1929)
– “Internal Combustion Engine” US patent 1,374,164 by H. A. Nordwick (granted 5 April 1921)
– “Internal Combustion Engine” US patent 1,528,164 by H. A. Nordwick (granted 3 March 1925)
– “Internal Combustion Motor” US patent 1,538,208 by H. A. Nordwick et al (19 May 1925)
– “Engine” US patent 1,654,378 by P. Marchetti (granted 27 December 1927)
– “Internal Combustion Engine” US patent 1,597,474 by H. A. Nordwick et al (granted 24 August 1926)
– “Internal Combustion Engine” US patent 1,624,277 by H. A. Nordwick et al (granted 12 April 1927)
– “Internal Combustion Motor” US patent 1,667,213 by P. Marchetti (granted 24 April 1928)
– “Motor” US patent 1,624,269 by P. Marchetti (granted 12 April 1927)
– “Duplex Cam Motor” US patent 1,630,273 by H. A. Nordwick (granted 31 May 1927)
Aerosphere 1939 by Glenn Angle (1940)

FIAT AS8 V-16 side

FIAT AS.8 Engine and CMASA CS.15 Racer

By William Pearce

Since 10 April 1933, Italy had enjoyed ownership of the 3 km absolute world speed record for aircraft. Warrant Officer Francesco Agello set the record at 423.824 mph (682.078 km/h) in the Macchi-Castodi MC.72 seaplane built for the Schneider Trophy Contest. The MC.72 was powered by a 24-cyllinder FIAT AS.6 engine. Agello went on to raise the record to 440.682 mph (709.209 km/h) on 23 October 1934 in another MC.72.

FIAT AS8 V-16 side

Side view of the FIAT AS.8 V-16 engine specifically designed for the CMASA CS.15 racer.

However, Germany captured the world speed record on 30 March 1939, when Hans Dieterle flew 463.919 mph (746.606 km/h) in the Heinkel He 100 (V8). Germany raised the record a month later on 26 April 1939, when Fritz Wendel traveled 469.221 mph (755.138 km/h) in the Messerschmitt Me 209 (V1).

Even before Dieterle’s record flight, the Italians had considered building an aircraft specifically for a new record attempt. FIAT, with the support of the Italian government, wanted to win the record back and had initiated an aircraft and engine design that was somewhat finalized before Wendel’s record flight. The new record aircraft was designed and built by Costruzioni Meccaniche Aeronautiche SA (CMASA), a FIAT subsidiary in Pisa. The engine would be designed and built at FIAT’s headquarters in Turin.

FIAT AS8 rear

A rear view of the FIAT AS.8 showing the valley between the engine’s banks. The small manifolds on each bank are to take the cooling water from the cylinders. They are installed backward in this photo; the outlet should be at the engine’s rear. The long intake manifold is reminiscent of the even-longer manifold used on the AS.6. The large port in the manifold elbow, seen just above the carburetor, is a relief valve to prevent over pressurization of the manifold (perhaps in the event of a backfire—a major issue in the early development of the AS.6).

The aircraft was designed by Manlio Stiavelli and was known as the Corsa (meaning Race) Stiavelli 15, or just CS.15. Lucio Lazzarino, an engineer at CMASA, analyzed and tested various aspects of the CS.15 design. The CS.15 was a small, mid-wing, all-metal aircraft with a very low frontal area. Its 29.5 ft (9.0 m) monospar wing had conventional flaps and ailerons. The cockpit was situated far aft on the 29.2 ft (8.91 m) fuselage and was faired into the long tail.

To keep the wing thin and the fuselage narrow, the main wheels of the CS.15 folded toward each other before retracting aft into the fuselage. The CS.15’s fuel tank was situated behind the engine, in front of the cockpit, and above the main landing gear well. Fuel capacity was very limited, and the CS.15 was only meant to have enough endurance to capture the speed record—about 30 minutes of flight time. The estimated empty weight of the CS.15 was 4,213 lb (1,910) kg, and its total weight was 5,000 lb (2,270 kg).

To power the CS.15, Antonio Fessia and Carlo Bona laid out the AS.8 (Aviazione Spinto 8) engine design at FIAT. The AS.8 was a completely new design but had many common elements with the AS.6 engine used in the MC.72. The AS.6 was designed by Tranquillo Zerbi, and Fessia had taken over Zerbi’s position at FIAT when he passed away on 10 March 1939. The AS.8 was a liquid-cooled engine with cylinders very similar to the AS.6’s, utilizing two intake and two exhaust valves actuated by dual overhead camshafts. The AS.6 and AS.8 shared the same 5.51 in (140 mm) stroke, but the AS.8’s bore was increased .08 in (2 mm) to 5.51 in (140 mm). Reportedly, the AS.6 and AS.8 used the same connecting rods and both engines were started with compressed air.

FIAT AS8 front

This view displays the four magnetos of the FIAT AS.8 just above the propeller gear reduction. Note the the air distribution valves driven by the exhaust camshafts for starting the engine. The outlet of the water pumps can be seen in the forward position, which differs from the first image on this page.

The AS.8 was unusual in many ways. Its two banks of eight individual cylinders were set at 45 degrees. The 16 cylinders gave a total displacement of 2,104 cu in (34.5 L). The cylinders had a 6.5 to 1 compression ratio. The single-stage supercharger was geared to the rear of the engine and provided pressurized air to the cylinders via a long intake manifold between the cylinder banks. The carburetors were mounted above the supercharger. Unlike the AS.6, which used independent coaxial propellers, the AS.8 featured contra-rotating propellers geared to the front of the engine at a 0.60:1 reduction. Two sets of two-blade propellers 7.2 ft (2.2 m) in diameter could convert the AS.8’s power into thrust for the CS.15. The engine weighed 1,742 lb (790 kg).

Nine main bearings were used to support the long crankshaft and to alleviate torsional vibrations. In addition, drives for the camshafts, magnetos, and water pumps were mounted at the front of the engine. Each cylinder bank had two magnetos to fire the two spark plugs per cylinder. The distributor valve for the air starter was driven from the front of the exhaust camshaft for each cylinder bank. The exhaust gases of the AS.8 were utilized to add propulsive thrust through specially designed exhaust stacks on each cylinder.

FIAT AS8 bank

A detailed view of the AS.8’s right cylinder bank. Each cylinder had one spark plug on the outside of the engine and one in the Vee. The pipe next to the spark plug is for the air starter. The manifold at the bottom fed cool water into the cylinder jacket. (Emanuele image via Flickr)

For cooling, pressurized water was drawn into a pump on each side of the engine, near its front. A manifold delivered the water to each cylinder on the outside of the bank. The water then flowed through the cylinders and exited their top into another manifold situated in the Vee of the engine. The heated water, still under pressure, was taken back to the CS.15’s tail, where it was depressurized and allowed to boil. The steam then flowed through the CS.15’s wings, where 80% of their surface area was used to cool the steam and allow it to condense back into water. The water was then re-pressurized and fed back to the engine. Engine oil was also cooled by surface cooling in the rear and tail of the aircraft.


A three-view drawing of the CMASA CS.15 racer. Note the thin wings, minimal frontal area, and main gear retraction.

By early 1940, full-scale mockups of various CS.15 components were built and the construction of the CS.15 was underway. Wind tunnel tests indicated the CS.15 would reach a speed of 528 mph (850 km/h). The AS.8 engine was running on the test stand at this time. During these tests, the AS.8 achieved an output of 2,500 hp (1,864 kW), but the engine was rated at 2,250 hp (1,678 kW) at 3,200 rpm. The engine accumulated tens of hours running on the test stand and encountered few, if any, major failures. It is not known how many AS.8 engines were built, but the number is thought to be very small. The AS.8 was also the starting point of another V-16 engine, the FIAT A.38.

After Italy entered World War II in June 1940, progress on the CS.15 and AS.8 continued but at a much reduced pace. The CS.15 was damaged in various air raids, and it was further wrecked by the Germans as they exited Italy in late 1943. Some believe that whatever remained of the CS.15 was taken to Germany, as the aircraft essentially disappeared. As for the AS.8 engine, one example survived the war and is on display (or in storage) at the Centro Storico Fiat in Turin, Italy.

The AS.8 achieved a power output greater than 1 hp/cu in and 1 hp/lb—accomplishments that were sought after by engine designers around the world.

MC 72 & Coppa Schneider Vol. 2 by Igino Coggi (1984)
Aeronuatica Militare Museo Storico Catalogo Motori by Oscar Marchi (1980)
World Speed Record Aircraft by Ferdinand Kasmann (1990)
Italian Civil and Military Aircraft 1930-1945 by Jonathan W. Thompson (1963)

Menasco Unitwin rear

Menasco 2-544 Unitwin Aircraft Engine

By William Pearce

Albert (Al) S. Menasco got his start in the aircraft engine business in 1926 when he was tasked with settling the estate of his friend Art Smith. Before he passed, Smith had purchased 250 Salmson Z-9 water-cooled 9-cylinder radial engines. Waldo Waterman approached Menasco with an idea to convert the Salmson engines to air-cooling. Menasco ended up progressing on his own with the project and made further modifications to the Salmsons. Despite his best efforts, Menasco could not make the Menasco-Salmson B-2 engine reliable enough to pass the new Department of Commerce’s 50-hour test.

Menasco Unitwin front

This front view of the Unitwin illustrates the slight contrary angle of the Buccaneer engine sections. Visible are the brackets that bolt the two crankcases together to make the Unitwin more rigid. Note the oil supply lines on each side of the gear case for spraying oil on the freewheeling clutches.

In 1928, Menasco found himself with a good shop and a good crew but no engine to manufacture. Jack Northrop was visiting Menasco one day and suggested he should build an inverted, in-line, air-cooled, four-cylinder aircraft engine. This was the start of the 90 hp (67 kW) four-cylinder Menasco Pirate engine and quickly led to the 160 hp (119 kW) six-cylinder Menasco Buccaneer in 1931. Remembering the troubles with the Salmson, Menasco designed these engines to run at 125% rated power for 100 hours straight. The Pirate and Buccaneer were very popular and very successful engines with air racers. Over years of continued development, the engines were supercharged and their output increased to 150 hp (112 kW) and 260 hp (194 kW) respectively.

In mid-1935, Robert Gross, Cyril Chappellet, and Hall Hibbard discussed with Menasco the possibility of coupling two six-cylinder Buccaneer engines together side-by-side to make an inverted U-12 engine. Gross, was the President of the Lockheed Aircraft Corporation, Chappellet its corporate secretary, and Hibbard its chief engineer. Menasco thought the Buccaneer could be developed to produce 350 hp (261 kW), giving the coupled engine 700 hp (522 kW). Through freewheeling (or overrunning) clutch mechanisms, the two engines would power a single propeller. If one engine were to fail, the other would be unaffected and continue to power the constant-speed propeller. The propeller’s pitch would change to compensate for the decrease in power. This arrangement would give twin-engine reliably without the drag of a conventional twin-engine installation or the asymmetric thrust during an engine failure. The men from Lockheed thought the engine would be well suited to power personal aircraft or small feeder aircraft for airline service.

Menasco Unitwin

The Menasco Unitwin engine with the air-cooling baffles in-place. Note the intake manifold: on a standard Buccaneer engine, this manifold was on the opposite side. On the Unitwin, both engine sections had the intake manifold on the outside of the engine. Note the revised oil lines to the gear case compared with the previous image.

In 1936 and with Lockheed sponsorship, Menasco coupled two 90 hp Wright Gipsy four-cylinder engines to test the feasibility of a freewheeling gear case. This coupled engine endured 300 hours of tests and paved the way for the Menasco Unitwin. Lockheed formed a new subsidiary, the Vega Airplane Company (originally the AiRover Company), to manufacture an aircraft powered by the Unitwin. In addition, Lockheed explored the possibility of installing Unitwin engines in its Model 12 Electra Junior. By 1937, Vega had taken over the Unitwin project which was behind schedule. Issues were encountered with the Buccaneer engine being able to produce the desired 350 hp (261 kW) output. In addition, the Menasco Manufacturing Company was in poor financial health. Lockheed’s Gross and Chappellet personally invested in Menasco to keep the company going.

The Menasco 2-544 Unitwin was comprised of two 544 cu in (8.9 L) C6S-4 Super Buccaneer six-cylinder engines. The Buccaneer  engines were positioned side-by-side and coupled together by a common gear case. Each engine was canted out 10-degrees from vertical. The gear case housed hydraulic freewheeling clutches that allowed the engines to be operated completely independent of each other. In addition, the rear of the gear case had provisions to run essential accessories, including the prop governor and an oil pump. The gear case had its own oil supply, independent from the engine sections. The engine sections were modified to rotate opposite the normal direction, and once through the gear case, rotation returned to normal for the use of a standard propeller. The gear case also incorporated a 0.667 (may have been 0.6375) propeller gear reduction.

Menasco Unitwin rear

Rear view of the Menasco Unitwin showing the separate superchargers, carburetors, magnetos, and starters.

Rigid supports connected the two Buccaneer crankcases together to utilize one engine mount. The two rows of cylinder shared baffles to direct the cooling air through their fins. Later in development, the intake and exhaust on the left engine section were reversed; this allowed the intake manifolds to travel along the outside of both engine sections and for the exhaust manifolds to be located in the middle, between the sections.

The inverted U-12 had a 4.75 in (121 mm) bore and a 5.125 in (130 mm) stroke. Total displacement was 1,090 cu in (17.9 L). Each cylinder had one intake and one exhaust valve actuated by pushrods. Two spark plugs per cylinder were fired by Scintilla magnetos, two on each engine section. The compression ratio was 5.5 to 1, and each engine section had its own supercharger. The engine produced 580 hp (433 kW) at 2,400 rpm and had a maximum output of 660 hp (492 kW) at 2,700 rpm. The Unitwin was 80.0 in (2.0 m) long, 38.0 in (1.0 m) wide, and 30.5 in (0.8 m) tall. The engine weighed 1,380 lb (626 kg).

Other Unitwin gear case and engine configurations were considered. One gear case design raised the propeller shaft above the engine. With a hollow propeller shaft, this would allow a machine gun or cannon to be mounted above the engine with its barrel projecting through the propeller shaft. This design was intended for military use, but it is unlikely that it was ever built. A different engine configuration arranged the cylinders horizontally, to create a “flat” engine for installation buried in an aircraft’s wing. This engine configuration was never built.

Vega Altair Unitwin

Two views of the Vega-built Altair serving as a testbed for the Manasco Unitwin.

While the Unitwin was undergoing stringent bench tests to prove its reliability, Vega (AiRover) assembled a Lockheed Altair 8G (registered NX18149) from spare parts to serve as a flying testbed for the engine. This aircraft was the AiRover/Vega Model 1 and was also called the Flying Test Stand. The Unitwin-powered Altair first flew on 29 June 1938. In this aircraft, the Unitwin was put through its paces. One engine section would run at a steady power while the other was throttled quickly between full open and closed. With one engine’s throttle sealed closed, the Altair took off and climbed to 12,000 ft (3,658 m) without aircraft stability or engine cooling issues. However, the Menasco Manufacturing Company’s financial issues continued to worsen, and Gross and Chappellet essentially took over the company. This resulted in Al Menasco leaving the company in June 1938.

Encouraged by the results of the Unitwin in the Altair, Vega built a five to six place aircraft around the engine. Vega president, Mac Short, oversaw the design of this aircraft, known as the Vega Model 2 Starliner (registered as NX21725). The Starliner was meant to appeal as a feeder airliner and an executive and personal transport aircraft. Its first flight, on 22 April 1939, ended in an emergency landing when the propeller slipped into fine pitch. The pilot (Vern Dorrell) and observer (J. B. Kendrick) were uninjured, and the Starliner escaped with only minor damage.

Vega Starliner

The two-piece windscreen and twin tails of the Vega Starliner gave it a similar appearance to contemporary Lockheed transports.

The aircraft was originally built with twin tails. While it was being repaired, a single, conventional tail replaced the twin fins, and the rear of the fuselage was modified. The Starliner was soon back in the air but was later damaged again when the nose gear would not extend for landing. The aircraft was repaired again, but Vega was becoming increasingly occupied with government contracts. In addition, Vega realized the Unitwin would never be able to produce 700 hp (522 kW) and that the Starliner was too small for feeder line service. One aircraft was ordered by Mid-Continent Airlines, but this order was later cancelled.

After amassing 85 hours of flight time, Starliner development was discontinued. The airframe was sold off as a Hollywood prop. Although the Unitwin engine operated without issues and performed as designed, it had no prospects beyond the Starliner. Menasco Manufacturing Company, like Vega, was receiving a flood of government contracts; therefore, Unitwin development was halted in 1940. There are no known surviving examples of this engine.

Vega Starliner single tail

The Menasco Unitwin-powered Vega Starliner with a single tail. Note the updated paint job with “Starliner” on the engine cowl.

– “Unitwin Power Plant” by Mac Short, Aero Digest (February 1939)
Aerosphere 1939 by Glenn Angle (1940)
Race With the Wind by Birch Matthews (2001)
Jane’s All the World’s Aircraft 1940 by C. G. Grey and Leonard Bridgman
Multiple Motor Drive for Aircraft Propellers US patent 2,284,473 by Albert S. Menasco and Hall L. Hibbard (granted 26 May 1942)
Multiple Motor Drive US patent 2,180,599 by Albert S. Menasco (granted 21 November 1939)
Lockheed Aircraft since 1913 by Rene J. Francillon (1982/1987)
The Menasco Story by Ralph J. Schmidt (1994)
– “Menasco Aircraft Engines and their Air Racing Heritage, Part 1” by Larry M. Rinek, Torque Meter Vol. 2 No. 4 (Fall 2003)
Waldo: Pioneer Aviator by Waldo Dean Waterman with Jack Carpenter (1988)

Beardmore Tornado Mk III

Beardmore Tornado Diesel Airship Engine

By William Pearce

In the early 1920s, William Beardmore & Company Ltd. began to design a series of high-power, low speed, direct-drive aircraft engines. From this line of engines and the company’s experience with diesel locomotive engines, Beardmore experimented with diesel aircraft engines. One of these engines was the compression ignition Typhoon. Designed by Alan Chorlton, the Typhoon was an inverted, water-cooled, straight-six engine with a 8.625 in (219 mm) bore and a 12 in (305 mm) stroke, giving it a total displacement of 4,207 cu in (68.9 L). In 1924, the British Air Ministry ordered compression ignition Typhoons to be used in the hydrogen-filled R100 and R101 airships. This decision was largely influenced by the fact that diesel (a low volatility fuel) did not have the quick ignition tendencies of normal fuel, thus reducing the fire risk.

Beardmore Tornado Mk I

The Beardmore Tornado Mark I engine. Note the circular intake ports and access covers on the crankcase.

The R100 and R101 airships were part of the British Imperial Airship Scheme: a plan to improve communication with the far corners of the British Empire by establishing air routes. Both the R100 and R101 had a gas bag volume of over 5,100,000 cu ft (144,416 cu m), were over 710 ft (216 m) long, and had a maximum diameter of around 132 ft (40 m). The R100 was to be mostly designed and built by private industry using existing technology, while the R101 was to be designed and built by the government using experimental technology. After tests, the best aspects of both airships would be incorporated into later airships.

By 1926, with the airships under construction, the Air Ministry felt the Typhoon had reached its development potential. Beardmore offered a new Chorlton-designed six-cylinder engine that used steam-cooling and was not inverted. This engine was known as the Hurricane, but there was concern that it would not be powerful enough. Chorlton modified the Hurricane’s design by adding two additional cylinders. This engine was known as the Tornado and was expected to produce 700 hp (522 kW) at 1,000 rpm and 720 hp (537 kW) at the engine’s maximum rpm of 1,100. The Air Ministry ordered five Tornado engines for use on the R101, plus one additional engine as a spare. Tornado engines were also to be used on the R100. However, the R100 switched to standard fuel engines (Rolls-Royce Condors) because of developmental delays with the Tornado.

Beardmore Tornado Mk III section

Sectional view of the Beardmore Tornado Mk III. Note the two plain main bearings that sandwiched double Michell thrust bearings on the propeller shaft.

The Beardmore Tornado was a straight, eight-cylinder engine with a 8.25 in (210 mm) bore and 12 in (304 mm) stroke, giving a total displacement of 5,132 cu in (84.1 L). The engine’s compression ratio was 12.25 to 1. Each cylinder had its own aluminum-alloy head with two intake and two exhaust valves. The valves were actuated by rockers and short pushrods from a single camshaft that ran along the side of the engine, just below the head. One fuel injector for each cylinder was placed in the center of the head, between the valves. The fuel pump was positioned at the rear of the engine along with the water pump, oil pumps, and other accessories.

The Tornado utilized steam cooling. Water in the engine was allowed to boil; the steam was then condensed in radiators attached to the airship’s hull and circulated back into the engine. For starting, a decompressor opened one inlet valve to allow the engine to be spun over and primed. A 40 hp (30 kW) starting motor was used to start the Tornado through a 20 to 1 reduction.

During testing, the Tornado was revised three times (Mark I, II, and III) in an attempt to cure various issues, including problems with torsional vibrations. The crankcase / cylinder block was of monobloc construction and cast in aluminum for the Mark I engine. The aluminum did not have sufficient strength, and cast iron was used, adding substantially to the engine’s weight. The cylinder heads were prone to cracking until heads specially made in Switzerland of cast steel resolved the issue. A series of large access holes with aluminum covers were provided along the crankcase. An aluminum sump was bolted to the bottom of the crankcase. With the steel crankcase, the Tornado Mark III had a dry weight of 4,200 lb (1,905 kg)—much heavier than the 3,000 lb (1,361 kg) of the Mark I engine.

Beardmore Tornado Mk III

Beardmore Tornado Mk III engine. Note how the access covers are now oblong. No doubt the access holes were enlarged to help offset some of the weight of the cast steel crankcase.

The vibration issues of the Tornado were exacerbated by the long crankshaft. Effort was undertaken to strengthen the crankshaft by increasing the ten (two were at the propeller end) main journals from 5 in (127 mm) in diameter to 5.75 in (146 mm) in diameter. In addition, the crankshaft webs were increased to 8.5 in (216 mm). The Crankpins remained at 4.25 in (108 mm) in diameter. Other work to dampen vibrations included adding a flywheel to the rear of the engine and a spring coupling between the crankshaft and propeller. However, vibration issues persisted, being most evident at idle and at cruising engine speeds of 950 rpm. As a result of the issues, the Tornado had a continuous rating of only 585 hp (436 kW) at 890 rpm and a maximum of 650 hp (485 kw) at 935 rpm. Utilizing the permissible speed range, the engine was run 225 hours non-stop without issues. Fuel consumption was .385-.40 lb/hp/hr (234-243 g/kW/h).

On the R101, two of the Tornado engines were to be fitted with reversible pitch propellers to aid maneuvering, but these propellers failed during testing. As a stopgap measure, one engine was fitted with a propeller of reverse pitch; this would mean that only four engines provided forward thrust, and one engine was used as a reversing motor only. Later, two of the engines were fitted with a reversing gear that allowed them to be stopped and then run in the opposite direction, but all five engines could be used for forward thrust.

Beardmore Tornado in R101 car

Beardmore Tornado in the engine car for the R101 airship. The propeller flange on the right was at the rear of the car. Note the varying lengths of exhaust pipes on the far side. Also, the intake ports have changed from circular, as seen on the Mark I engine, to oblong. In the front of the car (left side of image) was a generator.

Each Tornado engine was installed in an enclosed engine car on the R101. The cars hung below the airship and allowed for easy servicing and maintenance of the engines while on the ground or in flight. The cars could also be removed and replaced as a unit. Each car contained the Tornado’s starting motor. As installed on the R101, each pod weighed a portly 8,580 lb (3,892 kg).

Reportedly, the Tornado engines were installed on the R101 by 24 September 1929. Its first flight, which was over 5 hours, was on 14 October. After a series of flights, the R101 was found to be very overweight, and modifications to lighten the airship started on 30 November. Some of the modifications were to increase the size of the gas bags in the R101, despite the possibility that they could rub on the airship’s framework. An additional gas bag was installed in a new midsection of the R101. While the ship was down, a Tornado engine in a complete engine car was test run the equivalent flight time from London to Karachi, British India (now Pakistan) and back without any issues. The R101 returned to the air in June 1930 but still experienced issues: hydrogen leaked from the gas bags, and its outer skin covering had deteriorated and was prone to ripping. The R101 was down for repairs again.

Beardmore Tornado-powered R101

The 777 ft (237 m) long R101 airship moored at RAF Cardington. Four of the five Tornado engine cars can clearly be seen. The one at the rear of the R101 also provided airflow over the rudder to aid maneuvering.

Following the repairs, the R101 made its first trial flight (of almost 17 hours) on 1 October 1930. This would be the airship’s last flight before setting off for Karachi on 4 October. The R101’s spare Tornado engine had been shipped ahead, in case it was needed. On the evening of 4 October, the R101 started its voyage. About eight hours later, the airship was caught in a storm over Beauvais, France. The airship began to nose down out of control. It impacted the French countryside and burst into flames, ultimately killing 48 of the 54 people on board.

A board of inquiry investigated the R101 tragedy to determine the probable cause. They believed that skin in the front of the airship ripped during the storm and caused a gas bag to rupture. With the hydrogen escaping, the nose of the R101 became heavy and dropped toward the ground; the airship was doomed. Despite being overweight and under-powered, the Tornado engines did not play a role in the airship’s demise. After the R101’s crash, the R100 was grounded and later scrapped even though it had operated without major issues, even completing a flight to Canada and back. Eventually, the accident put an end to Britain’s airship programs. One of the R101’s Tornado engines was salvaged and returned to the United Kingdom. It is currently on display as a partial cutaway at the Science Museum in London.

During World War II, a British soldier deployed in India stumbled upon the last of the Tornado engines. The spare engine that had been shipped ahead of the R101 had been installed in a train and pressed into service. Harkening back to its origins, apparently the Tornado made a good diesel locomotive engine.

Beardmore Tornado from R101 at SM

The salvaged Beardmore Tornado engine from R101 airship. This engine is currently on display at the Science Museum in London. (Andy Dingley image via Wikimedia Commons)

Beardmore Aviation 1913-1930 by Charles Mac Kay (2012)
Aeroshpere 1939 by Glenn Angle
Jane’s All the World’s Aircraft 1931 by C. G. Grey
The Modern Diesel fourth edition no date Illiffe & Sons Ltd
An Account of Partnership – Industry, Government and the Aero Engine by George Bulman and edited by Mike Neale (2002)
– “The Latest Beardmore Aero Engine,” Flight, 16 February 1928
– “R.101,” Flight, 11 October 1929