| Hispano-Suiza 8A | |
|---|---|
| Preserved "direct-drive" Hispano-Suiza 8 | |
| Type | V8 piston engine |
| Manufacturer | Hispano-Suiza |
| First run | 1914 |
| Number built | 49,800 |
| Variants | Wolseley Viper |
The Hispano-Suiza 8 was a water-cooled V8 SOHC aero engine introduced by Hispano-Suiza in 1914 and used by a number of Allied aircraft during the First World War. The original Hispano-Suiza 8A was rated at 140 hp (102 kW) and the later Hispano-Suiza 8F reached 300 hp (220 kW).
Sometimes referred to as the "Rolls-Royce Merlin of World War I", the Hispano-Suiza HS-8 engine was the most important Allied aircraft engine produced during the First World War. It powered over half the Allied aircraft.[1] A total of 49,800 engines were built, in twenty-one plants in Spain, France, Britain, Italy, and the U.S.[2] Derivatives of the engine were also used abroad to power numerous aircraft types and the engine can be considered as the ancestor of another successful engine by the same designer, the Hispano-Suiza HS-12 (and Soviet Klimov V12 derivative aero-engines) which served in World War II.
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When World War I began, production lines of the Hispano-Suiza, in that period of time Spanish engine and automobile company in Barcelona, were stopped to allow production of war material. Marc Birkigt began work on an aero engine based on his successful V8 automobile engine in Spain (One prototype of this aircraft engine is preserved in Spanish museum "Museo de Aeronáutica y Astronáutica" in Madrid). The resulting engine, called the Hispano-Suiza 8A (or HS-8A), made its first appearance in February 1915 and was a promising design.
Although engine reliability was a great concern in these opening stages of aviation, the HS-8A also provided good power-to-weight ratio and development potential. The engine and its accessories weighed 185 kg (408 lb), making it 40% as heavy as a rotary engine of equivalent power. The design also promised far more growth potential than rotary engines which (in spite of being the most common type then in use with airplanes) were getting close to the limits of the type. Rotary engines of increased power generally had increased weight, which in turn increased the already important gyroscopic torque generated by the engine's rotation. A further increase in torque was considered not acceptable, and the power-to-weight ratio of the new rotary engines under development did not appeal to aircraft designers.
The new engine was presented to the French Ministère de la Guerre (Ministry of War) in February 1915, and tested for 15 hours at full power. This was standard procedure for a new engine design to be admitted in military service. However, because of lobbying by competing engine manufacturers, the HS-8A was ordered to undergo a bench test that no French-made engine had yet achieved successfully: a 50-hour run at full speed. The HS-8A was therefore sent back to Chalais-Meudon on July 21, 1915 and tested for 50 hours, succeeding against all expectations.
French officials ordered production of the HS-8A to be started as soon as possible and issued a requirement for a new single-seat high-performance fighter aircraft using the new engine. The SPAD VII was the result of this requirement and would allow the Allies to regain air superiority over the Germans.
The Wolseley Viper was an improved 8A. Wolseley's engineers removed problems with the crankshaft and increased the compression ratio to give more power. It did not need the reduction gearing of the H-S8. The Viper II could deliver 210 hp at 2,000 rpm.[3]
The American Wright-Martin aviation firm license-produced the original 150 hp HS-8Aa engine as the Wright-Hispano E, for use in World War I combat aircraft to be built in the United States – it found its way into the JN-4H version of the Curtiss Jenny, replacing the Curtiss OX-5 liquid-cooled V8 engine of only 90 hp output.
The second version, the HS-8Bb, had a compression ratio of 5.3. A reduction gear (3:4 ratio) was fitted to compensate for the increased engine speed. However the reduction gear system was fragile, and often broke down, sometimes with spectacular results ending up with the entire propeller, driveshaft and driven gear parting company from the airframe. Progressive refinement of the engine brought the available power to 235 hp by the end of 1917.
The HS-8B was used to power the earliest versions of the S.E.5a, all examples of the SPAD S.XII and SPAD S.XIII, front-line versions of the Sopwith Dolphin and several other Allied aircraft types, with its gear reduction easily identifiable in vintage World War I photos, from its use of a clockwise rotation propeller.
| Model | 8A | 8Aa | 8Ab | 8B | 8F |
|---|---|---|---|---|---|
| Bore (mm) | 120 | 140 | |||
| Stroke (mm) | 130 | 150 | |||
| Displacement (l) | 11.76 | 11.76 | 18.47 | ||
| Compression ratio | 4.7 | 5.3 | |||
| Length (m) | 1.19 | 1.25 | 1.31 | 1.36 | 1.32 |
| Width (m) | 0.81 | 0.83 | 0.85 | 0.86 | 0.89 |
| Height (m) | 0.77 | 0.81 | 0.87 | 0.90 | 0.88 |
| Weight(kg) | 195 | 215 | 230 | 236 | 256 |
| Power output (hp) | 140 | 150 | 180 | 200/235 | 300 |
| at (rpm) | 1900 | 2000 | 2100 | 2300 | 2100 |
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