Peugeot 8Aa
| Company type | Aero engine |
|---|---|
| Industry | Aerospace |
| Founded | 1915 |
| Headquarters | Issy-les-Moulineaux, Levallois-Perret, La Garenne-Colombes (Paris) , France |
| Products | Water-cooled V8 aero engine |
The Peugeot 8Aa, also known as the L112, is a water-cooled V8 aero engine that powered the Voisin VIII bombers and escort fighters during the First World War.
Originating from a 1915 request by the French armament ministry for aero engines capable of extended endurance and high-altitude performance, Peugeot modified its proven racing car engines to meet these demands. Although an initial order of 250 units was placed in late 1915, the first engine successfully completed its 50-hour acceptance test only by February 1916.
For its time, the Peugeot 8Aa incorporated advanced features such as double overhead camshafts, four valves per cylinder, and a dry sump lubrication system. While it was recognized for remarkable fuel economy, it faced significant mechanical reliability challenges. These frequent malfunctions resulted in the removal of Peugeot-powered Voisin VIII aircraft from frontline duties by May 1917.
Design and development
The Peugeot 8Aa was engineered in response to a 1915 French military specification calling for aero engines capable of powering new bombers intended for deep penetration into German territory. These engines were required to sustain six-hour flights at altitudes near , pushing the boundaries of existing technology. The government solicited proposals from manufacturers including Panhard, Peugeot, and Renault. Peugeot’s design drew upon their pre-war four-cylinder racing engines that had secured victories at the Indianapolis 500 in both 1913 and 1914.
Technologically sophisticated for the World War I period, the Peugeot 8Aa incorporated double overhead camshafts, four valves per cylinder, and a dry sump lubrication system inherited from its racing predecessors.[1] The double overhead camshaft configuration permitted wider valve angles, enhancing air-fuel mixture flow compared to single overhead camshaft arrangements.[2]
The engine’s eight cylinders are arranged in a 90-degree V formation, cast in pairs of four with integrated water jackets. Each cylinder head contains four inclined valves guided by bronze bushings. Four camshafts—two on each bank—operate the valves through tappets; these camshafts are hollow to supply lubricating oil directly to their bearings.[3] Pistons are forged steel with two rings apiece, connected via fork-and-blade connecting rods.[3]
A reduction gear reduces propeller speed to half that of the crankshaft. The propeller shaft extends forward from the crankcase and is supported by ball bearings.[3] In Voisin VIII aircraft, this shaft was linked to a two-bladed wooden propeller.[4] A driveshaft passing through the Vee transmits power to camshaft gears, water pumps, magnetos, tachometer, and auxiliary components.[3]
Each cylinder is equipped with two spark plugs powered by dual magnetos, providing improved combustion efficiency and redundancy for increased safety.[3]
Valve timing followed conventional practice with no overlap; exhaust valve closure and intake valve opening occurred after top dead center.[1]
Two carburetors—one per cylinder bank—supply fuel-air mixture to heated inlet manifolds warmed by exhaust gases. This heating elevates intake temperatures above those of the water jackets, thereby enhancing combustion efficiency.[3]
The Peugeot 8Aa exhibited notable fuel economy relative to contemporaries. At optimal operating conditions, its specific fuel consumption reached , equating to thermal efficiency exceeding 30%.[1]
Production
Mass production of the Peugeot 8Aa commenced prior to the completion of formal engine testing, with an initial order of 250 units placed by late 1915. The first batch successfully completed their 50-hour endurance tests by February 1916.
Manufacturing of the engines took place at Peugeot’s facilities located in Issy-les-Moulineaux, Levallois-Perret, and La Garenne-Colombes within Paris. Furthermore, production licenses were granted to other French companies such as Darracq. By the close of 1917, the total output reached 1,054 engines.
During the First World War, Peugeot also produced Hispano-Suiza aero-engines under license and became the leading manufacturer of the 200 hp Hispano-Suiza 8, delivering 5,506 units. The Peugeot 8Aa shared numerous components—including camshafts, piston rings, and certain bearings—with both the Hispano-Suiza 8 and its British variant, the Wolseley Viper.
Operational history
The Peugeot powerplant was installed in the Voisin VIII, a larger aircraft designed to carry heavier bomb loads compared to earlier Voisin pushers equipped with Salmson water-cooled engines. Throughout World War I, a total of 1,123 Voisin VIII aircraft were constructed.
While primarily deployed as a night bomber, some Voisin VIIIs were adapted for escort fighter roles. These aircraft entered operational service with French bomber units in November 1916 and by early 1917 constituted the backbone of France’s night bombing squadrons.
Nevertheless, the Peugeot 8Aa engine was plagued by frequent mechanical failures. As a result, by May 1917, the Voisin VIII was gradually replaced by the nearly identical Voisin X model powered by the Renault 12Fe engine. By February 1918, only 51 Voisin aircraft with Peugeot engines remained active at the front lines. Limited production continued into 1918, with these planes serving as training aircraft until the war’s conclusion.
Reliability problems
Crews operating the Voisin VIII voiced concerns over the Peugeot 8Aa’s lack of dependability, citing issues such as inadequate lubrication, carburetor malfunctions, and ignition troubles. Gabriel Voisin attempted to substitute it with Hispano-Suiza 8 engines; however, these were unavailable due to priority allocation to fighter aircraft.
The carburetors on the Peugeot 8Aa were heated using exhaust gases—a method that proved insufficient in cold temperatures at high altitudes and resulted in carburetor icing. The Renault 12Fe engine that succeeded it on Voisin bombers resolved this problem by warming carburetors through circulating jacket water.
Applications
- Voisin VIII
- Voisin LAP – factory code for VIII configured as a night bomber
- Voisin LBP – factory code for VIII outfitted as an escort fighter equipped with a cannon
Engines on display
A partially sectioned Peugeot 8Aa engine is showcased at the Musée de l'air et de l'espace in Paris. Another example is exhibited at the Polish Aviation Museum located in Kraków.
See also
References
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