Peugeot 8Aa

The Peugeot 8Aa, or L112, is a water-cooled V8 aircraft engine that equipped the 1,123 Voisin VIII bombers and fighters built during WW1. The 8Aa was the first engine designed by Peugeot for airplane use and the only one that saw service in WW1. In publications the engine is often referred to as the Peugeot 200 hp, or 220 hp. Voisin VIIIs formed the bulk of the French night bomber force through 1916-17 before being replaced in front line service by the Voisin X which was fitted with the more powerful and reliable Renault 12Fe.

Design and development
The Peugeot 8Aa was developed to meet a French military requirement for 200 hp aero-engines to equip a new class of bomber aircraft designed to hit targets inside Germany. To achieve this the engines needed to run for six hours with most of the journey taking place at altitudes around 4400 m. The requirement pushed the limits of contemporary engine technology. To meet the specification the French government turned to the nation's automobile manufacturers.

Peugeot's design followed that of their successful racing car engines which had been in production since 1910. For its time period, the engine had advanced features including double overhead camshafts (DOHC) and a dry sump design patented by Peugeot.

The engine's eight cylinders are in a 90 degree Vee arrangement. Reduction gears rotated the propeller at half the speed of the crankshaft. The propeller shaft extends far out in front of the crankcase and is mounted on ball bearings.

A shaft, extending directly back through the Vee, drives the camshaft spur gear train and the accessory units. The crankcase is of the barrel type with the four-throw crankshaft supported on three large double-row ball bearings. The crankshaft is made from two sections and is joined at the center bearing by a taper, key, and nut.

The cylinders are cast from iron in blocks of four with integral water jackets. In each cylinder head there are four inclined valves guided in bronze bushings. The engine's four camshafts (two per cylinder bank) are enclosed in aluminum housings and operate the valves through tappets.

The pistons are machined from steel forgings and fitted with two rings. The connecting rods are of the forked type.

Each cylinder has two spark plugs. One spark plug is situated in the center of the cylinder head and the other in an inverted position just below the inlet valve on the outside. Spark plugs were powered by two magnetos.

2 carburetors (one for each cylinder bank) are attached to the out-side inlet manifolds. Carburetors were heated by the exhaust however this arrangement was ineffective at the cold temperatures found at high altitudes which contributed to the type's poor reliability.

The Peugeot 8Aa shared many common parts with the Hispano-Suiza 8 and its British derivative the Wolseley Viper. Camshafts, piston rings and some bearings were interchangeable. Peugeot was one of the main licensed producers of Hispano-Suiza 8 engines.

The Peugeot 8Aa was a remarkably fuel efficient engine for its time. At its most efficient point, the engine's specific fuel consumption was 0.252 kg/kWh corresponding to a thermal efficiency of more than 30%.

Applications

 * Voisin VIII
 * Voisin LAP - factory designation for VIII night-bomber fitted with the Peugeot engine.
 * Voisin LBP - factory designation for VIII armed with 37 mm cannon fitted with the Peugeot engine.

Engines on display
A partially cutaway Peugeot 8Aa is on display at the Musée de l'air et de l'espace.

A Peugeot 8Aa engine is on display at the Polish Aviation Museum in Kraków.