The Renault 70 hp, (8Ab , 8C) was a French V-8 aero engine that first ran in 1910. The type powered many early military aircraft including the Farman MF.7 Longhorn and the Royal Aircraft Factory B.E.2. In addition to French production, these engines were also built in the United Kingdom[1] and equipped the majority of British aircraft sent to France at the start of WW1.[2]
As with other Renault air cooled V-8s, the engine had an early form of reduction gearing where the propeller was fixed to the end of the camshaft and turned at half engine speed. Since the engine turned twice as fast as the propeller, it acted as a flywheel removing the need for any additional counterweights. Engines intended for pusher aircraft were fitted with a centrifugal blower which fed cooling air over the large finned cast iron cylinders.
Compared to contemporary air cooled rotary engines built by Gnome, the 70 hp Renault had a worse power to weight ratio but better fuel economy.[3] Aircraft powered by the Renault 70 hp set distance and duration records in 1912.
The first military orders were placed in 1911 with 81 engines delivered to the French army for use in Farman observation aircraft. In 1912 Farman aircraft powered by the Renault 70 hp equipped two out of the five French squadrons.
In the UK the 70 hp air cooled V8 model was manufactured by Renault’s UK subsidiary and their licensees; Rolls Royce, Wolseley and Airco. Renault refused to sell licenses to German firms in the years before WW1.
Data from Wolseley Motors's 1917 instruction manual. Weights shown include flywheel, exhaust branches, cowl and propeller boss.[4]
Type W.B - Version with internal lube oil pump. Dry weight: 440abbr=onNaNabbr=on
Type W.C - Version with external lube oil pump. Dry weight: 440abbr=onNaNabbr=on
Both the W.B and W.C variants were available for pusher (propeller at front) and tractor (propeller at back) aircraft. Engines fitted to tractor aircraft had a cowl scoop which directed part of the propellers air steam across the cylinders. Engines fitted to pusher aircraft were equipped with a back mounted (opposite end from prop) centrifugal blower. The blower added an extra 50abbr=onNaNabbr=on of weight and consumed 4abbr=onNaNabbr=on.
Type W.X - 75 hp variant. Outwardly almost identical to the 70 hp models but with a larger 100mm cylinder bore and redesigned connecting rods. The connecting rods used the same side by side layout as the 70 hp model but had a two stud design and were interchangeable between left and right cylinder banks. Available in tractor configuration only. Dry weight: 455abbr=onNaNabbr=on