Renault 90 hp

The Renault 90 hp, or 12A, was the world’s first V12 aircraft engine. The engine was developed in 1911 from Renault’s earlier V8 engines and used the same air-cooled design.

Renault 90 hp
Renault 90 hp fitted to a Maurice Farman biplane
Type	Air-cooled V12 aero engine
National origin	France
Manufacturer	Renault
First run	1911
Number built	130
Developed from	Renault 70 hp
Developed into	Renault 100 hp

The engine was first exhibited in December 1911 at the Paris Air Show and powered several aircraft during the 1912 competition season. Renault followed up the 90 hp model with a, similarly designed, 100 hp model during the summer of 1912.

Design and development

By 1911, V12 engines had been built for boats and automobiles however Renault's was the first designed for aircraft use.^[1] As with other V12s and straight-six engines, Renault's V12 design had the inherent advantage of primary and secondary engine balance. The 60 deg angle between two rows of 6-cylinders resulted in even firing intervals for smooth power delivery and gave the engine a narrower profile than Renault's 90 deg V8s thereby reducing aerodynamic drag.^[1][2]

In addition to being the world's first V12 aero engine, the 90 hp model was the first Renault aero engine with articulated master-and-slave connecting rods allowing corresponding cylinders in each row to be arranged directly opposite each other which improved dynamic balance. This arrangement also made the engine crankcase shorter than would have been the case if the "side by side" connecting rods (found on the earlier V8 Renault 70 hp) had been used.^[1]

The ignition system used two magnetos, one for each bank of six cylinders. Each cylinder had one spark plug.^[3]

As with Renault's V8 air-cooled models, engines intended for pusher aircraft were fitted with a centrifugal blower while those engines intended for tractor aircraft used a cowl mounted air scoop to feed cooling air over the twelve separate large-finned cast iron cylinders.^[4] Pistons were made of steel with cast iron piston rings. Cylinder heads were separate castings attached to the aluminum alloy crankcase with four long stud bolts which held each cylinder assembly in place.^[3]

Another feature inherited from earlier Renault air-cooled V8 engines was the form of reduction gearing where the propeller was fixed to the end of the camshaft allowing it to turn at half engine speed. This method of gearing allowed the engine and propeller to be run close to their optimum speeds without the additional weight penalty of a gearbox^[1][4] while the reverse rotation of the crankshaft and propeller reduced gyroscopic forces improving aircraft handling.^[5]

Operational history

Renault aircraft engine advert c.1912 showing the 5 available models

The Renault 90 hp was first exhibited during December 1911 at the Paris Air Show held in the Grand Palais. The engine was offered at a price of 17,000 francs (the 70 hp V8 model was priced at 12,500 francs). The engine was noted for being both large and complex.^[6]

Three Renault 90 hp-powered aircraft built by Astra, Farman, and Breguet entered the first-ever aviation grand prix organized by the Aéro-Club de France, held on the 16-17 June in Anjou. The Renault 90 hp was the heaviest engine in the competition.^[7] The weather conditions during the event were terrible, with heavy rain and gale-force winds. The only Renault 90 hp-powered aircraft to complete the course was a two-seater Astra-Wright biplane piloted by Louis Gaubert, who ranked fifth out of five finishers in a special race held on the final day of the event.^[7][8][a]

The 90 hp engine was quickly followed by a 100 hp (75 kW) model in the summer of 1912.^[9]

Applications

• Astra-Wright biplane^[10][11]
• Breguet Type IV^[10][12]
• Farman MF.7^[10]

Specifications

Data from Angle^[4] and L'Aéro^[5]

General characteristics

• Type: Air–cooled, upright, 60-degree, V-12 piston engine
• Bore: 90 mm (3.54 in)
• Stroke: 140 mm (5.51 in)
• Displacement: 10.66 L (650.76 cu in)
• Length: 1,585 mm (62.40 in)
• Width: 803 mm (31.61 in)
• Height: 710 mm (27.95 in)
• Dry weight: 289.4 kg (638 lb)

Components

• Valvetrain: One exhaust valve and one inlet valve per cylinder. Both valves located in a lateral pocket with the exhaust on top and the intake on the bottom.
• Fuel system: Carburetor mounted on the left side of the engine block.
• Fuel type: 40–50 octane petrol
• Oil system: Wet sump. Internal oil pump.
• Cooling system: Air-cooled
• Reduction gear: 0.5:1, left hand tractor (there is no reduction gear as such; The reduction was achieved by mounting the propeller on the camshaft).
• Rotation (looking end on at the propeller hub): Engine crankshaft, 1800 rpm counter-clockwise. Camshaft and propeller, 900 rpm clockwise.

Performance

• Power output: 90 hp (67 kW) - Nominal
• Power-to-weight ratio: 0.232 kW/kg (0.141 hp/lb) at nominal power output

See also

• List of aircraft engines

Notes

1. The competition's rules favored the larger, heavier aircraft powered by the Renault 90 hp by granting a time bonus based on the number of passengers carried. However, weather conditions during the event were poor. Many entrants withdrew on safety grounds or were unable to take off as their aircraft got bogged down in the muddy ground. The overall winner of the Grand Prix was Roland Garros in a Blériot single-seater monoplane.^[8]