All Aero

The 12WI was a water-cooled 60° V-12 with a 2:1 reduction gear ratio. With a 135 mm (5.315″) bore, 140 mm (5.512″) stroke, 24.047 l (1,467.4 in³) displacement and 5.5:1 (later 5.9:1) compression ratio, it was rated 540 hp at 2,260 rpm and could produce 603 hp at 2,700 rpm. It was 59.1″ long, 43.34″ wide and 35.46″ high. Cylinder construction was similar to the 18WI. A Zenith carburetor supplied the mixture, and Ducellier magnetos the ignition. Bare dry weight was 902 lb, and complete weight was 1010 lb. Fuel consumption was 0.539 lb/hp/hr and oil consumption was 0.026 lb/hp/hr. A Farman two-stage supercharger maintained rated output up to 2,000 m (6,562 ft) with the first stage, and up to 5,100 m (16,732 ft) with the second stage.