Lawrance A-3 / Model A
The Lawrance A-3 or Lawrance Model A was an American twin-cylinder aircraft piston engine. Designed by Charles Lawrance in the mid-1910s the engine was produced by the Lawrance Aero Engine Company and under license by Excelsior. Weighing 200 lb (90 kg) the engine produced 28 horsepower (21 kW). A feature of this engine was the shared use of a single crankpin for both cylinders, this caused vibration as the pistons moved in the same direction.
First run circa 1916, around 450 were built.