Curtiss Ricardo R-6

Among the most successful early engines marketed in the United States were those designed and built by aviation pioneer and inventor Glenn Curtiss in his factory at Hammondsport, New York. Early Curtiss engines powered motorcycles, and were air cooled. Later, to achieve higher power, Curtiss began to develop liquid-cooled engines. Curtiss built this engine for the U.S. Navy in 1921 for experimental purposes. It incorporated the Ricardo supercharging system, designed to increase engine power at high altitude and decrease fuel consumption. The piston and cylinder assembly were designed so the underside of the piston compressed air on the intake stroke of the piston. The compressed air then passed through an intercooler back into the cylinder above the piston during the compression stroke. The Navy did not consider the experiment successful, as the improvements that resulted did not offset the increased weight and mechanical complexity. Artist Curtiss Aeroplane and Motor Company. (Photo by Heritage Art/Heritage Images via Getty Images)