Once the largest independent manufacturer of automotive engines, Detroit’s Continental Motors purchased the rights to a single-sleeve valve engine design in 1925, believing this technology might replace poppet valves in aircraft engines. However, after considerable testing the company only became successful in aviation after reverting to poppet valves and production of four cylinder horizontally opposed engines. The Continental A-40 was the predecessor of a long line of successful horizontally-opposed Continental engines built for general aviation and military aircraft.

For example, the Continental A-40 made the classic Piper J-3 Cub possible, and powered other aircraft such as the Taylor Cub E-2 and Taylorcraft Model A.

An advantage of horizontally-opposed engines is better forward visibility than radial or V-type engines. Today opposed engines have replaced all other types of piston engines for various reasons, including fewer cylinders for equal power and smooth running. And Continental is one of the world’s largest manufacturers of general aviation engines.