A COMPOUND engine, consisting of a piston engine mechanically connected to a turbine, with the turbine receiving the piston-engine exhaust, is suggested by Mr. Bachle as a method of converting into useful work some of the exhaust-gas energy of both diesel and gasoline engines that is usually wasted.
The combination of a gasoline engine compound with gas turbine and driven by a propeller is considered by Mr. Bachle to offer the minimum weight of powerplant plus fuel for long-range aircraft cruising at 300 mph; for short-range cruising at 300 mph, the gas turbine and propeller combination is best, with the gas turbine driven by jet propulsion offering the next best possibilities.
Only when higher speeds become more practical, as a result of reduced aircraft drag, does Mr. Bachle believe that piston engines may be replaced by jet-propulsion turbines.