Top 10: Totally bizarre engines fitted to aircraft

A roundup of unusual aircraft propulsion highlights how experimentation has produced wildly different engine concepts, from rotary designs to vertical-lift systems. The article explains that the Wankel engine uses a rotor in a stationary combustion chamber, lacking oscillating pistons, which can make the powerplant smooth and relatively quiet. It cites early aviation use in the Wright Aeronautical RC-2-60, fitted in the late Lockheed Q-Star prototype intended for surveillance in Vietnam-era operations with the goal of being nearly inaudible from 1,500 feet. It also notes that a Citroën Wankel helicopter project was tested but dropped, while today Wankel engines appear mainly in drones. For vertical operations, the piece describes “lift jets” mounted for takeoff and landing only, noting they were operational on the Soviet Yakovlev Yak-38 “Forger” and tested on larger concepts such as the Dornier Do 31, which combined Harrier-type engines with eight lift jets. The article continues beyond these examples, discussing additional rare propulsion approaches.