Push-pull configuration

An aircraft constructed with a push-pull configuration has a mixture of forward-mounted (tractor) propellers and backward-mounted (pusher) propellers.

An early example of a "push-pull" aircraft was the Caproni Ca.1 which had two wing-mounted tractor propellers and one centre-mounted pusher propeller.

Claudius Dornier was the first aviation designer to heartily embrace the concept for production aircraft, as his Dornier Wal, Dornier Do 18 and Dornier Do 26 flying boats all used tandem "push-pull" engine locations.

While pure pushers decreased in popularity during the First World War, the push-pull configuration has continued to be used. The advantage it provides is the ability to mount two propellers on the aircraft's centreline, thereby avoiding the increased drag that comes with twin wing-mounted engines. It is also easier to fly if one of the two engines fails, as the thrust provided by the remaining engine is symmetrical, unlike a conventional twin-engine aircraft, which will yaw in the direction of the failed engine, and becomes uncontrollable below a certain airspeed, known as Vmc, which varies based on the type of aircraft. Conventional push-pull designs, such as the Cessna Skymaster and Adam A500, have the engines mounted on the nacelle so that the aircraft's tail, suspended via twin booms, is behind the pusher propeller. In contrast, the World War II-era Dornier Do 335 had the pusher propeller at the rear of the fuselage.

Pilots in the United States who obtain a multi-engine rating in an aircraft with this push-pull, or "centerline thrust," configuration are restricted to flying centerline-thrust aircraft; pilots who obtain a multi-engine rating in conventional twin-engine aircraft do not have a similar limitation with regard to centerline-thrust aircraft.