Pusher configuration

“Pusher configuration” describes the specific (propeller or ducted fan) thrust device attached to a craft, either aerostats (airship) or aerodynes (aircraft, WIG, paramotor, rotorcraft) or others types such as hovercraft, airboats, and propeller-driven snowmobiles.

Many early aircraft (especially biplanes) were "pushers", including the Wright Flyer (1903), the Santos-Dumont 14-bis (1906), the Voisin-Farman I (1907), and the Curtiss Model D used by Eugene Ely for the first ship landing on January 18, 1911.

Well before the beginning of the First World War, this drag was recognized as just one of the factors that would ensure that a Farman-style pusher would have an inferior performance to an otherwise similar tractor type.

[citation needed] At least up to the end of 1916, however, pushers (such as the Airco DH.2 fighter) were still favored as gun-carrying aircraft by the British Royal Flying Corps, because a forward-firing gun could be used without being obstructed by the arc of the propeller.

During the long eclipse of the configuration the use of pusher propellers continued in aircraft which derived a small benefit from the installation and could have been built as tractors.

Biplane flying boats had for some time often been fitted with engines located above the fuselage to offer maximum clearance from the water, often driving pusher propellers to avoid spray and the hazards involved by keeping them well clear of the cockpit.

The so-called push/pull layout, combining the tractor and pusher configurations—that is, with one or more propellers facing forward and one or more others facing back—was another idea that continues to be used from time to time as a means of reducing the asymmetric effects of an outboard engine failure, such as on the Farman F.222, but at the cost of a severely reduced efficiency on the rear propellers, which were often smaller and attached to lower-powered engines as a result.

These include: The drive shaft of a pusher engine is in compression in normal operation,[5] which places less stress on it than being in tension in a tractor configuration.

In military aircraft, front armament could be used more easily on account of the gun not needing to synchronize itself with the propeller, although the risk that spent casings fly into the props at the back somewhat offset this advantage.

[7] A pusher needs less stabilizing vertical tail area[8] and hence presents less weathercock effect;[9] at takeoff roll, it is generally less sensitive to crosswind.

[note 6][10][11] When there is no tail within the slipstream, unlike a tractor, there is no rotating propwash around the fuselage inducing a side force to the fin.

A remote or buried engine requires a drive shaft and associated bearings, supports, and torsional vibration control, and adds weight and complexity.

[17][note 7] Due to a generally high thrust line needed for propeller ground clearance, negative (down) pitching moments, and in some cases the absence of prop-wash over the tail, a higher speed and a longer roll may be required for takeoff compared to tractor aircraft.

[18][19][20] The Rutan answer to this problem is to lower the nose of the aircraft at rest such that the empty center of gravity is then ahead of the main wheels.

Due to the generally-high thrust line to ensure ground clearance, a low-wing pusher layout may suffer power-change-induced pitch changes, also known as pitch/power coupling.

Pusher seaplanes with especially high thrust lines and tailwheels may find the vertical tail masked from the airflow, severely reducing control at low speeds, such as when taxiing.

Due to the pitch rotation at takeoff, the propeller diameter may have to be reduced (with a loss of efficiency[22]) and/or landing gear made longer[6] and heavier.

[citation needed] On tailless pushers such as the Rutan Long-EZ, the propeller arc is very close to the ground while flying nose-high during takeoff or landing.

In early pusher combat aircraft, spent ammunition casings caused similar problems, and devices for collecting them had to be devised.

[23] Full-scale wind tunnel investigation of the canard Rutan VariEze showed a propeller efficiency of 0.75 compared to 0.85 for a tractor configuration, a loss of 12%.

In case of propeller/tail proximity, a blade break can hit the tail or produce destructive vibrations, leading to a loss of control.

The Wright Flyer , a “pusher” aircraft designed in 1903
1871 Planophore
A Farman MF.11 , showing the classic Farman configuration with engine between tail booms
Buhl A-1 Autogyro , the first pusher autogyro
The post-WWII Convair B-36 was unusual in its size, era, number of engines, and combining both propeller and jet propulsion, with six radial piston and four jet engines
Typical of many UAVs , the General Atomics MQ-9 Reaper has a propeller at the extreme tail
NAL Saras , with pushers mounted on pods on either side of the rear fuselage
Aero Dynamics Sparrow Hawk II
Gallaudet D-4 with pusher prop rotating around the rear fuselage
Rhein Flugzeugbau RW 3 Multoplan with propeller between the rudder and the fin
Progenitor to a large number of canard pushers, the experimental Miles M.35 Libellula had its engine at the rear of the fuselage
Lippisch Delta 1 tailless pusher
Voisin III bomber, the most numerous pusher design, with 3200 built
Flexwing microlight with engine and propeller at the pilot's back
SAAB J 21 fighter, with the pusher propeller mounted between two fuselage booms
The Supermarine Walrus pusher flying boat is a typical flying boat, with the engine mounted high to avoid spray; however, throttle changes then induce pitch changes.
Piaggio P.180 Avanti with engines mounted on the wing trailing edge, away from passengers, allowing safer boarding.