Tractor configuration
An aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 constructed with a tractor configuration has the engine mounted with the propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...

 facing forward, so that the aircraft is "pulled" through the air, as opposed to the pusher configuration
Pusher configuration
In a craft with a pusher configuration the propeller are mounted behind their respective engine. According to Bill Gunston, a "pusher propeller" is one mounted behind engine so that drive shaft is in compression...

, in which the propeller faces backward and "pushes" the aircraft through the air.

In the early years of powered aviation both tractor and pusher designs were common. However, by the mid-point of the First World War
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

, interest in pushers declined and the tractor configuration dominated. Today, propeller-driven aircraft are assumed to be tractors unless it is stated otherwise.

Early usage of term

In the early days of flying, a distinction was made between a propeller ("pushes the
machine") and a tractor-[air]screw ("pulls the machine through the air")

World War I military aviation

From a military perspective, the problem with single-engine tractor aircraft was that it was not possible to fire a gun through the propeller arc without striking the propeller blades with bullets. Early solutions included mounting guns (rifle
A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...

s or machine gun
Machine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....

s) to fire around the propeller arc, either at an angle to the side — which made aiming difficult — or on the top wing of a biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...

 so that the bullets passed over the top of the propeller.

The first system to fire through the propeller was developed by French engineer Eugene Gilbert for Morane-Saulnier
Aéroplanes Morane-Saulnier is a French aircraft manufacturing company formed in October 1911 by Raymond Saulnier and the Morane brothers, Leon and Robert...

 and involved fitting metal "deflector wedges" to the propeller blades of a Morane-Saulnier L monoplane
A monoplane is a fixed-wing aircraft with one main set of wing surfaces, in contrast to a biplane or triplane. Since the late 1930s it has been the most common form for a fixed wing aircraft.-Types of monoplane:...

. It was employed with immediate success by French aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...

 Roland Garros and was also used on at least one Sopwith Tabloid
Sopwith Tabloid
|-See also:-References:* Bruce, J.M. "". Flight. 8 November 1957. pp. 733–736.* Bruce, J.M. "". Flight. 15 November 1957. pp. 765–766.* Bruce, J.M. "". Flight. 29 November 1957. pp. 845–848....

 of the Royal Naval Air Service
Royal Naval Air Service
The Royal Naval Air Service or RNAS was the air arm of the Royal Navy until near the end of the First World War, when it merged with the British Army's Royal Flying Corps to form a new service , the Royal Air Force...


The final solution was the interrupter gear
Interrupter gear
An interrupter gear is a device used on military aircraft and warships in order to allow them to target opponents without damaging themselves....

, more properly known as a gun synchronizer, developed by Fokker
Fokker was a Dutch aircraft manufacturer named after its founder, Anthony Fokker. The company operated under several different names, starting out in 1912 in Schwerin, Germany, moving to the Netherlands in 1919....

 and fitted to the Fokker E.I
Fokker E.I
|-See also:-References:NotesBibliography* Boyne, Walter J. The Smithsonian Book of Flight for Young People. Washington, DC: Smithsonian Institution, 1988. ISBN 0-689-31422-1....

 monoplane in 1915
1915 in aviation
This is a list of aviation-related events from 1915:- Events :* The United States Navy establishes a lighter-than-air arm, charged with the operation of airships and of kite balloons to be towed behind warships...

. The first British "tractor" to be specifically design to be fitted with synchronization gear was the Sopwith 1½ Strutter
Sopwith 1½ Strutter
The Sopwith 1½ Strutter was a British one or two-seat biplane multi-role aircraft of the First World War. It is significant as the first British-designed two seater tractor fighter, and the first British aircraft to enter service with a synchronised machine gun...

 which did not enter service until early 1916.

Other solutions to avoiding the propeller arc include passing the gun's barrel through the propeller's spinner (the nose of the aircraft) or mounting guns in the wings. The latter solution was generally used from the early 1930s until the beginning of the jet age
Jet age
The Jet Age is a period of history defined by the social change brought about by the advent of large aircraft powered by turbine engines. These aircraft are able to fly much higher, faster, and farther than older piston-powered propliners, making transcontinental and inter-continental travel...

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