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In an aircraft with a pusher configuration (as opposed to a
tractor configuration In aviation, the term tractor configuration refers to an aircraft constructed in the standard configuration with its engine mounted with the propeller in front of it so that the aircraft is "pulled" through the air. Oppositely, the pusher c ...
), the
propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
(s) are mounted behind their respective engine(s). Since a pusher propeller is mounted behind the engine, the drive shaft is in compression in normal operation. Pusher configuration describes this specific (
propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
or
ducted fan In aeronautics, a ducted fan is a thrust-generating mechanical fan or propeller mounted within a cylindrical duct or shroud. Other terms include ducted propeller or shrouded propeller. When used in vertical takeoff and landing (VTOL) applicatio ...
) thrust device attached to a craft, either aerostat (
airship An airship or dirigible balloon is a type of aerostat or lighter-than-air aircraft that can navigate through the air under its own power. Aerostats gain their lift from a lifting gas that is less dense than the surrounding air. In early ...
) or aerodyne (
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It 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 ...
,
WIG A wig is a head or hair accessory made from human hair, animal hair, or synthetic fiber. The word wig is short for periwig, which makes its earliest known appearance in the English language in William Shakespeare's ''The Two Gentlemen of Verona' ...
,
paramotor Paramotor is the generic name for the harness and propulsive portion of a powered paragliding, powered paraglider ("PPG"). There are two basic types of paramotors: foot launch and wheel launch. Foot launch models consist of a frame with harness ...
,
rotorcraft A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft with rotary wings or rotor blades, which generate lift by rotating around a vertical mast. Several rotor blades mounted on a single mast are referred to as a rotor. The Internati ...
) or others types such as
hovercraft A hovercraft, also known as an air-cushion vehicle or ACV, is an amphibious Craft (vehicle), craft capable of travelling over land, water, mud, ice, and other surfaces. Hovercraft use blowers to produce a large volume of air below the hull ...
,
airboat An airboat (also known as a planeboat, swamp boat, bayou boat, or fanboat) is a flat-bottomed watercraft propelled by an aircraft-type propeller and powered by either an aircraft or automotive engine. In early aviation history the term ''airboat ...
and propeller-driven
snowmobile A snowmobile, also known as a Ski-Doo, snowmachine, sled, motor sled, motor sledge, skimobile, or snow scooter, is a motorized vehicle designed for winter travel and recreation on snow. It is designed to be operated on snow and ice and does not ...
s. "Pusher configuration" also describes the layout of a fixed-wing aircraft in which the thrust device has a pusher configuration. This kind of aircraft is commonly called a pusher. Pushers have been designed and built in many different layouts, some of them quite radical.


History

The rubber-powered "Planophore", designed by
Alphonse Pénaud Alphonse Pénaud (31 May 1850 – 22 October 1880), was a 19th-century French pioneer of aviation design and engineering. He was the originator of the use of twisted rubber to power model aircraft, and his 1871 model airplane, which he called ...
in 1871, was an early successful model aircraft with a pusher propeller. Many early aircraft (especially biplanes) were "pushers", including the
Wright Flyer The ''Wright Flyer'' (also known as the ''Kitty Hawk'', ''Flyer'' I or the 1903 ''Flyer'') made the first sustained flight by a manned heavier-than-air powered and controlled aircraft—an airplane—on December 17, 1903. Invented and flown b ...
(1903), the
Santos-Dumont 14-bis The ''14-bis'' (french: Quatorze-bis), (), also known as ("bird of prey" in French), was a pioneer era, canard-style biplane designed and built by Brazilian aviation pioneer Alberto Santos-Dumont. In 1906, near Paris, the ''14-bis'' made a m ...
(1906), the Voisin-Farman I (1907) and the
Curtiss Model D The 1911 Curtiss Model D (or frequently "Curtiss Pusher") was an early United States pusher aircraft with the engine and propeller behind the pilot's seat. It was among the first aircraft in the world to be built in any quantity, during an era ...
used by
Eugene Ely Eugene Burton Ely (October 21, 1886 – October 19, 1911) was an American aviation pioneer, credited with the first shipboard aircraft take off and landing. Background Ely was born in Williamsburg, Iowa, and raised in Davenport, Iowa. Having c ...
for the first ship landing on January 18, 1911.
Henri Farman Henri Farman (26 May 1874– 17 July 1958) was a British-French aviator and aircraft designer and manufacturer with his brother Maurice Farman. Before dedicating himself to aviation he gained fame as a sportsman, specifically in cycling and moto ...
's pusher Farman III and its successors were so influential in Britain that pushers in general became known as the "Farman type".The
Royal Aircraft Factory Royal may refer to: People * Royal (name), a list of people with either the surname or given name * A member of a royal family Places United States * Royal, Arkansas, an unincorporated community * Royal, Illinois, a village * Royal, Iowa, a c ...
referred to all the early pushers they built as Farman Experimentals - or F.E.s.
Other early pusher configurations were variations on this theme. The classic "Farman" pusher had the propeller "mounted (just) behind the main lifting surface" with the engine fixed to the lower wing or between the wings, immediately forward of the propeller in a stub fuselage (that also contained the pilot) called a
nacelle A nacelle ( ) is a "streamlined body, sized according to what it contains", such as an engine, fuel, or equipment on an aircraft. When attached by a pylon entirely outside the airframe, it is sometimes called a pod, in which case it is attached ...
. The main difficulty with this type of pusher design was attaching the tail (empennage); this needed to be in the same general location as on a tractor aircraft, but its support structure had to avoid the propeller. The earliest examples of pushers relied on a canard but this has serious aerodynamic implications that the early designers were unable to resolve. Typically, mounting the tail was done with a complex wire-braced framework that created a lot of drag. Well before the beginning of the
First World War World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
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. The U.S. Army banned pusher aircraft in late 1914 after several pilots died in crashes of aircraft of this type, so from about 1912 onwards the great majority of new U.S. landplane designs were tractor biplanes, with pushers of all types becoming regarded as old fashioned on both sides of the Atlantic. However, new pusher designs continued to be designed right up to the armistice, such as the
Vickers Vampire The Vickers F.B.26 Vampire was a British single-seat pusher biplane fighter built by Vickers during the First World War. Four were built by Vickers at Bexleyheath, one of these was subsequently modified to become the F.B.26A. Design and deve ...
, although few entered service after 1916.. At least up to the end of 1916, however, pushers (such as the Airco DH.2 fighter) were still favoured 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. With the successful introduction of
Fokker Fokker was a Dutch aircraft manufacturer named after its founder, Anthony Fokker. The company operated under several different names. It was founded in 1912 in Berlin, Germany, and became famous for its fighter aircraft in World War I. In 1919 ...
's mechanism for synchronising the firing of a machine gun with the blades of a moving propeller, followed quickly by the widespread adoption of synchronisation gears by all the combatants in 1916 and 1917, the tractor configuration became almost universally favoured and pushers were reduced to the tiny minority of new aircraft designs that had a specific reason for using the arrangement. Both the British and French continued to use pusher configured bombers, though there was no clear preference either way until 1917. Such aircraft included (apart from the products of the Farman company itself) the
Voisin Voisin (French for "neighbour") may refer to: Companies *Avions Voisin, the French automobile company :*Voisin Laboratoire, a car manufactured by Avions Voisin *Voisin (aircraft), the French aircraft manufacturer * Voisin, a Lyon-based chocolat ...
bombers (3,200 built), the Vickers F.B.5 "Gunbus", and the Royal Aircraft Factory F.E.2, however even these would find themselves being shunted into training roles before disappearing entirely. Possibly the last fighter to use the Farman pusher configuration was the 1931
Vickers Type 161 The Vickers Type 161 was an unusual 1930s pusher biplane interceptor, designed to attack aircraft from below with a single upward-angle large calibre gun. The aircraft flew well but the concept was abandoned and only one was built. Development ...
COW gun fighter. 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 boat A flying boat is a type of fixed-winged seaplane with a hull, allowing it to land on water. It differs from a floatplane in that a flying boat's fuselage is purpose-designed for floatation and contains a hull, while floatplanes rely on fusela ...
s, 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 Supermarine Walrus was a late example of this layout. 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 The Farman F.220 and its derivatives were thick-sectioned, high-winged, four engined monoplanes from Farman Aviation Works. Based on the push-pull configuration proven by the F.211, design started in August 1925 and the first flight of the prot ...
, 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. By the late 1930s the widespread adoption of all-metal stressed skin construction of aircraft meant, at least in theory, that the aerodynamic penalties that had limited the performance of pushers (and indeed any unconventional layout), were reduced; however any improvement that boosts pusher performance also boosts the performance of conventional aircraft and they remained a rarity in operational service—so the gap was narrowed but was not closed entirely. During
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, experiments were conducted with pusher fighters by most of the major powers. Difficulties remained, particularly that a pilot having to bail out of a pusher was liable to pass through the propeller arc. This meant that of all the types concerned, only the relatively conventional Swedish SAAB 21 of 1943 went into series production. Other problems related to the aerodynamics of canard layouts, which had been used on most of the pushers, proved more difficult to resolve.See stability issues of the
Curtiss-Wright XP-55 Ascender The Curtiss-Wright XP-55 Ascender (company designation CW-24) is a 1940s United States prototype fighter aircraft built by Curtiss-Wright. Along with the Vultee XP-54 and Northrop XP-56, it resulted from United States Army Air Corps proposal ...
One of the world's first
ejection seat In aircraft, an ejection seat or ejector seat is a system designed to rescue the pilot or other crew of an aircraft (usually military) in an emergency. In most designs, the seat is propelled out of the aircraft by an explosive charge or rock ...
s was (per force) designed for this aircraft, which later re-emerged with a jet engine. The largest pusher
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It 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 ...
to fly was the Convair B-36 "Peacemaker" of 1946, which was also the largest bomber ever operated by the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
. It had six
Pratt & Whitney Wasp Major The Pratt & Whitney R-4360 Wasp Major is an American 28-cylinder four-row radial piston aircraft engine designed and built during World War II. First run in 1944, at , it is the largest-displacement aviation piston engine to be mass-produced in ...
radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ca ...
s mounted in the wing, each driving a pusher propeller located behind the trailing edge of the wing. Although the vast majority of propeller-driven aircraft continue to use a tractor configuration, there has been in recent years something of a revival of interest in pusher designs: in light
homebuilt aircraft Homebuilt aircraft, also known as amateur-built aircraft or kit planes, are constructed by persons for whom this is not a professional activity. These aircraft may be constructed from "scratch", from plans, or from assembly kits.Armstrong, Kenn ...
such as
Burt Rutan Elbert Leander "Burt" Rutan (; born June 17, 1943) is a retired American aerospace engineer and entrepreneur noted for his originality in designing light, strong, unusual-looking, and energy-efficient air and space craft. He designed the recor ...
's canard designs since 1975, ultralights such as the
Quad City Challenger The Quad City Challenger is a family of one and two seats-in-tandem, pusher configuration, tricycle landing gear ultralight aircraft that is designed and produced by Quad City Aircraft Corporation of Moline, Illinois. The Challenger was ...
(1983), flexwings,
paramotors Powered paragliding, also known as paramotoring or PPG, is a form of ultralight aviation where the pilot wears a back-pack motor (a paramotor) which provides enough thrust to take off using a paraglider. It can be launched in still air, and on ...
,
powered parachute A powered parachute, often abbreviated PPC, and also called a motorized parachute or paraplane, is a type of aircraft that consists of a parafoil with a motor and wheels. The FAA defines a powered parachute as ''a powered aircraft a flexible o ...
s, and
autogyro An autogyro (from Greek and , "self-turning"), also known as a ''gyroplane'', is a type of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. Forward thrust is provided independently, by an engine-driven propeller. Whi ...
s. The configuration is also often used for
unmanned aerial vehicle An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controller ...
s, due to requirements for a forward fuselage free of any engine interference. The Aero Dynamics Sparrow Hawk was another homebuilt aircraft constructed chiefly in the 1990s.


Engine installation considerations

In a pusher configuration, the force provided by the propeller is ''pushing'' towards the engine, rather than away. To convert a tractor engine and propeller combination to pusher operation it is not sufficient to simply turn the engine and propeller round, since the propeller would continue to "pull" driving the aircraft to the rear. Assuming the engine cannot be run in the reverse direction, the "handedness" of the propeller must be reversed. The loads on the thrust race (bearings that prevent fore and aft movement of the crankshaft) are also reversed, because the pusher propeller is pushing into the engine rather than pulling away from it as in a tractor. Some modern engines designed for light aircraft are fitted with a thrust race suitable for both "pushing" and "pulling", but others require a different part depending in which sense they are operating. Power-plant cooling design is more complex than for the tractor configuration, where the propeller forces air through the system.


Configurations

Airships are the oldest type of pusher aircraft, going back to Frenchman Henri Giffard's pioneering airship of 1852. Pusher aircraft have been built in many different configurations. In the vast majority of fixed-wing aircraft the propeller or propellers are still located just behind the trailing edge of the "main lifting surface", or below the wing (paramotors) with the engine being located behind the crew position. Conventional aircraft layout have a rear tail (
empennage The empennage ( or ), also known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an arrow.Crane, Dale: ''Dictionary of Aeronautical Terms, third e ...
) for stabilization and control. The propeller may be close to the engine, as the usual direct drive: * The propeller may be ahead of the tail: inside the framework ( Farman III), in line with the fuselage (
RFB Fantrainer The RFB Fantrainer (or Fan Trainer) is a two-seat flight training aircraft which uses a mid-mounted ducted fan propulsion system. Developed and manufactured by German aircraft company Rhein-Flugzeugbau GmbH (RFB), it has been used by the Luftwaf ...
), between tail booms (
Cessna Skymaster The Cessna Skymaster is an American twin-engine civil utility aircraft built in a push-pull configuration. Its engines are mounted in the nose and rear of its pod-style fuselage. Twin booms extend aft of the wings to the vertical stabilizers ...
), above the fuselage on wing (
Quad City Challenger The Quad City Challenger is a family of one and two seats-in-tandem, pusher configuration, tricycle landing gear ultralight aircraft that is designed and produced by Quad City Aircraft Corporation of Moline, Illinois. The Challenger was ...
), on nacelle or axial pod (
Lake Buccaneer The Lake Buccaneer is an American four-seat, light amphibious aircraft derived from the Colonial C-2 Skimmer, itself a development of the three-seat Colonial C-1 Skimmer. Development The Colonial Aircraft of Sanford, Maine developed the C-2 ...
), or coaxially around rear fuselage (
Gallaudet D-4 The Gallaudet D-4 was an unusual biplane designed and built by Gallaudet Aircraft Company for the United States Navy. It was powered by a Liberty L-12 engine buried within the fuselage which turned a large, four-bladed propeller attached to a ri ...
). * The propeller may be located behind the vertical tail, under the horizontal tail ( Prescott Pusher). * Engines and propellers may be located on wings (
Piaggio P.180 Avanti The Piaggio P.180 Avanti is an Italian executive transport aircraft with twin turboprop engines mounted in pusher configuration. It seats up to nine people in a pressurized cabin and may be flown by one or two pilots. The design is of three-su ...
) or on lateral pods(
Embraer/FMA CBA 123 Vector The Embraer/FMA CBA 123 Vector (originally EMB 123 for Embraer and IA 70 for FMA) was a 1990 turboprop aircraft designed for regional flights, to carry up to 19 passengers. The program arose from a partnership between the Brazilian company Emb ...
). The engine may be buried in a forward remote location, driving the propeller by drive shaft or belt: * The propeller may be located ahead of the tail, behind the wing (
Eipper Quicksilver Quicksilver is a line of single and two-place high wing, single-engine, ultralight aircraft that evolved from weight-shift hang gliders including Bob Lovejoy's High Tailer. The earliest powered version, the Quicksilver C, was created as a se ...
) or inside the airframe (
Rhein Flugzeugbau RW 3 Multoplan The Rhein Flugzeugbau RW 3 Multoplan is a two-seat light pusher configuration aircraft that was produced in small numbers by Rhein Flugzeugbau GmbH between 1958 and 1961. Design The prototype RW 3 Multoplan was designed by Hanno Fischer who fou ...
). * The propeller may be located inside the tail, either cruciform or ducted fan ( Marvelette). * The propeller may be located at the rear, behind a conventional tail (
Bede BD-5 The Bede BD-5 Micro is a series of small, single-seat homebuilt aircraft created in the late 1960s by US aircraft designer Jim Bede and introduced to the market primarily in kit form by the now-defunct Bede Aircraft Corporation in the early 19 ...
). * The propeller may be located above the fuselage such as on many small flying boats (
Lake Buccaneer The Lake Buccaneer is an American four-seat, light amphibious aircraft derived from the Colonial C-2 Skimmer, itself a development of the three-seat Colonial C-1 Skimmer. Development The Colonial Aircraft of Sanford, Maine developed the C-2 ...
) In canard designs a smaller wing is sited forward of the aircraft's main wing. This class mainly uses a direct drive,An exception is the
Raptor Aircraft Raptor The Raptor was a four to five-seat single-engined canard-wing homebuilt light aircraft, whose prototype was under development by Raptor Aircraft of Ball Ground, Georgia, United States. The Raptor's tricycle landing gear was fully retract ...
whose Audi V6 diesel engine drives the propeller via PRSU belts.
either single engine, axial propellerCanard aircraft: wartime
Curtiss-Wright XP-55 Ascender The Curtiss-Wright XP-55 Ascender (company designation CW-24) is a 1940s United States prototype fighter aircraft built by Curtiss-Wright. Along with the Vultee XP-54 and Northrop XP-56, it resulted from United States Army Air Corps proposal ...
and Japanese
Kyushu J7W The Kyūshū J7W ''Shinden'' (震電, "Magnificent Lightning") was a World War II Japanese propeller-driven prototype fighter with wings at the rear of the fuselage, a nose-mounted canard, and pusher engine. Developed by the Imperial Ja ...
(with a drive shaft), Ambrosini SS.4; Rutan
VariEze The Rutan VariEze is a composite, canard aircraft designed by Burt Rutan. It is a high-performance homebuilt aircraft, hundreds of which have been constructed. The design later evolved into the Long-EZ and other, larger cabin canard aircraft ...
and
Long-EZ The Rutan Model 61 Long-EZ is a tandem 2-seater homebuilt aircraft designed by Burt Rutan's Rutan Aircraft Factory. The Long-EZ has a canard layout, a swept wing with wingtip rudders, and a pusher engine and propeller. The tricycle landing g ...
,
AASI Jetcruzer The AASI Jetcruzer was an American single turboprop light civil transport made by Advanced Aerodynamics and Structures Inc. The Jetcruzer had an unusual configuration, with a single turboprop engine driving a pusher propeller, a prominent canar ...
or twin engines with a symmetrical layoutCanard symmetrical layout:
Wright Flyer The ''Wright Flyer'' (also known as the ''Kitty Hawk'', ''Flyer'' I or the 1903 ''Flyer'') made the first sustained flight by a manned heavier-than-air powered and controlled aircraft—an airplane—on December 17, 1903. Invented and flown b ...
,
Beechcraft Starship The Beechcraft Starship is a twin-turboprop six- to eight-passenger pressurized business aircraft produced by Beech Aircraft Corporation. Development Development of the Starship began in 1979 when Beech decided to explore designs for a succe ...
or an in line layout (push-pull) as the
Rutan Voyager The Rutan Model 76 Voyager was the first aircraft to fly around the world without stopping or refueling. It was piloted by Dick Rutan and Jeana Yeager. The flight took off from Edwards Air Force Base's 15,000 foot (4,600 m) runway in the Moja ...
. In
tailless aircraft In aeronautics, a tailless aircraft is an aircraft with no other horizontal aerodynamic surface besides its main wing. It may still have a fuselage, vertical tail fin (vertical stabilizer), and/or vertical rudder. Theoretical advantages of the ...
such as Lippisch Delta 1 and
Westland-Hill Pterodactyl Pterodactyl was the name given to a series of experimental tailless aircraft designs developed by G. T. R. Hill in the 1920s and early 1930s. Named after the genus Pterodactylus, a well-known type of Pterosaur commonly known as the pterodactyl, a ...
type I and IV, horizontal stabilizers at the rear of the aircraft are absent. Flying wings like the
Northrop YB-35 The Northrop YB-35, Northrop designation N-9 or NS-9, were experimental heavy bomber aircraft developed by the Northrop Corporation for the United States Army Air Forces during and shortly after World War II. The airplane used the radical and p ...
are tailless aircraft without distinct fuselage. In these installations, the engines are either mounted in nacelles or the fuselage on tailless aircraft, or buried in the wing on flying wings, driving propellers behind the trailing edge of the wing, often by extension shaft. Almost without exception flexwing aircraft,
paramotor Paramotor is the generic name for the harness and propulsive portion of a powered paragliding, powered paraglider ("PPG"). There are two basic types of paramotors: foot launch and wheel launch. Foot launch models consist of a frame with harness ...
s and
powered parachute A powered parachute, often abbreviated PPC, and also called a motorized parachute or paraplane, is a type of aircraft that consists of a parafoil with a motor and wheels. The FAA defines a powered parachute as ''a powered aircraft a flexible o ...
s use a pusher configuration. Other craft with pusher configurations run on flat surfaces, land, water, snow or ice. Thrust is provided by propellers and ducted fans, located to the rear of the vehicle. *
Hovercraft A hovercraft, also known as an air-cushion vehicle or ACV, is an amphibious Craft (vehicle), craft capable of travelling over land, water, mud, ice, and other surfaces. Hovercraft use blowers to produce a large volume of air below the hull ...
, lifted by an air cushion, such as the 58 passengers
SR.N6 The Saunders-Roe (later British Hovercraft Corporation) SR.N6 hovercraft (also known as the ''Winchester'' class) was essentially a larger version of the earlier SR.N5 series. It incorporated several features that resulted in the type becoming ...
. *
Airboat An airboat (also known as a planeboat, swamp boat, bayou boat, or fanboat) is a flat-bottomed watercraft propelled by an aircraft-type propeller and powered by either an aircraft or automotive engine. In early aviation history the term ''airboat ...
, flat bottomed vessels planing on water, * Propeller-driven
snowmobile A snowmobile, also known as a Ski-Doo, snowmachine, sled, motor sled, motor sledge, skimobile, or snow scooter, is a motorized vehicle designed for winter travel and recreation on snow. It is designed to be operated on snow and ice and does not ...
s, also known as aerosleighs or
Aerosani Aerosani (both singular and plural; russian: aэросани, literally aerosled) is a type of propeller-driven snowmobile, running on skis, used for communications, mail deliveries, medical aid, emergency recovery and border patrolling in northern ...


Advantages


Practical requirements

Placing the cockpit forward of the wing to balance the weight of the engine(s) aft improves visibility for the crew. 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. Aircraft where the engine is carried by, or very close to, the pilot (such as paramotors, powered parachutes, autogyros, and flexwing trikes) place the engine behind the pilot to minimise the danger to the pilot's arms and legs. These two factors mean that this configuration was widely used for early combat aircraft, and remains popular today among ultralight aircraft,
unmanned aerial vehicle An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controller ...
s (UAVs) and
radio-controlled airplane A radio-controlled aircraft (often called RC aircraft or RC plane) is a small flying machine that is controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter continuously communicates with a receiver ...
s.


Aerodynamics

A pusher may have a shorter fuselage and hence a reduction in both fuselage wetted area and weight. In contrast to tractor layout, a pusher propeller at the end of the fuselage is stabilizing. A pusher needs less stabilizing vertical tail area and hence presents less weathercock effect; at takeoff roll it is generally less sensitive to crosswind.Because of less weathercock stability 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. At takeoff, a canard pusher pilot does not have to apply rudder input to balance this moment. Efficiency can be gained by mounting a propeller behind the fuselage, because it re-energizes the
boundary layer In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary condi ...
developed on the body, and reduces the
form drag Parasitic drag, also known as profile drag, is a type of aerodynamic drag that acts on any object when the object is moving through a fluid. Parasitic drag is a combination of form drag and skin friction drag. It affects all objects regardless of ...
by keeping the flow attached to the fuselage. However, it is usually a minor gain compared to the airframe's detrimental effect on propeller efficiency. Wing profile drag may be reduced due to the absence of prop-wash over any section of the wing.


Safety

The engine is mounted behind the crew and passenger compartments, so fuel oil and coolant leak will vent behind the aircraft, and any engine fire will be directed behind the aircraft. Similarly, propeller failure is less likely to directly endanger the crew. A pusher ducted fan system offers a supplementary safety feature attributed to enclosing the rotating fan in the duct, therefore making it an attractive option for various advanced unmanned air vehicle configurations or for small/personal air vehicles or for aircraft models.


Disadvantages


Structural and weight considerations

A pusher design with an empennage behind the propeller is structurally more complex than a similar tractor type. The increased weight and drag degrades performance compared with a similar tractor type. Modern aerodynamic knowledge and construction methods may reduce but never eliminate the difference. A remote or buried engine requires a drive shaft and associated bearings and supports, torsional vibration control, and adds weight and complexity.


Center of gravity and landing gear considerations

To maintain a safe
center of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weight function, weighted relative position (vector), position of the distributed mass sums to zero. Thi ...
(CG) position, there is a limit to how far aft an engine can be installed. The forward location of the crew may balance the engine weight and will help determine the CG. As the CG location must be kept within defined limits for safe operation load distribution must be evaluated before each flight.In the case of the Cozy IV, a side-by-side four-seater, an absent copilot must be balanced with 20 kg (40 lb) in the nose of the aircraft (Cafe Aircraft Performance Report) 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. The
Rutan Rutan may refer to: * Rutan, Iran, a village in Hormozgan Province, Iran * Burt Rutan, American aircraft designer * Dick Rutan, American test pilot, and brother of Burt Rutan * Erik Rutan, American metal guitarist and producer * Rutan (''Doctor Who' ...
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. In
autogyro An autogyro (from Greek and , "self-turning"), also known as a ''gyroplane'', is a type of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. Forward thrust is provided independently, by an engine-driven propeller. Whi ...
s a high thrust line results in a control hazard known as power push-over.


Aerodynamic considerations

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. The absence of prop-wash over the wing reduces the lift and increases takeoff roll length. Pusher engines mounted on the wing may obstruct sections of the wing
trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 1997. ...
, reducing the total width available for control surfaces such as flaps and ailerons. When a propeller is mounted in front of the tail, changes in engine power alter the airflow over the tail and can give strong pitch or yaw changes.


Propeller ground clearance and foreign object damage

Due to the pitch rotation at takeoff, the propeller diameter may have to be reduced (with a loss of efficiency) and/or landing gear made longer and heavier. Many pushers
Dornier Do 335 The Dornier Do 335 ''Pfeil'' ("Arrow") was a heavy fighter built by Dornier for Germany during World War II. The two-seater trainer version was called ''Ameisenbär'' ("anteater"). The ''Pfeil''s performance was predicted to be better than other ...
, LearAvia Lear Fan, Prescott Pusher, Grob GF 200,
Beechcraft Starship The Beechcraft Starship is a twin-turboprop six- to eight-passenger pressurized business aircraft produced by Beech Aircraft Corporation. Development Development of the Starship began in 1979 when Beech decided to explore designs for a succe ...
, Vmax Probe
have ventral fins or skids beneath the propeller to prevent the propeller from striking the ground at an added cost in drag and weight. On tailless pushers such as the
Rutan Long-EZ The Rutan Model 61 Long-EZ is a tandem 2-seater homebuilt aircraft designed by Burt Rutan's Rutan Aircraft Factory. The Long-EZ has a canard layout, a swept wing with wingtip rudders, and a pusher engine and propeller. The tricycle landing ...
the propeller arc is very close to the ground while flying nose-high during takeoff or landing. Objects on the ground kicked up by the wheels can pass through the propeller disc, causing damage or accelerated wear to the blades or, in extreme cases, the blades may strike the ground. When an airplane flies in
icing conditions In aviation, icing conditions are atmospheric conditions that can lead to the formation of water ice on an aircraft. Ice accretion and accumulation can affect the external surfaces of an aircraft – in which case it is referred to as ''airframe ...
, ice can accumulate on the wings. If an airplane with wing-mounted pusher engines experiences icing, the props will ingest shedded chunks of ice, endangering the propeller blades and parts of the airframe that can be struck by ice violently redirected by the props. In early pusher combat aircraft, spent ammunition casings caused similar problems, and devices for collecting them had to be devised.


Propeller efficiency and noise

The propeller passes through the fuselage wake, wing and other flight surface downwashes—moving asymmetrically through a disk of irregular airspeed. This reduces propeller efficiency and causes vibration inducing structural propeller fatigueThe only approved prop for the Rutan pushers is wood, which is more resistant to fatigue damage. and noise. Prop efficiency is usually at least 2–5% less and in some cases more than 15% less than an equivalent tractor installation. Fullscale wind tunnel investigation of the canard
Rutan VariEze The Rutan VariEze is a composite, canard aircraft designed by Burt Rutan. It is a high-performance homebuilt aircraft, hundreds of which have been constructed. The design later evolved into the Long-EZ and other, larger cabin canard aircraf ...
showed a propeller efficiency of 0.75 compared to 0.85 for a tractor configuration, a loss of 12%. Pusher props are noisy, and cabin noise may be higher than tractor equivalent (
Cessna XMC The Cessna XMC was a prototype technology demonstrator designed to show advanced aerodynamics and materials. The marketing name of XMC stood for "Experimental Magic Carpet" with the single test aircraft designated Cessna 1014 and later 1034 in ...
vs
Cessna 152 The Cessna 152 is an American two-seat, fixed- tricycle-gear, general aviation airplane, used primarily for flight training and personal use. It was based on the earlier Cessna 150 incorporating a number of minor design changes and a slightly ...
). Propeller noise may increase because the engine exhaust flows through the props. This effect may be particularly pronounced when using turboprop engines due to the large volume of exhaust they produce.


Engine cooling and exhaust

In pusher configuration, the propeller does not contribute airflow over the engine or radiator. Some aviation engines have experienced cooling problems when used as pushers. To counter this, auxiliary fans may be installed, adding additional weight. The engine of a pusher exhausts forward of the propeller, and in this case the exhaust may contribute to corrosion or other damage to the propeller. This is usually minimal, and may be mainly visible in the form of soot stains on the blades.


Propeller and safety

In case of propeller/tail proximity, a blade break can hit the tail or produce destructive vibrations leading to a loss of control. Crew members risk striking the propeller while attempting to
bail out A bailout is the provision of financial help to a corporation or country which otherwise would be on the brink of bankruptcy. A bailout differs from the term ''bail-in'' (coined in 2010) under which the bondholders or depositors of global sy ...
of a single-engined airplane with a pusher prop. At least one early ejector seat was designed specifically to counter this risk. Some modern light aircraft include a parachute system that saves the entire aircraft, thus averting the need to bail out.


Engine and safety

Engine location in the pusher configuration might endanger the aircraft's occupants in a crash or crash-landing in which engine momentum projects through the cabin. For example, with the engine placed directly behind the cabin, during a nose-on impact the engine momentum may carry the engine through the firewall and cabin, and might injure some cabin occupant(s).Crash of Ambrosini SS.4


Airplane loading and safety

Spinning propellers are always a hazard on ground working, such as loading or embarking the airplane. Tractor configuration leaves the rear of the plane as relatively safe working area, while a pusher is dangerous to approach from behind, while a spinning propeller may suck in things and people nearby in front of it with fatal results to both the plane and the people sucked in. Even more hazardous are unloading operations, especially mid-air, such as dropping supplies on parachute or skydiving operations, which are next to impossible with a pusher configuration airplane, especially if propellers are mounted on fuselage or sponsons.


See also

*
Ducted propeller A ducted propeller, also known as a Kort nozzle, is a marine propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and is especially used on heavily loaded propellers or propellers with limited dia ...
* List of pusher aircraft by configuration * List of pusher aircraft by configuration and date


References


Notes


Citations


Sources

* * * * * *


External links

*{{Commons category-inline, Aircraft with pusher-propellers Aircraft configurations