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In an aircraft with a pusher configuration (as opposed to a tractor configuration), the propeller(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 or ducted fan) thrust device attached to a craft, either
aerostat An aerostat (, via French) is a lighter-than-air aircraft that gains its lift through the use of a buoyant gas. Aerostats include unpowered balloons and powered airships. A balloon may be free-flying or tethered. The average density of the c ...
(
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 flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or by using the Lift (force), dynamic lift of an airfoil, or in ...
, WIG, paramotor, rotorcraft) or others types such as
hovercraft A hovercraft, also known as an air-cushion vehicle or ACV, is an amphibious 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, or air cushion, ...
, airboat and propeller-driven snowmobiles. "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 (1906), the Voisin-Farman I (1907) and the Curtiss Model D used by Eugene Ely for the first ship landing on January 18, 1911. Henri Farman'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 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 attache ...
. 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 List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
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, 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 bombers (3,200 built), the
Vickers F.B.5 The Vickers F.B.5 (Fighting Biplane 5) (known as the "Gunbus") was a British two-seat pusher military biplane of the First World War. Armed with a single .303 in (7.7 mm) Lewis gun operated by the observer in the front of the ...
"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 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 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 World War II by country, vast majority of the world's countries—including all of the great power ...
, 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 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 flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or by using the Lift (force), dynamic lift of an airfoil, or in ...
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 Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. It had six Pratt & Whitney Wasp Major
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 ...
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'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 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 or ...
s, and autogyros. 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 controll ...
s, due to requirements for a forward fuselage free of any engine interference. The
Aero Dynamics Sparrow Hawk The Aero Dynamics Sparrow Hawk MK II is an American homebuilt, two seater, single-engine, pusher monoplane, manufactured by Aero Dynamics Limited. It was designed by former Boeing design engineer Charles "Chuck" Herbst. Design and developmen ...
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), 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 rin ...
). * The propeller may be located behind the vertical tail, under the horizontal tail (
Prescott Pusher The Prescott Pusher is an American, four-seat, pusher configuration homebuilt aircraft, with a large cockpit, retractable or fixed gear and a T-tail. The pilot and passengers enter the aircraft through a large left-side clamshell door. Design an ...
). * Engines and propellers may be located on wings ( Piaggio P.180 Avanti) 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 sel ...
) 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 foun ...
). * 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 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 retracta ...
whose Audi V6 diesel engine drives the propeller via PRSU belts.
either single engine, axial propellerCanard aircraft: wartime Curtiss-Wright XP-55 Ascender and Japanese Kyushu J7W (with a drive shaft),
Ambrosini SS.4 The SAI-Ambrosini SS.4 was an Italian fighter prototype developed in the late 1930s, featuring a canard-style wing layout and a pusher propeller. Development of the SS.4 was abandoned after the prototype crashed on its second flight. Developme ...
; Rutan VariEze and Long-EZ,
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 succes ...
or an in line layout (push-pull) as the Rutan Voyager. In tailless aircraft such as Lippisch Delta 1 and Westland-Hill Pterodactyl type I and IV, horizontal stabilizers at the rear of the aircraft are absent.
Flying wing A flying wing is a tailless fixed-wing aircraft that has no definite fuselage, with its crew, payload, fuel, and equipment housed inside the main wing structure. A flying wing may have various small protuberances such as pods, nacelles, blis ...
s like the Northrop YB-35 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, paramotors 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 or ...
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 capable of travelling over land, water, mud, ice, and other surfaces. Hovercraft use blowers to produce a large volume of air below the hull, or air cushion, ...
, lifted by an air cushion, such as the 58 passengers SR.N6. * Airboat, flat bottomed vessels planing on water, * Propeller-driven snowmobiles, also known as aerosleighs or Aerosani


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 controll ...
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 developed on the body, and reduces the form drag 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 weighted relative position of the distributed mass sums to zero. This is the point to which a force ma ...
(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 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 autogyros 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, 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 oth ...
,
LearAvia Lear Fan The LearAvia Lear Fan 2100 was a turboprop business aircraft designed in the 1970s, with an unusual configuration. The Lear Fan never entered production. Design and development The LearFan was designed by Bill Lear, but not completed before his ...
,
Prescott Pusher The Prescott Pusher is an American, four-seat, pusher configuration homebuilt aircraft, with a large cockpit, retractable or fixed gear and a T-tail. The pilot and passengers enter the aircraft through a large left-side clamshell door. Design an ...
,
Grob GF 200 The Grob GF 200 was a business aircraft of unorthodox design developed in Germany during the 1990s. Design and development The GF 200 was a low-wing cantilever monoplane with retractable tricycle undercarriage and a highly streamlined fuselage. ...
,
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 succes ...
, 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 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 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 vs Cessna 152). 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 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 The SAI-Ambrosini SS.4 was an Italian fighter prototype developed in the late 1930s, featuring a canard-style wing layout and a pusher propeller. Development of the SS.4 was abandoned after the prototype crashed on its second flight. Developme ...


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 *
List of pusher aircraft by configuration A pusher aircraft is a type of aircraft using propellers placed behind the engines and may be classified according to engine/propeller location and drive as well as the lifting surfaces layout (conventional or 3 surface, canard, joined wing, taill ...
* List of pusher aircraft by configuration and date


References


Notes


Citations


Sources

* * * * * *


External links

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