Pusher configuration
Encyclopedia
Craft (vehicle)
The word craft since the 17th century has denoted a vehicle or vessel that is used for transportation on the sea, in the air or in space. But it can be applied to fictional vessels such as time craft, dimensional craft, and probability craft...
with a pusher configuration the propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
(s) are mounted behind their respective engine(s). According to Bill Gunston
Bill Gunston
Bill Gunston OBE FRAeS is one of the most internationally respected and published aviation and military authors. He flew with Britain's Royal Air Force from 1943 to 1948, and is a flying instructor. He has spent most of his adult life doing research and writing on aircraft and aviation. He is the...
, a "pusher propeller" is one mounted behind engine so that drive shaft is in compression. Pusher configuration describes also more commonly the specific layout of a fixed-wing aircraft of which the thrust device has a pusher configuration.
Pusher configuration describes this specific (propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
or ducted fan
Ducted fan
A ducted fan is a propulsion arrangement whereby a fan, which is a type of propeller, is mounted within a cylindrical shroud or duct. The duct reduces losses in thrust from the tip vortices of the fan, and varying the cross-section of the duct allows the designer to advantageously affect the...
) thrust device attached to a craft, either aerostat
Aerostat
An aerostat is a craft that remains aloft primarily through the use of buoyant lighter than air gases, which impart lift to a vehicle with nearly the same overall density as air. Aerostats include free balloons, airships, and moored balloons...
(airship
Airship
An airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms...
) or aerodyne
Aerodyne
Aerodyne may refer to:*Heavier-than-air aircraft, deriving lift from dynamic motion through the air.*The Fender Aerodyne Telecaster, a contemporary model of the classic Fender Telecaster Electric guitar....
(aircraft
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...
, WIG, paramotor
Paramotor
Paramotor is a generic name for the propulsive portion of a powered paraglider . It consists of a frame that combines the motor, propeller, harness and cage...
, rotorcraft
Rotorcraft
A rotorcraft or rotary wing aircraft is a heavier-than-air flying machine that uses lift generated by wings, called rotor blades, that revolve around a mast. Several rotor blades mounted to a single mast are referred to as a rotor. The International Civil Aviation Organization defines a rotorcraft...
) or others types such as hovercraft
Hovercraft
A hovercraft is a craft capable of traveling over surfaces while supported by a cushion of slow moving, high-pressure air which is ejected against the surface below and contained within a "skirt." Although supported by air, a hovercraft is not considered an aircraft.Hovercraft are used throughout...
, airboat and propeller-driven snowmobile
Snowmobile
A snowmobile, also known in some places as a snowmachine, or sled,is a land vehicle for winter travel on snow. Designed to be operated on snow and ice, they require no road or trail. Design variations enable some machines to operate in deep snow or forests; most are used on open terrain, including...
s.Such as Propeller-Driven Sleighs http://www.aqpl43.dsl.pipex.com/MUSEUM/TRANSPORT/propsleigh/propsleigh.htm or Aerosani
Pushers have been designed and built in many different layouts, some of them quite radical and some early definitions are no longer applicable.Examples of tractors with aft propeller: Radab Windex
Radab Windex
|-See also:-External links:*****...
motor glider, Seawind 300C
Seawind 300C
The Seawinds are a family of composite, four-seat, amphibian airplanes that all feature a single tail-mounted engine.The Seawind line consists of the kit-built Seawind 2000 and Seawind 3000 that were marketed by SNA Inc. of Kimberton, Pennsylvania, USA and the Seawind 300C that was developed by...
seaplane, A-90 Orlyonok
A-90 Orlyonok
-External links:* * * * * *...
amphibian, e-Genius
E-Genius
The e-Genius is a manned electric airplane, which was developed by the Institute of Aircraft Design at the University of Stuttgart. The maiden flight took place on May 25, 2011.- Development :...
GFC 2011 competitor
History
An early successful model aircraft with a pusher propeller was the rubber-powered "Planophore", by Alphonse PénaudAlphonse Pénaud
Alphonse Pénaud , was a 19th-century French pioneer of aviation, inventor of the rubber powered model airplane Planophore and founder of the aviation industry.-Biography:...
, 1871.
Many early aircraft (especially biplanes) were "pushers", including the Wright Flyer
Wright Flyer
The Wright Flyer was the first powered aircraft, designed and built by the Wright brothers. They flew it four times on December 17, 1903 near the Kill Devil Hills, about four miles south of Kitty Hawk, North Carolina, U.S.The U.S...
(1903), the Voisin-Farman I
Voisin-Farman I
The 1907 Voisin biplane was the first successful powered aircraft designed by aeronautical engineer and manufacturer Gabriel Voisin. It was used by the French aviator Henri FarmanBorn in France to British parents, Henry Farman took French nationality in 1937 to make the first heavier-than-air...
(1907) and the Curtiss Model D
Curtiss Model D
|-See also:-External links:...
used by Eugene Ely for the first ship landing on January 18, 1911. Henri Farman's pusher Farman III
Farman III
|-See also:-Bibliography:*Opdycke, Leonard E French Aeroplanes Before the Great War Atglen, PA: Schiffer 1999 ISBN 0 7643 0752 5-External links:**...
and its successors were so influential in Britain that pushers in general became known as the "Farman type". Other early pusher configurations were minor 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
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
. 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 relyed 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, and drag invoking, wire-braced framework. Well before the beginning 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...
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
Tractor configuration
thumb|right|[[Evektor-Aerotechnik|Aerotechnik EV97A Eurostar]], a tractor configuration aircraft, being pulled into position by its pilot for refuelling....
.
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; 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, although few new ones entered service after 1916..
At least up to the end of 1916, however, pushers (such as the Airco DH.2
Airco DH.2
|-DH.2 aces:Distinguished pilots of the DH.2 included Victoria Cross winner Lanoe Hawker , who was the first commander of No 24 Squadron and ace Alan Wilkinson. The commander of No. 32 Squadron, Lionel Rees won the Victoria Cross flying the D.H.2 for single handedly attacking a formation of 10...
fighter) were still favoured as gun-carrying aircraft by the British
Royal Flying Corps
The Royal Flying Corps was the over-land air arm of the British military during most of the First World War. During the early part of the war, the RFC's responsibilities were centred on support of the British Army, via artillery co-operation and photographic reconnaissance...
because a forward-firing gun could be used without being obstructed by the arc of the propeller. With the successful introduction of Fokker
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....
's mechanism for synchronising the firing of a machine gun with the blades of a moving propeller
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....
, followed quickly by the widespread adoption of synchronisation gears by all the combatants in 1916/17, 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
Vickers F.B.5
The Vickers F.B.5 was a British two-seat pusher military biplane of the First World War...
"Gunbus", and the Royal Aircraft Factory F.E.2
Royal Aircraft Factory F.E.2
The Royal Aircraft Factory F.E.2 was a two-seat pusher biplane that was operated as a day and night bomber and as a fighter aircraft by the Royal Flying Corps during the First World War...
, 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
Vickers Type 161
|-See also:...
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
Flying boat
A flying boat is a fixed-winged seaplane with a hull, allowing it to land on water. It differs from a float plane as it uses a purpose-designed fuselage which can float, granting the aircraft buoyancy. Flying boats may be stabilized by under-wing floats or by wing-like projections from the fuselage...
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
Supermarine Walrus
The Supermarine Walrus was a British single-engine amphibious biplane reconnaissance aircraft designed by R. J. Mitchell and operated by the Fleet Air Arm . It also served with the Royal Air Force , Royal Australian Air Force , Royal Canadian Air Force , Royal New Zealand Navy and Royal New...
was a late example of this layout.
The so called push/pull layout
Push-pull configuration
An aircraft constructed with a push-pull configuration has a mixture of forward-mounted propellers and backward-mounted propellers.-Historical:...
, combining the tractor and pusher configurations (that is – with one or more propellers facing forwards 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 failing, such as on the Farman F.222
Farman F.222
|-See also:-Bibliography:* Ketley, Barry, French Aces of WWII, Osprey Publishing, p. 45* William Green, War Planes of the Second World War, Volume 8, 1967...
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.
During the Second World War
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
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 be drawn into the propeller. This meant that of all the types concerned, only the relatively conventional Swedish Saab 21
Saab 21
|-See also:-References:NotesBibliography* Billing, Peter. "A Fork-Tailed Swede." Air Enthusiast Twenty-two, August–November 1983. Bromley, Kent, UK: Pilot Press Ltd., 1983....
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 seats was (per force) designed for this aircraft - which later re-emerged with a jet engine
Saab 21R
|-See also:-References:NotesBibliography* Andersson, Hans G. Saab Aircraft since 1937 . London: Putnam, 1989. ISBN 0-85177-831-3....
.
The largest pusher aircraft ever flown was the Convair B-36
Convair B-36
The Convair B-36 "Peacemaker" was a strategic bomber built by Convair and operated solely by the United States Air Force from 1949 to 1959. The B-36 was the largest mass-produced piston engine aircraft ever made. It had the longest wingspan of any combat aircraft ever built , although there have...
of 1946, which was also the largest bomber ever operated by the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. It had six 3,800 hp Pratt & Whitney Wasp Major radial engine
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...
s mounted in the wing, each driving a pusher propeller located behind the trailing edge of the wing.
Burt Rutan
Elbert Leander "Burt" Rutan is an American aerospace engineer noted for his originality in designing light, strong, unusual-looking, energy-efficient aircraft...
's canard
Canard (aeronautics)
In aeronautics, canard is an airframe configuration of fixed-wing aircraft in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing...
designs since 1975, ultralights such as the Quad City Challenger
Quad City Challenger
|-See also:...
(1983), flexwings, paramotors, powered parachutes, and autogyros. The configuration is also often used for unmanned aerial vehicle
Unmanned aerial vehicle
An unmanned aerial vehicle , also known as a unmanned aircraft system , remotely piloted aircraft or unmanned aircraft, is a machine which functions either by the remote control of a navigator or pilot or autonomously, that is, as a self-directing entity...
s, due to requirements for a front fuselage free of any engine interference.
Engine installation considerations
Specifically, 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.Pusher aerodyneAerodyneAerodyne may refer to:*Heavier-than-air aircraft, deriving lift from dynamic motion through the air.*The Fender Aerodyne Telecaster, a contemporary model of the classic Fender Telecaster Electric guitar....
aircraft configurations
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 layout
Conventional aircraft layout have a rear tail (empennageEmpennage
The empennage , also known as the tail or tail assembly, of most aircraft gives stability to the aircraft, in a similar way to the feathers on an arrow...
) 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 IIIFarman III|-See also:-Bibliography:*Opdycke, Leonard E French Aeroplanes Before the Great War Atglen, PA: Schiffer 1999 ISBN 0 7643 0752 5-External links:**...
), in line with the fuselage (RFB FantrainerRFB Fantrainer-See also:-References:*"Concept Aircraft" by Jim Winchester, ISBN 978-84-662-1370-7, MMV International Master Publications BV-External links:***...
), between tail booms (Cessna SkymasterCessna SkymasterThe Cessna Skymaster is a United States 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, with the rear engine between them. The horizontal...
), above the fuselage on wing (Quad City ChallengerQuad City Challenger|-See also:...
), on nacelle or axial pod (Lake BuccaneerLake Buccaneer|-See also:-External links:...
), or coaxially around rear fuselage (Gallaudet D-4). - 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) or on lateral pods(Embraer/FMA CBA 123 VectorEmbraer/FMA CBA 123 Vector-References:* Lambert, Mark . Jane's All The World's Aircraft 1993-94. Coulsdon, UK: Jane's Data Division, 1993. ISBN 0-7106-1066-1.* "South American Vector". Air International, September 1990, Vol 39 No. 5. pp. 122–128.-External links:*...
).
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) or inside the airframe (RFB RW3).
- The propeller may be located inside the tail, either cruciform or ducted fan (Marvelette).
- The propeller may be located at the back, behind a conventional tail (Bede BD-5), a T-tail (Grob GF 200Grob GF 200The Grob GF 200 was a business aircraft of unorthodox design developed in Germany during the 1990s. It was a low-wing cantilever monoplane with retractable tricycle undercarriage and a highly streamlined fuselage. The engine was mounted within the fuselage, to the rear of the passenger cabin, and...
), an inverted V-tail ( Taylor Mini IMP ), an Y-tail (LearAvia Lear Fan) or a cruciform tail (Dornier Do 335Dornier Do 335The Dornier Do 335 Pfeil was a World War II heavy fighter built by the Dornier company. The two-seater trainer version was also called Ameisenbär . The Pfeils performance was much better than other twin-engine designs due to its unique "push-pull" layout and the much lower drag of the in-line...
). - The propeller may be located above the fuselage such as a glider with a retractable propeller (Schleicher ASH 26Schleicher ASH 26|-External Links:***Simons M, Segelflugzeuge 1965-2000, Equip, 2004...
).
Canard layout
In canard designs a smaller wing is present at the front of the aircraf. This class mainly uses a direct drive, either single engine, axial propeller Canard aircraft: wartime Curtiss-Wright XP-55 Ascender and Japanese Kyushu J7WKyushu J7W
|-See also:-References:NotesBibliography* Green, William. Warplanes of the Second World War, Volume Three: Fighters. London: Macdonald & Co. Ltd., 1961 . ISBN 0-356-01447-9....
(with a drive shaft), Ambrosini SS.4
Ambrosini SS.4
The SAI-Ambrosini SS.4 was an Italian fighter prototype developed in the late 1930s but never mass produced. The radical design for its day featured a canard-style wing layout and a 'pusher' propeller...
; Rutan VariEze
Rutan VariEze
-See also:-References:* "Flying the VariEze", Air Progress, April 1978.* * * * Taylor, John W. R. Jane's All The World's Aircraft 1982–83. London:Jane's Yearbooks, 1982. ISBN 0-7106-0748-2.* * Flight International 1976...
and Long-EZ
Rutan Long-EZ
-See also:-External links:****...
, AASI Jetcruzer
AASI Jetcruzer
|-External links:****-See also:...
or twin engines with a symmetrical layoutCanard symmetrical layout: Wright Flyer
Wright Flyer
The Wright Flyer was the first powered aircraft, designed and built by the Wright brothers. They flew it four times on December 17, 1903 near the Kill Devil Hills, about four miles south of Kitty Hawk, North Carolina, U.S.The U.S...
, Beechcraft Starship
Beechcraft Starship
The Beechcraft Starship is a twin-turboprop six- to eight-passenger pressurized business aircraft produced by Beech Aircraft Corporation .-Development:...
or an in line layout (push-pull) as the famous Rutan Voyager.
Flying wing and tailless layout
In tailless aircraft such as Lippisch Delta 1Lippisch Delta IV
Alexander Lippisch's Delta IV was a continuation of his work on delta wing designs pioneered in his Delta I, Delta II and Delta III aircraft. The project began with an order from Gerhard Fieseler for a design that his company could build for him to fly in the 1932 Europarundflug air rally...
and Westland-Hill Pterodactyl
Westland-Hill Pterodactyl
The Westland-Hill Pterodactyl series of experimental tailess or flying wing aircraft designs were developed starting in the 1920s. They are named after the genus Pterodactylus, a well-known type of Pterosaur commonly known as the pterodactyl....
type I and IV, horizontal stabilizers at the rear of the aircraft are absent. Flying wing
Flying wing
A flying wing is a tailless fixed-wing aircraft which has no definite fuselage, with most of the crew, payload and equipment being housed inside the main wing structure....
s like the Northrop YB-35
Northrop YB-35
The Northrop XB-35 and YB-35 were experimental heavy bomber aircraft developed for the United States Army Air Forces during and shortly after World War II by the Northrop Corporation. It used the radical and potentially very efficient flying wing design, in which the tail section and fuselage are...
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 trailling edge of the wing, often by extension shaft.
UL trike, paramotor, powered parachute layout
Almost without exception flexwing aircraft, paramotorParamotor
Paramotor is a generic name for the propulsive portion of a powered paraglider . It consists of a frame that combines the motor, propeller, harness and cage...
s and powered parachute
Powered parachute
A powered parachute is a parachute with motor and wheels. The aircraft's airspeed is typically about 25–35 mph . PPCs operate safely at heights ranging from a few feet off the ground to altitudes as high as 18,000+ feet...
s use the thrust device pusher configuration.
Other pusher types
These crafts are running onto a flat surface, land, water, snow or ice. Thrust devices are propellers and ducted fans, located at the back.- HovercraftHovercraftA hovercraft is a craft capable of traveling over surfaces while supported by a cushion of slow moving, high-pressure air which is ejected against the surface below and contained within a "skirt." Although supported by air, a hovercraft is not considered an aircraft.Hovercraft are used throughout...
s, lifted by an air cushion, such as the 58 passengers SR.N6. - Airboat, flat bottomed vesels planning onto the water,
- Propeller-driven snowmobileSnowmobileA snowmobile, also known in some places as a snowmachine, or sled,is a land vehicle for winter travel on snow. Designed to be operated on snow and ice, they require no road or trail. Design variations enable some machines to operate in deep snow or forests; most are used on open terrain, including...
s or aeroleighs, Aerosani
Most built Pushers
- Manned aircraft
- Voisin bombers - 3,200
- Quad City ChallengerQuad City Challenger|-See also:...
ultralight - 3,000 - Royal Aircraft Factory F.E.2Royal Aircraft Factory F.E.2The Royal Aircraft Factory F.E.2 was a two-seat pusher biplane that was operated as a day and night bomber and as a fighter aircraft by the Royal Flying Corps during the First World War...
, biplane fighter and bomber - 1,939 - Rutan Canards VariEze and long-EZBurt RutanElbert Leander "Burt" Rutan is an American aerospace engineer noted for his originality in designing light, strong, unusual-looking, energy-efficient aircraft...
, homebuilts - > 1,000- UAVs
- AeroVironment RQ-11 Raven, hand-launched UAV - 13,000
Advantages
- Placing the cockpit forward of the wing to balance the weight of the engine(s) aft improves visibility for the crew. Similarly any front armament can be used more easily. Consequently, this configuration was widely used for early combat aircraft, and remains popular today among ultralight aircraftUltralight aviationThe term "ultralight aviation" refers to light-weight, 1- or 2-person airplanes., also called microlight aircraft in the UK, India and New Zealand...
.
- The absence of front engine allows special equipment (radar, AUV cameras) to be efficiently installed in the fuselage nose.
- 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.
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 layerBoundary layerIn physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...
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. Also, this effect is not nearly as pronounced on an airplane as it is on a shipShipSince the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...
, due to the higher Reynolds number at which aircraft operate.
- 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 does not have to flow past personnel; any leak will vent behind the aircraft, and any engine fire will be directed behind the aircraft (however, this arrangement puts the empennageEmpennageThe empennage , also known as the tail or tail assembly, of most aircraft gives stability to the aircraft, in a similar way to the feathers on an arrow...
at greater risk—if there is one—but this is less of an issue if the fire occurs at the time of, or as a consequence of, landing). Similarly, propeller failure is less likely to directly endanger the crew.
- Leaks of fuel, oil or coolant from the engine stream away from the aircraft instead of becoming a risk to the pilot, other occupants, and any whole-aircraft parachute installation.
- In case of a crash or crash-landing, fuel and oil in the aft engine area are less likely to be a fire hazard and high-energy propeller fragments are less likely to enter the cabin area.
- At the time when many military aircraft were pushers, the engine afforded some rear protection to the pilot.
- 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 dragDrag (physics)In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
degrades performance compared with a similar tractor type. Modern aerodynamic knowledge and construction methods may reduce but never eliminate the difference. - A remote (buried) engine requires a drive shaft and its associated bearings and supports, special devices for torsional vibration control, increasing mechanical requirements, weight and complexity.
Center of Gravity (c.g.) and landing gear considerations:
- To maintain a workable CG position, there is a limit as 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 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 lbs) 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 moment and sometimes absence of prop-wash over the tail, higher speed and longer roll is required for takeoff compared to tractor aircraft. Main gear located too far aft (aft of empty aircraft c.g.) may require higher takeoff rotation speed ) or even prevent the rotation. The Rutan answer to this problem is to lower the nose of the aircraft at rest such that the empty c.g. is then ahead of the main wheels.
- Due to the center of gravityCenter of gravityIn physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
often being further back on the longitudinal axis than on most tractor airplanes, pushers can be more prone to flat spins, especially if loaded improperly.
Aerodynamic considerations:
- Due to the generally high thrust line (aft propeller/ ground clearance), a low wing pusher layout may suffer pitch changes with power variation (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 edgeTrailing edgeThe trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...
, 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
Foreign object damage
Foreign Object Debris is a substance, debris or article alien to a vehicle or system which would potentially cause damage.Foreign Object Damage is any damage attributed to a foreign object that can be expressed in physical or economic terms that may or may not degrade the product's required...
:
- Because of pitch rotation at take off, propeller diameter may have to be reduced (with a loss of efficiency) and/or landing gear made longer and heavier. Many pushers Dornier Do 335Dornier Do 335The Dornier Do 335 Pfeil was a World War II heavy fighter built by the Dornier company. The two-seater trainer version was also called Ameisenbär . The Pfeils performance was much better than other twin-engine designs due to its unique "push-pull" layout and the much lower drag of the in-line...
, LearAvia Lear Fan, Prescott Pusher, Grob GF 200Grob GF 200The Grob GF 200 was a business aircraft of unorthodox design developed in Germany during the 1990s. It was a low-wing cantilever monoplane with retractable tricycle undercarriage and a highly streamlined fuselage. The engine was mounted within the fuselage, to the rear of the passenger cabin, and...
, Beechcraft StarshipBeechcraft StarshipThe Beechcraft Starship is a twin-turboprop six- to eight-passenger pressurized business aircraft produced by Beech Aircraft Corporation .-Development:...
, 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-EZRutan Long-EZ-See also:-External links:****...
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 conditionsIcing conditionsIn aviation, icing conditions are those atmospheric conditions that can lead to the formation of water ice on the surfaces of an aircraft, or within the engine as carburetor icing. Inlet icing is another engine-related danger, often occurring in jet aircraft. These icing phenomena do not...
, 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 VariEzeRutan VariEze-See also:-References:* "Flying the VariEze", Air Progress, April 1978.* * * * Taylor, John W. R. Jane's All The World's Aircraft 1982–83. London:Jane's Yearbooks, 1982. ISBN 0-7106-0748-2.* * Flight International 1976...
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 XMCCessna XMCThe Cessna XMC was a prototype technology demonstrator designed to show advanced aerodynamics and materials.The marketing name of XMC stood for "Experimental Magic Carpet" and the single test aircraft was designated Cessna 1014 and later 1034.-Development:...
vs Cessna 152Cessna 152The Cessna 152 is an American two-seat, fixed tricycle gear, general aviation airplane, used primarily for flight training and personal use.-Development:...
). - 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 impact the tail or produce destructive vibrations leading to a loss of control.
- Crew members may strike the propeller while attempting to bail outParachuteA parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon...
of a single-engined airplane with a pusher prop. At least one early ejector seat was designed specifically to counter this risk. Modern light aircraft, may have a parachute systemBallistic Recovery SystemsBallistic Recovery Systems is a manufacturer of aircraft ballistic parachutes .The company was formed in 1980 by Boris Popov after he survived a fall in a partly collapsed hang glider in 1975...
that saves the entire aircraft, so there is no need to bail out, though baling out is no longer as common as it once was. - Engine location in the pusher configuration might endanger the aircraft's occupants in a crash or crash-landing. If the engine is placed behind the cabin, it may drive forward under its own momentum during a crash, entering the cabin and injuring the occupants.Crash of Ambrosini SS.4Ambrosini SS.4The SAI-Ambrosini SS.4 was an Italian fighter prototype developed in the late 1930s but never mass produced. The radical design for its day featured a canard-style wing layout and a 'pusher' propeller...
, killing the pilot Conversely, if the engine is placed in front of the cabin, it might act as a battering ram and plow through obstacles in the airplane's path, providing an additional measure of safety.
See also
- Push-pull configurationPush-pull configurationAn aircraft constructed with a push-pull configuration has a mixture of forward-mounted propellers and backward-mounted propellers.-Historical:...
- Tractor configurationTractor configurationthumb|right|[[Evektor-Aerotechnik|Aerotechnik EV97A Eurostar]], a tractor configuration aircraft, being pulled into position by its pilot for refuelling....
- List of pusher aircraft by configuration
- Ducted FanDucted fanA ducted fan is a propulsion arrangement whereby a fan, which is a type of propeller, is mounted within a cylindrical shroud or duct. The duct reduces losses in thrust from the tip vortices of the fan, and varying the cross-section of the duct allows the designer to advantageously affect the...
- Ducted propellerDucted propellerA ducted propeller is a propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and are especially used on heavily loaded propellers or propellers with limited diameter. It was developed by Luigi Stipa and Ludwig Kort .Advantages are increased efficiency,...