Editing Pusher configuration (section)

==In aircraft==
===Advantages===
The drive shaft of a pusher engine is in compression in normal operation,<ref name=Gunston>{{cite book|first= Bill|last= Gunston|title= The Cambridge Aerospace Dictionary|publisher= Cambridge University Press|date= 10 May 2004|page= 480|isbn= 978-0521841405}}</ref> which places less stress on it than being in tension in a tractor configuration. {{Dubious|Driveshaft Stress|date=February 2025}}

==== Practical requirements ====
[[Image:G-LOAM MotorFloater first flight.jpg|thumb|Flexwing microlight with engine and propeller at the pilot's back]]
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.{{citation needed|date = March 2014}}

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 minimize the danger to the pilot's arms and legs.{{citation needed|date = March 2014}} These two factors mean that this configuration was widely used for early combat aircraft, and remains popular today among [[ultralight aviation|ultralight aircraft]], [[unmanned aerial vehicle]]s (UAVs), and [[radio-controlled airplane]]s.{{citation needed|date = March 2014}}

==== Aerodynamics ====
A pusher may have a shorter fuselage and hence a reduction in both fuselage wetted area and weight.<ref name= "Aircraft Design">{{cite book |last= Raymer|first= Daniel P.|date= 1989|title= Aircraft Design: A Conceptual Approach|location= Reston, Virginia|publisher= American Institute of Aeronautics & Astronautics|pages= 222–223|isbn= 9781600869112}}</ref>

In contrast to tractor layout, a pusher propeller at the end of the fuselage is stabilizing.<ref>{{Cite book|title=Fluid-Dynamic Lift: Practical Information on Aerodynamic and Hydrodynamic Lift |journal= NASA Sti/Recon Technical Report A |volume= 76 |last= Hoerner |first=Sighard | chapter=XIII Directional characteristics of aeroplanes: IV Influence of Propulsion |page=17|bibcode= 1975STIA...7632167H |year= 1975 }}</ref> A pusher needs less stabilizing vertical tail area<ref name= "ask don">{{cite web |title= Don discusses propeller effects in detail...|first= Don|last= Stackhouse|url= http://www.djaerotech.com/dj_askjd/dj_questions/propeffects.html|access-date= 15 October 2011|url-status= dead|archive-url= https://web.archive.org/web/20111121020132/http://djaerotech.com/dj_askjd/dj_questions/propeffects.html|archive-date= 21 November 2011}}</ref> and hence presents less [[Weathervane effect|weathercock effect]];<ref>{{cite book |last= Roskam|first= Jan|date= 1999|title= Airplane Design Part II: Preliminary Configuration Design and Integration of the Propulsion System|volume= 2|location= Lawrence, Kansas|publisher= Design, Analysis and Research Corporation|page= 132|isbn= 9781884885433}}</ref> at takeoff roll, it is generally less sensitive to crosswind.<ref group="note">Because of less weathercock stability</ref><ref>{{citation |url=http://www.flightglobal.com/pdfarchive/view/1992/1992%20-%201611.html |title=Grob tests highlight exhaust problem |journal= Flight International|date= 24–30 June 1992|page=11 |url-status= dead|archive-url=https://web.archive.org/web/20110520124243/http://www.flightglobal.com/pdfarchive/view/1992/1992%20-%201611.html|archive-date= 20 May 2011 }}</ref><ref>{{cite tech report |first= Philip W.|last= Brown|title= Flight test Results for Several Light, Canard-Configured airplanes|number= |institution= NASA Langley Research Center|date= 1 October 1987|doi= 10.4271/871801|issn= 0148-7191|eissn= 2688-3627|url=https://saemobilus.sae.org/content/871801/|url-access= subscription}}</ref>

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.<ref>{{cite book|first= Darrol|last= Stinton|date= 1983|title=The Design of the Aeroplane|chapter= Propeller Effects|pages= 304–307|publisher= Granada Publishing|location= St Albans, Hertfordshire, England|isbn= 9780632018772}}</ref>

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.<ref name= "ask don" />

Wing profile drag may be reduced due to the absence of prop-wash over any section of the wing.{{citation needed|date = March 2014}}

==== Safety ====
{{More citations needed section|date=April 2021}}
The engine is mounted behind the crew and passenger compartments, so fuel oil and coolant leaks 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.{{citation needed|date = March 2014}}

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 UAV configurations or for small/personal air vehicles or for aircraft models.<ref>{{cite web|last1= Abrego|first1= Anita I.|last2= Bulaga|first2= Robert W.|title= Performance study of a ducted fan system|date= 23 January 2002|publisher= American Helicopter Society International, Inc.|url= http://rotorcraft.arc.nasa.gov/publications/files/Abrego2_AHS02.pdf|url-status= dead|archive-url= https://web.archive.org/web/20111018033811/http://rotorcraft.arc.nasa.gov/publications/files/Abrego2_AHS02.pdf|archive-date= 18 October 2011}}</ref>

===Disadvantages===
====Structural and weight considerations====
[[Image:Saab J 21A-3.jpg|thumb|[[SAAB 21|SAAB J 21]] fighter, with the pusher propeller mounted between two fuselage booms]]
A pusher design with an empennage behind the propeller is structurally more complex than a similar tractor type. The increased weight and [[Drag (physics)|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, supports, and torsional vibration control, and adds weight and complexity.<ref name= "Technicalities">{{cite web |first= Peter|last= Garrison|title= Technicalities|date= 29 June 2009|publisher= Flying|url= http://www.flyingmag.com/technicalities-2|access-date= 12 October 2011|url-status= live|archive-url= https://web.archive.org/web/20120329185615/http://www.flyingmag.com/technicalities-2|archive-date= 29 March 2012}}</ref><ref>{{cite magazine |last= Hassenaur|first= Donald P.|date= 1 January 1996|title= Propeller Drive Systems and Torsional Vibration|pages= 167–172|magazine= Alternative Engines|volume= 1|others= compiled by Mick Myal|location= Phoenix, Arizona|publisher= Fiesta Publishing|isbn= 9780964361324}}</ref>

==== Center of gravity and landing gear considerations ====
To maintain a safe [[center of gravity]] (CG) position, there is a limit to how far aft an engine can be installed.<ref>{{cite web |first= J. Mac|last= McClellan|title= Flashback to 1981: A Look Back at the Lear Fan|work= Flying|date= 24 June 2006|url= http://www.flyingmag.com/pilot-reports/turboprops/flashback-1981-look-back-lear-fan?page=0,1|access-date= 20 October 2011|url-status= live|archive-url=https://web.archive.org/web/20110905231551/http://www.flyingmag.com/pilot-reports/turboprops/flashback-1981-look-back-lear-fan?page=0,1|archive-date= 5 September 2011}}</ref> 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.<ref>{{cite web|title=Cozy Mk IV|first1= Brien|last1= Seeley|first2= C.J.|last2= Stephens|others= The CAFE Board|publisher= CAFE Foundation|work= Aircraft Performance Reports|url= http://cafefoundation.org/v2/pdf_cafe_apr/Cozy%20IV%20APR.pdf|url-status= dead|archive-url= https://web.archive.org/web/20101027001413/http://cafefoundation.org/v2/pdf_cafe_apr/Cozy%20IV%20APR.pdf|archive-date= 27 October 2010}}</ref><ref group="note">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)</ref>

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.<ref>{{cite web|first= David|last= Odum|date= 2003|url= http://www.airplanezone.com/Oshkosh/Scrapbook2003/Prescott_Pusher.html|title= Oshkosh 2003 Scrapbook|website= www.airplanezone.com|publisher= Airplane Zone|url-status=live|archive-url= https://web.archive.org/web/20120425061601/http://www.airplanezone.com/Oshkosh/Scrapbook2003/Prescott_Pusher.html|archive-date= 25 April 2012}}</ref><ref>http://www.kitplanes.com/magazine/pdfs/Grinvalds_Orion_0409.pdfOrion{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes }} V1(rotation speed): 65 kn</ref><ref>{{cite tech report|first= Lester H.|last= Berven |title= BD-5 Flight Test Program Report|institution= Bede Aircraft Corporation|via= Journal of the Society Of Experimental Test Pilots|url=http://www.bd5.com/testberven.htm |url-status=live |archive-url=https://web.archive.org/web/20111119134850/http://bd5.com/testberven.htm |archive-date= 19 November 2011}}</ref> The [[Burt Rutan|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 [[autogyro]]s, a high thrust line results in a control hazard known as [[power push-over]].

====Aerodynamic considerations====
[[Image:Supermarine Walrus.jpg|thumb|The [[Supermarine Walrus]] pusher flying boat is a typical flying boat, with the engine mounted high to avoid spray; however, throttle changes then induce pitch changes.]]
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.<ref>{{cite book|first1= Sighard F.|last1= Hoerner|first2=Dr. -Ing|last2= Habul|first3= Henry V.|last3= Borst|date= 1985|title= Fluid Dynamic Lift: Practical Information on Aerodynamic and Hydrodynamic Lift|edition= 2nd|chapter= XII: Propulsion Lift and Stability, 2. Influence of Propeller Slipstream on Wings|page= 12{{hyphen}}8|url= http://docshare02.docshare.tips/files/3609/36093604.pdf|url-status= live|archive-url= https://web.archive.org/web/20210508132615/http://docshare02.docshare.tips/files/3609/36093604.pdf|archive-date= 8 May 2021}}</ref> 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<ref>{{cite book|first1= Malcolm J.|last1= Abzug|first2=  E. Eugene|last2= Larrabee|date= 2002|title= Airplane Stability and Control: A History of the Technologies that Made Aviation Possible|page= 257|publisher= Cambridge University Press|isbn= 9780511607141|doi= 10.1017/CBO9780511607141}}</ref>) or landing gear made longer<ref name= "Aircraft Design" /> and heavier. Many pushers<ref group="note">[[Dornier Do 335]], [[LearAvia Lear Fan]], [[Prescott Pusher]], [[Grob GF 200]], [[Beechcraft Starship]], Vmax Probe</ref> have ventral fins or skids beneath the propeller to prevent the propeller from striking the ground, at an added cost in drag and weight.{{Citation needed|date=October 2011}} 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; in extreme cases, the blades may strike the ground.

When an airplane flies in [[icing conditions]], ice can accumulate on the wings. If an airplane with wing-mounted pusher engines experiences icing, the props will ingest shredded 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 wake, and other flight surface downwashes—moving asymmetrically through a disk of irregular airspeed. This reduces propeller efficiency and causes vibration inducing structural propeller fatigue<ref group="note">The only approved prop for the Rutan pushers is wood, which is more resistant to fatigue damage.</ref> and noise.

Prop efficiency is usually at least 2–5% less and in some cases more than 15% less than an equivalent tractor installation.<ref>{{cite web|first= Don |last= Stackhouse|url= http://www.djaerotech.com/dj_askjd/dj_questions/pushtractor.html|title= Al Bowers gave us an excellent explanation of the stability issues of a tractor vs. pusher installation. However, there are some other issues that need to be considered.|access-date= 25 September 2011|url-status= dead|archive-url= https://web.archive.org/web/20111121030726/http://djaerotech.com/dj_askjd/dj_questions/pushtractor.html|archive-date= 21 November 2011}}</ref> Full-scale wind tunnel investigation of the canard [[Rutan VariEze]] showed a propeller efficiency of 0.75 compared to 0.85 for a tractor configuration, a loss of 12%.<ref>{{cite tech report|first= Long P.|last= Yip|first2= Paul F.|last2= Coy|date= March 1985|title= Wind-Tunnel Investigation of a Full-Scale Canard-Configured General Aviation Airplane|institution= NASA Langley Research Center|location= Hampton, Virginia|url= https://permanent.fdlp.gov/lps54941/lps54941/ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19850011615_1985011615.pdf|url-status= live|archive-url= https://web.archive.org/web/20210508143622/https://permanent.fdlp.gov/lps54941/lps54941/ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19850011615_1985011615.pdf|archive-date= 8 May 2021}}</ref> Pusher props are noisy,<ref name= "Technicalities" /> and cabin noise may be higher than tractor equivalent ([[Cessna XMC]] vs [[Cessna 152]]).<ref name="1000aircraftphotos.com">{{cite web|first1= Johan|last1= Visschedijk|first2= Walter van|last2= Tilborg|first3= Karl|last3= Smith|date= 14 December 2003|url= http://1000aircraftphotos.com/HistoryBriefs/CessnaXMC.htm|title= Cessna XMC|website=1000aircraftphotos.com|url-status= live|archive-url= https://web.archive.org/web/20080130150407/http://1000aircraftphotos.com/HistoryBriefs/CessnaXMC.htm|archive-date= 30 January 2008}}</ref> 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.<ref name= "ask don" />

====Engine cooling and exhaust====
Power-plant cooling design is more complex in pusher engines than for the tractor configuration, where the propeller forces air over the engine or radiator. Some aviation engines have experienced cooling problems when used as pushers.<ref name="1000aircraftphotos.com"/> 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.

====Safety====
=====Propeller=====
[[Image:Piaggio P 180 Avanti 2004 by-RaBoe.jpg|thumb|[[Piaggio P.180 Avanti]] with engines mounted on the wing trailing edge, away from passengers, allowing safer boarding.]]
In case of propeller/tail proximity, a blade break can hit the tail or produce destructive vibrations, leading to a loss of control.<ref>[[Grinvalds Orion]] crash in 1985, Experimental magazine n°2, March 1986, pages 20-24, Extrait du Rapport d'expertise: "La cause initiale de l'accident la plus probable est la rupture du mécanisme de commande de pas d'une pale de l'hélice. Cette rupture a a engendré des vibrations importantes de la partie arrière de l'avion... ruptures structurales... privant les pilotes des commandes de vol de profondeur et de direction". Failure of the pitch command system of one blade, important propeller vibrations, structural break, loss of pitch and yaw control</ref>

Crew members risk striking the propeller while attempting to [[parachute|bail out]] of a single-engined airplane with a pusher prop.<ref>{{cite book |last= Brown|first= Eric|date= 1961|title= Wings on My Sleeve|location= London, England|publisher= Weidenfeld & Nicolson|pages= 150–151|chapter= Chapter 10|isbn= 9780753822098}}</ref> At least one early ejector seat was designed specifically to counter this risk.{{Citation needed|date=May 2021}} Some modern light aircraft include a [[Ballistic Recovery Systems#Products|parachute system]] that saves the entire aircraft, thus averting the need to bail out.{{Citation needed|date=May 2021}}

=====Engine=====
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 occupants.<ref group="note">Crash of [[Ambrosini SS.4]]</ref>

=====Aircraft loading=====
Spinning propellers are always a hazard on ground working, such as loading or embarking the airplane. The 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.{{undue weight inline|reason=Are pusher aircraft uniquely dangerous to ground crews compared to tractor aircraft?|date=April 2021}} 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.{{Citation needed|date=April 2021}}