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The only push propeller designs I know of are centerline/fuselage mounted which has obvious problems as far as having a tail on the rear of the aircraft.

It appears these challenges lead to all the push propellers I know of either being twin boom back from the wings to each end of the tail (Cessna Skymaster), or being canard aircraft so the tail swaps spots with the engine and the plane is "backwards" (Velocity XL, Rutan Long Ez, Rutan VariEze).

And yet, there is a lot of multiengine aircraft out there with one engine on each wing (see Beechcraft Baron, Cessna 310, lots of others). Those would sidestep the tail conundrum.

Is it possible or even reasonable to have pusher props on wings? What are the disadvantages? There must be a reason that we don't see every twin prop airplane (with an engine on each wing) with a pusher configuration! Are they just less efficient? Or have some dangerous "edge of the flight envelope" problem? Or present some hard engineering challenge?

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    $\begingroup$ The Piaggio Avanti and Beechcraft Starship are two examples of current push prop airplanes. This site has a good discussion of the advantages vs disadvantages of push vs pull:airplaneacademy.com/… $\endgroup$
    – user22445
    Nov 29, 2022 at 16:31
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    $\begingroup$ I wouldn't call the Starship "current" -- last I heard there were only two left flying and they were dependent on a boneyard for repair parts. $\endgroup$
    – Zeiss Ikon
    Nov 29, 2022 at 16:38
  • $\begingroup$ This should also help. $\endgroup$
    – sophit
    Nov 29, 2022 at 19:21
  • $\begingroup$ Yes, the Velocity 173 RG-E is certainly very sexy looking, but lands at 70 knots and flies on 200 hp. Much of the performance improvements on the "Starship" types came from weight savings from use of composites. OK, let's reduce the wing area of the Cessna 172 by 1/2, have retractable landing gear, and put the 200 hp engine on with 60 gallons of fuel. It'll land at 70 knots, with similar cruise performance, though the Velocity, with newer materials and lower aspect, will be a bit stronger. Better yet, put the engine in front of the Velocity, then see. $\endgroup$
    – Robert DiGiovanni
    Nov 29, 2022 at 21:04
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    $\begingroup$ @RobertDiGiovanni A Vans RV-7 gets similar numbers on similar power in a "normal" config design. After comparing a Cherokee 180 and an RV-7 I'm under no illusion that the trainer airplanes are really optimized for cruise performance. Heck, look at what a 160 HP RV-9 does, and it's cruise vs stall! $\endgroup$
    – Azendale
    Nov 29, 2022 at 23:42

4 Answers 4

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Is it possible or even reasonable to have pusher props on wings?

Yes, absolutely! If you strive for the highest efficiency, pusher propellers are a good solution. When Convair was tasked in 1941 with developing a bomber which could reach Europe from bases in the US, they decided on a pusher design. But they come at a price.

Advantages of pusher propellers:

  • The prop slipstream can flow off freely.
  • Clean leading edge, uninterrupted high-lift devices.
  • No accelerated flow around the wing, therefore less drag.

Disadvantages of pusher propellers

  • Long driveshaft between engine and propeller, or, alternatively, a heavier engine mount to transmit the forces from the engine to the spar.
  • Depending on engine location: Less flutter damping due to the backward center of gravity of the propulsion system.
  • No blown flaps.
  • Propeller must go through the wing wake, no clean inflow into the propeller.
  • Heavier engine installation due to driveshaft and interference with wing structure.
  • Cooling of the buried engine is more tricky.
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    $\begingroup$ Why does the driveshaft have to get longer? $\endgroup$
    – Michael
    Nov 30, 2022 at 9:27
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    $\begingroup$ @Michael You want to mount the engine close to a strong structural element, and in a wing that is obviously the wing spar. Since this is located at maybe 30% or maximum 40% of chord, the distance to the pusher propeller is larger than in a tractor arrangement. Alternatively, if you mount the engines at a distance to the spar, the engine mount will weigh more. $\endgroup$
    – Peter Kämpf
    Nov 30, 2022 at 11:12
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    $\begingroup$ @dotancohen The spar should go where the airfoil has its biggest thickness. The tapering rear part would make a spar structurally inefficient. $\endgroup$
    – Peter Kämpf
    Dec 1, 2022 at 13:58
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    $\begingroup$ @dotancohen: spar goes as close as possible to the load that it has to support in order it to be as light as possible. For a subsonic wing this is more or less 25% of the chord. $\endgroup$
    – sophit
    Dec 1, 2022 at 18:07
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    $\begingroup$ @U.Windl Not necessarily. Especially when all props turn in the same direction, tractor props will force a nasty rolling moment on the wing that is absent in pushers. A stall with pusher props will be more symmetric but occurs at a slightly higher speed because the accelerated flow over the wing of a tractor is missing. OTH, the pusher will suck air from the rear wing, so separation will be delayed there. Details of stall recovery depend less on engine placement than airfoil and overall configuration, especially tail size and cg. location. $\endgroup$
    – Peter Kämpf
    Dec 2, 2022 at 14:28
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Some disadvantages of pusher props are:

  • propellers are operating in "dirty air" - the air flowing towards the blades has been disturbed by the wings, engine pod, fuselage etc. This will have an adverse effect on efficiency
  • the propellers are susceptible to damage from ice shearing off the wings and other "proceeding" parts. While this may not lead to instant failure, it is a consideration, and the magnitude of risk is dependent on the deicing method and procedures
  • depending on exhaust arrangements, the pushers may be louder. For example the Piaggio P-180 has a very distinct and arguably irritating noise signature because the turbine exhaust is being blown through the propeller blades.
  • depending on landing gear arrangement, pusher propellers may be more exposed to debris such as gravel, stones and dirt
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From a very basic design point of view, the more prop/engine weight ahead of the wing means more fuselage and tail weight behind the wing. This allows for for a longer, more streamlined fuselage and a smaller tail, offering a savings in weight and drag.

With wing mounted prop aircraft, putting the wing in clean air puts the prop in wing turbulence, although long range cruisers such as the B-36 Peacemaker, benefitted somewhat as their cruise airflow off the wings did not cause enough interference to significantly degrade prop performance.

However, a major concern with pushers became engine cooling, especially when piston engines grew to the size of the P&W R-4360.

For all purpose aircraft, running with higher power settings more often, the extra drag from opening cowling flaps for engine cooling greatly offsets any advantages.

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    $\begingroup$ oh bloody hell, I both read your answer wrong, and then wrote my comment wrong as well... :) I removed my comment. $\endgroup$
    – Jpe61
    Nov 30, 2022 at 7:20
  • $\begingroup$ I was just walking past a B-36 the day after this question was posted and was loving it. Of course I love the P180, so maybe it's me. $\endgroup$
    – tedder42
    Dec 2, 2022 at 0:57
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There are a couple of good examples of pusher aircraft with wing mounted engines. The Convair B-36, Beechcraft Starship, and Piaggio Avanti quickly come to mind. I suspect the greatest reason is that in design of an aircraft it’s best to keep the engines and their respective fuel tanks very close to the intended center of gravity for stability reasons. For the larger aircraft with greater CG ranges in size, the pusher design can work well, particularly for minimizing noise in the cabin. One advantage for tractor engines that are wing mounted is that you get a boost a lift from the propwash over the wings. Some advantages to a pusher design, particular with turboprops is that you can use the engine exhaust to deice the propellers, so there’s no need for additional prop deicing equipment.

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