# Aircraft Question: reversed propellers? **URL:** \ **Category:** Factual Questions\ **Created:** [July 31, 2008, 3:32am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319 "2008-07-31T03:32:54Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [July 31, 2008, 3:32am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/1 "2008-07-31T03:32:54Z")
The Convair Peacemaker was originally fitted with piston engines driving propellers fitted _behind_ the wing, presumably pushing rather than pulling, like a ship propeller. Why? And the obvious followup- if there was an advantage to this design, why wasn’t it more popular? (Presumably if there was a disadvantage to it, that’s why no more rear-propeller designs were built, right?) ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 31, 2008, 3:38am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/2 "2008-07-31T03:38:45Z")
[QUOTE=Really Not All That Bright] The Convair Peacemaker was originally fitted with piston engines driving propellers fitted _behind_ the wing, presumably pushing rather than pulling, like a ship propeller. [/QUOTE] I don’t know why this particular configuration was chosen for this plane, but it needs to be noted that all propellers work the same way: by blowing a mass of air towards the rear of the plane it produces forward motion called thrust via reaction; this is expressed by Newton’s famous law. Rockets and jet planes work the same way, they just have different techniques for moving reaction mass. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [July 31, 2008, 3:52am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/3 "2008-07-31T03:52:41Z")
Well, yeah; I was distinguishing between the location of the engine relative to the propeller by saying “push” and “pull”. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [July 31, 2008, 3:59am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/4 "2008-07-31T03:59:50Z")
According to the Wikipedia for the [B-36](http://en.wikipedia.org/wiki/Convair_B-36): > [@](#): > > Each engine drove an immense three-bladed propeller, 19 ft (5.8 m) in diameter, mounted in the pusher configuration. This unusual configuration prevented propeller turbulence from interfering with airflow over the wing. Basically, the [pusher configuration](http://en.wikipedia.org/wiki/Pusher_configuration) - that is indeed the term used in aeronautics - is used on airplanes for the same reason propellers on ships and submarines are in the back: reduced turbullence. For single-engine aircraft, there’s an additional advantage: increased visibility since the pilot doesn’t have to peer through the props. Nevertheless, the disadvantages of the pusher configuration are usually such that it’s only rarely used. ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [July 31, 2008, 4:01am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/5 "2008-07-31T04:01:19Z")
> [@](#): > > 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. However, this effect is not nearly as pronounced on a small airplane as it is on a submarine or ship, where it is quite important due to the much higher Reynolds number at which they operate. > > Wing efficiency increases due to the absence of prop-wash over any section of the wing. > > Rear thrust is somewhat less stable in flight than with a tractor configuration. This has the potential to make an aircraft more maneuverable. > > Visibility of a single-engined airplane is improved because the engine does not block forward vision. Consequently, this configuration was widely used for early combat reconnaissance aircraft, and remains popular today among ultralight aircraft. > > The propeller of a single-engined airplane can be placed closer to the elevators and rudder as illustrated in the picture of the Royal Aircraft Factory F.E.2 above. This increases the speed of the air flowing over the control surfaces, improving pitch and yaw control at low speed, particularly during takeoff when the engine is at full power. This can be beneficial while bush flying, especially when taking off and landing on airstrips bounded by obstacles that must be avoided while the airplane is moving slowly. > **[Pusher configuration](https://en.wikipedia.org/wiki/Pusher_configuration)** > > In aeronautical and naval engineering, pusher configuration is the term used to describe a drivetrain of air- or watercraft with propulsion device(s) after the engine(s). This is in contrast to the more conventional tractor configuration, which places them in front. > Though the term is most commonly applied to aircraft, its most ubiquitous propeller example is a common outboard motor for a small boat. > “Pusher configuration” describes the specific (propeller or ducted fan) thrust device attach... ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [July 31, 2008, 4:03am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/6 "2008-07-31T04:03:05Z")
That’s an interesting question. On a Vari-Eze or Long-EZ the engine is mounted aft. I’m guessing Rutan put it there because of the small area of the forward canard. With the engine aft, it makes sense to have a pusher propeller. The Cessna 337 Skymaster is a ‘push-me/pull-you’ configuration. This affords twin-engine power without the adverse thrust in case of an engine failure. ISTR that a pusher prop is less efficient because it’s working in disturbed air, and that two- and four-bladed pusher props are noisy because they pass through the disturbed air. (Odd-bladed props are less noisy because only one blade is going through the disturbed air at any given time.) In the case of the Vari-Eze/Long-EZ and the 337 it’s obvious why the configuration was chosen. The B-36? Not so much. One thing that I see is that leading edge of the the B-36 wing is swept. I’d assume that a semi-swept wing was decided upon for performance. But if the engines were on the front then they’d be staggered aft with the sweep and there may not have been enough clearance for the big props. Perhaps they could have used extended nacelles, but that would have changed the weight-and-balance. EDIT: Looks like I may be wrong about turbulence. I’d like to hear more about that, as ISTM there’s be less turbulence in clear air than in air that is going around a structure. ---
**Author:** ![sqweels](https://avatars.discourse-cdn.com/v4/letter/s/f19dbf/32.png) [@sqweels](https://boards.straightdope.com/u/sqweels)\ **Post date:** [July 31, 2008, 4:04am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/7 "2008-07-31T04:04:17Z")
[QUOTE=Terminus Est] Nevertheless, the disadvantages of the pusher configuration are usually such that it’s only rarely used. [/QUOTE] My WAG has it that the tractor configuration (that’s what _they’re_ called) are more advantageous center-of-gravity-wise. Notice how the B-36 has a very long forward fuselage. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [July 31, 2008, 4:19am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/8 "2008-07-31T04:19:58Z")
[QUOTE=sqweels] My WAG has it that the tractor configuration (that’s what _they’re_ called) are more advantageous center-of-gravity-wise. Notice how the B-36 has a very long forward fuselage. [/QUOTE] Yes, if the engines should fail, you’d want the aircraft to nose down rather than up. ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [July 31, 2008, 4:35am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/9 "2008-07-31T04:35:55Z")
Tractor props in a multi engine plane have the added benefit of increasing lift at low speeds, since the prop airflow is blowing right over the wing at high speeds. That is good for planes intended for STOL (Short Take OFF and Landings) like the [de Havilland Canada Dash-7](http://en.wikipedia.org/wiki/De_Havilland_Canada_Dash_7) but not so good for speed and efficiency as a long range bomber would need. For that particular plane I’ve read that when it revs up with brakes applied you can actually see the plane’s landing gear oleo absorbers expanding as the wings lift increases. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [July 31, 2008, 5:44am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/10 "2008-07-31T05:44:29Z")
On small airplanes, the biggest problem with the pusher configuration is where to put the engine. The traditional location for a single-engine pusher is behind the wing above the fuselage. This is most common in single-engine seaplanes, because it keeps the prop up high and out of the water. Water spray can destroy a propeller pretty quickly, so getting it up high is a big advantage. But this moves the thrust line above the drag line, which causes all kinds of pitch problems - power changes cause the nose to want to pitch up and down. On some airplanes, the engine is mounted behind the cabin between twin booms, as in the Cessna 337. One problem with this configuration is keeping the engine cool. Another is that power changes change the effectiveness of the elevator, whch also causes some controllability issues. Finally, there are some designs, like Molt Taylor’s plane, that put the propeller way out at the back of a convential tail, with the engine mounted behind the cabin and connector to the propeller with a long driveshaft. The big problems here are cooling, driveshaft vibration/manufacture, and the chance of hitting the prop on the ground at rotation. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [July 31, 2008, 6:04am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/11 "2008-07-31T06:04:12Z")
Flying wings need to have sweep for control and stability… ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [July 31, 2008, 6:05am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/12 "2008-07-31T06:05:29Z")
[QUOTE=Sam Stone] But this moves the thrust line above the drag line, which causes all kinds of pitch problems - power changes cause the nose to want to pitch up and down. [/QUOTE] Which is true for other configurations as well, it’s just that a high mounted engine/propeller results in a nose up pitch with a power reduction which is the opposite from how conventional aeroplanes work. > [@Terminus Est](#): > > For single-engine aircraft, there’s an additional advantage: increased visibility since the pilot doesn’t have to peer through the props. I don’t think that’s much of an issue, the prop is essentially invisible when in motion, though it can be a problem at low RPM flying into the sun. > [@Johnny L.A.](#): > > The Cessna 337 Skymaster is a ‘push-me/pull-you’ configuration. This affords twin-engine power without the adverse thrust in case of an engine failure. ISTR that a pusher prop is less efficient because it’s working in disturbed air, and that two- and four-bladed pusher props are noisy because they pass through the disturbed air. (Odd-bladed props are less noisy because only one blade is going through the disturbed air at any given time.) I’ve also heard that the pusher engine can be prone to overheating when the other engine has failed as the pusher engine has less cooling airflow and is operating at high power while the aeroplane is flying at low speed. ---
**Author:** ![puppygod](https://avatars.discourse-cdn.com/v4/letter/p/ce7236/32.png) [@puppygod](https://boards.straightdope.com/u/puppygod)\ **Post date:** [July 31, 2008, 10:02am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/13 "2008-07-31T10:02:02Z")
[QUOTE=1920s Style “Death Ray”] I don’t think that’s much of an issue, the prop is essentially invisible when in motion, though it can be a problem at low RPM flying into the sun. [/QUOTE] It’s not so much problem with the propeller itself , but rather engine obscuring forward view. That’s especially true for radial engines that are rather bulky. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [July 31, 2008, 10:16am UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/14 "2008-07-31T10:16:26Z")
[QUOTE=puppygod] It’s not so much problem with the propeller itself , but rather engine obscuring forward view. That’s especially true for radial engines that are rather bulky. [/QUOTE] Yes although radials tend to be shorter, but fatter as you say. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [July 31, 2008, 1:14pm UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/15 "2008-07-31T13:14:37Z")
Pushing is fairly popular in radio controlled planes. I don’t know how relevant that is, but I believe that landing a pusher is easier. Landing might be the biggest challenge for all model plane fliers. However, once you get down to ultra performance, razor edge aerobatic planes, the configuration to have is the engine and prop right up front on the nose. All sorts of rolls, stalls and dives and full ‘3-D’ tricks are on the table with this configuration. How relevant is all this? I don’t know. 🙂 Figured it was worth mentioning. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [July 31, 2008, 1:21pm UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/16 "2008-07-31T13:21:23Z")
I have a lot of time in the Cessna 337. It was a dog. The pusher engine and prop were identical to the tractor, but developed only about 70% of the effective thrust due to being hidden behind the bulky fuselage pod. As well, the pusher cooling was really inadequate. If the tractor engine failed, you could either close the cooling doors (“cowl flaps” for the pilots) & overheat the engine or leave them open, where they stuck out in the breeze so much they acted like speed brakes & you sank like a stone. ---
**Author:** ![Ale](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@Ale](https://boards.straightdope.com/u/Ale)\ **Post date:** [July 31, 2008, 1:22pm UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/17 "2008-07-31T13:22:43Z")
[QUOTE=Philster] Pushing is fairly popular in radio controlled planes. I don’t know how relevant that is, but I believe that landing a pusher is easier. Landing might be the biggest challenge for all model plane fliers. However, once you get down to ultra performance, razor edge aerobatic planes, the configuration to have is the engine and prop right up front on the nose. All sorts of rolls, stalls and dives and full ‘3-D’ tricks are on the table with this configuration. How relevant is all this? I don’t know. 🙂 Figured it was worth mentioning. [/QUOTE] You won´t see an aerobatic pusher any time soon, either a model or a full sized plane. A tractor prop downwash flows around the control surfaces so you retain control even if the plane is hanging motionless in the air as in a [torque roll](http://www.youtube.com/watch?v=FT5QX8bHF1s&feature=related) or other low speed maneouvres. ---
**Author:** ![pullin](https://avatars.discourse-cdn.com/v4/letter/p/c57346/32.png) [@pullin](https://boards.straightdope.com/u/pullin)\ **Post date:** [July 31, 2008, 1:56pm UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/18 "2008-07-31T13:56:14Z")
I work in the plant where the B-36 was made. Some artifacts still remain (believe it or not). There is a local organization here dedicated to the history of this aircraft (and possibly a few old engineers who worked on it). I have emailed their prez with your question. I will return to the thread if and when I get an answer. pullin ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [July 31, 2008, 2:28pm UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/19 "2008-07-31T14:28:32Z")
A traditional rhyming joke seems to imply that the pusher configuration allows for thicker seat cushions in the cabin. 😉 ---
**Author:** ![jharvey963](https://avatars.discourse-cdn.com/v4/letter/j/54ee81/32.png) [@jharvey963](https://boards.straightdope.com/u/jharvey963)\ **Post date:** [July 31, 2008, 4:32pm UTC](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319/20 "2008-07-31T16:32:43Z")
While I don’t have the level of technical knowledge about pushers exhibited by some of these posts, I DID own a Velocity for a while ([http://www.velocityaircraft.com/](http://www.velocityaircraft.com/)) which is a pusher configuration. Some have said that not having the propeller in front improves visibility. But I was flying over Georgia one day when my engine started running very rough. I at that point realized the disadvantage of the pusher configuration: I couldn’t see the engine. So, is the engine on fire? How would I know? The engine could be on fire for a very long time before I noticed it! J. [Next page](https://boards.straightdope.com/t/aircraft-question-reversed-propellers/458319.md?page=2)