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Why do most single propellers have a clockwise rotation (seen from the pilot's point of view)?

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There are though multi-engine planes that have each propeller rotating different directions, but in the case of single propellers, it seems that clockwise rotation is dominant, or even the only option. Is there any single propeller plane with counterclockwise rotation?

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    $\begingroup$ Or maybe because some engineer wanted the angular momentum vector pointing away from the airplane in his drawing. $\endgroup$ – Keegan Oct 15 '14 at 18:12
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    $\begingroup$ To answer the last part of your question, yes, there are single propeller planes with counterclockwise rotation: Zlin 26 series and the older versions of the Zlin 42 series. $\endgroup$ – Emil Oct 16 '14 at 5:46
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    $\begingroup$ @KeeganMcCarthy Are there any twin engined planes that don't have their engines spinning in different directions? $\endgroup$ – SQB Oct 16 '14 at 6:42
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    $\begingroup$ @SQB, yes. I believe most transport twins have identical engines/props for ease of maintenance. Example: flickr.com/photos/thomasbecker/4714404607 $\endgroup$ – BowlOfRed Oct 16 '14 at 7:46
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    $\begingroup$ South of the equator they rotate counter-clockwise ;) $\endgroup$ – Matthew Peters Oct 1 '15 at 14:35
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I wasn't able to find any good historical references, so this answer is pure opinion. (sorry). I'll break this down into two separate questions.

  • Is there any reason for single-engine propellers to turn the same way?

Yes. When flying, the spin direction of the prop has several effects. Helical prop wash, p-factor, gyroscopic precession, differing blade angles of attack all are due to the asymmetry of spinning in a single direction. An experienced pilot will want to understand and compensate for these effects when necessary. It is easy to see that once this is understood, a single configuration will be preferred within a community to minimize differences between aircraft.

  • Is there any reason to prefer CW rotation over CCW as a convention in a single engine plane?

None that I am aware of. It appears to be simply an accident of choice. I had wondered if the majority of engines available to early manufacturers was in that direction and made it preferable, but I couldn't find anything suggesting that. Indeed today the majority of automobile engines rotate the opposite direction. Making (piston) engines rotate the other direction is not a huge problem. Twin-engined aircraft and watercraft often have counterrotating engines and propellers.

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    $\begingroup$ Note that helicopters with a single main rotor built in the USA rotate clockwise (looking up), but those built by Airbus/Eurocopter turn counter-clockwise. Pilots of US-built plane use the right pedal when adding power, and the Eurocopter pilots press the left pedal. $\endgroup$ – rbp Dec 10 '14 at 13:28
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    $\begingroup$ This seems to be the only answer that gets at the critical issue - (single-engine) pilots have an ingrained habit of pressing the right rudder pedal when climbing/accelerating that depends on rotation of prop direction. I would find it very difficult to fly with this reversed, myself. And the vast majority of twins have props that rotate the same way, FWIW. I can only think of a handful (Pipers) that have counter-rotating props as the advantage is small and the cost is high. $\endgroup$ – RobP Dec 11 '14 at 0:42
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    $\begingroup$ I don't try to remember which pedal to use, I step on the ball (airplane) or the based of the yaw string (heli) to fly in trim. $\endgroup$ – rbp Feb 4 '15 at 14:17
  • $\begingroup$ The reason I had heard (again, no citation available) was that by having this setup, the plane would be more likely to bank left due to the propellor, and with the pilot sat on the left of the cockpit, they would then have a good view to be able to remedy it. $\endgroup$ – Dudley Sep 7 '16 at 12:53
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Indeed today the majority of automobile engines rotate the opposite direction.

Not quite. The power output of a car engine is towards the rear. The power output of an aircraft engine is toward the front. If you look straight at the flywheel / propeller end they usually turn the same way.

Back in WWI the first-generation fighters (We're talking Sopwith Camels and Fokker triplanes here) did have props going in either direction. The airframe manufacturer made the whole thing and props were carved by hand, so it didn't matter much.

Today we have a small handful of prop makers, a smaller handful of engine makers, and both of them would be quite happy if everything turned the same way. Yes, it's really easy to make a piston engine go the other way, and it's really easy to flip the prop's airfoil over, but that means making and stocking different parts. The camshaft, pumps, ignition timing, prop governor, starter, mechanical meters etc. are all directional. And don't forget the pilots - if he's used to putting left boot to it on takeoff, and rents one that needs right boot, takeoff will be interesting.

If your twin or multi has counter-rotating props you have some advantages if one quits but you have extra maintenance costs. Imagine the language your mechanic will use after changing the camshaft and then remembering this engine is a leftie when he tries to start it.

If it's a geared engine then it's much easier - the engine and accessories are standard, there's just an extra (or one fewer) bit in the gearbox, plus the other-hand prop.

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  • $\begingroup$ Are there any aircraft with counter-rotating engines? I believe counter-rotating propellers usually have the same engines behind them and just different gearboxes. $\endgroup$ – Jan Hudec Feb 4 '15 at 7:54
  • $\begingroup$ Yes, a bunch us counter rotating engines. For example the Piper Seminole: en.wikipedia.org/wiki/Piper_PA-44_Seminole $\endgroup$ – Adam Oct 1 '15 at 13:07
  • $\begingroup$ It's really easy to design a prop or engine to turn the other way, but a lot less easy to make an existing one go the other way. You have to disassemble the engine and change the camshaft (and more), and put new blades on the propeller. $\endgroup$ – pericynthion Dec 2 '16 at 6:15
  • $\begingroup$ "And don't forget the pilots - if he's used to putting left boot to it on takeoff, and rents one that needs right boot, takeoff will be interesting." Wouldn't the pilot likely notice that already during the taxi, seeing that he needs to use a little more right boot? $\endgroup$ – a CVn Apr 1 '18 at 10:23
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The question for different prop rotation is very much like driving on the right side of the road (in North America), vs. on the left side (in the UK, Hong Kong, India, Japan etc.) It's all wrapped up in history and perhaps politics. BTW, Rolls-Royce turbofans turn CCW, but most GE and P&W fans turn CW. There's no performance advantage, one way or the other.

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One other thing to note. Standard airport traffic patterns have the airplane turn left. We're taught that this is because early airplanes like the Sopwith Camel had clockwise rotating rotary engines and propellers. The engine and propeller are a gyroscope and have a great gyroscopic effect on a light airplane like the Sopwith Camel. Gyroscopic procession for a clockwise rotating engine and propeller meant that right tuns tended to force the airplane down into the ground (bad) but left turns tended to force the airplane up (good as long as you don't stall). Also, pilots sit in the left seat, so they can see where they're going in a left turn.

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They don't! In s̶o̶v̶i̶e̶t̶ Russia, they rotate counterclockwise. Additionally, on some multiengine aircraft, they rotate opposite directions to cancel the p-factor.

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    $\begingroup$ [citation needed]. For example, Wikipedia claims that generally turn clockwise as seen from the rear of the aircraft, making no mention of exceptions except for contrarotating props. (Admittedly, Wikipedia needs a citation, too.) $\endgroup$ – David Richerby Oct 15 '14 at 19:20
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    $\begingroup$ The Su-29/Su-31 planes are examples of Russian planes with counterclockwise props. A non-Russian example that comes to mind is the Griffin-engined Mk. XIV Spitfire. The P-38 Lightning and Beechcraft Duchess are examples of twin engined planes with counter-rotating props. $\endgroup$ – Fred Larson Oct 16 '14 at 16:51
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    $\begingroup$ IIRC, My flight instructor (who is Russian) said that they usually spin counterclockwise in Russia. It's been a while, though, so I could be remembering incorrectly. $\endgroup$ – reirab Dec 12 '14 at 5:17
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    $\begingroup$ @DavidRicherby: Look at images of Russian planes such as the MiG-3 and the Il-2 on Wikipedia and you'll see that the props turn counter-clockwise. In fact, some articles even mention this but not all. But if you do look at all examples of Russian planes you'll find that almost all (or actually all) their props turn counter-clockwise. It is on Wikipedia - you just need to look closer. $\endgroup$ – slebetman Feb 5 '15 at 6:07
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I am quite amazed no-one has hit upon the obvious, its all to do with starting. Being both a pilot and totally arrogant of the unfortunate minority who are left handed. On a car with a starting handle, I would cup the handle in my right hand and with a mighty swing. Spin the handle from a low point 'upwards' and physically towards my center of gravity causing the engine to turn in a clockwise direction as viewed from the front.

Starting handles; what are they? Great lumps of bent iron which could be fed through a hole in the bumper and engage with a dog on the end of the crankshaft.(quite sure these keys and starter buttons will never catch on) And here is the reason; a petulant engine on a damp cold day will do anything to stay in the garage, include oiling its plugs and electrocute anyone's hand that is fiddling with the HT leads, and after half a dozen attempts at starting, the battery will go flat, hence out will come the handle.

In a politically correct world the majority would bow to the misfortunes of the minority but after swinging an engine for half an hour 'sod the left handed minority'.

So there you have it, its a throwback to the golden age of motoring and right handed people rule but what about aeroplanes.

There is no simple way of saying this but; stand in front of a PA28 with a 140 horse power engine with a metal prop and a flat battery, (probably the finest mincing machine known to mankind).

Facing the aircraft with mags and switches off, the propeller would be turned by hand to a point where the compression on the engine is just building then stand back. A command to make the engine live is given. If the rotation of the engine is counterclockwise as viewed from the front of the aeroplane, a stance is made forward and clear of the arc of the propeller. Just the fingertips of the right hand grasp the trailing edge of the blade and in a single pull; spin the propeller over top dead center and instantly clear the arc of the propeller. This is a highly dangerous practice but can safely be accomplished with care.

If the rotation of the propeller were to be to the right or clockwise as viewed from the front, I would then grasp the propeller with the finger tips on my left hand. (as I am right handed) I would hold hands with another person standing behind me to prevent any possibility in over balancing.

----------There is absolutely no reason why an engine or propeller should have a preference to turn in either direction apart from commercial considerations, custom and practice and the desire for safety in hand starting the contraptions-------For the record I ran an airflow test laboratory for many years and I can assure anyone that the absorbed power of a fan, provided it is of a mirror airfoil section will be identical.

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    $\begingroup$ ...when did you get your car with the starting handle? $\endgroup$ – Sean May 27 '18 at 1:35

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