Why do most single propellers have a clockwise rotation (seen from the pilot's point of view)?
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?
I wasn't able to find any good historical references, so this answer is pure opinion.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.
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.
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.
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.
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.
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.
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.
They don't! In s̶o̶v̶i̶e̶t̶ Russia, they rotate counterclockwise. Additionally, on some multiengine aircraft, they rotate opposite directions to cancel the p-factor.
The only case where I would consider an advantage or disadvantage may be observed in selective airflow is in that single engine German observation aircraft of WW2, the Blom & Voss 141 where the single engine is located to the starboard of the fuselage. Albeit the propeller is located forward of the main body, but the prop wash may have a disproportionate effect, depending on its direction of rotation when acting on the aircraft non symmetric profile.
I have designed a multitude of rotating and velocity activated systems, including the testing of a ballistic polymeric material at, of all places 'The Balloon and Cordage Department' at the RAE Farnborough, also piloting aircraft with CW & CWW rotating engines and nowhere in free field applications, will the direction in rotation of the propeller or the engine have any preferential effect whatsoever.
Dare I suggest a brave response may visit cyclic forces in the Northern/Southern Hemispheres!
