Seems like the thread on "why pull back to go up" was so popular, let's try this one: why do aircraft engines turn clockwise (as seen from the cockpit)? And to stir further controversy, why do Aerospatiale helicopter rotors turn opposite from almost every other helicopter?. Specifically excluded from this discussion are P-38 Lightnings and CH-46 and CH-47 helicopters, and the Flying Banana, whatever it's designation was. FO'ARD, HAARCH !!!!!!

The engineering standard is right-hand rotation. Point your right thumb at the propellor (from the engine side), and your fingers point in the direction of rotation. Same is true for right-hand rotation car & truck engines. Stand at the engine, point your right thumb in the direction torque is transferred, and your right fingers show the standard rotaion. If the engine rotates the other way, you have chosen a left-hand rotation design.

Seems reasonable to me,
Dave Olson

Wrong question -- not all of them turn clockwise.

Still doesn't answer why that particular direction, engineers could have arbitrarily chosen the other way. And to BriBrat--which engines turn the other way? Not doubting it, but interested to know. Left rotation on twins doesn't count. And what engineering standard, Scar? Aerospatiale's "standard" is opposite the "standard" used by Bell and other US manufacturers. Come on, guys, let's get some controversy goin'

Start with the Spit -- its Merlin rotated in the opposite direction of the Merlin in the Mustang. Keep looking -- as the initiator of the thread you should do the digging to support your assertion.

I noticed some itallian planes on my WW2 sim torq to the right on takeoff whereas most if not all(been a while) others torq left.

Hey, I never "asserted" anything. Sure, there are exceptions to everything. I was just sitting at my workbench today, working on a wooden prop that I'm putting a brass edge on, and recarving the shape, to make a scale display prop for my Grasshopper, and got to thinking about engine rotation and why the VAST MAJORITY of aircraft engines turn right hand. You make an interesting point with the left hand Merlin. Wonder why they did that?. Right hand works fine, why change it? If it was to get rid of P-factor and torque reaction, all it would do is change the reaction to its opposite......wait, I'VE GOT IT!!! I'll bet they (Rolls Royce) built a whole s***load of left-hand Merlins figuring that the Americans would want them for the left engines in their P-38's and the Americans said "No Way, guys, we got all these absolutely semi-adequate obsolete Allisons to use up first", so the Brits were stuck with them and had to find a good use for them. Fact is, I don't have the slightest clue about why some Merlins turn backwards, or why Alouette chopper rotors turn the other way from Hueys. I 'd like to know, though, just for kicks and true aerodynamic enlightenment. I knew this thread would push some buttons, just like the control stick one did, and wanted to see the reactions, and (maybe) get some good info.




Hey, Tonto, we're surrounded by Indians!


Whaddaya mean WE, Kemosabe?

Nay, NOT SO! Merlin was as per most others. Just like flipping your model engine. It was the GRIFFON powered Spits that had the opposite rotation.

The answer's obvious.

You can't have the prop turning in both directions so it turns in only one direction.

-David C.

(actually, I just thought. That's wrong, as a contra-rotating prop is fairly common!)

[]

NAH your all wrong. its like asking why countries like britain drive on the left and others drive on the right, well everyone knows the answer to that. if cars all were to drive in the same direction and airplane props all rotated in the same direction it would make earth spin too fast. so to keep it spinning at a constant safe speed some go one way and others go the other way to slow it down. if the world was to spin too fast then what would be the use of getting drunk at the bar, it just would not be the same to say to the wife oh i dont feel too good the room sint spinning

All excellent points!



-David C.

Pauluk2w,
you totally missed the main point: if the earth, as a result, started to spin too fast, how would we keep our balance ??? No way!! We would obviously fall right off the edge of the world into space, thus stopping the actions that caused the initial fatal acceleration !!!
So the earth rotation would eventually slow down. So now the real question is: just how long would that take???....[X(][X(][X(]

It boils down to a couple of things.... safety, and convenience.

The Spitfire is cthe classic example. All Mk's of the spit prior to the XIV, I believe, used the Griffon engine, which was "left hand rule" turning. This induced a yaw to the right on take-off. The MkXIV included the Merlin engine which was "right-hand rule". The only practical difference between the very popular MkV and IX was the change in engine. There were a number of incidents where people almost crashed on take-off because the Yaw was now to the left and the pilots were not expecting it. Ground-loops happened, etc. So, they standardised on one engine rotation direction to make it easier to anticipate the characteristics of a plane. The Americans mostly had "right-hand-rule" engines, and left hand engines were no longer developed.

The other reason is design simplicity. People have natural right-handed or left-handedness, and people engineering engines would have a natural "bent" to think of an engine in a particular way. Just like the production lines are set up to have the engines oriented a certain way. Basically, it is easier to just have to manage one basic engine concept than to have to manage two.

So, there is no scientific reason other than plain convenience.

gus

Gus -- you have it backward -- the early Spits had Merlins & the later spits had Griffons -- the Mk XIV was the definitive wartime Griffon powered Spit. The only early Griffon powered Spit was the MkIV -- which was the prototype for the Mk XIV. Also, some of the later Spits were still Merlin powered -- Mk XVI, for example.

Khodges -- you said "why do aircraft engines turn clockwise --?", not why do some, or why do most most. If you want more examples of left hand rotation -- Chipmunk, Tiger moth, Firefly, Gipsy Moth -- there are lots more.

Left hand rotation is/was more common in Europe. Most US engines turn clockwise, & today, the market in prop-driven a/c is dominated by Canadian & US powerplants, & US propeller manufacturers -- therefore clockwise rotation.

You know, I vaguely recall that subject of rotation direction coming up from time to time but whatever the answer was, it was not important enough for me to remember, "However", when jumping from one Helicopter to another such as Aerospatiale, The flight charateristics are the complete opposite. Thus the many emergency procedures would have to be done totally different.

Take a stuck right pedal (tail rotor). You just fly it on down to the runway with significant airspeed touching down similar to a plane. Right before touchdown , you decease throttle and the torque effect brings the front end around straight and you set it down while still controlling direction with throttle while sliding down the runway

I am guessing that doing this same trick in a French bird would only make things worse and you may have to increase throttle to bring it around.

You would be amazed at the countless numbers of Helicopter Pilots are not proficient in emergency procedures. In the military we waste the taxpayers money doing this over and over and "too the ground" so you know what the whole thing feels like. Can't do that in civilian world because "you" have to fix any wear or damage from your own wallet.

We're talking Northern Hemisphere, correct? Because in the Southern Hemisphere, it's all opposite rotation.

Yup. Have the Aussies confirmed?


Dave Olson

Well how could they tell, 'cause they're standing on their heads?

If you had two different groups working on the same project, do you think they would both come back with the exact same design?

Wrong Islandflyer, You can tell the earth speeds up and slows down on a yearly basis. Think about it, the days get longer and shorter. I think all the major earthquakes, volcanoes and storms get caused when the top and the bottom get a little out of sinc with each other.

---------

I'm just glad that most of the our engines rotate the way they do. My prop stash is large now, don't want to stock one of each!

Ed M

Should we be worried about this? [X(] Falling off the earth? Holy cow -- I never worried about that one before!! [] Top & bottom getting out of sync? OMG -- what happens if it doesn't get lined back up the right way? All of my props will be backwards -- I'll have to get reed engines that run backward -- what a pain [:@]

Don't spread this around -- it will cause a run on the supply of pusher props!![&:]

Boy, you guys are right about the props! I sure am glad that engines are not like the water in the toilet bowl while fushing! When I go back south of the equator it spins right, over here it spins left...
...looking from the outside, you idiot!!!

To standardize propellor design and manufacturing silly... In the old days props were started by hand and you wouldnt want some poor ******* walking under the prop to start it and have it back fire and hit him.. Here's one for you, I am an artilleryman btw.. NATO and US Cannons have a righthand twist in the bore and most soviet and others have a left hand twist.. Why? I guess Because cannon rounds when fired drift in the direction of the twist and this must be accounted for in deflection to hit the target..