Which way the rotors turn???
 

I asked the same question in the Mil aircrew bit, but then realised there were better placed experts.

Question was:

Chap in the pub asked me why some helicopters have a plane of rotation clockwise when viewed from above and some counter -clockwise.

I told him I would ask the experts.

So.......


Anybody know??

Simply cos the Frogs like to be ' le different ' and annoying !

It's traditional, set by the direction of the engine rotation and the transmission mechanism. One intermediate gear reverses the rotation, two gears brings it back.

Hehe, that'll get 'em going again... :E

I'm sure it is decided by the engineers, when they fit the blades. :ok:

If I remember right, Igor made the decision for the american helicopters and Heinrich Focke for the french.
The french company SNCASE used parts of a Focke-Achgelis FA-223 to build there first own helicopter. The FA-223 had two main rotors and they used the right one. During this time it was just technical question. I do not know why everybody sticks with "their" solution but apparently that is something people really believe in. I think most pilots who fly both kinds of helos have not problem to switch, but I know one pilot who refuses to fly an H300 and a AS350 on the same day. Probably he must shut down his brain and reconfigure the ini-files.

Focke-Achgelis Fa 223 "Drache"


:ok:

Tradewinds... :ok: In france the wind aways blows from the left.:E hehe

Rotorbee

I was admiring the Sikorsky VS300 at the Henry Ford museum last week and was surprised to note that the rotors turned the "French" way , something that was not continued with the later R4 and subsequent Sikorsky models. I wonder what made him change his mind?

VS300 is an exceptionally neat piece of engineering, not an ounce of excess weight and made for development from the start, you can see all the control run adjustment features designed into it to allow easy handling and response refinement during its initial development phase. Must have been fun to fly, I walked away wishing I had one!

W

Wunper
Yup, I know that. I read the book of the first Sikorsky testpilot. It was purely a technical question. The R4 turned the other way and since then I think they never changed. Probably Nick Lappos can tell us more about it.

BTW, eurocopters turn both ways.

As a boy pilot I was told that the direction the rotor turned in the early helicopters depended on the direction of rotation of the crankshaft of the piston engine that they used to power the machine, and that engines developed in Europe and those developed in North America had crankshafts that rotated in opposite directions. Over the years I have seen nothing published to contradict that theory.

Obviously they could have put additional gearing in to change the direction of rotation of the rotor but to do so would have been expensive, added weight and provided something else to fail. Standardization between the various manufacturers does not seem to have been an issue in the early days; or today for that matter.

Rotorbee – OK, you got me, which Eurocopter machine twirls its blades in an unpatriotic manner?

An explanation... sort of.
 

Hi,

Was looking for the same answer when I came across this website trying to explain why some helicopters have a direction of rotation clockwise and others anti clockwise.

Interesting to see that MBB/Kawasaki decided to follow the American convention and rotate anti clockwise. Now that MBB is part of Eurocopter, they have some rotating one way and some rotating the other way.

Production licensing explains some other reasons.

I have cut and pasted the explanation below from the following website:

http://www.aerospaceweb.org/question...s/q0212b.shtml


It doesn't explain why there's a difference, but it does explain why some companies/countries have gone in a particular direction.

Cheers
Conway
Is it true that the main rotors of American helicopters rotate counter-clockwise while European helicopters rotate clockwise? If so, why? I have been told this stems from a German twin rotor helicopter being halved and distributed between the Allies at the end of World War II.
- Glenn Dawkins, Steve, Tom

It is true that there are two consistently opposite trends in the direction the main rotor of a conventional single-rotor helicopter rotates. This difference appears to vary with the nation in which a particular helicopter was designed. When viewed from overhead, American helicopter rotors almost universally spin in a counter-clockwise direction. Many European helicopter rotors, on the other hand, tend to spin in a clockwise direction. However, there are several exceptions to these rules, particularly within Europe.
We confirmed these trends by comparing the rotor designs of a number of different helicopters from around the world. Overhead drawings are especially useful since the way in which the rotor blades are attached to the central hub makes it immediately obvious where the leading edge (LE) of a rotor blade is. Knowing which edge of the blade is the leading edge determines the direction in which the blades must rotate to generate lift. Based on the photos and drawings that we could locate, we found that rotors almost always rotate in the same direction depending on the nation the helicopter comes from. Examples are shown in the figure below.



Comparison of helicopter main rotor rotation direction
American helicopters manufactured by companies like Sikorsky, Boeing Vertol, Bell, and MD Helicopters all appear to rotate counter-clockwise like the SH-60 Seahawk illustrated above. The opposite convention is used in all French helicopters built by Aérospatiale, such as the Eurocopter Tigre, as well as all Russian helicopters built by Mil, like the Mi-8. However, the manufacturers in many other European nations use the same convention as the Americans. The helicopters built by Westland in the United Kingdom and Italy's Agusta all rotate counter-clockwise, as exemplified by the EH-101 Merlin and A109. German manufacturers like MBB and the Japanese companies Kawasaki and Mitsubishi also follow the American convention.

We've attempted to investigate how these two opposing philosophies emerged but have yet to find an answer. However, the story about a German twin rotor helicopter being split amongst the allies seems pretty unlikely. The American design layout with counter-clockwise rotor motion can be traced at least as far back as Igor Sikorsky's R-4 helicopter developed during the early 1940s, several years before the end of World War II. Other American helicopter pioneers like Larry Bell, Stanley Hiller, and Frank Piasecki subsequently copied this convention. Westland in the UK and Agusta in Italy as well as the Japanese manufacturers Fuji, Mitsubishi, and Kawasaki all entered the helicopter market by making licensing agreements to build American designs, so this sharing of technology may also explain how those nations came to adopt the American counter-clockwise rotation.

As for France and Russia, we have been unable to determine how manufacturers in those nations came to use a different convention. The same trends are also followed in countries like Poland, China, and India, probably because firms in these nations have also license-built helicopters from Russia and/or France. Whether the decision to adopt an opposite direction of rotation was made for technical reasons or was simply a matter of preference is unclear. If any readers are aware of the answer, please contact us.
- answer by Joe Yoon, 23 January 2005

Related Topics:

The French don't know what they want, the Super Frelon goes anti clockwise, the Puma /Super puma series goes Clockwise and on the NH 90 back to anti clockwise. At least all the US and German and Italian Machines are anti clockwise and the Russians clockwise, just the french can't make up there minds again !

Though i was told tongue in cheek that if in a crash the rotor comes thru the roof the Helo with the anti clockwise rotor will take out the Captain , while a clockwise rotor will only take out the the Co pilot! And we don't want to lose those crusty old Captains:)

Well just to add to the confusion ?
Can anyone tell me the concept or idea behind the S60 Blackhawk.

It has blades that turn Counter-Clockwise and the Tail rotor is mounted on the Right side as opposed to Bells, Robbies, etc.

What's the go there ?

Be gentle.

:ouch:

Why the Black Hawk has a T/R on the RHS
 

Hi,

About the Black Hawk. One of the design concepts of the BH was that it had a fully flying horizonatal stabilator, ie it is horizontal when in flight and as IAS decreases, it begins to droop down. Why? Well it increases the lift on the tail at low speeds.

But also for the following reason.

The Tail Rotor on the Black Hawk is huge and provides a lot of thrust. It is also canted so that it is not rotating in a vertical plane. It is actually tilted about 20 degrees from the vertical. (I think it's 20 deg. Can't remember).
What's more, it is designed to 'pull' the tail to the right unlike other rotorcraft where the tail rotor is designed to push the tail to the right. (That's why it's on the right and not the left of the vertical stabilizer).

Because of that, the T/R's significant rotor wash can also be used. Because it is forced to the left AND DOWN, the downwards vector provides about 400 lbs of lift to the tail... and because the horizontal stabilator is now 'drooping' down, there is no obstruction to this downwards force.

So there you have it. The Black Hawk's tail rotor pulls the tail to the right and the downwards component of the tail rotor rotorwash pushes the tail up. More efficient use of tail rotor aerodynamics.

I hope that makes sense.

Cheers
Conway

About the Black Hawk...

Sorry, forgot to add.

It\'s a UH-60 Black Hawk... but the civilian version, which Australia bought as a militarized model, is the S-70. UH-60 is military designation, S-70 is Sikorsky model number. S-70A-9 is the Australian version of the Black Hawk.

Sorry to be a pedant.

Conway

That was the answer I wanted from Nick ages ago !

Canted Tail Rotor
 

The H-60 tail rotor was located on the right as a tracter to provide additional TR ground clearence. Conversely, the H-53E tail rotor is located on the left as a pusher because total height was a issue. Also of note; The H-60 has a canted tail rotor (Vertical Pylon) while the H-53E has a straight tail mounted on a canted tail pylon. Both provide what Sikorsky termed free lift. Canting the tail rotor thrust line provides for an expanded CG envelope while supportiing a significant portion of the airframes tail mass.

I'm doing an EC135 converson at the moment and was surprised to note that the rotor turns anticlockwise (built by ex-MBB). Does it really make any difference? Is one better than the other in any way? That would be interesting to know

There is no "right" way to spin the rotor, neither gravity nor the air knows the difference!

Things that depend on direction of rotation (do you know why, for each?):

Which way the hover leans

The camber of the vertical fin

The usefulness of the pilot's vent window in cruise

The shape of the tip of the pitot tube

The number of gears in the transmission

The lateral CG envelope

Nick - is there any evidence that suggests the left or right hand seat is safer regarding bird strikes and rotor direction?

TFS,

I don't know of any distinction. I think the helo velocity dominates the flow effects that might exist. Most bird energy is due to the basic motions of the helo and the bird, not the air effects from the rotor flow, I think.

Direction of main rotor rotation
 

What is history of anti versus clockwise rotation - any benefits to either, why was one chosen over t'other, why US versus European differences?