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?

I found this on a French website a while ago.

During the Second World War, Mr Fokker invented in Austria an helicopter with 2 rotors contrarotatifs, on both sides of the cell and presented to the Fuhrer. At the end of the war, wreckage of this helicopter was recovered by the Allies in Cherbourg and dismantled in England. The Americans recovered a rotor with its transmission box and the French kept the second to increase their manufacturing programme helicopters. The 2 rotors working contrarotatif, one turned to the right and one left. It can therefore be inferred that the Americans have recovered the rotor turning to the left (BELL for example) and the French rotor turning to the right (EUROCOPTER for example).

Cdt Michel DRELON
http://www.heliairmonaco.com/page-faq-langue-uk.html

Just to confuse the issue....

Eurocopter 155 and 365 rotors turn cw, viewed from above.

Eurocopter 135 rotors turn the other way. :confused:

is that so they can put american engines in them ????

Aerospatiale(Alo, AS350, AS365,etc) and Sud Aviation(SA 330 before incorporated into Aerospatiale then changed to AS330, AS332,etc) turns cw. All French.

On the German side was Bolkow and a few others ie BO-105 and BK117 most known. They turn anti clockwise.

Eurocopter combines these manufacturers and all new models designed under the Eurocopter umbrella are EC's. So, all French based EC's ie EC120, 130, 155, 225 turns clockwise as per there predesessors. German EC135 and 145 turns anti cw as per their predecessors.

I think the above is close.

the EC 135 began life as the BO-108, and its fine German ancestry made its rotor spin the "right" way.

There is absolutely no physical reason for either direction being "best"

Unless of course you want the inflow roll to go a particular way! :E

Hi Squirrel..
 

Hi matey. have emailed you a lot. No replies. Hope your ok. drop me a line if you can. All the best matey :ok:

I thought Sikorsky went back and forth a couple of times with his early machines, mostly out of mechanacial convenience, then settled on a standard. I would assume this is to help the pilot's feet know what to do.

Clockwise / Counter-Clockwise Rotation
 

I remember hearing that the Sud-Est designers wanted to make their Alouette easier for fixed wing pilots to fly so they designed it to require right pedal on takeoff, as a fixed wing does.

The Frelon's rotor hub was developed in co-operation with Sikorsky so that's probably why it has the CCW mode of rotation.

Russian helicopters also rotate CW...

There is no problem swapping from one to the other as long as you use the correct pedal for the first take off! After mostly flying CCW aircraft I found myself swapping from Lynx (CCW) to Gazelle (CW) on a daily basis - since CCW was more natural, muscle memory and ingrained habit just did it's thing, when I got into a Gaz I would always say out loud 'right pedal forward' before take off and after that it was fine.

If you want a laugh, try doing the same instructional sortie (Advanced autos for example) on two different aircraft with two different rotations, limits, handling qualities etc within an hour or so of each other - that makes you concentrate:)

A good game at Shawbury in the 80's on the Wessex was to watch the student's first lift to the hover in a CCW rotation machine (Wessex) after 80 hours in a CW (Gazelle) - often the stude would try to select the hover attitude for the Gazelle (which was the only one he knew) and promptly zip off sideways to the right with an amused QHI saying 'I have control'

I still picture the piece of string from the end of the collective to the tip of my left boot.

Handy for the gazelle, but everything after that was opposite!

So now I just 'tie' that bit of string to my right boot! :ok:


KrisDon't fixed wing ac have different rotations also?

http://www.mccullagh.org/db9/1ds2-5/...152-n971fm.jpg

http://www.militaryaircraft.de/pictu...7_2415_800.jpg

As long as it continues to go around, that the main thing.

Well, boeing engineers apparently couldn't decide which direction was best, so decided to stop all arguments and make a Helo that does both at the same time.... :}, that is how the idea of the chinny came about...
http://www.enemyforces.com/helicopters/ch47_chinook.jpg




some or all of the above may or may not be true

Which begs the questions,

Why do the front set of blades go CCW and the rear set CW, and would it make any difference if it was designed the other way round?

Yup, they do...

In the early days of flight, the American aviation industry agreed on the 'CW when viewed from the cockpit' standard and stuck with it pretty well while the rest of the world muddled around and made do with whatever rotation dropped out after reduction gears were added to their engines and whatnot.

As time went on, particularly into the 1930s, Russia in particular and Europe to a lesser extent began to standardise on 'CCW when viewed from the cockpit'.

The British had tried to implement CCW before WW2 but by that time the Rolls-Royce Merlin had already been developed for the Spitfire, which turns the prop CW. The later Griffon-engined Spits rotated CCW, causing no end of problems for pilots transitioning to later marks of the Spit.

French designs from the WW2 era also show a mix like this - for example the Dewoitine 510 rotates CW, the Dewoitine 520 rotates CCW. But post-war the French settled on the 'American' mode of rotation, probably to tap into US engineering and to win export sales in the world's biggest aviation market.

So I think the original 'right pedal' argument still stands, as long as you're not flying Russian or certain WW2 era European aircraft.

I have no idea what logic Russian designers have for making their helicopters and fixed wings both rotate in exactly the opposite to the US mode of rotation though :ugh:

For the record, the 'American' CCW rotation mode makes a lot of sense when you consider naval aircraft that must operate with large immovable objects to the right of the aircraft. Or maybe the bridge was placed there for exactly that reason. Chicken/egg?

It's like the driving on the left/right side of the road discussion, this! As a Brit I've had to defend that to my American friends waaaay too many times...

A CW Main Rotor with the PIC on the right makes sense to me. If you're in a confined area with obstacles etc & need to turn the helicopter the tail can be moved towards the RHS without requiring more power, which happens to be the side with the most visibility for the PIC. This may not have been a consideration during the design stage, but it should have been!!

One thing I found useful as an instructor sitting on the right in the 300C was if my student screwed a pinnacle up I had a good view of my exit route down and to the right :ok:

I also feel a little more relaxed setting down when the first skid to contact the ground is on the opposite side to where I'm sitting for some reason. That could be 'cos I have about 80% of my flight time in that seat though. I'm currently flying the AS355 and I feel like I'm getting used to it slowly but surely.

Does anyone else have a preferred side to fly from?