Comments on: Anti-torque

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By: Bob Kuriger

Bob Kuriger — Thu, 16 Aug 2012 22:55:23 +0000

Tim,

I”ve never heard a satisfactory answer to the question of why blade flapping makes the sort of noise it does. Would you care to give it a try?

Thank you,
Bob Kuriger

By: Ehud Gavron

Ehud Gavron — Sat, 29 Aug 2009 14:17:31 +0000

That sound is called “blade flapping” and is exacerbated by maneuvers which cause more load on one blade or the other. High speed turns, descents, and low-G operations unload the rotor and allow much more flapping (the blades moving up and down and “chopping” the air down). The larger the rotor blade the more sound it makes, so the large helos necessarily make more sound than the small one.

Noise abatement procedures in many airports call on pilots to reduce this as much as possible. Often the simple answer is “don’t do rapid maneuvers.” One can also help reduce blade flap by raising collective pitch to add load to the rotor blades and therefore prevent the amount of flappage.

The same noise is heard inside the cabin, albeit differently, as the noise is brought through the rotor’s already-loud downwash, the body of the aircraft cabin, and the insulation of the headset over the ears (In larger helos there’s also the interference of the helmet.)

When flying the small Robinson helicopters in doors-off operation, when blade-flapping sounds occur, it’s extremely clear. A little up-collective and the sound-issue (not a flight issue) goes away.

Ehud
P.S. In some airports, the traffic pattern is so tight that rapid maneuvers are required (e.g. KTOA right traffic takeoff 11R but must stay east of PCH at all times due to noise abatement… requires rapid turn and climb, and a rapid turn on the north side to return for landing). Yes, that’s right — noise abatement restrictions and “do not overfly our neighborhood” rules make it harder on the pilots, and create more noise for the remaining neighborhoods under the flight pattern path.

By: Fred

Fred — Sat, 29 Aug 2009 13:17:54 +0000

Why do large helos make a whoop whoop noise from the rotor blades? Is the same noise heard inside the helo cabin as on the outside of the cabin?

By: Tim McAdams

Tim McAdams — Mon, 17 Aug 2009 12:45:57 +0000

Mike R, you’re right.

Unfortunately, I do not have the space to expand on all the details about a subject. However, all the comments are right on and I plan to write about those subjects in future blogs. Please keep the ideas coming as it gives me some insight into what readers are interested in.

By: Mike R.

Mike R. — Mon, 17 Aug 2009 07:13:34 +0000

Great Article on anti-torque rotors. In response to a couple of the comments here….There are a lot of differenty types of helicopters with different rotor systems…and that’s ok…but, I don’t think this article was meant to cover “all” of those different models flying…just the ones that use tail rotors!….

Thanks Tim for taking the time to educate those less fortunate…those that have never had the pleasure of learning about the Anti-Torque rotor under actual flight conditions!!!!

By: Don Pointer

Don Pointer — Sat, 15 Aug 2009 19:14:57 +0000

I fly a gyroplane. It’s a lot simpler, no torque to counter and infinitely safer. Helicopters and things with wings are dangerous things.

By: Ehud Gavron

Ehud Gavron — Fri, 14 Aug 2009 16:02:48 +0000

While the whine-fest is going on, the official FAA answer is that the tail-rotor counteract “the torque of the main rotor.” In actuality the torque is produced by the engine and transmission. Perhaps you could cover what produces the torque while you’re discussing the anti-torque methods (tail-rotor, NOTAR, counter-rotating MRs, multiple MRs, etc.)

Cheers,

Ehud
Tucson AZ

By: Joe Connell

Joe Connell — Fri, 14 Aug 2009 15:41:33 +0000

Your discussion about torque should include those helicopters not requiring anti-torque provisions such as the H-21 Shawnee, H-46 Sea Knight, H-47 Chinook, H-43 Huskie, and the Russin Kamov series helicopters. All of these aircraft were equiped with counter-rotatiing main rotors.

It has been estimated between 10 -15 percent of total generated power is spent counteracting torque…