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 27th Dec 2011, 21:59 #1 (permalink) Join Date: Apr 2011 Location: NL Age: 27 Posts: 98 flight controls on jet transports Hi, May I ask some basic questions about this subject? I am not enrolled on a flight school anymore at the moment so I think a new post on this forum is the best way to find out. First question is about ailerons and roll spoilers: If you give a certain roll input on the yoke, do you always get a certain amount of spoiler and aileron deflection, regardless of speed or altitude? The books say that ailerons are not useful at high mach numbers, and because of wing twisting e. a. But do ailerons still work at these speeds in the same way as on low speeds? Second question is related to the first: It is well known that yaw dampers are used to avoid dutch roll, but do they also give turn coordination? Because as far as I know, the rudder of a jet is not used in normal flight with the gear up, in normal cases. Is it perhaps because roll spoilers also give a yawing moment? I hope this is not too confusing and look forward to your replies! Thanks Last edited by Da-20 monkey; 28th Dec 2011 at 03:09.
27th Dec 2011, 23:36   #2 (permalink)

Join Date: May 2000
Location: USA
Posts: 2,266
Quote:
 If you give a certain roll input on the yoke, do you always get a certain amount of spoiler and aileron deflection, regardless of speed or altitude?
No. With conventional controls, some ailerons are locked out at high speed. However, the throw on the remaining surfaces will be the same.

With fly-by-wire, the computer figures it out and does what it wants.

Quote:
 The books say that ailerons are not useful at high mach numbers, because of wing twisting e. a. But do ailerons still work at these speeds in the same way as on low speeds?
Normally yes. The word "high" is relative, dependent on aileron position and wing stiffness.

However, "aileron reversal" may happen at speeds above Mmo.

[quoteIt is well known that yaw dampers are used to avoid dutch roll, but do they also give turn coordination?
Because as far as I know, the rudder of a jet is not used in normal flight with the gear up, in normal cases. Is it perhaps because roll spoilers also give a yawing moment?[/quote]
Depends on the installation... Turn coordination may be a function of flap position, airspeed, or what the computer decides. Spoilers do produce yaw in the proper direction, unlike the adverse yaw caused by ailerons. Airliners are usually rigged such that manual rudder input is not needed in normal cruise.

28th Dec 2011, 01:00   #3 (permalink)

Join Date: Apr 2011
Location: NL
Age: 27
Posts: 98
Quote:
 some ailerons are locked out at high speed. However, the throw on the remaining surfaces will be the same.
OK, do some aircraft have an input from the pitot/ static system for this, or is it only ram- air pressure that keeps them closed at high speed?

Quote:
 Spoilers do produce yaw in the proper direction
Thanks for confirming this Intruder. Much appreciated.

 28th Dec 2011, 01:52 #4 (permalink) Join Date: May 2000 Location: USA Posts: 2,266 Aileron lockout may be a flap position or Pitot (ADC) input.
 28th Dec 2011, 02:37 #5 (permalink) Join Date: Jun 2001 Location: Fragrant Harbour Posts: 3,755 For example, The 747 -1/2/300/SP (Classics) lock the outboard ailerons out when the flaps are extended. The 747-400 locks them out at 238 knots. Boeings tend to have inboard ailerons to prevent wing twisting. Other designs had stiffer wings, others geared the ailerons so thy deflect less at speed and some deploy a small amount of spoiler to assist roll. The Airbus Fly By Wire types are different. When the pilot moves the side stick, he/she are demanding a roll rate and the computers move the ailerons/spoilers accordingly.
 28th Dec 2011, 03:54 #6 (permalink) Join Date: Apr 2004 Location: Planet Earth Posts: 1,009 Dan, don't you mean that outboard ailerons are locked out with flap retraction ? Never flew the 747 but that is how it worked on the 727..
 28th Dec 2011, 11:07 #7 (permalink) Join Date: Aug 2000 Location: UK Posts: 1,917 Yes that is correct. It meant throughout the speed range, your control effect was the same, and I never noticed any change. The behaviour of the A380 ailerons is peculiar. jump to 40 seconds and watch for about 20 seconds. I can't understand that!
 28th Dec 2011, 11:36 #8 (permalink) Join Date: Apr 2011 Location: NL Age: 27 Posts: 98 @ Notso Fantastic: Were you referring to Stilton's answer? Never noticed the a380 ailerons before but here is an older thread with an explanation, just found: A380 Ailerons

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