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I was looking at a video of a A380 display that led me to the "valse des ailerons". This strange ailerons behaviour is available in normal law, but what happen when some fly-by-wire features are not available (alternate law and direct law)? Is this kinematic still available or do all the aileron move together acting as if there was only one aileron per wing?

EDIT: As I received no responses but multiple good comments, I add some clarifications: The "Valse des ailerons"' purpose and operating is documented in many places (see comments) but all those documentations assume the fly-by-wire system (sensors, actuators, computers,...) is healthy enough to stay in normal law. My question is: what happen when in alternate or direct law? Is there multiple cases, some in which the valse des ailerons is still available and some in which it is not?

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  • $\begingroup$ Good video of this here, and a thread with discussion here. $\endgroup$ – fooot Sep 16 '14 at 15:33
  • $\begingroup$ Some additional explanation about wing load on the 747-8: youtu.be/c26y2-j5KrY?t=19m48s $\endgroup$ – greener Sep 16 '14 at 18:43
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    $\begingroup$ The valse des ailerons is for gust alleviation. The local aileron deflection compensates gust loading on the wing, so it gets less dynamic loading. This increases structural life. I would not expect that this gust alleviation works also in direct mode (would be contradictory). Alternate law should also use gust alleviation, so the valse des ailerons would be displayed in alternate law as well. But I am guessing here, because I have no direct knowledge. That's why I post this as a comment and not as an answer. $\endgroup$ – Peter Kämpf Sep 19 '14 at 13:24
  • $\begingroup$ @PeterKämpf My understanding is that you switch from normal to alternate/direct law when there are some problems. The Valse des ailerons require 3 fully functional ailerons per wing. There are cases where some ailerons or spoilers are not available. In those cases, the aircraft should switch to alternate/direct law. But there are cases where the ariplane switch to alternate law with all ailerons available (e.g. when freezing a Pitot tube or when loosing an angle of attack sensor). I agree in those cases, it may be relevant to keep the Valse des ailerons while being in alternate law. $\endgroup$ – Manu H Sep 19 '14 at 15:21
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Valse Des Ailerons (Waltz of Ailerons) or VDA is a nickname for the Load Alleviation Function (LAF) which is part of the flight control system. LAF uses all ailerons and spoiler 6 to 8 to alleviate the fatigue and static loads on the wings by reducing the wing bending moment.

It consist of various sub functions dealing with passive load alleviation (based on commanded load factor from normal law) and active load control based on measured accelerations in pylons under the wing.

From this it already follows that passive load alleviation requires normal law for load factor inputs.

There is a document circulating on the internet which seems to be an official Airbus Pilot Briefing for A380 pilots called "Flight Deck and Systems Briefing for pilots, issue 2". In the section about the Flight Control Systems under auxiliary system the following is said about the LAF:

  • Load Alleviation Function (LAF)

    The objective of the LAF is to reduce structure fatigue and static loads on the wing during maneuvers and turbulence.
    Spoilers 6 to 8 and all the ailerons are involved in the LAF.
    The LAF is available in normal law only.

(Emphasis added by me)

So your feeling that Valse des Ailerons is only active in Normal Law is correct.


Update: Based on the A380 flight crew manual, it depends—

enter image description here

enter image description here

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    $\begingroup$ Nice document. Thanks for the extract that allow me to find it. I'm glad to see the bounty works well. $\endgroup$ – Manu H Sep 30 '14 at 9:14

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