A380 Cross Wind Take Off Auto Aileron into wind

[Capt Groper]

Can any body please explain how the A380 senses a cross wind on take off and to what degree aileron into wind is automatically input by the Flight Control system?

[Uplinker]

Don't know the answer to your specific question, but on A320/321/330; by 100 kts on the take-off roll, the ADIRS have worked out the wind speed and direction and display it on the ND's.

So it would be a relatively simple operation to write some software to work out the cross wind component, (the aircraft knows what runway it's on) and then have a 'look-up' table to apply an appropriate amount of into-wind aileron.

Interesting though, because on A320/321/330, Airbus recommend no into-wind aileron on take-off because roll spoilers could be deployed which would increase drag too much.

Is this a precursor to automatic take-off's I wonder ??


U

[nitpicker330]

?????

On the runway the HDG and TRACK are the same, so how does the computer workout the wind??? Headwind or Tailwind yes but crosswind??

[TyroPicard]

The A320 displays pure headwind or pure tailwind on T/O.. it has no way of calculating the correct wind direction.

[Cardinal]

Given this forest of vanes, one would think the wind could be resolved quite readily on the 380:

http://www.worldofstock.com/slides/TRA2424.jpg

[pipersam]

Boeing lets you enter runway wind and conditions on the fmc, perhaps this is the same for the airbus as well and the system simply uses this value?

[Trent 972]

....to what degree aileron into wind is automatically input by the Flight Control system
A380 FCOM
LATERAL CONTROL
GROUND LAW
The lateral ground law is a full authority control law in roll and yaw, with some yaw damping.
When the sidestick is at neutral, the law will aim to keep the wings level.

FLIGHT LAW
Is a roll rate demand law.
The flight law is available inflight, gradually phased-in during 5s after liftoff.
The control laws don't automatically put into wind aileron for crosswind take-offs. They keep the wings level if no lateral sidestick input.

[Uplinker]

?????

On the runway the HDG and TRACK are the same, so how does the computer workout the wind??? Headwind or Tailwind yes but crosswind??

Hi Nitpicker, sorry for the late reply to this, but I had to wait until I flew again to check.

The A321 I flew today does give a wind and direction at 100kts on the take-off roll, and not just head or tail wind. RWY heading was 078 but the wind displayed was 063/7. As to how it does this, I don't know, but the ADIRS do compute yawing as well as everything else, and the flight computers know how much rudder is being put in and what the resultant track is - even on the runway. So it is not inconceivable that some clever software is doing the sums to give a wind vector.

I would be fascinated to learn more.

U

[777fly]

Being (mostly) a Boeing devotee, I have very limited knowledge of how an A380 copes with a crossswind on takeoff. However, Trent 972 gives a clue to what happens from the FCOM quote. To paraphrase: 'With the sidestick neutral, ground law will try to keep the wings level'. There is only one way that this can be done, with neutral stick input, and that is by automatic application of aileron, rudder and possibly spoiler input, to eliminate or reduce roll and yaw.
Yaw will be sensed by the inertial systems and is a result of two effects: assymetric forces on the rudder ('weathercocking') or by excess lift on the 'into wind' swept wing which makes the aircraft want to roll, or on the ground, turn away downwind. I am fairly certain that the first effect is easily eliminated by rudder yaw damping , but the second effect is more subtle and would require an aileron input to minimise it.
However, in limiting crosswind conditions, the amount of aileron input that is sometimes required to keep wings level will cause the upwind spoilers to partially extend, increasing drag and reducing takeoff performance. That is why there is usually a limit to aileron input on takeoff and why, in limiting crosswinds, the aircraft wants to roll off downwind after rotation and you have to increase the into wind aileron input to keep the wings level. On the ground the aircraft's ability to roll downwind was prevented by the reaction of the downwind gear strut, but that restriction is removed as soon as the aircraft gets airborne.
The most elegant auto takeoff solution would be for the aircraft system to eliminate all yaw with rudder, sense gear strut compression and be allowed do what is neccessary with aileron to keep them equalised, without an excessive drag increase. Maybe that is what the A380 does already??