777 inboard aileron behaviour - takeoff
 

Can anyone explain to me why the inboard ailerons on the 777 cycle through their range of travel during the first part of the takeoff roll?

As the engines stabilise, both ailerons droop. As the aircraft accelerates they slowly retract until they are flush with the wing's camber. This is maintained for short time before they return to their original position (flush with the trailing edge flaps).

You'll see an example of what I'm referring to in this video


Initially, I thought it might be due to control column input for a crosswind. But the ailerons cycle through this same movement on every takeoff.

What purpose does it serve?

Many thanks!

They're not inboard ailerons on the 777, they are flaperons which are drooped in proportion to the trailing edge flap extention but also move around a mean position in response to roll inputs - which is what seems to be happening in the video.

FWIW on the 777 the outboard ailerons are also drooped with take-off flap settings.

Ah, I think I may have found the answer to my own question...

Apparently, during takeoff the flaperons enter 'bypass mode', whereby hydraulic pressure is removed to prevent fatigue to the actuators. This causes the surface do droop under its own weight. As the aircraft accelerates, aerodynamic forces cause the flaperon to slowly lift until it is flush with the wing. Above 80kts, hydraulic pressure is restored and so the flaperon returns to its 10deg droop.

Goes to show not everything is in the manuals..;) What was your source for the info?

Why are some portions of the spoilers very slightly raised and don't appear to close fully until the aircraft is fully airborne?

it's not to do with upper surface air flow / pressure is it?

If you look at the windsock, at 1:00 you will see that there is a very strong crosswind almost 90 deg to the heading and that the inputs are to keep the a/c straight and level.

spanner

Good spot

- Crosswind is from the right so you say you'd expect to the spoilers raised to some degree on the into wind wing.

Interestingly, it appears that boeing have adopted the same feature with the 787...

Ailerons also droop on the 747-8.