The question -
Curiuos if you could ask the flight test guys how a/c are certified for crosswind takeoff's, specifically the use of ailerons to prevent the upwind wing from raising.
Do they start with full control input prior to the start of takeoff roll, feed in aileron to keep the wing level as they accelerate, or don't use any aileron input until rotation starts?
The answer -
Since I am a flight test guy I will answer your question. We recommend that you start at neutral or less than one unit into the wind. Maintain the wings level by correcting when it starts to tilt over. This tends to minimize the amount of crosswind controls at rotation which is important related to tail clearance margins and controllability. The other method, which usually comes from the small airplane types, tends to keep a little wing low into the wind during the roll and rotation and reduces margin. It is also counter intuitive as you are putting input into the airplane when no effect is felt and taking it out as things happen. Not the design philosophy of control. An article in the new Boeing Aero magazine will also point this out soon.
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I've also heard it was related to acceleration performance but he makes no mention of this. So I'm not sure if it is related to acceleration performance or not.