Effect of lift at rotation in a crosswind

[Mister Geezer]

Thanks in advance for anyone that may be able to give some clarity to this conundrum I am facing.

I was chatting to a colleague recently about rotating a sweptwing aircraft which is subjected to a crosswind component and the what effect the rotation has on lift due to the requirement to feed in more aileron on rotation, in order to keep the wings level. I understand that the upwind wing will generate more lift due to the direction of the relative wind and obviously that at rotation, the increase in the angle of attack will increase the amount of lift that is generated.

- Is there a difference to the proportion of extra lift generated by the upwind wing during rotation compared to before rotation and does the deflection of into wind aileron aileron affect this difference?

- As the flow of the relative wind is no longer aligned with the chord wise flow, what is the effect on the lift that is generated by a wing, when this angle increases in turn with the component of spanwise flow.

I dug out my ATPL notes from many years ago and had a look online for some wisdom but could not find any clarity!

Thanks

[ShyTorque]

I think "V squared" is the relevant bit of the lift equation.

[dook]

The lift coefficient is.

[Intruder]

I've found that if you hold the aileron & rudder inputs needed to track straight & level down the runway, the airplane will settle into the proper attitude through rotation (747).

[Judd]

the airplane will settle into the proper attitude through rotation (747).

Maybe that is true for the real aircraft. But in one 737 simulator I fly this is not necessarily so. For example with the simulator, taking off with a substantial crosswind component from the right, even with the appropriate amount of aileron held to the right, left rudder will be needed to maintain the centreline. That is normal of course. As soon as the aircraft is lifted off the ground the simulator initially rolls/yaw markedly to the left possibly due to left rudder not being instantly removed. Then split seconds later some rudder and aileron juggling takes place to ensure the aircraft turns slightly to the right to track the extended centreline.
I don't recall that happening in a real 737 although that could be because we rarely experienced 35 knot crosswinds in my part of the world. Could be a fidelity problem in the simulator ?

[Bergerie1]

I totally agree with Intruder re the 747 aircraft but can't remember the precise simulator response. Programming a simulator for the transition into and out of ground is (was?) notoriously difficult. Can any simulator experts enlighten us?

[mustangsally]

I do hope some where this conversation took place over a couple of pints. Simulators are only as good as the folks programing the box. Not the real this and as close as it does get it is still simulated. Real world experience, L1011, 747, 727, DC 9, MD 90, 777, A-300, A320, and my favorite a Cub once off the ground tend to track into the prevailing wind. The most work was always the Cub, tricycle gear never a problem.

[Intruder]

Originally Posted by Judd

Maybe that is true for the real aircraft. But in one 737 simulator I fly this is not necessarily so. For example with the simulator, taking off with a substantial crosswind component from the right, even with the appropriate amount of aileron held to the right, left rudder will be needed to maintain the centreline. That is normal of course. As soon as the aircraft is lifted off the ground the simulator initially rolls/yaw markedly to the left possibly due to left rudder not being instantly removed. Then split seconds later some rudder and aileron juggling takes place to ensure the aircraft turns slightly to the right to track the extended centreline.
I don't recall that happening in a real 737 although that could be because we rarely experienced 35 knot crosswinds in my part of the world. Could be a fidelity problem in the simulator ?

I don't know if the OP is trying to fly an airplane or a simulator, but I answered in the context of flying an airplane. With almost 10,000 hours and over 500 takeoffs and landings in most versions of the 747 (includes -8 and LCF; no -100 or SP), I'm rather familiar with the handling characteristics. Not all versions handle exactly the same, but they are similar enough in this context. Granted, a lot of it becomes "muscle memory" (maybe another term for "air sense" here), and there is no set procedure or guide line for how quickly to relax the controls and allow it to fly off on the correct runway track.

A takeoff in a 35 kt crosswind is certainly not routine, and beyond the limits for many operations, so it is not the benchmark for citing useful techniques. Rather, what works in a more typical 10-15 kt crosswind should be the focus of discussion; then anyone is free to extrapolate from there.