Departure with a crosswind needs less runway than a departure with no wind?

@huv: we are discussing the takeoff run, not the landing. I have flown quite some hours in the Cirrus of which some in the SR20 and most in the SR22T. I can’t remember having to use differential braking on the takeoff run, but lots of left rudder. I do agree that with heavy crosswinds, you need more distance in takeoff and landing to accommodate any gusts. However, this is all becoming a very theoretical discussion.

Peter wrote:

But it is 16 degrees off axis. The Q is: how much does this matter? How much is the wing lift sensitive to the deviation from perpendicular of the airflow across it?

It is the same as slipping with 16 degree yaw. Pretty sensitive!

AnthonyQ wrote:

But the lift at Vr is calculated from the 70kt component at zero degrees…which is the same as the nil wind case

Yes I believe you are correct. The total relative wind doesn’t matter as for a lift equation, the wind perpendicular to the wing is used. On a runway this is 0 at 0kts and 70 at 70kts.

Peter wrote:

After liftoff (Vr) the picture changes. Over a few seconds, the plane turns into the relative wind (i.e. a heading change from 360 to 016 in this case). … a departure into wind gives you a briefly higher rate of climb.

Yes I believe you are correct, so many times as I have taken off with a XW, I have used this. At lift-off kick the nose into wind (you don’t need to do much for this really due to the weathercock effect), and get an instant lift. Now you experience the fact that all this time you were moving into 20kt XW, but you could not use it… until now!

That’s why I think you need less runway, as you can lift-off as early as ground effect kicks in, turn nose into wind, and fly away.

Unless there is trees or hangars lining the runway… then you will be held down due turbulence and rotors…