X-wind flying

[tom775257]

Hi all,
A quick question, I should really have asked my instructor at the time, but forgot.
I was performing some touch and goes in a Warrior with a 21kt x-wind 90 degrees to the runway for practice. After rotation at 65 kts, (no flap) during initial acceleration to Vy the stall warning buzzer was sounding with an IAS of around 70 kts and normal climb attitude. I was not getting any buffet or anything; so was I actually near stalling the aircraft? I obviously slightly lowered nose attitude reducing ROC, which immediately silenced the stall warner until achieving Vy, then resumed the climb out. Should I increase Vr with a heavy X-wind?? This happened on 2 occasions during the session, the instructor didn't really comment on it, and nothing was mentioned in the de-brief.
Cheers,
Tom.

[FlyingForFun]

Tom,

First of all, the demonstrated x-wind limit in the Warrior is 17kts. That doesn't mean it's illegal or dangerous to fly in x-winds greater than that, but it might invalidate your insurance, or break some club rules. I'm sure your instructor knows what he's doing, but it's probably worth checking with the club... at the very least, you might find that your club prevents solo students or private hirers from flying in x-winds greater than 17kts even if they allow it with instructors. Best to find out now.

Ok, now that's out of the way, I've never heard of this, but it's certainly conceivable. There are a few things I can think of.

What direction was the x-wind from? Someone who knows lots more about aerodynamics than me may well correct me, but basically the stall warner will tell you, pretty accurately, when the centre part of the left wing is a few degrees below the stall angle. That doesn't mean that the rest of the wing is close to stalling. And it doesn't mean that the right wing is close to stalling. This may explain why you heard the stall warner - the cross-wind (and resulting side-slip) would alter the angle of attack on each wing slightly.

Another explaination is this: I assume that you were using into-wind aileron during the take-off, and converting the slip into a crab shortly after take-off? Remember that, during a slip, the wind will not strike the pitot sensors at the "normal" angle. This could cause the airspeed indicator to read an incorrect value. You may have been doing a little less than 70kts.

And a third explaination: remember that the stalling of a wing is entirely related to it's angle of attack. Any relationship between airspeed and stalling is only really coincidental. The "stall speed" will only apply when flying straight+level, and when decelerating slowly. If you pull hard, it's possible to stall at much faster speeds - basically, the wing is at a high angle of attack, the aircraft's vertical speed hasn't had a chance to rise yet (the rise in vertical speed would normally decrease the angle of attack) and the airspeed hasn't had a chance to fall yet (thus giving you an indication which would be confusing if you thought of stalling purely in terms of airspeed). This is a very important point, although I have to admit I can't see how it could be related to a cross-wind.

In any case, the PA28 is very good (in my experience) at letting you know when it's about to stall. If you didn't feel a buffet, I'd guess you still had a bit to go before stalling, so there was no real danger. And your action of lowering the nose was completely correct.

I'd be interested to hear more informed opinions, though, because I've never heard of this before!

FFF
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[tom775257]

Hi FFF,
Thanks for the input.
To explain what I was doing first: It was one of those days where not many people were flying, due to fairly high winds; this was about 5 months ago. I had just been flying intensively for couple of weeks, so while I was in practise, I asked to do some x-wind landings. The CFI came up with me and we started off on a fairly into wind runway, practising landing in high wind conditions. Because of no circuit traffic apart from us, we continued to another runway with more X-wind, and then finally onto the runway with nigh on full x-wind 90 degress to the runway from the left. The reason I remember it was ATC asked to speak to my instructor rather than me, and then proceeded to give a warning of the 21kt x-wind. This was when I experienced what I described in my previous post. Yes I agree; I really must check the rules of the club…I have yet to read them…doh.

Regarding the flying, with a x-wind from the left I presume I did as follows: wind from left, left aileron during the roll, just before rotation centre aileron, just after lift off a fair bit of right rudder to stop weather-cocking due to x-wind from left and for the usual prop wash induced yaw; while simultaneously putting back left aileron….soon after crab into wind, balance the aircraft and continue the circuit..

Thanks for the ideas; it would be interesting to know what happened. It would be very interesting to know whether a strong x-wind can say lead to the upwind wing stalling while the downwind wing stays flying…nasty. Re. Pulling hard leading to stall. I was being fairly gentle in the rotation and climb, never had it happen from any other time I have taken off.
Cheers, Tom.