No full flaps if landing into strong wind?

[Ernie Martin]

As we're on final into a strong (25 kts) headwind, a person who heretofore I considered knowledgeable says "Don't put full flaps because of the headwind". When I, surprised, ask why, he says, "you'll float too much, take too much runway too land". I pushed a bit more, reminding him that full flaps adds considerably more drag than it does lift, but he wouldn't budge. I left it at that.

Here's my take. The aircraft doesn't know about the headwind. It doesn't affect drag or aerodynamics. The body of air in which I'm flying is going "backwards" at 25 kts, and the only consequence is that my ground speed is 25 kts less (say, 60 kts instead of the 85 kts airspeed). If anything, I'm going to use less runway (regardless of flap setting) because at, say, 70 kts touchdown I'm only doing 45 kts over the runway.

Am I missing something here? Is he right? Full flaps into a strong headwind will cause added float?

Ernie

[edasmus]

Ernie, you are correct. I suppose the confusion that the other individual has could stem from the possibility that a gusty wind causing a momentary increase in airspeed could delay touchdown but that has nothing to do with flap setting. That could happen at any flap setting. The other day with winds down the runway 19 gusting 31 I chose full flaps with no problem. I was on the alert however for things to change with little notice. The level of X-wind would normally be the driving force for me as to the amount of flaps I choose. Less flaps equals slightly higher approach speeds with a corresponding increase in rudder authority as well as all around control authority which is what one needs while landing in X-winds. Obviously the aircraft and pilot has limits but I suppose that limit is not cut and dry.

Ed

[tropical]

Apparently he isn't that "knowledgeable" if he makes an assumption like that.

[jchronic]

Your analysis is correct. The airplane only cares about the piece of air it's flying in, and the only way you should float excessively is if your approach speed (IAS) is fast. If you're on-speed or close when you touch down, the airplane should land normally, and full flaps will of course shorten your landing roll considerably, and/or require brake application at a lower groundspeed ($$). Drag is your friend.

Not to say that if the wind is gusty or flukey, you shouldn't probably add a bit of speed on final, just not too much. From my airline experience, the 'book' usually specified half the gust factor, not to exceed 10-15 knots. Of course, that's for heavier aircraft, less affected by wind transients, but I still can't imagine why adding anything over that in our Skymasters would be necessary.

[Roger]

Perhaps the thought should be : how do you best maintain a stabilized approach and airspeed, and then touch-down at the minimum ground speed. If that's the intent, then using full flaps in a strong headwind would not be a problem, if the wind is dead-nuts down the runway. I think this happens (20+ knots, dead down the runway) about 2% of the time, vs off by some degree, plus gusts, etc... So I always consider a strong landing wind to be other than optimal, and use no more than 2/3rd flaps, just to be safe. After all, there is no negative effect caused by decreased flaps into a strong head wind, because the goal is to touch down at a low ground speed, not a low air speed. You only want the airspeed to fly, not to drive You could think of it like the strong wind is really a percentage of flap. It is giving you the same result, ie. keeping you flying at a lower ground speed, which is really the intent (touching down at a low ground speed).

So my plan has always been to use less flaps when it's windy, to avoid the possibility of having errant gusts push the plane around by it having excess body parts hanging out to catch the cross or gusty wind.

As a side issue, I wonder if there is a component of ground effect that makes a plane "float" when you have full flaps down, vs no flaps. Does it get "caught in the cup" vs flow smoothly under the wing. This would then be aggravated by increased wind speed.