Gusty/Turbulence Approach, more flaps?

[extricate]

Hi there,

An aerodynamic question. Given a gusty approach, will you opt to land with flaps 25 or flaps 30 (flaps full)?

Flaps 25 being lesser exposure of the flaps and the aircraft can withstand the gust loads better.
Flaps 30 being stall speed is reduced, resulting in more margin to stall.

What's your thoughts?

Thank you.

[Intruder]

The 747 had better roll response with flaps 25.

[kenparry]

Your Vref should be dependent on flap setting, so slightly faster with F25 than F30 - thus no greater stall margin.

[FullWings]

Aircraft type not mentioned, but I find sometimes carrying more flap == drag reduces the speed excursions a little and makes things a bit more stable, especially in cross/tail winds, as you have more power against the drag and are deeper into the rapid acceleration range for large turbofans. On my type we have the option of Vref+10 in gusty conditions which works a treat keeping the pitch excursions down. YMMV.

[tdracer]

I can't say what the background behind the thinking was, but when I was sitting on the flight deck during a test flight during landing on a particularly gusty, turbulent day, the Boeing test pilot selected lower flaps (25 instead of 30 IIRC), and added 10 knots to V-ref for the landing.
The Boeing test pilots I flew with were all extremely good stuck and rudder types, so I presume he knew what he was doing....

[deltahotel]

Boeing here (75/76). With max wind addition of 15 kts (half the headwind + all the gust to a max of 15), at reasonably high weights, F25 gives more margin to the flap placard speed than F30.

[Check Airman]

Unless the gust additive takes me too close to Vfe, I’m partial to F30 on my type.

[Airmann]

Am I wrong in feeling that faster approach speeds help in gusty conditions? Crab angles are smaller and flight control surfaces are more responsive. And maybe the added inertia actually means that gusts cause less of a disturbance. The physics would indicate that my assumptions are correct. But I haven't officially read this anywhere.

I dread a light aircraft in gusty conditions, always my worst landings.

[extricate]

Thanks for the replies. Good considerations on the vfe.

[extricate]

Aircraft type not mentioned, but I find sometimes carrying more flap == drag reduces the speed excursions a little and makes things a bit more stable, especially in cross/tail winds, as you have more power against the drag and are deeper into the rapid acceleration range for large turbofans. On my type we have the option of Vref+10 in gusty conditions which works a treat keeping the pitch excursions down. YMMV.


good point too.

[stilton]

F25 made life much easier in strong / gusty winds in the 757, that aircraft had so much lift with F30 it was like a kite, didn’t make any difference in the 767

With F25 the 757 went where you pointed it, in fact it handled so much better I used that setting for all landings, another benefit was it reduced the tendency of the nose to crash down, it could be lowered gently with more control authority

[rudestuff]

F25 gives you maybe an extra 4kts on F30 on my type, but an extra 10kts on the flap limit speed. That makes for an extra 6kts 'spread' which is what you want in gusty conditions.

[mustafagander]

On the B744 I prefer F30 coz it's what we always use. F25 can be a bit harder to stabilise speed.
On the C172 I fly I always reduce flap to F10 coz it's not over endowed with power.
Horses for courses.

[vilas]

A320 is an exception. For turbulence it recommends flap full landing but expecting wind shear it's flap3 for better performance. The reason is in flaps ratio of spoiler deflection to aileron is much higher in flap3 making it more sensitive.

[Jwscud]

Though you will note that the latest edition of the FCTM has removed that advice with no explanation from Airbus!