Gusty/crosswind landing flaps

[Gryphon]

If you have the option of two or more landing flaps configuration, and you plan for a gusty crosswind approach and landing, is it true that the lower flaps configuration the better? and if it is, why?:confused:

Thanks a lot.:O

[catchup]

Well,

pro: the aircraft is more responsive to flight control inputs due to higher speeds with lower flapsetting

contra: the aircraft is a little bit more stable with higher flapsetting due to thrust/drag ratio.

regards

[average bloke]

A lower flap setting will be associated with a higher landing speed (1.3VS1 versus 1.3VS0), so the actual crosswind component is reduced (resolving triangle of forward speed and crosswind).

[Empty Cruise]

Catchup,

Yep, aircraft is more speed-stable with a higher flapsetting. However, with higher flapsetting, the difference in wing-loading when viewed spanwise increases, effectively generating more lift at the centre & root of the wing and proportionally (due to reduced speed) less at the tips. This would imply that the aircraft is less statically stable in the roll channel, and indeed, that is what is observed on (at least) the 737 when going from F30 to F40.

The speed-difference between the 2 flaps-settings is only in the order of 3-5 kts (about 3,5%), so the difference in actual drift angle to overcome is subtle.

Does anybody know if the increased gap between trailing edge/aileron and the flaps (and therefore the size of the generated vortex & the effect on spanwise flow) has anything to do with the decreased static roll stability?

Brgds,
Empty :)

[catchup]

@Empty Cruise

In my aircraft (not 737) the speed difference between max flaps and the notch before is 11 kts.

regards

[ant1]

Another factor relates to the fact that the aircraft has a higher tendency to weathervane into the wind with flaps down.

So the gusty winds would lead to higher directional (hence lateral) instability with higher flap settings.

[onthemagicbeam]

Empty Cruise,

I'm sure I'm meant to know all about what you have written in your post, but I don't, so off to the books again!!!:confused: :confused:

[flying_elvis]

I generally go full flaps for all x-wind landings.

X-winds over 15kts I'll think about reducing the flap settings.

With Gusty headwinds or or wind shifts lower flap settings are always a good idea. On the 757/767 you have to concern yourself with flap blow up speeds. so if the IAS is bouncing around you're better off flaps already in/or closer to their blow up position.

[411A]

Yes, the B707.

Flaps 40 or 50 were fully approved as a landing flap settings, flaps 40 increased the landing distance by an (average) 600 feet.

In addition, flaps 25 were used on occasion, for stage three modified aircraft, to achieve specific noise requirements and, in this case, the regulated landing distance was increased by 1200 feet.

Not a problem where the landing distance was not limiting.

One operator (PanAmerican) normally used flaps 40 for landing, to enhance control during gusty crosswinds...HKG, with southerly gusty winds, for example.

Been there, done that, and it works just fine.

As usual, follow the specific airlines' recommended procedures which, if you follow 'em, you cannot be faulted.

[stator vane]

at least three different books i have state the fact above, thereby reducing stability. (moment out to the CP reduced.)

by experience, i find in gusty winds, the B737's-flaps 30 are slightly better, if runway length is no factor.

[7FF]

One of the reasons, in addition to the aerodynamic explanations given above, is that in gusty conditions the flap load relief may operate, 747 varieties. The flaps will retract from 30 to 25 prior to touch down and then in the flare the flaps may well then extend back to 30. Not good when you are trying to sort out the crab.
Anything over 15 kts cross wind I recommend flap 25 and in any gusting conditions over 10 kts.

[Arctaurus]

Interesting discussion - What do people think of flap 3 v flap full in airbus aircraft with strong crosswinds?

[Ultralights]

as a general rule of thumb i have usedinevery aircraft i have flwon, is set flaps according to the windsock, gusty winds, = no flap, calm = full flap,

no flap means a higher wing loading and more stability, and better control response. not only that once you are on the ground, there is less chance of a gust picking up a wing.

[Pack2]

Average Bloke

I dont think what you said regards crosswind component is actually correct.

The crosswind component for any given runway = sin wind angle x wind speed. It has nothing to do with aircraft speed. The effect on the aircraft in terms of drift does however depend on aircraft speed.

[JW411]

Ultralights:

"gusty winds = no flap, calm = full flap"

What sort of aircraft do you fly for heavens sake? A flapless landing on most swept wing airliners will mean an increase in landing distance required of around 100%.

For example, for a no flap/no slat landing on a DC-10 a 12,000 ft runway would be good.

That cuts the choice of airfields available down just a little!

[411A]

....never mind the tyre speed.:}

[mutt]

I can just imagine the howls of protest when we advise crews to do No Flap landings in gusty conditions... :):)

Mutt

[I-2021]

Hello ! Using F40 on the 737 with X-wind increases the wing tip ground clearence. So it is a recommended setting. Is that a correct statement ?

[upwind]

speaking of flaps, how many degrees does the flaps extend for each stage of extension on the 744?
thnx in advance!