How efficient is aileron droop ?

[Volume]

Had several flights on the small Airbusses this winter and made an interesting observation. After deicing, the aircraft is covered with a thick coat of the green stuff which prevents icing. On the wings and the flaps most of it are already blown away before rotation, and once the gear is up, the wing is clean again. However, the aileron remains fully green until the flaps have been retracted and the ailerons have returned to their neutral position, only a few seconds after, they are clean as well. A litle bit of deicing fluid is still present at the trailing edge of the entire wing, even after an hour of flight, the same happens at the spoilers trailing edge.
So is the airflow over the drooped aileron separated, and how much drag does that cause compared to the increase in lift? How efficient is aileron droop?

[John Farley]

Clearly like any other wing characteristic the effects of aileron droop will be type dependant.

I can only speak for one type where under some circumstances the aircraft did not meet the takeoff performance guarantees in respect of distance. We added a bit of aileron droop and gobbled the spec.

In my view it is likely that when aileron droop is used people are only interested in the lift benefits and so ignore any drag issues as the time the droop is down is so short any drag delta does not matter.

It probably makes sense to think of droop as just increasing the amount of wing that is flapped.

[Jane-DoH]

Didn't some of the F-4's have drooping ailerons? I think the F-4J did...

[Machinbird]

Didn't some of the F-4's have drooping ailerons? I think the F-4J did...That is correct, and the earlier B model did not droop its ailerons.

[H Peacock]

The Buccaneer could droop its ailerons with flap selections, and I seem to recall the wonderful VC10 could make its ailerons both go up a tad to help with wing bending moment relief. Not sure how it affected the overall trim/drag, but still very clever. :D

[411A]

Not sure how it affected the overall trim/drag, but still very clever.
No nearly as clever as that on the Lockheed tri-motor...-500 model.:E

[Jane-DoH]

Machinbird

That is correct, and the earlier B model did not droop its ailerons.

That I actually knew. I assume the F-4C/D didn't have the drooped ailerons either; did the F-4E/G have them?


411A

No nearly as clever as that on the Lockheed tri-motor...-500 model.:E

You mean the active-control ailerons? That was for gust alleviation, not for increasing lift as I understand it...

[Avenger]

Correct JD, BA modified their Tristars in 1981 for improved blending and gust control, modern jets, B737, Airbus etc, do not suffer this problem to the same degree.

[411A]

...modern jets, B737...

Stretching the term 'modern' just a bit far, seems to me...:p

[rudderrudderrat]

Hi Volume,

On the wings and the flaps most of it are already blown away before rotation, and once the gear is up, the wing is clean again.

There shouldn't be any anti icing fluid on the flaps because the de / anti -icing is performed with the flaps up (0).
The front of the wing should clear of fluid first as it runs back due to the airflow. The Slotted Fowler Flaps ensure the airflow is better attached, so the last exposed section of flap should clear of fluid rapidly.

I'd expect the drooped ailerons to clear last, because they are at a greater chord angle than the wing.

[planett]

The Twin Otter had it too, with some amount of flap selected. It landed in such short distances with minimal flap settings, it made one wonder how often you needed to go full flap with such a nose down attitude and approach speeds so far below Vmc.
Then again I never flew it into eskers like my predecessors. You could literally land on a "long" 2600' runway and be bored by the taxi time to the ramp exit half way down.

[grounded27]

Suppose it has to do with the types of drag a wing encounters at different speeds and flap/slat configs. Parasitic drag occurs at lower speed's over the wing, as the wing changes (cleans up) the amount of drag changes and ofen moves inboard. Thus the inboard aileron performing better at higher speeds. Aircraft often land with deice fluid still evident on the fuscelage and other areas.

[TURIN]

Avenger,
Correct JD, BA modified their Tristars in 1981 for improved blending and gust control, modern jets, B737, Airbus etc, do not suffer this problem to the same degree.

LAF (Load Alleviation Function) on the A320. :ok:

rudderrat

There shouldn't be any anti icing fluid on the flaps because the de / anti -icing is performed with the flaps up

Not necessarily. I know of one A330 operator who sets flaps to a T/O position before de-icing. I assume it's just in case there is any accumulated snow/slush attached to the structure from a previous landing. But someone will enlighten us I'm sure. :)

[V1... Ooops]

...The Twin Otter had it too, with some amount of flap selected.

You mean, the Twin Otter HAS it - because Twin Otters are now back in production. :) I just delivered a new one from Canada to the Seychelles.

Below is a picture showing the ailerons of a Twin Otter in the neutral position when full flap has been extended.

Michael

http://i979.photobucket.com/albums/ae275/Paneuropean/TwinOtterWing.jpg