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Flap Setting

Posted: Fri Oct 29, 2004 7:40 pm
by Cathay744
How much flaps would a 747-400 set for takeoff on a 4000 meter runway?

RE: Flap Setting

Posted: Fri Oct 29, 2004 8:04 pm
by dl757md
I don't have access to 744 take off setting info, but someone who does would also need take off weight, ambient air temperature, and field altitude to answer your question accurately.


RE: Flap Setting

Posted: Fri Oct 29, 2004 9:22 pm
by andrej
Hello all,

as mentioned above there are many factors, as to what is TOW, wather, OAT, alt. of airport. However usually B744 has 2 T/o flap settings 10 and 20 degrees. It all depends on airline preferences.

The lower setting should give you lower V1, Vr and V2 speeds. But there are other disadvantages to this setting which I can not remember now.  Smile/happy/getting dizzy


Andrej Lippay

RE: Flap Setting

Posted: Fri Oct 29, 2004 11:59 pm
by Mr.BA
To add on to what Andrej has said..

Flaps 10 would give a better climb performance on climbout and 20 would be otherwise. Takeoff roll for 10 would be longer and Vr and V2 would be higher as compared to flaps 20. Vr should stay the same.


RE: Flap Setting

Posted: Sat Oct 30, 2004 12:04 am
by wilco737
Hi there,

yes, Flaps 10 and 20 for the 744! And for example in FRA (4000m) runway I would guess you use 10, because higher flap setting you use when you are field length limited and if you are climb limited then you would chose a lower flap setting.

I only know it in the 737, flaps 1 on long runways, 5 for normal, 15 for short field and in the NG737 you can use 25 also, on real short runways!

The higher flap setting will give you more lift, so you can get airborne sooner (lower speed). But you have a poor climb performance because of the also higher drag of the flaps.
If you are climb limited, you use lower flap setting, and then higher speeds (V1,Vr,V2) and then you can climb a lot better (less drag) but you need higher speeds to get airborne due to the reduced lift...

I hope that answers your question


RE: Flap Setting

Posted: Sat Oct 30, 2004 12:07 am
by SlamClick
The generalities are as follows.

Small flap settings give you a long ground run and higher V-speeds but better engine-out climb performance.

Greater flap settings will shorten the ground run with lower V-speeds but engine-out climb performance will be degraded.

Other factors are:
Aircraft gross weight
Airport elevation.
Air temperature
Runway in use (length, slope, obstructions in the departure corridor)
MEL/CDL limitations or restrictions

We don't really set them for their affect on all-engines-operating performance, but with an eye to engine failure. That is because an engine failure scenario is usually what limits our allowable gross weight when it is less than maximum certificated gross weight.

I have a B-747 manual or two out in the garage and could look up some numbers but I'd rather someone who actually knows that airplane answer up here.

Where is B747Skipper when you need him?

[Edited 2004-10-29 17:11:24]

RE: Flap Setting

Posted: Sat Oct 30, 2004 2:31 am
by goboeing
From the B-747 sim that I flew numerous times this past summer, flaps 10 would be used. I don't have any charts in front of me but flaps 20 wasn't needed on the longer runways and lighter weights in general.


RE: Flap Setting

Posted: Sat Oct 30, 2004 2:58 pm
by AJ
Some airline's SOPs dictate a specific flap setting, for example Qantas uses Flap 20 for all takeoffs on the 747-400.

RE: Flap Setting

Posted: Sun Oct 31, 2004 10:55 am
by Mr.BA
Apologies, I meant V1 would stay the same from my previous psot not Vr. And SIA too, dictates only flaps 20 for all takeoffs on the B744s.