747&737 leading edge flaps&stats
Joined: May 2003
Posts: 198
Likes: 1
From: france
b737 flaps/slats
hello capt greaser,
for the boeings, kruger flaps inboard & slats outboard, it' s all about stall behavior.
first mr boeing, for obvious reasons, doesn' t want us to stall their aeroplanes, hence the high lift devices(kruger/slats) on the leading edges & fowler flaps at the trailing edges, for slow speed flight.
if we do however insist, they want the wingroot(inboard) to stall before the wingtips(outboard), so that aileron control is not lost first.
kruger flaps by design are less stall resistant than slats, which have among other things, the added benefit of the gap effect(accelerating air à la bernouilly) between the wing leading edge & the deployed slats.
douglas with the dc10 achieves same with wing washout, the wing at the root has by design, a greater angle of fixed incidence(angle between longitudinal axis & wingchord) than the wing at the tips, so again root stalls before tips do. you can clearly see this wing twist, when viewing a dc10/md11 for that matter, from the rear.
kind regards,
bm,
for the boeings, kruger flaps inboard & slats outboard, it' s all about stall behavior.
first mr boeing, for obvious reasons, doesn' t want us to stall their aeroplanes, hence the high lift devices(kruger/slats) on the leading edges & fowler flaps at the trailing edges, for slow speed flight.
if we do however insist, they want the wingroot(inboard) to stall before the wingtips(outboard), so that aileron control is not lost first.
kruger flaps by design are less stall resistant than slats, which have among other things, the added benefit of the gap effect(accelerating air à la bernouilly) between the wing leading edge & the deployed slats.
douglas with the dc10 achieves same with wing washout, the wing at the root has by design, a greater angle of fixed incidence(angle between longitudinal axis & wingchord) than the wing at the tips, so again root stalls before tips do. you can clearly see this wing twist, when viewing a dc10/md11 for that matter, from the rear.
kind regards,
bm,
Thread Starter
Joined: Nov 2005
Posts: 58
Likes: 0
From: UAE
Tnx for that reply.Should have thought of that one myself.
A while since I flew the 74.What I should have said was why do the 2&4,s come out first when extending flap from 0 to 1. I think that was the way they extended.Then 1&3's from flaps 1 to 5. When your retracting isn't it 1&3's retracting flaps from 5 to 1 and then 2&4's from 1 to 0. Why is it arranged like this???
A while since I flew the 74.What I should have said was why do the 2&4,s come out first when extending flap from 0 to 1. I think that was the way they extended.Then 1&3's from flaps 1 to 5. When your retracting isn't it 1&3's retracting flaps from 5 to 1 and then 2&4's from 1 to 0. Why is it arranged like this???
Joined: Sep 2006
Posts: 120
Likes: 0
From: BRUSSELS
Got it.
When selecting flaps 1, INBOARD leading edge flaps only extend; this is to prevent too much bending and twisting moment on the wing tips. Once trailing edge flaps are extending (flaps 5 and further) there is no more excess of twisting moment, so OUTBOARD leading edge flaps can be extended too.
When selecting flaps 1, INBOARD leading edge flaps only extend; this is to prevent too much bending and twisting moment on the wing tips. Once trailing edge flaps are extending (flaps 5 and further) there is no more excess of twisting moment, so OUTBOARD leading edge flaps can be extended too.
Joined: Jan 2001
Posts: 348
Likes: 2
From: Canada
Quote: "if we do however insist, they want the wingroot(inboard) to stall before the wingtips(outboard), so that aileron control is not lost first."
In addition, one of the benefits of not having the wingtips stall before the rest of the wing is avoiding the center of lift, (what's left of it), from becoming too far forward on the whole machine.
If this occurs in the extreme in some types, the elevators may not be able to overcome the nose up tendency.
The type that comes to mind here is one I spent some time on, the F-101B Voodoo. Given the right conditions the elevators would become blanked out in the turbulent wing airflow with the result that the whole machine would pitch up.
That may be a bit extreme for a transport type but at least we could bail out if necesary.
In addition, one of the benefits of not having the wingtips stall before the rest of the wing is avoiding the center of lift, (what's left of it), from becoming too far forward on the whole machine.
If this occurs in the extreme in some types, the elevators may not be able to overcome the nose up tendency.
The type that comes to mind here is one I spent some time on, the F-101B Voodoo. Given the right conditions the elevators would become blanked out in the turbulent wing airflow with the result that the whole machine would pitch up.
That may be a bit extreme for a transport type but at least we could bail out if necesary.
Joined: Apr 2005
Posts: 41
Likes: 0
From: Aust
Lemper where do you get your info from ?
747 Classic, L.E flaps 2 & 4 extend at flaps 0-1, called Group A, and flaps 1-5 Group B extend which is L.E flaps 1 & 3. They ext and ret in these groups because when you take off you want all the lift so at flaps 20 all L.E flaps will be extended, on climb as air speed incr you dont req as much lift this is why they retract in groups .
744 is different , flaps 0-1 L.E flaps 2,3,4 all extend and flaps 1-5 L.E flaps 1 extend.
The numbers are related to the pneumatic drive units (PDU) that run the L.E flaps. 1,2,3,4 from o/b to i/b .
747 Classic, L.E flaps 2 & 4 extend at flaps 0-1, called Group A, and flaps 1-5 Group B extend which is L.E flaps 1 & 3. They ext and ret in these groups because when you take off you want all the lift so at flaps 20 all L.E flaps will be extended, on climb as air speed incr you dont req as much lift this is why they retract in groups .
744 is different , flaps 0-1 L.E flaps 2,3,4 all extend and flaps 1-5 L.E flaps 1 extend.
The numbers are related to the pneumatic drive units (PDU) that run the L.E flaps. 1,2,3,4 from o/b to i/b .
