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convair880mfan
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Boeing 727 Leading Edge Device Question

Mon Dec 20, 2021 8:05 pm

The LEDS on the 27 come out in two phases with 4 LEDs coming out at Flaps 2 and the remainder with the selection of Flaps 5. I am wondering what other jetliners use or used such a system. Since many types don't use Krueger flaps and have full-span slats for their LEDS, do other types have the 27 type system? Was the 27 type system used before it was rolled out? How about other later Boeing aircraft . . . the 37, the 47?
 
JustAnFO
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Re: Boeing 727 Leading Edge Device Question

Mon Dec 20, 2021 9:17 pm

The slats on the newer 737s and all 757/767 changed to a 3-position system. On those jets, the slats extend to a midrange position for takeoff flap settings, and a fully extended position for landing flaps.

I seem to recall that early 737-200s did use an “asymmetric” system, as it were, but I don’t remember the details. Slats 1 and 8 were possibly programmed to extend differently than the remaining inboard devices, but I don’t remember how so.


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convair880mfan
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Re: Boeing 727 Leading Edge Device Question

Mon Dec 20, 2021 9:35 pm

Thanks JustAnFO for that information! Someone, I think, told me that the 737 can take off with a flap setting to 2. I'm not sure that is good information, but if it is, I suspect that all the LEDS come at 1 since I can imagine a 37 taking off with some LEDS retracted. Not sure if early 37s had Kruegers. I am pretty sure the 27 cannot take off with a flap setting of 2 because it needs all the LEDS out for takeoff and they only all come out at flaps 5. Not sure about any of this of course.
 
GalaxyFlyer
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Re: Boeing 727 Leading Edge Device Question

Mon Dec 20, 2021 10:02 pm

Yes, B727 had F5, F15 and F25 take-offs. The noise mods changed that but after I left it.
 
CanadianNorth
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Re: Boeing 727 Leading Edge Device Question

Tue Dec 21, 2021 2:24 am

Good explanation of the 737 leading edges is here: http://www.b737.org.uk/flightcontrols.htm#Leading_Edge_Devices

Basically on the 737 up as far as the -500 (I've never worked on anything newer) there are krueger flaps inboard of the engines and slats outboard. Kruegers are two position, retracted or extended, slats are three position with retracted, extend and full extend. Flaps up brings everything in, selecting flaps 1, 2 or 5 puts the kruegers out and the slats to "extend" which is basically half way out, and then selecting flaps 10 or more puts the slats to all the way out to the "full extend" position. Normal takeoffs are usually with the slats in the extend position, but I'm pretty confident that flaps 10 or 15 are selected for takeoff in certain circumstances which would be a full extend on the slats. Never seen a 737 do a flaps up takeoff.

Anyways, sorry I've nothing on the 727.
 
convair880mfan
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Re: Boeing 727 Leading Edge Device Question

Tue Dec 21, 2021 4:31 am

Thanks to all for those explanations. Very, very helpful. I like the link left by CanadianNorth. That is a wonderful article. I bookmarked it. I wish there was something like that for the DC-10.
 
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fr8mech
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Re: Boeing 727 Leading Edge Device Question

Tue Dec 21, 2021 5:43 am

The 747 Classics, and I assume the newer ones, though I haven’t had the occasion to check, also came out in stages.

The #2 and #4 groups came out at flaps 1 and the #1 and #3 groups joined them at flaps 5. (It may have been the other way around, but the point Is the same.)

The #4 group, most inboard, were Krueger flaps, while the the other 3 groups were variable camber flaps. All LED’s had only 2 positions, stowed and deployed.
 
DH106
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Re: Boeing 727 Leading Edge Device Question

Tue Dec 21, 2021 10:56 am

The slat intermediate position usually has the slot between wing and slat sealed, making the slat effectively a 'leading edge droop' in this position. This is a compromise position that develops extra lift, but at much less drag than with the slot open (e.g. slat fully extended) - which is ideal for takeoff where lift is required without too much extra drag. For landing, extra drag isn't so much of an issue and with the slat fully deployed, accelerated air flowing through the slot creates a large amount of extra lift at the expense of higher drag.
 
JustAnFO
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Re: Boeing 727 Leading Edge Device Question

Tue Dec 21, 2021 1:52 pm

convair880mfan wrote:
Someone, I think, told me that the 737 can take off with a flap setting to 2. I'm not sure that is good information, but if it is, I suspect that all the LEDS come at 1 since I can imagine a 37 taking off with some LEDS retracted. Not sure if early 37s had Kruegers.

The 737 would happily take off at Flaps 2°, but it’s not an authorized TO flap setting. Data is not published for it. The approved takeoff flap settings are 1°, 5°, 10°, 15°, and 25°.
I’m 99% certain that all 737s back to the -100 had Kreugers.


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CanadianNorth
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Re: Boeing 727 Leading Edge Device Question

Tue Dec 21, 2021 5:43 pm

JustAnFO wrote:
I’m 99% certain that all 737s back to the -100 had Kreugers.


Upon further reading it looks like all 737s do have basically the same leading edge flap system. The original -100/200 had on each wing two kruegers inboard and three slats outboard, all normally powered by A system hydraulics. The Advanced introduced slightly bigger kruegers and some minor changes to how the slats extend. The classics were basically the same thing except for a slightly revised shape of the leading edge and now powered by B system hydraulics. The new longer wing on the NG added a fourth slat to each wing, but otherwise works the same as on the classics. A quick search didn't find much on the MAX, but I found three different lists of differences between NG and MAX and none of them mentioned anything about leading edge devices being different.
 
extender
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Re: Boeing 727 Leading Edge Device Question

Thu Jan 20, 2022 2:18 pm

The idea behind the Kruger Flap/Slat arrangement,was, in the event of a stall, that the inner part of the wing stall before the outboard part of the wing, thereby keeping roll control.
 
Max Q
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Re: Boeing 727 Leading Edge Device Question

Fri Jan 21, 2022 2:02 am

JustAnFO wrote:
The slats on the newer 737s and all 757/767 changed to a 3-position system. On those jets, the slats extend to a midrange position for takeoff flap settings, and a fully extended position for landing flaps.

I seem to recall that early 737-200s did use an “asymmetric” system, as it were, but I don’t remember the details. Slats 1 and 8 were possibly programmed to extend differently than the remaining inboard devices, but I don’t remember how so.


Sent from my iPhone using Tapatalk



Not an ‘asymmetric’ system !



That implies more high lift devices on one side than the other, highly undesirable and not the case here


What you have is symmetric operation of devices in different stages
 
DH106
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Re: Boeing 727 Leading Edge Device Question

Fri Jan 21, 2022 9:43 am

extender wrote:
The idea behind the Kruger Flap/Slat arrangement,was, in the event of a stall, that the inner part of the wing stall before the outboard part of the wing, thereby keeping roll control.


And also with the wing being swept, preventing a possible undesireable nose-up pitch should the tips stall first.
 
BoeingGuy
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Re: Boeing 727 Leading Edge Device Question

Tue Jan 25, 2022 6:29 am

JustAnFO wrote:
The slats on the newer 737s and all 757/767 changed to a 3-position system. On those jets, the slats extend to a midrange position for takeoff flap settings, and a fully extended position for landing flaps.

I seem to recall that early 737-200s did use an “asymmetric” system, as it were, but I don’t remember the details. Slats 1 and 8 were possibly programmed to extend differently than the remaining inboard devices, but I don’t remember how so.


Sent from my iPhone using Tapatalk


The 777 and 787 work the same also. As others noted, the slats are in the sealed position at Flaps 1-20. The slats are in the gapped position at Flaps 25-30.

Most Boeing models have an Auto-gap feature that will automatically move the slats from the sealed to gap position in the event of a pending stall condition. This is for extra lift.

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