Moderators: richierich, ua900, hOMSaR

 
User avatar
propilot83
Topic Author
Posts: 625
Joined: Sat Jan 27, 2001 2:41 am

Slat Retraction On 747's

Tue Sep 30, 2014 7:01 am

I have a question regarding the slat retraction process during take off and climb on 747's. I've noticed that all three are extended to provide additional lift, and the outer slat retracts first, then the inboard two retract together about 8 minutes after take off, do the pilots manually retract it? or does the autopilot/computer automatically retract the slats a few moments after take off? Thanks.
 
mmo
Posts: 1968
Joined: Thu Apr 18, 2013 3:04 pm

RE: Slat Retraction On 747's

Tue Sep 30, 2014 7:20 am

There are 3 groups - Inner, mid and outer. With Flap 1, the inner (Krugers) extend. With flap 5, the other sections extend. The extension/retraction of the sections is controlled by the flap handle itself. All the retraction/extension is all handled by the PNF during flap retraction/extension.
If we weren't all crazy we'd all go insane!
 
wilco737
Posts: 7275
Joined: Sun Jun 20, 2004 12:21 am

RE: Slat Retraction On 747's

Tue Sep 30, 2014 7:37 am

The slats on the leading edge of the 747 are called flaps as well. They are so called krueger flaps.

http://en.wikipedia.org/wiki/Krueger_flap

Quoting mmo (Reply 1):
There are 3 groups - Inner, mid and outer. With Flap 1, the inner (Krugers) extend. With flap 5, the other sections extend

That is correct for the 747-400. On the new 747-8 all the groups of flaps extend with flaps 1. and retract when selecting flaps up.

Quoting propilot83 (Thread starter):
do the pilots manually retract it? or does the autopilot/computer automatically retract the slats a few moments after take off?

We pilots do it on our own. When we have reached a certain spead (safe speed for the flaps) we put the flap lever to the next position and the flaps retract.

wilco737
  

[Edited 2014-09-30 00:39:00]
 
User avatar
747classic
Posts: 3003
Joined: Sat Aug 15, 2009 9:13 am

RE: Slat Retraction On 747's

Tue Sep 30, 2014 11:26 am

Quoting wilco737 (Reply 2):
The slats on the leading edge of the 747 are called flaps as well. They are so called krueger flaps.

This is only partly correct.

The slats are called Leading Edge (LE) flaps on the 747 , with actually two different types installed :

Between the fuselage and the inboard engines : krueger flaps.

Krueger flap (installed at Leading edge inboard of inboard engines at 747)


Between the engines and at the outboard wing : variable camber flaps.

Variable camber flaps


The 747- classic series (747-100/200/300/SP) has kreuger flaps inboard of the inboard engines, they help to ensure that in the event of a stall the inboard section of the wing will stall first. Outboard of the pylons 2 and 3 are variable camber leading edge flaps installed. All LE flap sections are controlled by the up, flaps 1 and five position of the (TE) flap lever.
Also during engine reverse (part) of the LE flaps retract to avoid heat/vibration damage.

747-400 : the only difference between the 747-100/200/300/SP (besides the flap programming) is that the -400 has 1 extra variable camber leading edge flap (per side!!!) on the outboard section due to the increased span.

The 747-8 series (new wing profile) are equipped with gapped krueger flaps inboard of the inboard engines, the rest are all variable camber flaps, operated by the flap 1 or up position of the (TE) flap lever.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
wilco737
Posts: 7275
Joined: Sun Jun 20, 2004 12:21 am

RE: Slat Retraction On 747's

Tue Sep 30, 2014 11:40 am

Quoting 747classic (Reply 3):
Between the fuselage and the inboard engines : krueger flaps
Quoting 747classic (Reply 3):
Between the engines and at the outboard wing : variable camber flaps.

Thanks for being more specific than me   

Just wanted to point out that it is no slat.

Thanks.

wilco737
  
 
User avatar
Buyantukhaa
Posts: 2327
Joined: Thu May 13, 2004 5:33 am

RE: Slat Retraction On 747's

Tue Sep 30, 2014 2:44 pm

Just wondered, doesn't the airflow get terribly disrupted during deployment/retraction of a Krueger flap? Is there a momentary loss of (some) lift?
I scratch my head, therefore I am.
 
User avatar
propilot83
Topic Author
Posts: 625
Joined: Sat Jan 27, 2001 2:41 am

RE: Slat Retraction On 747's

Tue Sep 30, 2014 5:53 pm

Wilco737 thanks for an easy answer. Now I know that its the pilots that retract the slats themselves and not the computer, thanks everyone for sharing, nice info.
 
Dalmd88
Posts: 3079
Joined: Fri Jul 28, 2000 3:19 am

RE: Slat Retraction On 747's

Tue Sep 30, 2014 11:00 pm

My question is why is the 747 so different than other Boeings? 727, 737, 757, 767 all only have Krueger on the inboard, if at all and slats outboard of the engines?
 
User avatar
DocLightning
Posts: 21778
Joined: Wed Nov 16, 2005 8:51 am

RE: Slat Retraction On 747's

Tue Sep 30, 2014 11:33 pm

Quoting Buyantukhaa (Reply 5):
Just wondered, doesn't the airflow get terribly disrupted during deployment/retraction of a Krueger flap? Is there a momentary loss of (some) lift?

If the slats retracted into the upper surface of the wing, there would be a disruption because it would cause a pressure rise along the upper leading edge that would disrupt the acceleration of the airflow. However, on the underside of the wing, the air is already traveling into a region of increased pressure and is decelerating, so the effect is minimal. What it does cause is a transient increase in drag, but I think the momentum of the aircraft overcomes that.

Quoting propilot83 (Reply 6):
Wilco737 thanks for an easy answer. Now I know that its the pilots that retract the slats themselves and not the computer, thanks everyone for sharing, nice info.

While on some new models (The A350) variable-camber flaps are computer-controlled in cruise, I am not aware of any model in which actual flap extension/retraction is on the autopilot.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
 
User avatar
Starlionblue
Posts: 19807
Joined: Fri Feb 27, 2004 9:54 pm

RE: Slat Retraction On 747's

Wed Oct 01, 2014 5:56 am

Quoting Dalmd88 (Reply 7):
My question is why is the 747 so different than other Boeings? 727, 737, 757, 767 all only have Krueger on the inboard, if at all and slats outboard of the engines?

If hazy memory serves the design was chosen due to the narrow wing profile and lack of space at the leading edge. A slat solution would have required more space, while a variable camber flap folds into itself, so to speak.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
747classic
Posts: 3003
Joined: Sat Aug 15, 2009 9:13 am

RE: Slat Retraction On 747's

Wed Oct 01, 2014 8:03 am

Quoting Dalmd88 (Reply 7):
My question is why is the 747 so different than other Boeings? 727, 737, 757, 767 all only have Krueger on the inboard, if at all and slats outboard of the engines

During development of the 747 it was essential that the low speed performance was the same as the much smaller 707 and DC8 aircraft.
See FAA stall speeds of the 747-100/200/300 with different flap settings, note :
largest speed reduction is obtained with flaps 1 and 5 selection, extending the LE flaps.

747-100/200/300 stall speeds


Because the Variable camber krueger flaps were at that moment in time the best solution (lowest approach speed), this kind of Leading Edge device was choosen for the 747, despite the increased complexity* and costs.

See for a technical comparisson of High lift systems on Commercial Subsonic aircraft (1996) :
http://www.southampton.ac.uk/~jps7/A...h%20lift/high%20lift%20systems.pdf

* In daily operation the 747 LE system showed to be fairly reliable. (compared to the DC10 slat system). More problems were encountered with the triple slotted TE flap system on the 747.

[Edited 2014-10-01 01:50:56]
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
User avatar
Buyantukhaa
Posts: 2327
Joined: Thu May 13, 2004 5:33 am

RE: Slat Retraction On 747's

Wed Oct 01, 2014 10:01 am

Quoting DocLightning (Reply 8):
However, on the underside of the wing, the air is already traveling into a region of increased pressure and is decelerating, so the effect is minimal. What it does cause is a transient increase in drag, but I think the momentum of the aircraft overcomes that.

That makes sense, thanks for the explanation!
I scratch my head, therefore I am.
 
User avatar
DocLightning
Posts: 21778
Joined: Wed Nov 16, 2005 8:51 am

RE: Slat Retraction On 747's

Wed Oct 01, 2014 5:25 pm

Quoting 747classic (Reply 10):
Because the Variable camber krueger flaps were at that moment in time the best solution (lowest approach speed), this kind of Leading Edge device was choosen for the 747, despite the increased complexity* and costs.

Thanks for this post. Can you elaborate for me a bit more on the reasons why this would be the case? The two other widebodies being developed at the time (DC-10 and L-1011) had traditional leading edge slats. Also, didn't the 707 have Kruegers?
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
 
Viscount724
Posts: 19316
Joined: Thu Oct 12, 2006 7:32 pm

RE: Slat Retraction On 747's

Thu Oct 02, 2014 3:05 am

As a sidenote, the first fatal 747 crash, a LH 747-130 just after takeoff from NBO en route to JNB on November 20, 1974 with 59 fatalities of the 157 aboard, was caused by the crew taking off with the leading edge flaps retracted.
http://aviation-safety.net/database/record.php?id=19741120-0

PROBABLE CAUSE: "The accident was caused by the crew initiating a take-off with the leading edge flaps retracted because the pneumatic system which operates them had not been switched on. This resulted in the aircraft becoming airborne in a partially stalled condition which the pilots did not identify in the short time available to them for recovery. Major contributory factors were the lack of warning of a critical condition of leading edge flap position and the failure of the crew to complete satisfactorily their checklist items."
 
OldAeroGuy
Posts: 3913
Joined: Sun Dec 05, 2004 6:50 am

RE: Slat Retraction On 747's

Fri Oct 03, 2014 3:36 pm

Please note that for Boeing airrplanes, the 707, 727, 737 and 747 have inboard Kruegers. The 757, 767, 777 and 787 all have inboard slats.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
User avatar
DocLightning
Posts: 21778
Joined: Wed Nov 16, 2005 8:51 am

RE: Slat Retraction On 747's

Fri Oct 03, 2014 10:29 pm

Quoting OldAeroGuy (Reply 14):
The 757, 767, 777 and 787 all have inboard slats.

However, the 767, 777, and 787 (IIRC) all have a tiny krueger just inboard of the engine pylon. I always wondered why that was.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
 
OldAeroGuy
Posts: 3913
Joined: Sun Dec 05, 2004 6:50 am

RE: Slat Retraction On 747's

Sat Oct 04, 2014 3:14 pm

Quoting DocLightning (Reply 15):
However, the 767, 777, and 787 (IIRC) all have a tiny krueger just inboard of the engine pylon.

It fills in the rather large leading edge gap between the deployed slat and the nacelle pylon, benefiting CLmax and takeoff L/D.

The 757 has less leading edge sweep than the 767, 777, and 787 so careful shaping of the slat end and the pylon eliminated the potential gap and the need for a seal Krueger.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
User avatar
DocLightning
Posts: 21778
Joined: Wed Nov 16, 2005 8:51 am

RE: Slat Retraction On 747's

Sat Oct 04, 2014 8:22 pm

Quoting OldAeroGuy (Reply 16):
It fills in the rather large leading edge gap between the deployed slat and the nacelle pylon, benefiting CLmax and takeoff L/D.

The 757 has less leading edge sweep than the 767, 777, and 787 so careful shaping of the slat end and the pylon eliminated the potential gap and the need for a seal Krueger.

Ahh. It always struck me as a very odd and complicated little device, and I know that Boeing wouldn't have put it there without a very good reason.

Why doesn't Airbus use this?
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
 
OldAeroGuy
Posts: 3913
Joined: Sun Dec 05, 2004 6:50 am

RE: Slat Retraction On 747's

Sun Oct 05, 2014 4:49 am

Quoting DocLightning (Reply 17):
Why doesn't Airbus use this?

Well, they did something similar on the A310, bout on the inboard end of the inboard slat

https://www.airliners.net/photo/Turki...d=42044e4803a4f733960b19faa16c16d3

This photo also shows a difference between Airbus and Boeing design practice on twin aisle airplanes. Airbus mounts engines lower on the wing than Boeing. The result is less interference between the slats and the nacelle/strut.

On the A310, the slat was continuous over the strut, with a small cutout to allow the slat to seal on the strut when fully extended.

On the A330 and A340, the low engine position allows tailoring of the strut and slat to have a good slat-to-strut seal.

https://www.airliners.net/photo/China...d=3c1b6827aed59d4be79cd7a85f032f46

https://www.airliners.net/photo/Swiss...d=d36b9d6162490211df6038ee1f4b58e5
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
User avatar
Jetlagged
Posts: 2564
Joined: Sun Jan 23, 2005 3:00 pm

RE: Slat Retraction On 747's

Mon Oct 13, 2014 9:34 pm

Quoting Dalmd88 (Reply 7):
My question is why is the 747 so different than other Boeings? 727, 737, 757, 767 all only have Krueger on the inboard, if at all and slats outboard of the engines?

The 747 isn't that different. The 727 and 737 also had similar staged extension and retraction of the LE devices.

On the 727:

At Flap 2 LE slat sections 2,3 and 6,7 extended. At flap 5 LE slat 1,4 and 5,8 and LE flap 1,2,3 and 4,5,6 extended. The reverse sequence on retraction.

On the 737:

At Flap 1 all LE flaps extend and the LE slats extend to an intermediate position. At Flap 10 the slats extend fully.

As with the 747 Classic, there is an array of amber and green lights to show the various sections in transit and extended. On the 727 it's by the F/E station, on the 737 it's on the overhead.

Quoting Viscount724 (Reply 13):
PROBABLE CAUSE: "The accident was caused by the crew initiating a take-off with the leading edge flaps retracted because the pneumatic system which operates them had not been switched on. This resulted in the aircraft becoming airborne in a partially stalled condition which the pilots did not identify in the short time available to them for recovery. Major contributory factors were the lack of warning of a critical condition of leading edge flap position and the failure of the crew to complete satisfactorily their checklist items."

Boeing were required to include LE flap positions in the TO config warning system as a result of this accident. Why the F/E closed the pylon bleed valves after engine start has always puzzled me. I can only assume they were doing a no bleed takeoff (it was at Nairobi) and rather than switch the packs off he closed the bleeds.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
AA737-823
Posts: 5492
Joined: Wed Mar 01, 2000 11:10 am

RE: Slat Retraction On 747's

Tue Oct 14, 2014 3:33 am

Does anyone know if there are EXCEPTIONS to the L/E flap retraction sequence logic?
I ask, because on my very first 747-400 flight, back in 2008, I observed the OUTBOARD section to remain extended for a really surprising amount of time. We're talking in the neighborhood of FL200. Long after I could see that the mid and inboard sections were retracted.
This was a KLM 747-400M, PH-BFC (the volcano victim).
It really surprised me, as I was a 747 line tech at the time, and had never observed the leading edges behave in that sequence.
 
RetiredWeasel
Posts: 773
Joined: Sat Jul 05, 2014 8:16 pm

RE: Slat Retraction On 747's

Tue Oct 14, 2014 3:44 am

Quoting Jetlagged (Reply 19):
Why the F/E closed the pylon bleed valves after engine start has always puzzled me. I can only assume they were doing a no bleed takeoff (it was at Nairobi) and rather than switch the packs off he closed the bleeds

Not sure about other airlines, but we always did no-pack takeoffs in our 40 or so classics back in the days. However after engine start, we would normally turn the packs on for PAX comfort until taking the runway just prior to T/O where we turned them back off. The SO flow pattern turned the packs on before the CPT called for flaps at start of taxi.

Possibly, instead of turning the packs on just after engine start, the FE may have mistakenly turned the bleeds off (even thought the position is 90 degrees out. As you well know, the knobs are right below the pack knobs and are identical. Then when taking the runway, either they didn't turn packs off (their procedure?) or he just said "Oops I forgot to turn the packs on for taxi" and still didn't notice the bleeds were turned off.

Just a thought.

[Edited 2014-10-13 20:46:58]
 
RetiredWeasel
Posts: 773
Joined: Sat Jul 05, 2014 8:16 pm

RE: Slat Retraction On 747's

Tue Oct 14, 2014 4:09 am

Quoting AA737-823 (Reply 20):
Does anyone know if there are EXCEPTIONS to the L/E flap retraction sequence logic?
I ask, because on my very first 747-400 flight, back in 2008, I observed the OUTBOARD section to remain extended for a really surprising amount of time. We're talking in the neighborhood of FL200

Leaving any flaps or L/E devices down or out until FL200 would be highly unusual normally.

Highly speculative, but it's possible the pneumatic motor on that section of LEDs broke and the crew went into the checklist to start the backup procedure. Meanwhile they kept flying their cleared route, were able to retract the offending LEDs electrically and decided just to continue to their destination....with a little aticipation that they may have to extend them manually again with backup electrical motors.
 
User avatar
747classic
Posts: 3003
Joined: Sat Aug 15, 2009 9:13 am

RE: Slat Retraction On 747's

Tue Oct 14, 2014 11:53 am

Quoting Jetlagged (Reply 19):
Why the F/E closed the pylon bleed valves after engine start has always puzzled me. I can only assume they were doing a no bleed takeoff (it was at Nairobi) and rather than switch the packs off he closed the bleeds.

The original design of the 747 engine bleed air valve was that the engine could be started with the bleedair vlv switch (F/E panel) closed. (return flow function).
After engine start you had to open all 4 valves by their switches (after starting checklist) to allow bleed delivery.

After the NBO accident (F/E failed to switch open the vlv's - no bleed manifold pressure - no L/E flap extension)) the bleed air switching logic was changed : engine start was only possible with the bleed air switch (F/E panel) in the open position, no bleed air switching necessary in the normal "packs on" T/O configuration.

Also the LE flap positions were added to the T/O warning system logic.

[Edited 2014-10-14 04:57:19]
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
User avatar
Jetlagged
Posts: 2564
Joined: Sun Jan 23, 2005 3:00 pm

RE: Slat Retraction On 747's

Tue Oct 14, 2014 2:13 pm

Quoting 747classic (Reply 23):
The original design of the 747 engine bleed air valve was that the engine could be started with the bleedair vlv switch (F/E panel) closed. (return flow function).
After engine start you had to open all 4 valves by their switches (after starting checklist) to allow bleed delivery.

That explains it. I didn't know the logic worked like that originally. Many thanks.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
BoeingGuy
Posts: 6313
Joined: Fri Dec 10, 2010 6:01 pm

RE: Slat Retraction On 747's

Tue Oct 14, 2014 7:38 pm

Quoting wilco737 (Reply 2):
Quoting propilot83 (Thread starter):
do the pilots manually retract it? or does the autopilot/computer automatically retract the slats a few moments after take off?

We pilots do it on our own. When we have reached a certain spead (safe speed for the flaps) we put the flap lever to the next position and the flaps retract.

No Boeing airplanes ever have a system automatically change flap or slat position (except for the Autoslat enable function during a stall), raise or lower landing gear, or select reverse thrust. It's all done manually. That is by design.

Quoting Jetlagged (Reply 19):
On the 737:

At Flap 1 all LE flaps extend and the LE slats extend to an intermediate position. At Flap 10 the slats extend fully.

On the 757, 767, 777 and 787 the slats extend into the sealed position at Flaps 1-20. The go into the gapped position at Flaps 25-30.
 
User avatar
Jetlagged
Posts: 2564
Joined: Sun Jan 23, 2005 3:00 pm

RE: Slat Retraction On 747's

Wed Oct 15, 2014 2:50 pm

Quoting BoeingGuy (Reply 25):
No Boeing airplanes ever have a system automatically change flap or slat position (except for the Autoslat enable function during a stall), raise or lower landing gear, or select reverse thrust. It's all done manually. That is by design.

Not quite true. Several Boeing types have flap load relief, which reduces TE flap position if speed is excessive.

Airbus philosophy is very similar.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
BoeingGuy
Posts: 6313
Joined: Fri Dec 10, 2010 6:01 pm

RE: Slat Retraction On 747's

Wed Oct 15, 2014 8:07 pm

Quoting Jetlagged (Reply 26):
Quoting BoeingGuy (Reply 25):
No Boeing airplanes ever have a system automatically change flap or slat position (except for the Autoslat enable function during a stall), raise or lower landing gear, or select reverse thrust. It's all done manually. That is by design.

Not quite true. Several Boeing types have flap load relief, which reduces TE flap position if speed is excessive.

You got me on that one. I'm fully aware of the function, but I forgot about it when I was writing the post. 767 only does load relief for Flaps 25-30. 777 and 787 do it for all flap settings (although I forget about Flaps 1).

Who is online

Users browsing this forum: ArdWar and 39 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos