Steve332
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747 Wing Slats?

Tue Apr 03, 2007 2:07 am

http://www.youtube.com/watch?v=ZJa3FTExWuA

In the above video of a 744 landing in Sydney as soon as it hits the ground the 1st two slats retract and the 3rd one at the end of the wing stays out. Is this controlled by the pilot or is it automatic? it seems timed with the extension of the spoilers but I could be wrong.
Also the video cuts after the aircraft exit's the runway and the 1st 2 slats are back out the the last one is now retracted

Anyone know what this does??

Steve.
 
LH526
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RE: 747 Wing Slats?

Tue Apr 03, 2007 2:16 am

This is usual automated procedure to reduce stress on the slats during thrust reverse and give clear airflow to the spoilers. This is not linked with spoiler extension though.
(Slats are no longer needed after touchdown anyway)

Mario
LH526
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Steve332
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RE: 747 Wing Slats?

Tue Apr 03, 2007 2:23 am

Quoting LH526 (Reply 2):
LH526

Cheers, Iv never noticed it before (Iv never been looking for it tho!)

Do other aircraft have this feature yes?
 
PhilSquares
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RE: 747 Wing Slats?

Tue Apr 03, 2007 4:09 am

Quoting LH526 (Reply 1):
This is usual automated procedure to reduce stress on the slats during thrust reverse and give clear airflow to the spoilers. This is not linked with spoiler extension though.
(Slats are no longer needed after touchdown anyway)

Partially true. The LE Edge devices retract to prevent damage from debris thrown up during the reverse thrust operation.
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LH526
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RE: 747 Wing Slats?

Tue Apr 03, 2007 5:42 am

Quoting PhilSquares (Reply 3):
The LE Edge devices retract to prevent damage from debris thrown up during the reverse thrust operation

That's what I meant ..  Smile Thanks anyway for making things more clear.
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jetdoctor
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RE: 747 Wing Slats?

Tue Apr 03, 2007 6:01 am

Hey all

Even more cool, is when use of the reverse thrust is completed, they extend again. (only to see all of them being retracted for taxi to the gate or wherever it is parking) This is in the case of a late "go-around" procedure, so they are back out again for lift.

Regards,

Jetdoctor
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RichPhitzwell
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RE: 747 Wing Slats?

Tue Apr 03, 2007 10:16 am

Here is a shot of the back of the wing (different flight of course) into JFK. Kinda cool seeing everything that goes on. Sorry for the low quality, my cam is not the worlds best.

Landing

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N231YE
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RE: 747 Wing Slats?

Tue Apr 03, 2007 11:03 am

This comes up quite frequently in the Tech/Ops forum:
Question On 747-400 Slat Retraction (by UPSMD11 Jun 28 2006 in Tech Ops)
747 Automatic Slat Retraction (by Rducky Jun 14 2004 in Tech Ops)
Slat Retraction During Reverse Thrust? 747-400 (by Ajaaron Nov 5 2006 in Tech Ops)
Leading Edge Slat's On 747-400? (by Rducky Apr 14 2004 in Tech Ops)

Quoting PhilSquares (Reply 3):
The LE Edge devices retract to prevent damage from debris thrown up during the reverse thrust operation.

...is correct.
 
Viscount724
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RE: 747 Wing Slats?

Tue Apr 03, 2007 11:14 am

Quoting RichPhitzwell (Reply 6):
Here is a shot of the back of the wing (different flight of course) into JFK. Kinda cool seeing everything that goes on.

Not as much as goes on on a B727 wing on approach/landing! Sitting over the wing on a 727 and watching it gradually disassemble itself on approach was one of the highlights of flying on a 727!
 
RichPhitzwell
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RE: 747 Wing Slats?

Tue Apr 03, 2007 11:28 am

Quoting Viscount724 (Reply 8):


Not as much as goes on on a B727 wing on approach/landing! Sitting over the wing on a 727 and watching it gradually disassemble itself on approach was one of the highlights of flying on a 727!

It would be pretty cool if we had vids like the two above clearly showing the leading edge as well as trailing for 727 or others. 727's still fly, maybe someone has a vid (not that I would ever encourage using electronic devices).
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Viscount724
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RE: 747 Wing Slats?

Tue Apr 03, 2007 11:58 am

Quoting RichPhitzwell (Reply 9):
It would be pretty cool if we had vids like the two above clearly showing the leading edge as well as trailing for 727 or others.

There probably is a 727 video of the wing activities somewhere. There are quite a few A.net photos, including the following:


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Photo © Chris Waser
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Photo © Peter Kesternich



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Photo © Bruce Leibowitz
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Photo © Bruce Leibowitz



And a few things were happening at the front of the wing too!


View Large View Medium
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Photo © Andy Jung
View Large View Medium
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Photo © Andy Jung

 
RichPhitzwell
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RE: 747 Wing Slats?

Tue Apr 03, 2007 2:01 pm

Great photos. Period.

Unfortunately still photos dont really show the complexity and as an amateur, I'm having a difficult time seeing the complexity vs the 744. Perhaps someone could explain how and why.
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LASoctoberB6
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RE: 747 Wing Slats?

Tue Apr 03, 2007 2:52 pm

i just dont understand why the slats retract upon reverse thrust activation and when deactivated, the 2 slats come back out and then all 3 retract....makes no sense but okay......
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PhilSquares
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RE: 747 Wing Slats?

Tue Apr 03, 2007 3:32 pm

Quoting LASOctoberB6 (Reply 12):
i just dont understand why the slats retract upon reverse thrust activation and when deactivated, the 2 slats come back out and then all 3 retract....makes no sense but okay......

It's very simple, the slats retract during reverst thrust to prevent damage to the inboard leading edge devices. Once reverse thrust is cancelled, then the slats return to the selected position. After the aircraft is clear of the runway, the crew does the "after landing check" and the flaps are retracted. Retracting the flaps will cause the LE devices to retract and stow.

Simple!!!
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TheJoe
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RE: 747 Wing Slats?

Tue Apr 03, 2007 4:51 pm

Sorry to be picky, but aren't they leading edge flaps? There is a very distinct difference! Classic example, 737 outboard of the engine = leading edge slats. Inboard = Kruger flaps!

Slats allow air to pass up between them and the leading edge of the wing. Kruger flaps generally have an aerodynamic seal that stops air flowing between them and the leading edge of the wing. Slats are generally part of the leading edge of the aircraft at all times and extend when required, kruger flaps fold out from inside the leading edge and are tucked away when not required!

Regards,

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AmericanB763ER
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RE: 747 Wing Slats?

Tue Apr 03, 2007 4:58 pm

Quoting PhilSquares (Reply 13):
the slats retract during reverst thrust to prevent damage to the inboard leading edge devices

Not to be a nitpicker here but aren't the 744's leading edge devices called something like 'Kruger flaps' rather than slats? IIRC all 747's have them. (what about the 748 ...?). Technically 747's don't have slats at all correct me if I'm wrong.

Quoting PhilSquares (Reply 13):
It's very simple, the slats retract during reverst thrust to prevent damage to the inboard leading edge devices. Once reverse thrust is cancelled, then the slats return to the selected position. After the aircraft is clear of the runway, the crew does the "after landing check" and the flaps are retracted. Retracting the flaps will cause the LE devices to retract and stow.

Is this a unique feature of the 747 or is it found on other aircraft types as well?

Marco
 
PhilSquares
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RE: 747 Wing Slats?

Tue Apr 03, 2007 5:03 pm

Quoting TheJoe (Reply 14):
Sorry to be picky, but aren't they leading edge flaps? There is a very distinct difference! Classic example, 737 outboard of the engine = leading edge slats. Inboard = Kruger flaps!



Quoting AmericanB763ER (Reply 15):
Not to be a nitpicker here but aren't the 744's leading edge devices called something like 'Kruger flaps' rather than slats? IIRC all 747's have them. (what about the 748 ...?). Technically 747's don't have slats at all correct me if I'm wrong.

They are technically leading edge flaps. Not Kruger flaps, not slats. The 748 will have leading edge flaps and double slotted trailing edge flaps rather than the triple slotted flaps on the existing 747/744.

Quoting AmericanB763ER (Reply 15):
Is this a unique feature of the 747 or is it found on other aircraft types as well?

It's not on any other Boeings I know of, it's not on any Airbus aircraft, nor is it on the DC-10/MD-11.
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BoeingOnFinal
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RE: 747 Wing Slats?

Tue Apr 03, 2007 5:57 pm

What is the definition of a kruger flap? Because in many explainations the term leading edge flap and kruger flap is used for the same thing.

Would also appreciate a good explaination of the difference between slats and leading edge flaps.
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PhilSquares
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RE: 747 Wing Slats?

Tue Apr 03, 2007 6:11 pm

Quoting BoeingOnFinal (Reply 17):
What is the definition of a kruger flap? Because in many explainations the term leading edge flap and kruger flap is used for the same thing.

Would also appreciate a good explaination of the difference between slats and leading edge flaps

Here's a good place to start. http://www.desktopaero.com/appliedaero/airfoils2/HighLift.html
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RE: 747 Wing Slats?

Tue Apr 03, 2007 8:23 pm

Quoting BoeingOnFinal (Reply 17):

Would also appreciate a good explaination of the difference between slats and leading edge flaps.



Quoting BoeingOnFinal (Reply 17):
What is the definition of a kruger flap? Because in many explainations the term leading edge flap and kruger flap is used for the same thing.

As I understand it, and I may be wrong:

Slats flit the (normally leading) edge like a glove and extend out. That is, in the retracted state they encase the edge. Slats allow an increase in angle of attack without stalling. They do not lower stall speed per se.

Leading edge flaps extend like the flaps you normally see on the trailing edge, increasing chord and camber. These allow both in increase in AoA and lower stall speed.

Krueger flaps are hinged along the leading edge and fold out forward from their storage position under the wing. Variable camber variants like those on the 747 have an extra hinge in the flap itself, allowing the camber to vary along the flap. These allow both in increase in AoA and lower stall speed.
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RE: 747 Wing Slats?

Tue Apr 03, 2007 8:44 pm

Quoting PhilSquares (Reply 16):

They are technically leading edge flaps. Not Kruger flaps, not slats. The 748 will have leading edge flaps and double slotted trailing edge flaps rather than the triple slotted flaps on the existing 747/744.

Phil,

I know what you have said is what the 744 FCOM says, however I think inboard of the engines they are Krueger (kruger) flaps, the outboard sections have variable camber flaps, I have seen these referred to in NASA papers as bullnose Krueger flaps and variable camber Krueger flaps respectively.
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Steve332
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RE: 747 Wing Slats?

Tue Apr 03, 2007 8:48 pm

Quoting LASOctoberB6 (Reply 12):
the 2 slats come back out and then all 3 retract....makes no sense but okay......

At the end of the video I noticed that the 2 that had originally retracted came back out while the 3rd hadn't retracted on landing but did when the other 2 came back out.

Any reason for this??
 
AmericanB763ER
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RE: 747 Wing Slats?

Tue Apr 03, 2007 10:13 pm

Quoting Steve332 (Reply 21):
At the end of the video I noticed that the 2 that had originally retracted came back out while the 3rd hadn't retracted on landing but did when the other 2 came back out

I've noticed exactly the same thing. The odd part of it is that the 3rd outboard-flaps actuallly retract some time AFTER the engines have stopped T/R' ing and the 2 inboard devices hade come back out.

Strange indeed
 
PhilSquares
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RE: 747 Wing Slats?

Tue Apr 03, 2007 10:53 pm

Quoting Zeke (Reply 20):
Phil,

I know what you have said is what the 744 FCOM says, however I think inboard of the engines they are Krueger (kruger) flaps, the outboard sections have variable camber flaps, I have seen these referred to in NASA papers as bullnose Krueger flaps and variable camber Krueger flaps respectively.

No, they aren't Kurger Flaps. The 727 had Krugers on the inboard segment and the 744/747 doesn't. They might look like Kurgers but they are all considered "leading edge flaps"

Quoting AmericanB763ER (Reply 22):
I've noticed exactly the same thing. The odd part of it is that the 3rd outboard-flaps actuallly retract some time AFTER the engines have stopped T/R' ing and the 2 inboard devices hade come back out.

Strange indeed

You might want to get your eyesight checked. They are all retracted when the "after landing check" is performed. If they were deployed when the engines were shut down, they would stay extended. They are pneumatically driven and mechanically locked in place. Please see my post 13.
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zeke
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RE: 747 Wing Slats?

Tue Apr 03, 2007 11:25 pm

Quoting PhilSquares (Reply 23):
No, they aren't Kurger Flaps. The 727 had Krugers on the inboard segment and the 744/747 doesn't. They might look like Kurgers but they are all considered "leading edge flaps"

I guess we are going to have to agree to disagree, I might add the FAA, NTSB, UK CAA amongst others also call them Krueger flaps.
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David L
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RE: 747 Wing Slats?

Tue Apr 03, 2007 11:33 pm

Quoting PhilSquares (Reply 23):
They are all retracted when the "after landing check" is performed.

I can see what AmericanB763ER is saying. In the video above, the inboard LE flaps redeploy when reverse thrust is cancelled, as you described, but shortly after that, the outboard LE flaps retract, leaving the inboard flaps extended. I think that's what he means.
 
boeingfixer
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RE: 747 Wing Slats?

Tue Apr 03, 2007 11:51 pm

Quoting Jetdoctor (Reply 5):
Hey all

Even more cool, is when use of the reverse thrust is completed, they extend again. (only to see all of them being retracted for taxi to the gate or wherever it is parking) This is in the case of a late "go-around" procedure, so they are back out again for lift.

Regards,

Jetdoctor

The LE devices extend back to their pre-selected position for sequencing only, not for a late "go-around". Once reverse thrust is selected, you are committed to landing and no "go-around" is allowed after this point.

Cheers,

John
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AmericanB763ER
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RE: 747 Wing Slats?

Tue Apr 03, 2007 11:51 pm

Quoting PhilSquares (Reply 23):

It says "some time AFTER the engines have stopped T/R' ing" - NOT "some time AFTER the engines have stopped"  Yeah sure maybe I used the wrong letters, it was supposed to mean 'Thrust reversing'...

Quoting David L (Reply 25):

That's what I meant indeed
 
boeingfixer
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RE: 747 Wing Slats?

Wed Apr 04, 2007 12:00 am

Quoting Steve332 (Reply 21):
At the end of the video I noticed that the 2 that had originally retracted came back out while the 3rd hadn't retracted on landing but did when the other 2 came back out.

Any reason for this??

What you're seeing is the normal flap retract sequencing. Upon retracting the flaps from position 5 to 1, the outboard LE group will retract. From flaps 1 to up, both the mid and inboard LE groups will retract.

Cheers,

John
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boeingfixer
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RE: 747 Wing Slats?

Wed Apr 04, 2007 12:06 am

Quoting PhilSquares (Reply 23):
If they were deployed when the engines were shut down, they would stay extended. They are pneumatically driven and mechanically locked in place. Please see my post 13.

As long as electrical power is available, won't the LE devices retract in Secondary mode if pneumatics are lost?  Smile

Cheers,

John
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PhilSquares
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RE: 747 Wing Slats?

Wed Apr 04, 2007 12:12 am

Quoting BoeingFixer (Reply 29):
As long as electrical power is available, won't the LE devices retract in Secondary mode if pneumatics are lost?

Cheers,

John

Not automatically. You'd have to use ALTN FLAPS system, which is not normally used for "normal" flap extension or retraction. Normal procedures would be to clear the runway, then clean the aircraft up. So, you'd be under aircraft power at that time and have the pneumatics available. At the gate, you'd most likely have the APU available if you happened to forget to accomplish the "After Landing Check".

 Wink
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Steve332
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RE: 747 Wing Slats?

Wed Apr 04, 2007 12:17 am

Quoting PhilSquares (Reply 23):
You might want to get your eyesight checked.

No he's seeing the same thing I saw! (I actually had an eye test last week and passed with flying colours 'Excuse the pun' Smile) They extend again while the ones out by the winglet by no4 retract.

Quoting BoeingFixer (Reply 28):
What you're seeing is the normal flap retract sequencing. Upon retracting the flaps from position 5 to 1, the outboard LE group will retract. From flaps 1 to up, both the mid and inboard LE groups will retract.

Thanks I was wondering that from when I 1st say the video.
 
PhilSquares
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RE: 747 Wing Slats?

Wed Apr 04, 2007 12:30 am

Quoting Steve332 (Reply 31):
No he's seeing the same thing I saw! (I actually had an eye test last week and passed with flying colours 'Excuse the pun' ) They extend again while the ones out by the winglet by no4 retract.

Ok, when reverse thrust is selected, the inboard 2 leading edge segments on both wings retract. When reverse thrust is cancelled, they retract. Once the aircraft is clear of the runway, the pilots do the "after landing check" . The flaps are selected to up. When the flaps get past 5 on their way to 1 the outboard segment retracts and when the flaps go from 1 to UP the remaining segments retract.

Assuming normal ops, it doesn't work any other way than that. What else can I say!
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boeingfixer
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RE: 747 Wing Slats?

Wed Apr 04, 2007 2:02 am

Quoting BoeingFixer (Reply 29):
Quoting PhilSquares (Reply 23):
If they were deployed when the engines were shut down, they would stay extended. They are pneumatically driven and mechanically locked in place. Please see my post 13.

As long as electrical power is available, won't the LE devices retract in Secondary mode if pneumatics are lost? Smile

Cheers,

John



Quoting PhilSquares (Reply 30):
Not automatically. You'd have to use ALTN FLAPS system, which is not normally used for "normal" flap extension or retraction. Normal procedures would be to clear the runway, then clean the aircraft up. So, you'd be under aircraft power at that time and have the pneumatics available. At the gate, you'd most likely have the APU available if you happened to forget to accomplish the "After Landing Check".

My reply was to your comment that with the engines shut down, the LE devices would stay extended. I understand the normal procedure is pneumatics for the LE and hydraulics for the TE in Primary mode.

If the engines are shut down, and all bleed air is lost (APU AC power or ground power available and ON), the LE devices are moved by electric motors, 1 each for the IB and OB groups and 2 for the Mid groups. The FCU's sense when a LE group isn't moving to its selected position and 'automatically' switches to Secondary mode for that group to power them electrically. For the flaps to Not move at all, power would have to be removed from the aircraft or the ALTN FLAPS switch armed.  Wink

Cheers,

John
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Steve332
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RE: 747 Wing Slats?

Wed Apr 04, 2007 4:50 am

Quoting PhilSquares (Reply 32):
PhilSquares

Exactly what I asked in the first place, Cheers for the answer.
 
David L
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RE: 747 Wing Slats?

Wed Apr 04, 2007 5:13 am

Quoting BoeingFixer (Reply 28):
Upon retracting the flaps from position 5 to 1, the outboard LE group will retract. From flaps 1 to up, both the mid and inboard LE groups will retract.



Quoting PhilSquares (Reply 32):
When the flaps get past 5 on their way to 1 the outboard segment retracts and when the flaps go from 1 to UP the remaining segments retract.

D'oh! Of course. Rusty brain - I haven't used it for a couple of weeks (I shouldn't have left it outside, though).
 
PhilSquares
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RE: 747 Wing Slats?

Wed Apr 04, 2007 7:04 pm

Quoting BoeingFixer (Reply 33):
My reply was to your comment that with the engines shut down, the LE devices would stay extended. I understand the normal procedure is pneumatics for the LE and hydraulics for the TE in Primary mode.

If the engines are shut down, and all bleed air is lost (APU AC power or ground power available and ON), the LE devices are moved by electric motors, 1 each for the IB and OB groups and 2 for the Mid groups. The FCU's sense when a LE group isn't moving to its selected position and automatically switches to Secondary mode for that group to power them electrically. For the flaps to Not move at all, power would have to be removed from the aircraft or the ALTN FLAPS switch armed.

We're now getting into the realm of trying to take off on a move able track with the aircraft full of birds flapping their wings.

If the aircraft loses all hydraulics, it's not going to the gate. The flaps both trailing and leading edge will be left out to aid trouble shooting. If you have air available sure it can be used to retract the flaps, but the normal and easier way to do it is through the normal hydraulic system. Sure we really don't heed tugs to position aircraft, we could just get a load of people and some rope to pull the aircraft to the gate. That would work, but it's not normal procedure.

People have been trying to give "normal" "responsible" answers, but if the other writers want to continue the nonsense....

Count me out!
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boeingfixer
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RE: 747 Wing Slats?

Thu Apr 05, 2007 12:49 am

Quoting PhilSquares (Reply 36):
We're now getting into the realm of trying to take off on a move able track with the aircraft full of birds flapping their wings.

No need to resort to insults! Sorry if my reply to your comment wasn't what you would like.

Quoting PhilSquares (Reply 36):
If the aircraft loses all hydraulics, it's not going to the gate. The flaps both trailing and leading edge will be left out to aid trouble shooting. If you have air available sure it can be used to retract the flaps, but the normal and easier way to do it is through the normal hydraulic system. Sure we really don't heed tugs to position aircraft, we could just get a load of people and some rope to pull the aircraft to the gate. That would work, but it's not normal procedure.

Losing hydraulics on the way to the gate wasn't part of my reply either. You clearly stated that with the engines shut down that the flaps won't move. I disputed that with the way the system is designed to work..... that's all. You seem to feel I know nothing about aircraft and therefore respond in a derogatory manner...... Once again, sorry if my reply isn't to your liking.

Quoting PhilSquares (Reply 36):
People have been trying to give "normal" "responsible" answers, but if the other writers want to continue the nonsense....

If the above remark is directed at me, please point out where I have not given a "normal" "responsible" answer and what nonsense have I posted??

Quoting PhilSquares (Reply 36):
Count me out!

 Confused
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jetmech
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RE: 747 Wing Slats?

Thu Apr 05, 2007 11:39 am

Quoting PhilSquares (Reply 23):
No, they aren't Kurger Flaps. The 727 had Krugers on the inboard segment and the 744/747 doesn't. They might look like Kurgers but they are all considered "leading edge flaps"

G'day Phil  Smile,

I'm gonna respectfully add a point of discussion here;


View Large View Medium
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Photo © D.Lausberg
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Photo © Stéphane Burckard



From the looks of these photos, the inboard leading edge lift enhancement devices appear to be the same for the 727 and 747. When I was working on 747's, they were always referred to as leading edge Kruger flaps, with the leading edge devices between the engines and outboard of # 1 & 4 engines referred to as variable camber leading edge flaps (VCLEF). A reference I checked prior to posting this seems to think that the 747 VCLEF's are a form of Kruger flap  Confused. I am pretty sure that the inboard leading edge lift enhancement devices were referred to as Kruger flaps in the MM, and I will check to be sure.

Quoting PhilSquares (Reply 36):
If the aircraft loses all hydraulics, it's not going to the gate. The flaps both trailing and leading edge will be left out to aid trouble shooting. If you have air available sure it can be used to retract the flaps, but the normal and easier way to do it is through the normal hydraulic system

I'm reading this paragraph to mean that you can retract the flaps without hydraulics if you have pneumatics available. Pneumatics will allow you to drive the # 1 and 4 hydraulic system ADP turbine units, but if prior to this, the respective hydraulic systems have been "lost" (leakage etc.) for some reason, this will not allow you to retract the flaps. I'm not sure how pneumatics alone can move the 747 trailing edge flaps  Confused .

Regards, JetMech
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Jetlagged
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RE: 747 Wing Slats?

Thu Apr 05, 2007 12:31 pm

Quoting PhilSquares (Reply 23):
No, they aren't Kurger Flaps. The 727 had Krugers on the inboard segment and the 744/747 doesn't. They might look like Kurgers but they are all considered "leading edge flaps"

Technically the variable camber flaps on the outboard leading edges are a type of Krueger flap. The 747 inboard LE flaps are most definitely Krueger flaps. VCF and Kruegers are both types of leading edge flap. Boeing Ops Manuals keep this simple enough for pilots by referring generically to leading edge flaps.

Quoting JetMech (Reply 38):
I'm not sure how pneumatics alone can move the 747 trailing edge flaps

I think the original comment referred to moving the leading edge flaps, which are normally pneumatically powered. Pneumatic power can drive the trailing edges (via the ADPs) if the engines have been shutdown, which is how this whole circular argument began.
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jetmech
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RE: 747 Wing Slats?

Thu Apr 05, 2007 2:54 pm

Quoting Jetlagged (Reply 39):
Pneumatic power can drive the trailing edges (via the ADPs) if the engines have been shutdown, which is how this whole circular argument began.

Yep, I understand that, but if there is no fluid in systems 1 or 4, the ADP's could spin all day with no effect. What I was getting at is there is no way for pneumatics to directly move the trailing edge flaps.

Regards, JetMech
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Jetlagged
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RE: 747 Wing Slats?

Thu Apr 05, 2007 9:43 pm

Quoting JetMech (Reply 40):
What I was getting at is there is no way for pneumatics to directly move the trailing edge flaps.

Agreed, but I don't think anyone actually meant that that could happen. Obviously with no hydraulic fluid in the system none of the pumps will work, which leaves only the alternate electric motors. The ADPs are there as a backup in case of EDP failure and to boost flow for high demand (like when flaps and gear are moving).

Quoting Starlionblue (Reply 19):
As I understand it, and I may be wrong:

Maybe you've not been getting enough sleep lately. Don't worry, it will get worse.  Wink

Quoting Starlionblue (Reply 19):
Slats flit the (normally leading) edge like a glove and extend out. That is, in the retracted state they encase the edge. Slats allow an increase in angle of attack without stalling. They do not lower stall speed per se.

Slats (and LE flaps for that matter) increase the AOA you can reach before stall, lift is increased, ergo the stall speed is reduced.

Quoting Starlionblue (Reply 19):
Leading edge flaps extend like the flaps you normally see on the trailing edge, increasing chord and camber. These allow both in increase in AoA and lower stall speed.

Not all LE flaps increase chord (e.g. hinged droops as installed on the DH Trident and A380). The lower stall speed results from the higher AOA which can be achieved (more AOA = more lift).

Quoting Starlionblue (Reply 19):
Variable camber variants like those on the 747 have an extra hinge in the flap itself, allowing the camber to vary along the flap. These allow both in increase in AoA and lower stall speed.

The variable camber Krueger flaps on the 747 do not have an extra hinge, the section is flexible and bends with the four bar linkage underneath. If you watch the video you can see this happening.

All Krueger flaps (VC or not) have a hinged section at the leading edge (the "bull nose"). The video clearly shows all these hinged sections moving. A Krueger flap, when extended, is like the upper surface of a large drooped leading edge flap. The lower surface is not necessary due to the separation bubble created by the bull nose (the flow separates at the bull nose and re-attaches on the undersurface of the wing).

Basically, trailing edge flaps increase lift for a given AOA, but don't affect stall AOA. However for a given airspeed you need less AOA to maintain lift. Leading edge devices (flaps and slats) increase the AOA at which stall occurs. Both TE and LE devices have the effect of reducing stall speed. Slats tend to work better because of the slot effect, but Krueger Flaps (and VC Krueger Flaps) have the advantage of increasing wing area. Droops have neither advantage so are not seen so much unless less effectiveness is what is wanted (as on the inboard section of the A380).
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Tristarsteve
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RE: 747 Wing Slats?

Thu Apr 05, 2007 10:55 pm

Quoting Jetlagged (Reply 41):
(e.g. hinged droops as installed on the DH Trident

Glad to see there is someone else that remembers the droop leading edge on the Trident 1C.
I spent many happy nightshifts trying to rig them!
Later Tridents had slats.
The droop leading edge was similar to a slat, but there was no slot. It was sealed to the wing, and was very effective.
Read the accident report on RPI at Staines. The droops were retracted, and the aircraft crashed. In those days the slats and flaps had separate handles in the cockpit, so you could retract the slats, and leave the flaps out. Soon after that baulks were fitted to prevent this, and all later aircraft had a single lever.

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