ajaaron
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Slat Retraction During Reverse Thrust? 747-400

Sun Nov 05, 2006 8:29 am

747-400...Why do the inboard and centre slats retract on selection of reverse thrust during landing roll?

Thanks.
 
BAE146QT
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RE: Slat Retraction During Reverse Thrust? 747-400

Sun Nov 05, 2006 8:41 am

To reduce lift and keep the wheels firmly planted?

::EDIT::

Found this for you:

Quoting VC-10:
To prevent debris being thrown up into the LE and causing damage plus reducing wear on the LE mechanism through T. Rev buffet


[Edited 2006-11-05 00:44:34]
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411A
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RE: Slat Retraction During Reverse Thrust? 747-400

Sun Nov 05, 2006 8:59 am

It was the same on the B707, except that ALL the leading edge devices (no 'slats' on this airplane) retracted during reverse selection.

This was done so that IF you landed on a slush covered runway, the slush would not then be thrown up under the leading edge devices, where it could then freeze on the cold structure, and thereby cause damage when the flaps/LED's were retracted.

In addition, once reverse was canceled, the LED's extended once again.
Operated pneumatically.

A VERY reliable design.
 
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LTU932
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RE: Slat Retraction During Reverse Thrust? 747-400

Sun Nov 05, 2006 9:16 am

Will this slat retraction on the 747 continue to be used on the 747-8 or will the -8 use newer slats à la 767 or 777 along with the one-slotted/double-slotted flaps?
 
113312
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RE: Slat Retraction During Reverse Thrust? 747-400

Sun Nov 05, 2006 3:24 pm

Actually, on the 747 they are LE Flaps. Variable camber Kreuger Flaps to be specific. This automatic retraction during reverse thrust reduces the chance of damage from debris thrown up by the reverse thrust.
 
YWG
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RE: Slat Retraction During Reverse Thrust? 747-400

Mon Nov 06, 2006 7:43 am

Quoting BAe146QT (Reply 1):
To reduce lift and keep the wheels firmly planted?

Exacty. By reducing the lift being produced by the wings, you transfer most of the weight onto the wheels which increases friction.
Contact Winnipeg center now on 134.4, good day.
 
411A
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RE: Slat Retraction During Reverse Thrust? 747-400

Mon Nov 06, 2006 10:36 am

Sorry, YWG, wrong.
The spoilers do that.

Nice try, though.
 
BoeingOnFinal
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RE: Slat Retraction During Reverse Thrust? 747-400

Mon Nov 06, 2006 7:37 pm

Now is the slat controlled by the flap lever? Cause I've always hear callouts like: "Flap 20", but never seen any slat lever. So how do you for instance take off with only slats extended, or retract the slats during reverse thrust? (I assume that the last one is automatic?)
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PhilSquares
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RE: Slat Retraction During Reverse Thrust? 747-400

Mon Nov 06, 2006 7:54 pm

Quoting BoeingOnFinal (Reply 7):
Now is the slat controlled by the flap lever? Cause I've always hear callouts like: "Flap 20", but never seen any slat lever. So how do you for instance take off with only slats extended, or retract the slats during reverse thrust? (I assume that the last one is automatic?)

On the 744 the Flaps 1 position extends the inboard and midspan LE flaps and the TE flaps are extended slightly. At Flaps 5, all the LE flaps are extended. Flaps 10, 20 are the only takeoff flap settings authorized. Flaps 25, 30 are the only authorized landing flap settings.
Fly fast, live slow
 
411A
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 12:53 am

Phil has nicely described the 744.
In the L10, the slats are extended fully as the flap handle passes the 3 degree position, toward the first detent...4 degrees.
With the standard body airplane, the following flap settings are authorized for takeoff...
4
10
18
22
27

Landings are performed at 33 degrees, unless a malfunction dictates otherwise.
The only jet transport airplane that I am aware of that had a separate control (handle) for the leading edge devices was the Hawker Siddley HS.121 Trident...which was, as some might know, the FIRST jet transport capable of complete automatic approach/land (autoland) maneuvers.
Quite a unique design.
 
Pihero
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 2:48 am

Quoting 411A (Reply 9):
the Hawker Siddley HS.121 Trident...which was, as some might know, the FIRST jet transport capable of complete automatic approach/land (autoland) maneuvers.

Factually wrong, but this myth seems to stick : the SE 210 Caravelle was the first.
Contrail designer
 
vikkyvik
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 3:33 am

Quoting 411A (Reply 9):
Phil has nicely described the 744.
In the L10, the slats are extended fully as the flap handle passes the 3 degree position, toward the first detent...4 degrees.
With the standard body airplane, the following flap settings are authorized for takeoff...
4
10
18
22
27

On the L1011 (and other aircraft), can you select flap settings between detents (similar to the MD-11 "Dial-a-Flap")? Or do the flaps only start to transit when you reach the next detent?

Thanks...

Oh Pihero, your post confused me a bit. Which was the myth, and which was actually first? Thanks.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
Pihero
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 4:09 am

Vikkyvik,
My apologies, I wrote too fast :
The myth is that the Trident was the first jet transport capable of complete autoland.
History shows that the Caravelle obtained its cat III autoland certification on the 28th of December 1968,after having demonstrated more than 1500 successful approaches/landings and the very first in-service cat III autoland was performed by an Air Inter Caravelle III, flying Lyon-Orly on January 6th 1969.
It is true that a BEA Trident 1C performed an automatic landing in 1965, but it was more a stunt than a regulation procedure.
The Trident was certified by the CAA for cat III autolands in 1972, at which time Air Inter had already logged more than 6000 autolands on their Caravelles on revenue flights.
As an aside, the trident system was not an adept of kiss landings ! to the point that the wingspars had to be changed, every automatic landing amounting to a classified "hard" landing.
Regards
Contrail designer
 
David L
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 4:38 am

I must confess, I thought the Trident had performed the first autolands in commercial service till Pihero dispelled the myth a while back. I think it came about because some think the Tristar was the first. That was followed by claims that the Trident did it before the Tristar and it was left at that.

Quoting Pihero (Reply 12):
every automatic landing amounting to a classified "hard" landing.

And now something else becomes clear. I always thought the French said we had no flair while all the time you meant we had no flare.
 
Pihero
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 5:13 am

Quoting David L (Reply 13):
no flare

That, of course is cause for a go-around !.
Cheers, David !
Contrail designer
 
Tristarsteve
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 5:22 am

Quoting 411A (Reply 9):
The only jet transport airplane that I am aware of that had a separate control (handle) for the leading edge devices was the Hawker Siddley HS.121 Trident.

The Trident 1 had a very special leading edge design called 'droop'. It looked like slats but there was no slot. It was very effective as was demonstrated on G-ARPI at Staines when on climb out of LHR the crew retracted the Droop instead of the Flaps, and the aircraft crashed. Soon after that we fitted an interference device so you could only retract the droop when the flaps were fully retracted.
 
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Jetlagged
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 7:01 am

The VC10 also had separate flap and slat levers. Though they were usually locked together they could be easily separated if necessary. I read somewhere that the DC-9 flap and slat levers could be separated, but I don't know this for sure.

Quoting BoeingOnFinal (Reply 7):
Now is the slat controlled by the flap lever? Cause I've always hear callouts like: "Flap 20", but never seen any slat lever.

On the 747-200 the cross check call on approach from the F/E is something like "Flap 20, eight greens". The eight greens are the LE flap extended position agreement lights, on the F/E panel.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
BoeingOnFinal
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 7:27 am

Quoting Tristarsteve (Reply 15):
The Trident 1 had a very special leading edge design called 'droop'. It looked like slats but there was no slot. It was very effective as was demonstrated on G-ARPI at Staines when on climb out of LHR the crew retracted the Droop instead of the Flaps, and the aircraft crashed. Soon after that we fitted an interference device so you could only retract the droop when the flaps were fully retracted.

Is "droop" more effective than slats with slots according to lift produced? Slots are there to have lower stall speeds and bigger AoA, not to produce any lift, isn't that correct?

Thanks for clearing up the extending/retracting of slat/flap, much appreciated!
norwegianpilot.blogspot.com
 
411A
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 9:57 am

With the L1011, only the detented flap positions are used, no dial-a-flap system on the TriStar.

Many operators of the TriStar only used one flap setting for takeoff however.
SaudiArabian is a good example.
Only 18 degrees was used, mainly for reduced tire fatigue in the very hot ambient temperatures encountered.
Also, for a very long time, only NEW tires were fitted, for the same reason.

Later on, retreaded tires were used (Kliber) with good success.
 
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Jetlagged
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RE: Slat Retraction During Reverse Thrust? 747-400

Tue Nov 07, 2006 11:17 am

Quoting BoeingOnFinal (Reply 17):
Is "droop" more effective than slats with slots according to lift produced? Slots are there to have lower stall speeds and bigger AoA, not to produce any lift, isn't that correct?

You aren't far out about slats. They enable higher AOA before flow separation and stall and so allow higher lift. The basic lift curve (CL vs. AOA) is not much affected except the stall angle is increased. Trailing edge flaps give more lift at the same AOA.

Droops are somewhere between Krueger flaps and slats in effectiveness. Slats are most effective because the slot energises the airflow and ensures the airflow stays attached at higher AOA. A Krueger flap does nearly as good a job as a drooped LE with a much simpler mechanism.

The A380 uses a drooped leading edge on the inner wing to ensure the inboard section stalls first (outboard sections have slats). For the same reason, the 747 uses Krueger flaps inboard but variable camber flaps outboard.
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