744 - Slat retraction on touch down
 

Noticed when paxing home the other day that the slats on the 747 retract just after touch-down. Would someone care to explain how and why this works?

Cheers,
RS

Does it on reverse selection.

Avoids FOD from engine. They re-extend when you cancel reverse.

Saw this question on another forum so, having never heard about it, consulted the Maintenance manual.
The outer sets of leading edge devices are retracted automaticaly on selection of reverse thrust to reduce fatigue on the outer LE pannels.

Rgds Dr I.

Pretty sure you will find it is the inboards and midspans, the outboards stay as is.

I do not know if this is an "option" on the 744. On the Classic it seems to have been as some will and some won't.

A Boeing idea, from long ago.

Same on the 707. When reverse selected, the LED's retracted pneumatically, then re-extended again when reverse cancelled.
This was to avoid slush contamination behind the LED's when landing on contaminated runways.

Worked good...:ok:

The later -200 a/c and on had this feature.

edit to add it was available on earlier a/c as an SB:ok:

Just to be a bit pedantic i know, but there are no slats on any 747, just kruegers inboard and LE variable camber flaps outboard.

Sorry gang got it wrong, jtr is right.

http://www.!!!!!!!!!!!!!!/open.file/770568/L/

but it is to reduce the fatigue on the LE divices.
I will now go and read the entire 747-400 mm from cover to cover as punishment!


Rgds Dr I

Leaner Question Please?
 

Private Jet,

Please could you explain for the benefit of all the non experts, what is the difference between "kruegers", "variable camber flaps", and "slats".

From your comment I understand that these are all variations in the movable LE parts of the wing, which protrude out in front in order to increase the circulation and/or to reduce the stall speed of the wing, but there must be a specific reason why they all have a different name?

Thanks,
Tallsandwich.

Krugers (should be an umlout over the U but can't do it on my keyboard in pprune) are the simplest form of LE device. They are simply a panel which folds out forward. The variable camber devicesa are flexbible composite panels which lie flat whe stowed, but flex into a curved shape to cmplement the natural shape odf the aerofoil when deployed.

Slats aren't fitted to 747s. Technically, a slat is part of the aerofoil which moved forward of the wing to extend the leading edge forward and downward. Airbusses use slats, they tend to be more difficult and expensive to construct. They can also have slots which allow some of the higher pressure air on the undersurface to leak to the upper surface which re-energises the upper surface boundary layer thus delaying the onset of separation and delaying the stall.

Hi TS,

Dan got there before me, his reply explains the differences as good as anyone. Hope its enlightening.

QUOTE

They re-extend when you cancel reverse.

UNQUOTE

Why do they need to extend again? Surely they get tucked away again on the way back to the gate?:confused:

Because the contoller uses simple logic. The LE is deployed by selecting Flaps away from "up" thus when reverse is selected the "retract" command simply interrupts the deployment. As soon as reverse is cancelled they redeploy to the commanded position. Then they can be retracted as part of the after landing procedure.............

Thus adding redundancy against the reverser retraction system malfunctioning and not extending the LE devices properly when you really do need them...

Redundancy achieved through making a system intentionally simple, in other words.

I am now educated...
 

Thanks for the details guys.

Does anyone have any knowedge about their respective cost, complexity as well as a maintenance standpoint. Is one cheaper than the other to make, maintain etc?

The B747 krugers extend again on deselection of reverse thrust to cater for a go around.

at the risk of being a pedant - doesn't the MLG have to contact the ground before the reversers are engaged?

can you still GA once your feet are on the ground?

out if idle curiosity.
ROC:ok:

Yes, there is offcourse in the 747 a reverse interlock which will be removed upon touchdown so that the reverse levers can be moved to the "unstow position" and after they have reached 90 percent of their travel to the extended position the second interlock will be removed so that you can increase rpm off the engines using the reverse levers.

Offcourse in my boing manual it states that after selection of reverse thrust it is not recommended to make a go around due to possibility of not fully retracting reverser shells.

It does not say anything about a go-around once the wheels are on the ground, it will basically be the same as a touch and go in that case