747 Leading edge devices
 

In a recent interview, I was asked about a 747's leading edge devices, what they are, what positions and why. Having never flown one before, i had to guess. I was probally wrong, but they never gave a hint if i was or not.:confused:

Tried to research, afterwards, via the net but have come up with conflicting answers.

What i have so far is Krueger flaps, not slats, on the outer sections of the wing. True or false, & why?

Thanks in advance:ok:

Kruegers-inboard,less efficient,promote root stall,because the swept wing stalls at the tips if left unchecked.

If you dont know the answer,don't gues,just say''I dont know,sorry''.

Yes, Kreuger flaps between fuselage and inner engines and 'variable camber leading edge flaps' between the engines and outboard to the tip.

The VCLEFs are unique, as far as I am aware, on commercial aircraft in that they bend as they are deployed. When retracted they are flat (in line with the under side of the leading edge) but as they extend, a clever scissors support mechanism bends them to a more efficient aerodynamic curve. The very tip of each flap is in the form of a 'nose' which unfolds and provides a blunt leading edge to the whole affair.

Disadvantages include:

Wing bleed air de-icing does not work with them extended;

During extension/retraction they are momentarily at right angles to the airflow and therefore increase drag, reduce lift and reduce the manouever margin (watch your bank angle!); and

The flexing material sometimes causes the paint to crack and peel off.

Good luck with your next interview!

Leading edge flaps are pneumatically driven, but can also be driven electrically. The LE flaps are signalled from the trailing edge flap position.
There are a total of 26 leading edge flaps. There are 20 Variable Camber leading edge flaps (10×left, 10×right) and 6 Kruger flaps between the inboard engine and the fuselage (3×left, 3×right). The LE flaps are grouped in 4 sets each side: Set 1 (most outboard), set 2, set 3, set 4 (most inboard) TE Flaps 0° - 1°, LE Flaps 2 & 4 signalled and extend TE flaps 5°, LE Flaps 1 & 3 signalled and extend

747 vs 340
 

I got asked, in interview, why 747 and A340 have different LE devices, I think it was Kruegers on the 74 and slats on the 340, he wanted to know why. Memories a bit rusty, as it was about 6 months ago.

That's the Classic. The 400 is a bit different. There are 3 groups - Inner, mid and outer. With Flap 1, the inner (Krugers) extend. With flap 5, the other sections extend.

Sorry Dan but not on the 747-400 they don't.

The LE flaps are extended in two groups. Group A LE flaps, consisting of flaps No. 6 through 13 in the left wing and No. 14 through 21 in the right wing, will extend together when the flap control lever is moved to the 1 unit detent. The remaining LE flaps, group B, will extend when the flap control lever is moved to the 5 unit detent.

The LE flaps are sequenced to retract in two groups. Group A LE flaps will retract when the flap control lever is moved to the full UP detent and after the outboard TE flaps is fully retracted. Group B LE flaps will retract when the flap control lever is moved to the 1 unit or full UP detent and the inboard TE flaps are less than 5 units.

You're correct. It's been over 4 years since I've flown the beast. It's the inner and midsections that move with selection of flap 1. BTW, the Ops Manual refers to them as Inner, Mid and outer sections and not by the surface numbers or groups.

And also, with selection of flap 1 on the 744, the TE flaps remain retatracted - it's onlt the LE flaps you get. Wheras on the Classic, the TE flaps move on selection of flap 1/