9th May 2002, 07:50
I have heard of Kruger flaps in conjunction with older aircraft types(e.g. B 727) and that they are "high lift" devices. I have a couple of questions about these:
What is about them that makes them "high lift" in comparison with other leading edge flap designs?
Are they in use on more modern aircraft types?
Do they make the aircraft handle differently than standard designs? (apart from giving more lift I guess!)
Many thanks for any info.
9th May 2002, 10:54
Lemmee see now...
1. All leading-edge devices are "high-lift" devices, be they a leading-edge slat (fixed as on Globe Swift, or deployable such as on DC-10, 767 etc), a "drooped" leading-edge (as on the Trident) or a Kreuger-flap.
Basically, the addition of any device on the leading edge that increases camber will result in a serious increase in lift, often exceeding that made by the deployed trailing-edge devices at takeoff settings. As a general rule, for takeoff leading-edge devices will be fully deployed but trailing-edge devices will be set at relatively early stage of extension where they add some lift with little increase in drag.
2. Kreuger-flaps are still used on 747s, they are an elastic structure which actually changes shape from very slightly curved (stowed on underside of leading-edge) to noticably curved (deployed).
3. As for handling, don't know, you'll need an ATPL-holder with experience of these devices and other types to tell you if there are any handling differences.
10th May 2002, 15:44
The point of a Kreuger flap, in addition to increasing CL and lowering the stalling speed, is all to do with the attitude at which the stall occurs. As a result of it being on the leading edge, it increases the stalling Angle of Attack and the level flight stalling 'attitude'.
This gives the pilot an excellent clue if his aeroplane is about to stall because of the ridiculously high nose attitude. It is my assumption, having seen the fully deployed Krueger flaps on my 737 that, in view of the apparently large amount of flat plate drag they must produce, they are only really effective at high angles of incidence anyway.
10th May 2002, 16:55
The addition of leading edge devices to modern aircraft also make flying slightly different.
In older aircraft eg. the DC-8, to flare the plane, it was necessary to make a very large pitch change to raise the nose gear above the main gear before landing.
In aircraft fitted with leading edge devices, the final descent is made with the aircraft in a pitch-up attitude, therefore almost precluding a nose gear landing.
11th May 2002, 03:43
Think about upwash. ;)