View Full Version : The purpose of a leading edge droop?

24th Nov 2004, 12:46

to increase wing camber, and delay separation of the airflow when trailing edge flaps are lowered.

Can anyone try to explain me, what a leading edge droop is? I would be very grateful.

24th Nov 2004, 17:24
An analogy using your forearm & hand to represent a cross section through the wing ie leading edge to trailing edge:

Hold your forearm horizontally in front of your eyes. Your hand represents the leading edge of the 'wing'. Relax your wrist. That's LE droop.

Bally Heck
24th Nov 2004, 17:50
Tinstaafl's analogy is more convincing if the other hand is placed on your hip and you pout your lips.


gas path
24th Nov 2004, 18:33
Leading edge droop is a transonic wing thing isn't it to improve low speed lift? As opposed to leading edge flaps and slats etc.
Droop being fixed as opposed slats etc that move.:confused:

24th Nov 2004, 18:34
Nope, slats are different in that they create a slot, or gap between the slat and the main part of the wing. Aircraft types that feature slats/slots include the Tiger Moth and the Socata Rallye, as well as larger transport types. Handley Hage, a UK aircraft manufacturer, is usually credited with the invention of the slat/slot.

Look here (http://adg.stanford.edu/aa241/highlift/highliftintro.html) for more information than you ever realised you wanted to know about flaps, slats, slots, Krueger leading edge devices, droop snoops, the lot!

The Odd One

Droop being fixed as opposed slats etc that move.

The leading edge of the Hawker Siddley Trident moved downward to create a \'droop snoop\' to change the shape of the wing for low-speed flight. Boeing in particular seems to favour the Krueger leading edge device, that looks like it shouldn\'t work but does seem to.

The Odd One

gas path
24th Nov 2004, 18:59
Did Hawker Siddleys finest, leading edge device stay sealed to the wing through all phases of it's operation?

25th Nov 2004, 06:20
...Or put simply, a droop is a slat without a slot !

Astra driver
25th Nov 2004, 16:12
Odd one,

Thanks for that link, I learned a couple of new things from it.

AD :ok:

25th Nov 2004, 18:00
(non-pilot) As I recall, the Vickers VC-10 had leading edge droops as well? Were those droops or slats or slips and slops? (Can't get all of this fly-thingummy-jargon) :p

"I tell you, we are here on Earth to fart around, and don't let anybody tell you any different." Kurt Vonnegut, Jr.

26th Nov 2004, 09:52
Thank you very much for your replies, that was very helpful!

26th Nov 2004, 11:20
...especially the K. Vonnegut quote, PAXboy. Did he really say that? It fits rather well with my own philosophy.

29th Nov 2004, 11:39
hello everyone,

leadingedge droop & krugerflaps have the same aim : lift augmentation by increased camber allowing for lower stallspeeds & thus lower approach speeds. both systems have advantages & disadvantages.
krugerflap : advantage : it's retractable, so you get rid of the extra drag in cruise flight.
disadvantage : relatively complex mechanical retraction/extension system & extra weight.

leading edge droop : opposite : mechanical simple & permanent, but extra drag in cruise.

both systems have their over/underpressure zones modified, compared to a normal cambered profile without kruger or le droop.
also the impactpoint(v=0), moves from intrados(wingunderside) to extrados(wingupperside).

eg: b737 has krugerflaps on the inboard leading edges, the venerable french caravelle had leading edge droop.

29th Nov 2004, 16:42
keithl: This is the attribution that I have:

"And I tell you, we are here on earth to fart around, and don't let anybody tell you any different."

(Kurt Vonnegut Interview in Inc. Technology January 1996, Vol.17, No. 17)

1st Dec 2004, 10:03

If anybody wants to worry about RJ's and CRJ's and Challenger wings and lack of LE devices, read that link.

For the knowledgeable it will send chills up your spine. Challenger pilots should be very careful about icing, de-icing and rotating at too slow an airspeed ( or too rapidly ).

With the sort of wing-sweep the CL600 has, it should have been given a leading edge device (same with CRJ's).

Mad (Flt) Scientist
1st Dec 2004, 12:04
Since that report discusses theoretical work on two nominal sections and CFD work on the Fokker F28, I'm not sure I 'get' the link to Canadair products.

Elliot Moose
2nd Dec 2004, 00:49
There are around 1600 CRJ 100/200 and Challenger aircraft in service today (don't count the 700/900 series as they have slats) and until VERY recently, everybody flew them with no problems through all types of weather.

That said, all decently trained pilots of these aircraft are made well aware that the lack of leading edge devices combined with a supercritical airfoil means that the airfoil will brook very little contamination without serious consequenses:uhoh: . It is actually a maintenance function to polish the leading edges of these aircraft at designated intervals as flying with them unpolished will affect the performance, so obviously even a little bit of ice buildup before takeoff will cause grief if not dealt with. In flight, however, there is negligible effect as the anti-ice system works well, and there is seldom need for extended flight in significant ice in jet aircraft anyways.

At the time that both of these series of aircraft were designed, Canadair was basically called foolish. Who would buy a wide-body business jet when sleek lears and citations were the norm? 500-600 airframes later we see it to have been a good idea. The CRJ was an even wilder design idea. Nobody bought the idea that a jet could be fiscally viable with only 50 seats. The 1000th of the 50 seater will soon come off the line. My point here is that the cost of adding the complexity of slats to these aircraft was not prudent at the time that these were being designed. It is a bit of a pain to have to respect the limitations of the airfoil, but that is about it. Full stalls (to the pusher) as we do in production test flights are definitely a no-no and the almost complete lack of pre stall buffet is not an exaggeration. Not to be done except under very controlled conditions! By the time the 700 was designed, almost 1000 of the 50 seaters had been ordered and it made sense to go the extra distance and add slats. Yes circling approaches are a lot easier in the 700 with its slats and lower speeds, but they are certainly not dangerous in a 200 if proper procedures are followed.

By the way, Odd One, Thanks for the neat link!:ok: Some absolutely fantastic nerd material there, which I will definitely spend some time perusing!:ok: (EM dons his anorak and puts fresh cello tape on the glasses.............)