leading edge cuffs
- Thread starter dbrault17
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meritflyer
Well-Known Member
Wing cuffs give the wing two AoAs. They reduce the AoA on the outboard edge similar to wing washout which, during a stalled or near stalled condition, allow the wing to stall at the root and work its way out towards the tips. As a result, pilot is able to maintain better control of the aircraft during slow flight and/or near stalled situations. Think of it as when the wing is stalled, the outboard section of the wing, due to its lower AoA, is still flying which is supposed to prevent or reduce the possibility of a spin and make the ailerons more effective.
This design was primarily a result of NASA's tests by Jim Patton, who developed such a concept.
This design was primarily a result of NASA's tests by Jim Patton, who developed such a concept.
the way i understand it is the wing is warped with a higher angle of attack at the wing root and a lower angle of attack at the wing tip to delay seperation of airflow in the area of the ailerons. However looking at pictures of wings like this one from an american aviation yankee (which looks like a Cirrus wing)
it looks as though the wing root is is at a lower angle of attack. Why is Cirrus supposed to have a better design then say a Cessna wing warping? Also how does the break between the wings work? If anybody has any articles on leading edge cuffs, Cirrus wing design, etc it would be much appreciated. Its for a report.
it looks as though the wing root is is at a lower angle of attack. Why is Cirrus supposed to have a better design then say a Cessna wing warping? Also how does the break between the wings work? If anybody has any articles on leading edge cuffs, Cirrus wing design, etc it would be much appreciated. Its for a report.
desertdog71
Girthy Member
Must be a different kind of leading edge cuff than I am used to seeing. The leading edge wing cuffs installed on our Twin Comanche as part of the Robertson STOL kit are there to increase the camber of the wings upper surface.
What you aere refering to, I forget what its called exactly but its common in GA aircraft to have a higher AOA at the root than at the tip. This is to increase aileron effectiveness when in a near stall condition thus giving you more controlability.
desertdog71
Girthy Member
meritflyer
Well-Known Member
You're talking about washout. Wing cuffs do the same thing on certain aircraft such as the Cirrus and Col 400.
Here are some thoughts from a safety article and ideas proposed by Jim Patton, the director of NASA, and to some degree pioneered the wing cuff design for GA.
A) "Back in the mid-1980's, the first test pilot on our kit plane was a man by the name of Jim Patton who had been the Director of Flight Test at NASA's Langley Research Center. Patton's NASA Langley team developed the concept of the leading edge wing cuff and he firmly believed that General Aviation flying could be made safer through new wing designs.
We wanted to take the next step and build an airplane that was much more difficult to get into a spin. With the cuffs, we have improved slow flight and stall handling characteristics. We've made an airplane that's much more difficult to get into a spin than a typical straight wing plane."
B) "Traditionally, most pilots have been taught to control roll with aileron until they're near a stall. At that point they're supposed to use only the rudder, but that's not intuitive so it causes problems. Also, if they use too little or too much control input, they can have a rapid break into an inadvertent spin which may not be recoverable, especially if it happens anywhere near the ground."
C) "An aircraft with a cuff designed wing will shake nearing a stall, the controls will get mushy, and the stall warning horn will be blowing but the outboard section of the wing is still flying. The segmented leading edge creates a natural stall fence which helps to keep the ailerons effective. One of the deadliest stall/spin events in aviation is the 'base to turn' final with a trailing wind. In that scenario, the plane is low and slow and even the best spin recovery technique in the world will not save you."
The aircraft they are discussing in these paragraphs is the Cirrus.
tgrayson
New Member
Sharp edge of the cuff creates a vortex, which helps keep the boundary layer from separating.
So what makes Cirrus so much different then say a Cessna wing?
tgrayson
New Member
Because the "break" creates the vortex from the spanwise flow to keep the boundary layer from separating.
Cessnas don't have cuffs, they have drooped leading edges.
O.k. so the air striking the wing of the inboard segment flows laterlly to the wingtip and upon striking the blunt "break" (leading edge cuff) creates a vortex that keeps the boundary layer from separating on the outboard section of the wing thus delaying the stall on the outside of the wing and keeping the ailerons effective?
Am I close? Is there a fixed change in angle of attack between the inboard section and the outboard?
How is the vortex created?
tgrayson
New Member
Bingo.
Good question. I would have supposed so, but I guess there doesn't have to be.
Air has trouble flowing around sharp edges...that's why our leading edges are smooth. The sharp edge causes the air to separate, so it curls up into a vortex, mixing the faster air outside the boundary layer with the air inside the boundary layer.
desertdog71
Girthy Member
View attachment 1556
Here you go. Very similar setup to the Cirrus wing. Oh and this design goes way back before the 80's.
Here you go. Very similar setup to the Cirrus wing. Oh and this design goes way back before the 80's.