Stall Proof Ailerons

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GESchwarz

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There are a number of ways to prevent the aileron from stalling at high AoA, like fences, vortex generators, slots, slats, and Junkers ailerons, (did I miss any). But which one is, the simplest, and more importantly, the most effective in staying out of a spin?

I really like what happens on the Grumman E-2 Hawkeye, but it is a bit complicated; when the flaps are deployed, the ailerons drop down and aft just a little to open a slot, allowing high energy air over the top of the aileron, this is effectively a retractable Junkers aileron, with a little flaperon-down-angle action thrown in for the carrier landing.

On the simple side, I have seen leading edge vortex generators that only generate a vortex when the AoA is approaching the stall angle.
 

Topaz

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There are a number of ways to prevent the aileron from stalling at high AoA, like fences, vortex generators, slots, slats, and Junkers ailerons, (did I miss any). But which one is, the simplest, and more importantly, the most effective in staying out of a spin?

I really like what happens on the Grumman E-2 Hawkeye, but it is a bit complicated; when the flaps are deployed, the ailerons drop down and aft just a little to open a slot, allowing high energy air over the top of the aileron, this is effectively a retractable Junkers aileron, with a little flaperon-down-angle action thrown in for the carrier landing.

On the simple side, I have seen leading edge vortex generators that only generate a vortex when the AoA is approaching the stall angle.
Or, you know, adequate unblanketed rudder area, coupled with effective pilot training.
 

Dana

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Outboard ailerons, and a bit of washout to insure the root stalls first is the simplest solution. With a rectangular wing the lift distribution is such that you often don't even need the washout.

Dana
 

Matt G.

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Set up your control linkage so the ailerons reflex a few degrees when the stick nears the aft limit of its travel.
 

cluttonfred

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A plain "Hershey bar" constant-chord wing without taper or twist and a typical aspect ratio will normally stall inboard first, so keep the plain hinged ailerons to about the outer 1/3 of the wing and no special devices are necessary.

If you want to further reinforce that behavior in a wing already built, then the simplest solutions in order of complexity are: stall strips inboard to force partial stall at a desired angle of attack; a fence between the two sections to delay the propagation of the stall; vortex generators outboard to energize the air over the ailerons.

Slotted ailerons, fixed or manual or automatic slats, fixed or manual or automatic slots, or increasing the leading edge radius forward of the ailerons can all work as well but are best incorporated when the wing is designed and built.

Interestingly, some ailerons lose effectiveness at low speed because of vortices from the wing tips at low speeds, so they can be made more effective simply by moving them inboard a little bit.
 

TFF

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You can have some authority when stalled but not full. No airflow. The important part is how fast the wing fully unstalls. You don't want something that could inhibit flying again; something that may need to be retracted to get the airflow started again in its position.
 

deskpilot

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This is my latest version of Hugh Lorimer's tailless plane. This outboard wing panel now has a 15% reflexed aileron and tip fences. They will be applied in a differential manner to reduce risk of a yaw induced spin. Any other ideas that I should look at?
Hope you get more ideas from this GES.
Latest outer panel_600x375.jpg
 

PTAirco

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If you wanted to get really complex, you could use Junkers-type aileron and gear them to some linkage that senses angle of attack. They would deflect up or down together to keep them at 0 degrees incidence at all times, regardless of what AoA the wing is at (within limits of course.) This would keep Rube Goldberg happy, but I question its usefulness.
 

GESchwarz

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If you wanted to get really complex, you could use Junkers-type aileron and gear them to some linkage that senses angle of attack. They would deflect up or down together to keep them at 0 degrees incidence at all times, regardless of what AoA the wing is at (within limits of course.) This would keep Rube Goldberg happy, but I question its usefulness.
Matt suggested that they be linked to the elevator, which controls AoA. I think it's a great idea, however I have already built my flight controls. That change would require a major retrofit. Forget it!

I think what they did on the E-2 is a pretty good way to go. When the flaps deploy, the ailerons drop down and aft like a Junkers.
 

Tiger Tim

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Why not just go with differential ailerons with as close to zero downward travel as you can get? Maybe even have the hinge somewhere aft of the aileron's leading edge so the up going one opens a big slot for even better control?
 

GESchwarz

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Why not just go with differential ailerons with as close to zero downward travel as you can get? Maybe even have the hinge somewhere aft of the aileron's leading edge so the up going one opens a big slot for even better control?
That is an interesting idea. It certainly does make the aileron less prone to stall. To a degree, a lot of designs are rigged this way to reduce adverse yaw, but not for the purpose of preventing aileron stall.

What do the rest of you guys think? What might the draw backs be to doing this?
 

cluttonfred

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Up only ailerons have bee used successfully, which is about as extreme differential as you can get, but that's for preventing adverse yaw, not stall resistance.
 

ekimneirbo

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There are a number of ways to prevent the aileron from stalling at high AoA, like fences, vortex generators, slots, slats, and Junkers ailerons, (did I miss any). But which one is, the simplest, and more importantly, the most effective in staying out of a spin?

I really like what happens on the Grumman E-2 Hawkeye, but it is a bit complicated; when the flaps are deployed, the ailerons drop down and aft just a little to open a slot, allowing high energy air over the top of the aileron, this is effectively a retractable Junkers aileron, with a little flaperon-down-angle action thrown in for the carrier landing.

On the simple side, I have seen leading edge vortex generators that only generate a vortex when the AoA is approaching the stall angle.
Only experimenting will tell you what gives satisfactory results with your airplane. If you are looking for the most effective, then it probably isn't going to also be the simplest. Since I assume that you like myself want an airplane that will do its utmost not to allow a stall with a subsequent spin, I think you have to accept the premise
that the most effective will probably be more work...and thats why so many planes don't include it in their design. Check out the Pegazair site and read some of their emails. Slow flat turns are possible because the wing has movable slats and high lift flaps. Whether you consider the airplane or just incorporating the slats/flaps to an existing airplane, that will give you the most effective design. Sometimes you just have to decide whether you are willing to do the work to do it right, or just bandaid it and hope it works satisfactorily. In life I have found that I usually do more work by trying to avoid work than if I just went about something the right way to begin with.:)
 

Dan Thomas

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Flow_separation.jpg

The air above the wing is all messed up in the stall. Any aileron that's effective in this scenario would have to be the Junkers style, below the wing in the clean flow. A slotted aileron would have its flow through the slot all torn up once it got on top.

Got to remember that the usual aileron setup is merely part of the wing's airfoil. It doesn't raise or lower the wing by deflecting air; it does it by changing the camber (increasing or decreasing lift over the whole airfoil) and angle of incidence (which changes the AoA of the whole airfoil). Aileron down brings on a stall sooner in that area of the wing.

A rectangular wing, or one with washout, is difficult to get fully stalled. The stall starts inboard and moves outward as AoA increases, and eventually enough lift is lost that the nose drops before stall ever reaches the aileron. If one holds the nose up and adds a lot of power--maybe full power--he might be able to get the stall out to the aileron, too, but the break is impressive and violent. For this reason, many airplanes with Robertson and other STOL kits are placarded against intentional spins; the various lift-enhancing devices delay the stall inboard so long that the break gets sudden and wicked. A friend who flew a Robertson 185 on pipeline patrol took it up high (12,000 IIRC) and did a full power stall. He said that it shook and shuddered and seemed to be asking him if he really wanted to see this. He kept it up until it broke and flicked into the worst spin he'd ever been in. Took him several thousand feet to get it sorted out.

The best spin control feature is inside the brain of the nut behind the panel. Spin training. Spins out of various scenarios and how to handle them. Once that's done, that nut never gets the airplane into a spin. The problem with docile airplanes that resist spins is that they foster a sense of security and proficiency that is not justified. The guy that gets his PPL in a 172 goes out and buys an airplane he can afford--a Champ, say--and skids it around like he did the 172, and it kills him. And a Champ is a docile airplane compared to many others, especially some homebuilts. He should have been trained for some time in that airplane.

Training leads to proficiency, experience and wisdom. It doesn't weigh anything and its maintenance is minimal. It doesn't reduce performance of the airframe, like a lot of safety features do.
 

bmcj

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What about an aileron that was hinged at the tail end instead of the nose? Move the aileron and its nose moves to scoop the air from above or below the wing.

Aileron.jpg
 

cluttonfred

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What about an aileron that was hinged at the tail end instead of the nose? Move the aileron and its nose moves to scoop the air from above or below the wing.
That's a neat idea, bcmj, but an aileron like that would "grab" meaning that when you move it a little it would want to move a lot.

Dan Thomas, while I appreciate your point of view, I don't agree. I certainly support stall and spin training, but to me, stall prevention and avoidance is a bit like anti-lock brakes in wet or icy conditions for a car. Very competent drivers can pump the brakes just so and actually stop shorter than the ABS can, but most of us are far better off with ABS. IMHO, an aircraft designed to prevent the stall in the first place, while it annoys the very competent pilots, is a safer alternative for most of us.
 

BJC

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There are a number of ways to prevent the aileron from stalling at high AoA, like fences, vortex generators, slots, slats, and Junkers ailerons, (did I miss any). But which one is, the simplest, and more importantly, the most effective in staying out of a spin?

I really like what happens on the Grumman E-2 Hawkeye, but it is a bit complicated; when the flaps are deployed, the ailerons drop down and aft just a little to open a slot, allowing high energy air over the top of the aileron, this is effectively a retractable Junkers aileron, with a little flaperon-down-angle action thrown in for the carrier landing.

On the simple side, I have seen leading edge vortex generators that only generate a vortex when the AoA is approaching the stall angle.
It is not clear to me just what you want to accomplish.

My airplane has a simgle vortex generator near the leading edge of the wing ahead of each aileron. Because of that, the aileron comtinues to provide roll control in a full stall with the flaps retracted. With the flaps down, it acts more like a traditional high AR (for powered airplane; not close to sailplane range) rectangular wing.

My airplane will spin with the flaps retracted or extended.

The primary control to avoid an unexpected spin is, as reportd above, the person manipulating the controls. Proper coordination of the rudder with the bank to avoid unwanted yaw is what prevents spins.

There is a famous multi-million dollar fat LSA that, following an announcement that they had developed a "spin-proof" wing, spent another two or three years trying to actually achieve what they has previously claimed. I would bet that any competent aerobatic pilot could make it spin, and that the modifications that they made simply made the airplane less responsive to control inputs.

So, please focus your question. Are you simply asking about how to have ailerons that do not stall? And if that is the question, what type of wing and flap arrangement does it apply to? Or is your question how to build an airplane that will not apin?


BJC
 

cluttonfred

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I agree completely with BJC that a stall-proof plane and ailerons that continue to function when the wing is stalled are two very different questions.

However, it certainly is possible to create a plane that cannot spin if you make one that cannot stall. As long as the whole wing is still flying, then it should be possible to enter a spiral dive but not a true spin. A case in point is one of the Mignet formula designs by Emilien Croses, I think it was the B-EC-7 Tout-Terrain (All Terrain), which began the French certification process. It was thought that the stall- and spin-proof three-seater with good short-field performance would make a good light utility and even medical evacuation plane. It was the certification process which "stalled," however, because the French authorities required than any aircraft seeking certification demonstrate exit from a spin. Since no one could get the plane to spin, no matter what they did, they could not meet that requirement. There was some talk of suspending the plane on a swivel beneath a helicopter, allowing it to spin in the downwash, and then dropping it, but that never happened.

7587L.jpg
 
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