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Anti-Spin Ideas

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REVAN

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This thread is derived from a conversation that was going on the thread "Crashes In the News". The discussion had to do with the ways that aircraft design could be improved to reduce loss-of-control accidents, and specifically to improve the spin characteristic of an aircraft by improving/correcting the fundamental yaw instability of the aircraft's wings, a characteristic that is manifested in a wing's differential induced drag distribution which traditionally creates adverse yaw tendencies with aileron input.

Regarding the spin, I had said:
While pilots have become accustomed to this situation and consider it 'normal', I hope that with a bit more careful reflection on the situation, most of you can see that there is a functional problem with the aircraft when the control system is intended to bank left when the pilot pulls the stick left, but it sometimes works opposite, and similar reversals with the pitch control. For decades, the solution has been to have pilots be responsible for recognizing that they need to change the control law that has been reinforced through hundreds of hours of flying and automatically switch to something that is fundamentally different. When there is an emergency and panic sets in, the predominate muscle memory often wins over the known, but rarely or never practiced (because it can be dangerous) control law to recover the aircraft. When it doesn't work and people die, everyone puts the blame on the pilot and inadequate training.


Watch this video to see how a simple control reversal can take something easy we all can do, and turn it into a nearly impossible control problem.
https://youtu.be/MFzDaBzBlL0


Now imagine I made a flying machine that has been carefully crafted to challenge pilots by implementing a control reversal at specific times to correlate with emergency conditions just to see if the pilot can figure it out and do something they are aware must be done, but that is in conflict with their reflex actions and what is familiar. Why would I make such a machine? Maybe I'm an evil SOB, but I'm going to be nice enough to give you the heads up that I put this trap in the design... and by the way, if you fail the test, you will probably die. Would you volunteer to test your skills against my machine of mayhem?


My point of this is that instead of identifying poor pilot training as the main problem behind these unfortunate spin accidents, maybe it's time to recognize the very significant role that excessively challenging aircraft design has been playing all along. There's only so much a task loaded person can be expected to do, and compensating for difficult control problems in an emergency is, too often, more than than the pilot will actually accomplish with success, even though he/she may 'know' what they need to do.
Adverse yaw is one of the contributing factors that will drag a stalling wing into a spin. Adverse yaw is a symptom of yaw instability that requires a vertical tail and rudder action to tame. Fix the instability in the wing and a whole host of problems are alleviated, spin tendency among them. IMO, the guys designing tailless flying wing designs should not be the only ones concerned with making a wing that is yaw stable.

The common misconception is that spin avoidance is achieved through stall avoidance; no stall, no spin. When you get into the aerodynamics of the situation, it turns out that the spin has much more to do with the yaw instability of the airframe than it has to do with a stall. This is why appropriate rudder authority can be used to prevent a stalled airplane from spinning (or force it into one if applied inappropriately). IMO, a plane should be able to stall and maintain full control authority without risk of spinning. The stall is a very useful maneuver when not rendered unsafe by unstable design, and it's a great way to dissipate energy (far more effective than spoilers or speed brakes).

Lift distribution is how roll authority is created. When the lift distributions of the left and right wings are differentiated without regard to the drag profile of those lift distributions, it is likely the wing will exhibit undesirable yawing characteristics. This is what is commonly done. However, the computational tools exist to predict and integrate the lift distributions. Designers could be designing favorable characteristics into their wing designs, but instead the same old wing concepts are repeated over and over again because it is familiar and everyone has accepted that the result is normal.


The analytical tools are there and available for designers to use to create better functioning designs. I'd prefer to not lock anyone's thinking into a single possible solution. There are many ways to add yaw stability to a wing design. I referenced several earlier; the BSLD is one that has a fair amount of understanding behind it already. Wing-grid technology is another very promising architecture that has been around for about 20 years, but has been ignored by just about everyone. I like the concept of using a variable geometry outer wing section (i.e. - wing tip device) to modify the span loadings, as it would leave the entire main wing section available to host flaps for improved low speed flight performance.


Personally, I think the aileron, as it has been applied to contemporary aircraft, is a terrible concept. While it does what is desired for the induced lift profile of the wing to roll the aircraft, it does everything wrong for the induced drag profile of the wing. The solutions for replacing the ubiquitous aileron need to address both lift and drag profiles simultaneously, causing each to differentiate in a favorable manner to control the aircraft.
So, fix the adverse yaw, and you'll likely fix the spin problem as well. I need to say likely, because it is possible to correct adverse yaw without improving spin characteristics. The Ercoupe with interconnected rudders and ailerons is an example of this. Free the elevator travel enough to stall the Ercoupe and it could easily spin. Frise ailerons are another commonly applied method for reducing the 'apparent' adverse yaw of a wing, but that will do little for improving the spin tendency. The adverse yaw should be corrected by favorably differentiating the induced drag profiles of the left and right wings to coordinate yaw with roll.

A Boeing engineer once said to me, "Nothing is harder to fix than something that almost works. Management's position is that it almost works, so don't change anything... just fix it.". My reply was that it is even harder to fix something that works most of the time. That is the modern airplane. Most of the time it works as intended, but occasionally it spins and kills everyone onboard. I think it's time to try changing that situation.

Consider this thread a place to brainstorm and discuss methods to make better and safer flying airplanes through better aerodynamics. The goal is to break the mold, do aircraft control better than it has historically been done, even if it means making planes that look different to do it.
 
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wsimpso1

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Interesting theory on the topic...

If you can fix adverse yaw, you can take out one source of spin entry, but I will contend that this is the smaller of the sources.

I can tell you that I have entered spins (aerobatic training) on purpose with zero aileron, just rudder at stall break. To really defeat accidental spins, you will have to get outside the box to beat all autorotation tendencies. If you keep at it, you may solve the riddle. Good luck to you on this.

What I do know of spin proofing are these features:

Leading edge cuffs, which are drooped leading edges out in the region of the ailerons. These tend to prevent wing stall from progressing to the outer portion of the wing, give reduced autorotation, and keep the ailerons alive down into the stall. This feature plus stall strips inboard can produce a benign stall with resistance to spin entry. This type of device in a negative g stall will have an increased tendency to break and thus stall and spin in negative g;

Slightly drooped leading edge airfoils (Riblett airfoils are an example). These tend to give soft stalls, which can avoid a hard stall break, and reduce the autorotation effect. Like the cuffs, it has to have an increased tendency to negative g misbehaviour;

Avoiding thin tip designs. The classic NACA work on tapered and on swept wings had thinner (%-wise) tips than roots, which combined with the designed-in decreased leading edge camber of the thinner NACA foils, they found a tendency toward undesireable stall progressions in tapered foils.

Carry the same foil from root to tip (taper the wing by scaling the entire foil, not the % thickness). In the NACA work where they discovered unfavorable stall progression with tapered and with swept wings, they found that even an elliptical wing had favorable stall progression, but it had another feature that appears to be helpful - the elliptical wings tested carried the same airfoil from root to tip. It runs out that using the same foil from root to tip gives much more desirable stall progression much more docile behavior. While you can do what looks like a spin entry, with yaw increasing and roll into the yaw, it tends to be slower and has a strong tendency toward developing into a spiral dive rather than a spin.

Boundary layer devices near the leading edge that energize entire tip portion of the wing. These can be classic vortex generators, or the tiny elevated little delta shaped fence used on the Glastars. These have a tendency to keep the wing flying way into stalls even when cross controlled.

Good luck with finding the configurational solution to spins. I shall watch this discussion with interest.

Billski
 

BJC

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Boundary layer devices near the leading edge that energize entire tip portion of the wing. These can be classic vortex generators, or the tiny elevated little delta shaped fence used on the Glastars. These have a tendency to keep the wing flying way into stalls even when cross controlled.
The designers of the GlaStar/Sportsman wanted an airplane that could be flown in slow flight (not like the new FAA definition, but true slow flight a knot or two above stall) and still have aileron control of the roll axis. They accomplished that for the flaps retracted configuration. The Sportsman (I haven't flown the GlaStar) retains aileron control through the flaps-retracted stall throughout the power range. Power off, with full back stick, it settles into a stable sink with full aileron control. With full flaps, some rudder is required to keep the wings level. I'm still, slowly, evaluating the effects of different aileron rigging.

The Sportsman will spin. One has to intentionally make it spin with flaps retracted. It is easier to enter a spin with full flaps. I have no experience spinning the Sportsman with half flaps.

The crash that started this discussion, the ICON over the lake, would have been easily avoided in the Sportsman (and likely the ICON also) with the turn technique that I described in that thread.


BJC
 

BJC

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So, fix the adverse yaw, and you'll likely fix the spin problem as well.

Consider this thread a place to brainstorm and discuss methods to make better and safer flying airplanes through better aerodynamics. The goal is to break the mold, do aircraft control better than it has historically been done, even if it means making planes that look different to do it.
A free-wheeling discussion about methods to make better and safer flying airplanes will be interesting, but may not lead to any useful conclusions. (To me, a better flying airplane would be one capable of pulling to vertical without losing too much speed, like a modern monoplane, but still have snap roll - spin - charactersitics of a Pitts.)

The first step necessary to find a way to eliminate a problem is often overlooked because it is assumed that the problem is clearly understood. The first, and necessary, step is to clearly and succently state the problem.

Please state the spin problem that you would like to fix.

Thanks.


BJC
 

Jay Kempf

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The only way you are going to stop a wing from entering a spin when it stalls is to keep the entire outer wing with ailerons from stalling. Ailerons being what they are and people being what they are that is going to be a hard task. But with extreme aileron differential and extreme twist it can be done. The question is should it? What have you done to both the lift distribution and efficiency of the wing and what have you done to handling balance if you do that? In the end airplanes stall and we have to be trained to fly them safely.

I am not a big fan of dumbing down machines so that untrained people can use them without hurting themselves. I like my chainsaw.

Canard?
 

Mcmark

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The flying community has been trying to design the perfect airplane for decades, one that goes like he!! and won't stall/spin.
Been said before and will be said again, learn how to fly the airplane. That includes the FULL stall series AND SPINS.
Off my soap box.
 

Dan Thomas

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Interesting theory on the topic...

If you can fix adverse yaw, you can take out one source of spin entry, but I will contend that this is the smaller of the sources.
Yup. Stalling with yaw is the recipe for a spin. Doesn't need to be adverse yaw. One could design an airplane that prevents spin in one condition, but it would still spin in some others.

There is no substitute for training. None. Anything else just dumbs down the pilot, just like ABS has dumbed down a lot of drivers. See them in the ditch on snowy days, or crashing into other vehicles when they can't stop in time.
 

Dana

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Remember that the Ercoupe wouldn't stall or spin, but had a safety record no better than its spinnable contemporaries. Anything you do to eliminate the possibility of spinning had other undesirable effects on handling or performance.

The ultimate (and easiest, nowadays) solution is fly by wire where the computer won't let you stall the aircraft.

Dana
 

cheapracer

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The only way you are going to stop a wing from entering a spin when it stalls is to keep the entire outer wing with ailerons from stalling.

But with extreme aileron differential and extreme twist it can be done.
That's me, but not twist so much as a cuff and shaped wing end/tip.

Lots of fin/rudder area too.
 

Himat

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Yup. Stalling with yaw is the recipe for a spin. Doesn't need to be adverse yaw. One could design an airplane that prevents spin in one condition, but it would still spin in some others.
To make a wing spin proof from all attitudes will then be very difficult or have some interesting side effects. Removing the ailerons will not help, it will still be possible to stall one wing with rudder only. Just apply rudder the opposite as used to pick up a wing when flying close to stall and hey, asymmetric stall and spin entry do follow. This shows that two axis control with elevator and rudder do not make a plane spin proof.

What about the canard configuration? With the canard span short enough to not overpower directional stability if stalled asymmetric and a large enough margin against stalling one side this configuration offer a large resistance to stall initiated spins. Until stalled when inverted.

About two axis control of airplanes there are one more possibility. Delete the rudder and wing ailerons. With two axis control by tailerons and sufficient fin area the plane should resist asymmetric stall well. Probably not entirely impossible as forcing one wing down do raise the angle of attack on that wing as the plane is rotated along the longitudinal axis.

The only way to make a wing not stall asymmetric I see is to make the wing circular and symmetric about the airplane longitudinal axis. Two axis control with elevator and rudder should now be ok as there is no need to bank for turning if a symmetrical airfoil is chosen! This configuration should be very spin resistant from all attitudes, probably only an inertia induced spin would be possible.;)
 
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Himat

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The only way you are going to stop a wing from entering a spin when it stalls is to keep the entire outer wing with ailerons from stalling. Ailerons being what they are and people being what they are that is going to be a hard task. But with extreme aileron differential and extreme twist it can be done. The question is should it? What have you done to both the lift distribution and efficiency of the wing and what have you done to handling balance if you do that? In the end airplanes stall and we have to be trained to fly them safely.
I differ on that one. On a tailed airplane a large enough horizontal and vertical tail area can make the airplane directional stable even with one wing stalled. The airplane will still “spin” but now around its longitudinal axis, not the vertical axis. After an asymmetric wing stall some sort of spiral dive or rolling dive may follow, depending on control input and amount of dihedral.

The large tail area do make the airplane spiral unstable, less excessive dihedral is applied, something that may lead to the vehicle have an interesting dynamic behaviour.:gig:
 

lr27

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I have a model with a vertical stab volume considerably smaller than most. Plus, IMHO, the outer panels of the wing are a bit heavier than they need to be. I'm not absolutely certain. Unless stall recovery is done very quickly, it will spin immediately. I'm not sure, but I think it will spin without any rudder input. Certainly another glider I had would spin without any input, as I learned trying to sneak over a line of trees. I don't know about vertical stab volume, but I recall that the fuselage was a bit shorter than one might expect for the wing span. Plus it too was heavier in the tips than it might have been. Most of the models I've flown don't do that, but these two had higher aspect ratios than most of you are flying.
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I forget what the stall/spin behavior of the Horten flying wings was supposed to be, but most didn't have adverse yaw. With respect to span, they were less efficient than normal aircraft. However, per Al Bowers of NASA, they weren't so inefficient in relation to wing root bending moment, which has some correspondence to weight. Plus, of course, one could leave off the tail.
My guess, though, is that the spin characteristics were interesting. Certainly they were tricky with the Horten IVb, which apparently liked to spin. It was destroyed when it fluttered after a spin recovery. Part of the problem was the use of an airfoil from a captured or downed P-51, combined with fairly low Reynolds numbers on the outer part of the wing.
 

Himat

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So, will a free-wing stall or spin?
Depending on the execution of the design I would think. If an asymmetric stall can be forced, a spin is a possibility. By design enough rudder authority and a to low stall margin at flying speed a stall spin could be possible.
 

lr27

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Warning: only one of the following meets the strict requirements of the OP's question:

Some wacky ideas:
-A really big Estes rocket motor in each end of the horizontal stab. However, it would be really important to light the correct one! ;-)
-Spoilers in each wing tip activated by small sliding weights. I suppose electronic versions would be lighter.
-A lightweight spin chute carried at all times. If reusable, it could also be handy as a source of drag to avoid shock cooling on descent or to steepen an approach. Obviously it would be something else added to the annual inspection.
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Not so wacky:
-It's my understanding that some sailplanes with really long wings have a short aileron section near the tip with extreme aileron differential. Or something like that. I don't recall exactly what kind of mechanical mixing was set up.
-Some airplanes, such as some versions of the DeHavilland Tiger Moth and, I think, the Super Chipmunk, had horizontal strakes along the fuselage extending forward from the horizontal stab. This was to keep more attached flow for the rudder when it was being blanked by the stab. Or so I've heard. Of course, attention to the relative positions of the horizontal and vertical stab might make this unnecessary.
UfoFh.png

-I think the ventral strakes on the rear fuselage of some aircraft may improve spin characteristics, though I don't know the specifics. Certainly such a strake won't get blanked, and I've heard sometimes they help keep flow attached to the rudder.Sometimes there's a pair in a v configuration. I've read that in some cases a pair can reduce drag slightly, though I'm not sure how authoritative that statement is.
Bombardier_Learjet_60_exterior_000.jpgstrakes-large.jpg
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P.S. In the case of a free wing, there's probably something wrong with it. I wouldn't be surprised if it was rigged with wash-in. In that case it would spin at the drop of a hat. Particularly if that hat is a large sombrero dropped in front of the outer wing. ;-)
 
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