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BBerson

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I think the Helio Courier with blade interceptors in front of and assisting the ailerons to prevent aileron reversal is a pretty good engineering solution. (I watched it demonstrated, talked to pilots, but never flew one myself)

The spin starts when the pilot flicks the ailerons to come out of the bank. All explained in Stick and Rudder. But I don't think any students are reading Stick and Rudder.

So, what was misleading about my oversimplified last sentance in post #739? :)
 
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jedi

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Adverse yaw is created by lift distributions on the wing that create an unstable yawing moment. Differential ailerons don't correct that by themselves. The aileron, itself, is a usual suspect for exacerbating the problem and elevating it to dangerous levels in many cases. But, at the core of the situation is the lift distribution of the wing, and secondly, what does aileron deflection do to that lift distribution. Most aircraft designers don't think about this at all when designing the wing for their airplane. They just build a wing with inherent problems, add a rudder, and then tell the pilots to use the rudder to actively correct these problems in flight. My opinion is that it is time to start correcting these problems on the design board. The tech is there, but it requires approaching wing design differently than how it was done in the 1930's.



This is the common misunderstanding. 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).

Emergency situation: the engine has quit running and you need to set down in a small field surrounded by 100 foot tall pine trees... glide in over the tops of the trees, stall the wing to quickly drop to flaring altitude without gaining energy, recover from the stall to slow the descent, touchdown and then stall the wing again to stop quickly. This maneuver should be something a good design could do without any risk of the plane spinning close to the ground.
This is the approach and zero rollout landing Witold Kasperic demonstrated many times in the BKB according to the stories and film records.
 

REVAN

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Well, how do you control in roll without changing the lift distribution of the wing? Or should I ask, how do you maintain yaw stability during the stall? And if yaw instability is caused by the lift distribution as suggested in the first paragraph of post #754, then back to my first question...
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.

You've been asked several times what you propose and have given no answer. You say "the tech is there;" please tell us what it is.
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 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 do differentiate in a favorable manner to control the aircraft.
 
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REVAN

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This can be accomplished perhaps with twist or BSLD, but of course this comes at some cost. This is why I said anything you propose will be a trade-off. Is there something else you propose that will not be a trade-off? Please be specific.

And again I ask, by stall-prone, do you mean adverse yaw-prone, or do you mean something else?
Everything is a trade and comes with costs. Contemporary aircraft have many compromises built into them. Most of the time they work as intended. Once in awhile, they cost the pilot everything he has, and will ever have.

I'm not sure how to answer the last question. Did you mean to write spin-prone instead of stall-prone? If so, I'm saying that there is a connection between the aerodynamic forces that create adverse yaw, and the aerodynamics forces that can diverge into a spin when a wing is partially stalled or very close to a stall and with certain aileron input states.

Fix the adverse yaw, and you'll likely fix the other 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.
 
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vtul

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I'm interested in UL, and minimal complexity for them, and no acrobatics. I haven't seen any discussion here, so I'm only posing this as a question. How does this all apply to a 2 axis control plane with sufficient dihedral?
 

Autodidact

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The only thing I can think of to do is to increase the drag on the down going wing, and that's because decreasing the drag on the up going wing doesn't seem like a possibility. BSLD would be less efficient on a conventional design, wouldn't it? Adding drag to the down wing shouldn't be difficult with drag rudders or some type spoiler; wing grids are on both wing tips so you're still increasing the lift asymmetrically along with the induced drag - unless the grid is retractable...and that's assuming that it really works and you're still adding wetted area to the up going wing so it seems like it might be a wash. The old wing warping airplanes wouldn't turn in the direction of stick movement because of the asymmetrical drag and had to use the rudder. I don't see a universal aerodynamic fix for this, I wish I was smart enough to, though.

2-axis aircraft are turned (and rolled) with the rudder; to do this involves purposely un-centering the ball, doesn't it? Which to most pilots is anathema, isn't it? On the other hand I was taught how to side-slip, or did I teach that to myself? I think I remember reading or being told that the C152 shouldn't be slipped with the flaps down. Maybe every flight school should have a Morane monoplane with wing warping and a tiny rudder (or not :gig:).
 
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jedi

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I'm interested in UL, and minimal complexity for them, and no acrobatics. I haven't seen any discussion here, so I'm only posing this as a question. How does this all apply to a 2 axis control plane with sufficient dihedral?
No ailerons. You have solved half the problem. You have likely created other unintended problems however. Probably a good idea to keep normal three axis pilots away from it.
 

BBerson

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I'm interested in UL, and minimal complexity for them, and no acrobatics. I haven't seen any discussion here, so I'm only posing this as a question. How does this all apply to a 2 axis control plane with sufficient dihedral?
I have not flown in any 2 axis (rudder only) aircraft. But the models seem to be very spin resistant.
 

Vigilant1

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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.
So,this whole "campaign" boils down to:
- It is dangerous that conventional planes sometimes spin after stalling, and I think designers should make planes that don't do that.
- Maybe some technology would work to make things better. I don't like ailerons, so don't use that particular technology (though they are now fitted to the vast majority of aircraft and perform very well for every single moment of flying, unless a pilot doesn't respect the aircraft's performance characteristics. In this way, the ailerons are as "faulty" as the engine, landing gear, flaps, etc)

Speaking of tradeoffs, let's consider what we have to leave on the ground (Structure? Fuel?) to achieve these hoped-for reductions in adverse yaw. Or what the performance penalties will be.

New thread idea:
- Why do designers deliberately make airplanes with inadequate landing gear? Incompetent, negligent idiots! They know these planes are going to be in the sky, and they know that sometimes they come down very fast and hit the ground. People die, and we just accept this state of affairs. If the landing gear were not faulty and could safely handle the well-known loads of the weight of the plane coming to the ground at, say, the anticipated cruise speed, how many lives would be saved? Everyone just thinks things are fine, and that training should handle everything. "Just train pilots to limit their descent rate upon landing." How long have we been saying that, and yet we know many pilots hit the ground faster than that. Stop the madness! Make landing gear better! And putting it only on the bottom is little more than a mocking indifference to the many people killed by aircraft that meet the earth other than bottom-first. I suppose we'll ascribe that to "lack of training," too!
 
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BBerson

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I was reading an article in Sport Aviation by Robert T Jones about floating tip ailerons. Used on the Curtis Tanager STOL.
Not sure how they work better (or not) Seems impractical because of the size.
 

vtul

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BBerson, I haven't either. But two well know ULs, Skypup and Bloop both are 2 axis machines. I'd say 80 % of the R/C models I've flown are 2 axis. I've even flown AE two axis planes, but I was naturally meaning RE.

You can only control return from a bank by speeding up the inside wing. In a bank the inside wing is also at less of a bank angle than the outside wing because of the dihedral (up to a bank angle a little past 90 degrees).

Jedi, It isn't just the removal of ailerons (as a control problem) that makes it different, in terms of a spin. It's quite different with dihedral in terms of lift distribution as a response to control inputs. Neutral control in a bank produces a righting force. A lot of things are different.
 

mcrae0104

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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.
Sure, we can compute the lift distribution for any given aileron position. And if the differential mechanism is well designed, the yaw produced can be close to nil. So why go to heavier, more complex solutions, or ones that result in less efficient lift distribution in cruise (which is 90% of flight for GA)?

...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.
Short of a computer system to second-guess the pilot, perhaps the best that could be hoped for is a system that always results in coordinated flight, and take away the rudder (setting aside for the moment the fact that the rudder does have functions other than correcting adverse yaw). But do any of these alternate proposals save the ham-fisted pilot who turns final too low and too tight for his airspeed? No, he just increases his sink rate and hits the ground.

Everything is a trade and comes with costs. Contemporary aircraft have many compromises built into them.
Thank you; previously it seemed you were advocating a magic bullet that involved no compromise.

I'm not sure how to answer the last question. Did you mean to write spin-prone instead of stall-prone?
Oops, yes. Spin-prone.

The adverse yaw should be corrected by favorably differentiating the induced drag profiles of the left and right wings to coordinate yaw with roll.
Which is precisely the goal of Frise and differential aileron movement. I'll ask it a different way this time: How does an aircraft that produces negligible adverse yaw have "undesirable yawing characteristics?"
 

12notes

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BBerson, I haven't either. But two well know ULs, Skypup and Bloop both are 2 axis machines. I'd say 80 % of the R/C models I've flown are 2 axis. I've even flown AE two axis planes, but I was naturally meaning RE.

You can only control return from a bank by speeding up the inside wing. In a bank the inside wing is also at less of a bank angle than the outside wing because of the dihedral (up to a bank angle a little past 90 degrees).

Jedi, It isn't just the removal of ailerons that makes it different, in terms of a spin. It's quite different with dihedral in terms of lift distribution as a response to control inputs. Neutral control in a bank produces a righting force. A lot of things are different.
If you have passengers, they would much prefer to ride in a plane with ailerons and rudder. The gross weight will be much less on the three axis version, since you won't need nearly as many towels to clean up after any turn made after the drink service.
 

Autodidact

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Here's a polar chart from Norman's article on the Junker's flap; notice that at a negative Cl of -0.2, the profile drag is the same as at a positive Cl of 1.10. Granted, this is not induced drag, but it is a substantial difference and may help if not completely off setting the increased induced drag. Maybe someone more familiar with the mathematical results of these different coefficients (profile and induced) could comment to confirm or debunk my assumption?

J-flappolars.jpg
 

Turd Ferguson

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BBerson, I haven't either. But two well know ULs, Skypup and Bloop both are 2 axis machines. I'd say 80 % of the R/C models I've flown are 2 axis.
No telling how many people learned to fly in a 2-axis Quicksiver MX ultralight. I had a friend that bought one and learned to fly it from a neighborhood street. I believe the FAA essentially used the MX as the model to write Part 103 regs. If there was a place for a resurgence in aviation popularity, that would be it.
 

jedi

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I'd like to see. Do you have a link?
......

Jedi, It isn't just the removal of ailerons (as a control problem) that makes it different, in terms of a spin. It's quite different with dihedral in terms of lift distribution as a response to control inputs. Neutral control in a bank produces a righting force. A lot of things are different.
No link now. I am on my cell phone and don't have an Internet connection for a decent search.

The biggest benefit of two access control is that all turns are accomplished with the correct control input for spin recovery.
 

radfordc

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No telling how many people learned to fly in a 2-axis Quicksiver MX ultralight.
As did I and have several hundred hours in MXs. You can't spin one....at least I couldn't and I tried every way I could think of. Full stall and full rudder and the plane spirals down. Probably not a safer plane made if your happy doing 35 mph.
 
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