Experimental Aircraft Control Concept: Raked Swing-Wingtip

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REVAN

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I'm spinning off this new thread from the thread Anti-Spin Ideas - http://www.homebuiltairplanes.com/forums/showthread.php?t=27801

There, I had proposed the concept of using a wing design that replaces the standard aileron with an outboard raked swing-wingtip that would trade sweep and polyhedral for span, area and washout angle. I drew this concept on a Sportsman. The question here is to gather ideas for what would be the best aircraft choices for a testbed on which to test an idea like this. The second goal is to reach out to see if anyone is working on a project for one of these candidate aircraft that may be interested in incorporating this in their project to demonstrate efficacy.

This quote from the other thread is brief summary of the concept.

A Hershey Bar wing modified with a raked swing-wing tip as was described in the pdf file posted earlier may be completely yaw stable, exhibiting proverse yaw characteristics. While the fuselage will still need a vertical stabilizer to make the fuselage yaw stable, a wing as described here may remove the need for a rudder.


Neutral control position:
View attachment 62910


Left turn control deflection:
View attachment 62911


Right turn deflection:
View attachment 62912


Superposition:
View attachment 62913


Superposition from the front:
View attachment 62914


What's good about this type of concept is that when raising a wing to turn, the wing tip swings forward. When this happens the tip speed increases, and the span increases. With a higher 'q' and a more efficient span loading than the other wing, it will both climb and accelerate, affecting a coordinated roll and yaw without the need for any rudder input from the pilot. This is the desired control behavior for a wing to have.

I believe a wing of this design should exhibit proverse yaw characteristics in normal flight. Furthermore, in a stall, the pilot should be able to fly the plane with the stick the same as when the plane is not stalled (i.e. - stick left to lower left wing, stick right to lower right wing). The benefit being that the pilot does not need to recognize the wing is stalling and mentally change from stick control to rudder control to prevent spinning the plane. One control law for the pilot simplifies task loading and reduces the chances for pilot error contributing to an aircraft loss of control.
 

TFF

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With anything that moves, it either has to have a fail safe position or have enough control to fly with all deployment options
 

Victor Bravo

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Seems like a pretty neat idea in terms of aerodynamic effect. It appears from the graphics that it was designed in such a way that as the "Swing-Tip" (that's the name you need to use for this... go trademark that :) :) :) ) creates a little more drag as it moves aft, creating the proverse yaw effect.

The big problem with all of this, of course, is that in order to make this work on an actual airplane you will have to deal with an awful lot of loads and stresses out at the tip where the wing structure usually gets lighter and thinner. The entire wing structure is going to get heavier and stiffer in order to deal with this, as well as the mechanical linkages and hardware to make it all work. There's likely going to be about a five or six inch diameter pivot of some sort (or upper and lower Lazy Susan device) in order to deal with all those loads.
 

Victor Bravo

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What is the advantage of the swing-wing-tip over just having a large spoiler or Schempp-Hirth airbrake on a fixed wingtip? The spoiler is crude and low-rent, but I believe it would have the exact same net effect, without all the complexity of variable sweep.
 

REVAN

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What is the advantage of the swing-wing-tip over just having a large spoiler or Schempp-Hirth airbrake on a fixed wingtip? The spoiler is crude and low-rent, but I believe it would have the exact same net effect, without all the complexity of variable sweep.

If a wing is stalled the spoiler will have little authority over the roll angle.

The advantage of this raked swing-wingtip or "Swing-Tip" is that even if the plane is in a deep stall and descending near a 1:1 glide ratio, the control device will differentiate both the wing area and the wing span in such a way that the pilot should be able to control the plane's roll angle with the stick the same as if the plane were not stalled.

With authority over roll, the pilot won't need to take any unusual action to prevent the plane from spinning, and recovery from the stall is as easy as reducing the AOA. With a stable stall, there is no need for spoilers or speed brakes. The wing can be used as a speed brake, which expands the plane's performance envelope and ability to shed energy when needed. Also, the plane can be flown close to the stall speed without major concerns over being surprised by a spin. Plus, the raked wing will make the plane more efficient by reducing induced drag. The hook is that pilots will want it for better performance, but it comes with the safety and improved control.

On structural loads, only the wing tip is moving. On a plane the size of a sportsman, we're looking at a relatively small segment 6 to 7 feet long that is lightly loaded from sweep and washout. The structural hinge will be very lightly loaded compared to a full swing-wing such as is on a B-1B, F-14 or F-111. If those planes could swing the whole wing, this should be easy by comparison.

Feel free to recommend or volunteer RC model testbeds as well. I'm not an RC modeler, but it'd be great so see someone do something with this.
 

BJC

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How powerful, relative to normal 1.3 Vso roll power, will the tips be in knife edge flight with zero lift on the wing, i.e., when upset by wake turbulence?

Thanks,


BJC
 

Victor Bravo

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Feel free to recommend or volunteer RC model testbeds as well. I'm not an RC modeler, but it'd be great so see someone do something with this.

Well, this is a perfect candidate for a larger generic R/C trainer type airplane, with the addition of onboard video or data collection. The classic choice would be the 12 foot span version of Hobby Express' "Telemaster" aircraft (formerly Hobby Lobby), because this model has been used for soooo many different exotic uses, tests, etc. The 12 foot span version is also a lot more "heavy duty" construction than the original 8 foot "Senior Telemaster".

The 12 footer will give you plenty of room for a whole lot of data recording equipment, room for ballast weight to experiment with different loadings and stall speeds. It will also provide a lot of wing area for tuft testing, "oil test" paints, etc.

Depending on the speeds and aerodynamic fidelity that your testing requires, I would possibly suggest replacing the angular "stringered" wing leading edge with a balsa or thin plyqood "sheeted" style construction so that you get more realistic airflows over the top surface of the wing at low speeds.

tele1.jpg
http://www.hobbyexpress.com/12_foot_telemaster_arf.htm
 

Sockmonkey

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If you had rotating wingtips for roll control, you could also link them to the elevator control so that they would both pitch down when you pull back on the stick and still have them move differentially like elevons on darts and flying wings do.
It would prevent tip stall and maintain roll control when the rest of the wing stalls.
 

wsimpso1

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REVAN,

Have you done a thorough search of the internet and patent databases to see if anyone else has done a scheme where roll/yaw control is achieved via variable configuration of the wing tip. Get creative about the words you use in the searches, as other inventors may have used a different taxonomy than you are. Seriously, if in 114 years of powered flight someone else has not thought of this, I would be very surprised. Remember also the old adage "Every man has a good idea that will NOT work".

You need to recognize that nobody sane will just jump in with adding your scheme to their pride and joy without a lot of reason to believe it will work and motivation to play in this area. Long before you go building one in a full sized airplane, you need to man-rate it. Flight simulation and RC demonstrations of the entire flight envelope are not strictly required but are the responsible way to go. I suspect that this is actually going to be entirely on you.

You have to do some modeling (detailed calcs) and then some computer based flight simulation before you should build any flight article. I assure you that surprises await, and they will mostly be bad surprises. They always do when inventing... I understand that your scheme is to use a vertical axis for your angled winglet and to simultaneously change the angle of attack and the span of winglet, but there are a bunch of things that have to made to work from the beginning. Try to remember that there are many ways to screw up a good idea and conclude that it won't work. If there is a workable scheme in there, you really want to find it and eliminate ways it will not work as early as possible.

First is you will have to size these winglets, determine correct dihedral and hinge angles, how far the controls should swing, etc, and get the hinges and actuation worked out. You may need to make significant adjustments to size, shape, airfoil, hinge orientation, etc. Adequate roll/yaw initiation and termination over the entire clean and flapped envelopes as well in the stall/spin entry/snap roll entry regime will have to be assured. You will have to determine the bearing loads for the system as well as determine the wing's new shear and bending moment diagram, and perform an analytical check that the testbed wing is up to these loads. You will have to determine control loads and travels required to operate over the envelope, and come up with ways to apply these loads. These are all doable, but you should have a pretty good idea what your loads are and then build/modify to suit. Trial and error is NOT an efficient way to do any of this.

I strongly suspect that the control moments in the swing tips as sketched will be huge, totally out of scale for a human stirring a conventional stick, so, you should start thinking about how to make these tips aerodynamically balanced. Schemes used on large airplanes with unpowered controls have included shifting the hinges aft, use of tabs geared to servo the surface, and all flying tabs where you do not move the big surface, you move the small surface and the small surface moves the big one. Sure, there will be some counterbalancing through the linkage from one side to the other, but you need to know the magnitude of these loads so that you can actuate the surfaces. It would be bad indeed to get airborne and then find out you can not control the airplane in roll.

You will also need to do some fail safe design work. If the control linkage comes adrift on one side, can the airplane be flown and landed with only one winglet being moved? The winglet that has lost its control connection must not hinder your ability to fly the airplane with the one that is still connected.

No, I am not interested in doing the analytical work or building any of it.

Good luck with the project.

Billski
 

REVAN

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How powerful, relative to normal 1.3 Vso roll power, will the tips be in knife edge flight with zero lift on the wing, i.e., when upset by wake turbulence?

The answer will depend on the final tip geometry one settles on. This may be one of the design considerations to gauge against when determining efficacy of a particular geometry. Although I expect to have positive roll authority at zero-G, it will likely be reduced from the 1-G roll authority. At what point would you consider the zero-G roll authority to be inadequate, knowing that a little back pressure on the stick will increase it?
 

BJC

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The answer will depend on the final tip geometry one settles on. This may be one of the design considerations to gauge against when determining efficacy of a particular geometry. Although I expect to have positive roll authority at zero-G, it will likely be reduced from the 1-G roll authority. At what point would you consider the zero-G roll authority to be inadequate, knowing that a little back pressure on the stick will increase it?
Sure, back pressure could increase it, but that may not be acceptable in a recovery from a wake turbulence upset. It also violates your criteria of being able to control the roll axis with just one control input.


BJC
 

Aesquire

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I haven't quite figured out how your system works, but testing it should be simple.

Paper airplanes. Build a Barnaby Special, then bend each tip to see the effects in the real ( if small ) world. Bend one side, expect a spiral flight path. bend both and see what pitch effects you get. A ream of printer paper, a roll of Scotch tape, and a room reasonably free of furniture, and you've got Micro-Edwards at your disposal.

Best is that injuries are at worst minor paper cuts, or falls from over zealous launches, and mistakes or breakthroughs can be sanitized in the fireplace so they can't fall into the hands of an enemy spy.

The Barnaby Special is the greatest design, ever. Stable, stunt capable, good glide, and simply by skipping the cutting, adding elevons to trailing edge, you've got a plank. ( The use of tape to hold the leading edge spar fold may be cheating in origami. Who cares? it's composite construction. ) Planks are less stable than the Barnaby, and may be a better choice to see yaw effects, the Barnaby is very yaw stable.

http://howardfink.com/?p=66

Notes: The kink in figure L is not needed. The inverted V tail acts as horizontal stabilizer with downforce, and the angles also provides powerful yaw stability. At the cost of drag. You will notice that by reducing the angle of the tail, glide performance improves, at the cost of pitch stability, until before you reach zero, there is no longer enough downforce to balance the wing's pitching moment.
 

REVAN

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How powerful, relative to normal 1.3 Vso roll power, will the tips be in knife edge flight with zero lift on the wing, i.e., when upset by wake turbulence?

The answer will depend on the final tip geometry one settles on. This may be one of the design considerations to gauge against when determining efficacy of a particular geometry. Although I expect to have positive roll authority at zero-G, it will likely be reduced from the 1-G roll authority. At what point would you consider the zero-G roll authority to be inadequate, knowing that a little back pressure on the stick will increase it?

Sure, back pressure could increase it, but that may not be acceptable in a recovery from a wake turbulence upset. It also violates your criteria of being able to control the roll axis with just one control input.

That didn't answer the question. Please let me know if you have a recommendation and the criteria/justification for a particular zero-G roll rate requirement.

I looked on Wiki for a roll rate spec on a Diamond HK36, but didn't see anything listed. It seems that may be a reasonable place to start discussions for a zero-G roll rate spec. Anyone know what the roll rate is for that plane or some similar motor glider?

Also, does anyone have any figures for wake turbulence crashes relative to stall-spin related crashes? Personally, I've never experienced a wake turbulence incident and don't have a feel for what it would be like. Seems like it would be a rare and largely avoidable condition. That is, it's easier to avoid flying behind a big heavy on takeoff and landing, than it is to avoid flying close to the stall speed on takeoff and landing.
 
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REVAN

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I took a look at this accident:
[video=youtube_share;KXlv16ETueU]https://youtu.be/KXlv16ETueU[/video]

It looks like the wake turbulence set up the roll condition, but it was the application of the aileron to fight the wake spiral which led to the right wing stalling and then dropping in the initiation of a spin condition that caused the crash. As I'm seeing it, loss of aileron authority due to flow separation is how the plane got to a 90 degree bank to begin with. It could have gone better if the plane had been flying faster so that it had more AOA margin to the wing/aileron stall, or if the design was more robust against stalling a wing that is being command to rise quickly at low speed.

Maybe the zero-G roll rate is not the most important factor to consider here.
 
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pictsidhe

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I haven't quite figured out how your system works, but testing it should be simple.

Paper airplanes. Build a Barnaby Special, then bend each tip to see the effects in the real ( if small ) world. Bend one side, expect a spiral flight path. bend both and see what pitch effects you get. A ream of printer paper, a roll of Scotch tape, and a room reasonably free of furniture, and you've got Micro-Edwards at your disposal.

Best is that injuries are at worst minor paper cuts, or falls from over zealous launches, and mistakes or breakthroughs can be sanitized in the fireplace so they can't fall into the hands of an enemy spy.

The Barnaby Special is the greatest design, ever. Stable, stunt capable, good glide, and simply by skipping the cutting, adding elevons to trailing edge, you've got a plank. ( The use of tape to hold the leading edge spar fold may be cheating in origami. Who cares? it's composite construction. ) Planks are less stable than the Barnaby, and may be a better choice to see yaw effects, the Barnaby is very yaw stable.

http://howardfink.com/?p=66

Notes: The kink in figure L is not needed. The inverted V tail acts as horizontal stabilizer with downforce, and the angles also provides powerful yaw stability. At the cost of drag. You will notice that by reducing the angle of the tail, glide performance improves, at the cost of pitch stability, until before you reach zero, there is no longer enough downforce to balance the wing's pitching moment.

I just looked across the room at a small, low Re open wind tunnel. Well, it's missing about 6000 drinking straws stacked behind it. A box fan, If you 'built' several paper or foam models, each with different tip swings, you could tether them to the 'tunnel' film them and see how fast they roll and and with what sideslip. Or you could go highbrow and mess around with force balances etc...
 

REVAN

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...does anyone have any figures for wake turbulence crashes relative to stall-spin related crashes? Personally, I've never experienced a wake turbulence incident and don't have a feel for what it would be like. Seems like it would be a rare and largely avoidable condition. That is, it's easier to avoid flying behind a big heavy on takeoff and landing, than it is to avoid flying close to the stall speed on takeoff and landing.

From: https://flightsafety.org/fsd/fsd_mar-apr02.pdf

It looks like there were 130 wake turbulence accidents in the US from 1983 to 2000, an average of about 7 per year. That's got to be a lot lower than the number of spin accidents, but I'm having trouble finding an actual number for that that's not a percentage.
 
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