I once saw a documentary on making a model pterodactyl (the flying dinosaur). They built the wing skeleton, and then covered the frame with condoms.

But seriously, if you could have a flexible skeleton, the condom (or multiple condoms) will give you a taught, efficient, and flexible skin.

gus

P.S. Strawberry flavoured - glow-in-the-dark wing-tips, anyone?

How about taking the last third of all the wing ribs in a standard symmetrical wing kit, and instead of sparring them together, put them on an aluminium tube "axle". Then near the TE of the wing, cut a groove through each of the last third of the ribs. Through this groove you slide a bent control-rod. As the rod rotates in the grooves, it causes the ribs to rotate on the axle, with the outermmost ribs moving the most. Cover the ribs with the above mentioned condoms, and voila, you have a tiperon.

gus

There's a certain amount of unpredictability in this configuration that no one has mentioned. Imagine the tip loads you will get in a gust... Transferred to the tiny little torque tube holding the tiperon in place! Try using a large hollow torque tube. You know what I mean? Use a lot of supporting structure too. This is probably why they are not used on traditional aircraft.

You will be able to achieve a high angle of attack (with attached flow) due to the geometry of the tiperon... essentially a low aspect ratio wing... at the end of a wing. I mentioned using an end plate before. You may want to try putting an end plate before the tiperon as well. Maybe just a cuff... anything to help keep flow attached to the main part of the wing.

Ken - www.litkoaero.com
R/C Laser Cutting and Design

I had not mentioned how I was going to construct the tiperon and move it so that others may possibly suggest better configurations than what I was thinking of. Nice to see someone came up with the same idea that I thinking of.

I'm seriously thinking of putting small end plates on both edges of the tiperon (tip and joint). It's a pitty because I wanted to keep the wing looking clean. I hate it when a plane looks like a lab experiment with stuff hanging off it all over the place.

-Q.

Yip, I'm aware of their roll control methods.

Not my style, I must say. The thought of a wing warping reminds me of sitting inside a Beoing-747 and watching the wings flap in severe turbulance. It just feels queezy.

-Q.

I just started reading this interesting post and I wanted to share a thought that I had. It was initially stated that these control surfaces are intended for an aerobatic plane. If this includes 3D style flying then a lot of time is spent hanging by the prop and high angle of attack flying where the relative airspeed is close to zero. The only thing that allows you to control the plane in this flight mode is the blast created by the propeller. Obviously this blast is stronger close to the fuselage then at the wingtips (close to zero). Now if it is only the outer 1/3 of the wing tip that is movable then the roll authority of the "ailerons" should be close to zero.

Something to keep in mind if you intend to do 3D. If you intend to do more pattern style flying then this should not be a big issue.

Christian

Good eyes there Christian. I missed that in my enthusiasm over something different.

a088008?

Don Incoll in Australia did this some time ago....

A key passage in the technical report is ...

........ as flow over the wing became parellel to the aileron hingeline (ref.2). The tiperons, designed to take advantage of this spanwise flow, remained effective at higher angles of attack .......

That paticular geometry is not any more effective than a regular aileron when used on unswept wings.

Notice that the configuration (supersonic capability with a high alpha maneuvering range) that they did test didn't include the all moving tip roll control device.

You are quite correct about the prop wash aspect. My intention is, however, pattern style flying and not 3D. I do, however, plan to build something with 3 (three) props that is intended for 3D. All I can say at this point is that there will be prop wash on ALL flying surfaces.

-Q.

Well ... I'm speachless. I don't know how to respond to the picture.

Ok, I'll try: It's the ugliest thing I've ever seen. I thought I hated those flying lawn mowers and witches, but this takes the cake! Yuggghhhh!

-Q.

Good eyes, Ben. I know I can count on you to keep us armchair designers honest. I did also notice in the article that they used thrust vectoring, and they coupled conventional ailerons to the tiperons. It seemed they were trying out quite a few concepts and trying to marry them together. They even included feedback in their aileron/tiperon coupling.

My design goal is merely to investigate a tiperon in a conventional aerobatic plane not unlike a CAP or Giles. I feel the tiperon has merit and hope to prove it useful. I may, however, be way off base but nothing ventured nothing gained.

-Q.

One thing to mention about using the tiperons.

It has the advantage of only needing to create a small lift differential to achieve an equivalent amount produced by conventional ailerons since the tiperon operates more toward the tip of the wing. Now, the wing tip does suffer from decreased efficiency of lift production due to the drop in pressure difference at the tip. However, this means that the tiperon is not sygnificantly changing the overall lift produced by the wing. This should allow for a more axial roll and less severe drop in lift when a snap occurs due to one tiperon stalling.

Does anybody else want to guess at the characteristics of a wing with tiperons? All predictions of both good and bad characteristics are welcome.

-Q.

I got this far a couple years ago...
Did the chuck glider thing to try to find a useable c.g.
I was going to use an OS 15 but decided the plane woulg have too high a wing loading to be flyable.
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Now that I'm back sloping it could be flyable as a glider. If I can find the other wing tip. Uses an MH 42 section...

Let me encourage you to finish it, good stuff, but the hinge line seems a little aft.

Any reason you went for a tiperon, instead of ailerons?

I'd love to hear how it flies, so find that wing tip for us!

-Q.

I agree that the hinge line is a little aft, but your tip area is not large. I don't think it will be much of an issue, unless you fully deflect at 100 mph!

-Q.

If nothing else, that sharp tip will create a nice bound vortex. I don't know if it will create much -lift- for it's location and size, but it probably won't stall that easily!

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Some time back someone asked why deltas always had the pointy end at the front.
So I ginned up this thing... (chuck glider shown)
The r/c version has sufficient wing area to be useful as a glider, but I'm dreading the toss-slide-down- the- slope-puff-back-up-the-slope-fix-toss routine of finding the proper c.g., and whether the odd placement of the elevators gives them any control at all. And the bending of the axles for the tiperons....

"Wouldn't it be great if the skin of our plnes could just move the way it needs to move, without any control surfaces at all? No gaps, no mechanical linkages, more options... (Really just more sophisticated, effective wing warping) "
- Mike James

Well, we're not quite there, but I have been working for some time on a 24" morphing platform. The airplane, lovingly called "Morpheus", has a flexible, thin-undercambered wing surface that can be articulated to generate roll moments. The mechanism, which is intentionally simplistic, consists of a set of torque tubes that run from the fuselage to approx 3" from the wing tip. The structure of the wing is entirely carbon fiber, with a relatively stiff leading edge and carbon fiber ribs that extend from the LE to the TE. The trailing edge is left open. The wing is covered with a thin nylon (vacuum bag), which is both strong enough to withstand flight loads and flexible enough to allow the wing to deform.

I'm using two TS-15 mini servos for the actuation, which yields approx. 15 degrees deflection each way. Since the torque tube only connects on one rib, the rest of the structure morphs in compliance. It ends up having a nice linear taper from the torque point back to the root, and flares out the twist similarly towards the tip.

In flight, Morpheus is pretty much amazing. The previous configuration of this airplane used strictly rudder-elevator for control, which was enough for just flying around. With the addition of morphing control, however, the roll command is SO much nicer. At full deflection, it will roll approx 3 times per second. I've never actually counted it, as many times it's too fast to see (especially given the size and 60-70MPH speed). What's especially nice is that it rolls very axially... you can watch the spinner stay nicely centered as the wings roll madly about it in the whoosh-whoosh-whoosh sound.

There's another interesting aspect to the Morpheus and likely the airplane that Mr. a088008 is working on - spin control. I unintentionally came across some extremely amusing spin characteristics with the morphing wing throughout my flight testing. It turns out that gross deformation of the wing surface, or gross deflection for that matter, can "stall-on-demand" and induce very violent spin behavior. In particular, a snap-spin entry with the Morpheus will cause just an outrageous tumble initial and will very quickly decay into a variety of vertical spins. My favorite one is a cyclic/periodic spin mode, where an inverted snap entry will cause the plane to snap roll, spin for a few revolutions, then stop...pause, and snap-spin again.

This behaviour is repeatable and occurs during constant control input. i.e. with the sticks hard over, you can simply watch as it goes through this bizarre repeating spin pattern. The flight data from this maneuver shows that roll, pitch, and yaw rates are equally affected by the spin, and that the repetition occurs on all three axes.

If you're interested in the paper and some pictures of the airplane and morphing deflection, go to http://mil.ufl.edu/~mujahid/publicat...ASD-US-241.pdf

I suspect that the tiperons will result in similar behavior, both in roll rate achievable and in other affected characteristics. Likely the only way to find these out is to build it and fly it. Just be ready to chop the throttle and recover in case things get hairy.

Best of luck with the tiperon project!

Joojoo,

Are you sure that it is actually stalling and not maybe a coupled control?

JooJoo, very interesting.

Have you tested the same model with conventional ailerons to see if the morphing is really giving anything more. I noted that a similar configuration was flown rudder, elevator but that is not a good comparison. A direct comparison would be interesting, with ailerons, to see not only if airplane response would be the same but if the work to do the morphing wing was worth the results even at the MAV scale you are working at.

At any rate it is a project worth doing and reporting on because it is certainly a chance to get new good data.

I am not too certain why you didn't measure the servo deflection on the ground and assume that it was approximately that in flight and use that for the input control angle. Granted the morphing makes a representative angle difficult to define, maybe average value across the morphed area.

Years ago at McDonnell Douglas we were trying to use a least squares method to analyze flight test data. This was in the infancy of the process. We had just stopped using punch cards the year before. When we could finally convince the pilot to give us a good stick input the answers still were not too great and we gave up on it at the time. Thank goodness things have progressed. I am impressed with the minaturaziation of your electronics. It makes small airplane investigations practical.

Were there any flutter concerns with the flexible wing?

Mujahid, did you ever get any successful tests with the flutter models I sent you?
"Curmudgeon Paul"

KenLitKo,

I cannot be certain that it is in fact a stalled condition during extreme morphing as I have only done flight tests with it. Besides, as Paul might tell you, I don't have the best record in the wind tunnel (more on that later). We've never put this particular model in the wind tunnel, so honestly I have little idea what is going on in terms of the lift distribution over the wing or any other measure of flow property.

My statement "stall-on-demand" is not to say that you can simply deflect the wing as you would ailerons and have it stall. For one, the rotation will substantially change the actual angle of attack the wing sees. So in that sense, it is very much a coupled effect. For my brief spin tests, I found that morphing the wings in conjunction with initiating a conventional spin/snap entry will aggravate the effects you'd already expect to see. For instance, if you look at the control input plots, you'll see that up-elevator and rudder deflection are given. Normally, this will give the benign textbook spin. With morphing command, however, the response is far more violent and has other transient characteristics.

A brief sidenote, I've encountered several instances of control reversal on the 10", 12", and 24" morphing planes. This is where the wing is twisted or otherwise deformed too much and the increase in lift suddenly turns to a complete loss of lift. This results in a very undesirable death spiral in the opposite direction to the command.


Ben,

No, I haven't tested the same model with ailerons. I agree 100% that comparing rudder and aileron or morphing is not a fair comparison, but do keep in mind that much of this argument is based on how well it can be implemented on a flexible membrane wing. Part of the difficulty we've had with other vehicles has been compromising between the beneficial effects of a flexible wing (giving rise to adaptive washout and disturbance alleviation) with the need for positive wing control surfaces.

Note, however, that Morpheus is a direct descendent of a flying wing model that DID have elevons. This is the one airplane I have the most number of flight hours on, so I've tested this fairly extensively. Granted it is difficult to compare the responses of a flying wing to a conventional configuration, but we are strictly talking roll effectors. The two airplanes share the same wing, differing only in the airfoil used (reflexed for the flying wing, undercambered for the Morpheus). The flying wing (called the TooGruven) will roll at a maximum of 450 degrees per second. Definitely nice, but not nearly as fast as can be achieved by morphing.

With regards to the control deflection, I thought that we did exactly what you said! I hacked the servos to use the potentiometer for feedback and assumed that this was always representative of the extent of morphing or surface deflection. This, as you say, is not considering the effect of airloads. It should be good enough though for a close approximation.

Throughout the flight testing, which saw motors ranging from an AstroFlight 010 to a dynamite-like-power Hacker B20 15L, I have never seen any instance of flutter on this model. It will occassionally make a buzzing sound as it flies by, but I suspect this is due to the torque rod vibrating against the fuselage exit hole.


Finally...

Paul!!

My last post on RCO was the extent of my work on the flutter model. I still have it with me, but shortly after we stopped discussing it, the wind tunnel was moved to a different lab where I no longer have free and easy access. My only conclusion was that flutter is a frustrating problem that is not easily understood. One thing to note, however, I DID learn that we were not after flutter at all. Supposedly, the phenomenon we were engrossed with is actually called control surface buzz. This is said to be different from flutter, which is a divergent interplay between aeroelastic and aerodynamic forces. Flutter, as was explained to me, involves gross deformations of the structure, not simply a control surface resonating and flying off.

Whatever the symantics are, both are highly unpleasant. I recently lost an airplane to flutter. My venerable Telemaster... workhorse of the lab never came out of a simple barrel roll. Apparently, the wing structure had weakened in many months of storage, likely causing aileron reversal as the plane continued to spin and eventually oversped. On the way down, I tried to push forward and input opposite control to recover... only managing to smash into the ground in a shallow inverted dive.

The plane itself is a total loss, but the pan-tilt video system and all the electronics appear to be ok.

Thanks again for the awesome thread!

Mujahid

"A brief sidenote, I've encountered several instances of control reversal on the 10", 12", and 24" morphing planes. This is where the wing is twisted or otherwise deformed too much and the increase in lift suddenly turns to a complete loss of lift. This results in a very undesirable death spiral in the opposite direction to the command. "
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Mujahid, this sounds exactly like what happens with flaperons at full down extension. When a roll command is issued, the surface on the upgoing side reduces the drag on that side, while the other side is already at maximum deflection. The drag on that side stays the same, so the result is a turn towards that side, opposite the command. Disconcerting to feel and see.
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The prevention is don't deflect the surface that much.
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Your morpher resembles a Taube... you might consider morphing the horizontal as -tailerons- instead of warping wing, if manuverability isn't a primary concern.
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There's another thread here or on E-zone where an obstacle avoidance system is being developed . Something like that would ease the strain on a reat-time pilot flying remotely.
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The stuff you get to play with! I'm jealous!