[Bob Kuczewski]

Excellent video find Rick!!!!

As Frank pointed out, imagine how that could be built with today's materials!!

[Rick Masters]

It is exciting! Our flying wings could bend like a bird's wings under extreme loading, gaining dihedral and stability, then instantly pop back to a performance configuration when the turbulence is gone. Perhaps this is the way to true variable geometry in freeflight because a wing "cast" with sets of different length threads inside, each of which define a distinct airfoil shape at a certain pressure, could conceivably be designed - the fastest and best l/d at the highest pressure, ease of handling and landing at lower pressure, perhaps even varying pressure from side-to-side for thermaling or steering combined with weight-shift.*

The Holy Grail would be a correct bird-like flare powered by a charged carbon fiber canister. It's awesome to think about.

And a lightweight solar-powered diaphragm pump using paper supercaps (or leg-powered piston pump) could keep the wing pressurized if a small leak developed.



*Weight-shift is fun. All you rigidwing guys can go pound sand.

[KaiMartin]

I'm imagining that a 25 lb hang glider could be built using modern material like my packraft uses.

Hi Frank.

Did the brain behind Alpacka Raft provide you with some numbers to fuel the imagination?
Specifically:
* What is the weight per m² of their recommended hull material?
* What is the maximum tensile stress they would recommend for their material?
With these two parameters an inflatable Alpacka based wing might take the step from wishful dreaming to reality based day dreaming.

---<)kaimartin(>---

[Frank Colver]

I don't know much about the materials except these things: The standard Alpacka packraft product line is urethane coated nylon and is inflated only to lung pressures. It is definitely not rigid enough for our use. Not only because of the low pressure but also the base material (stretches) and the type of weave.

However, The Vectran material that the boats like mine are made of is a base cloth of a newer generation material that is somewhat like Kevlar and is a diagonal weave. It is very light and strong and very low stretch, unlike nylon. I pressurize it with a hand pump to two lbs and the boat is very rigid at that pressure. The seams are sewn with thread and then RF heat welded with a tape. I posted a link to the Vectran manufacturer's description of the material earlier ( a few months back) in this thread when I was posting about inflatable possibilities and also referring then to my packraft. I highly suspect that the Air Force inflatable drone experiments used this material. The Mexican border surveillance balloons use it also.

I don't think that the dropstitch type construction is available with this material so shaping a wing like Goodyear did would be difficult. It would probably have to take a flexwing approach where it is a sail supported by an inflatable spar and leading edges. Another technique would be to use different diameter inflated tubes and then have an outer sail cloth covering top and bottom to smooth out the wing shape. That would be heavier but very rigid since it essentially would be a wing of many spars. Sort of a tapered air mattress with different diameter ribs. That's what I had in mind when I mentioned it being a rigid wing with roll control surfaces (also inflated).

I love to watch the look on a person's face when they pick up my boat the first time. Total shock at how light it is. Because of it's size they expect 30 or 40 pounds not 6-3/4 lbs. I often pick it up with one finger to show how light it is. When deflated and rolled I keep it in an REI small day-pack.

River runners are hiking distances to rivers, with these boats, that would have been thought impossible 10 years ago. They usually are using light carbon breakdown paddles also.

One of these days Joe F will come to my shop and see my boat and then I think he will be inspired with many HG design ideas.

Frank

[JoeF]

Distinct:
Festo Air Ray


Flying Mobula Ray
http://blogs.bu.edu/biolocomotion/2011/09/26/the-flying-mobula-ray/

[Harry]

It may fly but can it swim like this thing?

[KaiMartin]

CONTROL.

I totally agree.
There are some aspects where even small improvements would make a difference.

1) roll
Mainstream hang gliders show frighteningly slow roll rates. This makes hill launches more risky than they should be. If the wing is for some reason slightly skewed on take-off, there is often not enough time to correct before the flight path deviates beyond recovery. Almost all footage of failed hang glider launches on youtube seem to be this kind of mishap.

2) yaw
Mainstream hang gliders do not provide any means to the pilot to directly affect yaw. The glider totally relies on the strong pointing moment induced by the sweep of the wing. This is both good and bad. It automatically counter acts adverse yaw when initiating a roll. But it also means, in order to yaw, the pilot has to initiate a roll and wait for the adverse yaw to be overruled by the sweep induced yaw. It also means, we cannot pull off a slip like the sail-planes do to great effect to increase descend rate.

3) transition into stall
Flare landings depend critically on the ability to put the wing into deep stall at will. Unfortunately, there is a conflict of interest. To achieve pitch stability during normal flight, our wings are configured so they try to return to trim pitch by itself. Certification procedures like the ones by the DHV explicitly require the wing to return to trim by itself after a moderate stall. As a side effect this necessarily means the centre of the wing will stall significantly before the tips. Since the lift of the outer wings applies more to toward the back, we get a strong nose-down torque just when we want the nose to go up fast.
If this counter productive nose-down torque could be eliminated, landing a hang glider would turn into a complete non-issue. IMHO, any other means to improve landing abilities can only provide marginally effective band aids.

It is not all bleak, though. We do have good pitch control during glide. It is easy to achieve whatever attitude the pilots intends. Want to go faster? Just pull in as much as you want. There is little delay, no coupling to other modes of movement, no control reversal and control range covers the whole envelope. An ideal hang glider should achieve the same for the other rotational angles, too.

---<)kaimartin(>---

[Dayhead]

Thanks to everyone posting here.
I'll be eagerly awaiting criticism of some ideas I'm presenting here. Don't be afraid of hurting my feelings, I can take it. I think this topic is an important one, and I find the subject to be a fascinating one.

In watching the Ravens playing on that windy ridge, with large boulders and big bushes everywhere, I realized that maximum control and good streamlining is want I want in a HG.

The inflatable concept has some promise, I think. Perhaps a hybrid could be designed, where we would have a rigid spar, perhaps telescopic or foldable, but for a first effort it's not that important. Wire bracing could be an asset as well.

Basically what I'm getting at is that for a revolutionary new design, it's probably a good idea to not bite off more than you can chew at one time.

I see this topic as covering a wide range so far. While that is interesting, I've decided that just for myself, I'm not going to try too many new things at once. For example, the portability issue isn't that important to me, personally.

What is most important to me is the Stability and Flight Control issues.

For some time now I've been questioning the wisdom of staying with the swept-aft wing planform.

It is understandable why we embraced this planform in the beginning, and for very basic hang gliders, such as trainers and intermediates, it may still be the way to go.

As Kai mentioned, there is a conflict between stability and flight control. This issue has been with us for as long as aviation has existed. I was impressed when the F-16 Falcon jet fighter was introduced, because AFAIK it was the first production aircraft to have "artificial" stability in the pitch axis. The computer allows the plane to be more like a bird, which can use it's tail for more lifting surface. The F-16 was tail-heavy, and so with computer control, the plane could turn tighter and pull more G's, due to the tail being used as a lifting surface.

There's a lot of interesting stuff going on in the RC model area now. Modern airborne radio receivers have various stability enhancement systems, you can go to RCGroups.com and find more info if you're so inclined. And of course there's the "drone", usually multi-motored sorta/kinda helicopters. They have computer controlled stability, and the "pilot" merely tells it where to go. They use GPS for navigation. There use is getting a lot of bad press due to irresponsible operation by a few idiots.

But I mention the above because these systems are small, light-weight, and affordable. And if properly harnessed, they could make HG's more controllable and also more stable as well.

Now like most others, I don't totally trust cheap Chinese assembled circuit boards, and so if I were to use any of that stuff, I'd want a a string or lever I could pull that would disable such a system, and allow me to return to a "default" condition of purely manual control and inherent aerodynamic stability. But there's some fascinating meditation material there....

The more I meditate on it, I think a wing planform having little or no sweep, and possibly a little forward sweep, may have some advantages. A bird-like tail, that can float upwards during the landing flare, makes some sense. Another place where such a tail might help is when flying in turbulence.

When you watch the smoke from a campfire, you can see a model of thermal activity. On the edges, where rapidly rising air is mixing with cool air, we often see "rotors", where air is spilling outwards from the thermal.

It is my belief that the atmosphere is alive and complex, and there's no one single explanation for why a HG can get upset by air currents. That said, I believe that most of the "over-the-falls" tucking incidents were caused by my flying into this "outflow" I described above.

Flying into a tailwind suddenly reduces airspeed, the glider drops, the AoA goes up dramatically, and our swept-aft wing tries desperately to get back to it's trim condition, by nosing down rapidly. An inexperience pilot will instinctively push out, or do nothing. If he pushes out, the AoA will remain high, and the nose-down moment can result in further rotation.

Way back in the late '70's, Gary Valle and others studied this stuff, and what they decided we should do is design and build gliders that would have gobs of positive pitching moment whenever G force went low, which of course is usually the case when the glider points straight down. This was achieved primarily by reflex-inducing cables and also washout struts. I remember folks saying that the washout struts were there to twist the leading edge tube off of the glider if it inverted, This was a sick joke, but did seem to be the case sometimes, and may be the reason why some gliders dispensed with the struts and went to extra "luff lines" mounted further outboard than the gliders with struts. Of course, those long bridles created more drag than washout struts. So now we have topless gliders with extra washout struts, or "sprogs", if you prefer surfer dude lingo to the drier, more conventional aeronautical terminology.

Over the years since that time, I meditated on all this and came to the conclusion that this design philosophy concentrated on treating a symptom, and wasn't considering the cause.

The "cause" of course is the strong negative pitching moment induced by having a high AoA.

The problem with our current understanding of the situation is that we need a negative moment to provide feedback to the pilot when the AoA is at a higher positive value than it should be, so that we won't inadvertently stall the glider.

And so I propose a different approach to this problem.

We get rid of most or all of the Aft-sweep in the planform. We use a hinged tail, which can be an integral part of the wing root chord area, like a bird does. In normal flight, the tail simply streamlines, and has only parasitic drag. But the hinge only allows the tail to lower a certain amount, so when the AoA is lowered to a certain value, the tail provides a nose-up moment, just like our currently used washout struts and/or luff lines do today.

Since the tail can "float" upward, it would allow the the glider to have little or no negative moment at high AoA. This would reduce the tendency of the glider to nose down when it is "kicked in the a**" by a rogue air current spilling out of a thermal, thereby reducing tucking incidents, and by extension, tumbling accidents.

So if we did this, we would need to invent a harness system that would would resist the pilots effort to push out, a sorta/kinda "artificial stability" if you will. Or some other way to provide the feedback necessary to give the pilot the knowledge that he's exceeding the trim AoA. Feel free to help me with this.

The advantage of this design is that there would be minimal or no aerodynamic resistance to flaring the glider. When the pilot pushes out on the downtubes, he would only feel "bar pressure" from the artificial feedback system we'll have to invent. The glider itself, however, would not resist the pilots desire to operate the aircraft at a high AoA.

So let's say you're going for the orange traffic cone that designates the "target" landing in a contest. Or, you find yourself shooting an approach into a small field, with the proverbial 50' obstacle on the downwind side. You could avoid over-shooting the target or small field by climbing up out of ground effect, slowing down in the process, and as the glider stalls and settles, you would have no problem holding the nose way up. The tail would also be limited in how far up it can hinge, so that at extremely high AoA it would prevent the glider from sliding backwards. Only in a vertical rearward descent, such as a whip-stall, would the tail provide any significant nose-down force, and we could address that issue by having the tail's "up stop" be of an elastic nature. Obviously, while I've put a lot of meditative thought into this, I can't foresee every possibility.The only way to learn everything is by actually building the glider and flying it.

I'm 63 and not as eager to be the test pilot that I've been in my more youthful years, so I'll start with a model first.

Well, these are some of my current thoughts about pitch stability and control. I'm gonna take a break, due some "honey do" chores, and meditate on how roll control can be improved using weight shift initiated aerodynamics. If I can "parachute" down onto that target, I'll need good roll authority in the post-stall regime.

Now THAT is definitely gonna provide some food for thought, but since I find that food to me spiritually nourishing, I'm looking forward to the grueling ordeal it promises to be.

I well remember flying long root chord gliders in the late mid-seventies, that did allow for "parachute" landings, although of course it wasn't practical to do it for more than 15 or 20 feet, as usually a wing would drop. But still....

Your Friend in the Spirit of Flight For The Simple Joy of it, Steve

[Rick Masters]

Essentially, you seem to be saying, "Do away with flying wings!" because the twist and positive reflex works against flare at landing.
The twist in flying wings serves the same purpose as the tail in conventional configurations, however it exacts a performance penalty in flight.
A hinged tail boom serves the same purpose as a rotating wing.

A rotating wing serves the same purpose as a STOL configuration.

This has all been tried in "GA." It all works.
But something that hasn't been tried, to my knowledge, is instant de-tensioning of positive reflex at flare on flying wings.
Oh boy, did I know some people who would have loved that in the early days of XC!
Not for flare but to go faster in flight (with the risk of very bad things happening).
So here's another idea: How about a GPS or other vertical orientation sensing device that automatically increases positive reflex when required?
Instead of doing away with the flying wing, we make it respond better to our wishes.
Birds do it.

[Dayhead]

Rick, I get what you're sayin'....

For many years I was hopelessly addicted to the "Nurflugel", or pure flying wing design, not having any vertical surfaces. I even originated and patented a toy Nurflugel, called "Sling Wing", that folded for high catapult launches.

As time passed, I began to lose some of my fascination for the lay-out. For HG, it worked very well for a number of years. It had the advantage of being the simplest, and therefor potentially the lightest way to build a glider. But now I wonder if "the gross defects obscure the actual gains".

In the early days, I'd say up until about 1980, the swept-aft flying wing was an obvious choice. But as we've reached for more performance we're starting to see where the "gross defects" may actually be hindering our progress.

Swept-aft wing planforms have been around since the very early days of aviation. The Dunne tail-less biplane was an early example, I believe the Icarus 2 and the Easy Riser owe their existence, at least in part, to this design.

One problem with the configuration, as I see it, is the necessity of a high degree of torsional rigidity. Even beginner gliders often use washout struts for pitch stability when things get tough.

And high performance gliders need torsional rigidity to control twist, the enemy of span efficiency. The topless gliders have two washout struts per side for when things get tough. And of course the outboard leading edges have to be extra strong to withstand the loads imposed on them by the washout struts. Since we're discussing "trying a different way" here, maybe we should consider that any component of the HG that is "extra strong" is, by extension, "extra heavy". And those four washout struts are just along for the ride MOST of the time.

Ok, so if swept-aft wing planforms have the washout angle and pitch stability married, perhaps by getting rid of the sweep-back we can allow pitch stability and washout to get a divorce.

It just seems to make sense that if these two get a divorce, we can reduce weight, by reducing the need for such high-strength outboard LE's.

My Sensors have repeatedly demonstrated just how light weight and simple to assemble a vertical fin can be. So perhaps we don't need the sweep as much as we've always thought we did.

And another thing: Designers have told me that as nose angle widens, or sweep decreases if you prefer, controlling twist in a sail becomes more difficult. So maybe sail tension alone isn't the most effective means of controlling twist for us.

Back in May we celebrated Otto's 123rd B'Day at the beach. One of the "vintage" gliders there was the Aolus, a very wide nose angle flex wing that sported a bird-like tail.

I think this concept deserves a second look, but this time by eliminating the sweep altogether, and moving the spar further aft within the wing. If the spar is located in a thicker part of the airfoil section, it can be made taller, and I heard somewhere that if you double the spar's thickness, you quadruple it's stiffness. So a built-up spar, made from a vertical-grain balsa shear web and carbon capstrips, could be built much lighter, for the same strength as what we now get from a 2" diameter tube.

Ah, a Different Way, indeed. Somehow this sport got hooked on doing things a certain way, and I for one think that it's high time we stopped and took a second look at the direction we've been going in for three and a half decades, and maybe see if we shouldn't do a U-turn and look for a Different Way.

I keep hearing that HG is in decline. Even if it isn't, it sure as hell isn't growing, by much if at all.

I'm not saying that our approach to the design issue is the primary cause, but everything is guilty until proven innocent.