[KaiMartin]

I think you will find that birds use their tails in various ways at different stages of flight.

Yes and no.
Yes, different birds use their tail in various ways for various purposes.
But I was specifically referring to big soaring birds during soar. Small birds operate in a different regime of Reynolds numbers. And moves which involve flapping, or major reconfiguration of the wing cannot be replicated by our gliders. And after all, who would not like to soar like an eagle, a condor or an albatross? When I was researching how these big birds initiate a controlled turn, I skipped through literally hundreds of videos and images. And I watched a few birds in nature, too. None of them used their tail the way human planes do. That is, put it at a lower angle of attack than the main wing.

Sea birds tuck their tail away as much as they possibly can when on cruise. So they are out of the tail game. The large land birds by contrast have their tail unfolded when they soar. The hawk image on the upper left of this forum provides a perfect example. They actively rotate their tail the other when they start a turn. This can be seen in this remarkable video by the BBC:



When they start coordinated turns, the condors use the tail to compensate the adverse yaw by wing warping. This can only work if the tail is at a significant positive angle of attack. Tail planes on aircraft are configured for close to zero or even negative angle of attack. This is a necessity if the tail is to provide pitch stability.

It is able to move in sync with the billow shift of the sail to give a rudder effect to enhance turning.

Billow shift induces adverse yaw in addition to the desired roll. So you intend to pull a similar trick as the condors?

Lilienthal, Pilcher and Chanute all employed tail planes that floated up. This can be seen in a video of Stephan Nitsch's replica :- https://www.youtube.com/watch?v=mpDrGLF51SY

Very nice footage!
I noticed a familiar guest pilot name in the closing credits...

The tail of the Lilienthal glider did indeed go up very visibly. It has a bottom stop, though. Looks like the tail was meant to prevent a sudden dive but deliberately allow to pitch up.

In my version the tail was fixed as I feared that no corrective force would allow the wing to pitch up too much and stall. The very thing that killed Lilienthal.

That's why I proposed to unlock the tail only at flare time.

---<)kaimartin(>---

[ARP]

Kai,

I gave the "bird like" description to indicate the configuration of the glider as I could not post the picture. Linking the tail to the billow shift is intended to aid the control in a turn and so mimics, to some degree,soaring birds. How efficient this will be remains to be seen. Birds have far more control of their wings and tail than we will ever have and so some degree of auto stability is needed to make flight practical. The Wright's aircraft was unstable making it difficult to fly requiring constant input from the pilot. Modern fighter jets are also made unstable and can only fly with the aid of computer controlled systems. They need to do this for rapid manoeuvring in a dog fight where stability would have to be overcome before the manoeuvre.

I found the stall on the Lilienthal glider to be very abrupt which is not surprising with it's very sharp leading edge. Stephan had not fitted the back stops which prevent the pilot weight moving too far back. In the last scene my weight moves back too far and the forearm cuff broke. The wing stalled and nosed in.

Your proposed tail lock could work but requires additional pilot input at a critical stage of the flight. I was able to flare with the tail fixed so it may not be necessary. With the splitwing gliders the stall speed was very low and most landings were no step. This latest design should be more efficient and hopefully still retain this slow speed capability.

Tony

[ARP]

Kai,

Much of this discussion we have already had on the Oz Report and we seem to be heading in much the same direction. Until I can get something built and tested I cannot take the discussion much further. Trying to get it to a reasonable breakdown size requires some thought but to be practical I have allowed a 2m pack length. The wing battens remain in the sails which are gathered to the keel after the wing tubes are removed. The tail plane is removed from its pivot arm and folds for packing with the keel. The two wing tubes are in three sections and are packed in the same manner.

Set up time should be reasonable but having to connect cables and bolt up slows things down. Quick release hardware could be developed in time but not for the prototype. Weight should be a good bit less than most flexwing HGs.

Tony

[JoeF]

DRAFT COMMENT:

On my High Hat monoplane Dockweiler Handy Dandy 5-ft-Pack HG Mark 1, I am strongly considering "sock sail" that will allow the sock sail to be toted via multiple invaginations forming a wearable sail (shirt) or forming a container holding frame beams and rib parts. Cables will be externally clipped into soft loops that stay on frame parts.

[Frank Colver]

Joe, you could consider an inflatable high hat.

There are some incredible materials available now for inflatables that are extremely light weight, very thin and strong, and very air tight. I could show you my whitewater raft that only weighs about 8 pounds and yet is extremely tough. The material it's made from is also used for the surveillance balloons positioned along our border with Mexico. Downside: It's $25 per yard.

If you came to my shop in Costa Mesa and saw the raft I think you would be impressed with the material and weight. The raft is made by Alpacka Raft Inc., in Mancos CO. I think there is a new potential for very light, and very small deflated volume, inflatable parts for hang gliders.

Frank

[JoeF]

Yes, right on.


Paper: PHOENIX A Polyester-Film Inflatable Man-Powered Aircraft by F.E. To
http://aerosociety.com/Assets/Docs/About_us/HPAG/Papers/HP_phoenix.pdf

https://en.wikipedia.org/wiki/Francis_Rogallo#/media/File:Parawing.jpg

https://tensegrity.wikispaces.com/file/view/tensairity.GIF/131855241/286x117/tensairity.GIF

Would like to see your raft and and shop too! Thanks.

Joe

[Frank Colver]

You would be welcome to visit my shop any time I can be there Joe!

The material that I was referring to is a Kevlar diagonal weave cloth, urethane coated. If you consider those two things you can realize what a fantastic inflatable can be made. I think to inflatables this is what carbon fiber was to rigid structures. My packraft has been sitting in my shop, inflated, for about seven months now and is still firm with about 2 psi.

In my previous post, however, I wasn't suggesting a fully inflatable glider, although that would be great, but to make smaller HG parts, stabilizers, rudders, etc., inflatable.

Every September, when I stay a couple of weeks in Bluff Utah, I make arrangements to visit the Alpacka Raft factory in Mancos CO. I'm fascinated by the boating developments there which come from the brain of owner, engineer, inventor, Sheri Tingey.

Here's a photo of the boat called the "Gnu", with yours truly paddling, on the Owens river last Oct. I can pick the raft up with one finger!

Frank

Gnu on the Owens River.jpg (461.2 KiB) Viewed 5957 times

[ARP]

Pneumatic airframe may solve the pack size issue but adjusting internal pressure to match atmospheric pressure changes, at different altitudes, also needs a solution. Venting and re-pressurisation has been mentioned but how to do it, within the weight constraints of the glider, needs attention.

Frank, how are the panels of the canoe joined? Are they glued or heat welded and is there any stitching involved?

I know Fred To the designer of this HPA design http://aerosociety.com/Assets/Docs/Abou ... hoenix.pdf and he has been involved with other inflatable aircraft . He may have some answers to the pressure change question.

Tony

[JoeF]

Great shares Frank and ARP !
===========================================

Notice some airbeam options:
1. Coated fabric option for the integrated bladder.

2. Distinct two parts: bladder held inside of an encasement. This allows some things different from the 1. option. Here, the bladder may be a focused material that also could be changed out for replacement or repair. Also, the separate bladder could be slightly oversize compared to the exterior abrading encasement; such slightly oversize permits the bladder part to be NOT TENSED while the casing takes the tension; this is way different from what occurs in option 1. where the leak-stop coating is tensed upon inflation. Different game; one could go high tension for the case while the badder(s) remain untensed. Notice the wider choices of encasement material in this option space; one need not worry encasement leaking air, as the encasement is not playing that role; only the separate part bladder (s) are concerned with holding the air. LEI power kites are majorly using this option space of two distinct parts.

3. Air beams may be simple without splinting of compression members (ancient art, but recently a company focused and coined the word tensairity; they cannot own the fundamental mechanics of the ancient splinting, but they have moved the art forward). The simple airbeam does not have the enhancement of the splinting.

4. Splinting air beams. The details of good splinting could be mastered for hang glider parts. Not much has been actually done yet for HG using such splinting.

5. Internal web walls. E.g., have in one gross encasement two separate bladders (see option 2 for the one-bladder case); the two separate bladders may press a web wall; that web wall could be a veneer of carbon-fiber veneer or thin plate; and the thin plate could be lightening-holed. The arts of this direction have some explorations, but HG has not seen the tech applied yet, to my view. Also,consider three interior bladders with a tri-web; or four bladders with a cross web.

======================================
Pressurizing inflated beams? Deflating and inflating? Some non-comprehensive notes:
1. There may be a choice to have a HG that is fit only for up to 30 seconds of flight at a conservative-weather situation, say Dockweiler small bluff in ocean breeze. Even there the temperature changes and there would be some attention to pressure-point keeping. I am aiming for pilot-muscle power as one of the choices. Have pressure meter method; then top off the pressure by a little pilot muscle movement between those 10-to-30 second flight, if the HG is leaky : )

2. ARP's mention about this area of concern seems to face the the other end of HG where soaring occurs with significant altitude changes and thus air-pressure changes for the inflated parts. Temperature and altitude affect the challenge. Relief valves set for pressure points is probably the more easy part of this deal. The perhaps more challenging is the inputting of air to get the pressure back up to wanted pressures. ARP is moving on that question some as told. I am keeping in this file the pilot muscle movement during flying. And also the movement of the hang lines that might drive a little air pump. Relief valves could keep over-inflation from occurring; pump, pump, pump as the pilot controls the flight. A metering system might report on the status of pressure on parts.

============================
Some related teasers:
http://www.schmidtocean.org/file/show/635

[Frank Colver]

Frank, how are the panels of the canoe joined? Are they glued or heat welded and is there any stitching involved?

The seams are stitched and a tape of the same material is heat welded over them. I've been to the factory many times and how they do this operation is still a mystery to me.

These boats do not use a bladder of any kind so the material itself is what seals the air and it does it very well.

Most of Alpacka's rafts use a straight weave nylon fabric and tend to stretch as the pressure is increased. They also don't get very rigid. As I mentioned, my latest raft from them is a Kevlar diagonal weave. It doesn't stretch and gets very rigid with about 2 lbs of pressure. I had this boat made with requested changes from one of their standard 2 place canoe models which have to use this fabric for rigidity with a paddler at each end. I wanted the rigidity so that I could position a seat toward the center of the boat instead of at one end. Their nylon fabric based boats would "Taco" under those conditions. The Kevlar fabric based material is called "Vectran". Alpacka had to have a batch run at the mill where it is made, so it was no small investment for them. I'm sure the high cost will change as it gets used in more products, just as carbon fiber did. I remember "prophet" Joe Faust telling me many years ago, when carbon fiber was extremely expensive, and only being used in the aero-space industry, that someday they would be using it in golf clubs and other common things. Right on Joe!

Of course, anything made from Kevlar is more expensive than many other synthetics.

Frank