[KaiMartin]

My ideas on possible future hang gliding designs are a bit farther from current design than a modified sprog but not as far as gravity control. I think, I mentioned them before either here, or in the oz forum. But here they are again:

1. Main beam at about 1/4 of the chord.
   Reasoning: Aerodynamic load bends the wing up but does not twist the wing. Reasonable upward bend hardly affects lift. So light weight construction can be chosen.
2. No sweep.
   Reasoning: Aerodynamic load on a swept wing introduces strong twisting moments. Straight wings are more efficient than swept wings. Straight wings can do without a spar.
3. Pitch unstable configuration.
   Reasoning: The traditional means to achieve pitch stability necessarily compromise efficiency (tail planes, canards, twisted swept wings, or airfoils with positive Cm) There is a reason why all birds fly severely pitch unstable configurations. Proposed solution: Achieve stability by lateral movement of the pilot relative to the wing. This adjustment of the centre of mass is analogous to steering a bicycle.
4. Attach the pilot to the wing rather than hang him a metre below.
   Reasoning: The attached pilot gets a much more immediate feel for the current angular movements of the wing. This is a prerequisite to reliable pitch control by weight shift.
5. Decent positive dihedral.
   Reasoning: Dihedral induces both, roll stability and directional stability.
6. Initiate turns by wing warping combined with drag devices at the tip.
   Reasoning: Wing warping is the most efficient way to induce differential lift. A straight wing is easy to warp at the root. Unfortunately, differential lift also induces adverse yaw. Bird of prey compensate with counter rotation of their fairly large tail. Sea birds soar without engaging their tail. They use the instability of the anhedral of hanging wings. Asking the pilot to dynamically control unstable pitch is already a tough call. The sea birds way is probably not feasible for humans. A large flat tail like the falcon of this forum adds more mechanical complexity than I like. In addition, the tail might stall and induce "interesting" manoeuvres. Drag devices at the tip may not be the most efficient way to counter averse yaw. But they are reliable from a control point of view.
7. Use cheap, mass produced materials.
   Reasoning: I'd like to build my wing without a NASA scale budget. Compared to the 1960s we have access to a few more light weight materials. In particular, I feel, the potential of polymer foam has not yet been explored for hang gliding.
8. Use feathers rather than a sail.
   Reasoning: Birds beat pterosaurs and bats in the game called evolution. Seriously, feathers are modular, easy to replace when broken. Bird type wings do not apply bending loads to their bones. Other than the actual lift, feathers don't pull on the spars, errm, bones. The big challenge is of course, to construct man made equivalents to bird feathers scaled up by about an order of magnitude. Currently, I am in favour of XPS foam layered between sheets of BoPET with a shaft made of a regular carbon tube. Experiments will have to show if this is viable.

These are the main points. There are some more aspects. E.g. how the pilot would interact with the wing. But these are still subject to brain storming and idea tossing in the bath tub.

---<)kaimartin(>---

[reluctantsparrow]

[*] Use feathers rather than a sail.
Reasoning: Birds beat pterosaurs and bats in the game called evolution. Seriously, feathers are modular, easy to replace when broken. Bird type wings do not apply bending loads to their bones. Other than the actual lift, feathers don't pull on the spars, errm, bones. The big challenge is of course, to construct man made equivalents to bird feathers scaled up by about an order of magnitude. Currently, I am in favour of XPS foam layered between sheets of BoPET with a shaft made of a regular carbon tube. Experiments will have to show if this is viable.[/list]


we all made models as kids I think.....the use of feathers is giving me flashbacks.....Best model glider I eve built was made from two seagull wingtip feathers, a left and a right, no sweep. joined at the root to a stick of balsa running back to a regular T-tail made from balsa and a short section of a split feather.
I was thirteen years old. that thing had an amazing glide and tracked beautifully. very stable....I lost it on the same day I built it though.....took it up on to our roof in West Seattle and let it go. It went out on a very flat glide with a very sleight turn and a thermal broke off at the same time. I did not know what a thermal was at the time but I sat on that roof and watched that thing climb completely out of sight in West Seattle....
Just two feathers about 10 inches long, wingspan must have been around 20 inches.....now...could a wing be developed using modern materials that duplicates a feather when spread outward but al veins and membranes fold neatly against the quill (which would be the main spar) as it is folded up against a keel?
The cross section of the feathers I used were a perfect airfoil and created the most amazing glider I have ever built. It seemed to defy gravity (oops, theres that word again ...gravity....

I totally forgot about that glider I built from two seagull feathers and how efficient it was. What modern materials and construction techniques would be used to recreate an ordinary feather 15 feet long down to the last detail?
instead of simply affixing each end to a keel of some sort perhaps the end of quill # 1 could be attached five feet out or so to the main spar of quill #2 via a pin or hinge so when spread outward the four feet or so that cantilevers beyond the attachment point swings back to attach via one more pin to quill # 1 forming a fully cantilevered mainspar....???

[Bill Cummings]

We might need a beak to align and attach the little hooks on each feather with the adjacent feather.
Also synthesize bird gland oil for feather maintenance. (This might be difficult.)

Run your beak down the length to engage with next feather..PNG (576.16 KiB) Viewed 5542 times

[reluctantsparrow]

I like the blueprint KaiMartin has laid out so clearly.
I realize the feathers Kai was visualizing were probably not the single feather per side design i built as a kid. I only shared because it worked exceptionally well.....too well in fact...., that was the last I ever saw of that glider model.
it had dihedral stability built into it. Roll could be accomplished via Wingspans wing warping sprog device.
I like the idea of using cheap materials and building a mold of some sort where the entire wing is popped out in one single operation. any part of the ....feather....that needs to hinge could be built right into a semi flexible material that varies the shape of the material according to desirable functions, such as:
Tubular and thicker for areas that require strength, flattened out longitudinally and thinner for areas that need to hinge laterally, such as the veins that emerge from the mainspar with membrane material attached. or flattened out laterally for areas that need to move longitudinally, such as control surfaces.....oh yes, I can see it now. I like it.

perhaps the entire wing could perpetually rock back and forth like a vultures wing. I have a theory about how a Vulture attains additional thrust without flapping. What a vulture might be doing is,... he is flapping without flapping. the rocking motion creates a downward thrust from the descending wing which, at the same time, creates an increase in efficiency in that wing due to a temporarily more efficient angle of attack with the relative wind flow , resulting in increased lift on that side that drives that wing back upward as the opposite wing is in a descending dive mode that builds up stored energy to be converted to lift as it now takes its turn at a more efficient angle of attack....kind of like dynamic soaring in a way.....Maybe I am way off....I really have not studied Vultures that much....saw one yesterday doing the rocking thing and he never had to flap to maintain altitude even with no discernible lift nearby. Seemed to just rock along his/her merry way just fifteen feet off the ground defying GRAVITY on all counts....OHHHH..theres that word again...
As far as little hooks to join several feathers together Bill, (if the several feather idea works better than the single feather idea).... Why not velcro?

[reluctantsparrow]

Okay.....now that I posted about vultures I am curious. I need a close up video that shows all the details of a vulture in rocking flight. Does the Vulture change the angle of attack of the descending wing to build up energy that is converted into lift...I dont know....But I bet someone here does...or I could youtube it

[Rick Masters]

What pterosaurs tell us about the evolution of feathers
Mark Witton
Palaeontologist and palaeoartist, based at the University of Portsmouth and specializing in flying reptiles.
http://markwitton-com.blogspot.com/2015/09/what-pterosaurs-tell-us-about-evolution.html

"Proto-feathers have been attributed to two
pterosaurs which are of similar animals (Ji and Yuan,
2002; Wang, et al., 2002). Even more so, the
morphology details seen in Pterorhynchus
demonstrate that the integumentary structures of
pterosaurs are not like hair, but are analogous to
being proto-feathers. Specifically, they resemble
natal down feathers where individual filaments are
seen to spread from a single follicle."
http://www.dinosaur-museum.org/featheredinosaurs/rhamphorhynchoid.pdf


http://pterosaurnet.blogspot.com/2014/08/another-claimed-feathered-dinosaur.html

[reluctantsparrow]

so the albatross is using the wind gradient, flying in a perpetual pattern that transforms a build up of energy into lift as it turns again into the wind.....What I am theorizing (and cant find anything on a google search about) is that a turkey Vulture does much the same thing not using the wind gradient.
What I need to see some close up imagery of is does a vulture constantly change the twist angle as he/she flies or constantly alter the angle of attack of his or her wings?
Online I only see examples of Vultures not flapping while in thermals. Heck, we can all do that.
what I have observed that I am trying to find an answer to is observing Turkey Vultures flying prolonged distances only ten or twenty feet off the ground without ever flapping....simply rocking back and forth.
Is he/she altering angle of attack to provide a screw-like propulsion that maintains altitude?...or
Is he/she creating another form of dynamic soaring where one wing is diving for speed as the other wing is transferring that speed into lift?
Now that I have proposed two possible solutions the screw like propulsion idea seems more plausible. Like a skateboarder fishtaling back and forth to create forward momentum on level ground without taking either foot off the board to push.
perhaps a Turkey Vulture actually may be swimming its way through the sky via the rocking motion.
I have watched these birds travel great distances in this fashion in zero wind conditions with no evidence of thermal activity. I have seen them never stop to work a thermal just keep rocking back and forth only a few feet off the ground.
I guess I am going to have to prove my theory corrrect before attempting to incorporate it into some sort of glider design.....okay...tangent over......back to the Feather glider idea.

[Rick Masters]

My impression is that turkey vultures are using as little energy as possible to fly.
Any deliberate change of the shape of their wings would use energy, so it seems unlikely to me.
The high dihedral they hold in flight appears to me a way to decrease the efficiency of their high performance wings.
The rocking motion is a result of the center of mass being located so far below the mean lift line - sort of like a very lightly loaded paraglider.
You will notice these vultures go to low dihedral configurations when they get too low, prior to flapping.
The reason for this behavior is vultures like to fly low to spot dead animals for lunch.
The rocking, in my opinion, is caused by the effects of very small patches of rising and falling air giving uneven lift across the vulture's wingspan.

Dynamic soaring requires the input of a shear (dissimilar velocities of airflow).
In the absence of this, it is impossible to utilize a changeless or "dead" atmosphere to perform work (soaring).
In still air, for example, the vulture will eventually end up on the ground if it doesn't flap.
Luckily for the lazy vulture, the atmosphere is "alive" so this rarely happens.

[KaiMartin]

http://www.dinosaur-museum.org/featheredinosaurs/rhamphorhynchoid.pdf

This paper contains a hidden gem. It mainly deals with the abundance of proto-feathers, their properties and their evolutionary benefits. But there is also a section which concludes that most likely every pterosaur had a significant crest of some sort. Such prominent structures represent a significant "cost" to the species. This is particularly true for flying creatures as every ounce must be lifted on take-off. Still, crests were wide spread over millions of years and dozens of species. So they certainly served an important purpose.

At the very end of the paper the authors surmise that the crests were used for steering. They speculate that the pterosaurs initiated a turn by turning their head. I agree, that crests and the almost absurdly large head some of the most prominent pterosaurs sported, were probably used as a control surface. But I my humble opinion, the head was used in tandem with wing warping. The wing warp would induce roll and the head would be turned to counter the inevitable adverse yaw.

I think, I saw this kind of adverse yaw compensation utilized by white storks. These birds tend to soar thermals with their already diminutive tail only partly engaged and their neck fully extended. When they initiate a tighter turn, they tend to shift their head and neck toward the intended direction. Given the length of the neck, any off axis drag probably has noticeable impact on flight dynamics.

Looking at their teeth, pterosaurs most likely were the dominant air predators.Unlike storks they had good reason to make fast and swift turns. So they needed to deal gracefully with massive amounts of adverse yaw. It seems plausible to me, that this may have been the evolutionary driver behind the large head structures of pterosaurs. If this is true, Quetzalcoatlus must have been as fearsome as it gets. Imagine a hang glider sized predator souring above, looking for human sized prey to speed hunt and feed to its hyper active metabolism...

Back to the future of potential hang glider concepts: When I tried to come up with a convincing way to deal with adverse yaw, I rejected the stork style of yaw control. It exhibits some positive feedback -- the more you are yawed with respect to the current air flow, the stronger the yawing force of the "head" becomes. I suspected that this may run out of control, leading to catastrophic aerodynamic failure. But maybe I was wrong. If the pilot can warp the wing by arbitrary amounts, the resulting adverse yaw may be sufficient to overcome any torque by the "head". My head is spinning If I missed something important again, the only way to know for sure would be a test with a modified RC model plane.

As an aside, I like the idea of some structure in front of the (human) head. Safe-splat anyone?

---<)kaimartin(>---

[KaiMartin]

Hi Bill.

We might need a beak to align and attach the little hooks on each feather with the adjacent feather.

IMHO, it is hopeless to try and copy the microscopic structure of bird feathers. This would require a degree of three dimensional micro structuring which is well beyond any technology currently available outside of certain high level material science labs. And even they struggle to produce more than some precious tiny samples. A hang glider needs like 15 m² wing area. Even totally available high tech materials may just be prohibitively expensive.

To me, barbs and barbicels do not look like necessary requirement for feathers to do their aerodynamic job. They are just the ingenious solution mother nature came up with, given the tools she had. So what is the aerodynamic job of bird feathers in the first place? IMHO, it boils down to:

1. prevent air to freely move from the top side to the bottom of the wing
2. transfer lift to the main structural component of the wing (the bone)
3. bend but not fold under aerodynamic load
4. be as light weight as possible and still achieve the goals above

Nr. 1 is only partially fulfilled by bird feathers. Human made materials easily achieve completely impenetrable surfaces. If a certain degree of leak tuns out to be desirable, then it should be possible to perforate to whatever leakage may be needed.

Bird feathers achieve Nr. 2 with the rachis. Modern technology provides us with mass produced carbon composite tubes. A perfect man made rachis would ask for a continuously tapered tube. But a sectioned approach may be close enough. Coincidently, sectioned tapered carbon tubes are sold for surprisingly low prices as "fishing rods"

Nr. 3 in conjunction with Nr 4 is the tricky one. The traditional 6 g maximum load translates to about 10 N per dm² of aerodynamic load. So the figure of merit would be stiffness over weight. The best readily available material I could come up with is extruded polystyrene foam (XPS). This stuff is used to insulate houses. So it can be bought at any home improvement market for cheap. It is the material of choice for many model planes, too.

The weight per area is the property bird feathers really excel at. Luckily, feathers of a hang glider may get away with less, err, more. Traditional hang glider cloth is about 2x 250 g / m² (for a double surface flex wing). This is something to work with. Feathers may contain somewhere between 10 mm and 20 mm of XPS foam thickness on average. I imagine feathers to be tapered to save weight and gain flexibility. To prevent the foam from braking, a layer of tear resistant foil should be applied to top and bottom. I am looking at space blankets for this job. Glueing the foil to the foam is the tricky part. First trials were a bit underwhelming. But there are still options. The next challenge will be to attach the carbon rachis to the XPS vane. Will report when I try again. (But don't hold your breath...)

---<)kaimartin(>---