The concept of flapping flight will eventually succeed!

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jedi

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Anyone have a link to a video of that?


BJC
?? There have been many videos posted of work done in the past. I am not sure what video you want.

This is my favorite as it demonstrates how much interest the public has. This video went viral and made the national news when it was first released. It clearly demonstrates what a large segment of the population wants. This is a very simple mission that demonstrates what the goal could be as well as highlighting the work needed to progress from the fancy video deception to an actual working demonstration.

 
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Dan Thomas

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?? There have been many videos posted of work done in the past. This is my favorite as it demonstrates how much interest the public has and what the goal should be.

Fascinating. So much fun that would be. Definitely limited to the most fit among us, and even then the range is tiny. But fun anyway.

Doing that, even for 100 yards, would make one realize just how far away we are from flying like birds, who are optimized for flight.

How is it steered?
 

DennisK

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Same way it’s flown: with CGI. Unfortunately that video was in the end just a sort of viral resume for an animator.
Yep. But that is one reason I don't have much interest in real human-powered flight. Generating enough power to even remain level is so much effort that you don't have much focus left to steer the thing or enjoy the view.

And the most powerful human muscle motion is leg extension, so logically that's what should be used to power flapping wings. But if you're in upright position like the paper from Henryk's post #60, then most of your thrust goes to counter the added drag compared to regular hang gliding. And if you're in prone position to reduce drag, then the constant shifting of your center of gravity will cause trouble. One of those intractable problems of human morphology.

Though I would like to see a powered version of that idea, where you fly in prone position and have a piston pumping up and down on your back to oscillate the wing. I wonder if it could launch from flat ground with a good running start.
 
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Tiger Tim

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Had me completely fooled then. Just vaporware?
I guess so, though I’ve always defined vapourware for myself as trying to sell the depicted imaginary thing. In this case it was just to show off animating and video compositing skills. They did a pretty good job, didn’t they?
 
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Please post a link showing that a lifting tail is a stable configuration.
Stability is not necessarily about whether the tail lifts. It's about the relative slopes of the lift curves that relate Cl to alpha for the wing and tail. As long as the tail has a shallower curve, it can provide lift in some portions of the flight envelope and still be stable. In fact, most modern sailplanes (mine included) are like this. At the lowest end of the speed range, the tail provides a modest upward lift.

And it gets a bit crazier. For most modern sailplanes, because of the pitching moment of their cambered airfoils, the tail is providing the most downforce, but with the greatest nose-down elevator, at the high end of the speed range, while it provides the least down force (and often some up force), with the most nose-up elevator, at the slow end of the speed range.
 
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Getting back to the OP, my take on it is that ornithopters won't practically scale up large enough to carry people until we have much stiffer and more elastic materials at our disposal. I dunno, maybe things like graphene and its boron analogues might do the trick.

Basically, what we need are springs that can store a crap-ton of energy on the up stroke, and release it on the down stroke. And what we have for springs these days, even the best ones made from titanium and carbon fiber, won't store enough energy per unit mass. The square cube law being what it is, birds get away with using their wishbones for this energy storage. But unfortunately that approach just doesn't scale up.
 

jedi

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Basically, what we need are springs that can store a crap-ton of energy on the up stroke, and release it on the down stroke. And what we have for springs these days, even the best ones made from titanium and carbon fiber, won't store enough energy per unit mass. The square cube law being what it is, birds get away with using their wishbones for this energy storage. But unfortunately that approach just doesn't scale up.
Sounds like time for some math here. I agree with the scale issues but are they really impossible on a ultralight or lighter ornithopter? What about McKibben Artificial Muscle as both a spring and a motor?

 

jedi

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Sounds like time for some math here.
Assume 15 foot semispan. Center of lift 6 foot from flap hinge and 60 degree flap angle. 500 pound GW, = 250 pounds per side. 6 feet (stroke) x 250 pounds = 900 ft pound per side per stroke. If air at 900 psi is used, delta volume of air is 12 cubic inches.

Rough numbers but it looks like a two foot long McKibben Muscle with a 2 square inch cross section would have adequate power if it contracted to 18 inch length. 6" x 2"" = 12""" (cu in)

Don't know if 900 psi is doable. Perhaps use two at 450 psi, 4 at 225 psi or 8 at 112.5 psi.

Convert this to a leaf spring wish bone and do the math is probably going to be heavier but a hybrid between the McKibben and the wishbone is a likely good solution.

Like I say, someone needs to do some engineering and applied physics. If it was easy it would have been done already. It seems that 9 out of 10 won't even try. It doesn't sound impossible to me.

Is it hope, faith or a day dream? Does it matter if it works? If it doesn't work we still end up smarter.
 
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Tiger Tim

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I’m curious, has it been demonstrated that flapping wings are more efficient, or more powerful, or more of anything that we would want? Could it be that flapping only exists in nature because nature can’t produce a ball bearing or a turbine or one of the other zillion compromises that must be met for a bird or a bug?
 

DennisK

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Basically, what we need are springs that can store a crap-ton of energy on the up stroke, and release it on the down stroke. And what we have for springs these days, even the best ones made from titanium and carbon fiber, won't store enough energy per unit mass. The square cube law being what it is, birds get away with using their wishbones for this energy storage. But unfortunately that approach just doesn't scale up.
My plan is to use a supercapacitor and regenerative braking. Elastic energy storage would take some load off the actuators and allow them to be lighter weight, but as you say the specific energy of elastic materials is poor. Supercapacitor is around 5x higher than rubber or 15x higher than steel, and it will probably need to be there anyway to provide the peak power during downstroke.

You can also utilize your own momentum as an energy storage medium for stroke reversal. Change angle of attack just before the reverse, using aerodynamic force to accelerate the wings, at the expense of a little forward speed and/or altitude.
 

jedi

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has it been demonstrated that flapping wings are more efficient, or more powerful,
In nature, yes. In mechanical design practice, no. In theory yes. In the 21st century, we are working on that.

more of anything that we would want?
Would you like more performance and better control than your Cessna 172 182?
 

BBerson

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I’m curious, has it been demonstrated that flapping wings are more efficient, or more powerful, or more of anything that we would want? Could it be that flapping only exists in nature because nature can’t produce a ball bearing or a turbine or one of the other zillion compromises that must be met for a bird or a bug?
No. Human powered fixed wing can fly for hours even across oceans. Flapping only seconds. They Said It Couldn't Be Done!
 

DennisK

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Assume 15 foot semispan. Center of lift 6 foot from flap hinge and 60 degree flap angle. 500 pound GW, = 250 pounds per side. 6 feet (stroke) x 250 pounds = 900 ft pound per side per stroke. If air at 900 psi is used, delta volume of air is 12 cubic inches.

Rough numbers but it looks like a two foot long McKibben Muscle with a 2 square inch cross section would have adequate power if it contracted to 18 inch length. 6" x 2"" = 12""" (cu in)

Don't know if 900 psi is doable. Perhaps use two at 450 psi, 4 at 225 psi or 8 at 112.5 psi.

Convert this to a leaf spring wish bone and do the math is probably going to be heavier but a hybrid between the McKibben and the wishbone is a likely good solution.

Like I say, someone needs to do some engineering and applied physics. If it was easy it would have been done already. It seems that 9 out of 10 won't even try. It doesn't sound impossible to me.

Is it hope, faith or a day dream? Does it matter if it works? If it doesn't work we still end up smarter.
These guys have done 5MPa (725psi) with hydraulic fluid
McKibbens sound really light weight until you consider that they have to be powered by compressed air (poor specific energy) or a pump (poor specific power), and each muscle needs valves to pump fluid into and out of it (more weight, and expensive). And pneumatic is particularly difficult to control due to volume change with temperature and compliance of the muscle.

But if you're only flapping for thrust and not for control, so you can just pump air in and out without worrying about the exact position you get to, it could work.
 

Urquiola

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The video in response by jedi poses a doubt. No power besides the man's arms is visible, and we know that this muscle power is not enough to take off and fly.
A possbility would be having hydraulic 'actuators', 'muscles', moving the wings.
Even if efficiency of hydraulic transmissions is poor, around 60% I guess, a lightweight Wankel engine, with a pressure reserve tank, could probably move wings with enough energy as to fly, the arms of pilot just controlling the flapping.
Concept is same as in assisted armors, that allow to lift weights several times heavier than what a human being could.
A German company offered not long ago a quite large flapping pterodactyl toy, also there is a flapping wings 'flying cow' for sale, but can fly only in circles, hung from ceiling with a string.
The Pterodactyl toy was able to free flight, and could be controlled as any other aeromodel, by radio.
Blessings +
 
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