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All techie stuff here
User avatar
By spork
#369462
Greg - that's an exciting and interesting project. But you sure have a LOT of variables there. Red is absolutely right in suggesting you prove out the non-flapping design at a bare minimum with an unmanned model.

As you have mentioned, flapping flight and propulsion is some very tricky stuff. Controlling the torsional flex and articulation of the wing is critical to getting reasonable efficiency. It's hard to imagine how you'll do that in flight with this design. I think you'll find it very difficult to match the propulsion efficiency of a well designed slow turning propeller. And given the size, airfoil, and aspect ratio of the wings, I think it will be a tremendous challenge for even an athlete to maintain level flight for any period of time.

Of course I'm very happy to be proved wrong on all of that. But I really do think you should consider Red's advice to take a more cautious approach to getting in the air with a machine you know you can control.

Very best of luck.
User avatar
By Greg Vandenberg
#369473
I hear you Spork, trust me nobody is jumping off anything just yet. I am progressing with the next test in May to running down gently inclined sand dunes with a prototype that I have already controlled (see skybike update) and has proven inherently static and dynamically stable. The risk factor of that is way less than on the back of a moving vehicle, and a model helps me very little, as I am my main test data collection device. You couldn't learn how to fly a HG by flying a remote controlled model. As to the efficiency and of this prototype...............jeepers man, its a prototype...... it is the begining of an evolutionary process, not the end. Compare a penny farthing bicycle to a modern day racing bike or a WW TC3 to a bogrog. Those guys didn't give up because they couldn't achieve the efficiency and building finesse that I'm sure a lot of them saw coming. Wait until I actually get a budget to throw at this thing. My prototype is built out of old donated hanglider parts, speaker stands, light stands, pup tents, garden hose, washing line chord plumbing fittings, recording studio paraphenalia and some kids toys :)
If your up for a good laugh go to my other youtube channel and look at some of the hilarious prototypes that where part of this ones evolution, it's been a long road and I've only just begun :) I'm not allowed to post links yet, but its under Wingbike on youtube.
User avatar
By spork
#369478
Greg Vandenberg wrote:As to the efficiency and of this prototype...............jeepers man, its a prototype.....
Let's say you take it as far as Todd Reichert took the Snowbird. That was a very impressive piece of engineering and it was just barely able to maintain altitude for a few brief flaps with an athlete pedaling it. It necessarily had a huge wingspan, and certainly wouldn't withstand the rigors of everyday type HG flight. It's just a matter of humans being too weak to fly under their own power.
User avatar
By red
#369482
Greg Vandenberg wrote:I am progressing with the next test in May to running down gently inclined sand dunes with a prototype that I have already controlled (see skybike update) and has proven inherently static and dynamically stable. The risk factor of that is way less than on the back of a moving vehicle, and a model helps me very little, as I am my main test data collection device. You couldn't learn how to fly a HG by flying a remote controlled model.
Greg,

From the little that I have seen of your prototype, I am impressed with the mechanism itself; for your "selfless" approach to your own safety, however, maybe not so much. 8) I (for one) really want to see you succeed, and probably for a reason that has escaped you so far.

I have long believed that the next real advancements in HG performance will come with the pilot flying prone inside the wing. I also know that a fair part of HG pitch stability comes from the pilot being below the wing (pendulum stability) in extreme flight attitudes. TjW has correctly pointed out that the center gap for the pilot creates a huge loss of efficiency in your prototype. Maybe you have noticed that some HGs even seal up the kingpost hole in the sail, and I believe it is only a matter of time for you to cover that gap. At that point, we will have the basis of the next advance in HGs, although totally unrelated to the ornithopter concept. The pitch stability of HGs with the pilot in the wing has never been resolved, to my satisfaction. If you can do what nobody else has, that would be great, but you need to stay healthy, first and foremost.

I do disagree with your dismissal of RC models, and the Flight Deck.

Please note, the Flight Deck has various tethers to keep the glider flying (a tow-line), with pitch and roll limiters, and a line to prevent the glider from flying into the vehicle during a sudden stop. This set-up is all quite respectable. Replacing all that with one strong man seems very unwise; I would not recommend the human tether trick on a moving vehicle. Too much can go wrong, and these problems can be well beyond the strength of any one man to prevent or correct. The Flight Deck is safe and proven, and also uses an assistant on board.
Flight Deck videos:
https://www.youtube.com/user/hgflyer11/videos

There are many RC HGs on YouTube, and I believe there is much to learn in that approach, with any prototype. Control effectiveness, and stability (recoverability) in extreme flight attitudes can be researched safely with RC models. At some point, the RC models will have reached a limit in what they can teach, but you are not close to that limit yet. I think you will find that flying an RC HG has many parallels that apply to personal flight. Even as the proven HG designs, they can teach a new pilot much.
RC Hang Glider:

Lots of RC HG videos:
https://www.youtube.com/results?search_ ... +glider%22

To your good health,
User avatar
By Greg Vandenberg
#369488
Spork, that is simply not true. Humans are actually relatively powerful animals. Many bat species have worse power to weight ratios than a fit young homo sapien . Google it. The problem arises when you load that human with extra weight to carry. The viability of self sustained flight hinges entirely on power to weight ratio coupled with lowest possible min sink (not necessarily a high L/D ratio). The skybike approach is radically different to Tods, Human power output is linearly proportional to body weight for same build. With the Snowbird the aircraft was 63% of the pilots weight. The skybike at 25kg (I saved 3 kg since Jans test) represents 33% of my 75kg build. Try jogging with a backpack of 45 kg vs 25kg. Further to that comes the issue of drag, Induced drag of the two approaches can be thumbsucked at roughly equal with snowbirds higher aspect ratio offset by 20% greater takeoff weight. Form drag however is less on the skybike because it is tiny compared to the snowbird, which no doubt has a superior Cd, however that lower Cd is multiplied over far greater frontal area at pretty much identical flying speeds. Finally comes the issue of thrust. the snowbird achieved an abismal 57% efficiency with its flapping action. I would equate it to walking on tip toes with your knees tied together :) I have yet to discover my ideal flapping motion, and it will be thru trying various different motions in flight, because the skybike has very articulate, low inertia, lighter, shorter wings that laugh at wind speeds and stresses that would break every single HPA on the planet at the moment. Beating 57% will be achieved the first time I flap them.
So after carefully comparing the facts of the two approaches I find myself even more optimistic.
User avatar
By spork
#369489
If only Todd had thought of making the Snowbird much smaller and less aerodynamic I guess he would have had a much easier time of it - and had much better success. :roll:
User avatar
By spork
#369490
Let's run some optimistic numbers real quick...

200 lb gross weight (man and machine)
L/D: 10:1

This gives you 20 lbs of drag.

Speed: 30 ft/sec (about 20 mph)

30 ft/sec x 20 lb drag = 600 ft-lb/sec = 36000 ft-lb/min = 1.1 H.P.

Assuming a flapping propulsive efficiency of 75%, that would put you at 1.45 H.P.

From Wikipedia: "adults of good average fitness average between 50 and 150 watts for an hour of vigorous exercise."

So let's put you at the top end of that range. 150 watts = 0.2 H.P. So you'd only need about 7 times as much power as you can produce.
Last edited by spork on Sun Apr 26, 2015 2:12 pm, edited 1 time in total.
User avatar
By Angelo
#369491
While I like the spirit of adventure presented here, looking at that vid - it doesn't inspire confidence. Glad you are starting near the bottom of a hill.
User avatar
By Greg Vandenberg
#369492
Red..... sir, you do speak excellent sense. Reading your description of the flight deck convinces me that it is just a matter of time before we meet in person :thumbsup: My bakkie (what we call pick up trucks here) tests where very unsafe and not something I am willing to do with the present wing which will actually pick me up. To do testing in the environment you just painted will speed up the development exponentially. You have also spotted my possibly greatest motivation. Regardless of whether the flapping is sustainable or not, the fully matured Skybike is gonna be one hell of a ride with degrees of control and dexterity never seen before in human flight full stop. The flapping is just a bonus.
As an erstwhile radio modeler I just kicked myself. It's not a one or the other thing anyway. Lets do both. I love building and flying rc and you are entirley correct that I can only learn from the process (and have a blast!)

Spork.......... humans have flown hundreds of kilometers under their own power since the sixties. That humans are strong enough to power their own flight is a matter of historical fact, not my opinion. We are merely experimenting with a new approache......
User avatar
By spork
#369494
Greg Vandenberg wrote: Spork.......... humans have flown hundreds of kilometers under their own power since the sixties. That humans are strong enough to power their own flight is a matter of historical fact, not my opinion.
I'm very well aware of the history of human powered flight. But at the moment we're talking about you and the ornithopter you're building. My numbers above are pretty straight-forward - and the conclusion is a matter of math - not my opinion. You want to change my assumptions - have at it. Are you 7 times as powerful as the average human? Can you get 20:1 L/D? Are you planning on a propulsive efficiency greater than 0.75?
User avatar
By dayhead
#369495
I am skeptical that a human powered ornithopter capable of sustained flight is possible.

However, when I see a soaring bird use a low frequency, low amplitude flap to get a slight boost in performance, I have hope that maybe someday we'll be able to do that much.

Even if it were quite strenuous, It would be helpful if I could momentarily get a glide angle boost for a few seconds, just enough to clear that ridge, or make it to a thermal just out of normal reach.

The model ornithopters I've played with seemed to require a lot more rubber band/ watts than propeller driven planes.

For a temporary boost in performance, a pedal powered propeller would likely be more practical.

Just my $.02.
User avatar
By spork
#369497
dayhead wrote: For a temporary boost in performance, a pedal powered propeller would likely be more practical.
Probably so. But you have to carry the weight and mechanics for flapping flight the whole time. Perhaps it could be done, but I think it would be quite an engineering challenge to end up with a net gain. In the case of the current design, the pilot position would cost you much more drag in the long run than you would gain back during your pedaling periods. Certainly you could put the pilot prone, but it's going to be hard to make an ornithopter with the aerodynamic efficiency of a non-flapping wing - not to mention the extra weight.

As I said - I wish I were wrong. Hell - I hope to be proved wrong. But the numbers look extremely challenging to say the least.
User avatar
By Greg Vandenberg
#369501
Spork, ...... to avoid any of our readers becoming to despondent at their apparent human feebleness, I must correct you. Your power for flight calcs are impeccable, and Power required of just under 1kW straight and level, is what I am working on. The figure you use for human power output is however the wrong one. You are quoting metabolic power consumption which is calculated according to the amount of oxygen consumed by the cells in 'burning' glucose. It is basically the fuel usage of the muscles over time. Wikepedia is unusually pessimistic in this instance. NASA puts human metabolic rates at 0.75kW - 1kW for short bursts (a few minutes) and 300W - 400W sustained up to an hour.
The amount of mechanical power, or work over time, achieved by those muscles burning that fuel is where the fun starts. A number of scientific methods have been developed over the past few decades. There is the Lewis formula, Harman formula, the Johnson and Bahamondi formula and the Seyers formula to mention a few. They all approach human power output through the physics of a vertical jump and they then quote peak power and average power. ALL of these rate the human power output of one vertical jump from standstill to 60cm altitude (altitude......yay!) by a 75kg person at peak between 5kW and 8kW and average power between 1.2kW and 2.4kW.
This is based on the phsical work done and not your oxygen consumption. You can stand still holding a bag of cement and achieve 0 work done over a time period (equals 0W) but have a metabolism of say 150W the whole time due to tense muscles. Now the fun really starts. I can jump vertically to an altitude of 1.2m every 1.2 seconds almost indefinitely with a probable metabolic power consumption of around 50W and a mechanical average power output of around 5kW ?!!
Its called a trampoline, and beautifully exhibits the 'magic' of closed oscillating systems. Kangeroos have been tapping into that for millions of years. Don't let me get started on swings:)
Thank you for this great discussion by the way, I do love a good, honest debate........... it brings everyone to better understanding, including me :)
User avatar
By spork
#369502
Greg Vandenberg wrote:I can jump vertically to an altitude of 1.2m every 1.2 seconds almost indefinitely with a probable metabolic power consumption of around 50W and a mechanical average power output of around 5kW ?!!
Its called a trampoline, and beautifully exhibits the 'magic' of closed oscillating systems.
The numbers I used are for the energy required to maintain level flight. Your trampoline is returning nearly 100% of your energy on each bounce. The ornithopter will return none of your energy from the numbers I used.

I want to see you succeed. I think you have your work cut out for you. I personally wouldn't attempt to make a "practical" HPV.

Incidentally, no matter how you measure human output, the Gossamer Albatross required about 0.4 H.P. to maintain level flight in still air. On the one hand that may have been a much longer flight than you have in mind. On the other hand the pilot was an elite athlete putting out everything he had. I think it's unrealistic to assume many HG pilots are going to put out more than 1/2 H.P. even for a 5 minute burst.
User avatar
By red
#369509
Greg Vandenberg wrote:I can jump vertically to an altitude of 1.2m every 1.2 seconds almost indefinitely with a probable metabolic power consumption of around 50W and a mechanical average power output of around 5kW ?!! Its called a trampoline
Greg,

Okay, now ya done it. 8) The real ornithopter that I saw used a DaVinci rig to flap, with both feet on a flat plate. It was "real-world" to me, because that flappin' machine was built of HG components, not gossamer Mylar, unobtanium and carbon fiber. It protected the pilot with a hang cage, and landed nicely on skids, with a great landing flare and a final flap, like the birds do it. Pushing the foot plate rearward caused a down-beat of the wings. Weight of the pilot and craft made the up-beat happen, of course, but the arms helped the flapping, and the arms could pull the wings up, if necessary. The foot platform slid rearward on the metal tubes of the frame, to flap down. There were long coil springs on the frame tubes that were compressed as the foot platform moved forward, so a down-beat of the wings then had compressed springs to assist the leg power. The inventor said about 80% of the power needed for each down-beat of the wings came from the springs. I had no way to verify that estimate, but that guy sure could flap. It is not exactly a trampoline, but a lot of energy was stored in those coil springs that would otherwise get lost.

While the following "brake" trick would not apply easily to your design, the DaVinci rig I saw could be locked at any part of the flap motion, by tilting the foot plate to bind on the frame tubes, rather than slide. This lock mechanism made gliding easy and restful. The foot plate worked as brakes rather like stepping on the car brakes with your toes. Push with the feet flat, to resume flapping. The "brake" was set to lock the wings in position for launching.

From the little that I have seen of your invention, I believe a leaf spring may be better suited to your craft than coil springs. That leaf could possibly replace or parallel a rigid member now in your airframe. You might be interested in the unconventional carbon fiber rear leaf spring of the newer GM Corvettes, for this purpose. This part would have good test information available, and the part is relatively light and obtainable (existing hardware). Changing the width or thickness of the CF leaf would give you various spring rates, as needed.

Have fun!

:mrgreen:
User avatar
By Greg Vandenberg
#369519
Uh oh....... I think you've been infected. Thats the kind of thinking that takes you to yet unexplored places :mosh:
I actually have the energy retention system made already, I'll install it when the flap tests are imminent. Once mutiple glide test are complete together with the mods that they will inevitably incur I'll be ready for that. I have gone with a pneumatic cylinder / piston rig similar to the things that hold a cars tailgate. Reason being that I can vary the pressure easily on the field to experiment with different elastic modulus'. Theory says I should be able to harmonise the Skybikes eigenfrequens with my own via the elastic modulus to set up a borderline dynamically unstable oscillation and hitch a ride on physics.........I can see the headline now 'Skybike ryder caught in runaway Pilot Induced Oscillation crosses North Atlantic.............by mistake :mrgreen:
User avatar
By Greg Vandenberg
#369656
My next test with new improved wings incorporating cutting edge technologies from the windsurfing industry, is happening early June 2015. I will be streaming it live on my channel. Please subscribe to my channel by clicking on the link below and then click the subscribe button. You will receive notification of the date and time of broadcast automatically. You will also receive notification of my update clips as soon as I post them. All no charge of course :)
User avatar
By Angelo
#370722
Is anything structural holding those wings besides your arms? From the video I see, there is nothing to keep those wings from folding up under load besides your arms, is that correct? If so, I can't see just your arm strength keeping those wings from folding up under load.
User avatar
By Skyvine
#371418
Good luck with your project, Gregory.

One item that make me nervous is that your wings have independent angle of attack that appears to be controlled solely through the pilot's (your) arms.

Based on design testing we did at Bright Star in the late 1980"s with alternate roll control systems, we decided that independent wing halves presented more problems than they were worth. In low bank angle situations, the glider can be controlled by weight-shift to actuate the separate wing halves. However, as soon as any slipping or yaw was introduced, asymetrical loads increased almost instantaneously to where aerodynamic forces exceeded the pilot's ability to counteract them. The result was totally loss of control.

Please be very careful in your progression, and fly only as high as you are willing to fall until you have fully explored the limits of your control systems. And, as Red said, please, please, please wear a decent full-face helmet.

Again, all the best to your success.

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