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Flyboy51
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Posted: Tue Aug 18th, 2009 10:45 pm |
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David,
Thanks for the moral support. My first post was understandably short; to see if anyone was interested. Consequently, I didn’t go into much detail.
I don’t want to overstate my successes. I was definitely in the “development” mode. Most flights ended in either a structural component breaking, which planted me on the ground, or a failure of the flapping system to function as desired, which, again, planted me on the ground. Luckily, not much altitude was ever achieved in those cases, so my falls were short. Although the aircraft may have suffered, I never got more than a few scratches and bruises.
I’m an aerodynamicist, structural analysis is not my strong suit. Paul McCready’s philosophy on the Gossamer Condor was, “If it hasn’t broken, it’s probably too heavy.” I mirrored that philosophy. My structural safety factors were small to start with. When I started flapping, all too frequently, the loads were greater than I’d expected and the structures responded accordingly.
The control system was a single “T” joystick that hung down from the main spar. Fore-aft movement controlled pitch, side-to-side movement controlled roll, and twisting controlled yaw. That freed up my feet to pump pedals that controlled the flapping. My legs would force the wingtips down; aerodynamic forces brought them back up. During a foot launch, I’d have to simultaneously pull back on the stick, control roll and yaw, and swing my legs up into the pedals. If I missed the pedals, I was back on the ground. If I focused too much on getting my feet up, I’d miscontrol the aircraft and end up back on the ground.
Although difficult, launching was just the start of takeoff problems. Wingtip travel was ±45°. To keep the tips from going to full up during launch, a pin locked the wing at small positive dihedral angle. Of course, with aerodynamic forces trying to lift the wingtip, there was a significant load on the pin. I would have to apply enough pressure with my feet to offset the aero load but not apply too much load to bind the pin in the other direction. More than one flight ended with me unable to free the pin, and therefore, unable to start flapping. The ground was always there for me.
Ideally, that pin would be re-engaged after flapping to altitude to lock the wing into a soaring position. Tolerance, air loads, structural twisting, etc. made it that I never achieved re-engagement. Any post-flapping flight I achieved required me to hold the wingtips steady with my feet. So, my already tired legs had to apply a constant, steady force. If I let the tips deflect to their full 45° up, the glide ratio deteriorated, and the ground was again ready for me.
The only successful flights I had were launched downhill, into an uphill wind. I really don’t know how much altitude gain was due to ridge soaring and how much was due to flapping. I’d like to think that all that effort pumping my legs wasn’t for nothing.
In the end, I’d had a couple of good flights, McCready had won the Kremmer prize, and my wife had impressed upon me that the next structural failure might occur at an altitude that would be less forgiving. At most, my achievement is a small footnote in aviation; I am still in awe of what others have accomplished, maybe more so, having been there.
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D.Bernardin
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Posted: Sun Aug 23rd, 2009 12:12 pm |
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Flyboy51 wroteThe inboard portion of the wings were fixed. The outboard 5' flapped. The natural flexing and twisting of the wings, plus the extreme light weight, were accomplished by using a Princeton Sailwing.
Unfortunately, I have very limited photos and notebooks from back then. But I would be more than willing to share my experiences and knowledge with anyone interested
Hi, Flyboy51,
Very intersting results, I agree with your solution of 5' flapped . Can you tell us a little more about your realisation : blowing, airfoil(s), structure, how was obtained the flexibility of the winglets, stabilizer, spar ... ? Could you give us a 3 view drawing ? Anyway, congratulations and muxus thank yous .
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Jon Howes
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Posted: Mon Aug 24th, 2009 03:14 pm |
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Flyboy51,
Fascinating stuff, we may be pointing in similar directions, see http://www.ornithopterresearchgroup.com/view_topic.php?id=115&forum_id=8&page=1
About the 8th post down. My approach is to (hopefully) use the early hydrolytic energy burst to grab some height and then to use whatever is left for glide extension and thermal hunt. If you follow the thread above you will get the general idea.
I would be very interested in swapping notes as your experiments look very similar.
Jon.
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Flyboy51
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Posted: Mon Aug 31st, 2009 05:21 am |
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D.Bernardin
Unfortunately, after 30 years and numerous moves, any notebooks I had from my ornithopter project have long since disappeared. There are no 3 view drawings, or any other sketches, any more. There are, however, a few photos taken during various stages of construction.
The airfoil I used was a Princeton Sailwing. A Google search should turn up some technical papers on this section. If not, I can probably find something, if you’re interested. Basically, the Princeton Sailwing has a leading edge spar (either round or “D” section), a root rib, a tip rib, a trailing edge cable, and a fabric envelope. Its maximum lift coefficient is around 1.6. A couple of hang glider designs in the early 70s were flying with this wing. I choose it because of its extreme simplicity and light weight. I used the “D” section leading edge because it offered a slightly better L/D. I also added an intermediate rib at the end of the fixed spar, to anchor the tip flapping section. Because of its variable camber and flexibility, it lent itself well to tip flapping.
Roll control was through wing warping, by bending up or down the tip rib. I had no scheduled fore-aft movement or tip twist during flapping. Tip twist was just a natural outcome of the flapping load. This was not particularly efficient, aerodynamically, but it did save a lot of weight.
The first photo attached shows the basic structure of the machine. It’s just an aluminum tube tailboom attached to the spar. The spar was aluminum, probably 0.025” (hard to remember exactly, but I formed it by hand over a ½” rod so it couldn’t have been too thick). The rear side of the “D” was a truss work of aluminum stringers (see second photo). Even today, it would be hard to make that structure lighter by switching to composites.
The third photo shows more of the overall structural layout. This was an earlier version, when I was trying to provide a fiberglass pod for the pilot. (The wooden stand is just to hold the aircraft while I was working on it.) All cables, structural, trailing edge, power transmission, etc., were Kevlar. The Kevlar cables were as strong as steel cables but weighed only a fraction of what the steel ones would. In 1976 the company making the Kevlar cables was going out of business; I’ve never seen this product again.
All of the photos I have here show the early tail. This was an all-flying tail attached to the tailboom via a universal joint. With the anhedral in the horizontal surfaces, I had to add some mixing to the rudder and elevator controls. That pretty much cancelled out the weight savings I was shooting for. Later versions used a more convention fixed horizontal with movable elevator and fixed vertical with movable rudder. All were bent tube and fabric covered.
As the photos show, I did most of my work in my backyard and my garage. Flight testing was done at a nearby park. To put the aircraft away, and to transport it, it had to fold up. The simple structure allowed this. By removing a few bolts at the wing root and disconnecting some of the flight cables, the wings folded back and rested on the horizontal tail. The aircraft could be assembled or broken down in less than 15 minutes. I transported it on the roof of my car (a Pacer stationwagon!). One person could put it on the roof, but two made it a lot easier.
Jon,
I looked over your thread. Great minds do think alike!
Early on, I decided that sustained human-powered flight just wasn’t going to happen. Better to mimic the eagle than the sparrow; get a little altitude and find a thermal. With my 33 pound aircraft, I could run into a wind on level ground and pop up 10-15’. From that height, I never could swing me legs up and start pumping before I was back to ground level. I had hoped, with more experience, to overcome that shortcoming. Launching downhill, however, offered me more time to transition from running to pumping.
If I were to do it again (the benefit of hindsight), I’d probably pay the weight penalty to put a couple of lightweight bicycle wheels on the frame and never try to foot launch. I might even try to power the wheels to aid launching, by allowing greater ground speed. Strapping the pilot into one position for launch and flight just makes his/her task so much easier.
Attached Image (viewed 287 times):
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Flyboy51
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Posted: Mon Aug 31st, 2009 05:29 am |
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| Is there a way to post more than one photo per message? Here's the second photo referred to above. If you zoom in, you can see the truss work on the rear side of the spar. Attached Image (viewed 366 times):
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Flyboy51
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Posted: Mon Aug 31st, 2009 05:32 am |
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| And the third photo. This one shows the structure, prior to adding wing coverings. Please ignor the fiberglass pod and the wooden work stand. The pod didn't survive the first launch and "landing". Attached Image (viewed 364 times):
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robhannum
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Posted: Mon Aug 31st, 2009 03:59 pm |
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| Very impressive....
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D.Bernardin
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Posted: Mon Aug 31st, 2009 06:40 pm |
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Hi, FlapBoy,
Thank you for your complete description . I understand now what is a Princeton Sailwing .
With your work and your knowledge, you have shown that Human Flapping Flight is possible . Bravo !
Last edited on Fri Jan 22nd, 2010 08:19 pm by D.Bernardin
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D.Bernardin
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Posted: Fri Jan 22nd, 2010 08:26 pm |
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Looking for news of the HPO canadian team i have found the link of their photo-gallery . It shows the avancement of their work during 2009 summer :
http://www.flikr.com/photos/hpoproject/3820643290
I remain without understanding the flapping system of the HPO, ¿bending the spar?
Perhaps, ¿or is there an articulation they dont want to show? Wait and see !
And remember their page :
http://www.hpoproject.ca
Last edited on Fri Jan 22nd, 2010 08:54 pm by D.Bernardin
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