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PatriciaJB
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Posted: Wed Jul 30th, 2008 05:12 pm |
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Hello Everyone,
Georges Fraise sent me these links.
http://urvam.free.fr/modules/tinyd1/index.php?id=2
Flight test video, photo's and article - Yves Rousseau's ornithopter
[French and English]
http://urvam.free.fr/modules/tinyd1/index.php?id=3
Photo of Georges Fraise's ornithopter.
[ text in French]
Hello Georges,
I'm very happy to hear that you are recovering from your accident. I have been thinking of you.
Thankyou very much for sending me these links.
Patricia
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Flapangle
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Posted: Fri Aug 1st, 2008 12:46 am |
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Hi,
While watching the very good Yves Rousseau's video, I noticed that it was climbing on the upstroke and dropping on the downstroke. It is normal for a wing to have less lift and thrust on the upstroke, so the added lift may be due to the apparent pitching up. The confusing part is, what is causing the pitch up? The cg seems fixed and I don't see coupled elevator movement, so it might be caused by airfoil center of pressure travel. Since a typical airfoil would 'see' a lower relative wing angle during upstroke, I would expect that the center of pressure would move towards the trailing edge and would not cause a pitch up. Is it unstable? Is the tow responsible? Any ideas?
George
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Georges
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Posted: Fri Aug 1st, 2008 08:00 am |
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Hello everybody.
After more than a year of stagnation I go back to work.
Patricia was kind enough to present my orni on the site.
All criticisms are welcome, it is always useful.
To read you soon.
Cordially.
Georges.
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Jon Howes
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Posted: Mon Aug 4th, 2008 02:47 pm |
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"While watching the very good Yves Rousseau's video, I noticed that it was climbing on the upstroke and dropping on the downstroke. It is normal for a wing to have less lift and thrust on the upstroke, so the added lift may be due to the apparent pitching up. The confusing part is, what is causing the pitch up?"
This is something I have experienced on models with simple (ie, non-articulated) wings. On these it was caused by the high thrustline as the wing descends from the top of the stroke causing a pitch-down. One of my biplane models (dragonfly style) actually had a tendency to bunt at full power due to this.
The pitch up would then simply be the converse of the thrust-induced pitch-down, ie, more drag on the upstroke retarding the aircraft via a point well above the CG. This could also be pilot respnse as I think I can see some significant elevator motion.
Jon.
Last edited on Mon Aug 4th, 2008 03:09 pm by Jon Howes
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Flapangle
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Posted: Mon Aug 4th, 2008 06:08 pm |
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Hi Jon,
Jon said: "This is something I have experienced on models with simple (ie, non-articulated) wings. On these it was caused by the high thrust line as the wing descends from the top of the stroke causing a pitch-down. One of my biplane models (dragonfly style) actually had a tendency to bunt at full power due to this.
The pitch up would then simply be the converse of the thrust-induced pitch-down, ie, more drag on the upstroke retarding the aircraft via a point well above the CG. This could also be pilot response as I think I can see some significant elevator motion."
I forgot about the thrust line. I should keep a long checklist Handy.
The induced drag would increase as it zooms and slows, its requirement for twist to stay in a reasonable drag bucket would also increase as it slowed, but it wasn't getting more twist. The same thing happens to my model ornithopters when they fly too slow, even with active twist. Of course the models flap so much faster so watching this video was the first time I could actually see what the wing was doing during an airborne flap.
George
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PatriciaJB
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Posted: Sun Aug 24th, 2008 03:43 pm |
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Newspaper article about the human-powered ornithopter currently being designed and built by a group of UTIAS students. It sounds like it's almost ready for testing !
http://www.allistonherald.com/allistonherald/article/111886
Last edited on Sun Aug 24th, 2008 03:44 pm by PatriciaJB
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Jon Howes
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Posted: Sun Aug 24th, 2008 04:34 pm |
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The very best of luck to them, I hope they succeed.
Jon.
Last edited on Sun Aug 24th, 2008 04:34 pm by Jon Howes
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PatriciaJB
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Posted: Sun Oct 12th, 2008 03:20 pm |
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PatriciaJB wrote: Newspaper article about the human-powered ornithopter currently being designed and built by a group of UTIAS students. It sounds like it's almost ready for testing !
http://www.allistonherald.com/allistonherald/article/111886
Here's another article about this ornithopter with more info, photo's etc.
http://www.theaerodrome.com/forum/pioneer-aviation/14678-wing-flappers-16.html
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DDavis
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Posted: Sat Oct 25th, 2008 11:39 am |
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I’ve been reading of the latest human powered ornithopter project by the UTIAS students with interest… but finding myself critical of some aspects of its design. Particularly, the 28 metre wingspan they feel to be necessary. I could well be wrong… but I have a feeling the sheer size of this craft is going to work against it. I do like the rowing method they intend to employ, but feel it needs a little more refinement.
What I am getting to here, is the frequency of the wing beats. Having watched a large Wedge Tail eagle flying ahead of my car in an effortless display of power and grace, flapping its wings through a shallow angle and perhaps less than one cycle per second, I believe it likely that an animal the size of a large pterosaur is likely to fly in a very relaxed manner indeed. But I am going purely by intuition here… because I haven’t yet noticed any calculations as to the relationship between wing span and the flapping frequency in this forum or any other discussion on ornithopter flight yet. Correct me if I am wrong… but I am feeling that this highly critical factor has never been properly analysed.
If a 15 metre wingspan pterosaur were to flap its wings at the natural rate of a rowing athlete, I suggest a 28 metre wing might only require 10 or so cycles per minute to accomplish a comfortable powered flight. If so, then the rower has time to put in two or three strokes to every cycle of their wings. Obviously, if you can do this then you have the power of more than one athlete at your disposal for no extra weight but for the more complicated mechanism required.
I suggest that such a mechanism might employ hydraulic actuators combined with an hydraulic accumulator, or perhaps pneumatics… (though this might prove to have greater losses) Such a transmission might prove difficult to build sufficiently lightly, but with modern materials perhaps it can be.
Another approach might be electrical… perhaps combined with a flywheel to serve a similar function to an hydraulic accumulator. A lightweight flywheel spinning at high speeds will store energy more efficiently than the old-style approach of using a heavy flywheel, so perhaps this might be workable. (I read this in either New Scientist or Scientific American many years ago. It might sound counter-intuitive, but it was what the article concluded and it suggests to me that with even more modern materials might only prove truer and allow a very lightweight flywheel to be employed.)
A flywheel might offer a further advantage, in that it could be employed to store energy to power a winch for an assisted takeoff… (which could be released to fall free once having done its job) It would still be human power doing the job but would allow one to build up as much energy as required at one's leisure. I see nothing wrong with winch takeoffs. After all… an albatross needs to run to takeoff from level ground, so if we do as well it can hardly be called cheating.
A winch takeoff also gets us around the problems of clearing the ground with our wing tips if they were flapping… we can treat our craft as a fixed-winger for the takeoff and only begin flapping once clear of the ground.
A final note… the article on this latest attempt seems to ignore the fact of Vladimir Toporov’s partial success back in the early 1990’s. While I gather this wasn’t quite so successful as Toporov might have liked… I do read that he was able to maintain 50 kph (much faster than UTIAS srudents expect to achieve) and increase his height during his short flight on the power of his flapping wings alone. I haven’t heard just how long this flight was, but perhaps it was longer than the Wright Brothers first hop… which was less than the length of the cabin of a 747. The man should be a lot more famous than he is…
David.
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DDavis
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Posted: Sun Oct 26th, 2008 11:38 pm |
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A further thought on this subject... a winch takeoff also means we only need a simple undercarriage as a sailplane would use. Otherwise we have to allow plenty of height for wing clearance with a flapping takeoff, and that would also need to be sturdy to handle the bucking that would likely occur. Both of these factors inevitably means more weight.
Cheers, David.
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PatriciaJB
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Posted: Mon Oct 27th, 2008 12:17 am |
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DDavis wrote: A further thought on this subject... a winch takeoff also means we only need a simple undercarriage as a sailplane would use. Otherwise we have to allow plenty of height for wing clearance with a flapping takeoff, and that would also need to be sturdy to handle the bucking that would likely occur. Both of these factors inevitably means more weight.
Cheers, David.
Yes, that's true and that's why many current designs incorporate winches etc.....but, if you design an ornithopter for a winch - that is precisely what you will get !! ie: an ornithopter that has to use a winch to take-off !! The design is automatically restricted to assisted take-offs [due to weight, structure etc] and can never go beyond that because the designer wasn't thinking beyond that point when he/she decided to use an assistive device.
That kind of designing wouldn't easily lead to progression to unassisted take-offs anywhere. My view is that we should always be thinking of this ultimate goal when we are designing our ornithopters.
BTW: re: wing span, mass vs flapping frequency - there have been many studies done - see the Journal of Experimental Biology website.
http://jeb.biologists.org/contents-by-date.0.shtml click on 'search' and type in keywords to search.
Cheers,
Patricia
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PatriciaJB
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Posted: Tue Nov 25th, 2008 01:01 am |
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PatriciaJB wrote: Newspaper article about the human-powered ornithopter currently being designed and built by a group of UTIAS students. It sounds like it's almost ready for testing !
http://www.allistonherald.com/allistonherald/article/111886
The group now have a website which gives much more information on their ornithopter... [ including updates and photo's]
http://www.hpoproject.ca/?q=content/the-project
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DDavis
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Posted: Sat Nov 29th, 2008 10:15 pm |
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EDIT:
Hi David
This thread is for ' Manned ornithopter updates' [of ornithopters that are actually under construction]
So I've moved your message into the 'Flapping Flight - misc discussion' thread in the 'Flapping Flight - Misc' section.
Cheers,
Patricia
Last edited on Sun Nov 30th, 2008 02:09 pm by PatriciaJB
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Flyboy51
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Posted: Sat Aug 15th, 2009 05:47 am |
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Hello everyone,
I recently stumbled across your forum and found it brought back many memories.
30+ years ago I was competing against Paul McCready for the Kremer prize. His Gossamer Condor obviously beat me to the finish line. Where he followed fairly conventional methods, I took a more novel approach; something I'm sure you all would be interested in. I built, and flew, a foot-launched, human-powered ornithopter. This was pre-internet. Since I lost out on the prize, I never sought publicity and hung up the project to work on other endeavors.
The attached photo shows me, with my two daughters, prior to one of my test flights in 1978. The aircraft, Daedalus, had a 33' wingspan and a 33 lb empty weight. After running and foot launching, I would pull back on the stick to trade a little speed for altitude. With an altitude of 10-15' I only had a second or two to swing my feet up into the pedals and start pumping. After a minute or so of pumping, I could gain about 100'. At that time I was spent and became a glider, looking for thermals.
The 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.
Attached Image (viewed 1326 times):
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DDavis
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Posted: Tue Aug 18th, 2009 02:09 am |
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Flyboy51... your post is a revelation! It says that human-powered ornithopter flight has already been accomplished way back in 1978! You were able to climb by muscle power alone to 100 feet altitude, and then continue to fly by the use of thermals. This is a greater achievement than even that of Vladimir Toporov many years later. If you had done it today in front of the modern media and its cameras, I feel sure it would have made front page news all over the world.
With modern materials and methods of design, it should be possible to do even better. I look forward to seeing where this post of yours leads...
Cheers, David.
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