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Flapper Fan
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Posted: Fri Sep 28th, 2007 11:31 am |
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Patrica,
I am aware that you think that a true Ornithopter must take off under its own flapping flight thrust. I have found that the web sight for Prospective
concepts http://www.prospective-concepts.ch/html/site_en.htm has many interesting projects outlined.
In particular their Kanguruh http://www.prospective-concepts.ch/html/site_en.htm which uses a aircraft contained catipult is interesting for ornithopter launch as it is claimed to simulate the takeoff of a bird. Would you consider an ornithopter using this type of launch to be a true ornithopter for the purpose of establishing the claim of first successful ornithopter flight?
What do other member think?
Grant
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PatriciaJB
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Posted: Fri Sep 28th, 2007 04:34 pm |
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Hi Grant,
I think the most important item for ornithopter definition purposes is that the orni' does not have fixed wings or anything else that produces either thrust or lift while in flight.
I'm not as rigid on power assisted take-offs as I once was  ie: I think that powered wheels to assist in shortening the TO run might be OK for initial testing purposes. The main problem with auxilliary assisted TO is that it's dificult to tell whether the orni then truely does sustain flight by flapping it's wings or whether it just performed a 'zoom' ie: converted the airspeed produced by the power assist into altitude and then glided to a landing [this is not sustained flapping flight].......even if the aircraft stayed aloft for a considerable time, you still wouldn't be sure that it wasn't still using the power assist [ eg: jet engine such as the UTIAS hybrid aircraft has. During their flight last year, the jet engine was never turned off. The pilot is now claiming the first sustained flight in an ornithopter !! see http://www.ornithopter.ca/pilot_s_corner_e.html .... and this is an aircraft that not only has an auxilliary jet engine but also has auxilliary fixed wings !!!!!] ..... or thermalling etc whereas with no auxilliary power assist on the take-off, you are completely certain that it would never have got off the ground to start with without the flapping wings !........so, I think that a power assist that doesn't work in the air such as powered wheels MIGHT be OK [ but to completely avoid doubts even this should be avoided . After all, the purpose is not just to be first , the main purpose is to develop a successful ornithopter that doesn't need any auxilliary assistance]
Cheers,
Patricia
Last edited on Fri Sep 28th, 2007 04:37 pm by PatriciaJB
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Flapper Fan
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Posted: Fri Sep 28th, 2007 06:16 pm |
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Good answer and I assume that you are agreeing that the jump takeoff of the referenced web site (Kanguruh) is acceptable. As previously stated this looks like a good concept, the idea of separating the takeoff requirement from the sustained flight requirement.
With reference to the video of Denis Curry http://www.humanpoweredwing.co.uk/index.htm
I believe he would have better takeoff thrust if the wheel to wing linkage were reversed.
The motion should be wing-up wheel-down in order to amplify the flap effect. This is also opposite the motion of a typical sprung landing gear. It is not necessary to power the wheels if you instead power the landing gear strut. This is how the birds do it. It is my theory that this is perhaps how flight was developed. By swinging the fore legs (arms) opposite the rear legs power is added to the stride. This is a common gait amoung animals. The power can be added even though the fore legs never contact the ground. In that case the power transfer is through inertia and possibly aerodynamic forces. In this way you dampen the pitch and heave and obtain additional thrust for takeoff. Since the reaction is against a solid surface, the ground, it is more efficient than the wing flapping; especially at low speeds.
I have used this technique for hang glider launch and believe that it is effective. I would like to do more research in this area.
Grant
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murray
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Posted: Wed Oct 3rd, 2007 12:54 pm |
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I agree with Patricia that the primary interest in ornithopters is to combine the functions of lift and propulsion in one wing. Anything else is ploughing old ground.
For experimental ornithopters I don't reckon it matters how you get off the ground (the Wrights used rails and a slope). At this stage of development we should focus on the easiest goal, that is cruising flight at optimal airspeed. Actually I think that is also the main game. Once we learn to sustain level or climbing flight for a while and glide safely to the ground to repeat the exercise, then we might try something much harder, like taking off unassisted.
Unlike the pioneers such as Shmidt and Toparov, for whose experiments we can never know how much of a flight was simply zooming from the launch energy, today we can easily instrument the aircraft with something as simple as a pocket GPS to calculate the total energy at each point of the flight. It is simple.. measure the all up mass M, the instantaneous speed V and height h.
If the total energy E=1/2 MV2 + Mgh is maintained or increased, even briefly, you had sustained flight. Now do it again, for a bit longer, then again...
Murray.
Last edited on Wed Oct 3rd, 2007 02:14 pm by murray
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TedGM
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Posted: Thu Oct 4th, 2007 12:16 pm |
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I agree also with Patricia that the Orni's should rely on wings to provide lift and thrust without fixed wings. I may add that the wings should also use effectively in attitude control including the manipulation of the center of mass.
For take- off, which I believe is the biggest challenge we have to work hard for is to get the best and efficient power/drive source so that the wings can handle the take -off alone without using a runway.
Last edited on Thu Nov 1st, 2007 09:28 am by TedGM
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DDavis
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Posted: Sun Jul 20th, 2008 03:43 am |
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Driving down a narrow country road one day, I followed for some distance a giant Wedge Tail eagle cruising slowly along in front of me. It's great wings almost touching the trees on either side, beat at a relaxed pace of barely once per second. They barely moved through 30 degrees, in all. I imagine a craft of 16 metres span or so, suitable for supporting a pilot and possibly an engine, would require no more rapid a beat than might would suit a reasonably fit rower.
If powered by muscle, rowing seems to me the very best way of using all that we have got. We are up against it from the start... as we do not have the same kind of muscle as the typical wild animal, even those so closely related as are the great apes. A Kenyan mate used to say apes had 9 times the strength of we humans, and I thought him relating an old story. New Scientist magazine reported in recent years that they have 7 times the strength in their muscles for an equivalent weight... so clearly my mate knew what he was talking about!
(an aside here... I have a picture in my head that Hollywood should have thought of: 'Orangutan man' would be the only scientifically plausible superhero on the comic book market, and could include plenty of scope for craziness.)
By rowing, I mean the sliding-seat method as used by the Japanese ornithopter team. It uses the large muscles of the legs, back and arms and provides a long stroke at a steady, strong pace. I believe it is the only method of powering an ornithopter by muscle that makes any sense.
And, I've suggested this before... if a two man crew powered a craft similar to Toporov's dragonfly-craft, with the wings linked such that each rower looks after a wing at the rear and its diagonally opposite one at the front, we might have a quick success. I have a feeling about this one... it is unencumbered by need for neutral 'G' springs, it has a constant, steady thrust, and the strength of two athletes. If ornithopters ever get to be used in racing, it might be they're built along these lines.
Cheers, David Davis.
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Jon Howes
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Posted: Wed Jul 23rd, 2008 08:57 am |
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David,
We have a pair of herons that cruise around our local lakes with wonderful slow flap frequency and small amplitude, very inspirational and they certainly affected my views of flapping efficiency.
By the way, if wing pairs are mechanically linked then each rower does not need to look after one pair since the mechanical linkage will sort it out (as per Toporov in fact).
"(an aside here... I have a picture in my head that Hollywood should have thought of: 'Orangutan man' would be the only scientifically plausible superhero on the comic book market, and could include plenty of scope for craziness.)"
On the subject of superheroes missed by Hollywood, after Batman (man but with bat-like attributes), Catwoman (woman but with cat-like attributes), Spiderman (man with spider like attributes), we invented a new one based on my black, hairy assistant...... Catcat..... A cat with all the attributes of a cat with absolutely no special powers "You'll believe a cat can purr". This could run and run!
Jon.
Last edited on Wed Jul 23rd, 2008 09:35 am by Jon Howes
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D.Bernardin
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Posted: Tue Jun 9th, 2009 06:30 pm |
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Indeed , Jon ,
Your Cat-Cat assistant is "purpurring" since June 07 !
Then, thanks for its quite silent advices . It has to follow in this way : purring, it can give us a bit of wisdom !
I dont know if I am sufficiently mature to start back this discussion , I jump ! In the water, where The Cat will not follow me with its sarcastic purring !
As well as the horses and more animals , birds , bats , and probably pterosaurs , have various gaits . Why the ornithopters would not have it ?
With a nice surplus of power , animal can fly at a speed a lot below his own minimum speed of glide : I dont speak about hovering ( let it at humming-birds and insects ), only about the instantaneous take-off of most of birds , and the 45ยบ climb of pigeons and many other birds . The wake is completly irregular with perhaps any recuperation of energy at top or bottom of the loop ?
-First gait : flight at low speed ...
usually climbing hard ; wings are thrown down and forward ; so with help of extra- phenomenons , like unsteady aerodynamics , they create lift and thrust . Then , the wings are sent up in a short while to stop quickly the fall that is the direct consequency of no lift . To have as less drag as possible the run of the tips is up and backward . Really, animals does not fall but lose a part of the vertical speed gained before . In the case of an orni at low frequency (typically 1 hertz) no lift time would be dramatic !
-Second gait : sustentation speed is nearly reached ...
but not fully ; that means a great power expense too! A part of the lift comes from the own speed of the animal , another from the forward movement of the tips but lift is partially maintained at upstroke . It is the irregular wake gait often described , badly imitated but easy to understand . At upstroke AOA is low , lift too , and the drag of this run is little . At downstroke , AOA is high and the forces are thrust and lift . The flight is uncomfortable but animals are resistants at this kind of disagreements . And they use it just a while to reach 8-12 m/s , (or more , or less , "as you want it Charlie Brown") when they can use the ...
-Third gait : from the lower unassisted glide speed to top speed ...
it is the continuous wake gait ; lift must be a little more constant : it is one of the conditions of an economic flight . The positive balance beetween thrust and drag has to be obtained by different lift of the tips at upstroke and downstroke, and the mean is a longer downstroke than upstroke . That is why the movement direction remains down-forward and up-backward . At higher speed some animals could be rowing down-backward and up-forward ? What seagulls show me can be a little difficult to interpretate . Perhaps there is here an explanation of their intermittent flapping . Pigeons do send their wings down and backward . Perhaps the longer way at upstroke correspond with a light increase of lift (?): good for the wake , fatal for the thrust ! Or the animal accept a lower efficiency ? Or, downstroke has to be quicker than upstroke . Then, there is a lot of problems with the movements of the center wings : for little birds, not for manned ornis ... Perhaps, (I have to mind it) it could work in the case of a "semi" with little flapping parts .
Manned ornithopters are mostly interested in the third gait . Patricia has experimented bravely the second , necessary to accelerate the "heavy" UTIAS machine ! Man-powered HPO can try ! Or jump from the hill like paragliders ! Or anything else . Is it really so important ? We can ... first build an ornitho conceived for the third gait , and then ... try to fly it . If we dont forget the back and forward movement and are able to modulate it (the loop!) , we should be able to fly at various speeds . If the aircraft is light , efficient , and the pilot young and strong enough , we can try to use the second gait to take off from a runway . Problems like those encountered by UTIAS team have perhaps a solution : one only wheel with strong suspension , perhaps ? ... or at less a two wheels landing gear with a constant gauge .
I forgot to fold the wings at upstroke . No matter ! It is usefull at first gait , anything we will try later , or never! At second gait, less area at upstroke could be nice , but if we can avoid it ... More important is the constant wake of third gait . Does Jon's articulated wing reduce the area at upstroke ? It does'nt look , or just a few .
EDIT : I have made corrections . If you have some patience you could read it other time . I have left the "down backward" movement . It is an hazardous hypothesis, but I am not ashamed to risk a difficult idea and to be wrong or nearly . I comment it down there .
Last edited on Thu Aug 27th, 2009 01:03 pm by D.Bernardin
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D.Bernardin
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Posted: Sat Jun 20th, 2009 07:08 pm |
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Anyway , this thread being about "Defining an Ornithopter" I must risk to give my opinion : a real one is a machine that flies flapping his wings and is able , at less , to maintain his altitude . Better if it moves all the area of the wings ; I accept that my hybrid is not exactly an ornitho ! A built in assistance like winch or wheel that helps to reach take-off speed is acceptable , particulary the second one . Later , if we have anything like competitions , rules and categories should have to be defined , but only later ... At this moment the first thing is to fly with human power or a little motor .
Other thing : an ornitho has an interessant lifting-propeller that could have , in third gait, a very high efficiency. But as a propeller his pitch is very long . Consequency : poor thrust at low speeds . What happens if the center-wing has a very little amplitude ? (the outer-wing should have another articulation to obtain the desired loop) . But is it an ornithopter ? A better pitch would be obtained ?
Since it is more difficult to build than a fixed wing with flapping tips , I choose to simplify and fly an hybrid . But I conceive it as a first step . The seduction of full-flapping wing remains !
Indeed , cant you make a special place in your hearts , for those hybrids like Schmid Grunau Baby, "Karura", UTIAS students machine ( I suspect ), and so on ? They have quite the same problems as full , real ornithopters . Just simplify a bit ; isnt it ?
Last edited on Fri Jul 31st, 2009 07:18 pm by D.Bernardin
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D.Bernardin
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Posted: Thu Aug 27th, 2009 02:07 pm |
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About the gaits
I wrote : "Perhaps I am wrong" and later deleted it . I hope that there is less mistakes and sillyness after correction, but at first I was wrong !
Remain the case of the movement up-forward and down-backward !
In this case the thrust only can be obtained if downstroke is quicker than upstroke; that place us in a position similar to the usual third gait, but brings a lot of problems, at first with the center-wing movement . When tip goes up, center goes down by reaction, particulary if the movement is slow . And you cannot accept that this part of the wing is going up quickly! It would be making a lot of drag . Add that you cannot reduce the Cl of the center-wing : it is the rule to obtain a constant wake . Inertia, elliptic lift repartition, high frequencies, help to maintain the body and center-wing movement in a narrow range ... That is the case of little birds, perhaps of some medium sized one . A slow motion, heavy wings, rectangular lift distribution, impose that up and down strokes are executed in the same time : so the center wing in counter flapping can produce a little thrust at upstroke and moderate drag at downstroke !!!
I had set a trap (for myself at least), and had felt in it ! It was so nice to have a downstroke with lift directed strongly forward !
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