Coverage of Toronto Ornithopter

[nasredin hodja]

Originally Posted by mscott

I am inclined to agree with Audrey here. Some time ago the suggestion was aired on this forum of using a small engine (then postulated to be driving a propeller) as an initial power subsidy for training a pilot/athlete to fly a human powered ornithopter. UTIAS's jet is a bizarre and inefficient but perhaps convenient way to explore sustained motor-flapping. Using its steady thrust they could for example more confidently fly it out of ground effect, retaining power and control for a fixed-wing landing in case the flapper had to be stopped for structural or control reasons. Also by sustaining fixed-wing flight it would allow flapping tests to begin at low frequency and progressively increase to full power, yielding valuable in-flight control, thrust and efficiency data. Patricia you will recognise that lift-offs are not sustained flight. There are additional control, structural and power issues in accelerating beyond stall speed and climbing out of ground effect. The above considerations make this seem to me a reasonable step.

I agree with you however Patricia about the perversion of fitting a fixed wing! That is beyond the pale.
Murray.

Yes sure, Murray, but if they would have been able to reduce their jet propeller, it would have been better for manned ornithopter's reputation. A lot of people would'nt have nor seen at the fixed wings !

[KJELL]

Nasredin.
I think it is important to separate Forward thrust and lift.
http://www.youtube.com/watch?v=49Ha9qwvkAw
http://video.google.es/videoplay?doc...5214618267129#
Kjell

[nasredin hodja]

Separate Kjell, separate. Always it will remain anything.
A common glider use his lift to create thrust, and gets 100% efficiency of this transformation in all his flight domain. Drag remains although does'nt cost more than its own.
Using this marvellous property we can realise an efficient orni, and only by this way. You can have other conception, and I have a lot of consideration for your work, but you are far to persuade me. Even in the case of an hybrid, lift and thrust are in the same basket. The planes of your videos do not escape : the fan propeller changes flow around the fixed wings.

[KJELL]

Gliding has nothing common with Fan-flapping wing movements. The air movement is different and so the thrust is different.
I recommend you to study my videos
http://www.youtube.com/profile?user=...18/l8P4hTk15VA
http://www.youtube.com/profile?user=...17/vnl4NLOTTao
http://www.youtube.com/profile?user=...16/j28ZZSqD0Hk
Kjell

[nasredin hodja]

Other time, Magnus effect, that is all you demonstrate Kjell !

Back to our subject : flapping is nearly gliding and it's efficiency must be treated, at first step, by the same ways that for a glider. I dont put a list but mind at A/R, lift repartition and so on. And since there is a particular movement, flapping, it is not so easy !
Let me explain a little more my position : Down-stroke produce thrust because the wings are going down (!), the same as a glider that find a propulsive force in his way down. The difference is in the fact that orni's body does'nt lose height, all the contrary. That is due to the force applied, that is converted by the same mean as gliding : Inclinating the resultant until it is vertical in the case of gliding, a littlle more in the case of flapping since we have to fight drag of the following up-stroke. This one is more easily accepted as a gliding phase. Evidently, it does not need an external force to be realised. But it is a superficial point of view, better to see it as a gliding phase where the tips move up to avoid the fall of the body, as far as possible, since we can imagine the consequent heaving. Each thing on his time !
Then, what are the conditions to approach the 100% efficiency, I mean the efficiency that does not need a watt more than the glide of the same "bird".
At first the difference of lift must be obtained by a different way than changing the AoA, to avoid the formation at each TDC and BDC of a new "starting vortex" someone called it vortex release. Solution : the loop, a conical trajectory of the tips, whose base is an inclinated ellipsoïd, or anything like that... the best beeing "Marey's loop" from the name of the movement's photograph.
And more : As far as possible we have to keep a good lift repartition. It results difficult but not impossible at downstroke since the tips are accelerated. Its a little easier at up-stroke, the tips going backward can lose lift but can also be a little up the "best" gliding repartition. It depends of how much the loop is inclinated. Anyway they remain close of a correct distribution.
Now a third point : To have less energy in the wake, the induced drag would have to be the same at up-stroke and down-stroke (or not ?). Properly impossible, but, why a lot of birds reduce span at up-stroke and use a swept planform ?
There are more conditions at a high efficiency of flapping, I will post my ideas later, but yet you can see that most of the realisations and the projects do not fill these two first ones.
These mindings are for the cruising speeds.

[KJELL]

Originally Posted by nasredin hodja

Other time, Magnus effect, that is all you demonstrate Kjell !
.

What is you opinion?
The Fan-effect is a strong Magnus effect or The Magnus effect is a strong Fan-effect?
Kjell

[nasredin hodja]

Since the AoA change quickly at each top and bottom DC, the thrust can be quite strong, and at the same time you can have a big lift coef. at the beginning of each stroke if your machines are little and quick, but you cannot hope a big amount of thrust from this part in your static thrust proofs. I dont know what remains of added mass in your last disposition. Perhaps it participates of the propulsive effect, perhaps it enlarges the span ? Anyway the phenomenon however you call it, implicates a change of AoA, all the contrary of what I look for !
Nevertheless there are interesting results for pitching and plunging wings or fins, particulary in water.

[KJELL]

Originally Posted by nasredin hodja

Spanish women experiment it from a long time with their fans !
.

Nasredin.
When the Spanish women are using their fans.
They are not pitching and plunging. They are FANNING. The same do fishes with the tail and insects bats and birds with the wings.
Kjell

[nassir]

Originally Posted by nasredin hodja

Other time, Magnus effect, that is all you demonstrate Kjell !

Back to our subject : flapping is nearly gliding and it's efficiency must be treated, at first step, by the same ways that for a glider. I dont put a list but mind at A/R, lift repartition and so on. And since there is a particular movement, flapping, it is not so easy !
Let me explain a little more my position : Down-stroke produce thrust because the wings are going down (!), the same as a glider that find a propulsive force in his way down. The difference is in the fact that orni's body does'nt lose height, all the contrary. That is due to the force applied, that is converted by the same mean as gliding : Inclinating the resultant until it is vertical in the case of gliding, a littlle more in the case of flapping since we have to fight drag of the following up-stroke. This one is more easily accepted as a gliding phase. Evidently, it does not need an external force to be realised. But it is a superficial point of view, better to see it as a gliding phase where the tips move up to avoid the fall of the body, as far as possible, since we can imagine the consequent heaving. Each thing on his time !
Then, what are the conditions to approach the 100% efficiency, I mean the efficiency that does not need a watt more than the glide of the same "bird".
At first the difference of lift must be obtained by a different way than changing the AoA, to avoid the formation at each TDC and BDC of a new "starting vortex" someone called it vortex release. Solution : the loop, a conical trajectory of the tips, whose base is an inclinated ellipsoïd, or anything like that... the best beeing "Marey's loop" from the name of the movement's photograph.
And more : As far as possible we have to keep a good lift repartition. It results difficult but not impossible at downstroke since the tips are accelerated. Its a little easier at up-stroke, the tips going backward can lose lift but can also be a little up the "best" gliding repartition. It depends of how much the loop is inclinated. Anyway they remain close of a correct distribution.
Now a third point : To have less energy in the wake, the induced drag would have to be the same at up-stroke and down-stroke (or not ?). Properly impossible, but, why a lot of birds reduce span at up-stroke and use a swept planform ?There are more conditions at a high efficiency of flapping, I will post my ideas later, but yet you can see that most of the realisations and the projects do not fill these two first ones.
These mindings are for the cruising speeds.

the answer of your question is to vary the force which apply on the wing in the stroke and reduce the against gravity drag or the friction which is coming to the wing from the air if the bird doesnot reduce its span it will consume more energy in the fly

[nasredin hodja]

Thank you dear Nassir, but I still have a doubt ? Do they reduce area only to reduce lift and drag by the way of area and tip speed reduction, do they sweep the wings only for the loop, or do they increase at the same time induced drag to have more regularity in the WAKE ?
Its looks silly at first, but a continuous contraction-dilation of the wake must cost energy. So is it interesting to make a sacrifice ?
Only questions. I remain with the priority of maintaining AoA as regular as possible to have a wake more or less similar at a glider's one, and avoid, at he cruising speed, the formation of a vortex street as its produed when the ornithopter, bird or pterosaur changes lift by changing AoA.
When a fixed wing plane takes off, or when it changes of attitude, forms behind the wing the "starting vortex" and man consider that it does not change lift nor drag. But what about to trail a "tail" of these vortex ? That is why I believe in superiority of thrust by lift method, lift by thrust giving a stronger wake. Nevertheless if we can obtain a good flexibility of the wings allowing the constant AoA, why don't would we have a little more, particulary at upstroke, to accelerate at the take off run. Then, for a few time, a strong wake could be accepted. When the "bird" approach his cruising speed domain, it would be necessary to stiffen the wings moving a control dispositive.
By these words, I mean a control of stiffness, not an active control of AoA, that is a more involved system.