Coverage of Toronto Ornithopter

[Velko Velkov]

Originally Posted by nasredin hodja

Other necessity is to allow an easy movement of the ribs or battens around the spar with a torsionnal LE... or around a LE-spar.

I think this is necessary at hovering, when the wholl wing produce thrust, but not at horizontal flight, when the inner part of the wing produce lift.

[nasredin hodja]

I have put any "wish" of hovering as far of my mind as posssible : because it is sufficiently dificult to establish cruising speed conditions ! So I want at less 20º of positive twisting at upstroke, and a litlle less than -20º at downstroke : that is what is necessary at 20m/s and 1 Hz flap-frequency, for a very modest amplitud. If the wing is stiffer it is stalled on a large area at downstroke and gives negative lift at upstroke. All what I hate ! Sure we would hope delayed stall and so on, then stiffening our wings we will improve , or not, their efficiency. I have to complete my knowledge . Particulary I want to be able to analyse what happens with the dihedral-anhedral movement, for example in the case of an articulated wing. Sure it changes anything ! Perhaps we need less twisting, but less is not none.
Other point, Dear Velko, in all the cases wings of an ornithopter produce lift and thrust, at less at downstroke, and lift at upstroke. It is different in 45º flight of passerines : there is nearly no lift at upstroke, but we cannot mind in such a gait that is only valid for high frequency flapping. I don't want to speak about hummingbirds : their lift only can appear in very unsteady conditions. In quasi-steady conditions you would need a huge pair of wings to hover, at less in the range of a reasonable power applied at an alternative system.

[nasredin hodja]

I gave these angles as a minimum. They correspond at an amplitude quite feable, perhaps insufficient, I repeat, when flapping in quasi-steady conditions, wings are like a propeller at downstroke (but we are interested to the resistance at spinning, that is lift) and like a particular glider at upstroke. So the wings should follow the path corresponding !
Anyway, my purpose is to build very flexible wings, able to -45º, +45º if it is possible, and stiffen them by a very simple internal system, so I have them convenient for accelerations, slow flight and cruising speed, also a bit stiffer for gliding.
No doubt that here lies a big problem of conception !