Ok so we were testing our heli today and we got the ceiling bumper at the top of the prop stuck into a crack in the ceiling. the prop stopped spinning and it was only sustained by the lower prop. I am fairly certain of this because the whole copter moved up and down in the crack and after about 6 minuets it left the crack and flew down in the normal manner, as it would have had it not gotten stuck, and landed with a normal amount of winds left. This Leads me to believe that it is possible stop the rotation of the top rotor and still have a legal flight which lasts much longer than a normal flight. However one must find a way of stopping the rotation which does not support any of the mass of the copter.
--- In Indoor_Construction_at_yahoogroups.com, "Bill Gowen" <wdgowen@...> wrote:
>
> Note to the moderator - the below is not a rules related post!
>
> Without the benefit of any actual knowledge on my part I think you can say that when both rotors are spinning they are getting equal torque from the motor and would therefore have something close to the same RPM. When you stop one of them the torque to the other one does not increase so there shouldn't be any major change in the RPM of that rotor. Therefore it will take something close to twice as long for the motor to unwind.
>
> In the process of attempting to design a helicopter myself I experimented with fins replacing the bottom rotor. This configuration wouldn't generate enough lift to fly. My GUESS is that the same would probably apply to most twin rotor copters. I think without the benefit of support by the ceiling they probably wouldn't stay in the air.
>
> Notice all the disclaimers in the above opinions.
>
>
> And part of the issue with on-line responses, if you are not there to see it, it could be hard to judge if held up mechanically or aerodynamically. Which, to me, makes all the difference in the world.
>
> Its also why I asked the theoretical question. Because if I can't explain what I think I'm seeing 30 ft over my head against bright lights, is my interpretation correct?
> - Is the longer flight time reasonably explainable from a purely theoretical aerodynamic sense?
> - If some one could point me to the relevant propellor equations I might be able to puzzle it out with some examples.
> - Seems like a simple question, but I may be oversimplifying. Which has lower drag?
> --Two propellors identical but opposite pitch props working together.
> -- or one of those propellors working by itself
> -- to produce the same lift (or maybe exceed the minimum lift?).
> - True for all operating conditions, or just some?
> - Because if the drag isn't lower, how can the flight be longer?
> - And is it a small or large effect?
>
> Thanks,
>
> Jeff Anderson
> Livonia, MI
>
Received on Wed Mar 30 2011 - 13:47:35 CEST
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