That explanation doesn't work for me, at least at first blush.
With two rotors spinning, they each provide roughly half the lift (how roughly depends on how closely coupled they are).
If the single rotor doesn't accelerate (and I'm not seeing more torque to the single rotor just because the other is locked, correct me if my logic is wrong), it can only provide roughly half the lift, and that has to be adequate to hold the helicopter in the air by itself.
At minimum mass, 4 gm airframe plus 2 gm rubber, are these things producing 12 grams of lift with both rotors turning for significant portions of their flight? Because with one rotor stalled, the other has to provide 6 gm lift or more to keep it tight to the ceiling. But I can see (I think) no more torque is available to accelerate the rotor.
Hmmm, I can see I'm going to have to get out my static test rig and check this for myself. Now, if I can just find some time...
Jeff Anderson
Livonia, MI
--- 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 - 13:52:40 CEST
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