At 09:23 PM 9/19/2002 -0500, John Carmack wrote:
>At 07:10 PM 9/19/2002 -0700, you wrote:
>>At 09:01 PM 9/19/2002 -0500, John Carmack wrote:
>>
>>>With counter rotating blades you won't have any rolling torque, but you
>>>will still have a gyroscopic stabilizing effect that will make it resist
>>>changes in attitude.
>>
>>
>> Actually, no. The angular momentum of each pair of
>> counter-rotating engines cancels out, as long as they are spinning at
>> the same rate. There will be slight gyroscopic effects when the two
>> engines of a pair are at different throttle levels, but in the flight
>> regime contemplated for Gizmocopter, these throttling differences will
>> be slight and transient.
>>
>> -p
>
>I'm not sure about that. If you have a shaft with two wheels on it,
>spinning either wheel either way will provide a gyroscopic
>"stiffness". Two spinning wheels, even going opposite directions, should
>have twice the stiffness, not none.
Actually, the correct answer is none. The gyroscopic 'stiffness'
comes from the conservation of angular momentum, which is a vector. The
perceived stiffness is simply the resistance of angular momentum to change.
Say you have two identical wheels on a vertical shaft, spinning in opposite
directions and the same speed. The angular momentum vector for the one
turning to the right will point up and the one turning to the left will
point down. Their vector sum is zero, therefore there is no angular
momentum vector to conserve, and no stiffness.
>I am far from an expert on gyroscopic effects, so I could be completely
>wrong, but I don't think additional rotating masses can't help you do a
>"plane change" of a rotating mass, so there is no way to cancel the
>gyroscopic stabilization effect.
Angular momentum behaves in some mildly counterintuitive ways.
Also, there is a fly in the ointment here -- there may be some gyroscopic
effects as a result of the products of inertia of Gizmocopter. I haven't
done the math, so I am not sure, and in any case the answer depends
primarily on the specifics of Gizmocopter's final flight configuration.
-p
Mars or Bust!
www.marssociety.com
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