6 ms·

Well here is an experiment that I have done. I used a toy double blade helicopter, like these ones: http://www.rc-airplane-world.com/coaxial-rc-helicopters.htm

by hristov 16y ago

Well here is an experiment that I have done. I used a toy double blade helicopter, like these ones: http://www.rc-airplane-world.com/coaxial-rc-helicopters.html http://www.rc-airplane-world.com/coaxial-rc-helicopters.html And it sure seemed to have a lot of rotational inertia. If you were right, then I could touch one side of the helicopter slightly and since it has no rotational inertia it would tilt to the side and completely change direction and fly off somewhere into the wall or the floor. This did not happen however, even when I tried to tilt it the helicopter remained horizontal. And please do not tell me that a $50 toy has an active stability system with internal gyros and all the required electronics and super fast servos. And now that I think of it, I remember that the russians have been making counter rotational helicopters for ages. See for example this one: http://en.wikipedia.org/wiki/Kamov_Ka-25 http://en.wikipedia.org/wiki/Kamov_Ka-25 How does this helicopter stay horizontally stable in the air and does not fly off on a tangent when tilted by the slightest cross wind? Note that this one was designed in the late 50's before any electronic active stability systems could have been invented.

RiderOfGiraffes 16y ago
I have limited personal knowledge of RC helicopters, but a great deal of experience with rotational systems. Colleagues tell me that the counter-rotational systemson helicoptors are stable because the CoG is hanging from a point quite a long way above, and cross winds are applied more-or-less at the CoG because of the cross-sectional area distribution. I don't doubt that your experience of a toy double blade helicopter is that it seems to have a lot of rotational inertia. I am certain that it's not due to the gyroscopic stability of exactly matched counter-rotating blades.
- hristov 16y ago
  If you think about it, this explanation cannot be true. The main force the helicopter exerts on its surroundings is along the axis of rotation. If you tilt the axis of rotation significantly in any direction, the direction of the force will change significantly and the motion of the helicopter will also change significantly. Again, this does not happen.
  - RiderOfGiraffes 16y ago
    It's unclear what you mean by the "this" in the "this does not happen" However ... A helicopter changes direction by using the cyclic setting on its rotors. Then you get more lift from one part of the rotor cycle and less from another. That causes the plane of the rotors to tilt, and then the helicopter goes off in the appropriate direction. For example, having more lift in the rear portion of the cycle and less in the front means the helicopter gets tipped forward, effectively like lifting one part of a plate. The down-draft now has a significant rearwards component, so the rotors get pushed forward, taking the helicopter with it. If you then change the cyclic to "flat" so there is identical lift everywhere, the weight of the helicopter dangling from the rotors causes it come come back upright (after swinging a bit) It's a weird experience sitting in a helicopter when it's doing this, especially if you're mostly accustomed to ordinary aeroplanes. I don't see any contradiction in any of this, and it really doesn't seem to have any bearing on the fact that contra-rotating disks have no net gyroscopic effect.
    - nettdata 16y ago
      This is accomplished by way of a swashplate, as can be seen here: http://en.wikipedia.org/wiki/Swashplate_%28helicopter%29 http://en.wikipedia.org/wiki/Swashplate_%28helicopter%29
      - RiderOfGiraffes 16y ago
        When you say "this" you mean the translation of the pilot's controls into the angles of the blades at the various stages of their journey, mixing collective (giving overall lift) and cyclic (giving pitch and roll) Yes.

by hristov 16y ago

RiderOfGiraffes 16y ago

I have limited personal knowledge of RC helicopters, but a great deal of experience with rotational systems. Colleagues tell me that the counter-rotational systemson helicoptors are stable because the CoG is hanging from a point quite a long way above, and cross winds are applied more-or-less at the CoG because of the cross-sectional area distribution. I don't doubt that your experience of a toy double blade helicopter is that it seems to have a lot of rotational inertia. I am certain that it's not due to the gyroscopic stability of exactly matched counter-rotating blades.

hristov 16y ago
If you think about it, this explanation cannot be true. The main force the helicopter exerts on its surroundings is along the axis of rotation. If you tilt the axis of rotation significantly in any direction, the direction of the force will change significantly and the motion of the helicopter will also change significantly. Again, this does not happen.
- RiderOfGiraffes 16y ago
  It's unclear what you mean by the "this" in the "this does not happen" However ... A helicopter changes direction by using the cyclic setting on its rotors. Then you get more lift from one part of the rotor cycle and less from another. That causes the plane of the rotors to tilt, and then the helicopter goes off in the appropriate direction. For example, having more lift in the rear portion of the cycle and less in the front means the helicopter gets tipped forward, effectively like lifting one part of a plate. The down-draft now has a significant rearwards component, so the rotors get pushed forward, taking the helicopter with it. If you then change the cyclic to "flat" so there is identical lift everywhere, the weight of the helicopter dangling from the rotors causes it come come back upright (after swinging a bit) It's a weird experience sitting in a helicopter when it's doing this, especially if you're mostly accustomed to ordinary aeroplanes. I don't see any contradiction in any of this, and it really doesn't seem to have any bearing on the fact that contra-rotating disks have no net gyroscopic effect.
  - nettdata 16y ago
    This is accomplished by way of a swashplate, as can be seen here: http://en.wikipedia.org/wiki/Swashplate_%28helicopter%29 http://en.wikipedia.org/wiki/Swashplate_%28helicopter%29
    - RiderOfGiraffes 16y ago
      When you say "this" you mean the translation of the pilot's controls into the angles of the blades at the various stages of their journey, mixing collective (giving overall lift) and cyclic (giving pitch and roll) Yes.