3 ms·

Almost all helicopters have constant speed rotors and use the pitch of the blades to control all but 1 degree of freedom (the last is the pitch of the tail roto

by krallja 13y ago

Almost all helicopters have constant speed rotors and use the pitch of the blades to control all but 1 degree of freedom (the last is the pitch of the tail rotor blades, which directly controls the yaw in upright flight).

Crito 13y ago
My understanding is that quad/octo-rotor helicopters do not have constant speed rotors because they turn about by varying the relative speeds of each rotor. They don't have any sort of swashplate. My understanding is that this simplification is more or less the entire point of quad-rotors, since otherwise a single big rotor would be much more efficient.
- ericd 13y ago
  Yeah, and because of that they depend on the ability to very rapidly change the speed of the props, so they need the instant torque changes of electric.
- lsc 13y ago
  Yeah... but is scaling down the 'single big rotor' mechanisms used by real helicopters that difficult? would it be more expensive than developing a lightweight electric battery that could give you the same range? I don't know the answers to those questions; I'm just saying, if range is the problem there are solutions that don't involve breakthroughs in battery technology.
  - dragonwriter 13y ago
    > Yeah... but is scaling down the 'single big rotor' mechanisms used by real helicopters that difficult? TL;DR: Yes. TS;WM (Too Short, Want More): The top-and-tail rotor design relies on varying pitch on the individual blades of the top rotor at different points in their rotation (rather than varying speed on separate rotors) for translation, varying pitch (the baseline/average pitch of all blades throughout rotation) of the main rotor for lift, and pitch of the tail rotor for rotation. Quad/octorotor designs get all of that by just vary rotor speed without the additional machinery needed to vary blade pitch, which makes the vastly easier to build at small scale.

by krallja 13y ago

Crito 13y ago

My understanding is that quad/octo-rotor helicopters do not have constant speed rotors because they turn about by varying the relative speeds of each rotor. They don't have any sort of swashplate. My understanding is that this simplification is more or less the entire point of quad-rotors, since otherwise a single big rotor would be much more efficient.

ericd 13y ago
Yeah, and because of that they depend on the ability to very rapidly change the speed of the props, so they need the instant torque changes of electric.
lsc 13y ago
Yeah... but is scaling down the 'single big rotor' mechanisms used by real helicopters that difficult? would it be more expensive than developing a lightweight electric battery that could give you the same range? I don't know the answers to those questions; I'm just saying, if range is the problem there are solutions that don't involve breakthroughs in battery technology.
- dragonwriter 13y ago
  > Yeah... but is scaling down the 'single big rotor' mechanisms used by real helicopters that difficult? TL;DR: Yes. TS;WM (Too Short, Want More): The top-and-tail rotor design relies on varying pitch on the individual blades of the top rotor at different points in their rotation (rather than varying speed on separate rotors) for translation, varying pitch (the baseline/average pitch of all blades throughout rotation) of the main rotor for lift, and pitch of the tail rotor for rotation. Quad/octorotor designs get all of that by just vary rotor speed without the additional machinery needed to vary blade pitch, which makes the vastly easier to build at small scale.