3 ms·

>The problem with gas and this style of aircraft is that they would need to be hybrids, or else you would have a lot of weight dedicated to very complex transmi

by lsc 13y ago

>The problem with gas and this style of aircraft is that they would need to be hybrids, or else you would have a lot of weight dedicated to very complex transmissions. I believe that on airplanes they often solve the problem of internal combustion engines being much more efficient in a narrow RPM band (with the constraint that transmissions tend to be heavy) by using a constant speed propeller[1] that spins at the optimal speed of the engine, and adjusts the blade pitch to adjust the speed of the vehicle. I don't know if it would work on a VTOL type vehicle or not, but we've been using internal combustion engines for a while, and have reasonable work-arounds for many of their shortcomings. [1]http://en.wikipedia.org/wiki/Constant_speed_propeller http://en.wikipedia.org/wiki/Constant_speed_propeller

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 lsc 13y ago

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.