5 ms·

Is there any reason a drone couldn't autorotate like a helicopter does to slow its descent?

extropy 7y ago
For autorotation you need to passively stay upright and a certain propeller area to weight ratio. All of which are not present in a typical multirotor.
- FabHK 7y ago
  And you need pitch control ("collective").
rurounijones 7y ago
Helo autorotation largely requires the momentum of the blades to keep going after engine failure (as well as the pitch and forward momentum). I don't think the blades on small drones are heaby enough to store enough momentum for autorotation.
- baddox 7y ago
  More importantly, most drones cannot physically adjust the tilt of the rotor blades (which is called collective pitch control in helicopters). Helicopter autorotation requires rotors with a lot of angular momentum and usually an abrupt change in the collective pitch right before landing to turn that momentum into thrust and slow the helicopter down. There are RC aircraft with collective pitch controls, like most RC helicopters and even some multirotors. These RC aircraft generally can autorotate, as well as do things that are probably not practical for full-scale aircraft to do, like fly upside down. :) A collective pitch quadcopter flying upside down: https://youtu.be/MVL_Hf4ilLg?t=162 https://youtu.be/MVL_Hf4ilLg?t=162 An RC helicopter doing, well, all sorts of acrobatics that hardly make sense: https://youtu.be/KmPchrGW1TQ?t=48 https://youtu.be/KmPchrGW1TQ?t=48 An RC helicopter autorotating: https://youtu.be/bxQ5kwqiPN4?t=136 https://youtu.be/bxQ5kwqiPN4?t=136 (this one has an internal combustion engine, although that shouldn't make much of a difference for autorotation)
  - cmurf 7y ago
    >that hardly make sense Just a guess: stronger strength to weight, and power to weight ratios, compared to the real thing. The tail rotor in particular appears to be quite a bit more powerful for the weight of the model than would be expected in a full size aircraft. And then also, these kinds of movements with a person inside? Haha! No!
    - baddox 7y ago
      Yeah, I've been pretty deep in the RC community, but what doesn't make sense to me is the physical skills of pilots like that! Handling orientation changes like that is insanely difficult. I practiced flying RC helis for a while in a simulator and even the basic orientation exercises are pretty challenging.
Merad 7y ago
A helicopter's rotor has a complex control system that has you changing the pitch of the rotor blades and the angle of the rotor disk, with the rotor behaving similarly to the wing of an airplane. Quadcopters usually rely purely on thrust for control. For example to bank, the motors on one side spin faster (more thrust) and the motors on the other side spin slower (less thrust). If you lose a motor, or lose the ability to control a motor, you lose the ability to control the quad. In comparison, a helicopter will have a clutch that can disengage the rotor from the engine and let it turn freely. The pilot still has the ability to control the rotor, so she has some control during the autorotation. At the end, just before landing/impact, she will perform a flare, using the rotational energy in the rotor to slow the helicopter's descent.

For autorotation you need to passively stay upright and a certain propeller area to weight ratio. All of which are not present in a typical multirotor.

FabHK 7y ago
And you need pitch control ("collective").

rurounijones 7y ago

Helo autorotation largely requires the momentum of the blades to keep going after engine failure (as well as the pitch and forward momentum). I don't think the blades on small drones are heaby enough to store enough momentum for autorotation.

baddox 7y ago
More importantly, most drones cannot physically adjust the tilt of the rotor blades (which is called collective pitch control in helicopters). Helicopter autorotation requires rotors with a lot of angular momentum and usually an abrupt change in the collective pitch right before landing to turn that momentum into thrust and slow the helicopter down. There are RC aircraft with collective pitch controls, like most RC helicopters and even some multirotors. These RC aircraft generally can autorotate, as well as do things that are probably not practical for full-scale aircraft to do, like fly upside down. :) A collective pitch quadcopter flying upside down: https://youtu.be/MVL_Hf4ilLg?t=162 https://youtu.be/MVL_Hf4ilLg?t=162 An RC helicopter doing, well, all sorts of acrobatics that hardly make sense: https://youtu.be/KmPchrGW1TQ?t=48 https://youtu.be/KmPchrGW1TQ?t=48 An RC helicopter autorotating: https://youtu.be/bxQ5kwqiPN4?t=136 https://youtu.be/bxQ5kwqiPN4?t=136 (this one has an internal combustion engine, although that shouldn't make much of a difference for autorotation)
- cmurf 7y ago
  >that hardly make sense Just a guess: stronger strength to weight, and power to weight ratios, compared to the real thing. The tail rotor in particular appears to be quite a bit more powerful for the weight of the model than would be expected in a full size aircraft. And then also, these kinds of movements with a person inside? Haha! No!
  - baddox 7y ago
    Yeah, I've been pretty deep in the RC community, but what doesn't make sense to me is the physical skills of pilots like that! Handling orientation changes like that is insanely difficult. I practiced flying RC helis for a while in a simulator and even the basic orientation exercises are pretty challenging.

Merad 7y ago

A helicopter's rotor has a complex control system that has you changing the pitch of the rotor blades and the angle of the rotor disk, with the rotor behaving similarly to the wing of an airplane. Quadcopters usually rely purely on thrust for control. For example to bank, the motors on one side spin faster (more thrust) and the motors on the other side spin slower (less thrust). If you lose a motor, or lose the ability to control a motor, you lose the ability to control the quad. In comparison, a helicopter will have a clutch that can disengage the rotor from the engine and let it turn freely. The pilot still has the ability to control the rotor, so she has some control during the autorotation. At the end, just before landing/impact, she will perform a flare, using the rotational energy in the rotor to slow the helicopter's descent.