3 ms·

Helicopters have a height-velocity diagram with some areas marked unsafe (low speed, low altitude); when operating in the forbidden areas a pilot cannot be reas

Helicopters have a height-velocity diagram with some areas marked unsafe (low speed, low altitude); when operating in the forbidden areas a pilot cannot be reasonably expected to perform an emergency landing using autoration following complete engine loss. In all other areas this should be possible. Coincidentally, that's why helicopters avoid taking off vertically (they only do that in video games...); they want to gain some speed before gaining significant altitude, because forward speed helps autorotation. If a helicopter just climbs straight up at zero speed and the engine goes out, it's going to fall pretty much like a rock. Average multicopter designs would seem to be incapable of autorotation for aerodynamic and technical reasons. The technical reason being that the BLDC motors used are typically permanent magnet synchronous machines, which develop significant holding torque in most (driver) failure modes and there is no clutch to disconnect the motor from the propeller.

dreamcompiler 7y ago
There's also typically* no collective pitch control in small multicopters, so to autorotate the props have to have time to stop turning and reverse. Even assuming they could declutch from the motors they would usually crash first. *There are some exceptions: https://www.droneguru.net/collective-pitch-drones/ https://www.droneguru.net/collective-pitch-drones/
mikeyouse 7y ago
Notably - this is what killed the billionaire owner of the Leicester City football club. He liked to land his helicopter on the field after the game and depart from there (against many people's advice) which prevented any forward momentum on takeoff or landing. Last year, he was taking off after a game and had an engine issue which resulted in the helicopter crashing into the parking lot killing everyone on board. https://www.youtube.com/watch?v=Kvk6rslCDAI https://www.youtube.com/watch?v=Kvk6rslCDAI

dreamcompiler 7y ago

There's also typically* no collective pitch control in small multicopters, so to autorotate the props have to have time to stop turning and reverse. Even assuming they could declutch from the motors they would usually crash first. *There are some exceptions: https://www.droneguru.net/collective-pitch-drones/ https://www.droneguru.net/collective-pitch-drones/

mikeyouse 7y ago

Notably - this is what killed the billionaire owner of the Leicester City football club. He liked to land his helicopter on the field after the game and depart from there (against many people's advice) which prevented any forward momentum on takeoff or landing. Last year, he was taking off after a game and had an engine issue which resulted in the helicopter crashing into the parking lot killing everyone on board. https://www.youtube.com/watch?v=Kvk6rslCDAI https://www.youtube.com/watch?v=Kvk6rslCDAI