3 ms·
The kinetic energy required to spin up a rotor mounted on low-friction bearings says very little about its efficiency.
by ehvatum 6y ago
The kinetic energy required to spin up a rotor mounted on low-friction bearings says very little about its efficiency.
- na85 6y agoDon't forget that skin friction against the air also resists the rotation force, and does so to the tune of the square of velocity.
- carapace 6y agoAh yes, but you have the option to use more power. The way I describe it is: The Magnus effect rotor is to the wing as the wheel is to the sled runner.
- bernulli 6y agoBut the whole game of airfoil and wing design is to optimize the lift to drag ratio, i.e. how much lift is produced per propulsive power needed. Sure, given enough power, you can just remove wings altogether and simply fly an engine.
- carapace 6y agoWould it increase the drag if you spun the rotor faster? My intuition says not, or not by much, but I don't know. That's what I'm getting at, not increasing propulsive power, rather adding power to the rotation to get more lift.
- bernulli 6y agoIt probably (?) wouldn’t increase the drag of the aircraft significantly, but you’re still spinning a cylinder in a viscous fluid and that takes energy. So over all, you increase the power you need to put into the system to create a certain amount of lift. Whether the energy expense comes as an additional propulsion requirement to overcome drag or as an additional motor to spin the cylinder does not really matter if you’re interested in the lowest power expense for a desired lift.
- bernulli 6y agoBut increasing the radius would absolutely increase the drag.