4 ms·
The interesting thing about the Magnus effect is that the lift goes up with the second power of the radius of the rotor Due to E = mv^2, doesn't the energy req
by jackpirate 6y ago
The interesting thing about the Magnus effect is that the lift goes up with the second power of the radius of the rotor
Due to E = mv^2, doesn't the energy required to spin the rotor also go up with the square of the radius? Thus, the amount of energy is directly proportional to the amount of lift, so you don't get any magical quadratic gains for free like your post implies.
- frongpik 6y agoUnless you use carbon fiber or other super light materials. In other words, weight is more or less disconnected from size.
- ehvatum 6y agoThe 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.
- deleted 6y ago[deleted]
- carapace 6y agoThink of the cross-section of one of these rotors, it's a circle, yeah? We're not interested in the interior of the circle, just the perimeter, which increases linearly with the radius. (We can make the interior out of wire spokes like a bicycle wheel.)