Quote:
Originally Posted by All Darc
A bit of subject change.
Have you heard about a drone for Mars mission ?
On Mars, despite you get 1/3 of gravity, you have 1/100 of atmospheric pressure.
And sun's power, for sollar cells, it's 50% than on Earth.
But NASA will build a drone, mini helicopter, for Mars. Imagine the energy for blades rotation at 1/100 of air presure, despite 1/3 of gravity.
Someone will say that if blades run faster in a air pressure way lower, the energy to move the air would, in theory, be the same. But the key point it's the loss due friction, much more relevant in this case.
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I'll have to think about this one more, but a helicopter would be at more risk of "retreating blade stall" and advancing blade overspeed on Mars. The lower atmospheric pressure also lowers the speed of sound to a little over 500 MPH. Helicopter blades are not designed to approach the speed of sound. The advancing blade (blade traveling forward relative to the helicopter direction of travel) "sees" the speed of the blade tip plus the airspeed of the helicopter. The retreating blade (blade traveling backward relative to the helicopter direction of travel) "sees" the blade tip speed minus the airspeed of the helicopter. The side of the helicopter with the advancing blade has much greater lift (it's like a headwind on an airplane) than the retreating side (like a tailwind on an airplane).
You'd have to design the helicopter such that the advancing blade doesn't approach the relatively low speed of sound on Mars, while avoiding a retreating blade stall. This is probably accomplished by long blades.
Anyhow, I hope they do it since video/images are inspiring, even if the scientific value isn't as high as other experiments.
