Timeline for Why don't we build helicopter based space shuttles?
Current License: CC BY-SA 3.0
12 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jan 14, 2017 at 20:42 | comment | added | Lightness Races in Orbit | Emphasis on "AIRcraft". | |
| May 13, 2015 at 19:15 | comment | added | Mike Dunlavey | Can airplanes fly in no atmosphere? Of course not. There's nothing for the wing to react against. A helicopter rotor is just a wing that goes in a circle. (They are called "rotary wing aircraft".) | |
| May 13, 2015 at 14:32 | comment | added | dmckee --- ex-moderator kitten | Viscosity is certainly an important component in designing a lifting surface but the fundamental problem for a propeller driven system in space would be the simply lack of any reaction mass to use. Hellicopters use lift which is the reaction from pushing air the other way. Nothing to push on means no lift. That's why rockets carry their own reaction mass along. | |
| May 13, 2015 at 13:45 | vote | accept | lopata | ||
| May 13, 2015 at 13:45 | vote | accept | lopata | ||
| May 13, 2015 at 13:45 | |||||
| May 13, 2015 at 13:13 | comment | added | Floris | @mmesser314 - yes, with zero viscosity things get really weird. But with non-zero viscosity, the lift depends (for a given geometry and velocity of the blade) on density much more than viscosity. This is why (most) helicopters can't get to the top of Everest - the density of the air is lower at altitude, not the viscosity. | |
| May 13, 2015 at 13:07 | comment | added | mmesser314 | When I was an undergraduate, we got to play with superfluid He. We spun a paddle wheel to stir the He, and watch it move a second paddle wheel. It was amazing how the second paddle wheel sat still when below the critical temperature. | |
| May 13, 2015 at 13:06 | comment | added | Floris | See also this earlier answer describing the mechanism of lift for a helicopter. | |
| May 13, 2015 at 13:05 | comment | added | Floris | Sorry but I disagree. If you move a blade with a certain angle of attack at a certain velocity, you will hit molecules in the medium and change their direction. This change in momentum translates to a force on the blade. You can call it "friction" but you can have friction without lift (for example when the angle of attack is 90°). The change in momentum of the air (medium surrounding the propeller) results in lift. viscosity does not depend on density | |
| May 13, 2015 at 12:58 | comment | added | sailx | Density is no the key, it's the friction, the amount of work you are able to use to move forward is the work of the friction forces. However, the viscosity of your media is linked to it's density. For dilute gas, it's probable that there is a linear relation between thoses quantities. | |
| May 13, 2015 at 12:47 | comment | added | Floris | It is mostly the density of the air that matters - not so much the viscosity. You need to "push matter one way" in order to create an impulse in the opposite direction. If there is no "stuff to push", there will be no force on the blade. Viscosity is a given for all (non superfluid) substances - density is the key. | |
| May 13, 2015 at 12:42 | history | answered | sailx | CC BY-SA 3.0 |