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Honest question here; why would you need more power to fly a helicopter on Mars than on Earth? You’d likely need proportionally larger blades, but less power, a

by nickff 3y ago

Honest question here; why would you need more power to fly a helicopter on Mars than on Earth? You’d likely need proportionally larger blades, but less power, as the power goes into providing thrust, which is used to counter gravity (that is lower on Mars). Likewise, conventional aircraft would require longer wingspans, as they’d be flying in lower density air, but they’d also be lighter (less weight). In case it’s not obvious, I suspect that larger wings are required because of the lower density of Mars’ atmosphere, which would increase the stall speed relative to Mach number of any given aircraft.

samplatt 3y ago
You're not countering gravity, you're countering the mass of the helicopter vs. the mass of the air moved. Thus, since the air is thinner: to push larger blades going at the same speed, OR the same sized blades going at a faster speed, you'd need more power.
- nickff 3y ago
  I don’t think you can spin the blades much faster, as Earth-bound helicopters already have issues with blade tip speeds approaching the speed of sound. Short blades are less efficient anyway, and I’m not sure why pushing larger blades will require more power; that would have to do with the balance between density of atmosphere and its viscosity.
  - consp 3y ago
    As a bonus the speed of sound on mars is usually quite a bit lower than on earth, since it's usually colder. Or you'd have to wait for warmer weather at the right spot at the right time.
colechristensen 3y ago
Aerodynamic forces are proportional to density. Mars' surface gravity is 1/3 that of Earth's. Mars' surface air density is 1/60 that of earths. So to use lifting surfaces on Mars to fly, the situation is 20x harder. It's roughly equivalent to flying at 40,000 ft on Earth with an electric helicopter. The world record for highest helicopter ever flown is 42,500 ft on Earth. Flying on Mars is like flying more or less at the service ceiling of all but the most specialized aircraft can on Earth, and most of those are air breathing engines. The structural weight required to make equivalent lift to weight ratios (L/W) is very much harder and the lower gravity doesn't make up for most of the difficulty.
- nickff 3y ago
  From what I understand, the issues with flying high on earth is that engines don’t work as well at high altitudes, and you get into ‘coffin corner’ where an aircraft’s stall speed approaches the speed of sound (that is inconvenient for high aspect-ratio aircraft). These problems are not as challenging for electric aircraft flying in generally lower density atmosphere.
- robryk 3y ago
  Both lift and drag are aerodynamic forces, so your approximation causes one to conclude that one need to simply spin everything faster. (And then we run into problems with transonic blades.) > It's roughly equivalent to flying at 40,000 ft on Earth with an electric helicopter. The world record for highest helicopter ever flown is 42,500 ft on Earth. The record was established in a jet-engined helicopter, whose service ceiling is largely a function of engine power at appropriate altitudes (e.g. it varies a lot with temperature and humidity).

by nickff 3y ago

samplatt 3y ago

You're not countering gravity, you're countering the mass of the helicopter vs. the mass of the air moved. Thus, since the air is thinner: to push larger blades going at the same speed, OR the same sized blades going at a faster speed, you'd need more power.

nickff 3y ago
I don’t think you can spin the blades much faster, as Earth-bound helicopters already have issues with blade tip speeds approaching the speed of sound. Short blades are less efficient anyway, and I’m not sure why pushing larger blades will require more power; that would have to do with the balance between density of atmosphere and its viscosity.
- consp 3y ago
  As a bonus the speed of sound on mars is usually quite a bit lower than on earth, since it's usually colder. Or you'd have to wait for warmer weather at the right spot at the right time.

colechristensen 3y ago

Aerodynamic forces are proportional to density. Mars' surface gravity is 1/3 that of Earth's. Mars' surface air density is 1/60 that of earths. So to use lifting surfaces on Mars to fly, the situation is 20x harder. It's roughly equivalent to flying at 40,000 ft on Earth with an electric helicopter. The world record for highest helicopter ever flown is 42,500 ft on Earth. Flying on Mars is like flying more or less at the service ceiling of all but the most specialized aircraft can on Earth, and most of those are air breathing engines. The structural weight required to make equivalent lift to weight ratios (L/W) is very much harder and the lower gravity doesn't make up for most of the difficulty.

nickff 3y ago
From what I understand, the issues with flying high on earth is that engines don’t work as well at high altitudes, and you get into ‘coffin corner’ where an aircraft’s stall speed approaches the speed of sound (that is inconvenient for high aspect-ratio aircraft). These problems are not as challenging for electric aircraft flying in generally lower density atmosphere.
robryk 3y ago
Both lift and drag are aerodynamic forces, so your approximation causes one to conclude that one need to simply spin everything faster. (And then we run into problems with transonic blades.) > It's roughly equivalent to flying at 40,000 ft on Earth with an electric helicopter. The world record for highest helicopter ever flown is 42,500 ft on Earth. The record was established in a jet-engined helicopter, whose service ceiling is largely a function of engine power at appropriate altitudes (e.g. it varies a lot with temperature and humidity).