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Old 09-25-2018, 12:13 AM   #11 (permalink)
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redpoint5 — It's an interesting conjecture.
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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.
This part concerns me. For a given angular speed (RPM) a longer blade would have a higher tip speed.

Perhaps it requires a new architecture. A single blade with a twist in the middle and tip ramjets? https://en.wikipedia.org/wiki/Focke-Wulf_Triebflügel

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Old 09-25-2018, 04:18 AM   #12 (permalink)
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I didn't know the math, but considered that too. I figured the circumference grows at 2(pi)r, but the swept area increases at (pi)r^2, so the area increases more rapidly than the blade tip speed increases. But then, lift isn't equal throughout the swept area because the portion of the blade nearest to the rotor moves at a slower speed and produces less lift, while the portion of the blade towards the tip produces more lift.







I wonder if a lighter than air ship (blimp) would be more efficient?



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Old 09-25-2018, 10:11 AM   #13 (permalink)
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The pictures I saw in the BBC demonstrated a 2 rotor counter-rotating coaxial which limits the retreating blade stall
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Old 09-25-2018, 11:25 AM   #14 (permalink)
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Yeah, was thinking coaxial is better for several reasons.

1. The extra lift is needed
2. Smaller package
3. More efficient (tail rotor wastes about 15% energy)

It would be neat if a ground station had a solar panel that charges a battery, and the helicopter just has to land on it to recharge. The skids could be the charging wires.

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