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I've been looking at the Mars helicopter (Ingenuity) that will be onboard the Mars 2020 rover and I am having trouble figuring out how they determined the size of the rotor blades. Specifically, I'm getting stuck on calculating the kinematic viscosity of Martian "air". For rotors on earth-based helicopters, there are a lot of tables with data that you can interpolate or extrapolate from but I'm not sure how they could be used for a Martian atmosphere.

Does anyone have any useful information on this?

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  • $\begingroup$ See if the answers to this help: space.stackexchange.com/q/17176/6944 $\endgroup$ – Organic Marble Jun 3 '20 at 17:29
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    $\begingroup$ @OrganicMarble, Thanks for the link I hadn't seen that one in my search. It's closer to what I'm looking for. The answers there a little too hand-wavy for what I'm looking for though. A Figure of Merit value is usually experimentally determined, and I'm hoping to find a more analytic expression. Specifically, I'm working on an optimization problem and stuck on some unknown physical properties. This perhaps is a better question for fluid-dynamicists, rather than Astro-dynamicists? $\endgroup$ – Diesel Jun 3 '20 at 18:48
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    $\begingroup$ The averages and variabilities of the Martian atmosphere's composition, density, pressure, temperature etc. are pretty well characterized now, so they can simply be produced in a vacuum chamber and the helicopter tested. Because gravity is higher on Earth a force is applied with a cable to reduce its effect to the level on Mars, and flight can be characterized. This doesn't answer your question about calculations or modeling of the properties, but it does illustrate that those parameters could be known through independent measurements similar to this. youtu.be/GhsZUZmJvaM $\endgroup$ – uhoh Jun 4 '20 at 0:14
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    $\begingroup$ @uhoh Great videos, I wish I had Veritasium's access! I'm 100% sure that they have access to that data... I just can't find it! $\endgroup$ – Diesel Jun 4 '20 at 15:41
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    $\begingroup$ @OrangeDurito Thanks for linking to the PropGen program. I've got a windows 7 machine somewhere around my lab that I'll dust off and give it a try. I think that is probably as good of an answer as I can hope for until I hear back from JPL. Their reference links seem to be broken, but I should be able to come up with a crude design space based on that program if I can get it up and running $\endgroup$ – Diesel Jun 4 '20 at 15:46

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