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  • Helicopters on Mars

    NASA/JL is sending what is essentially a large drone to Mars. How does the physics play out here?

    Atmospheric density:

    Mars has a surface atmospheric density equivalent to about 100,000 ft in Earth's atmosphere: averaging 7.5 millibars on Mars to just over 1000 on Earth.

    Gravity:

    Mars has a gravitational factor of about .38G.

    Aircraft Mass:

    The test aircraft will weigh about 4lbs on Earth.

    Rotor Airfoil:

    There are two twin-bladed counter-rotating rotors. The rotor-span is about 4 feet. The airfoils are of a relatively low aspect ratio.

    Rotor RPM:

    About 2400rpm. That's about five times the speed of a typical terrestrial helicopter.

    Will it fly out of ground effect on Mars?

    Like this?

    https://mars.nasa.gov/multimedia/vid...egory=53%3A320


  • #2
    So they are drones not helicopters as stated in the post title, might need to look at what you post before you say as in the post it says drones and in your post title it says helicopters. NASA even says that they are sending drones up to Mars

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    • #3
      Originally posted by JoshD View Post
      So they are drones not helicopters as stated in the post title, might need to look at what you post before you say as in the post it says drones and in your post title it says helicopters. NASA even says that they are sending drones up to Mars
      Drones are unmanned air vehicles. Your typical military drone is an airplane. This Martian drone is a helicopter (i.e. a heavier-than-air aerial vehicle where lift is produced with rotary wings rather than by having the whole vehicle moving through the air). Of course you will need to replace "air" with whatever name you want to give to the mixture of gases in the Martian atmosphere.

      --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
      --- Defend what you say with arguments, not by imposing your credentials ---

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      • #4
        Originally posted by Evan View Post
        NASA/JL is sending what is essentially a large drone to Mars. How does the physics play out here?

        Atmospheric density:

        Mars has a surface atmospheric density equivalent to about 100,000 ft in Earth's atmosphere: averaging 7.5 millibars on Mars to just over 1000 on Earth.

        Gravity:

        Mars has a gravitational factor of about .38G.

        Aircraft Mass:

        The test aircraft will weigh about 4lbs on Earth.

        Rotor Airfoil:

        There are two twin-bladed counter-rotating rotors. The rotor-span is about 4 feet. The airfoils are of a relatively low aspect ratio.

        Rotor RPM:

        About 2400rpm. That's about five times the speed of a typical terrestrial helicopter.

        Will it fly out of ground effect on Mars?

        Like this?

        https://mars.nasa.gov/multimedia/vid...egory=53%3A320
        Another challenge is that the speed of sound on Mars is ~70% of that 0n Earth, so you cannot make your blades very long or they would go supersonic. (making the blades longer would be the most obvious trick to capture more air volume and compensate for its lower mass). That said, I don't know how bad would it be to go supersonic at an equivalent of 100,000 ft on Earth where the atmosphere is so thin.

        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
        --- Defend what you say with arguments, not by imposing your credentials ---

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        • #5
          Interesting - I hadn’t thought about Mach. A higher Mach number means a lower airfoil stall AoA, correct? I’m also wondering if these things are designed to fly on thrust (ground effect or thrust/weight advantage) rather than via lift. AFAIK The only way to fly at 100,000ft here on Earth is via thrust vector (zoom climb or rocketry) or lighter than air gasses. And the terrestrial record for rotorcraft is less than half of that altitude.

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          • #6
            Originally posted by Evan View Post
            Interesting - I hadn’t thought about Mach. A higher Mach number means a lower airfoil stall AoA, correct?
            Not sure where you are going, but correct. That is, higher Mach but still sub-sonic. Not sure what happens when supersonic, but stall is a completely different phenomenon past Mach 1.

            I’m also wondering if these things are designed to fly on thrust (ground effect or thrust/weight advantage) rather than via lift. AFAIK The only way to fly at 100,000ft here on Earth is via thrust vector (zoom climb or rocketry) or lighter than air gasses. And the terrestrial record for rotorcraft is less than half of that altitude.
            I don't see how a propeller can produce thrust in any way other than creating lift.

            And to your second point, perhaps it is not so interesting here on Earth to make a helicopter that can fly at 100,000ft when released from 100,000 ft (because it doesn't need to climb to 100,000ft on Mars) carrying a 250-grams payload.

            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
            --- Defend what you say with arguments, not by imposing your credentials ---

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            • #7
              The Mars helicopter has flown in a chamber with Martian atmosphere and pressure. I assume they compensated for weight by off loading payload and other items (perhaps a smaller battery).

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              • #8
                https://www.youtube.com/watch?v=GhsZUZmJvaM

                <iframe width="560" height="315" src="https://www.youtube.com/embed/GhsZUZmJvaM" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

                --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                --- Defend what you say with arguments, not by imposing your credentials ---

                Comment


                • #9
                  By my math, it is ~50 times harder to fly on mars. Air is over 100 times thinner, but 38% gravity.

                  In gross terms, any earth aircraft would work, it would just have to go ~7X faster.
                  Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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