# Could a helicopter fly on Mars?

Helicopter drones are awesome fun down here on Earth, but what if... we took one to Mars? This sounds like a good question for Randall Munroe. But I read about a proposal to send a helicopter drone (MHS) to Mars with Mars 2020.

Martian atmosphere's density is a fraction of a percent of Earth's (average 0.6% ASL). My off the cuff calculations say that such a drone would have to be 200 times more powerful than its Earth-bound cousins.

Is this a realistic proposal?

• You don't have to have 200 times more power. You have to spin much faster and have bigger rotor blades to generate lift, but you don't need to add much more energy into the process.
– GdD
Commented Jul 13, 2016 at 7:56
• I recommend xkcd what-if: Interplanetary Cessna for a crash course (no pun intended). See also NASA's Preliminary Research Aerodynamic Design to Land on Mars, or Prandtl-m (yes, that's what it really is called).
– user
Commented Jul 13, 2016 at 12:27
• They have done tests proving that a small drone-like helicopter (about 1 meter across) would be able to take off and fly in Mars' thin atmosphere. Commented Jul 13, 2016 at 15:13
• Increasing rotor size only works up to a point. Increase the diameter enough, and your rotor tips will go supersonic, which doesn't help lift. Commented Jul 13, 2016 at 15:50
• It has now been proven that a helicopter can fly on Mars. Finding reliable cites is left as an exercise for the interested student. Commented May 17, 2021 at 14:32

Gravity is about a third of Earth's and competitive aerobation helicopter models have a truly excessive power surplus. Just look at this.

There won't be any manned helicopter flight. The helicopter power scales poorly with size - there's a reason we have no VTOL Jumbo Jets. But the same up-scaling issue is our friend when down-scaling. A 6kg helicopter can lift 30kg of payload, so we have equivalent of TWR=6 on Earth.

Drag and lift are both identically (quadratically) proportional to airspeed, so the same loss of lift causes loss of the primary limiting force of the helicopter - air drag on the blades. What's left is mechanical losses (friction of bearings), and mechanical durability of the construction, but these can be built with much surplus - plus larger rotor blades will offset need for extreme RPM.

Of course other things must be taken into account. These flights will be more like "hops" - a short segment of flight followed by a looong recharging period. And the drone will need to be small - and that means not much scientific equipment. Unfortunately, that also means it won't be fully autonomous as there simply won't be enough room to fit a good radio and antenna to reach Earth, or even the satellites. But it could definitely serve as a "recon vehicle" for a large rover, fetching small samples, testing firmness of ground surface for driving over, and planning the best route.

2021.03.16 edit:

Ingenuity has performed its first flight.. Most of data in my post predicted Ingenuity's parameters correctly. 2,500 rpm at 60cm rotor radius gives 157m/s top linear speed of the rotor tips, vs 267m/s speed of sound in carbon dioxide (and 90m/s in aerobation RC helicopters), so they remained subsonic. It's lightweight - 1.8kg, comparable to heavier aerobatic models. It uses the rover as a retransmitter to contact the satellites and Earth. The rotor blades are both wider and longer than in aerobation RC helicopters to compensate for the thin atmosphere, but the motor is comparable to mid-shelf models regarding power output. The helicopter is capable of a 30s flight and requires a day to recharge the batteries.

2021-09-05 edit:

As the first phase - technology demonstration of feasibility of powered flight on Mars has ended, Ingenuity performs reconnaissance work helping Curiosity pick interesting targets.

• You need to address the factor of 100 atmospheric density difference in your answer, which is the question that was asked. To get the same lift, you need the airfoils to move 10 times as fast. Commented Jul 14, 2016 at 5:20
• @Mark: which I can, due to reduced air drag - same torque caused by air resistance. Regardless of speed and pressure, torque to lift ratio remains the same. (minus other resistances which are taken care of by the power surplus, and plus reduced lift requirements thanks to low gravity.) Air drag doesn't rise; other frictions increase by factor of ~60 (x200 density /3 gravity) but I believe they account for less than 10% of original losses, so the 6x power surplus is enough to overcome them.
– SF.
Commented Jul 14, 2016 at 6:27
• No, the air drag does rise, where the dimensionless drag coefficient goes up dramatically as you approach Mach 1, starting as low as Mach 0.6. So it doesn't scale to low density as nicely as you claim. Commented Jul 14, 2016 at 7:12
• @MarkAdler: What order of increase can we expect, with the blades designed for the purpose?
– SF.
Commented Jul 14, 2016 at 13:47
• It depends greatly on the details of the wing, and the other constraints you have on it. Could be a factor of 3, could be a factor of 10. See mhmaberry.files.wordpress.com/2014/04/2.jpg for an example. This sudden increase in drag is why there is a "sound barrier", since the drag drops off again above Mach 1. See this for the generic picture of the situation: history.nasa.gov/SP-367/f86.htm Commented Jul 14, 2016 at 14:44

There's nothing like seeing it flying in a Mars-density chamber to answer your question:

Crazy Engineering: Mars Helicopter

I have a really nice video of it in controlled flight in the chamber, but I can't find that one on the interwebs yet.

Update two years later:

Thanks SF for this link to nice video.

You can calculate the hover power required out of ground effect by using the following formulas:

Given $$m$$, the mass of the helicopter, the required lift force is $$L = g_{Mars}\cdot m$$

The required shaft power is:

$$P = \frac{\frac{L^{\frac{3}{2}}}{R} \cdot \sqrt{\frac {2} {\pi \cdot \rho} }}{FM}$$

where $$R$$ is rotor diameter and FM is the "figure of merit". For a small helicopter the FM is smaller than 0.66, say 0.55.

The density at low altitude on Mars is 0.0152 kg/m3

The gravitational acceleration $$g_{Mars}$$ is 3.8 m/s2.

Example:

• mass = 2 kg
• lift = 7.6 newton
• FM = 0.55
• rotor diameter = 1 meter
• density = 0.0152 kg/m3
• pi = 3.1416

The result is 264 watts.

The fact that the counter rotating rotors are coaxial does not significantly reduce the hover power. The effective diameter is nearly the same. Note that, when the mass is reduced to 1 kg the required power would be only 87 watts!

In summary: power required is proportional to (lift to the $$\frac{3}{2}$$ power exponent), inversely proportional to rotor diameter and inversely proportional to the square root of the density.

When flying forward instead of hovering the required power goes down significantly for a well shaped streamlined fuselage. In 1929 Glauert came up with an approximate formula (the solution of a quartic) which is still used today. A good reference text book is: B. W. McCormick: Aerodynamics of V/STOL Flight.