So if/when we send people to live on Mars would they be able to build airplanes that could fly there? As I understand it the atmosphere is very thin so I’m guessing the plane would have to get to a very high speed before takeoff. Of course they would have one advantage there in that Mars has 10% of the mass of earth so gravity would be less of a factor possibly making it much easier to fly there.
I’ve read of plans to use small camera aircraft to explore Mars. It would need very large wings, I would think.
XKCD dealt with this a few years in the former "What If" segment..
Per Randall;
With the atmosphere being ~100x thinner on Mars compared to Earth, and things weighing about a third of what they do here, I’m guessing you’d need incredibly huge flight surfaces to get something airborne.
No idea what the practicality of building and flying such a thing is.
Looks like XKCD is talking about a plane built for Earth-based flight.
The obvious alternative is to use balloons. Not surprisingly, NASA has been exploring this option:
The Martian atmosphere comes in around 0.8 kPa, which works out to the equivalent Earth atmospheric density at 33km.
A simpler idea would be either simple balloons, or potentially blimps with some sort of directional engine. The thin atmosphere for the engine vs. the large surface area of the balloon/blimp would make for interesting design choices.
The Nat Geo miniseries Mars featured the use of drones. At the time, I thought - nah, not enough atmosphere. But apparently I was wrong . . . [Note - link features an autoplay video]
Mars explorations envisioned by Wernher Von Braun would often depict a large powered winged aircraft or rocket: National Geographic
However this was before Mars atmospheric data was available. It turns out the Mars atmosphere – even at the surface – is close to a vacuum. Mars surface pressure is about 0.087 psi, and the pressure at 20,000 ft is about 0.04 psi. In terms of surface atmospheric density, Mars is very roughly 1% of Earth.
Sustained wing-borne flight would be extremely difficult in the Martian atmosphere, although not impossible given a sufficiently extreme design. The two main problems are:
(1) Near-vacuum conditions that would provide little lift.
(2) No readily-available source of sufficient energy to propel the vehicle at anything like the speed, altitude or duration of an earthly aircraft.
By contrast the highest-flying earth aircraft was the Lockheed A-12, a lighter version of the SR-71. Based on recently declassified flight test data, it could reach about 90,000 ft: https://www.cia.gov/news-information/featured-story-archive/2015-featured-story-archive/oxcart-vs-blackbird.html
At 90,000 ft the earth atmospheric pressure is about 0.25 psi. Mars surface pressure is 1/3 that much, and at 20,000 ft on Mars, atmospheric pressure is 1/6 that much.
NASA has tested a small prototype non-powered glider which they think might work on Mars. They want to test it on earth at 100,000 ft altitude which is still 2x the atmospheric pressure as the Mars surface, and 4x the atmospheric pressure as 20,000 ft on Mars: http://www.computerworld.com/article/2943377/space-technology/nasa-readies-test-for-first-mars-airplane.html
So to my knowledge no prototype aircraft has yet been built which could actually fly on Mars, but it might be possible. Instead of a large Von Braun-style manned vehicle it would probably be a small, flimsy gossamer winged glider carrying a minimal instrumentation payload.
If people lived on Mars and actually needed propulsive aerial transportation, this would be much more difficult due to the payload mass and required wing area. It would be more logical and technically easier to simply use surface-to-surface rocket transportation. Since methane and oxygen can be produced from the CO2 and water on Mars (given sufficient energy), they would probably use methane/LOX propulsion. That rocket structural design and flight profile would probably require some minimal attention to aerodynamic elements but it could probably be closer to a Lunar Module-type design than a streamlined aerodynamic shape.
Very roughly, wind dynamic pressure at the Mars surface is about 1/10th that of earth. IOW 100 mph wind on Mars would exert the same pressure as 11 mph on earth. So while there is wind on Mars, it will not knock over people or structures as depicted in the movie “The Martian”. This same effect means it is difficult to make winged aerial vehicles fly on Mars.
Dynamic pressure calculator: Dynamic Pressure
Mars atmospheric profile Java app: https://www.grc.nasa.gov/www/k-12/InteractProgs/index.htm
Although Mars has no appreciable oxygen in it’s atmosphere, you could still use something like a jet engine provided it was supplied with both fuel and oxidizer. By using the Martian atmosphere as reaction mass, it would be much more fuel-efficient than a rocket.
I’m surprised no one has mentioned a treadmill yet. 
Well, we could run a treadmill in reverse.
The record for jet engine flight is 123520ft. Looking up some tables (don’t use a calculator, temp is important) the pressure at that altitude seems to be around 5mbar. The surface pressure on Mars is 6mbar. Jet engines as we know them isn’t getting a big time energy gain for air at that low of a density.
If you were to get into jet engines with a really wide mouth on them, etc., then maybe. Just be careful you don’t end up sucking in any malagors.
No jet plane has flown level at 123,000 ft. It was a MiG-25RB which did a zoom climb, the engines probably flamed out below 100k feet, and it traveled in an unguided ballistic trajectory (like an artillery shell) which peaked at 123,520 ft.
It would actually be interesting to have more detail about that flight but it was done during the Soviet era so I don’t think much is available. However the engine was apparently the R-15BF2-300, a conventional turbojet with afterburner. I don’t think any turbojet will operate at 123,000 ft.
Nope, the lower gravity would be nowhere near compensating for the low air density. The atmospheric density is a much greater factor than gravity.
For an earthly example, compare an albatross and a penguin. They both locomote through a fluid medium using their forelimbs with the same sort of motion, but compare the surface area of an albatross’s wing to a penguin’s flipper. Both operate under 1g but the density of the fluid they move through has a huge impact on their shape and structure.
Excellent conceptual analogy.
Although it falls down on the practical physics side of things because penguins float in water. They have to use their “wings” to create negative lift to force themselves below sea level just as albatrosses have to use their wings to create positive lift to force themselves above sea level.
Said another way, sea level is attractive. 
I was aiming for a fairly simple analogy rather than a math-heavy technical discussion.
Submarine vs. airplane can also be a useful analogy, as subs “fly” underwater, and can use their dive planes to generate lift when at neutral or even negative buoyancy, but have much smaller lifting surfaces than airplanes… however, I thought the bird example would be more intuitive to the average reader.
I started wondering about this after posting, thinking about the famous flights Chuck Yeager made in the NF-104A, that the Soviet record was also set in a ballistic arc run. The NF-104A’s engines were shut down above 85k’ to prevent damage. More modern jets could do better. But something in the low 100k’ seems to be a reasonable max. for current technology. Note that the proprosed Reaction Engines A2 has a 100k’ ceiling. Similar techs like ramjets can’t be used at subsonic speeds. On Mars that would mean serious rocket assisted take-off and perhaps a “one time only” 
landing profile.
Here’s a whacko idea – You can “fly” on Mars without using a balloon or the limitations of air-breathing engines or rockets if you use Laser Propulsion Technology.
I’m not talking about laser Light Sail Propulsion, but Laser Ablation Technology.
I worked on this for a couple of years. The idea is that your craft caries your payload and your reaction mass (which, unlike rocket fuel, is pretty much inert, not highly reactive). The energy needed for propulsion comes from the laser system on the ground. It also controls the flight direction, speed, etc. You don’t need a pilot in the craft, although you could, in principle, carry passengers.
Your laser is pulsed, possibly with multiple pulses per cycle to perform different functions. The first pulse, or part of a pulse, ablates a thin layer of the bulk reaction mass, turning it to plasma. The second pulse, or second part of the single pulse, feeds energy into that plasma by inverse brehmstrahlung, heating and expanding the plasma so that it pushes the craft forward. Then you let the stuff dissipate before the next pulse/series of pulses a fraction of a second later. A string of such pulses can move a payload of reasonable size.
Timid folk suggested that you can use this for orbital corrections (no absorbing or distorting atmosphere in space, and you don’t need big pushes). More radical folks, like Arthur Kantrowitz, one of the proposers, suggest you could use it to lift small payloads from the earth to orbit (as in the stories High Justice by Jerry Pournelle, or The Pools of Space by Michael Kube-McDowall)
But you could also use the principle to fly craft around in an atmosphere, as suggested by Dean Ing and Leik Myrabo in the Future of Flight, or Ing’s novel the Big Lifters. (Myrabo’s Apollo Lightcraft has been experimentally verified out at White Sands – there are YouTube videos of it lifting off under a series of carbon dioxide laser pulses, and being caught afterwards in a fishnet. Myrabo’s lightcraft, however, didn’t use ablative reaction mass, but the surrounding air, so it’s an “air breathing” system)
If you could use this to fly around the Earth, it’d be even easier on Mars, where the atmosphere is thinner and clearer and the gravity is significantly lower. Of course, it’d be a line-of-sight system, but that could work in many applications. Or you could use a system of relay lasers to cover a longer track. And, of course, it wouldn’t work in the presence of those Martian Sandstorms.
But it’d work on most days on Mars, and better than it would on Earth. The reaction mass we’d hoped to use was ice, which would be possibly too precious on Mars, but you could also use other substances – we used plastics for our tests. It’s nonreactive, avoiding the considerable hazards of most rocket fuels. It doesn’t require an oxidizer (also precious on Mars), and it requires no atmosphere for operation (although you can use wings and ailerons and spoilers for additional control). All your power difficulties are re-assigned to your laser source, but at least that’s on the ground, and can be as big and complex as you need.
And, of course, you could have a hybrid system where a balloon provides the lift while Ablation Technology (using dedicated patches of ablative material – if not the entire exterior of the balloon) provides propulsion and direction. (You can shape the wavefront of the beam to provide different “push” on different parts of the patch. Or you can use more than one laser to apply different forces to different sides of the balloon). That way your laser only needs to be used for the less demanding task of Pushing, and not on the critical one of Keeping Things Up In The Air.