Arean Freight

Courtesy NASA/JPL-Caltech/MSSS

Let's set the scene

It is Martian year 2022 and you run a little business on one of the cities on Mars. Maybe you make environment suits or pottery. It isn't my place to judge. Anyways, you live in Olympus Mons and you love it there. The awe from living in one of the largest mountains in the solar system never wears off and the sunset from the upper city is spectacular. You may be happy where you live but you know that if you want your business to keep growing you need to expand to other markets and go global by making your product available to the other cities around Mars. But how would delivery work? Back on Earth, the brunt of the global logistics network is handled by ships, planes, and trains but here there are no oceans, the air is too thin, and none of the plans for a train network have been approved due to the monumental cost and a corruption scandal. When people need to move between cities, they use suborbital shuttles but they are too expensive for everything but the most important post. Rovers then? None of them are designed for freight transport or long distance voyages without stopping to recharge and for maintenance. Looks like you're going to have to come up with a new vehicle if you want to grow your business.

The atmosphere

Let's assume you want an aircraft to ship your good across the planet. Is it the best form of transport to choose? Probably not but I'm not stopping you. So it's not impossible to make something fly, Ingenuity made sure to prove that point, but it is quite hard. There are two reasons for that and they are both the Martian atmosphere.

The atmosphere is mostly made of CO2 and is really quite thin. I'm not sure I can convey in words how little atmosphere there is so have a look at the graph comparing the Earth's atmosphere to Mars'. If you can't really see the Martian atmosphere then mouse over or tap to compare the Earth equivalent altitude.

So the Martian atmosphere at the surface is roughly similar to the Earth's atmosphere 34 km up. Bearing in mind planes fly at a maximum altitude of around 10 km and even the SR 71 was only rated up to 26 km, the air density at 34 km is not in the realm of traditional aircraft. Ingenuity is evidence of this with how light it is and how massive its rotors are in comparison to its size.

The other main issue with martian air is that it doesn't burn. So no jet engines. Only propellers or rockets. Propellers produce very little thrust on mars and rockets use a lot more fuel than jet engines. Kind of a lose-lose. Ah well that's what we've got with today's technology and it's all irrelevant anyway if we can't produce lift.

Ground effect

Let me introduce you to my good old friend: the wing in ground effect. Famous for the Caspian Sea Monster and ... not much else really. In very basic terms, when wings are very close to the ground, a cushion of air forms under the wing that it can surf to generate more lift for free. Helicopters use it all the time to taxi. In principle this could solve all our problems apart from the fact that even with the bonus lift, we'd still have to go really fast to generate enough to be useful (because lift is proportional to speed2).

The problem with going really fast is that the air soon stops behaving. When you pass the speed of sound, traditional aerodynamics (including the ground effect theory) stops working as the air rebels whenever you disturb it, creating shocks and expansion fans. But we can use this to our advantage.

Whenever a shock forms, the air slows down and pressure after it increases. So if we create lots of shocks one after the other, we can create lots of pressure. And if we can do this under a wing by bouncing them about, more pressure means more lift and we get a get a form of Supersonic Wing In Ground effect by riding the shocks. No idea if this would work in practice.

Have a go designing a supersonic wing and see what lift and drag values you can come up with. I'm comparing the values to if the wing was in the free stream with no ground nearby. If the air slows down enough to be subsonic, all my current theory breaks so I just label it as invalid.




Kink Position

The orange line is a 2D wing section (imagine looking at a wing from the side) and it's flying a certain height above the ground. Because it is going supersonic (the speed from the Mach slider), shock waves are formed, represented by white lines. Whenever they hit something, they bounce. Each shock changes the pressure under the wing, affecting how much lift and drag it produces.

You can give the wing thickness with the toggle and adjust the position of where the top corner is. This position will affect the center of mass (purple dot) and the expansion fan which will slightly change the forces on the wing.

The blue dot is the center of pressure and the distance between the two dots is representative of the pitching moment on the wing or how much the wing wants to spin.

Coming soon™

Turns out 3D stuff is hard. It might take a while for me to get round to this.