Spaceplane aerodynamics on other planets

[tstehler1]

Alright, we all know the aerodynamic physics, as they apply to spaceplanes, kinda suck at the moment (I know it's a planned fix, don't attack me for whining). But so far, I've only used them as a local transportation system around KSC and in the immediate area for crew recovery. Are the lift/flight dynamics/etc the same on Duna as they are on Kerbin? Obviously the gravity would be different, but is there any other difference?

Edited April 10, 2014 by tstehler1

[quasarrgames]

Well on duna of course the atmosphere is 10 times thinner, so you need a LOT of wings to make it work, but other than that the aerodynamic physics work the same.

[Tery215]

I do believe the magic wing ratio is unachievable on Duna.

[MockKnizzle]

The atmospheric model is the same on all bodies, it's just the surface pressure and gravity that differ.

[KerikBalm]

Well on duna of course the atmosphere is 10 times thinner, so you need a LOT of wings to make it work, but other than that the aerodynamic physics work the same.

Its actually only 5 times thinner... or rather, 1/5th as thick.... at the lowest points.

Its scale height is also less, so it gets thinner faster.

[Pecan]

Don't forget though that the only other place jets work is Laythe, so you'll have to use rockets elsewhere.

[Geschosskopf]

If you're really interested in flying on Duna, check out this challenge thread to review what others have done there:

http://forum.kerbalspaceprogram.com/threads/50619-Flying-Duna-AGAIN

And maybe even enter the challenge if you feel up to it.

In general, though, flying on Duna requires the lightest possible airframe to do the job with absolutely the most wing area you can cram on it, plus about 2-3x as much control surfaces as you'd use on Kerbin. Also, it needs an engine that doesn't require oxygen, which basically limits you to A) ions, , electric props/rotors from Firespitter, c) the Kethane engine, and D) thermal turbojets from Interstellar. You can, of course, use rockets instead but in that case there's no point in having a wing. Spaceplanes aren't really a thing on Duna. Instead, you have a choice of a dedicated airplane or a dedicated rocket.

Of the above propulsion systems, ion and electric limit your to about 6000m maximum altitude and about 100m/s. The thermal turbojets let you go much higher and faster but by that point you're more of a rocket than an airplane so why have a wing? The Kethane jet DOES work on Duna but its very finicky. Unlike regular jets which are limited by IntakeAir, the Kethane jet is limited by KintakeAir which doesn't go away with higher altitude. Instead, it goes away with higher speed. The Kethane jet likes to fly full power at low speed (it was designed for Eve) so on Duna where there's very little drag, it tends to get too fast and flame out. It thus works best for boost-glide flights because once it flames out, you probably won't get it started again until you stop after landing.

Actually entering Dua's atmosphere from space and flying around there aren't that difficult. The 2 primary difficulties are 1) landing and 2) getting off from Kerbin. As to landing, about 80% of Duna's surface is rolling dune fields at about 2500-3500m elevation. The rest is mountains and a few depressions. It's relatively easy to land in the depressions because the air is thicker and the ground is fairly flat. But if you're stuck only landing in depressions, why bother sending a plane? So what you need to do is be able to land out in the dune fields, which are like 16,000m equivalent on Kerbin. To do this, you have to be able to fly VERY slowly so you can stop before the small flat spot between sand dunes ends tragically . Because the air is thin, airbrakes don't work very well and the low gravity limits wheel braking, so your best bet is some sort of retro thrust or VTOL.

Having solved these problems, you now have a featherweight plane with a huge wing, which will be utterly incapable of vertical launch atop a rocket on Kerbin. You might thus have to build a HUGE SSTO spaceplane ascent stage on the back and fly it up horizontally, or use some sort of cage lifter, or give up and use Orbital Construction instead of flying it to Duna.

Anyway, flying on Duna IMHO is one of the least-appreciated challenges in KSP. Certainly it's more of chore than landing on Tylo. I wish more folks would do it.