KSP Aerodynamics questions

[KerikBalm]

I know KSPs aerodynamics models is still a WIP... and its also probably the least realistic part of KSP.

So, question #1:

I've heard that drag is proportional to mass - or rather mass is used as a stand in for its aerodynamic cross section - thus any part witha drag coeeficient of 0.2 will have the same terminal velocity....

But is the mass of fuel in a tank included? Ie does a full tank have the same terminal velocity of an empty tank. If the mass of the fuel is added to the tank before the drag is calculated, I guess it would be like that... but if the weight of fuel does not affect this (as it shouldn't... really), then fuel optimal ascents would generally be done at much higher velocities, no?

Question #2:

If drag is proportional to the part's mass, does it work the same way with lift?

I saw a youtube video on making SSTs (ram air intake spamming, bassically), they recommended using swept wings because the lift rating/mass was higher than delta wings... but when I look at the stats (given that I fly and my dad is an aeronautical engineer), I look at the L/D, and that would imply that delta wings are best (at least within the atmosphere, I suppose there is a point where lighter wings are preferable for maunevers in space, even if they are aerodynamically less efficient - and getting to orbit uses ore fuel).

I've also heard that lift increases linearly with velocity, not ^2 ... does it work like this with drag as well?

If it was changed to exponential... would this allow control surfaces to work at higher altitudes (assuming you're going faster), or are they modeled in some funky way -perhaps like reaction wheel torque?

[Taki117]

Answer #1:

Yes, the mass of the fuel is included. Therefore as you burn fuel your drag decreases.

Since you do fly and seem to enjoy spaceplanes I suggest getting FAR as it will drastically change the Aerodynamics.

[numerobis]

The fuel mass is included in drag calculations indeed. Test by launching a rocket to, say, 2km, with three orange tanks and one mainsail. The mainsail will burn fuel from one tank. Decouple everything so you have the mainsail and the three tanks falling all separately. The half-empty tank will fall at the same speed as the rest. No, this does not make sense, but that's KSP physics.

Drag is calculated as 0.5 rho Cd A v^2 where rho is the air density, Cd is 0.008, A is the drag value times the mass (including fuel), and v is your surface speed. With mass in tonnes, you get drag in kN.

Lift is calculated as f(AoA) * lift * pressure * speed, which gives a value in kN. The function on the angle of attack is different between wings and control surfaces (if it moves when you hit wasd, it's a control surface); wings have the most lift near 25.7 degrees, whereas for control surfaces f(AoA) = sin(AoA), so the steeper the better. The direction of lift is perpendicular to the surface prograde vector, so if you're climbing, some of the lift is reducing your horizontal speed. That's called parasitic drag. Parasitic drag is linear in speed because it's just lift that's going the wrong way.

[RSwordsman]

Answer #1:

Yes, the mass of the fuel is included. Therefore as you burn fuel your drag decreases.

Since you do fly and seem to enjoy spaceplanes I suggest getting FAR as it will drastically change the Aerodynamics.

That's messed up. I'm glad I got FAR and never looked back. It does make conventional aircraft a lot more tricky, but for regular rockets, it's a godsend.

[Taki117]

That's messed up. I'm glad I got FAR and never looked back. It does make conventional aircraft a lot more tricky, but for regular rockets, it's a godsend.

I too have FAR and I must say it's now on my Must Have Mod List (Along with KER, TAC-LS, TAC fuel Balancer, and a few others)

[RoboRay]

That's messed up. I'm glad I got FAR and never looked back.

Yeah... seriously messed up. The stock aerodynamics (and I use that term loosely) system is two-years overdue for replacement. Most mods are optional, but FAR is absolutely essential. Every KSP install should come with it.

[Taki117]

Yeah... seriously messed up. The stock aerodynamics (and I use that term loosely) system is two-years overdue for replacement. Most mods are optional, but FAR is absolutely essential. Every KSP install should come with it.

I think what Squad is trying to do is finish with the Unity implementation (And get KSP running on more than 1 core and with > 4gb of RAM)