Air Intake Drag Question

[Carsogen]

Hi everyone,

Does anyone know why the drag multiplier of air intakes increases with velocity? (From about 0.2 to 2.0 I think, 0.3 when closed)

They are the only part to do this so I was wondering if there is some effect that happens in real life that KSP is mimicking? Cheers,

Cas.

[Jimbimbibble]

The stock drag model is horribly unrealistic so I don't think it's mimicking any real phenomenon. Drag coefficients in real physics are nonlinear and very difficult to calculate except for the simplest of shapes, especially when supersonic.

[Carsogen]

Yeah being based on mass is weird (fixed soon! ) but even so normal equation is:

(drag coefficient of part) x velocity^2 x airdensity x mass.

But for the intakes they've added a mechanic where drag coefficient of intakes increases to 2 with velocity, so their drag increases more than other parts leading to weird drag imbalances and flat spins. It just seems to me that the devs wouldn't add this if there wasn't something in real life to imitate.

To me it seems like there would be a change at mach1 rather than a gradual shift. Thanks for the reply!

Cas.

[Jimbimbibble]

Well, it's a lot more complicated than that. The drag coefficient typically decreases as velocity increases for low-mid subsonic flight. Then, it increases and reaches a local maximum around Mach 1. Then, it decreases again and reaches its minimum value a little later and increases once again for very high Mach numbers. KSP makes no attempt to model this behavior. My best guess is that because of the very low mass of intakes, the devs had to do something to increase drag because intakes should produce significant drag, since they are large flat objects.

[numerobis]

Drag is using a fairly standard equation, except that for the "area" of the part, KSP uses the mass. Intakes have an explicit area. Munging the drag coefficient appears to be an attempt to use the explicit area, and to properly take into account the angle of attack. But after getting all of that right, it feels like the final piece was rushed through to get the weird setup we have now.