Do KSP atmospheres have viscosity?

[Aelipse]

Or rather, do KSP planets have different viscosity?

Some time ago I was flying a test spaceplane in Eve's atmosphere, and even when I reached altitudes with pressure below that of Kerbin sea level, the handling still "felt" different compared to the home planet. Among other things, the ship would have a tendency to slip sideways, whereas on Kerbin it has always been perfectly stable. I was wondering if there is a hidden parameter like atmosphere viscosity which differs for Kerbin and Eve, if different temperature might cause different flight behaviour or if it's just the higher gravity at work.

[OHara]

No viscosity; KSP's atmospheric drag is all of the Cd×velocity² type from stirring up momentum the air. (At slow speeds the oceans act like they have viscosity -- so that your splashdown comes to rest and lets you hit 'recover' reasonably quickly.)

The density and force of gravity are the only mechanisms I know of that makes different planets feel differently to aircraft.  Eve has similar density to Kerbin at the altitudes where the have similar pressure, if the wiki is still correct.  There is an 'aero data' option in the alt-F12 debug menu that might show you more that you are interested in.

[Aelipse]

1 hour ago, OHara said:

No viscosity; KSP's atmospheric drag is all of the Cd×velocity² type from stirring up momentum the air. (At slow speeds the oceans act like they have viscosity -- so that your splashdown comes to rest and lets you hit 'recover' reasonably quickly.)

The density and force of gravity are the only mechanisms I know of that makes different planets feel differently to aircraft.  Eve has similar density to Kerbin at the altitudes where the have similar pressure, if the wiki is still correct.  There is an 'aero data' option in the alt-F12 debug menu that might show you more that you are interested in.

Thank you for your input! Browsing through the wiki (and I don't know why I didn't do that earlier *facepalm*) reveals more physical quantities that might differ from body to body, like adiabatic index and molecular weight. I'll look into it. 

[jimmymcgoochie]

Eve has higher gravity than Kerbin, this could explain why it felt different- your plane needed a greater angle of attack to generate the additional lift to counter the extra gravity which in turn can make it behave differently than at the same speed and atmospheric pressure on Kerbin.

[KerikBalm]

On 5/31/2020 at 9:08 PM, OHara said:

No viscosity; KSP's atmospheric drag is all of the Cd×velocity² type from stirring up momentum the air. (At slow speeds the oceans act like they have viscosity -- so that your splashdown comes to rest and lets you hit 'recover' reasonably quickly.)

The density and force of gravity are the only mechanisms I know of that makes different planets feel differently to aircraft.  Eve has similar density to Kerbin at the altitudes where the have similar pressure, if the wiki is still correct.  There is an 'aero data' option in the alt-F12 debug menu that might show you more that you are interested in.

Actually, Eve's density is higher at the same pressure, because its air has a MW of 43, compared to 28.8 for Kerbin... of course, a higher air temperature results in lower density for the same pressure (otherwise, hot air balloons wouldn't work).

This shouldn't be on the wiki anymore, its quite out of date:

and of course, is in conflict with this:

Which clearly shows that the pressure is not a simple scale height curve.

Anyway, the density is different for the same pressure, the gravity is different, so your AoA will be different, and things won't fly the same.

Another thing that is different is the speed of sound, so for the same speed, you'll have a different mach number, which will also affect the coefficient of lift and drag that you get at those speeds. At very low speeds (100 m/s or less), differences in mach number won't be significant though.

All this combines to a significantly different handling, yet still somewhat similar.

[Klapaucius]

If you want to check out more variations, check out Galileo's Planet Pack. Telummo has 10x the atmospheric density at sea level. Flying planes is quite a different experience.