Is there a way to make the "Aerodynamic Overlay" work in the VAB?

[Skorj]

The "Aerodynamic Overlay" (blue ball showing center of drag or pressure or whatever that's supposed to be) in the VAB never seems to work for me. It just appears on the floor of the VAB, obviously bugged. Been that way for many KSP versions now.

Anyone have a fix for that? It's rather frustrating when I have a rocket that flips out, and I can't see why.

[MechBFP]

Put something with lift, like those moveable wings, on your rocket and you will see it move.

[Jupiter3927]

That blue ball doesn't account for body lift or symmetrical wings.
Total lift cancels out completely when radial symmetry is enabled and the game doesn't know where to put the ball so it goes in the floor.

[Skorj]

The blue ball is just the center of drag on a craft with no wings. Don't make it out to be more complicated/realistic than it is.

On rockets without fairings is seems to work fine. Center of drag below CoM = stable rocket. It seems to bug out as soon as there's a fairing. Anyone else have this problem? Anyone found a work-around?

[Jupiter3927]

It's the center of lift.
It does not care about drag whatsoever.

[Skorj]

Can anyone actually help?

[MechBFP]

Originally posted by Skorj:

Can anyone actually help?

Not if you can’t read.

[Skorj]

Look man, it's just flat out wrong that you need wings on a rocket for the aerodynamic center to display properly. I'm not sure why you'd say that. I'm also not sure why you'd suggest fixing a VAB bug by building a spaceplane instead of a rocket. Those are very strange things to say, and they aren't helpful.

[Chibbity]

Here ya go. Makes COL indicator account for all lift sources correctly.

https://forum.kerbalspaceprogram.com/index.php?/topic/160231-18x-correctcol-stock-aerodynamics-design-aid-continued/

[Skorj]

Thanks. Turn out it didn't help, but it was certainly worth a try!

For clarity, let's see if I can link screenshots:

Rocket showing VAB bug

Rocket with no bug

[MechBFP]

Originally posted by Skorj:

Thanks. Turn out it didn't help, but it was certainly worth a try!

For clarity, let's see if I can link screenshots:

Rocket showing VAB bug

Rocket with no bug

That’s not a bug, that’s how fairings work. You can complain to the devs if you don’t like it.

[Knarrwinkel]

Originally posted by Skorj:

Rocket with no bug

This picture is a perfect example to show you that this whole system isn't working like you want it to work. The blue ball is only showing the center of lift of one single part: the command pod. And that is useless a) because it's the lift of the occluded bottom part and b) because it ignores the surface area and body lift of every other part on the rocket.

Like people already said, the CoL overlay only shows the lifting forces for a few select parts. It doesn't show the center of pressure or drag or even lift of the whole rocket. It is and always has been pretty much useless for rockets. What you need to do is look for the CoM and then guesstimate if there's much more stuff going on above it than below it.

[Skorj]

Except it usually does show the center of drag for the whole rocket. In the working example, it just happens to be up at the pod, because that's where all the drag is.

It boggles my mind that people have all these fan theories about the blue ball. Anyway, I'll ask on the real forums.

[Knarrwinkel]

Originally posted by Skorj:

Except it usually does show the center of drag for the whole rocket. In the working example, it just happens to be up at the pod, because that's where all the drag is.

No it is not. Really. Just take the pod, add afuel tank below it and then take it off again and put it on top. Does the indicator move at all? No? Does that mean that there's some extremely complicated formula that keeps the drag always centered around the pod or does that simply mean that the indicator only shows you some useless lifting force of a single part?

[Jupiter3927]

I'll say it again, the blue ball shows the center of lift.
Most parts don't generate lift but all the wings do.
They ONLY generate a net lift (the lift shown by the blue ball) when their combined lifting force is not 0, like on a plane where you want the lift to be up.

Wings will generate no lift if they are parallel to the expected velocity vector direction.
It's straight up in the VAB and horizontal in the SPH.
Wings ONLY generate lift when they are at an angle to this vector.
Wings will cancel out their symmetrical wings if they are placed in radial symmetry so the blue ball will show no lift.
Wings placed in mirror symmetry at an angle to the expected direction of motion will show a net lift.

Drag is not calculated in either the VAB or SPH.
It's honestly all guess work on your end to determine drag.

Lift =/= Drag.

[Toastie Buns]

L/D is dependant on airspeed and AoA

Distance / vertical altitude lost = L/D (sorta, but it works)

♥♥♥♥ knows why you wanna work that out on a rocket though. Providing the CoL is behind the CoM, nobody should care. Below the rocket? Even better.