drag inside cargo bay

[miklkit]

I just built a spaceplane for testing and noticed that it has a lot of drag, so turned on the indicators.  It sure looks to me that the rover is dragging but I don't know how this is so.  Even the wheels have red on them.  Am I seeing this wrong?

[Zhetaan]

9 hours ago, miklkit said:

It sure looks to me that the rover is dragging but I don't know how this is so.  Even the wheels have red on them.  Am I seeing this wrong?

You're not; the game thinks that your rover is exposed to the outside airflow.

Pardon my complete lack of technical expertise on this, but I understand it that there's a bug with occlusion such that objects docked inside closed cargo bays can be considered separate vessels by the game, which means that they are subject to drag.  Of course, they're still physically connected to the rest of the vessel, so that drag pulls on the whole works.

What I don't know is whether this appears always, or only when there are certain conditions at work (such as certain kinds of clipping).

What I do know is that if you want to eliminate it completely, then the only solution that I know will work is to install FAR, since FAR uses a completely different approach to figure occlusion.

Edited December 1, 2022 by Zhetaan

[Lt_Duckweed]

10 hours ago, miklkit said:

I just built a spaceplane for testing and noticed that it has a lot of drag, so turned on the indicators.  It sure looks to me that the rover is dragging but I don't know how this is so.  Even the wheels have red on them.  Am I seeing this wrong?

Everything has a drag vector with aero forces turned on, it will just be  extremely short for things producing no drag, like the wheels appear to be.

The aero forces view is a bad way to tell what is producing the drag anyways, since the vectors don't have a consistent scale.

If you want to actually tell exactly how much drag a part is producing, do this: Alt-F12 -> Physics -> Aero -> Show aero data in part action windows.

It's hard to tell from the screenshot, but it looks as if most of the drag is coming from your fuselage itself, and not what is in the fuselage.

[miklkit]

Yeah, those are not the best screenies.  As I see it the top red bar is the cabin and it is very long, the middle red bar is the fuel tank which is small, then the 3rd red bar is the rover with that blue vertical bar and the red bar going back.  It is pretty long.  What is not shown is the 4th bar, which is the rear ramp section.  That is surprisingly draggy. 

This is a newly built spaceplane just to test the viability of the ramp.  I took precautions to build it so that there would be no aero forces in the cargo bay, but there they are anyway.  I built the fuselage then the mounting system in the cargo bay, then the rover and the rover is dumb.  It has no control unit like an OKTO.  Did manage to get it to the Mun and the rover detached and ran around and reattached just fine.  Landed on Kerbin well too.  It is much better than at first when it could not even go supersonic. 

 

Not enthusiastic about installing FAR as it would most likely require me to redesign my entire fleet of spaceplanes.

[Lt_Duckweed]

Oh, one more question, is the cargo bay the root part?  That sometimes causes issues, and the solution is just to make one of the other fuselage parts (either the fuel tank or the cockpit) the root part.

[miklkit]

It should not be.  I started with the cabin and added onto that. 

[magnemoe]

4 hours ago, Zhetaan said:

You're not; the game thinks that your rover is exposed to the outside airflow.

Pardon my complete lack of technical expertise on this, but I understand it that there's a bug with occlusion such that objects docked inside closed cargo bays can be considered separate vessels by the game, which means that they are subject to drag.  Of course, they're still physically connected to the rest of the vessel, so that drag pulls on the whole works.

What I don't know is whether this appears always, or only when there are certain conditions at work (such as certain kinds of clipping).

What I do know is that if you want to eliminate it completely, then the only solution that I know will work is to install FAR, since FAR uses a completely different approach to figure occlusion.

In my experience with equipment bays is that you has to connect stuff to the center nodes, not surface mount, you can surface mount on the stuff connected to the center node however. 
Looks like you did that, and I don't think you get drag from the rover, you see you get some drag from the surface mounted RTG in the front but not the RTG on the rear of the rover.
One fast test would be to simply remove the rover and its structure and see if drag is much different. 

[miklkit]

Yeah I should try that.  I just started using that drag indicator and do not know how to read the bars yet.  Not sure what I'm seeing.

[miklkit]

Been experimenting with this drag thing and it is really weird.  Some things will not attach correctly in the cargo bay and some will.  Batteries, structural, cargo containers, and C&C stuff works fine.  Fuel tanks do not.  I built an ore carrier and it could not go supersonic because the ore tanks caused so much drag.  Here are 2 screenies, one with ore tanks and one without.

I accidentally found a way to get tanks into the cargo bay without causing drag.  Just dump them in any way they will fit.  They look ugly just sitting there randomly but do not cause drag.