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Cargo and Drag


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I'm finding that when I pack a lot of stuff into a cargo bay, I'm seeing a bunch of significant drag arrows that seem to originate from there. It appears that inside/outside a cargo bay is not how drag actually works.

What are the rules? I was hoping to put some Mk0 liquid fuel tanks into the extra cargo space in my spaceplane. With two radially attached on a center Mk0 tank, even though they are well inside the cargo bay, they appear to be causing much of my planes drag. It's hard to say with all the red arrows extending from the center of the craft.

Another source of drag appears to be the dual Mk2 coupler. Should those be avoided? I use it to put two rapiers on a Mk2 fuselage.

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The way it's SUPPOSED to work, the drag of stuff inside cargo bays is ignored (if the doors are closed).  However, this has never quite worked right.  How much it doesn't work has varied since cargo bays were introduced.  They have had all sorts of problems, not just with drag, but also overheating and disabling stuff mounted outside the bays (ex:  wings attached to the outside of the bays).  I THINK some of the worst problems have now been solved but I don't think drag yet works properly.  In general, though, it seems to me that stuff has to be attached to the bay's internal node to count as drag-less.  Stuff attached the walls to the bay seem to be treated as if on the outside.  But I'm not really sure.  Because they don't work very well, I try to avoid using cargo bays.

All the multi-coupler adapters have huge drag.  But you gotta do what you gotta do sometimes, and just suck it up.

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1 hour ago, cephalo said:

I'm finding that when I pack a lot of stuff into a cargo bay, I'm seeing a bunch of significant drag arrows that seem to originate from there. It appears that inside/outside a cargo bay is not how drag actually works.

What are the rules? I was hoping to put some Mk0 liquid fuel tanks into the extra cargo space in my spaceplane. With two radially attached on a center Mk0 tank, even though they are well inside the cargo bay, they appear to be causing much of my planes drag. It's hard to say with all the red arrows extending from the center of the craft.

Another source of drag appears to be the dual Mk2 coupler. Should those be avoided? I use it to put two rapiers on a Mk2 fuselage.

Remember that however you may have offset things with the move tool, the craft file is ultimately a tree and branch structure.   I believe there are two checks an item must pass before it is considered shielded from drag and re-entry heating

The most important one is that it must either be connected directly to the cargo bay's internal node or that further up the tree it ultimately connects to the aircraft via this cargo bay node rather than some other attach point on the aircraft.

In english, that means the two radial mk0 tanks should be shielded so long as the central one it hooks onto is attaching to the cargo bay's cargo node.

There is also some volumetric check that ensures the part isn't sticking out of the cargo bay too much, but this errs strongly on the "shielded" side, so items a bit too big for the bay which are partially poking out the ends still count as shielded.   This can cause problems with intakes and rcs ports which are near but not actually in the bay,  which can randomly stop working because of them suddenly becoming shielded.

You can check that the cargo bay is working properly before takeoff - go into the f12 menu, physics section, then aero.  Tick the box that says show drag data in action menus - now when you right click a part you will see "Shielded : True" or "Shielded : False".   Open the bay, right click each item with and pin the menu in place.  Close the bay doors, they should all flip to shielded, if not we have a problem Houston.  

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Great, I'll try to look at this more in depth.

EDIT: I just thought of another question: There is only one node on the cargobay right? Things can be attached on both fore and aft sides but only one is shielded?

Edited by cephalo
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So, I decided to get rid of the cargo bay, and I found that just having a cargo bay is a drag nightmare. I get the feeling that the parts fore and aft are not sheilded either. Like there was a gap between them exposing their large flat surfaces.

Without the cargo bay, and without the bi-coupler, I now have almost no red arrows.

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