RCS thrusters are never shielded from drag inside a cargo bay?

[fourfa]

While working on optimizing drag on a small multi-role ship, I noticed that RCS thrusters inside its Mk2 cargo bay are never shielded from drag in flight.  I've tried all three kinds of stock thrusters, and all placements near the center, near the perimeter, and surface-attached to the bulkheads at the front or rear of the bay.  I haven't found a single combination that does not show drag being applied in the stock AeroGUI interface.  Meanwhile other parts (node attached, surface attached, or attached to other interior node-attached parts) show zero drag in high-speed flight with the bay closed, and immediately show drag when I open the bay.  

Spoiler

https://kerbalx.com/fourfa/DAGGER-Scissor-Wing-Concept-x

The photo shows thrusters attached to a test 0.625m core - same result with a 1.25m core.  

(Incidentally, I have also learned that the 4-way mono thrusters are very draggy in any orientation.  The 1-way mono thrusters have about half the drag when mounted radially [as shown], and about half again when oriented axially.  The Vernor LF/O thrusters are relatively streamlined.  Also if other parts are clipped through or even near the edges of the cargo bay, drag will be applied.  Surface mounting to the front or back bulkhead is risky - worth checking it and maybe offsetting to the interior a bit.)

What's happening here?  I recall there was a bug with parts not being properly shielded in cargo bays, in fact there was a StockBugFix module for it.  I thought that had been fixed in 1.1.3.  I also recall that in a prior version RCS in cargo bays would not function unless the bay was open, but currently it works whether the bay is open or not. Is this perhaps related to the complex "cannot activate while stowed" mechanic?

This isn't an awful problem - the real version makes orbit as-is, and flies OK on Laythe - but this concept has a lot of excess drag from the sideways external docking ports, and the cosmetic parts that conceal them.  I'm looking for those last few percent as safety factor, and I just think it's weird that the cargo bay seems to affect these parts differently than all the other parts I've tried.  Any comments or ideas?

Edited September 5, 2016 by fourfa

[Foxster]

I just tried it like this....

The aero data for the RCS block showed zero drag with the doors closed and some drag as soon as I opened the bay. 

So, I don't know why you aren't seeing similar. Could it be where the part it is attached to is fixed to the bay? I used the rear (as you can see) but it might be different if I'd used the front of the bay? 

I don't have time now to look further but I will later. 

Update - I've tried attaching the various RCS thrusters to a small LF tank like your picture and no matter how I place that tank the RCS parts have zero drag with the bay closed. Could you post the craft file?

Edited September 5, 2016 by Foxster

[Nefrums]

Any part surface attached to the part in front or behind the cargo bay will not be considered as "inside" the cargo bay by the game. Even if it is surface attached to the side facing the cargo bay, and hence visually inside the cargo bay.

Attach the trusters to a part node attached to the node inside the cargo bay.

 

[Foxster]

8 hours ago, Nefrums said:

Any part surface attached to the part in front or behind the cargo bay will not be considered as "inside" the cargo bay by the game. Even if it is surface attached to the side facing the cargo bay, and hence visually inside the cargo bay.

Attach the trusters to a part node attached to the node inside the cargo bay.

 

He did that. See his hidden content pictures in the first post. 

[Signo]

In my experience they are shielded by the "unopened bay". As soon as you open it the first time... it is gone.

No matter how you try to close it, it will never work again properly against drag.

[OHara]

The craft in Fourfa's kerbal-x link worked as expected for me in 1.1.3:
 contents have drag when doors are open, no drag when doors are closed, repeatably after repeated open/close
I used the alt-F12 option to show drag in option menus, and roughly confirmed with steady-state airspeed.

The small fuel tanks are very slightly longer than the cargo bay, so in the SPH it is very easy to connect the rear fuel tanks to the small ones inside the cargo bay, when aiming for the back node of the cargo bay.  When I do that, the contents of the cargo bay have drag, and the bay itself has more drag from its unconnected tail.

The things known to have unwanted drag inside closed cargo bays in 1.1.3 are wheels, landing legs, EVA kerbals, and kerbals in chairs.  

[fourfa]

6 hours ago, OHara said:

The craft in Fourfa's kerbal-x link worked as expected for me in 1.1.3:
 contents have drag when doors are open, no drag when doors are closed, repeatably after repeated open/close
I used the alt-F12 option to show drag in option menus, and roughly confirmed with steady-state airspeed.

The small fuel tanks are very slightly longer than the cargo bay, so in the SPH it is very easy to connect the rear fuel tanks to the small ones inside the cargo bay, when aiming for the back node of the cargo bay.  When I do that, the contents of the cargo bay have drag, and the bay itself has more drag from its unconnected tail.

The things known to have unwanted drag inside closed cargo bays in 1.1.3 are wheels, landing legs, EVA kerbals, and kerbals in chairs.  

Thank you for loading it and testing!  This is an interesting data point.  Thing is - I get the opposite result with that exact craft.  The thrusters in the bay ALWAYS have drag, in all conditions, no matter what I do.  

So now what?

18 hours ago, Foxster said:

Update - I've tried attaching the various RCS thrusters to a small LF tank like your picture and no matter how I place that tank the RCS parts have zero drag with the bay closed. Could you post the craft file?

Did that - in the original post

 

10 hours ago, Signo said:

In my experience they are shielded by the "unopened bay". As soon as you open it the first time... it is gone.

No matter how you try to close it, it will never work again properly against drag.

That's interesting.  It's not the result I'm seeing - that RCS thrusters always have drag, but all the other parts I've tested are properly occluded from drag when closed, and show drag when open.  Over and over and over and over without problems.

Edited September 6, 2016 by fourfa

[Signo]

Well, I reformulate: there is something I usually carry in my cargo bays that, assuming the readings I am getting from MJ are correct, works as I described above - I made a few tests with low TWR SSTOs too and the performance hit is clearly notable.  

[fourfa]

Sad to report - I loaded the ship in a 100% stock save and drag was properly occluded in the bay.  Should have gone there right away before posting.  Now to begin the process of weeding out.

In further news, AeroGUI tells me these errant thrusters are responsible for roughly 2-3% of total ship drag.  That's worth tracking down to me.

EDIT - RCS Sounds is the guilty party.  Marking this answered and headed to the mod thread.

Edited September 6, 2016 by fourfa