Drag from parts inside a cargo bay

[lBoBl]

I'm having a weird bug with drag being produced by parts that are stowed inside a cargo bay.

The weird thing about it is how inconsistent it is. I designed my plane in the SPH, when I launch it it takes off, accelerates, goes supersonic and to orbit, no problem. If I revert to launch and try again though, this time the parts inside the cargo bay are producing excessive drag and this time my plane won't even pass the speed of sound. I had the bug once during testing, I sort of dismissed it, put a short fairing on one of the things inside the cargo bay just in case, and proceeded to send that spaceplane to another planet where it is now. Problem is, now the aero engine is freaking out again and I'm kind of stuck there moving at very low speeds.

I tried quicksaving and reloading, as well as opening and closing the cargo bay, hoping to force the game to recalculate what is shielded and what's not, but it didn't work. I also noticed after some time that the engines were maxing out at their stationary thrust (they're supposed to work like jet engines) instead of going past it as I gain some speed, which probably also contributes to my relatively slow speed.

I did tons of test flights with that craft where everything went fine, but now it seems to be stuck with that weird aerodynamics behavior and I obviously can't revert to SPH now.

I have a modded install but I don't think that any of the mods I have installed should affect aerodynamics (I might try installing FAR and seeing if it solves the problem though).

I was wondering if anyone ever had the same bug and managed to find a way to beat some sense into that stubborn physics engine

Edited May 6, 2021 by lBoBl

[FleshJeb]

There's an old bug (that I'm not sure still exists) where making the cargo bay the root part of the craft can prevent it from shielding the parts inside.

Are you closing it with the slider or the button? Even if the slider is set to 0% and the button says open, it's open.

I've never heard of that engine bug, I'm inclined to think it's mod-related. I'm assuming it's a mod engine? Did it work correctly on that planet before?

For diagnosing problems, it always helps to have pictures of the craft and a mod list.

 

[Guest]

Why do you think it’s drag inside a cargo bay? Sounds more like the engines which you’ve said aren’t powering up properly. And sounds linked to reverting the flight (I’ve seen occasional bugs with air intake/jet engine power when doing this as well in a recent version come to think of it).

You can check aerodynamics via the Alt-F12 menu, there’s an option to show forces acting  on the vessel, I think this will rule out the cargo bay theory though.

A list of your mods might help but if the same as above I think it’s a stock bug. My only fix was to rebuild the plane (maybe just replaced the engines I can’t remember 100%).

[lBoBl]

9 hours ago, FleshJeb said:

There's an old bug (that I'm not sure still exists) where making the cargo bay the root part of the craft can prevent it from shielding the parts inside.

Are you closing it with the slider or the button? Even if the slider is set to 0% and the button says open, it's open.

I've never heard of that engine bug, I'm inclined to think it's mod-related. I'm assuming it's a mod engine? Did it work correctly on that planet before?

For diagnosing problems, it always helps to have pictures of the craft and a mod list.

 

Ooooh I didn't know that. The cargo bay was the root part at some point in the build, I think I changed it in the end but it might be related. It was definitely still the root part when I added everything that's inside, so that might be it.

I was wondering if perhaps doing some on-site surgery with an engineer might cause the game to recalculate what is shielded and what's not, I'll probably try that later today.

Apparently the engine producing a fixed amount of thrust is normal behavior for that engine though, so forget that part I guess. Even when I test the craft out of the SPH and it's able to get to mach 4, they're not producing any more thrust.

2 hours ago, FruitGoose said:

Why do you think it’s drag inside a cargo bay? Sounds more like the engines which you’ve said aren’t powering up properly. And sounds linked to reverting the flight (I’ve seen occasional bugs with air intake/jet engine power when doing this as well in a recent version come to think of it).

You can check aerodynamics via the Alt-F12 menu, there’s an option to show forces acting  on the vessel, I think this will rule out the cargo bay theory though.

A list of your mods might help but if the same as above I think it’s a stock bug. My only fix was to rebuild the plane (maybe just replaced the engines I can’t remember 100%).

It's definitely not the engine, and yeah I know about F12, I even know about the "display aero data in action menus" option from the console menu, which I used to diagnose the problem. Parts inside the cargo bay are producing drag when the craft is stuck in slow mode, and the same parts are at 0 drag when the plane is just out of the SPH and working properly

Edited May 6, 2021 by lBoBl

[lBoBl]

What bothers me the most is that when it's working, it's definitely one of the best planes I've built in 3000 hours of playing KSP... It flies really well and really stable at any speed, it can reenter at any angle like it doesn't even care, and it's so easy to land that it's almost impossible to crash, you can slam it down and it's just fine 

[Guest]

32 minutes ago, lBoBl said:

It's definitely not the engine, and yeah I know about F12, I even know about the "display aero data in action menus" option from the console menu, which I used to diagnose the problem. Parts inside the cargo bay are producing drag when the craft is stuck in slow mode, and the same parts are at 0 drag when the plane is just out of the SPH and working properly

Fair enough, I wasn’t sure how experienced in the game you were, sorry if I came across as patronising.

Very difficult in atmosphere but I wonder what would happen if an engineer removed the dragging parts in flight? Would it right itself or blow up/crash? You might be able to rig something up with a command seat in the cargo bay if you fancy a challenge 

[lBoBl]

@FleshJeb was right, it was apparently because the cargo bay was the root part (I was quite sure I changed it but I must have reverted that change at the last minute). When I re-root the craft to the plane's cockpit the issue goes away. 

Problem solved, thanks guys!