0.25 - Some radially mounted engines give no acceleration

[Dickie Crickets]

KSP Version: 0.25.0.642, 32 bit

What Happens: Radially mounted engines provide no thrust if other parts are mounted directly beneath them.

Mods / Add-Ons: None.

Steps to Replicate:

1. Download tester craft file, it should look like this: http://i.imgur.com/SYu0bpb.png
   
2. Launch craft.
   
3. Go to full throttle and activate all the stages (like a proper Kerbal pilot)
   
4. Notice that the vehicle is going nowhere.
   
5. Revert to VAB
   
6. Move the landing gear such that they're offset from the engines and there is nothing radially mounted beneath them. Screenshot of the setup (the lower set of engines can be mounted higher on the tank and the result is the same).
   
7. Launch and notice that the vehicle moves just fine.
   

Result:

When parts (such as landing gear) are mounted below radial-mount engines (such as the Rockomax 24-77), the engines have no influence on the vehicle's velocity despite still burning fuel and making lots of noise.

Fixes/Workarounds: Offsetting the engines and landing gear such that the exhaust has a clear path to the bottom of the aircraft causes the vehicle to accelerate properly.

Other Notes/Pictures/Log Files: Testing screenshots with some notes. Some of those screenshots have mods in them, but this bug also repro'd with 0 mods.

Edited October 12, 2014 by Dickie Crickets
32 bit version

[SlimeCrusher]

It should work like that, the landing gear is blocking the exhaust, if you press F3 you should see a "Heavy landing gear has been damaged by rocket exhaust" or something like that.

[xrayfishx]

As already stated, that's intended behaviour, it's supposed to be like this. Obviously you can't thrust through another object. It won't work for the same reason an engine in the middle of a stack won't work.

[sal_vager]

Yeah this is intentional and not a bug, it's not going to be changed sorry.

Some things are unaffected though such as RCS, all you have to do is set thrust damage to false in the part.cfg if you're bothered by it

[Dickie Crickets]

Thanks for the responses everyone!

It should work like that, the landing gear is blocking the exhaust, if you press F3 you should see a "Heavy landing gear has been damaged by rocket exhaust" or something like that.

You are indeed correct; I didn't even think to look in the log.

As already stated, that's intended behaviour, it's supposed to be like this. Obviously you can't thrust through another object. It won't work for the same reason an engine in the middle of a stack won't work.

It is correct from a physics standpoint, but craft that worked in 0.24 have no thrust in 0.25, without me making any changes to them. That's why I posted the bug report.

Yeah this is intentional and not a bug, it's not going to be changed sorry.

Was this intentionally modified in 0.25? I have a lander that worked fine in 0.24 and now has no thrust in 0.25.

There's nothing wrong with the feature itself, but it'd be nice to have some sort of in-game indication this was happening (the silent warning in the log doesn't count). Or even better - show me the exhaust/aerodynamic colliders in the VAB when I'm installing parts so I can be sure I'm avoiding the problem. A few inches can make all the difference in the world: This guy flies fine without any damage to the lower engines, this one is completely inoperable.

Some things are unaffected though such as RCS, all you have to do is set thrust damage to false in the part.cfg if you're bothered by it

Ah, the lack of consistency with RCS is potentially confusing. I feel like I can mount an RCS thruster inside of other components, on Jeb's back, wherever and it'll work fine.

The only bother is that I have some expensive landers in orbit around Minmus that aren't usable, but you've just saved my career-mode pocketbook (and some Kerbonauts ). Thanks!