~0.5 Jet Fuel imbalance tears the whole plane apart.

[Artimus]

Good morning!

Yesterday I launched this SSTO Crew Jet to get some of my space station Kerbonauts back home. When I got close to the KSC again at an altitude of ~1200 meters parts of the plane suddenly disintegrated step by step (blue numbers - the same order every time) and finally almost every remaining part of the plane got torn apart (3), leaving only the cockpit and crew cabin on a free fall attached to each other.

While flying towards the KSC I moved ~20 units of liquid fuel from the rocket fuel tank 2 (RF2) to each of the jet fuel tanks (JF). "Luckily" I quicksaved a few seconds before the strange event occurred, allowing me to test dozens of ways to (hopefully) avoid that situation without loosing my whole crew. Just before giving up my buddy suggested it may be because of the transfered fuel. So I loaded the game another time, turned off SAS and the engines, moved the remaining ~12 Units of liquid fuel from the jet fuel tanks (JF) back to the rocket fuel tank 2 (RF2), then turned on SAS again and landed on the runway only by gliding with the remaining speed/altitude without any further complications.

While doing the fuel transfer (by hand) the left jet fuel (JF) tank got approximately 0.5 units of jet fuel more than the right one, so I guess this is why the left part disintegrated first. But honestly that should not happen, at least not with such a litte difference - but the most strange thing is the little front wing *poff*-ing off first, since it has no structural stress at all. There was no wobbling, no "Yaw" pitch that had to be equaled out or anything that would point you to what may happen soon. It just flew perfectly straight and suddenly things got weird - aka fell apart and created an explosive rain of jet parts all across the area.

I can solve the problem by adding fuel pipes so that an emergency transfer is not necessary, but that does not solve this really strange behavior of the physics.

Greetings

Artimus

[Jouni]

My guess is that the problem is caused by part clipping. You can't really expect that the physics simulation works correctly, if you have multiple solid objects occupying the same position. (In fact, there's no such thing as "working correctly" in such situations.)

[kujuman]

Sounds most likely to be the known (but the cause is not know) bug of invisible floating buildings. I think it's more commonly referred to as the "Collided with runway" bug, since after the wings and other parts fall off, the F3 screen says the vessel collided with the runway. The bug appears fairly random near the runway, but like I said, no known root cause.

More info http://forum.kerbalspaceprogram.com/threads/98232-Colliding-into-building-3km-away

Edited March 15, 2015 by kujuman

[Artimus]

@Jouni

This is very unlikely, since the problem got fixed by transfering the fuel back to center and thus restoring "great balance" and wing (1) *poff*-ed off first, where there is no intersecting.

@kujuman

This was my first thought, too, but the plane did not suddenly explode. I was still able to fly it and since my front wing (1) got solely destroyed first, this cannot be any building since it would have crashed through the whole plane. Also this occurred even when instantly changing the course, only with some time difference. Once the first and second sections got disintegrated I was still able to fly around and the parts also fell to the real ground, thus no wrong bounding boxes. It really were single parts that suddenly *poff*-ed into the grey dust clouds. Even as the plane totally fell apart everything continued flying until it hit the ground. The parts simply got detached...

Edited March 15, 2015 by Artimus

[vexx32]

Actually, the colliding with runway and/or other KSC buildings glitch tends to be very odd in that only the front-most wing parts get destroyed (and sometimes it's even very oddly specific about what kinds of wing parts get obliterated).

[Artimus]

But, as told, I did try many things to avoid the situation, even changing the course away from the KSC and the exact same thinng kept happening.

[Master Tao]

Do you still have the quicksave? It would help to let others reproduce it, too.

[BagelRabbit]

Do you still have the quicksave? It would help to let others reproduce it, too.

I think that the F3 Flight Log might be great to have, as well. Does it say that your wing "collided with the Launch Pad" or some other part of the KSC? Or maybe it was a structural failure on some linkages. Or something. Regardless, it would be interesting to grab the quicksave, let this problem happen again, and then find out what happened, step by step.

But yes, the quicksave would help, too.

[Artimus]

I'm sorry, but I had the quicksave overwritten shorty after. Maybe I'll try it again these days and see if I can reproduce it.