LV-N Falling off at 36,000m

[annallia]

So with the opening of my new space station it was time to stock it with snacks...well parts but Bill eats them (orbital construction mod). Rather than make several trips launching 2 or 3 of the 25 part containers into orbit I decided to make a super snack delivery vehicle. This one capable of lifting 500 tons of snacks into orbit.

Now however I have the issue of my nuke engines falling off for no apparent reason.

First attempt I figured was a fluke, after all one of the snack containers popped off on the launchpad, which shouldn't have happened. I launched got to 36,000 m and saw an explosion. At 42,000m I saw another explosion. It was at this point I realized I was down two of my LV-Ns.

Second attempt I took it back to the VAB added a few more struts to the part containers and just for good measure added another strut to the final stage fuel tanks and to the LV-Ns. No cargo drop on the launchpad, got her up to 36,000m and BOOM engine fell off, and again at 42,000m.

Third attempt went back to VAB, added more struts to the engines and attempted to launch again. 36,000m BOOM... revert.

Fourth attempted I dumped the whole thing and redesigned it. Slightly lower payload (400 tons) and added a fourth LV-N. I figured if I lost one again I could just shut down the engine on the opposing side and fly on two. Get it up to 36,000m and BOOM. Revert.

Add more struts, Fith attempt, 36,000m BOOM.

For the sixth attempt I changed some parts around. I dumped the tanks from nova punch and used some from AEIS, strutted them and the engines to hell and back. 36,000m BOOM

Seventh attempt I rebuilt the entire rocket. Aside from the part containers this one was completely stock. I even ditched the super heavy struts from NovaPunch and went back to the basic strut. In the end I wound up with a 653 part monstrosity. As soon as I passed the 36,000m mark BOOM...

Essentially what I am asking is there some bug/glitch that I am unaware of that is keeping these engines from staying super glued to the tanks? If so how do I fix it?

And before anyone asks on the few flights I let time warp back down to kerbin the first thing in the report was structural failure between LV-N and the tank it was on. They simply dropped.

If nothing else at least going stock had one redeeming feature. In all of the previous designs the engine struck a fuel tank, but never made them go boom. In stock however... Well lets just say there was an explosion big enough to see from Jool...

Edited August 23, 2013 by annallia

[Blue]

Are they overheating and exploding?

[TheDarkStar]

Show a picture of your ship. Do you have any mods?

[annallia]

Are they overheating and exploding?

They are not active yet, they are final stage just being used to deliver the payload to the station.

Show a picture of your ship. Do you have any mods?

AEIS, Nova Punch, Orbital Construction are the ones in play here. Can't do a screenshot right this minute as I have work to do.

[Johnno]

Now however I have the issue of my nuke engines falling off for no apparent reason.

There's always a reason, mainly 'because physics'.

Essentially what I am asking is there some bug/glitch that I am unaware of that is keeping these engines from staying super glued to the tanks? If so how do I fix it?

Not that I'm aware. It's 'because physics'. The LV-N engines are heavy and long, with just a 1.25m attachment point. If you put them on a smallish rocket and give it a bit of a shake they have a tendency to snap off. If you have some on a craft that's parachuting down they have a tendency to snap off. Even if you give a craft in space a proper shaking they can snap off. It really is down to physics, the fact that they're so heavy combined with how long they are.

And before anyone asks on the few flights I let time warp back down to kerbin the first thing in the report was structural failure between LV-N and the tank it was on. They simply dropped.

Structural failures don't "simply happen". The very apparent reason for structural failures is too much mass or too weak connections. Aka physics at work. The fact that your failures kept taking place at 36km and 42km should be an indicator of something specific in the flight taking place there, causing more stress on the craft. Did you just light a new stage or are your tanks getting empty, are you in the middle of your gravity turn or did you just turn off your main stage to coast to AP? There's so many things that could create stress and make those engines snap off.

Go back and redo your launch(es), with the specific mindset "because physics". Keep an eye on your gmeter, keep an eye on your staging, fuel, shaking, tilt, etc etc. Or post a craft file where you've been able to reproduce this (preferrably stock).

My money is on physics, not bugs.

[annallia]

I went back in, loaded up the exact same craft (pre stock configuration) and it worked... sort of. Engines no longer fell off but I did find a new problem though it is due to my design.

Before scrapping it I relaunched it again several times (ok two more...) and every time it worked. I don't know what was going wonky with these launches before but whatever it is has completely disappeared.

As such the civilian oversight of my space program has decided to halt funding to the super heavy lifter project meaning we have to make use of our lifters currently rated for 350 tons.

Or in real world terms I have been futzing with what should have been a simple craft for over 8 hours and I give up... for now.

[capi3101]

It sounds to me like your TWR goes too high for the stability of your stack about the time you get to that 36,000-42,000 meter mark. How many gees are you pulling when the engines pop off? If it's more than two, my advice is to throttle back; used to lose heavy payloads all the damn time and it's because the design was pulling too many gees...

Lower it to about 2/3 and see if that helps any. Watch the gee meter and be prepared to throttle back further if the gee-meter tries to climb out of the green zone; that ain't just for Kerbals, you know.

Edited August 23, 2013 by capi3101

[Blue]

KSP does also simulate MaxQ with respect to acceleration and air resistance, right?

[capi3101]

KSP does also simulate MaxQ with respect to acceleration and air resistance, right?

Yes, the game does calculate dynamic pressure. Scale height for atmospheric pressure for Kerbin is Pk = e^(-Altitude/5000) according to the wiki; you can use the Ideal Gas Law to get atmospheric density for various levels of the atmosphere from that, of course (rho = P / RT).

My understanding is that max-Q typically occurs somewhere in the 10-14 km zone (about the time most folks in KSP are making their gravity turns); that's in RL, though, so that may or may not apply to KSP.

[BES]

I had the same thing happen with modified ION engines (hypercharged 300power) ... had them on a quad mount trying to lift over 30 tons ...the whole quad mount would pop off and the engines would be gone...chose the lower power (100 power) ones and the ship got into orbit without a problem..