Rockets detaching during lift off

[sy2]

Cannot seem to figure this out. When I hit F3 it tells me the decoupler detached from the tank, but during my setup I've strutted everything I can think of to keep the damn things attached.

I have the decoupler attached to the central rocket and reinforced with struts.

Then I put the other tank onto the decoupler - I struck that tank to both the decoupler and the original tank. As I make my circle of rockets I'm strutting each rocket to the one beside it also. So each rocket is strutted to surrounding rockets, strutted to the decoupler it's resting on, and then the decoupler itself is strutted to the rocket that it's attached to.

Any yet during takeoff these rockets are detaching and just taking off. Generally just 1 rocket detaches but I've had a group of 3 detach also. I've kept my speed below 2/3 and it doesn't seem to matter. Also tried above 2/3 and got a bit higher but still decoupled.

I'm sure others have run into this - what's the best solution? For some context here these are all Mainsails and the goal is launching a huge fuel component into low Kerbin orbit so that I can attach it to what-will-be a refueling depot.

Here's an imgur album:

http://imgur.com/a/POPSR

You can see the detached rocket in these pics - first one you can see the flame behind the main ship. Second one you can see the same detached rocket just further up. In this particular scenario I was testing using more than 2/3 power.

Edited September 17, 2013 by sy2

[locustgate]

Do you have the bottom tanks strutted? If so No clue.

What are you Lifting?

Edit: I mean strutted to each other?

[Bengsch85]

Do have the gimbals locked on the outer engines? When lifting my interplanetary drive I have to lock the gimbals on the outer boosters or else the decouplers will break no matter how much I strut them to the inner tanks.

[capi3101]

Hmm...the only thing I can come up with is that there's too much weight for the decoupler to handle. Which decoupler are you using, the TT-38K? I might suggest uprating to Hydraulic Detachment Manifolds for this design.

You say you've got all the tanks strutted to the surrounding tank...how exactly? You might need to make even more connections than what you already have.

This is a perplexing problem. Ordinarily I'd suggest throttling back to make sure the gee meter stays in the green, but it looks like that's not what's happening in your case.

[Moar Boosters]

Build big asparagus rockets using this technique and this won't happen. Unfortunately you will probably have to rebuild the whole launch stage.

It happens because as the fuel is drained from the outerstages, their thrust to weight ratio goes up dramatically. It increases the stress on their decoupler to the point it can't hold and they shoot up skyward. The technique in the video puts plates and I-beams on top of the tanks which cope with the changing forces a lot better.

[sy2]

Do you have the bottom tanks strutted? If so No clue.

What are you Lifting?

Edit: I mean strutted to each other?

Yes the bottom tanks are strutted to the decouplers as well as to the immediately surrounding tanks. They are also strutted to the upper piece that I'm launching. I'm lifting a huge payload - one of 2 attachments to my fuel station. It's the equivalent of 6 full orange fuel tanks.

Do have the gimbals locked on the outer engines? When lifting my interplanetary drive I have to lock the gimbals on the outer boosters or else the decouplers will break no matter how much I strut them to the inner tanks.

I tried locking the gimbals of all of the outermost tanks but that didn't work - however I only tried that once. Prior to this I haven't really messed with gimbals because I'm not that familiar with what they do and how they work.

Hmm...the only thing I can come up with is that there's too much weight for the decoupler to handle. Which decoupler are you using, the TT-38K? I might suggest uprating to Hydraulic Detachment Manifolds for this design.

You say you've got all the tanks strutted to the surrounding tank...how exactly? You might need to make even more connections than what you already have.

This is a perplexing problem. Ordinarily I'd suggest throttling back to make sure the gee meter stays in the green, but it looks like that's not what's happening in your case.

I'll try replacing the decouplers if nothing else works. Personally I believe those tanks are as strutted as they can be. I've only been playing for a few weeks, but I've got the grey tanks strutted to orange, orange strutted to surrounding tanks as well as to the decoupler itself and even the main body of the craft. I doubt G's are a problem because, as you pointed out, I'm still in the green and this beast is HEAVY. Frankly I'm not certain I'd get into orbit even I can prevent the orange tanks from splintering off, but I'm trying to exhaust my efforts before I start removing fuel.

Build big asparagus rockets using this technique and this won't happen. Unfortunately you will probably have to rebuild the whole launch stage.

It happens because as the fuel is drained from the outerstages, their thrust to weight ratio goes up dramatically. It increases the stress on their decoupler to the point it can't hold and they shoot up skyward. The technique in the video puts plates and I-beams on top of the tanks which cope with the changing forces a lot better.

I'll take a look. I'm already set up with asparagus staging on this craft but maybe some plates and i-beams are what I need. Going to watch the vid now and see what I can take away from it.

Thanks so much for all of the replies! I'll update when I have some results, good or bad.

[sy2]

So I checked out that Youtube video (

) and that turned out to be the problem. The sheer created by the downward force of my payload's weight as the outer stages detached caused the side rockets to rip right off.

Here's a quick pic of the monstrosity I have created based on the video. This baby's firing 41 mainsail's and is sold as a rock during my brief trial run. Now I'm arranging it for asparagus pairing and we'll see if it's enough to launch my fuel into low orbit.