Load Bearing Stage Separators?

[Nexus-7]

I'm either missing something crucial in rocket design or I'm in need of some different way to attach stages together.

My problem is that between stages, basically my rocket engines are all that is holding upper and lower stages together, and this is putting huge stresses on the rocket engine and consequently it keeps breaking off.

Simplified example build: parachute-capsule-decoupler-fuel tank-ENGINE-DECOUPLER-bigger fuel tank-bigger engine

In the above example I can't find any way to get around having the DECOUPLER (in caps above) which separates stages be attached to anything other than the ENGINE (in caps above). In bigger rocket builds this means the bigger lower stages are putting huge stresses on that engine. An engine shouldn't be a load bearing part like that, I would think a monocoque or other structure would be a better way to join stages. Does this exist? Like a hollow decoupler that the engine will fit INSIDE, and the decoupler itself bears the load, shared with the skin/fuel tank of the vehicle? (This is really hard to describe in words, lol)

For example, ideally, the above build would be this:

parachute-capsule-decoupler-fuel tank-HOLLOW DECOUPLER-larger fuel tank-larger engine

(In this example the engine is still attached to the fuel tank, but it's inside the HOLLOW DECOUPLER and is not attached to anything BENEATH it.)

Thanks for any help, I hope this was an understandable question.

[rdfox]

Not that I know of. However, you can use the strut connectors in the Structure section of the VAB as braces, both to rigidize the booster and to transfer loads at least partially around the engines.

[Rocket Surgeon]

That's a good idea. A ring of vertical struts between the stages.. Could look kind of cool, too, especially with the vanilla parts.

[rdfox]

It's not easy to see, but I used that technique on my VK Nova Mark Two (see http://kerbalspaceprogram.com/forum/index.php?topic=1910.0 for the screenshots!), connecting each stage to the decoupler above it and the decoupler below it. Most of them, they're so short that they look more like clamps than struts, which is also cool. The result was a stable and solid ship, even with seven M-50s in the first stage running at full throttle. (I also strapped the 3m-to-7x1m adapter and the engines themselves to the bottom of the first stage, so they wouldn't shake themselves off.)

[SteevyT]

That's a good idea. A ring of vertical struts between the stages.. Could look kind of cool, too, especially with the vanilla parts.

Don't forget the added head dissipation bonus.

[HarvesteR]

I used this technique myself on a few large stacks here. The lower stage engines were powerful enough to plow though the upper stages by themselves, with very entertaining but nonetheless catastrophic results.

So I used struts with 8-sided symmetry to brace the large fuel tanks from top to bottom, adding a lot of structural strength.

Cheers

[rdfox]

I usually use struts with tri-symmetry, but that's because I use the add-on shroud decouplers that're stronger than the stock one; the tri-symmetrical struts provide stiffening with the minimum in weight penalty, plus I can add some rotated 60 degrees for the lower set to make them look more 'balanced.'

[Moach]

a general ground rule here would be, for every 'G' of accel you intend to put your parts through - add one level of symmetry for your reinforcement struts... that should (hopefully) keep your vehicle in one piece the same number of pieces you expect it to be

[foamyesque]

That rule breaks down quite dramatically with heavy rockets, where a hundred boosters produces an overall acceleration of 2g, but a local one of around 7g.