Going from big to doube to single engine stage

[KerbMav]

How would I build a rocket with one big engine and a big tank as the first/lowest stage, going to a double medium engine and then a single as the upper stage?

Building the double engine via bi-coupler below the single engine is obvious.

But how would I connect the single big engine (or any single part for that matter) below two side-by-side engines?

I tried to connect a flipped over bi-coupler numerous times - sometimes the second engine has no "connector-ball" (new to the game, what is the common word here?) or the flipped bi-coupler has only one.

It somehow lets me built what I want but the two decouplers/seperators below the twin engines more oft then not show different results when moused over: Sometimes they both just light up by themselves when moused over, but (often after a while and further building) one (lets say the left) - and just the left - will light up together with the whole lower part of the rocket, the other one (lets say the right) only by itself.

The whole thing - propably only for sake of heavy strutting - manages to lift off and get into space (I wont go into the difficulties of attaining an orbit with this monster here ... ) and everything works out fine: stages decouple, tanks and boosters drop clear, engines fire up, nothing gets damaged ... until it is time to seperate the stage below the double engines.

After some tweaking with sepratrons I managed to push the lower stage away without their exhaust damaging the next stage. To make things more easy I set it up to first seperate the lower stage from my flipped bi-coupler and then the bi-coupler itself. (In separate stages, I was already trying to find the reason for my problem and wanted to rule out the big lower stage.)

But thats when S h's the F: For no recognizable reason the bi-coupler damages the right separator which then does not unpack (the casing which envelopes engines built above separators) to free the engine above - I somehow suspect the right separator is not even able to do its thing although it is in the same stage as the left.

The left engine usually seems fine at first - firing the engines up in the next step either results in a big boom or both engines coming loose - the right one loosing his casing at last ... although it looks like the model only shows two halves of a cylinder casing flying into space by then.

What am I doing wrong?

Is the bi-coupler not supposed to be used upside-down?

What alternative is there to built twin-engines above single ones?

On a similar note/thinking about alternatives:

How to put more than one big engine below one big fuel tank? (Or how to build an engine group anyway?)

And what would be the best way to connect three big fuel tanks (each with its own engine) to form a single stage?

[Johnno]

I just had a quick test of this issue and realized it must be because of the single parent way things are handled when attaching. Like when you try to attach a tank to two radial decouplers it'll only attach to one, it's because it can codewise only be attached to one thing. So the bi-coupler is in reality only connected to one of the tanks/engines.

Which leads to engines clusters, there's various ways to do it, I've used the cubic octagonal strut, set to symmetry mode (as many engines as you wanna have) and free (not click to angle), put them on the underside of your tank/ship, then rotate them up into the tank. sometimes the top of the framework/strut is visible, sometimes not, but the connection points will show up when you go to attach engines.

To connect the cluster to a stage below you'll need an engine or strut/item in the middle of the tank to connect your decoupler to.

[Joe_Bender]

May I suggest you look up 'asparagus' staging?

It would be more effective if you put boosters on the main tank that you jettison as they empty instead of trying to duel-prop your second stage.

To do a tri-tank, just use the tricoupler and strut the heck of the tanks down at the bottom......unless you are launching a really heavy payload, three large orange tanks is just a little bit of overkill and youre just launching fuel.

[KerbMav]

unless you are launching a really heavy payload, three large orange tanks is just a little bit of overkill and youre just launching fuel.

I am still new - but already in love - to this game. So I am trying out ... well, everything!

And lifting heavy payloads is an example for which I am constructing this rocket now - and because I want to try out, what works, what can work, what should not be done - and ... because I can!! *thunder*flash*

[Awaras]

You can do something along these lines:

It looks ugly unless you use custom fairings, but it gets the job done...

See this video for instructions on how to place multiple engines onto a large tank:

Edited June 12, 2013 by Awaras

[KerbMav]

It looks ugly unless you use custom fairings, but it gets the job done...

Yes, it is, but thank you, it worked!

Although I might still be trying to lift to much at once - I cant get that thing into an orbit ...

[Spyritdragon]

I've played the demo, and i just felt i HAD to have some way of recovering two kerbals in one ship, so i eventually managed to flip over the one-to-three divider from the demo and plug three command pods on there (demo only supplies a small single-man command pod). Both had something on top (parachutes) and i had a big launch system underneath. It took some time to make KSP realise what i wanted and quite a few tries to get it to actually put all three pods on correctly, but i just kept trying and once all three were attached they worked fine :-)

[KerbMav]

Did you land them with the 1-3-divider or did you decouple the pods?

I even think that this might work in your case. It is the engines that seem to give me trouble respectively the separators below them.

Regarding my failed attempts to reach orbit - if one does not pay attention to every number on the facts sheet of every engine ... lifting heavy cargo into orbit with atomic engines even in the third stage ... nope, not gonna happen ...