How to have engine clusters in upper stages

[thox]

The KSP update 0.21 brought us multi-couplers in all varieties, giving us the ability to create engine clusters, which is the good part (we basically could do that before with cubic struts but with the new couplers it looks way better ). The bad part is that we still have the limitation that one new element in the editor can only be connected to one existing element and not multiple ones, which means that a coupler placed below a cluster (kind of a "re-coupler") to have it connected to the stage below will only connect to one of the engines, making the overall connection totally unstable. However, there is a solution that was brought up by allmhuran in this post, which I thought deserves to be made into a tutorial (with nice colorful pictures, yay ). So here we go:

First things first, we have an upper stage with an engine cluster on it, but... well , placing a tri-coupler below it shows us that we can't just connect it that way with the lower stages since only one connection is made

But there is a solution and it is called docking ports! Besides strut connectors and fuel lines, those are the only parts that can connect a ship to itself, and since they are in-line elements, they are perfect for us.

We will want the stage to decouple later, so we first place decouplers below the engines and then add docking ports (facing downwards!) for our connection

Then we attach one (!) docking port to one of those above and add our lower tri-coupler to that

Having that done, the only thing left to do is add docking ports to the remaining free attachment nodes of the coupler

Those are now (in the editor) in fact not connected to the ports above, but as they are in the perfect position to dock they will instantly do so when physics kick in on the launch pad.

So there you go with a stable connection for an upper stage engine cluster. If that is still not stable enough for you, cubic struts and connectors will always help

This solution using docking ports is the best we can have at the moment (more struts could also do the job, but that would look terrible in my opinion).

The engine fairings even stay on the jettisoned stage, which is perfect for everyone who cares about the looks of his spacecraft at all times (including me )

I hope I could help you, may your ships never crash (unless you want them to, 'cause explosions are just awesome )

[astropapi1]

Thanks.

[Specialist290]

Extremely clever, and much more practical than the old way of doing things. This one's definitely going on the Drawing Board.

[saik0]

This is my method. At the top of the truss stack is the small half meter decouper. It's fairly old, if I did it again I'd go with the steel girder to reduce part count. Most of the time I just mount the engines radially instead, but this is worth exploring again with the new cylindrical procedural fairings.

[rottielover]

Wow, I never figured out that you only get one solid connection. I've been using these parts but leaving out the docking ports. So essentially to borrow your example, I would do tri-coupler , engines, then attach the decouplers, the. Mount an upside down tri-coupler. Since it snapped into place with the three green connection balls I figured it was "good".

This is excellent stuff to know and probably the source of some of my frustrations with unstable rocket designs.

[allmhuran]

Just make sure that when you attach the additional "upwards facing" docking ports, that you are in fact attaching them to the multicoupler part below, and *not* to the downwards facing docking port above. They will want to connect to both, and since they are at exactly the right height to connect to either side, this can be tricky. It comes down to using the right camera angle and making sure that when attaching the extra ports the highlighted part (showing what is being attached to) is in fact the multi-coupler.

Another way to get around this is to stick something below the downwards facing docking port first... like a structural fuselage piece. Then add your upwards facing docking port to this fuselage piece, multi-coupler piece to that, and additional ports to the multi coupler. Now detach the lower section from the structural fuselage, chuck the fuselage in the bin, and lift your lower section into place.

[SRV Ron]

If you are not opposed to mods, check out Novapunch parts for 0.202. They have several multiengine parts that will behave as a single engine when you place one standard diameter decoupler under them. That will eliminate the several parts needed to use multi engine staging using stock parts. BTY, the multiengine part counts as a single part. You will likely have to stitch parts together with braces, like any of the larger designs require, for stability.

Edited August 5, 2013 by SRV Ron

[codepoet]

I rolled my own engine cluster enclosure part to solve this problem. See the pictures below. I was going to do some work to make it have "procedural attachements" so you specify how many engines of what size and it creates the attachemnt node automatically, and also automatically adjusted the sie of the fairing to fit, however real life got in the way. I also thought I could use the Procedural Fairings mod to do the enclosures for me. Anyhow any of this stuff is of interest get in touch and I will see if I can add your reqirements in next time I work on it. If you would like to have a go with the enclosure part as it is let me know and I will send you a copy.

First attach the enclosure baseplate to the bottom of your stack:

Then add the cluster of engines:

Finally add soething on the bottom of the stack (probably a decoupler) and the engine enclosure fairing will be added automatically.

Here it is in flight:

[mellojoe]

When you use the docking ports, does it mess up the staging? Do you have to use an action group to decouple the three ports at the same time? Or do the decouplers work in the normal stages?

[allmappedout]

Lovely rocket design, very nice!

[codepoet]

I have released my solution to this problem here

[KatzOhki]

My problem was that on decoupling, the engine fairings of the nuclear engines would fly out and knock engines off.

[mellojoe]

My problem was that on decoupling, the engine fairings of the nuclear engines would fly out and knock engines off.

I get this same problem, too. If you flip the decouplers over (have the little red arrow point TOWARD the engine instead of AWAY from the engine) that can help.

[shand]

the procedural fairings mod can do a neat solution to this problem!

theres a custom fairing part that you put below the engines and you define the final width and height of the fairing. SORTED

[thox]

When you use the docking ports, does it mess up the staging? Do you have to use an action group to decouple the three ports at the same time? Or do the decouplers work in the normal stages?

No it doesn't (as you might have figured out by now, idk). Since you are using decouplers to jettison the lower stage and not the docking ports (which are only part of the lower stage) there are absolutely no problems with staging getting messed up.

[thox]

My problem was that on decoupling, the engine fairings of the nuclear engines would fly out and knock engines off.

The problem maybe is that one of the two fairing parts of every nuclear engine is pointing directly inwards, smashing directly against the other engines when ejected. Instead try pointing the cut between the fairings outwards (exactly away from the center of the rocket is best) like this:

The cut can be seen as a fine line on the fairing side (I put green dots on its ends so you can easily find it).

I tried this positioning and it worked for me, so it will most probably work for you as well

Edited September 13, 2013 by thox

[Kerbol Prime]

Never thought of this. I usually used radial attachment point things to make engine clusters, then stuck some girders/struts down the middle and put some structural panels as "fairings". This is way simpler.

[British_Rover]

I don't even think you need the second set of upward facing docking ports. I have attached parts a few times with just a single docking port directly connecting to a node and it still holds fine. Just make sure to disable fuel crossfeed if they are no decouplers around in the way to stop fuel flow. If you do that you need to either create an action group or manually stage the decouple node on the docking port.

[thox]

I don't even think you need the second set of upward facing docking ports. I have attached parts a few times with just a single docking port directly connecting to a node and it still holds fine. Just make sure to disable fuel crossfeed if they are no decouplers around in the way to stop fuel flow. If you do that you need to either create an action group or manually stage the decouple node on the docking port.

Yep, usually it is possible to attach a docking port to any construction node, but it will only be able to undock from there, while we need the docking abilities that only 2 docking ports facing each other can give us. That's because the normal construction logic will let us attach a part via one node only, but for attaching a lower stage to an engine cluster we need more than that (just read the complete tutorial for a bit more detail on that ).

Edited September 17, 2013 by thox

[jake9039]

I'll do this, but my worry that the docking port may attach to the docking port in editor,instead of the tricoupler.

[Tex_NL]

Are you aware you're replying to a thread that has been dead since September 2013. 15 months!

[phunk]

I'll do this, but my worry that the docking port may attach to the docking port in editor,instead of the tricoupler.

After you attach the coupler to the first docking port, detach the docking port and decoupler, and rotate it so the other two spots are sticking out from the side of the rocket, add the last two ports, then rotate it back into place.

ETA: Needed an excuse to figure out imgur albums, so here's one.

Javascript is disabled. View full album

Edited December 10, 2014 by phunk