How to have more than 1 engine in the later stages of simple (long) rocket?

[phemark]

Hi,

I can create stages of rockets fine, as long as above stages have less or equal engines than bottom stages. However, if I want more engines at further stages, I cant seem to make them connect properly.

Imagine the configuration:

...

tank

1-to-2 slots extender

engine engine

decoupler decoupler

flipped 1-to-2 extender (so 2-to-1)

tank

...

In assembly mode, everything looks fine, but once on launchpad, it becomes obvious that one of the engines are not connecting properly. So then I have to use struts to keep it in place.

Are there better ways of achieving this?

Thanks

P.S. Sorry, I dont have a picture right now, but can upload it in the evening (if my explanation is unclear).

[KvickFlygarn87]

That will not work because of how KSP saves the crafts.

However, you can do like this:

1. place both engines

2. place docking ports on both engines

3. place a single docking port attached to one of the engines' docking port

4. place a flipped bicoupler (what you call a "2-to-1 extender") on the docking port

5. place a docking port on the other side of the bicoupler

6. launch

This works because at launch the second pair of docking ports are perfectly aligned and will instantly dock.

Have fun!

[UmbralRaptor]

KSP (usually) treats rockets as trees, so the 2-to-1 portion is... problematic. Putting docking ports below the decouplers and above the 2-to-1 extender is a possible workaround.

An alternative is not doing a direct connection with multicouplers. Only use decouplers on the central engine (or a structural part that reaches above and between the engines from the lower stage), while the rest of the engines hang free on the sides. (Taking advantage of how tanks can be radially attached)

[Kasuha]

If you want more engines in higher stages, it is usually better to use radially mounted engines instead of couplers.

If you really want to use couplers, you need to remember that the ship structure is always a tree - you can branch things out, but never really join them together again - except using struts. But struts will always disappear between parts you disconnected in the "skeleton" of the ship.

So if you want your plan to work, you need to use some struts in places where you'd otherwise expect connections.

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[phemark]

That will not work because of how KSP saves the crafts.

However, you can do like this:

1. place both engines

2. place docking ports on both engines

3. place a single docking port attached to one of the engines' docking port

4. place a flipped bicoupler (what you call a "2-to-1 extender") on the docking port

5. place a docking port on the other side of the bicoupler

6. launch

This works because at launch the second pair of docking ports are perfectly aligned and will instantly dock.

Have fun!

If you want more engines in higher stages, it is usually better to use radially mounted engines instead of couplers.

If you really want to use couplers, you need to remember that the ship structure is always a tree - you can branch things out, but never really join them together again - except using struts. But struts will always disappear between parts you disconnected in the "skeleton" of the ship.

So if you want your plan to work, you need to use some struts in places where you'd otherwise expect connections.

http://imgur.com/a/nuLCT

Thanks for advice, will try it.

1) Someone in another thread mentioned, that launching while having parts docked, can decrease PC performance a bit, is this true?

2) Has Squad ever mentioned changing connection possibilities (like the one I tried), or is it low in their priorities?

Edited April 17, 2014 by phemark

[Kasuha]

1) Someone in another thread mentioned, that launching while having parts docked, can decrease PC performance a bit, is this true?

Docking ports stuck together in VAB behave like any other parts joined axially.

Docking ports which are left to stick together on launchpad behave as if there is a strut added in between them.

I don't think either has any noticeable impact on game performance but it's true I never tried to launch a ship with tens or hundreds of these.

If you use a lot of them, you may get performance impact just from increased number of parts, though.

2) Has Squad ever mentioned changing connection possibilities (like the one I tried), or is it low in their priorities?

I don't remember them ever mentioning anything about that. Also, the structure of the ship plays role in some parts of game implementation, such as drawing fuel from fuel tanks which sometimes depends on which part is parent and which part is child in the structure. Such relations may be unclear in ships with cycles.

[Grumman]

Another option you may want to consider is launching the top section of the ship upside-down. In other words, on the launchpad you'd have the main engines pointing down, and the space engines pointing up, with the usual decoupling mechanisms in between.

[Mystique]

When I need to launch something really heavy (like ~150 tons biomass refueling craft) that has several parallel engines, I tend to continue "column" from each engine. So it looks like this:

Another option you may want to consider is launching the top section of the ship upside-down. In other words, on the launchpad you'd have the main engines pointing down, and the space engines pointing up, with the usual decoupling mechanisms in between.

Just need to make sure that "main" part is in lower stage, otherwise controls will be flipped over.

[cantab]

Thanks for the technique btw Kashua. I've been strutting past my multi-couplers on the outside, but that method is more elegant.

[metl]

There is an easy solution. Under one engine, place a cube strut or similar under it, then the decouplers on top of the reversed bi-coupler. Next, place a strut link fron teh other engine to the 2nd coupler that is not attached to the cube strut. Lift the assembly at the coupler connected to the cube strut. Remove the cube and replace the assembly directly to the engine. The strut link that was previously attached between the engine and decoupler will reattach, but now they will be flush mounted and decouple appropriately and look exactly as you are wanting it to look.

[metl]

Edit: Disregard, I completely missed where someone already demonstrated how to do it. Sorry

Edited April 17, 2014 by metl

[Tortoise]

You can put some of those radial mount engines on (and if you need more power, some of those tiny ones).

Or do what Kasuha said.

An alternative would be to build your vessel in space, and have the pieces in the lower center of the rocket.

[godefroi]

Also, there's at least one addon being developed that will give you this: http://forum.kerbalspaceprogram.com/threads/66694-WIP-FloatNode-Procedural-Engine-Housing-(23-2-2014-New-download-v0-4)

[rkman]

So if you want your plan to work, you need to use some struts in places where you'd otherwise expect connections.

http://imgur.com/a/nuLCT

That is the neatest stock workaround i have seen yet. But if we ever want those engine clusters to fit inside a fairing that's flush with the rocket, Squad will have to scale down the size of the engines.