Engine thrust.

[7499275]

Hey guys! I got this command ship that is driven by 4 nuclear engines... As you can see they are out on beams but when I try to launch its spins... Ive always had this problem and usually just went and redid the entire engine design but for this one... I kinda need it to be set up like this so anyone give me a hand?

Thanks

[blizzy78]

It should work if you add some active control surfaces (wings) and perhaps a few struts here and there to minimize wobble. Also, are you sure you want to use nuclear engines to launch? They are most effective when there's no atmosphere.

[Death Engineering]

Sometimes those medium structural beams don't snap perfectly to the longer beams. Did you create one pod and clone it to make 4, or build them all separately?

[capi3101]

Are you launching that straight from Kerbin? Be advised that LV-Ns are lousy launch stage engines - they don't get their awesome Isp until you hit space.

Rockets without some kind of central engine have a tendency to spin due to leverage. Unless you absolutely absolutely have to have it exactly that way, I'd advise you to put an engine on the bottom of that 32 tank. Preferably something with good steering authority like an LV-T45 or maybe even a Skipper. Winglets too.

[7499275]

Yes I want to use these because I edited the CFG and their ISP is over 20k and their power is 300 each now lol. Call it a cheat if you want but hey it works

Anyway I thought of control surfaces for the atmosphere flight but what about when in space? I would have to have mechjeb to "Kill rot" The entire time to keep it from spinning.

And I just made one and added symetry x4 and put them on the side.

[Skorpychan]

Needs moar struts, and better alignment of the engine struts. They look SLIGHTLY off-center, so that's probably your spin right there. Otherwise, add a regular SAS module for increased torque.

Could also be due to uneven drag, so move those batteries around a bit. Lower down is better for stability, so try that?

And why do you have two sets of RCS thrusters?

[paxy97]

The problem lies in the fuel ducts (the yellow pipes). They are off center and produce torque. Just Place them parallel to the struts, like this . Not to the side of the rocket

[7499275]

Thank you guys for all the suggestions! I added a SAS module under the shielded docking port above the command pod and added 2 sets of struts per engine arm.

There is NO rotation with SAS on when I turn it off there is a very small amount but I think mechjeb with RCS can handle as it is very very slow. Gravity turn may prove to be slighty difficult due to this but will mange, thanks again guys!

[MalfunctionM1Ke]

Your Fuellinse are probably the cause of the Spin.

In fact they are also counted as struts and give your thrust a tiny angle.

Try to put more struts on the opposite side or in general.

[Rosco P. Coltrane]

Just a note: fuel lines are not needed. The beams are cross feed capable.

Also, remember that engines can't compensate for spin. They can move your nose if the are vectoring, but the ASAS can't control them to control rotation over the longitudinal axis (Q/E).

[Johnno]

Just a note: fuel lines are not needed. The beams are cross feed capable.

They're crossfeed capable but radially attached engines don't get fuel from the centerstack (only their own stack). Without fuel lines the engines wouldn't run at all, and if you had them mounted on tanks (yet still radially out with trusses/beams) they'd drain their own tanks and then fail to take any fuel from the centerstack.

[Skorpychan]

What? I've found they work fine when mounted straight onto tanks.

[7499275]

One of the reasons I needed the engines off to the side in case any one is wondering... After getting the spin corrected I threw on a SR docking port on the bottom of the fuel tank and made this capable of doing Mun deliveries. Its a lander basically but also can serve as a main engine drive for large vessels anyway thanks again to all of you!

[Rosco P. Coltrane]

They're crossfeed capable but radially attached engines don't get fuel from the centerstack (only their own stack). Without fuel lines the engines wouldn't run at all, and if you had them mounted on tanks (yet still radially out with trusses/beams) they'd drain their own tanks and then fail to take any fuel from the centerstack.

Hmm, interesting, I didn't know that.

But in his particular design it will work because his using only a central tank. I win!

[stupid_chris]

Hmm, interesting, I didn't know that.

But in his particular design it will work because his using only a central tank. I win!

No it does not work. He's using a central stack, but the engines are radially mounted to the stack through other parts. Try it yourself, you won't get it to work without fuel lines.

Besides, people mentioned earlier to add SAS modules. Those don't add torque, they just can be used to stop your ship's rotation when activated, so it's useless to add them to that ship.

[Johnno]

Hmm, interesting, I didn't know that.

But in his particular design it will work because his using only a central tank. I win!

I went to test this to make sure and you're actually right, I was under the impression that it was both for engines and tanks but it actually only applies to tanks.

Engines will draw fuel as long as they're somehow attached to a tank, but a tank attached radially to another tank is not in theory connected.

Made a quick demonstration screenshot. The tank with a fuel line emptied of course, but none of the other tanks did as they are in essence attached radially, no matter if they're above or below, only the center stack node counts.

Learn something new everyday.

[stupid_chris]

I went to test this to make sure and you're actually right, I was under the impression that it was both for engines and tanks but it actually only applies to tanks.

Engines will draw fuel as long as they're somehow attached to a tank, but a tank attached radially to another tank is not in theory connected.

Made a quick demonstration screenshot. The tank with a fuel line emptied of course, but none of the other tanks did as they are in essence attached radially, no matter if they're above or below, only the center stack node counts.

Learn something new everyday.

-snip-

Actually, there's a way to make radial fuel tanks work if you use the radial connection port. It's weird enough but it works. I use it to make most of my skycrane designs work.

[NoMrBond]

They'll automatically crossfeed monopropellant, electric charge and, for some reason, IntakeAir, just not fuel/oxidiser

You might get a more stable ship by rotating your radial engines outward one notch, probably via the structural members attached to your central stack (using shift-ASDWQE to rotate by small increments)

[Johnno]

Actually, there's a way to make radial fuel tanks work if you use the radial connection port. It's weird enough but it works. I use it to make most of my skycrane designs work.

You'll have to explain how, I poked at some just now and haven't gotten it to work. I wanna learn more today!

[stupid_chris]

Alright, I did a basic construction:

As you can see, all the tanks on the side and the one lonely engine are all attached through radial connection ports. Those allow the fuel to flow outwards. Basically, the engines can go pick up to whatever is behind the radial connection. They act a bit like fuel lines, expanding the stack radially.

[Johnno]

Alright, I did a basic construction:

Thanks for that. I've done some more testing and it's making me dizzy trying to remember all these things, it'll take some getting used to.

I confirmed your way of doing things, but it's the opposite way of what I was trying. If you mount those tanks radially out from the centerstack and put the engine onto the centerstack, it won't get fuel from the radial tanks. While if you put the engine out onto the last radial tank it'll first take fuel from the centerstack, then the tanks outward.

Quite an interesting find chris, I'll have to try and incorporate it into some of my designs in the future.

[stupid_chris]

I confirmed your way of doing things, but it's the opposite way of what I was trying. If you mount those tanks radially out from the centerstack and put the engine onto the centerstack, it won't get fuel from the radial tanks. While if you put the engine out onto the last radial tank it'll first take fuel from the centerstack, then the tanks outward.

Yeah like I said they act a bit like a fuel line going outwards, so the fuel won't naturally go back to the center, although you could probably manually transfer it.