How to stop this beast from spinning out?

[Hammer Tech]

I am planning on launching a modular space station into Kerbin orbit, and I have the first module ready to launch, but I can't get it to fly straight. It's just too top-heavy. I tested it with just the orange tank and corresponding booster and it flipped out almost immediately so I figured maybe it had too much drag (I use FAR), so I added the fairings on the scaffolds and a large third stage to boost it up to where the atmosphere thins a bit- but it burns straight as an arrow 'til I ditch the stage, then flips out again. I added the SRB's to try to lower the CoM, to no avail, and I tried adding fins to stabilise but they actually made it worse... Any ideas guys?

Cheers.

Edited December 17, 2013 by Hammer Tech
Answered!

[Taki117]

I'm no expert with FAR, but I think you should try putting the entire structure inside one large fairing. Procedural Fairings is a really good mod for this as it automatically adjusts to fit, just don't forget the struts and decouplers. also, make sure your fins are symmetrical around your tank, and maybe add more (Or larger) ones. As an alternative you could also use lots of reaction wheels on your lower stages such that as you use up those stages and no longer need them you can drop them with the spent stage.

[Hodo]

Your "arms" still create a fair amount of drag with fairings slapped on them like that. I have a set of arms on my station I just launched up to 350km orbit, but I used infernal robotics to make the fold up alongside the body of the station while it was on the rocket inside the fairings. After it reached its target altitude and finished its final orbital burn I deployed them.

I should really get some pictures of that ugly thing.

You are also lacking any form of control on that rocket, so as it starts to slip out of the flight path it will become more and more unstable. Till finally it will be unrecoverable.

[acc]

maybe you can compensate the drag by adding SAS-modules, for more torque.

FAR imnproves the aerodynamic, so it's the best way to orientate your design on real rockets, because they have to handle real aeronymaics too. if your module doesnt fit in any of your transport rockets, you should cut the module in more pieces, to fit in fairings.

[Zander]

You should be ashamed of yourself that rocket is completely unrealistic and in any realistic simulation those arms would rip off long before you get to orbit.

that said The problem is not that your COM is too high., its too low. The center of mass needs to be farther forward on the rocket because the heaviest part wants to be in the front. If your heaviest part is in the bottom it will turn upside down.

[Keldor]

Yeah, with aircraft you want the center of mass to be in front of the center of lift. With rockets, you want the center of mass to be in front of the center of drag (actually, you want this with aircraft too). Try adding winglets at the bottom to increase drag.

A fairing might actually make things worse since it would be so wide that it could actually increase drag.

As an aside, why are you using solid boosters in the second stage??

[Hammer Tech]

...putting the entire structure inside one large fairing...

That's a good plan. I actually have procedural fairings but I hadn't considered using it- however;

...but I used infernal robotics to make the fold up alongside the body of the station...

I also have Infernal Robotics and it didn't even occur to me to have folding arms! Will definitely do that.

maybe you can compensate the drag by adding SAS-modules, for more torque...

Good plan- I have several SAS modules already, but I guess more is better?

You should be ashamed of yourself...

that said The problem is not that your COM is too high., its too low...

Definitely not ashamed; after all, insane rockets is the Kerbal Way! I will raise the CoM and see if that helps. Slightly counter-intuitive to think that it wants to be higher but I'll give it a shot.

...you want the center of mass to be in front of the center of drag... Try adding winglets at the bottom to increase drag...

...As an aside, why are you using solid boosters in the second stage??

The SRB's were an attempt to lower the CoM and rebalance the ship, but it didn't work.

Edited December 17, 2013 by Hammer Tech
Punctuation

[Nibb31]

There isn't much point in installing a realism mod like FAR if you're going to build an unrealistic rocket with modules sticking out off the sides.

Do you have MechJeb? Is your command pod the right way up?

[Hammer Tech]

There isn't much point in installing a realism mod like FAR if you're going to build an unrealistic rocket with modules sticking out off the sides.

Do you have MechJeb? Is your command pod the right way up?

I have FAR because I like the way it handles aerodynamics; and I don't really think it's so ridiculous to want degrees of realism is it? Can I not want more realistic physics but not build 100% realistic rockets? No i don't use MechJeb any more- I began to feel I was using it as a crutch so I got rid, and yeah the pod is fine .

Anyway I motorised the arms, which clip nicely into the body of the rocket , tried raising the CoM, but the only way I could get it significantly higher was to attach modified Xenon tanks that weigh 40t each :s needless to say, this happened:

After fiddling about I managed to get it relatively stable, so now the only challenge is balancing thrust with heat generation. The main thruster overheats and explodes VERY fast, resulting in this situation: