Rocket losing control

[UnthinkableThinker]

Hi guys, I'm new to KSP and I really want to know why my rocket is going out of control at around 10km, just when passing the first atmosphere layer, during gravity turn. The rocket is carrying my crane which is pretty big since I'm trying to land it on the Mun so I can build a Station there. The entire ship weights around 100t.

[Genius Evil]

It's most likely asymmetrical drag from those struts. Could you explain how it goes out of control? Does it roll uncontrollably, do the Rockomaxes start pointing toward space, or does something else happen?

[AmpsterMan]

This... This has GOT to be a joke right?

I am going to hazard a guess, probably a misplaced strut.

[Specialist290]

Another thing that strikes me is that you don't seem to have any sort of reaction wheels on what must undoubtedly be a very massive rocket. That might help with some of the control issues. For that matter: Do you have SAS enabled during your ascent?

For that matter, taking a closer look at what I'm assuming is the final payload, your rocket might be slightly off-balance, which definitely can't be good. Do you think you could take another set of screenshots with the center of mass and center of thrust icons turned on, as well as one of the payload by itself, without the launcher? Both of those might help with making more specific diagnoses.

[UnthinkableThinker]

It's most likely asymmetrical drag from those struts. Could you explain how it goes out of control? Does it roll uncontrollably, do the Rockomaxes start pointing toward space, or does something else happen?

Once I start the gravity turn it starts kind of like falling back to Kerbin, the nose points down and I can't get it back up, so the whole thing breaks apart.

[UnthinkableThinker]

Another thing that strikes me is that you don't seem to have any sort of reaction wheels on what must undoubtedly be a very massive rocket. That might help with some of the control issues. For that matter: Do you have SAS enabled during your ascent?

For that matter, taking a closer look at what I'm assuming is the final payload, your rocket might be slightly off-balance, which definitely can't be good. Do you think you could take another set of screenshots with the center of mass and center of thrust icons turned on, as well as one of the payload by itself, without the launcher? Both of those might help with making more specific diagnoses.

Yes, I did try to fly it with SAS on, but the problem seems to persist.

Here is the screenshot with the center of mass, center of lift and center of thrust:

[Specialist290]

Hmm... Taking a closer look at your screenshots, it doesn't seem to be a problem with your center of mass and center of thrust being misaligned. However, judging from both what I'm seeing and what you're describing, I think the big problem is that your CoM is off-center on the craft itself, and thus whenever you tilt it towards horizontal, it naturally tends to want to lean further in the direction of the imbalance.

Tell me one thing about how it flops over: Does it want to turn over so that the cabin on the rover itself is always on the side closest to the ground?

[UnthinkableThinker]

Not the cabin on the rover, but the entire rocket flips over upside down.

[Specialist290]

Well, yes, but does it stay completely vertical when it flips, or does it tend to want to settle so that its nose is offset in one direction or another?

[UnthinkableThinker]

It starts a corkscrew movement, I've noticed it is happening right after I decouple the most outer tanks(The ones with Mainsail engine).

[Person012345]

Dare I ask for the craft file (forget crying, it will no doubt make my computer bleed from it's vital parts)?

[UnthinkableThinker]

Well certainly I would love to share my build with the community, I just want to make it work first

[Person012345]

I was asking so I could try to replicate the problem. I might be able to understand what is happening better if I could see it.

[UnthinkableThinker]

Ah, right, I just don't know how I share it, is it through Space Port?

I could try to make a video of the launch though, but it's really laggy and idk how it will work with Fraps on.

Edited October 14, 2013 by UnthinkableThinker

[Person012345]

Ah, right, I just don't know how I share it, is it through Space Port?

Upload to any file hosting site (I guess the spaceport is one?) then link it.

[UnthinkableThinker]

Here's the link, http://kerbalspaceprogram.com/unthinkables-crane-probe-with-issues/

[Person012345]

Oh, it's modded.

You'll either have to remove the mod parts, give it a different save name and re upload (although idk if thiss will change the balance) or maybe someone else with the right mods can help.

[UnthinkableThinker]

Oh, right, forgot to say, I have KAS and Mechjeb on it.

But it is most likely that it won't change the balance, since it's only a couple of small parts.

Edited October 15, 2013 by UnthinkableThinker

[Sirine]

I have give up on trying to remove the KAS, and Mechjeb on your .craft file. Its damn too many KAS module in it.

[UnthinkableThinker]

Mechjeb is only 1 part, the remote thing, and KAS there is like 5 winches, 2 of those container holders and 2 containers all on the probe itself.

[Starwhip]

I think your problem may be the size of the thing. All those fuel tank need to be drained independently in the coding, if the game is draining them in real time, the ship would easily become unbalanced.

[Shrike42]

I think starwhip's on to something; asymmetrical fuel drain would shift your Center of Mass and cause torque that would result in nose over. Also, if it's corkscrewing in the atmosphere, maybe a few control surfaces would help.... but first, definitely check into the possibility that your lifter isn't draining fuel from all the tanks quite right. Save it as a new ship, then take the save and remove as much of the payload as possible, see if it flies straight, or if you keep seeing this bad behavior.

[UnthinkableThinker]

I will try that, but like I said, the ship goes out of control right when the most outer tanks get depleted and are ejected out.

[MisterFister]

I have the same mods installed already anyway. I'm in class right now, but will download this later and try to fly it and let you know.

[Motokid600]

Well for starters make sure the brakes are activated. The wheels spinning won't help. But when you perform your gravity turn at 10km how far over are you pitching? If its too much too soon yea it'll fall right back down. With a craft that large.. delay your gravity turn until about 250m/s then SLOWLY start pitching over. You say the craft tumbles over after the first stage. Is this before ( ideal ) during ( not ideal lol ) or after the pitch?

Other then that.. idk. Honestly I'm sorry to say, but that rocket looks like a nightmare. The problem could be a little bit of what everyone said. Something like that is very hard to diagnose. You may be better off starting back at the drawling board. Look at your payload by itself ( the crane ) is the mass on center? Switch off gravity in the debug menu ( alt - f12 ) and see if there's any phantom torque. Make sure the payload is tested so you can rule that out.

Then build and test the rocket a section at a time. Sub orbital tests to orbital tests and so on. Also it might not hurt to take a look in the space craft exchange. Look at some heavy lift, asparagus launchers. Just to get some ideas.

Something I just noticed... Is that the space plane hangar you built that in? Correct me if I'm wrong ( been awhile since I've been in the SPH ) but your only allowed up to 2x symmetry. NOT good for rocket builds.

Edited October 15, 2013 by Motokid600