Rocket Spinning

[Rogan]

I been getting great success at launching simple rockets but most, if not all, of my larger designs goes into a uncontrollable spin upon entering a gravity turn. RCS and SAS does nothing to help so any advice would be much appreciated. Thanks!

I'm also really new to this game so please elaborate on any jargons used (such as controlled surface....what is a controlled surface?!?).

[Vanamonde]

Pictures of your ship would help others give you advice. Can you upload screenshots to a service like Imgur and use their links in your posts? Meanwhile, the ship could be spinning from a shift in weight distribution as you burn fuel, or not enough engines with the thrust vectoring capability (whether they have this or not is indicated on the VAB parts list). And if it's rolling around the long axis, that is a nuisance which makes steering harder, but doesn't actually prevent you from getting where you need to go.

[Payload]

You have what is called an over stable rocket. Your center of mass is moving down too close to your center of LIFT. You need to redesign so that you have drag aft and the center of gravity forward. Think of how a throwing dart is made. The tip has little drag and high weight, the fins have low weight and high drag. These two things in conjunction are what make it fly tip first.

It's a little counter intuitive at first, but it essentially means that your payload to orbit isn't heavy enough for the size rocket you are building. It's a common occurrence in this game. People try to throw more fuel at the problem when what is needed is the proper ascent profile.

No amount of wings or RCS will solve this problem. RCS is for maneuvering in orbit. Wings only insure that you can fly the profile you intend to. They will not save an over stable rocket.

Edited May 3, 2013 by Payload

[GROOV3ST3R]

I thought they were the same thing but some research proved me wrong. Still, isn't KSP using a greatly simplified model? There is only the Center of Mass button as far as I can work out, why would there be a separate center of gravity if we can't check where it is?

[MBobrik]

center of mass = center of gravity

[Payload]

Ah indeed. That's what you get when you post on your way out the door and before you have had your coffee. But Of course I meant to say center of lift certainly.

Edited May 3, 2013 by Payload

[capi3101]

Try throttling back a bit; I have a DSTO rocket that has an initial stage TWR of greater than 2.2 and it spins like mad if I go full burn. Plus it wastes fuel; ideally you want your launches to follow the terminal velocity curve of Kerbin's atmosphere. It also increases the risk of catastrophic failure by telescoping stack.

What I usually have to do is burn at two-thirds, pitch over to 45 degrees on heading 090 around 10,000m, wait for Stage 1 to flame out, throttle up and seperate; the second stage's TWR is usually around 1.5 by that point and she's stable the rest of the way up.

[Jason Patterson]

There is a center of lift button. Most rockets don't have any lift at all though.

A control surface is one of the aerodynamics parts that can move, things like the AV-8 winglet (getting the name from memory, so it's probably off a bit) or the flaps that fit on the backs of wings. They can help you maintain control over a vehicle when its in the atmosphere, but when it reaches vacuum they become dead weight.

What kind of spin are we talking about? Do you mean that you begin pitching downward (toward 90 degrees/east with no pitch, ultimately) and go further than you want to, or is it a roll or yaw?

You can probably add control surfaces or an additional command module or use vectoring engines (the engines say that they have vectoring in the part description) and maintain control.

It could also be a fundamental problem with your design that only happens to show up at about teh same time you're making your gravity turn - a missing fuel line, need extra struts, whatever.

[Sovek]

Probably means it enters a roll, I have this issue to on alot of my rockets, and this tends to happen on multi-engine rockets...

[magnemoe]

Probably means it enters a roll, I have this issue to on alot of my rockets, and this tends to happen on multi-engine rockets...

I found that rockets who are to wide tend to roll. That is wider than the 1+6 asparagus. Using KW rocketry huge parts tend to give this effect unless the center stage is larger than the boosters.

For roll problems during the start of gravity turn, especially then using mechjeb, activating rcs for an short time help, some deactivate gimballing on boosters as it might cause overcompensation.

For roll right after takeoff, this is usually because of errors in fuel piping or damage to parts. One easy way to check fuel piping is to just run the engines and not release docking clamps. Now you can inspect the fuel use over time.l

Another problem is wobbly rockets, however this often result in spin or the rocket fall apart.

[Sovek]

in other words, this is a problem with the areodynamics model... lovely.

[Payload]

It's a problem in the real world also my friend. It's a problem of your ship being too heavy on the bottom. Probably. We really need to take a look at it so we can to make a better judgement call. If it's tumbling end over when you go for the G-turn, that is almost certainly the answer. You may be able to wait a little bit later to start the turn and get a more stable flight profile. Depends on how bad it is.

I am all for a center of dynamic pressure indicator and a center of mass indicator in flight. Man that would make building the heavy lifters a whole bunch easier.

[Psycho0124]

Radial stacks twisting maybe? It'd be great to see the actual rocket you're having trouble with but from what I've experienced, you're probably getting a little tilting/twisting in your outboard engines/tanks. They like to lean to one side a little while under thrust if they're not supported well (and a single radial decoupler/hardpoint/pylon is almost never enough). If they lean at different angles, it will set up lots of ugly momentary forces and send you tumbling. If you get lucky, they'll all lean one direction and you'll only get an axial roll.

Add a strut at the top and bottom between your radial stacks and maybe one to the center stack at the top of each to stiffen the whole structure up.

Edited May 3, 2013 by Psycho0124

[Sovek]

It's a problem in the real world also my friend. It's a problem of your ship being too heavy on the bottom. Probably. We really need to take a look at it so we can to make a better judgement call. If it's tumbling end over when you go for the G-turn, that is almost certainly the answer. You may be able to wait a little bit later to start the turn and get a more stable flight profile. Depends on how bad it is.

I am all for a center of dynamic pressure indicator and a center of mass indicator in flight. Man that would make building the heavy lifters a whole bunch easier.

No, its rolling along its roll axis during the gravity turn. Its not so prevalent going straight up, but once you start turning 45° or so, it starts picking up, making things difficult.

Radial stacks twisting maybe? It'd be great to see the actual rocket you're having trouble with but from what I've experienced, you're probably getting a little tilting/twisting in your outboard engines/tanks. They like to lean to one side a little while under thrust if they're not supported well (and a single radial decoupler/hardpoint/pylon is almost never enough). If they lean at different angles, it will set up lots of ugly momentary forces and send you tumbling. If you get lucky, they'll all lean one direction and you'll only get an axial roll.

Add a strut at the top and bottom between your radial stacks and maybe one to the center stack at the top of each to stiffen the whole structure up.

Stability isnt the issue. Last one was my apollo clone, almost no wobble, and the little that is there as at the top but it starts rolling around instead of staying there. Move on to the second stage and its fine, but not the first stage. This effect is also diminished the further out of the atmosphere you get.

[kiwiak]

My rockets sometimes start spinning too.. usually it doesnt end witch unplanned disassemmbley.. usually.

And im not talking about stability issues, as Sovek above mentioned there is no wobbling.

Just shortly after launch, during vertuical ascent, rocket starts to roll slowly.

Is it center of mass issue? Or somehow gimbal of rear boosters engines is causing this?

[maccollo]

This usually happens to some extent when you use radial stacks, and it happens in both vanilla KSP and in FAR.

What is usually the case is that the strutting isn't uniform, and as the engines push up they skew. Because everything is usually symmetrical they all skew in the same way, producing a very powerful twisting force that can be very hard to counter.

Another thing I've noticed is that sometimes the engines-tank joint becomes skewed aswell. This is very noticeable on single stack rockets because the rocket will suddenly want to turn really hard. Usually this happens right before the 10 km mark, and the engine typically skews in the exact same direction every time, so I think this could also be the cause of sudden violent spinning with radial stacks.

Edited February 4, 2014 by maccollo

[SRV Ron]

Uneven flexing of the boosters or asparagus on big launch vehicles will cause unwanted spin. With the proper use of bracing, such spin can be eliminated entirely.

[Claw]

Try reading this thread. Especially page 3.

http://forum.kerbalspaceprogram.com/threads/68424-Question-about-slow-rotating-craft-%28gyro-reaction-wheel-what-is-gimbal-%29

And a control surface are items on the aerodynamics tab. Some of them are winglets, canards, small control surface, etc. You'll know that you actually have a "control surface" when you right click on the parts. The extra info that pops out on the side will actually say "control surface." You'll have to just poke around in there and read the descriptions.

[Claw]

I just added some info related to this question on the other thread linked above. Maybe it'll help you out. I would post it here too, but I'm trying to not be all forum hoggy.

[kBob]

One thing I'll mention (besides struts)-- I had a similar problem on my latest creation, it was a radial asparagus staged rocket and went ok on it's own (a bit hard to turn but manageable) but got into orbit without enough fuel for my purposes, but when I added boosters it would spin out of control every time I did a gravity turn. I tried a lot of things, but finally I redid all the boosters lowering them a bit and wow nice and stable got rid of my winglets even. This goes with the earlier post about not wanting everything too balanced, I just found it out by trial and error. Also hopefully the next version is going to reduce the need for so many struts.

[Specialist290]

Since this thread is a bit old and we've already got a newer, active thread on this issue (that Claw has helpfully already linked to), I'll be closing this one. In general, it's better to start a new thread for your specific issue or finding a thread that someone's posted fairly recently, since bringing older threads like this one to the top runs the risk of bringing up information that might be outdated (and thus, confusing to new players) for the current version of the game.

Have a nice day