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Please help! Every single rocket i build slowly slides off to one side, no matter what. Everything is in line, center of mass is in the bottom middle if my rocket, i am using fins, sas is on, and im not touching the engine. I have no idea what is going on and how to fix it. The game is nearly unplayable because i can't reach orbit to collect science so i can't unlock halfway decent parts. Please help

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1 hour ago, Imbadatksp said:

center of mass is in the bottom middle if my rocket, i am using fins

If your center of mass is too low down then aerodynamic pressure can push the tip of your rocket around causing it to flip. Place the fins as close to the bottom of the rocket as you can and check that your center of lift is below your center of mass. Also, try not to steer very far from your direction of flight, especially during the speed range between 300 and 600 m/s. Use frequent slight nudges instead of turning it hard over.

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1 hour ago, HvP said:

If your center of mass is too low down then aerodynamic pressure can push the tip of your rocket around causing it to flip. Place the fins as close to the bottom of the rocket as you can

^ This.  You want your CoM to be in the front of your rocket, not the back.

1 hour ago, HvP said:

check that your center of lift is below your center of mass

^ ...Careful about this, it's not really accurate-- "CoL behind CoM" does not equal aero stability.  (Lots of people think it does, which is why there have been so many "why is my shuttle replica so unstable" threads in the forum.)  :wink:

It's only marginally related; you can have a horribly unstable rocket that has its CoL behind CoM.

But certainly, "fins in the back and CoM as far forward as possible" is a good thing.

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Screenshot or description would be helpful.  But sounds like you're in the very early game.  Are you just using solid rocket motors, like the Flea or Hammer?  These are supposed to be hard to control - the liquid fuel engines are much better once you get them.  You may want/need to collect more science on Kerbin (the Kerbal Space Center has a bunch of little biomes you can run experiments on) or in flight before unlocking engines that can take you to space more reliably.  The Swivel, which has both throttle control and engine gimbal, is your best bet.  

Also, how much are you tipping over?  You do want to tip over a bit, to get a gradual "gravity turn" so that you're horizontal by the time you reach high atmosphere.  But if you're going upside-down within seconds, obviously that's a problem.  

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1 hour ago, Imbadatksp said:

By sliding i mean it yaws over about 10 degrees, then and by that point ive lost all control. I cant bring it back around, and its not my gravity turn. I forget the name of the engine but it is one if the first two LVTs you unlock. No SRBs. 

Are you putting a single Goo cannister on your rocket? I ask because goo cannisters are fully-fledged "parts" with non-negligible mass, so if you don't use symmetry when placing them they can easily make your ship drift off to one side.

If you don't have control fins, or a rocket with gimbal (the Swivel has gimbal, the Reliant does not) then any slight deviation from prograde can easily become fatal. In addition:

- never put fins high up on the rocket. They may look like they should help, but they actually do the exact opposite.

- put weight high up on the rocket if possible. It may feel intuitively wrong, but intuition can be wrong and is here. To do so, you might want to lock a fuel tank at the top of your current stack and unlock it when fuel gets close to running out.

- balance everything. The only exceptions are the tiniest (0.005t) science instruments and antenna, and batteries: they add mass to the part they are connected to, so if that other part is balanced, all is well.

- never allow your ship to drift more than a few degrees off prograde after you've exceeded a speed of about 100m/s. When you have more powerful control fins, you'll be able to drift further off but until then, you have to follow the airflow as closely as possible.

Edited by Plusck
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2 hours ago, Imbadatksp said:

I forget the name of the engine but it is one if the first two LVTs you unlock. No SRBs. 

Might be the Reliant- that's the first liquid fuel engine you unlock.  But since it does not have engine gimbal, it's hard to control, especially if you don't have controllable winglets to use as fins.  If it is the Reliant, I would try the Swivel and see if that works better for you.  

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