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Thread: Rocket stability

  1. #1

    Rocket stability

    I feel dumb for having to ask for help on this since I haven\'t been having too many issues until now, but its getting really annoying and I don\'t know how to fix it.

    Any time I tack some SRBs on the outside of my center-line fuel tank and have those lift-off first, my rockets will begin to spin (and usually pitch to the left or right). Even using SAS, ASAS, and RCS, I can\'t stabilize anything that might have a chance of going to the moon. I\'m not over-balancing anything or making anything too extreme.

    Any suggestions?

  2. #2
    Senior Rocket Scientist
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    Re: Rocket stability

    Radial decouplers have a tendency to be a bit... flexible. Try putting struts from one booster to the next, at the bottom and at the top. See if that makes things better.
    Kerbals and bits, anyone? -SynMonger

  3. #3

    Re: Rocket stability

    Radial fins on the SRBS can also help, provided they\'re well aft of the decoupler.

    In general decoupler torquing is a semi-intentional aspect of the game\'s design, and one approach is that if you can keep the nose on the right spot rolling actually doesn\'t matter. It\'s also guaranteed to last only 25 seconds.

  4. #4
    Senior Rocket Scientist
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    Re: Rocket stability

    The problem is that when you light the boosters, they all hammer up against the decouplers, which bend and point the thrust outward. If that thrust gets off-center or off-axis at all, it\'ll snowball into chaos.
    Kerbals and bits, anyone? -SynMonger

  5. #5
    Rocket Scientist cardgame's Avatar
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    Re: Rocket stability

    It helps to have a very massive (as in mass-heavy) center of the rocket to increase the force needed to destabilize its vertical inertia into an angle.

  6. #6

    Re: Rocket stability

    Here\'s my solution to the problem. It gave me a very stable, very rotation free and quite manageable rocket.

    Put the decouplers as low on the SBRs as you can. The reason is quite simple: The closer the decouplers are to the engine nozzle, the lower the lever on the decouplers.

    Connect the lowermost points on your SBRs with the SBRs next to it, so the 6 (or however many you use) SBRs are linked to each other with struts. This reduces the lever even more and equalizes the forces executed inwards between the SBRs.

    Connect the top of the SBRs to the rocket inside with another set of struts. This is basically mostly for balancing and to lower the shear force on the couplers from the SBR trying to push 'up', less tear on the couplers.

    That results usually in VERY solid booster behaviour. I had an array of 18 boosters arranged around my rocket without them going bonkers.

  7. #7
    Senior Rocket Scientist
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    Re: Rocket stability

    It simplifies things if you put the decouplers at the top and strut the boosters together at the bottom; decoupler placement doesn\'t affect much in terms of leverage, but it means that there will be less force on the struts at the bottom (decreased mechanical advantage, don\'t feel like elaborating). It also removes the need for top struts, without decreasing stability.
    Kerbals and bits, anyone? -SynMonger

  8. #8
    Flight Director Tim_Barrett's Avatar
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    Re: Rocket stability

    A combination of ASAS and wings mounted on the isdes of the boosters it probably the way to go. On the other hand make sure you aren\'t stacking the boosters directly on top of eachother

    If all else fails, use the power of struts!
    Okay... one of you guys thought it would be funny to smash the rocket into the command center... very funny...

  9. #9

    Re: Rocket stability

    Besides struts the immobile fins seem to help
    I TOLD YOU NOT TO FART IN THE SPACESUIT !!!!!!!!!!




    You smell what i mean

  10. #10

    Re: Rocket stability

    If it\'s the solid boosters that are causing the radial attachments to bend, then I suggest struts to keep things rigid.

    As said before, flexible things can cause the thrust to go off center and potentially cause spins/wrecks. Even in the best scenario it\'s wasting a bit of fuel.

    If they\'re bending and you put wings on them, then it will just cause those boosters to flap more.
    Wings will help AFTER you make the attachments rigid.

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