Second Stage Cartwheels After Separating Booster

[SafteyLessThanSpeed]

I dont have screenshots right now (I was flying inside the cockpit). I was trying to reach orbit with a rocket that was 1) Booster Stage: 5 thumpers (one central then 4 around) 2) Main Stage: 1 x swivel engine 3 x 2nd upgrade fuel tank 3: Please God Let Me Come Down Stage: 1 x swivel engine, 1 x 2nd upgrade fuel tank, capsule (its got both telemachus antenna on it bcz IDK which one I need, 2 goo containers, one radial parachute, parachute on top, barometer, thermometer).   

 

 When the booster stage separates the rocket immediately begins to cartwheel. Is it all the crap on the capsule? If so can how can I fix that by sticking the science/comms stuff into like a faring shell or something else? 

 

Edit: Thanks everyone! Ill see what I can do with the advice in the thread

Edited March 24, 2017 by SafteyLessThanSpeed

[Streetwind]

Welcome to the forums

There are at least half a dozen reasons (and solutions to) why a vessel tries to flip on ascent. A lot of it has to do with the golden rule of rocketry: "heavy bits at the front, draggy bits at the back". So yes, it's quite possible that you have too much stuff stuck to the capsule. Not only will they be creating drag on the wrong end of the vessel, but it also looks like you are not using symmetric attachment. This may result in one side of the rocket having more drag and/or mass than the other side, and that tends to pull you off course in a hurry.

I recommend employing a service bay, attached right below the capsule. Service bays are parts that have a high heat and impact tolerance, have doors, and are empty inside. So you can stick things like goo canisters, antennas, batteries and other such stuff in there, and they won't be generating any drag. Once in orbit, you can open the bay doors and access everything. The 1.25m service bay is unlocked in the same node that includes radial parachutes, so you already have access to it.

Another thing that can cause your rocket to flip over is bad piloting. Make sure that you are flying a nice and smooth turn, and don't let the nose deviate too much from the prograde marker. The way I see it, you have five hammers in your first stage; that's way more thrust a rocket of this size needs. If they're not thrust limited by hand in the VAB, they're going to shoot you into the sky like a cannon. And because they are so heavy, generate so much drag, and don't have thrust vectoring, you probably cannot turn your rocket sideways as much as you need to. Then when you decouple, you try to correct your trajectory by turning sideways hard, and boom, you flip because you deviated too much to the side.

Finally, it bears noting that your rocket is overbuilt and inefficient. Normally, staging more helps you get more range, but because the Swivel engine is so heavy (it's not designed for use in upper stages - you'll unlock better engines for that soon), this actually works against you in this case. Too little fuel on too much dry mass means each stage barely gets you a little further. For example: you can actually push a capsule to orbit with just a single swivel engine, no other stages and no boosters necessary. Your rocket has five boosters and two swivel engines across three stages - you can see the difference, I'm sure.

Try the following rocket - it should do everything you need with plenty margin for error.

1x Mk1 Pod
1x Mk16 Parachute
1x 1.25m Service Bay (put anything you like in there)
1x TR-18A Decoupler
8x FL-T200 fuel tank (or equivalent in other tank sizes)
1x LV-T45 "Swivel" Engine
2x TT-38K Radial Decouplers (attached in symmetry to the bottom fuel tank)
2x RT-10 "Hammer" Solid Boosters (attached to the radial decouplers)

Thrust limit the Hammers to 70% by right-clicking them in the editor. They are your first stage. The Swivel is your second stage and will take you all the way to orbit with fuel to spare. Your third stage has no propulsion and is for reentry only. Use the second stage to deorbit before decoupling.

 

Edited March 23, 2017 by Streetwind

[Dr.K Kerbal]

Do you have senator a in the wrong spot? Or maybe one of your decopoulers has more force than another decoupled, making the spacecraft uneven...

[bewing]

Rockets flip in this way because there is more drag in the front than in the back. Your booster stage has a lot of drag -- more than your top stage. When you get rid of your booster stage, then what's left in the back end has less drag than your top stage, so the rocket flips.

Fairings or service bays can sometimes fix the problem. Sometimes adding some fins at the bottom of the main stage can fix the problem. Sometimes launching straight up can fix the problem. Sometime adding control surfaces at the very top of the rocket can fix the problem. Sometimes adding control surfaces at the bottom of the main stage can fix the problem. Sometimes just moving all the draggy parts on the top stage down just a little can solve the problem.

Alternately, you can understand that this is an aerodynamics problem. Once your rocket is above 35km altitude, there is no more aerodynamics to worry about. So one other thing you can do is to use kickbacks, or otherwise modify your booster stage so that it does not burn out until you are at 35km altitude. Then you can stage it away and the air will be too thin to flip your rocket.

 

[Kryxal]

I don't know what's where on this rocket, but ONE radial chute means you MUST have it non-symmetrical.  The tiny science parts probably aren't a problem, but the goo might be.  Your third stage is too much rocket and not enough fuel, better to just add fuel to the second stage, and probably some fins right above the engine.  Launch profile sounds likely to be the biggest problem if you haven't dialed down the outer 4 SRBs for the launch, since you won't be able to turn fast enough off the pad (and may not even know you needed to) ... turn a few degrees to the east immediately then try to hold prograde.

By the way, the service bay's nice to protect stuff, but can make the reentry stage flip-happy if you don't weight the bottom.

[linuxgurugamer]

4 hours ago, Dr.K Kerbal said:

Do you have senator a in the wrong spot? Or maybe one of your decopoulers has more force than another decoupled, making the spacecraft uneven...

Methinks the above was entered on a phone, cause I'm not aware of any senators in the game :-)

 

[Spricigo]

12 hours ago, Streetwind said:

Try the following rocket - it should do everything you need with plenty margin for error.

1x Mk1 Pod
1x Mk16 Parachute
1x 1.25m Service Bay (put anything you like in there)
1x TR-18A Decoupler
8x FL-T200 fuel tank (or equivalent in other tank sizes)
1x LV-T45 "Swivel" Engine
2x TT-38K Radial Decouplers (attached in symmetry to the bottom fuel tank)
2x RT-10 "Hammer" Solid Boosters (attached to the radial decouplers)

Thrust limit the Hammers to 70% by right-clicking them in the editor. They are your first stage. The Swivel is your second stage and will take you all the way to orbit with fuel to spare. Your third stage has no propulsion and is for reentry only. Use the second stage to deorbit before decoupling.

 

personal addition: 4 basic fin at the bottom tank (cheap, lightweigth and helps with stability)

 

also this guide my be usefull: