Design cause uncontrollable spin at reentry

[Ream]

 

Hello!

I'm (rather) new to KSP, been playing a month or so. So far managed to get around all obstacles via searching/reading online, but currently i'm having a problem i cannot figure out.
I've started working on a prototype for an eve lander (and possibly return vehicle). I'm trying to land a multistage design as seen in the attached image.

Started off with just the one heatshield on the buttom, which would obviously cause the craft to tip over during reentry. Hence i added 4 more heat shieldss higher upp to raise the center of drag over the centre of mass.

On reentry tests on kerbin, this works great - the craft is naturally aligned retrograde and the heat shields do their job.

However: For some reason the craft starts to spin around the prograde/retrograde axis, in a runaway manner, eventually causing the craft to spin so fast that it explodes. This does not make any sense to me, the craft should be completely symmetric. Even wierder is that during the first parts of the reentry, the spin is somewhat controllable with the RCS thrusters. Then at about 400 m/s, the spin becomes weaker and i can stop it. Then, going down towards the 200's m/s there is some kind of a feedback loop, causing the craft to rapidly start spinning clockwise until the centrifugal forces rips it apart.

Am i missing something obvious, did i find a bug in the game or is there some aspect to this type of design i have'nt considered?

Grateful for any help,

Denniss

 

Album 6kQWbut will appear when post is submitted

[bewing]

Welcome to the forums.

Are your parachutes open at that point? Have you tried turning off SAS when it starts to rotate and see what happens? Have you tried turning off RCS when it starts to rotate and see what happens? Is this version 1.4.3 you are running? I see you are running at least one mod. You may need to start removing mods to see if they are causing the problem.

 

 

[TheWildDefender]

I have sent a small probe to Eve before. I only had one heat shield at the bottom, and it didn't flip; the probe entered Eve very well. I suggest that you remove the extra heat shields and try that.

I think this works because when the craft tilts, there is a small force applied to the exposed side that corrects the rotation.

[Foxster]

Your "drogue" heatshields don't look to me as though they are far enough towards the back. If you go that way then they need to be right at the back or even behind the capsule. 

Personally I find the trouble of carting extra heatshields, along with their supports, to Eve a bit of a waste. I prefer to mount a lot of disposable air brakes near the back end. You might need 10 or 20 of them.  Just make sure they are within the occlusion cylinder of the heatshield when deployed or they will burn up. 

[Freshmeat]

I am not certain due to the small picture, but do you have steering fins on your rocket, they will enter facing the wrong way (you are flying backwards). If any miniscule rotation takes place, SAS will try to counter it, but as your fins are turned backwards they will instead accelerate the rotation. It happened to me when I build SSTO rockets, and turning off roll authority during descent for all controllable fins did the trick.

My shot at Eve entry was build very much like yours, but I added structural wings for stabilizers. This picture is kinda bad, but the best I have uploaded atm.

[Corona688]

Uncontrollable spinning can be caused by radial flex.  Try strutting it up.