Total loss of control after new update - design issue or something else?

[zekib88]

Hi all, -- please help! -- Heres my question = Why does my rocket lose control at around 5-6k (note that at the time of 1.0 release it had 4 more boosters at first stage but no problems reaching the mun)

Just a quick background on my issue.... couple of days ago when 1.0 was released I opened up ksp and played as usual (with added excitement of course), no problems at all with ship design or reaching orbit or anything. After 1.0.2 - I used the same design but this time couldn't reach past 50k without it tilting slowly and then spiralling out of control.

--- first thing that comes to my mind is elements of drag, design symmetry, fuel payload imbalance, - but all seems fine (seems so), and it worked a day before but not after?

Since then I have tried all I can think of. Added and took off various parts, changed to very basic design, but anything that has the potential to bring me anywhere near the mun spirals out at around 30-40k. I've even reinstalled the game and started fresh.

Im hoping that its just the gameplay has got more difficult - in any case - any help is greatly appreciated

Edited May 3, 2015 by zekib88

[FancyMouse]

at 50k-60k aero shouldn't matter that much... if you completely lost control, maybe you're running out of electricity?

some pictures will help clarify what you exactly mean.

[zekib88]

Here's an image of the rocket design in question

what happens is that it starts to tilt even though it is going straight up, then just spins out and there is nothing I can do about it

Edited May 3, 2015 by zekib88

[Gaarst]

Could you upload a picture of the rocket at the point when it is actually spiraling so we can see the stage, engine... ?

A cause could be too high TWR and no gimbaling but you seem to have RCS and SAS...

It is strange though as aerodynamics >40km are negligible.

And that's a bit out of topic but your rocket seem to be really fast, this may be linked although very unlikely.

[MrCynical]

If it was an aerodynamic issue you'd be seeing a problem at 10km up, not 50+. At that point there's barely any drag and your rocket is probably on a trajectory that'll take it clear of the atmosphere anyway. Is it uncontrollable in space? That would suggest an issue with the SAS, which does seem rather flaky on the current version.

[zekib88]

The image above shows the point of no return when it starts to tilt and within seconds spirals out of control. I've tried a new design and when I keep it at full thrust the same happens, but when its kept to about 50% thrust its fine (no boosters on it). Could it possibly be what you mentioned that with boosters it can't be controlled and the high accelleration somehow is affecting it? what confused me more was that this issue arised not with 1.0 but 1.0.2 update.

[ghpstage]

396m/s at 6km altitude is far too high and is the primary cause of your problem.

Turn down the thrust on those SRBs in the VAB and it should perform better.

[zekib88]

When I build a simply 2 stage design to go into orbit its fine and control in space is normal as expected. Its just weird that without me doing anything it starts to tilt and as a result spins out.

[MrCynical]

OK, your rocket is only at 6 km in that image, not 50-60. You're going much too fast for that altitude which will cause you issues when you hit mach 1. Take off two off those solid rocket boosters, and aim to be reaching that speed at more like 15 km.

[zekib88]

Too many boosters, too little brain - that was my problem! Thanks so much guys, I just panicked that it was working before but not after the update and only thought it must be a rocket design flaw (which is pretty flawed to begin with). Much much appreciated. Back to KSP now

[Gaarst]

Ok so your rocket is actually spiraling at ~6km instead of 60km, which is very reassuring as the cause can be easily determined then.

First, as it has been said before, slow down: your can either remove some SRBs or limit their max thrust in the VAB (right click on them)

This will make the rocket much more controllable and will spare delta-v.

High acceleration also make your rocket less stable inside atmosphere and outside.

Then, add fins to your boosters.

SRBs do not have thrust vectoring / gimballing therefore they do not help in turning the rocket.

Fins placed at the very bottom of your rocket will make it much easier to control.

Finally, this is just a general advice: your ascent profile is not the best since 1.0, you should be starting to turn a little at ~100 m/s and gradually follow the prograde marker so that you are at 45° by 10km and ~30° by 25km, then aerodynamic forces don't matter and you can do whatever your want.

Always remember to keep your navball chevron inside the prograde marker while in low atmosphere as if you don't, strong aerodynamic forces will flip your rocket or worse...