Getting tourists into orbit

[KerbalPlayer]

Hi!

I am having problems with a mission, getting tourists into space. The problem is that i need to get 3 tourists(+ my astronaut) into orbit and back again. According to a couple of tutorials, my rocket layout is the best suited for the mission. But my rocket is extremely unstable. After takeof it pitches to 90 degrees, and wont right itself. It gets worse as more time goes by. My guess is that the rocket is getting more top heavy when the fuel is beeing used up in the rockets.

Can anyone point me in the right direction?

https://imgur.com/a/xpziM

Edited November 16, 2017 by KerbalPlayer

[Aegolius13]

Somewhat counterintuitive, you want a rocket to be top heavy.   (This is an old conundrum called the "pendulum rocket fallacy").   For a stable rocket,  you want mass concentrated at the front,  and drag at the back.   Like a dart or arrow.

I think your main problem is that you have too much drag at the front.  Those inverted command pods are probably created more drag than they look - changes in the diameter of parts tends to cause a lot of drag.   If you have parts available,  you might look at other passenger cabin options. Or you could try to enclose the top in a fairing.

You can also try adding fins to the very bottom of the rocket.   But a draggy front end will always impair stability. 

[Urses]

I would insist fins on the downside end of the mainstack. I tend to say the cocpit solution generates but you can controll it through aero oberlay in floght (F12) and do  a step for sure ab change the fuelflow priority that the upper tanks stay longer fueled. Dart example is right, but you build more like a bowling pin. And as your fuel burns down your rocket becomes more nose heavy=>good, but is nose dragier to through concept=> not realy stable. Try to get your most dragier point as near as possible to CoT and your CoM as far as possible above it.

 

Edited November 16, 2017 by Urses

[GoSlash27]

Too much drag in the nose, but it's probably still serviceable if you accelerate more slowly.

1)Try turning down the thrust on the SRBs so you leave the pad at 1.2G. Note the %throttle that achieves that. See if this is enough to tame it. If not...
2) Replace the SRBs in 2 pairs instead of one group of four. Readjust the thrust so the first pair of SRBs produce 25% more thrust, and the second pair 25% less. This will even out your acceleration through the boost phase so you're not pulling like 4g at burnout.

HTHs,
-Slashy

 

 

Edited November 16, 2017 by GoSlash27

[Plusck]

The parachutes aren't helping the drag or stability problem either since they are not centred. Parachutes (unlike most science instruments and some other radially-attached parts) obey "proper" physics. You can put 50 thermometers on one side of a rocket and it'll behave like they were spread evenly around it. Not so with parachutes.

You don't need 4 parachutes for 4 command pods. Two main parachutes (and two drogues, to avoid lawndarting) should be more than enough, so attach them in pairs to one or at most two of those command pods.

[Cheif Operations Director]

On 11/16/2017 at 10:21 AM, KerbalPlayer said:

Hi!

I am having problems with a mission, getting tourists into space. The problem is that i need to get 3 tourists(+ my astronaut) into orbit and back again. According to a couple of tutorials, my rocket layout is the best suited for the mission. But my rocket is extremely unstable. After takeof it pitches to 90 degrees, and wont right itself. It gets worse as more time goes by. My guess is that the rocket is getting more top heavy when the fuel is beeing used up in the rockets.

Can anyone point me in the right direction?

https://imgur.com/a/xpziM

Ok your theory about weight is correct if you think it's BECOMING Top heavy. 

My suggestion is to Stage your rocket. Another suggestion is to merge your capsules into one capsule. Via offset.