Mun Rockets tipping over on launch

[Dave Kerman]

I am learning how build rockets to fly to the mun but all of them tip over during flight after I jettison the first set of SRB's.  My latest attempt is a highly modified PT Series  Munsplorer with three side boosters and BACC Thumpers.  Do you have any idea of what my issues are?

[Superfluous J]

The most likely thing is your rocket is back-heavy, so the engine part is heavier than the pod part. Aerodynamics will act very strongly on back-heavy things and cause them to flip over. It's why darts and arrows are heavy at the front.

There are various ways to mitigate this, like with fins and strongly gimbaling engines, but the best way to fix it is to make sure you keep heavy things in front. This can be tricky because engines are typically very heavy. The center-of-mass indicator in the VAB (looks like a ton weight, icon in the lower left of the screen) can help.

Another thing to watch for is a draggy front of the rocket, like with a huge fairing or lots non-aerodynamic parts jutting out various ways. Remember, the bigger the fairing, the more volume you have without appreciable mass, which is bad.

Also, going too fast too low can be a problem, as can turning too much all at once. A picture of your ship and a description of your launch profile could help us help you.

Edited November 14, 2018 by 5thHorseman

[Geonovast]

Hello @Dave Kerman, and welcome to the forums!

Your flipping issues could be any number of things, but I'm gonna go out on a wild guess and say that you have way too much drag up on the front of your rocket.  There are multiple ways to handle things, but first, we need pictures of what you're dealing with!  Please see my signature for a guide on uploading pictures

 

[Chumpes]

yo

your center of drag may be above your center of mass, which will certainly cause the flip of your vessel.

make sure you add some winglet at the tail of your craft so the center of drag switches below the center of mass...

Edited November 14, 2018 by Chumpes

[Vanamonde]

Many of the early tech tree parts do not contribute to steering (fins and engines which don't pivot) , and you may not have as much control over your ship as you think you do. Pictures often help diagnose such problems. How about some of those? 

[Tyko]

On 11/13/2018 at 7:05 PM, Dave Kerman said:

I am learning how build rockets to fly to the mun but all of them tip over during flight after I jettison the first set of SRB's.  My latest attempt is a highly modified PT Series  Munsplorer with three side boosters and BACC Thumpers.  Do you have any idea of what my issues are?

It would help a lot if you posted pictures of your rocket. Otherwise we are all just guessing

[DocMike]

A rather simple but less fuel-effective solution is to keep vertical ascent until 15-20km and turn to orbit only then. Thus:

1) less turning force when thrust vector is not aligned with center of drag

2) even if the rocket starts to tumble, it will still climb. Then cut the engine and restart it when nose points between 0 and 90 deg in your desired prograde direction. You will gain some speed, and eventually regian stability once you clear the denser atmosphere.

(Above works in normal difficulty, haven't checked in harder diff levels) 

Edited November 16, 2018 by DocMike

[Snark]

Moving to Gameplay Questions.

Also, +1 to "please post a screenshot of your rocket".

[Kryxal]

Agreed to posting a screenshot, but assuming the boosters are mounting radially and relatively low, chances are they're helping to keep the rocket straight ... until you drop them.