Rockets flipping at stage separation.

[Axor]

I'm sorry if this has been asked and answered before, but I looked around and I nothing mentioned seems to work when I try it.

Ever since 1.0 I can't for the life of me launch a rocket into orbit, I'm in very early career with FL-T200 fuel tanks and Reliant engine.

I'm using a very simple 2 stage rocket, I tilt very slowly towards 45 degrees as I ascend and everything is fine until the first stage burns out and I separate, after which the rocket just flips over uncontrollably.

I've looked around and people are saying fins fins fins, but even with fins on the upper stage it flips over as soon as I separate the stage.

[diomedea]

I'd suggest not to rush for the orbit goal, unlocking more techs will certainly make the achievement easier.

Anyway, here is the pic of a 2-stage rocket able to achieve orbit with just those few parts (Reliant engines, FL-T200 tanks, small fins), without too much correction and not even SAS.

My suggestions for a successful orbit are:

1) stability: while building the rocket, each stage must remain stable even when almost empty of fuel. Place fins at the tail so the Center Of Lift is visibly lower then the Center of Mass at all times. With a CoL much lower then the CoM, the rocket will be very hard to steer, but that is not so bad during the ascent, because ...

2) during ascent, always keep the nose of the rocket very close to the prograde direction. Sure, you want to pitch down during the ascent, but pitching too fast will make the rocket travel within the lower and denser atmosphere for longer, and drag will waste much of your DV. Not pitching enough will not provide the horizontal speed required, in the end you need a horizontal speed of about 2200 m/s for a LKO. So, you need to angle the nose of your rocket just a little at a time in the correct direction (generally, pitch down towards heading 090°), the smaller the angle, the more similar the ascent profile is to a true gravity turn (the most efficient profile).

3) After the separation of the second stage, rocket will be much more maneuverable (due to less moment of inertia, but also due to lower aerodynamic effects on the fins). Apply some angle (never more than 5°, the size of the prograde marker of the navball) if needed to start gaining horizontal speed. Start looking at the apoapsis altitude in the map view, you need to achieve 70-75 Km: so, throttle down if you are already at that value. If the profile was correct, you would have gained considerable horizontal speed already, and with a final burn when aoutside the atmosphere you'll get to the orbital speed. It always requires a bit of experience to judge the correct profile.

[nikolay-spb]

give screenshot of the rocket.

What is your second stage engine?

[capi3101]

There's a lot of factors that may be at work here. The most common cause I've seen of folks flipping out so far, however, has been CoM too far aft (i.e. the dart problem). To better diagnose problems and give you advice as to what you should do, we really do need to see a screenie.

Here's another question: about what altitude are you at when you begin your turn, when do you cross 45 degrees, and what's your rough altitude when the first stage is done burning?

[Juicy]

For testing (also works as a simple fix) whether it's the Center of Mass of your upper stage being too low, add another fuel to the upper stage, and disable the top fuel tank manually before take-off, wait for re-enabling it untill the bottom fuel tank of the stage is (nearly) empty.

Canards also don't go well on rockets. If you add fins, always keep them below the center of mass, or they may generate enough drag to flip you as well.

[Eric S]

There's a post here that goes into the forces that cause rocket flipping.

Staging can be a particularly vulnerable moment in an ascent because you're dropping a mostly-empty stage. This means that it doesn't have a lot of mass, so your center of mass isn't going to change much, but it's got all of its surface area still, which means your center of pressure is going to move more significantly.