Jeb, you hot dog!

[Entropiated]

I don't know what it is about version 1.0.2, but Jeb is being an awful show-off! A rocket that worked just fine in version 1.0 now has this amusing (yeah, "amusing"... that's what it is) habit of flipping over ONCE when I jettison the SRBs around 8000 meters. I have tested it many times and it happens without fail. The SRBs fall away, then the rocket flips around its center of mass a single time, then resumes its stable flight as if nothing happened.

I flew a lander to Minmus with this setup last night and the rest of the mission went off without a single problem. Oh Jeb, you so silly!

[KerbMav]

My best guess: The summersault slows the rocket down enough to become stable once more at an altitude that is not bothered by the high TWR after loosing the mass of the boosters?

[Blaf]

That might be worth GIFing

[Commissioner Tadpole]

Agreed. Give us a GIF!

[jarmund]

This used to happen to me with one of my launchers on 0.90, as I was flying with FAR back then. Unless I was dead center on prograde when decoupling boosters, it flipped once or twice. I usually managed to recover just fine, tho.

It stopped when I moved the finns from the boosters and onto the center tank.

[BagelRabbit]

I don't know what it is about version 1.0.2, but Jeb is being an awful show-off! A rocket that worked just fine in version 1.0 now has this amusing (yeah, "amusing"... that's what it is) habit of flipping over ONCE when I jettison the SRBs around 8000 meters. I have tested it many times and it happens without fail. The SRBs fall away, then the rocket flips around its center of mass a single time, then resumes its stable flight as if nothing happened.

I flew a lander to Minmus with this setup last night and the rest of the mission went off without a single problem. Oh Jeb, you so silly!

First of all, welcome to the Forum! I hope you enjoy your stay

My first thought is that your rocket is borderline unstable when the boosters are decoupled, as boosters mounted near the bottom of your rocket increase stability (they have a lot of drag, which lowers the center of drag enough to make your rocket stable). Once your boosters are jettisoned, your ship is just unstable enough to flip once.

This flip decreases your speed. As your speed decreases, aerodynamic forces begin to matter less and gimbal and SAS matter more. So your craft can stay in an upright position without too much of a problem after the flip.

By the time you reach the speed you were previously at, you're high enough in the atmosphere that aerodynamic forces begin to matter a bit less, so your rocket can stay stable.

Hopefully this makes sense. To learn more about aerodynamics, I humbly recommend my Simple Guide to Rocket Aerodynamics. It will help you avoid flipping and teach you how your rocket behaves in the atmosphere.

-Upsilon

[TimberWolffe]

I'm thinking slightly off-centre COM or thrust, usually not noticeable until you've spent a few minutes in flawless flight

[Xacktar]

I've had the same thing happen a few times. If it happens again I'll try and GIF it for all of you.

[Entropiated]

I'll try to gif it for you guys. I've since unlocked bigger parts and made a correspondingly bigger launcher that doesn't have this issue, so it's more about having a good laugh than anything else at this point! LOL

[Entropiated]

First of all, welcome to the Forum! I hope you enjoy your stay

My first thought is that your rocket is borderline unstable when the boosters are decoupled, as boosters mounted near the bottom of your rocket increase stability (they have a lot of drag, which lowers the center of drag enough to make your rocket stable). Once your boosters are jettisoned, your ship is just unstable enough to flip once.

This flip decreases your speed. As your speed decreases, aerodynamic forces begin to matter less and gimbal and SAS matter more. So your craft can stay in an upright position without too much of a problem after the flip.

By the time you reach the speed you were previously at, you're high enough in the atmosphere that aerodynamic forces begin to matter a bit less, so your rocket can stay stable.

Hopefully this makes sense. To learn more about aerodynamics, I humbly recommend my Simple Guide to Rocket Aerodynamics. It will help you avoid flipping and teach you how your rocket behaves in the atmosphere.

-Upsilon

Thanks! I understood your point perfectly. I'm just still adjusting to 1.0.x. I was used to designing things a certain way in the Beta, and I'm going through some growing pains right now (which explains why Jeb and Bill are in Munar orbit needing rescue at this point... but I have a plan. LOL)

[Temeter]

Afaik it's the top of the rocket creating a bit of body lift. Should be easily corrected by putting 4 of the tiny fins to the main rocket.

[Entropiated]

Afaik it's the top of the rocket creating a bit of body lift. Should be easily corrected by putting 4 of the tiny fins to the main rocket.

Yeah, I was thinking about that as a solution. Also, perhaps putting some fins farther towards the top would help as well.

[StrandedonEarth]

The lower the fins the more stable. Putting fins higher moves the Center of Pressure higher. The CoP naturally wants to stay below the Center of Mass. CoP above CoM will make the rocket want to fly bass- ackwards. Note: the editor calls CoP "Center of Lift," but they're really two different things.

Edited May 7, 2015 by StrandedonEarth

[Entropiated]

The lower the fins the more stable. Putting fins higher moves the Center of Pressure higher. The CoP naturally wants to stay below the Center of Mass. CoP above CoM will make the rocket want to fly bass- ackwards. Note: the editor calls CoP "Center of Lift," but they're really two different things.

Ah, I would've thought that since the front end wants to tip over, putting fins up high would have created a bit more resistance to that unwanted movement. Thanks for the feedback!

[BDelacroix]

I had rockets do that, too. Tailfins made it stop. I did think of it as Jeb hotdogging it, though.