Why does this rocket always flips over?

[Commissioner Tadpole]

As I got my new computer yesterday, I recently started playing KSP again(in glorious 60fps/30fps instead of 4fps), and decided to head for Laythe instead of Duna this time. Unfortunately, it has been a long while since I last played KSP, and I lost my flight abilities. I designed a rocket that seems to look aerodynamically stable, but every damn time it suddenly flips over and flies on its butt at around 6km altitude, no matter how fast I am going. I am not doing the "head straight up and then turn 45° at 10km" strategy as I am aware it does not apply anymore - I am slowly doing the gravity turn as soon as I take off. What am I doing wrong here?

This is the rocket:

Note: The rocket had asparagus staging when I took the picture, but I later removed it, thinking the staging was the problem. It wasn't - the rocket still flipped.

[ElWanderer]

That fairing looks quite large. Are you aware that the fairings are currently a bit buggy in that drag is applied in the wrong place (way out in front of the rocket where it does much more to encourage flips)? This is to be fixed in v1.1, or alternatively Claw's "stock bug fix" mod has a temporary fix.

The aerodynamics generally encourage taller, pointer rockets with fewer boosters. Do you need that many?

 

[FancyMouse]

This indeed doesn't look too bad. My suggestion is, make fairing more pointy, and make sure the rocket is always in prograde direction during ascent. I do not quite suggest using control surfaces when engines have plenty of gimbal, because it gives you too much control and might screw things up (especially with SAS).

Edited March 7, 2016 by FancyMouse

[Snark]

Yeah, +1 to that, I'd say the fairing looks like the most likely culprit. Other than that, everything about the rocket looks good.

It's true that the new aero encourages tall/pointy rockets, which is a slight ding against asparagus, but in general the bigger the rocket the less it has to care about aerodynamics, so I don't think there's too much of a problem with your design there.

• Streamlined design? Check.
• Fins on the back?  Check.
• Steerable fins?  Check.
• Engines with gimbal ability?  Check.
• Reasonable launchpad TWR?  Check.

About the only other thing I can think of (besides the fairing itself) is, what's inside that fairing?  How massive is it?  If it's something really light, that could also be a problem. Perhaps a screenshot from the VAB, showing the CoM marker and the fairing contents?

[DerekL1963]

1 hour ago, ElWanderer said:

Claw's "stock bug fix" mod has a temporary fix.

This fixed 90% of my flippy/tippy rocket problems.

[Commissioner Tadpole]

Just now, Snark said:

Yeah, +1 to that, I'd say the fairing looks like the most likely culprit. Other than that, everything about the rocket looks good.

It's true that the new aero encourages tall/pointy rockets, which is a slight ding against asparagus, but in general the bigger the rocket the less it has to care about aerodynamics, so I don't think there's too much of a problem with your design there.

• Streamlined design? Check.
• Fins on the back?  Check.
• Steerable fins?  Check.
• Engines with gimbal ability?  Check.
• Reasonable launchpad TWR?  Check.

About the only other thing I can think of (besides the fairing itself) is, what's inside that fairing?  How massive is it?  If it's something really light, that could also be a problem. Perhaps a screenshot from the VAB, showing the CoM marker and the fairing contents?

The payload is the base I'll use on Laythe.

The payload's mass is around 7000kg, if you're wondering.

Edited March 7, 2016 by Commissioner Tadpole

[Snark]

Okay.  So, yes, it's a light and fluffy payload, which is exacerbating your problems.

My advice:  Lose the fairing.  You're getting virtually zero benefit from it.  Your payload is already fairly streamlined, with just a few radial parts sticking out.  And with a rocket as huge as yours is, it's not even going to notice the drag from a few landing legs and solar panels.  Replace that short conical adapter with the taller one, so that it'll be more streamlined.  Rotate your Gigantors so that they're in the default vertical orientation, rather than horizontal, so that they're  more streamlined on ascent.  Ditch the fairing entirely.

(Do you have the tech for an RTG?  If so, put on a couple and ditch the Gigantors entirely.  Solar panels really suck, out by Jool.  You get more power-per-mass with an RTG, out there.)

Edited March 7, 2016 by Snark

[Norcalplanner]

Mounting the gigantors vertically would also allow the fairing to be smaller.  They'll rotate automatically once they're deployed.  And another +1 for Claw's Stock Bug fixes.  There's also a stock clamshell fairing mod which will give you a much more satisfying fairing separation.

[Warzouz]

Many good advice here, I would only add that your fins are attached to your asparagus parts. So when you dump your empty tanks and engine, you loose fins. Fins are usefull not as take-off, not in high atmoshpere but in the low-middle (between 5 to 25km). In that location, you're dumping your fins/wings. You loose their advantage.

To be usefull, you should stick you fins on the central tank so they wouldn't be discarded too soon. But this is not always possible. that's why I gave up using asparagus.

 

You could try to have a bigger central engine/tank, and smaller lateral booster (liquid or solid). That way you would be able to dump your stage and still have your wings.

For my part, I use SSTO rockets : their flight profile is the same all the way up. It's much eaiser to design

 

[RocketSquid]

I used to have just about every large rocket flip, seemingly for no reason. However, I later realized it was because the payload would bend slightly, giving the pod, atop the payload, a false heading, which it would try to correct using thrust vectoring, which would cause it to bend the other way, and so on, until it eventually couldn't recover from the flip. So, I would recommend you put a probe core or Sr. Docking port somewhere in the stack, or just put a bazillion struts under that fairing.

[Mjarf]

I add several strategically placed struts and A LOT of "Vernor" RCS thrusters on my lifting stage combined with a Large Reaction Wheel to pretty much brute force the damn thing to go straight. Yesterday I did encounter a similar bug though, my rocket started tilting at approx 15k altitude before it suddenly exploded and the pod went down with zero air resistance. It seems like there's definitely some kind of aerodynamics bug in the current game version.

[Commissioner Tadpole]

Just now, Snark said:

Okay.  So, yes, it's a light and fluffy payload, which is exacerbating your problems.

My advice:  Lose the fairing.  You're getting virtually zero benefit from it.  Your payload is already fairly streamlined, with just a few radial parts sticking out.  And with a rocket as huge as yours is, it's not even going to notice the drag from a few landing legs and solar panels.  Replace that short conical adapter with the taller one, so that it'll be more streamlined.  Rotate your Gigantors so that they're in the default vertical orientation, rather than horizontal, so that they're  more streamlined on ascent.  Ditch the fairing entirely.

(Do you have the tech for an RTG?  If so, put on a couple and ditch the Gigantors entirely.  Solar panels really suck, out by Jool.  You get more power-per-mass with an RTG, out there.)

Thank you, this worked perfectly!