Can you tell me why this rocket is rolling?

[Travisfv]

It goes up straight. No weird edges or anything to cause drag on one side. What I notice is that during the gravity turn, it wants to roll hard right. It spins to a point and then stops. There is no separation at this point either so its not that bug coming into play.

I tried so many different configurations. Extra ASAS units in the center rocket. ASAS on the liquid boosters. ASAS on both center and liquid booster. I feel like whats happening is that the game wants one of those liquid booster to be on the bottom, kinda like the keel of a ship. I'd really like it if this thing would go up and act like a real rocket though, having those boosters separate safely to the sides instead of risking crashing into the rest of the rocket.

[stupid_chris]

Most probably, the problem is because gimbaling engines don't have roll control, and because to steer this big rocket, torque is just insufficient. As you said, the boosters tend to be on sideways configuration during the gravity turn, it's more stable this way. The new SAS is impressive, but it's not an act of god and it can't do miracles, so yeah, this kind of things can happen.

Is the roll really hindering your controls to a point you need to get it fixed or was it just as an informative question or because you were annoyed by it that you made this post? :l

Edited July 27, 2013 by stupid_chris
Got dumb again and missed a part of the post.

[Travisfv]

The problem happens before I decouple those booster. And yes it affects control quite badly. Just moving down to 45 degrees is very tedious due to trying to maintain level flight. I can get it to do it, but it's a fight all the way to separation. Once those booster separate, the rocket flies straight and true.

And I'm not sure what you are implying but this is a help section. I asked for help in the help section. Do I need to have more reason to post or am I not allowed to ask for help in the help section?

[stupid_chris]

  Travisfv said:

The problem happens before I decouple those booster. And yes it affects control quite badly. Just moving down to 45 degrees is very tedious due to trying to maintain level flight. I can get it to do it, but it's a fight all the way to separation. Once those booster separate, the rocket flies straight and true.

And I'm not sure what you are implying but this is a help section. I asked for help in the help section. Do I need to have more reason to post or am I not allowed to ask for help in the help section?

Sometimes people here ask questions for informative purposes, I was just asking.

Since it seems to be affecting your launcher before separation, I guess you could solve the problem by adding winglets. Usually when I do similar designs, I place four winglets on the core booster and two on each side booster, and those tend to give me the stability I need to prevent things from rolling unexpectedly in the lower atmosphere, and probably those would help a lot.

[Travisfv]

Sorry, coming from the Total War: Rome II forum at twcenter.com, you have to be defensive. Merciless bastards over there. Not joking, every poster is subject to personal attack for any opinion whatsoever. Not used to a community who is actually civilized.

But I have added winglets also. I'll try a new configuration of winglets like you said though. I had six on my bigger variant of this for the center and three on both boosters. I only went smaller to see if that changes the problem.

And my whole reason for this design is that separation comes at about 15-20 km up in the air. It keeps debris from falling on KSC, is a strong rocket (minus the spin), is perfect for crew changes on a Space Staion, and finally it can lift a lot of weight on my bigger version.

[stupid_chris]

Hm, did you try disabling the gimbals on the boosters? They could cause some instability and produce the roll you see. Else, you could try going with the flow and manually rolling the rocket this way during the vertical portion of your ascent. You could even rotate it yourself in the VAB so that the boosters are already sideways, it might already give the craft it's stable orientation for the gravity turn and prevent additional roll.

[Travisfv]

Disabling gimbal on the boosters made the rotation worse, but the winglets in that configuration helped a bunch. It gave me slight roll to the right, maybe 10-12 degrees, but corrected itself. I'm thinking possibly a couple more winglets on those boosters may reduce that roll by a few more degrees?

EDIT: That was it. She launches as close to perfect as she can get. Really good separation where the parts miss KSC, main rocket carried it to an apoapsis of 125 km, injection stage put her into a perfectly circular orbit, and the final stage has a full take for maneuvering and topping off the station.

Thanks a bunch for your help. Sorry I got defensive too.

Edited July 27, 2013 by Travisfv

[AmpsterMan]

I've had similar issues with strap on boosters as well. My suggestion would be to check your strut connections and make sure they are perfectly placed.

[stupid_chris]

Heh, no problem, always glad to help ^^

[Skorpychan]

I'd try winglets, personally. My current booster setup has two sets, and they do stop most of the roll.

Related question; my rocket spins like CRAZY after I decouple the boosters around 120k. Is it the loss of winglet area at that height that's doing it, or are they catching the rocket on the way up?

[Travisfv]

  Skorpychan said:

I'd try winglets, personally. My current booster setup has two sets, and they do stop most of the roll.

Related question; my rocket spins like CRAZY after I decouple the boosters around 120k. Is it the loss of winglet area at that height that's doing it, or are they catching the rocket on the way up?

At that altitude winglets don't do anything. It's probably just the ASAS freaking out. I'd suggest you switch off ASAS before separation, then turn it right back on after.

[Skorpychan]

I usually need it firmly on at that point to stop the whole thing going crazy, but it's worth a shot. Maybe it won't point the rocket downwards, now...

[acealeam]

  Travisfv said:

Sorry, coming from the Total War: Rome II forum at twcenter.com, you have to be defensive. Merciless bastards over there. Not joking, every poster is subject to personal attack for any opinion whatsoever. Not used to a community who is actually civilized.

I know the feeling, hah.