launching help

[thorodin84]

Why is it that sometimes my rocket launches work out perfectly fine and sometimes all hell break loose under the exact same conditions? I have been trying to launch a 2880 fuel tank up which has been successful before for many times but, it is now screwing up. It is getting extremely frustrating. Btw i use mech jeb 0.19 for the acent autopilot.

[Akalaël]

Can you provide a pic of your launcher, it'll help !

As I can tell, the 2880 fuel tank you are talking is the orange one, the Jumbo 64.

It's known to be really heavy, and if you don't put many struts to sustain it, it won't work.

Also, no matter the numbers of struts you put, if you stack too mutch of these, physiX will collapse your Orange thing ontop of the stage beneath...

Edited June 5, 2013 by Akalaël

[Vanamonde]

Each time you go to the Launchpad, the game assembles a rocket according to the design you made in the VAB. As odd as it sounds, there are sometimes tiny variations in exactly how the rocket is put together, which can result in weird things like structural failures or uncontrollable rotations even in designs that you've tested and flown successfully many times. It can be extremely frustrating, but the fact of the matter is that if this problem comes up, your rocket is pretty close to failure tolerances anyway, and some reinforcement or a re-design is called for. In short, add struts or move components around until you get a more stable ship.

[Epic DaVinci]

What exactly is going wrong? loss of control? explosions? spinning?

[thorodin84]

Sorry for the late reply totally forgot about this post... Anyway it spins out of control at around 900m/s.

My fuel ship

and spinning out of control

[zekes]

if you don't have gimballing engines that might be your problem.....

[hansman1982]

Run struts from that 5M fuel tank as high up as you can. Run as many as you can. That will help a lot. Basically, the top of your rocket (and, probably, where your command pod is located) is flopping all over the place, MechJeb is then trying to correct this and the ship will flail wildly (basically, it is thinking the ship is going whichever direction the top is going and trying to correct).

If that doesn't work, do you have FAR installed? FAR and MechJeb don't get along well (I have long since abandoned FAR).

If that doesn't work, I now launch with this configuration most of the time and get super smooth ascents (I no longer use the fairings since I don't have FAR)(don't forget to lock the gimbal on the outside engines):

[hansman1982]

basically, step 1 is strutting the **** out of it.

[Margaul]

Yup. The wobble at the top is going to cause you hell. It wobbles and mechjeb and the ASAS will try to correct. as it wobbles more, it corrects more making an oscillation that will eventually spin it out of control The air resistance will help hold it steady at lower altitudes, but as that decreases, bad things will happen. If you have trouble running struts up that high, attach some hardpoints halfway up, strut those from the bottom, and then run struts up from the top of the hardpoint to the wobbly top.