(stock) Rocket randomly veers to navball east

[Quantum_Matter]

So I'm having a problem with a rocket I recently build, trying to get a multi-purpose satellite into orbit.

Important:

It is a polar orbit, so on launch I follow the "north" marker on the navball.

Craft File: http://www.filedropper.com/showdownload.php/qstoss

Whatever I try, it always starts turning to the navball left even more while time passes.

Maybe it's because the boosters are put there using symmetry x3, and they interact with the airflow strangly?

O = booster

# = air

U = main fuel tank

north

##O

OU# east

##O

south

That would be the top view of the rocket.

get what I mean? since I'm pitching north, maybe it causes the craft to turn because it hits the northmost booster first?

Thanks for your responses.

[sal_vager]

Hi Quantum_Matter, I'm fairly sure this is precession (I think that's the right term) of the planet beneath you, as you track north, Kerbin rotates anti-clockwise as viewed from above.

[Quantum_Matter]

I heavily doubt that as it's not like I'm gradually turning that way, but it's as if suddenly some fast wind hit my craft from the other side and made it hard to control.

[Murph]

Hi Quantum_Matter, I'm fairly sure this is precession (I think that's the right term) of the planet beneath you, as you track north, Kerbin rotates anti-clockwise as viewed from above.

Yeah, not sure about the term, but something like that. Kerbin's rotation gives you a "free" 100–200m/s (can't remember just how much) velocity in an eastward direction, before you even leave the pad. In the early stages of the ascent, that's very significant in relation to the magnitude of your prograde vector. On anything other than east and west launches, you need to compensate for it with your heading (not a huge amount, just a little, correcting it over the full duration of your ascent thrust). I can't recommend a specific heading to correct to, as I personally just launch heading directly north or south, then eyeball the correction once established in stable flight. (And obviously it's helping you if you launch eastwards, and hurting you if you launch westwards, but won't change your course, just dV required to orbit.)

[sal_vager]

Not really getting it Quantum_Matter, can you provide pics? F1 takes screenshots and Imgur.com can host them.

[cybersol]

Welcome to the Coriolis effect of Kerbin rotating under you with its eastward sidereal velocity of 175 m/s. However, if the force is stronger than about 10-15 degrees deflection, then there might also be something about your rocket causing it. Have you tried a roll maneuver so the boosters are symmetric in respect to the northern direction? From your ASCII art a 90* roll either way should make it symmetric while headed north.

[Bev7787]

You can always add a fourth booster to the side.

[FancyMouse]

To verify whether it's because of Coriolis force - go south and did you get the hidden force exerted from the other direction? If not, then it's something else.

[Reactordrone]

The planet gives you an eastward vector of 174.5m/s so if you head directly north you'll end up following the red line.

[Murph]

The planet gives you an eastward vector of 174.5m/s so if you head directly north you'll end up following the red line.

Correct. In the very early stages of your flight, the horizontal component of your prograde is tiny, so that 174.5m/s horizontal east vector dwarfs it, and your achieved course will be mostly east despite heading directly north. As you gain speed, the achieved vector (the red one in the pic) starts to correct itself (but will still need some actual correction by putting a little of the dV slightly towards west of north, to fully cancel the starting 174.5 east). Even at orbital speed of a bit more than 2000m/s, that's just a little bit less than 9% of 2000, so significant overall unless corrected.

[pincushionman]

Quantum Matter, do you mean "I'm heading due north all nice and fine, but at about 25-30ish km, my prograde marker jumps suddenly about 8-12 degrees to the right on the navball"? Or "the rocket twists about the long axis as I apply pitch/yaw"?

The first is the navball switching from surface coordinate system to orbit mode. The second I haven't seen a good explanation for.

[pendant]

Quantum Matter, do you mean "I'm heading due north all nice and fine, but at about 25-30ish km, my prograde marker jumps suddenly about 8-12 degrees to the right on the navball"? Or "the rocket twists about the long axis as I apply pitch/yaw"?

The first is the navball switching from surface coordinate system to orbit mode. The second I haven't seen a good explanation for.

I admit this is a wild guess, but it may be relevant:

If you've had KSP a good long while, it's possible that your key bindings may be incorrect. I would suggest trying this:

1. delete your settings.cfg file (or rename it, to, say, 'settings.BACKUP.cfg')

2. restart KSP (this will create a new settings.cfg file, with key bindings correct for post-version 1)

3. try your launch again

If this doesn't cure your 'second problem', my wild guess is wrong -- in which case I apologise for having wasted your time...

[SanderB]

I haven't seen your craft, but if you have side boosters and they have only 1 point at which they connect to the main booster they need at least one strut to connect them to the main booster to ensure that they don't wiggle and cause rotations. This may cause some rotating or mucking around otherwise.