Imbalance

[Artie]

Can anyone tell me why my rocket keeps tipping over once the bottom tank has been dumped? Is it top heavy, or something? I've tried moving the main engines up and down along the body, to no effect. There are also two sets of canards and two sets of reaction wheels (installed after the instability began), as you can see:

Edited November 2, 2013 by Artie

[Taki117]

That's quiet a bit of fuel lines. Also, what type of engine are you using on your Orange tank? And have you tried Asparagus Staging?

[Artie]

That's quiet a bit of fuel lines. Also, what type of engine are you using on your Orange tank? And have you tried Asparagus Staging?

In order:

The drop tank needs to drain first, then the individual tanks, then the central tank, hence the lines. I put in a separator to try and stop the individual tanks from being drained directly, but that doesn't seem to be working.

Atomic. It activates once in space.

As I understand it, Asparagus is an exploit. While I appreciate creative licence, Asparagus frankly takes it to ridiculous lengths.

[Traches]

It's tough to tell from here, but it looks like with your fuel line setup one side of tanks might be emptying before the other.

Also, putting your engines up high won't help with stability. Make your rockets look like real life rockets and you won't go too far wrong.

Edit: keep your control surfaces down low, well below the CoM.

[Taki117]

You could try making a main lifter stage to get your contraption into space and get rid of the drop tank issue entirely. (Doesn't need to use Asparagus) Alternatively you could swap out your canards for RV-8 Winglets, they tend to work a little better.

[capi3101]

Lose the top set of canards; they are doing nothing. I imagine your design is indeed top heavy as well (at least, it gets that way as you go up). Is the tip over happening at a roughly consistent altitude?

What's the mass of your payload and how far along are you on the tech tree (assuming you're playing a career game)?

If you object to asparagus, what's your stance on parts clipping?

[Artie]

Lose the top set of canards; they are doing nothing. I imagine your design is indeed top heavy as well (at least, it gets that way as you go up). Is the tip over happening at a roughly consistent altitude?

What's the mass of your payload and how far along are you on the tech tree (assuming you're playing a career game)?

If you object to asparagus, what's your stance on parts clipping?

I've already redone the canards - I'm testing now.

I, uh, wouldn't know. If this one fails, I'll make a note of its and subsequent failure altitude, but I was tinkering with everything trying to hunt down the cause before, that it likely wouldn't have been consistent anyway.

Depends on the part. Minor things like bracers are okay.

EDIT: First test over. Fatal tilt began at 4500m, but was present before drop tank separation. Will try to shift mass below orange tank.

Edited November 2, 2013 by Artie

[Traches]

Seriously, your fuel lines on that thing are crazy. An imbalance that only happens after you've burned up a stage screams of a fuel imbalance. If you right click on a tank, you can see how much fuel is in it-- next attempt click around and see where your fuel is draining from.

[Artie]

I've been thinking about it, but I can't think how - the engines are all of the same type, and I only ever laid a line from one tank/engine to another, using symmetry to copy over to the other two tanks/engines.

For the record, the layout is as follows: Drop tank -> individual tanks -> central tank -> engines.

[Artie]

Update: I was just able to get it into space after removing the drop tank, and replacing it with three smaller ones atop the individual tanks.

[toomuchbrew]

At launch, if a tank doesn't have an engine, it is working against you. That is why asparagus staging works so well. At launch, it's the most critical because that is the heaviest your rocket will ever be. If you have a good TRW, you can mitigate the malus though.

[capi3101]

That's good to hear.

If you ever need to know the mass of your payload:

1) Go into the VAB and load up your rocket.

2) Discard the booster; leave the part that you're sending into space. Don't save.

3) If it's a manned rocket, go into the crew selection tab while still in the VAB and deselect everything. The game may gripe at you; it's okay. You want it empty.

4) Hit launch.

5) Go to map mode and click on the little "i" button to the right. It'll display info on your craft, including its part count and its mass.

I was asking about the payload mass to see what could be done about designing a serial-staged booster, but if you've got everything worked out, then there's no need.