Re-connecting fuel tanks? Is this a bug or am I doing it wrong?

[SpaceGoblin]

So I have a ship with a few rocket stages around the outside. Some have 2 fuel tanks, some have 3.

It gets to be a lot of different pieces in front of me, and I misclick and accidentally pick up the top fuel tank in a stack of 3 tanks, which make up a rocket column. I can't seem to put it back exactly, and decide to just grab a new tank from the menu of the same type and put it in the empty spot I created.

I do this, and it seems to be exactly in the right spot. But when I launch, it becomes immediately clear that fuel is not being drawn from this replacement. Even though it's in the same position in the vertical stack, The engine is pulling from 2 fuel tanks now instead of 3. I have to fully rebuild that entire rocket column to get it to use all 3 tanks.

So I try another test. Same thing. I can break apart a rocket and put it back together (same pieces) and I will see the fuel not being used in the piece I picked up.

Am I doing something wrong? How can I force tanks to feed into each other?

[phunk]

It sounds like when you attach the replacement tank, you're attaching it to the tank next to it instead of the tank below/above it. Play close attention when you reattach it, you should be able to see where it's connecting before you click. Try changing the camera angle so the tank next to it is not behind the mouse pointer when you're trying to position it.

[Smidge204]

Some screencaps would help. It sounds like maybe you're accidentally sticking the tank to your rocket via the side, rather than the end. In other words, you have a stack of tanks that is connected radially to a central column, and you're sticking the new top tank to the center column instead of to the top of the stack. If you can remove the lower portion of the stack and the top tank stays attached, that's what is happening. It can be very tricky to get things to snap into the correct place sometimes.

If you're sure it's attached correctly, that's probably a genuine bug. You CAN manually transfer fuel (Right click on one tank, Alt+Right click on another and click "In/Out" as appropriate to transfer fuel)... but that's not a solution at all.

Edit: Ninja'd by one second!

=Smidge=

[SpaceGoblin]

Cool thanks. I will get some screencaps tonight, because I was sure I had it lined up exactly on the decoupler, and with the tank below it.

Might have a bug here.

[phunk]

What kind of decoupler? If you mean a radial decoupler, that can't work, the tank can only be connected to the decoupler OR the other tank, not both. A stack of tanks will need to be attached with a single decoupler, then struts if you need to strengthen the connection (the struts will disappear when the decoupler is activated).

[SpaceGoblin]

Here's a MS Paint I did of my rocket. I can take actual screenshots later tonight if it helps.

So I have a central rocket, and 2 side rockets. On the left is all the pieces (fuel tanks, decouplers in green, capsule on top, engines below).

On the left is everything joined together. When I put it together, I make the central rocket first. Then I attach the decouplers on the sides. I then attach the side fuel tanks onto the decouplers, making sure visually that they are not crooked or attached wrong.

On the finished rocket, I was busy putting other pieces on and I accidentally grabbed the tank marked with the X. I was having trouble getting it back on perfectly. So I grabbed same size fuel tank from the menu, and attached it to the empty decoupler in the same spot. I made sure to line it up with the tank below, and I do this by moving the tank on my cursor down until it turns red from being inside the tank below it, and then up slowly until it turns green. Also the round edges get lined up perfectly, so it is straight up and down.

But when I launch it, this side rocket where this happened depletes fuel faster on the bar. It isn't using 3 tanks of fuel. If I rebuilt that entire rocket column, all 3 tanks replaced, it works fine.

It is as if the replacement tank isn't being considered as part of the "group" any more. This hasn't happened every time. I've only noticed it on rockets with a lot of tanks and parts, and after I've already launched once and aborted to fix something.

[phunk]

The way you describe building it, only one of the decouplers will actually be connected on each stack. The game engine won't allow what you're attempting.

Two options:

1) Get rid of two of the decouplers, add struts for strength. The struts will disappear when you decouple, but they will also eliminate the decoupling force so you may want to add seperatrons to push the stack away when it decouples.

2) Add the side tanks individually, attached to the decouplers instead of the tanks above/below, and then connect them with fuel lines.

[SpaceGoblin]

Whoa, that is very interesting. This could change a lot of things.

I've built about 15 rockets using this somewhere in each. It has been difficult for me to get a stable rocket into orbit, without it leaning during liftoff or not having the stability or fuel to get there. I did manage to get a guy to the Mun but stuck there (wasn't easy), and all attempts so far to built a better rescue rocket have not been successful. This is with a few science unlocks, so I've began to wonder what I'm doing wrong. I don't mind learning through failure, but I would have never figured this out.

I will experiment with this new info tonight! Thanks much!

[aimeilian]

A few other things to note in addition to the comments about radial decouplers:

1) ctrl (or cmd if you're on a Mac) Z will undo any kind of foul-up you make grabbing the wrong part Note that, at least in .22 (I haven't upgraded to .23 yet) it is just a little buggy in that A) it leaves an unattached copy of what you just ripped off (i.e. it doesn't "erase" what you accidentally moved), and occasionally it re-connects struts wrong... but I can't tell you how many times that key command has saved me a lot of fiddly work fixing things that I pulled apart by mistake!

2) Stability issues can be caused by a number of different things -- weight being placed asymmetrically, a rocket being too top- or bottom-heavy, turning too hard or going too fast, etc. There are some parts that can help with stability, all found under the Control tab in the VAB/SPH. Namely in-line stabilisers (reaction wheels) which act as big gyroscopes to help keep a craft going straight. Try experimenting with these to see if they help your rocket fly true.

3) Also note, the stabilisers and any aerodynamic control surfaces won't do you much good unless you turn on SAS. Think of SAS as cruise-control for your craft: it activates stabilisers and control surfaces automatically to keep your vehicle on the same trajectory, but manual control input (WASD) will override it and "set a new course." Turn on SAS by hitting "t" before launch; if your craft is built well it should help keep it going the right way.

Hope this helps!

[Kasuha]

There are two ways how to attach things.

Either you attach them by their attach points. These are the green balls at both ends of each fuel tanks. When connected through them, the fuel can flow between them.

Or you attach them radially. If you attach a fuel tank this way, fuel cannot flow from it unless you attach something to it which will use that fuel (e.g. engine).

You can affect how the thing will attach.

First two images show how you attach things via attach points - you rotate the rocket so you keep the new part in space. Then you bring it near the attach point and it snaps in. You can tell it's attached correctly because it's snapped in position and won't move even if you move the mouse a bit.

Second two images show how you attach things radially. You point your mouse at the surface where you want to attach the part and if it can be attached to that surface, it will be visible there. Even if you move it over an attach point, these attach points won't connect, the part will still be attached only radially and won't allow fuel to flow to the tank which is below it. If you move your mouse, the part will follow your mouse movement.

Attach point attachment:

----------------------------

Radial attachment:

Edited December 19, 2013 by Kasuha

[John FX]

I think what is happening is that when you removed a tank connected to the green blob, you reattached it radially to the tank next to it which stops fuel flow (very very easy to do). Make your center stack first then add full stacks to the side. This will maintain fuel flow. Tank adjustment on side stacks can be unreliable.

Also, if you accidentally pick up a part and it is hard to replace try CTRL-Z to undo (pointer must not be on the part list for this to work, move your pointer to the main VAB/SPH window)

That is the easiest solution for your particular problem although it does not help you currently...