Space plane fuel balancing question, am I on the right path?

[Wingnutt]

So I built a (for me) pretty solid space plane, it looks promising in terms of fuel usage to get to orbit etc etc.. but Im having an issue.

Fresh off the runway it handles like a dream, better than any other plane I have built.

The problem is I have 3 fuselage fuel tanks in a line. the one upfront is being drained first, then the center then the rear..

Due to the order the tanks are being drained the COM is shifting far aft and the plane stalls out..

I was thinking of running fuel lines as such as the center tank drains first, so Then the front then the rear, by the time the COM gets out of wack I should be into orbit.

I wish I could get the to drain equally at the same time but that doesn't seem to be possible.

Am I going down the right road here? Im at work so I cant test it till later.

[Keras]

If you use Jet engines the fuel is drained equally from all tanks disregarding all fuel lines and separators/docking ports. CoM shifting should only happen when you enter the rocket stage and by that time lift shouldn`t be an issue anymore. Then just pump some fuel forwards while you are in orbit to prepare for reentry.

Are you running an older version or mods that change engine behaviour?

[Wingnutt]

Ah, well the issue is the engine I am using isnt liquid fuel only, its rocket engine technically, the one that comes with the OPT Spaceplane V1.7 pack to fit their fuselage parts.

[capi3101]

If you're not adverse to mods (and I'm assuming you're not since you're already using a parts mod), I'd suggest two of them - first, TAC Fuel Balancer: it would allow you to set your fuel tanks to balance automatically, so they'd drain evenly. Second, RCS Build Aid - I would say that one is a mod worth serious consideration if you plan on doing anything more than just tinkering around with spaceplanes. Its key useful feature - a marker that shows you where your plane's CoM will be when its fuel tanks have drained, allowing you to predict if your plane will become flip-happy in flight (more to the point, allowing you to design your plane so that it most definitely won't get that way regardless of flight conditions).

Stock option is going to be a manual pumping of fuel forward. That'll work up to a point, but your CoM will still shift just as far aft as that final tank drains out. It's better to try to correct the issue while you're still in the SPH; lengthening your fuselage and trying to pull some dead mass forward is the standard diagnostic process for this particular problem.

[xtoro]

If you can get into orbit using one tank, then just lockout the fuel from the front tank so that the center tank gets used first. Once you're coasting to AP, unlock it. I suggest mods already suggested above, but if you don't want to use mods then locking should work fine.

[Fearless Son]

I use the same idea as xtoro. With almost all my spaceplane designs, I keep a small(ish) tank of fuel near the front of the craft, which is locked down so no fuel will be drained out of it without specific instructions on my part. I usually try to get to orbit on the tanks further toward the back, then once I am secure with my engines idling, I transfer the fuel from the locked front tank to the rear tanks. It helps keep the center of mass forward for most of the flight, but without reducing the total amount of fuel I have to operate on.

[ajburges]

As a bonus, a locked tank in front means you enhance aerodynamic stability as you ascend. Almost all my designs have the forward tank locked if the is a high moment of inertia with the fuel.

[tbarcello]

If you're not adverse to mods (and I'm assuming you're not since you're already using a parts mod), I'd suggest two of them - first, TAC Fuel Balancer: it would allow you to set your fuel tanks to balance automatically, so they'd drain evenly. Second, RCS Build Aid - I would say that one is a mod worth serious consideration if you plan on doing anything more than just tinkering around with spaceplanes. Its key useful feature - a marker that shows you where your plane's CoM will be when its fuel tanks have drained, allowing you to predict if your plane will become flip-happy in flight (more to the point, allowing you to design your plane so that it most definitely won't get that way regardless of flight conditions).

Stock option is going to be a manual pumping of fuel forward. That'll work up to a point, but your CoM will still shift just as far aft as that final tank drains out. It's better to try to correct the issue while you're still in the SPH; lengthening your fuselage and trying to pull some dead mass forward is the standard diagnostic process for this particular problem.

I agree on the RCS mod part, but you must be careful: let's say you have 2 tanks, one full of lf and other lf+ox and the center of mass somewhere between them. The rcs aid may show your CoM at the same spot when empty, but because you aren't using that oxidizer, it will actually shift back.

And I really wanna try the first mod you mentioned, thank you!

[Wingnutt]

Plane works great...

But.

I flew the shuttle up to the station, then switched back to the tracking station so I could jump to the science station and retract the solar panels.

I can't select or go to the station, or the shuttle or anything else that's in orbit..

What the hell?

[DCWarHound]

Plane works great...

But.

I flew the shuttle up to the station, then switched back to the tracking station so I could jump to the science station and retract the solar panels.

I can't select or go to the station, or the shuttle or anything else that's in orbit..

What the hell?

It's a bug,close and open ksp and it should work fine.

BTW the OPT parts are unbalanced (too powerful) so you should have an easy time making an SSTO with them.