How do I make a tank of 'emergency fuel' that doesn't get used? (unless I need it of course)

[SignalCorps]

Sometimes (often in spaceplanes) I'll end up using more fuel than I expected, and not have enough left over for the air breathing engines, which makes it problematic for the pilots once they get back in atmo, and decide they rather not land nose first in the mountains at 300m/s.

I'll have a basic design of one central body with fuel for the rocket, and two liquid fuel tanks on either side for jet fuel, but the rocket engine is sucking up the fuel for the jet engines. How can I designate a tank 'no use', until I want to allow fuel flow or transfer it myself? (using ver 1.x)

Edited May 21, 2015 by SignalCorps

[Drew Kerman]

right-click to bring up the part menu and next to the bar that tells you how much fuel is remaining you'll see a Play arrow. Toggle it off and that will not allow any resources to be drained. Works for anything (batteries too)

[SignalCorps]

Oh, simple enough. Thanks.

[Snark]

That can come in quite handy for unmanned probes that may be in danger of going completely dead when they run out of juice. Just keep one battery in reserve. If the probe dies, you just toggle the battery back on and voila. (The game lets you toggle resource containers on/off even on a deactivated craft.)

[Murph]

If you've only got 2 wing tanks and you turn 1 off, you're going to have a serious fuel imbalance that compromises the ability to maintain straight and level flight.

Jet engines will draw fuel from anywhere, so you would be much better leaving the wing tanks enabled and allowing the rocket to use them. The rocket will be unable to use liquid fuel when it runs out of oxidiser, so the amount of LF-only that you start with is dedicated to jets only, regardless of the rocket engines draining the tanks themselves, assuming you start out with all LF-only and LF+O tanks 100% full. The amount of dedicated LF-only will remain unused in the rocket tanks. If need be, isolate the LF part of one of the rocket tanks instead, which will avoid compromising lateral weight balance (do it to the furthest forward tank, ideally, as too much tail weight is much more of a problem than too much nose weight).