How to set tank drain order when using jets?

[John FX]

So I built a laythe lander which uses jets and a rapier to get back to orbit. I have 4 tanks, set in pairs, with fuel lines which (so I thought) would drain the tanks with jet engines first which would then be dropped to save weight, then leave a couple of drop tanks for the rapier.

When I lift off, the jets start draining all drop tanks equally ignoring the fuel lines.

Is there a way (without setting the tanks to not be drained as this would take too much time to remedy during launch) of forcing fuel to be drained the way it used to, as in the fuel lines dictate which tanks are drained first even when using jets?

Edited October 16, 2015 by John FX

[Tex_NL]

You can try TAC Fuel Balancer. It allows you to pump fuel around at will.

If you set your droptanks to transfer out those will be drained first. And the rest to balance to avoid nasty weigh issues.

[Superfluous J]

I would suggest GPOSpeedFuelPump instead of TAC. It's a different paradigm for fuel pumping that I think is far superior and has a much cleaner interface.

If you want to go stock, disable the front tanks, then (possibly quickly) re-enable them when you drop the back tanks. Or set up action grou.... Oh never mind stock doesn't have that either does it?

[tseitsei]

Just pump the remaining fuel from the drop tanks to other tanks when there is enough room for it... works in stock and it's not that hard...

[sebi.zzr]

Well i don't know what your design looks,but it's not that complicated.You don't need any fuel lines,only decouplers!

1st: attach radial decouplers and first pair of fuel tanks

2nd: attach radial decouplers on drop tanks and fuel tanks with jet engines

Now use offset tool to drag decouplers in position you want.

This way the tanks with jet engines will drain 1st,then drop tanks and finally the main tank.

Edit:i'm using this to get rid of stock offset restriction.

Edited October 15, 2015 by sebi.zzr

[Red Iron Crown]

Decouplers++. Airbreathers (and Rapiers in rocket mode) don't care about fuel lines, they only care about decouplers. They will drain tanks evenly in a stage, with stage determined by the number of decouplers between a tank and the root part.

[John FX]

You can try TAC Fuel Balancer. It allows you to pump fuel around at will.

If you set your droptanks to transfer out those will be drained first. And the rest to balance to avoid nasty weigh issues.

I already have TAC fuel balancer and may well go that route although I was hoping for a reasonable way to handle fuel flow in stock.

Well i don't know what your design looks,but it's not that complicated.You don't need any fuel lines,only decouplers!

1st: attach radial decouplers and first pair of fuel tanks

2nd: attach radial decouplers on drop tanks and fuel tanks with jet engineshttp://i.imgur.com/9LIg1yn.jpg?1

Now use offset tool to drag decouplers in position you want.http://i.imgur.com/gCYNAEq.jpg?1

This way the tanks with jet engines will drain 1st,then drop tanks and finally the main tank.

Edit:i'm using this to get rid of stock offset restriction.

It`s a very similar design to the one you have posted and this looks like a good solution although one still requiring an odd construction method and yet another mod. I ended up just making the jets have their own tanks and not having any crosstank fuel flow at all.

I`ll take a look at GPOSpeedFuelPump, sounds interesting. I much prefer a solution where I don`t need to remember that I built the craft in a non obvious way.

Must say, I don`t like this way of not being able to force fuel to flow in the way your design needs in stock. Just because I have an airbreathing engine on board does not mean I completely wish to throw away staging and my control of fuel flow and be an SSTO...

I would hope things like this would not be an issue in a released game.

Myself (after around 10 seconds thought) I would make a new tab in the VAB where you set which way fuel flows. You could select a group of tanks, set them as the first set of tanks to drain and also set them to drain in a balanced way if you like, then you could set the remaining tanks in a similar way to drain in a specific order and in specific groups. You could even set which engines are fed by which group of tanks allowing for `interesting` designs.

It seems to be a natural thing to do while building the craft and would remove the need for external fuel lines which can explode on re entry.

Then rocket builders get complete control over fuel flow and so do plane builders. No need to learn fuel flow rules, you set them yourself.

That or, you know, just set fuel lines to have priority...

[Majorjim!]

Controlling fuel flow in a 100 per cent stock install is easy but it uses a few parts to achieve.

If you use the nodes between tanks twice (requires you to enable clipping in the console). In doing this you isolate that tank from the ship.

You are then free to route the fuel in any way you like using the fuel lines. This enables full control over fuel flow.

[Red Iron Crown]

^^ Neat trick for rockets, but doesn't work for jets.

[John FX]

Just had a look at GPOSpeedFuelPump and it seems to work exactly in the way I was wanting.

Setting priorities for groups of tanks to force them to drain in the manner you desire, even if you change your engine to an air breathing one.