Setting desired fuel flow in VAB/SPH and in flight - equal fuel levels in plane tanks

[Fifi]

I would like to suggest an option to setup fuel flow in each fuel tank during construction in VAB/SPH and during flight (like the fuel usage on/off option).

I made a picture (sorry for this quality) about how the center off mass moves in an aircraft after burning about 1/2 of fuel now and how it gonna look if my suggestion would be approved:

With this option we would be able to (for example) make a plane and set all fuel tanks to have the same fuel level (so the fuel will be pumped all the time), which will stop planes from losing mass balance (by the moving center of mass D: ) during longer flights.

I would also like to suggest an option for enabling/disabling fuel usage of a certain tank in VAB/SPH (it's already possible, but only in flight), so we don't have to do this every launch.

Thanks in advance for taking this into consideration.

Edited August 11, 2013 by Fifi

[Scoundrel]

You can manage your fuel flow easily enough via the clever use of cubic struts and a handful of fuel lines. Check out Rune's or Cupcake's (or even my own, if you can find them) VTOLs to see how it's done.

[Fifi]

You can manage your fuel flow easily enough via the clever use of cubic struts and a handful of fuel lines. Check out Rune's or Cupcake's (or even my own, if you can find them) VTOLs to see how it's done.

But this increases number of parts, which would cause lag on bigger designs. And it's a workaround, because normal fuel tank weights so much, that two additional valves wouldn't be a problem, while it would look more aestetic than complex designs.

In your and Rune's constructions it actually looks good, because they are not jet planes. But jet plane looks better if it doesn't have a lot of stuff standing out of the fuselage (I know that some people will just clip the part inside, but it's bug using and it looks awful).

[Scoundrel]

But this increases number of parts, which would cause lag on bigger designs.

Not by any noticeable amount. Fuel lines have virtually no effect on lag, so you shouldn't be afraid to use fuel lines.

But jet plane looks better if it doesn't have a lot of stuff standing out of the fuselage (I know that some people will just clip the part inside, but it's bug using and it looks awful).

Actually you (usually) have to insert fuel lines without using parts clipping because, unlike other parts, fuel lines don't react well to clipping. The best way to do it is by zooming in and placing them in the gap between tanks, though there are some people who install them inside, which doesn't work that well a lot of times. That said, you do have a point about aesthetics, which means that as builders we sometimes have to accept that functionality trumps aesthetics. My early non-clipping X-4 (my x-48 tribute) looked decent enough... except for the fuel lines that ran to the engines, which was something I had to accept in order for it to maintain its CoM... nowadays I'd just clip the intakes for airhogging and run the fuel lines through the wings.

Anyways, you can either look at it as a negative, and hope fuel balancing becomes stock or use a mod; or you can think of it as an engineering challenge to overcome, and see if you can't problem solve it.

[Fifi]

Och, I didn't know that it doesn't affect lag.

But anyway it would look better if the fuel tanks would manage fuel balance by themselves.

I have, for exampe, very simple supersonic plane (with non-delta wings xD but they looked better and KSP doesn't notice the difference ):

But with more fuel lines it will start to look strange.

(as for now it begins to increase pitch after burning 1/2 of its fuel)

Edited August 11, 2013 by Fifi

[Fifi]

*bump* I think this would also help non-jet planes.

[Scoundrel]

There's a lot wrong with your plane that balancing the fuel won't help: CoM is too far forward of your fuel 0 state; CoL is forward and low of where it needs to be (it should be just above and a little bit behind your CoM), and as your fuel is reduced, it moves even more forward, making the craft more unstable; and a bunch of other things that I won't mention because this thread is about fuel flow.

But let's say for the sake of argument that Squad implemented fuel balancing and your plane remains as you have designed it: your plane would still pitch up as it is now because your fuel 0 state would push the CoM back enough that your plane becomes unstable (less noticeable now in .21 though). Now, if you built your plane so all your fuel flowed into one tank zeroed at the plane's CoM, and fuel lines ran from there to the engines, you wouldn't have any problems with fuel drainage. You just have to engineer it that way.

Also, this would cause problems for some people's non-plane landers, as their main tank drains at the same rate their drop tanks do rather than empty their drop tanks first so their ascent stage wouldn't be half empty upon landing. We'd start seeing "we need assymetrical fuel flow" threads!

[Fifi]

Without fuel balancing I could only make it barely-flyable all the time or good-flying with the full fuel tanks. I just took the second choice, because I don't want to workaround missing valves and make my plane looks bad. The first choice would also destroy aerodynamic specification.

Even perfect design with CoM and CoL in proper places will became messed up after time, because the CoM moves while CoL can't. Of course we can fix this by adding fuel ducts, but it doesn't make sense because in normal, real-life planes valves exists (and we can even redirect fuel flow and crossfeed as we wish). So why do we have to make our design ugly or more complex instead of having realistic fuel flow?

Now the only thing we can do without fuel ducts mess is to do a lot of test flights and put CoM at fuel 0 CoM - but it will fix only the begining and ending state, not the interim state. Even with full and 0 fuel CoM at the same point, the 50% fuel state will have CoM moved backward - because planes lack fuel balancing.

The second problem is that even current workaround is uncomfortable, because precise centering the fuel 0 state to always be CoM is impossible without any marker (like CoM, CoL and CoT markers).

Of course we shouldn't make KSP too easy, but - to don't make a contrast - we shouldn't also make it much harder than reality.

Edited August 15, 2013 by Fifi

[Fifi]

(I only want to notice that I changed my previous message and want to say sorry about the previous one - I just had a bad day)

[Scoundrel]

Without fuel balancing I could only make it barely-flyable all the time or good-flying with the full fuel tanks. I just took the second choice, because I don't want to workaround missing valves and make my plane looks bad. The first choice would also destroy aerodynamic specification.

I built a copy of your plane from your pic (the only major differences being that I had 1 ladder and the rear landing gear was on the engine tanks rather than the wings) and it flew fine as the SAS auto-trimmed the craft as fuel drained; the only time I really noticed a pitching problem was high speed/high altitude flight and that once that first tank was drained things got a little dicey for me because the CoM was a little too far back and low from the CoL so when the fuel drained it became really unstable. So I do understand your frustration.

Even perfect design with CoM and CoL in proper places will became messed up after time... <snip> ...Of course we shouldn't make KSP too easy, but - to don't make a contrast - we shouldn't also make it much harder than reality.

Okay, I just typed out a massive reply that was essentially a 2000 word essay on fuel distribution and fuel feed systems - complete with fuel feed diagrams from 747s and other aircraft - and all about how fuel systems in "real life" aircraft are incredibly complex and that KSP's problem is that it's fuel system is really, really oversimplified... and I had to delete it because as I went to post I asked myself "What the hell am I doing?!"

After some introspection I realized that what we're really talking about here is whether or not the devs should make a solution for us or if we should have the option to engineer the solution. Now, I like to engineer solutions - it adds depth to the game for me. Thus my position will be opposite yours no matter how many rationalizations we post because your priorities are different from mine. We are then left with 3 questions: 1) how can you (and people who agree with you) get what you want, without impacting what I (and people who agree with me) want?; and 2) could this be implemented stock without wrecking a whole bunch of people's asparagus designed rockets and drop-tank designed long-range aircraft and spaceplanes?; and 3) is this so vital that we really want the devs to spend time implementing this when they could be doing something else?

Judging by the fact that the only posters are you and I, and that this thread has a low number of views, I suspect that the community doesn't feel that it's a priority that the devs should be pursuing... at least at this time. Therefore I would suggest playing around with TaranisElsu's TAC Fuel Balancer first before bumping this thread any further to see if it really is the solution you're looking for.

(I only want to notice that I changed my previous message and want to say sorry about the previous one - I just had a bad day)

No worries. I felt bad because it seemed to me that you took my post as a personal attack, so I wanted to wait a few days before responding so I didn't try to make things worse. I honestly didn't mean to imply that you're a crappy designer or anything like that; I just wanted to illustrate that fuel balancing wouldn't solve all the problems with aircraft design. Likewise I know the X-4 I posted hasn't flown worth beans since .19 - prior to that it was a plane that you flew just by trimming it; I posted it because I wanted you to see the tank setup and the plumbing so you could use it for your own designs since I too used to get frustrated at KSP for its fuel management issues (I had about a dozen or so aircraft threads that were lost in the forum crash back in April that explored fuel symmetry). Using that as a base, I have no doubt that you could set up your planes to not only be balanced no matter the fuel state, but that I bet you'd find a way to make them look good too!

[Haze-Zero]

I wonder if you could yourself could possibly make a new resource 'JetFuel' that flows like RCS and then make all your jet engines use the new Jetfuel?

[Fifi]

After some introspection I realized that what we're really talking about here is whether or not the devs should make a solution for us or if we should have the option to engineer the solution. Now, I like to engineer solutions - it adds depth to the game for me. Thus my position will be opposite yours no matter how many rationalizations we post because your priorities are different from mine.

First of all - thank you for not being angry at me. And sorry again, I just posted the first version without thinking how it all looks from your perspective.

And about the problem - I also think that engineering things by myself would be better, I just want it to be done via setting fuel flow chart or something, instead of putting pipes everywhere.

(because on a real plane all of that stuff would be hidden inside the tanks/fuselage and looked a lot better)

I suggested option for fuel autobalance, because it would be easier to implement, but of course some "fuel management computer" part with fuel flow diagram designer will be way better and more challenging.

About my designs - I actually completely ignored the 0 fuel states, because there's no other way to check it other than burning all the fuel or counting tanks (which fails if they are of different size and/or different empty weight). I mainly took care of good flying abilities at full tanks, aiming for fuel flow corrections after Devs make it more configurable.

I wonder if you could yourself could possibly make a new resource 'JetFuel' that flows like RCS and then make all your jet engines use the new Jetfuel?

I guess yes, but it would be better if we could adjust how it should flow manually, like Scoundrel said. I just want to hide all those yellow pipes and focus on planning them instead of pushing editor to its limits to place them in a strange configurations. xD

Edited August 15, 2013 by Fifi

[Scoundrel]

First of all - thank you for not being angry at me. And sorry again, I just posted the first version without thinking how it all looks from your perspective.

It's all good my friend. I try not to take things on here personally because sometimes people have bad days, and sometimes people are not reading and writing in their native language so occasionally a little miscommunication happens - and I recognize that I too played in a part in that, so I don't judge.

And about the problem - I also think that engineering things by myself would be better... <snip> ...but of course some "fuel management computer" part with fuel flow diagram designer will be way better and more challenging.

That suggestion is much more reasonable than an auto-leveller, and I would support that idea. We could even do a more primitive "hands on" version using radial "valve" parts that go on or in between tanks to control fuel flow direction. Since they wouldn't have to have physics on them, they wouldn't truly count as parts, and they wouldn't have to be more than 50 polygons in size so it wouldn't affect graphics performance to any real degree. It would keep with the spirit of KSP and, as being just a part, it wouldn't ruin asparagus stage rockets or older designs.

About my designs - I actually completely ignored the 0 fuel states, because there's no other way to check it other than burning all the fuel or counting tanks (which fails if they are of different size and/or different empty weight). I mainly took care of good flying abilities at full tanks, aiming for fuel flow corrections after Devs make it more configurable.

That's fair enough. I've built so many spaceplanes that I just use the old trick of building around a single fuel tank that feeds the engines, and set up the rest to feed to it so I always can control my CoM. There's a few other tricks too, but unless you really spend a lot of time messing with setting up fuel flow it probably isn't worth the while to develop them.

I wonder if you could yourself could possibly make a new resource 'JetFuel' that flows like RCS and then make all your jet engines use the new Jetfuel?

It sounds like a nice idea, except that on multi-stage rockets or planes you would find your upper stages drained of fuel to keep the lower stages going. There are plenty of threads with "RCS tanks in action groups" and such because of it. It would be even worse if you had drop tanks for your plane.