Tracing Imbalanced Fuel Flow; (Story And Screenshot Heavy)

[Titler]

Well then, my Kerbals decided to go slow and steady on their way to the Mun; first they built an orbiting station with plenty of fuel storage space, a detachable crew compartment, with the windows nicely lined up so they could wave farewell to the brave Kerbals who would make that first trip down from the final docking attachment. No robotic probes first, every step would be manned! Which is why the docking ports have extending ladders (closed in the shot below) to catch Kerbals who might fall off the station...

The first lander was tested heavily on Kerbil for stability and control; and although Mechjeb's mechanical brain was sometimes too precise, and crashed replacement crew right on top of of Munbase Alpha and Beta, eventually Jeb and his brave crew learned to pull Mechjeb's circuits out a little early, docked up with Munbase Gamma, and on the first try for the surface, made it into the history books inside Budgerigar 1 (Humans have Eagles, majestic soaring birds; Kerbals have small green Budgerigars!). Rolling a D6 dice on the surface for the honor, it turned out Bill would be the first Kerman on the Mun... but after pootling about quite effortlessly, they all stayed to enjoy watching the Sun rise over the horizon, before turning for home...

Except! Disaster! They didn't have enough fuel to make a connecting orbit back to the station. And this is where my question comes in... The Munar lander was redesigned again and again, slowly getting heavier as it took on more fuel to try and get the complete unit back to the station, ready for redeployment, in the next stage of searching for Munoliths. But in the Marks 3 to the current 5, a problem with fuel balancing has arrived, and I can't work out where it is. I've uploaded the file for the current lander here. I've also taken a comparison shot on the Munar surface near the original lander to illustrate the new design. I may have to settle for abandoning the wheels to return the crew, but I'd like to understand what's happening with the tanks, because I can't solve the issue myself...

A newer model is to the left; as you can see I've used a little overlapping to mount small tanks around the inner framework. 2 between the frames, 2 pushed into the central tank, and 2 small ring-tanks on the end of the central ones. On the original, the engines burn identically, and run out of fuel at the same time. In the current, the central tanks won't empty unless linked to the tanks mounted horizontally by the engines. Linking all of them up with mirrored fuel transfer drains them correctly, but the engine on the opposite side to the ladder runs out of fuel about 30 seconds before the other. As far as I can see both have access to equal fuel reserves, and I expected the central tank to fill both as they drained. They are mounted in identical positions, and the craft is correctly balanced for both thrust and centre-of-gravity. But that engine always burns out first, and sends the craft into a fatal spin. I've tried transferring fuel to the central tanks, and the central to the engines directly to try and force balancing that way but that hasn't helped. I've added a single engine central, under the lander to provide more thrust and hopefully change engine flow but again, the rear engine always drains too quickly, even though it should only be drawing from identical doubled tanks between the struts.

So... does anyone know how to regulate the fuel flow to the engines in the above design? Please download the file, mess around with it on Kerbal, and tell me if so!

[Jason Patterson]

You've got tanks inside of other tanks and all sorts of crazy mess in that rover. Somewhere or other you've created a fuel feed loop. As a result, the rockets are only pulling fuel from one of the two branches, leading to your problem. Solution - rebuild at least moderately sanely.

[Titler]

Well that's the million-kerdollar question; where the loop could be. The model accepts placement like this, and all the fuel is visible to the lander and in it's Resources tab. The two middle tanks, and the roundel tanks drain to the central, and the two horizontal on each side drain left tank first then right tank (when looked at by an observer) so I can see where the usage is going... what I can't see is why the rear mounted engine is running out of fuel quicker, because it doesn't, as far as can be traced, have access to more fuel than the other radial on the opposite side (both start with 2x 90), nor is the centre of gravity off enough to suggest it's trying to move more weight. Mounting the central to both horizontal tanks to try and balance out usage doesn't solve the issue either. I'd prefer to keep the tested chasis if possible of course, rather than start from scratch again... the bill may not have been presented yet, but Kerbal Accounting may not be quiet forever!