Outpost Landing, What am I doing wrong?

[Wulfonce1988]

So after 200 hours of playing ksp, I still can't seem to land an outpost on the moon.  I'm basically building a horizontal "hotdog looking" base complete with all the required components that sits on several landing struts along its length.  I have no problem getting it into orbit around the moon, however when I try to land it, the weight balance shifts as the fuel burns up, making it completely un-flyable after about 20 seconds.  I've tried everything I can think of.  Keeping the fuel in the middle, keeping the fuel on the ends, keeping the engines in the middle/ends, adding a butt load (unit of measurement) of RCS thrusters all over the place, adding an excessive amount of stabilization wheels,   but nothing seems to work.  The balance is dead center before the decent but due to the different modules all over the base, the balance changes once the fuel starts to drop.  I even made a prototype, just using fuel tanks alone without the other modules, to try and make it stable.  It sort of worked but again, once the fuel gets to low it might as well be a flying brick.

I feel like I'm missing something obvious.  I see all these youtube videos of people landing horizontal bases, and at much higher speeds then what I'm attempting to do.  They fly it in like Tom Cruise and set it down effortlessly... probably while drinking a beer with there other hand.  What am I doing wrong?

[TheFlyingKerman]

1 hour ago, Wulfonce1988 said:

the weight balance shifts as the fuel burns up

That is obviously the problem. Design your base so that the center of thrust aligns with the COM when empty. Then adjust fuel level in various tanks so that the COM remains along the same line.

[DeadJohn]

The easiest way IMO is to keep all your fuel near the middle (mass-wise) of your base, so that the center of mass does not shift as you burn fuel during landing. Here are some ways to do that:

1) Design your base starting with fuel tank and engine as the center core, then build 2 or more "wings" that extend sideways. All wings need to be similar masses.

2) Design your base without any fuel or engine. Then find the center of mass indicator, place a docking port or decoupler just above or below, and add fuel and engines to that port. This is similar to a "skycrane" concept.

3) Build your horizontal base in a straight line, more like a rocket and have the engine aimed lengthwise. Land vertically on the engine, then use reaction wheels or RCS to tip over.

[Fierce Wolf]

What i did: Use 8 side mounted engines and a main engine on the back of the base module. Once the landing starts, turn off the main and on the side rockets. Adjust thrust limit on the one's that are pushing too hard and try to keep it even, you should have enough time to check which rockets need compensation. Sounds complicated but it's actually simple, becames routine after the second module of your base.

[Foxster]

I'm guessing that even though you have an even distribution of fuel tanks they aren't being used evenly and so the CoM shifts. Check out the fuel priority setting for the tanks and make sure that it is set the same for symmetrically mounted tanks.