This has vexed me as well.  I haven't been able to find a reference table listing appropariate CG ranges.   Nonetheless, others in this forum have said to go ahead and insert the default value listed in the FMC (27% I think).  I do that but have found that the aircraft can sometimes nose up too easily slightly before Vr.   I generally add a few clicks of nose down trim from my joystick to compensate and don't have any problems.  My apologies to CS for this clumsy work-around in an otherwise superb sim. 

Chris

Any more ideas?

Let me say this- the CG value you see (which cannot be changed) in the weights page of the FMC is ***NOT*** your CG.  Do ***NOT*** use that number when computing your takeoff speeds and such on the next page.

You need to use your actual CG number.  So long as you've loaded the plane accurately, your CG will be close to 50.  In my experience it's quite usually 46-47.  I load the plane with FSPassengersX, and it's manifest pages (where it gives you the ZFW and such) will tell you what the CG % is.

Your take-off trim calculation should not ever show something outside the green band of the trim position indicator (left of the throttles from the captain perspective) and typically will be around 1.00-1.75 if you're loaded in a balanced state.

The 27-28-ish number that I'm telling you above NOT to use is why ALH is getting a 5-5.75 trim calculation.  If you put that in, and you're not that nose heavy (and you never should be) your plane will pitch up abruptly, perhaps even before you reach V1 speed!

Hope it helps.