Hi Thanks for the various contributions.
>From the discussion then, I get the impression that the quarter cord figure is empirical - but pretty close to the calcutated figures for RAF48 and AS504x wings. I guess that the important thing in designing a wing is that the spar is as close as possible to the centre of lift, so as to minimise twisting forces inside the wing. I guess also that the most important consideration regarding CG is that it must never move aft of the center of lift, you want to ensure that if the fan stops pulling, then the plane will tend to dive rather than nose up into a stall. If there a rule of thumb for calculating safe CG? Pete
