For the horizontal tail efficiency, let’s pick a number...we’ll assume that the tail is in the normal location, so we’ll use 0.5 in our formula. Here’s what our formula will look like.

Formula :

CG = [ 0.17 + (0.30 x (( TMA ) x ( SH ) x HTE ))] x 100
                                       MAC         SW

Formula with example values :

CG = [ 0.17 + (0.30 x (( 33 ) x ( 165 ) x 0.5 ))] x 100
                                       12          875

Formula results :

CG = 24.35% of the M.A.C. or 3.09"

It is important to remember that this is measured from the leading edge at the M.A.C., not at the wing root...or event worse, at the wing tip.

For those incline to utilize "T" tail designs, let’s look at what happens when you change to that configuration HTE will now be 0.9 instead of 0.5. All the variables appear below. We have changed the desired location of the CG by almost 1" just by making changes to the tail feathers. Remember, this formula was championed because it includes consideration for the tail feathers.