The formula is actually a simple one.
Start by measuring the distance from a fixed point
on the plane. I use the end of the prop shaft or spinner
because it makes the math simple (no negative numbers)
and it works for tail draggers and tricycles.
Multiply distance from the fixed point back to the main axle
and the weight on the main gear.
Multiply distance from the fixed point back to the tailwheel
(or nosewheel) axle and the weight on that wheel.
Add these two numbers and divide by the total airplane weight.
The result is the distance from the FIXED POINT to the CG.
Jenny
ps.
It doesn't matter what units you use to measure and weigh
as long as you don't switch in the middle. (Don't weigh the
whole airplane in pounds and the tail in ounces or grams.)
Don't try to measure with mixed units like 2 pounds 4 ounces
or 2 feet 3 inches. Use 2.25 pounds and 2.25 feet
(or 36 ounces and 27 inches).
It does matter if you don't raise the tail on a tail dragger
to make the plane level. If you don't raise the tail when
you are weighing, the CG will be slightly farther forward
when the plane is in level flight.
Last edited by Jennifer Curtis; 04-08-2015 at 06:20 AM.