The formula is the sum of all moments both positive and negative divided
by the total weight regardless of what reference point is chosen.

Usually a reference point is chosen at the tip of the tractor spinner so

all the

moments are of the same sign. The CG position is then the distance aft from
the tip of the spinner. As I recall this is the way it is taught in PP

ground school.

Another strategy is to use a point in space, far enough ahead of the fire
wall to account for the longest spinner and lightest engine, say five feet.
(make a spot on the bottom center of the fire wall to hang a plum bob from).
With the plane in flying attitude, mark the floor at the tip of the plum bob
and the reference point for all further calculations is five feet out in
front of the mark on the floor. The calculations are easy, and the point the
calculations are based on won't change even with the spinner, prop or engine
off.

Lynn E. Hanover

 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

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