Jerry wrote:

   If we want to angle the engine off thrust, where is the pivot
point?  Center of engine?   Prop flange face?  I have often wondered
about this.

Paul Lamar responded:

Looks real good. Good idea with the laser.
Prop flange center as that brings the flange out
in the center of the cowl regardless of the off set angle or
down thrust angle. That should be our reference point.

More precisely: in unaccelerated level flight(*), the thrust vector is
perpendicular to the prop disc and passes through the center of the prop
flange. So you can "pivot" the engine around any point you want, but
recognize that using a pivot point that is *not* the center of the prop
flange will both rotate the thrust vector (the desired "offset") *and*
translate the thrust vector (relative to the airframe). Translating the
thrust vector will cause the airframe to fly in a different attitude
(center of drag will *always* be in line with the thrust vector).

Russell Kent

(*) things get funky in climb out, thus "P factor".



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