Re: [...I thought that the angle of incidence was set by the airframe being
level with the waterline.  In my mind that has nothing to do with the center
of gravity and the size of the engine, but rather the front to back leveling
of the aircraft...   Curtis Krouse]
-----------------------------------

Hi Curtis,

Yes, I agree that the angle of incidence is set and measured relative to the
airframe -- for both the wing and horizontal stabilizer (HS).  What I'm
trying to do is optimize our HS angle of incidence for our airplane/engine
combination.  I'll try to explain the rationale...

The Legacy, as I understand it, was originally designed for an IO-360 engine
with the IO-550 a follow-on development.  The IO-550 weighs about 100 lbs
more -- so with no other changes the c.g. is farther forward.  This requires
a larger balancing tail load/force to maintain balance in the pitch axis.
If no change is made to the horizontal stabilizer's (HS) angle of incidence
(AOI) then the elevator will have to fly more nose up to provide this
increased downward force.  This increases the drag a little bit compared to
having the elevator fly in the neutral/zero degree position.  I'd like to
save any slight drag penalty by increasing the HS AOI (in the negative
direction) to get the elevator to fly at zero degrees while in cruise.  I'm
guessing that the -0.6 degrees end of the factory's HS AOI range is for the
heavier engines...  Thinking about how I wrote my question, I should not
have said "for the middle of the c.g. range" -- but "for the typical c.g.
for your airplane..."

Now, all that being said, a few degrees of cruise trim elevator deflection
isn't going to change the drag/cruise speed significantly.  But, the more I
read the LML the more I'm becoming (as I think Larry Henning once said) a
"Quarter-Knot Freak"...

Valin -- New QKF  :)
Legacy 173