On May 23, 1:53*pm, "
wrote:
I'm working with a Cessna 172A, which is the '59 model.

It has a full panel with a pair of KX170s, and an ADF. *It has been
modified with the 0-300D engine which supports a vacuum pump.
This is the 6 cylinder engine with Millenium cylinders. *I don't think
they add much weight -- but it would be forward if they did.

According to the paperwork, the empty CG is so far forward that
I can *barely load it in limits. *With one in the front seat, it
requires
a 40# weight in the baggage compartment. *With two in the front seats,
I don't think you could put enough weight in the baggage compartment
to get it in limits, tho leaving some gas out does help. *With 3 in
the
airplane, it is at gross and in CG but is still close to the forward
limit.

It flies as if the CG is forward. *Takes a good effort to really get
it
planted on the main wheels without touching the nosewheel.

What is your empty weight and CG? We have four 172s here but
they're all at the airport along with the paperwork so I can't quote
it exactly, but I think the CG is around 38" aft of datum. I'd have to
check.

Are you landing with zero flaps? That'll make the nose heavy
in the flare. Have you looked back while in level cruise to see where
the elevator is? It should be angled down slightly with respect to the
stab if the CG is OK. If yours is streamlined or up a little, you
probably really do have a forward CG. Is the trim properly rigged? Do
you have the trim indicator centered during climb, or is set nose up?
Misrigged controls on old airplanes is distressingly common.

But where would the weight come from" The TCDS for the O-300
indicates that the engine weight for the D is the same as the old A
model, which that airplane started with. The Millenium cylinders won't
be any heavier, at least not enough to notice.

Check your CG range numbers. From the TCDS for your airplane:

C.G. Range Normal (+40.8) to (+46.4) at 2200 lbs.
(+36.4) to (+46.4) at 1733 lbs.
Utility category (+38.4) to (+40.3) at 1950 lbs.
(+36.4) to (+40.3) at 1733 lbs. or less
Straight line variation between points given.
Empty Weight C.G. Range: None

Dan