For a perfect w&b you'd measure the position of the wheels relative to
whatever reference place is selected for the rest of the plane. In the
absence of this information you will probably use the position that the
original w&b used for wheel location. You add the main gear together, not
average them. They should be in the same location (for/aft). Did you
level the plane laterally? That could easily explain the difference.
Cushions, equipment, bent gear, side loaded scales are also possibilities.

Maybe the most important part is to identify in detail what equipment was
in the plane at the time of the weighing and it's location. If it was
moveable, both weight and location needs to be noted. Exact
fuel state should be noted also. Plus or minus a gallon is not good.
Note the oil quantity.

A good example of the detail needed -- in what notch were the seats?
What was in the pockets in the seats? Was the towbar in the plane and
exactly where was it? Did you have any control locks installed? Where
were they? How much did they weigh? Everything that is not a permanent
non-moveable part needs to be identified and measured. This would be
a good time to make sure that everything that is installed is documented.
No extra stuff like mounts for portable GPS's, handheld radios, or headsets.

Obviously, it is much cleaner to do a weight and balance with NO loose
stuff in the plane and absolutely empty tanks.




In article , "Wayne"
wrote:
My plane, a 175B has an O-360 engine and a constant speed prop. I had
the plane weighed and and about to begin the calculations of finding the CG,
and it's measurement behind the datum. I'm a bit rusty there and would
appreciate what ever help you could do. Here is what I have.

While plane is leveled according to specs
Left main gear 644 pounds
Right main gear 631 pounds
Nose gear 528 pounds
Total, 1803 pounds.

I'm not real sure how they get the CG while the left and right weights are
different. Do they average them? I don't have the measurements for the gear
with me at the moment, I intend to use the standard values for the plane
rather than measing my particular plane.

What further information do I need? The shop is going to calculate it as
well, but I want to understand it as I do it. Thanks in advance for your
help.
Wayne