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> Yeah, but now back to the original question by Ian, "Where is 11 to 29%
> of MAC? No one has answered that specific question yet and he and I
> would both benefit from an answer. Greg Nelson
<SNIP>
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Ian, the CG range is expressed in distance from (your) datum. Only if you
use the aft face of the firewall as your datum will the CG range be in FS
numbers. I used the aft face of the firewall for mine for the following
reasons:
1. The arms of the various stations are the same as the FS.
2. It's easier to measure stuff inside the airplane from the aft face of
the firewall.
3. It keeps the numbers a little smaller.
4. It's a fixed point that doesn't move on a particular airplane or
between airplanes.
The only possible disadvantages I could come up with (and they are pretty
minor) are:
1. In your initial W&B calculations the nosewheel moment is negative.
2. Oil moment is negative. (to solve this one, I computed a basic
operating weight and CG that includes oil)
By the way, here's what I measured as arms for various items:
Empty AC 22.46 (mine, yours will be different for sure)
Oil -24 (depends on engine and mount)
Header tank 7.1 (should be fairly close on all planes)
Wing tanks 37.8 (should be the same on all planes)
Seats 43.0 (should be close)
Baggage 1 63.0 (should be close if you seperate the
Baggage 2 82.0 areas, otherwise use 72.5)
Aft shelf 100.0 (should be close)
I separated the baggage compartment into two areas just like Cessna does on
the C150.
The arms for the fuel and seats were calculated from adding weight (fuel,
humans) and noting the change in CG on the scales and verified as reasonable
with a tape.
Hope that this helps,
Bill Harrelson
harrelson@erols.com
N5ZQ
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