Here are the arms for our 320. The datum is the aft face of the firewall.

 

Oil                    -24.0   

Header tank         7.1

Wing tanks        37.8

Seats                43.0

Baggage (1)       63.0 *

Baggage (2)       82.0 *

Aft shelf           100.0

 

*Since the baggage area spans such a large range of arms, we broke it into the front half (1), and the aft half (2).

 

Hope that these numbers help.

 

Bill Harrelson

N5ZQ   LNC2   Long engine mount    O-320    small tail    standard gear

Duane & Bill,

 

Here's mine measured during very formal weigh in:

 

I/O 320, Aft face of firewall datum, short mount, standard gear, small tail, slightly overweight pilot....

 

-13.1 = Oil

   7.4 = Header

 36.4 = Wing tanks

 44.3 = Seats

 67.5 = Baggage - Front limit arm

 88.3 = Baggage - Aft limit arm

 74.0 = Baggage arm used in W&B calculations since most stuff fits forward where it's wider.

 

Eventually you will note that each aircraft is slightly different in W&B locations.  Theoretically, the CG range is measured from the aft face of the firewall - this compensates for different engines, mounts, props, etc.  Again, theoretically, the wing and the firewall haven't moved and neither has the CG range as measured from the aft face of the firewall.

 

What Bill (and most others) don't report is the location of the wheels (plumb dropped from the  axles, longeron level) and the weight on each for the empty weight with the canopy closed and latched.

 

I.E.  Mine:

 

-6.75  432# Nose (extension angle can cause a difference)

37.5   398# Right Main (Battery, Hydro, etc, dressed right - usually fly solo)

37.5   385# Left Main (190 # Pilot added has left main carrying 30# more than right.)

        ----------

        1215#

 

With a Moment of 26446, that yiedls an empty CG of about 21.8.  You can figure out what the pilot must weigh with a full header tank in order to keep the CG within the forward suggested limit.

 

Take some measurements and with some calculations and guesswork, you should be able to make some good judgements.  Who knows how heavy your engine compartment will end up being - I used all steel braided liquid lines, fireshielded everything, mounted the oil cooler on the firewall, used a remote oil filter, used more than 3000 tie wraps, added heavy silicon baffle seals, etc.  Who knows how much this would make my CG different than someone that used less heavy fluid lines, oil cooler on the front baffle, etc.

 

Enjoy,