I42 ...
A bit more info for you as promised. I hope it's of interest. Please note that the diagram/data below is for a Mk21 Chipmunk
NOT a UK Mil TMk10. The data is also 'representative' and
NOT specific to a particular aircraft. The diagram also shows a Narrow Chord Rudder and the absence of Spinning Strakes, both these MOD's will impact CoG Calcs. RAF Chipmunk equipment, e.g. Radios, were significantly different (heavier).
The CoG position is determined with the aircraft in the 'Rigging Position' (Fuselage Datum Line, Horizontal) as determined by physically levelling the aircraft with respect to the Forward Levelling Peg and the Datum Point, and is found in the usual way of taking moments about the Datum Point.
The Datum Point (Port Side) is an arbitrary position some 36 inches Aft of the Forward Levelling Peg ... both these positions are on the FDL).
In this example the CoG Limit of Travel is ...
Forward Limit (-) 6.80 inches Forward of CoG Datum Point
Aft Limit (-) 0.77 inches Forward of CoG Datum Point
MAUW 2,100 lb
Max Luggage Locker Limit 40 lb
Measured parallel to the Fuselage Horizontal Datum Line. The vertical position of the CoG was ignored provided published loading limits were respected.
For reference the RAF Pilots Notes (AP 4308 3rd Edition) quoted the following limits ...
Forward Limit (-) 6.48 inches Forward of CoG Datum Point
Aft Limit (+) 0.257 inches Aft of CoG Datum Point
MAUW 2,100 lb
Max Luggage Locker Limit 40 lb