topwinguk,

Your model has a wingspan that differs from the more common Seagull and Lanier ARF’s.

I have compared yours and the 68.75” wingspan model made by Seagull, finding that yours is 19% bigger (Yours is 26% scale of original airplane).
Hence, if you don’t have a better reference, the Seagull specs could be used for a first approach, in the following way:

The CG of your model would be located at 1.79” (1.5” x 1.1927) aft the LE at the wing tip.
The throws of your model would be as follow (Seagull throws x 1.1927):
Aileron: 7/32” (Low) and 7/16” (High)
Elevator: 7/16” (Low) and 1-1/32” (High)
Rudder: 7/8” (Low) and 1-1/2” (High)

I have attached a schematic of a graphical calculation based on a drawing of a full-scale kit.
I have found that the ¼ chord for every section of the wing remains on the same line, which can be measured as 4.55” (4-9/16”) from the leading edge at the wing root.
That location of ¼ chord of the wing is a safe and conservative first location of the CG, which should be fine adjusted according to what the first test flights indicate.

The graphical location is very close to the location calculated above.

Please understand that these numbers have been determined on airplanes that may have slight differences in shape with yours; hence, take them with a grain of salt.
For a more accurate first location of the CG, I recommend you to use the following on-line calculator:

http://www.geistware.com/rcmodeling/cg_super_calc.htm

Other interesting links:

http://www.horizonhobby.com/Products...ProdID=SEA2100

http://www.seagullmodels.com/Admin/c...amImage/28.pdf

http://www.nasm.si.edu/collections/a...d=A19990171000

http://en.wikipedia.org/wiki/Leo_Loudenslager

http://findarticles.com/p/articles/m.../ai_n13641172/

Best luck with your project!