This is what they emailed me today:
Thank you for contacting Product Support. Yes, the Cap 21 was made by Great Planes Model Manufacturing. I would need to know which version of the Cap 21 airplane you have.
The Cap 21 L version was sold to Kitty Hawk many years ago (I have a copy of the archive manual). The manual does not list the CG
We also have a copy of the Cap 21 40 Size
We have a copy of the plans on disc and would unable to check the CG location this way.
Cap 21 L:
Section 18: Prepare the aircraft for flying
Complete the installation of the radio, engine, and linkage. Springs provided in the kit are used to connect the tail wheel steering arm to the rudder horn. Add the rudder cables and aileron servo clevis rods. Following are the recommended control surface throws for general sport flying.
Aileron: 5/8" up and 5/*" down
Elevator: 3/4" up and 3/4" down
Rudder: 7/8" to the right and 7/8" to the left
For maximum aerobatic performance, including snap rolls, the recommended control surface throws are:
Ailerons: 1" Up and 1" down
Elevator: 7/8" up and 7/8" down
Rudder: 1 3/8" to the right and 1 3/8" to the left
Add the engine "off" switch as recommended by the engine manufacturer. Perform a tip-to-tip balance of the wing by holding it upside down and supporting it from the leading and trailing edge at the center. Add weight to the light wing tips as necessary.
The manual for the Cap 21 40 airplane can be found on the Great Planes website (please refer to partss listing and manuals)