ESM A-1 SKYRAIDER VIETNAM CAMO MANUAL in pdf located at link below:
C.G. / Balance of all brands and types of models:
CG – In general, the CGs stated in the ESM, ECOMRC, and High Ridge Soaring manuals are accurate. Sometimes they are a little too far rearward, and this can have dire consequences. We recommend that the CG be a little forward of the suggestion in the manual. Make it easy to reduce the nose weight so that you can balance the plane after flying it. Use 25% as a good starting point for the CG.
For instance the ESM Skyraider’s wing is 420mm at the root. 25% of 420 is 105, so start with the CG at 105mm. The manual suggests 120mm, so we recommend a CG which is a little further forward. Once you fly the airplane a few times and get used to it you can make small changes at a time. Don’t change it a lot all at once. If a lot of elevator and a lot of speed is required on landing to keep the nose up (because it is too nose heavy), then remove a few ounces of nose weight.
With most planes which have a semi symmetrical wing (not flat bottom wing), flying them inverted is a good way to check the CG. This method does not work well with a Cub due to the flat bottom wing. In the Skyraider or similar plane, fly it inverted. If the plane slowly dives towards the ground with no down elevator, it is fine.
If it dives a lot and you must use a lot of down elevator to keep it level, it is nose heavy (or it has a flat bottom wing) remove some nose weight.
If the plane goes up when inverted, then yell to people to watch out because it will be an interesting landing. Aerobatic planes with huge control surfaces and large throws can overcome being tail heavy. Warbirds cannot be flown tail heavy because they will snap uncontrollably.