Many times a kit will have instructions that say something like: "Balance the model at 5-7/8" behind the leading edge of the wing." A range may not be specified. You'd not believe how many calls we get when a range IS specified: "Where in the range do I balance it?"...."The range says 5-7/8" plus or minus 1/2, mine is on the edge, is that OK?"?......and on and on.

Also, if the model is at or below the manufacturer's suggested maximum weight once it's balanced, it's OK. There are just some designs that cannot fly without large amounts of weight in the nose or tail. That may not be due to "poor" design, but due to the configuration of the model. Many WWI and WWII models have very short noses, which means that there's little chance to use the engine and RC equipment to balance the long tail. Adding weight is the only solution.

With sport models, variance in the density of the wood can mean that the amount of weight needed will vary from model to model. Again, as long as the model's within its weight guidelines, it will fly OK. However, the lighter the model is, the better.