When you get into the really large models, there is a real value to aerodynamically counterbalancing the control surfaces to reduce loads on the servos. MikeSell and I recently completed a practice plane for his son Taylorcraft1947's SAE cargo competition. The plane was built to the class's design specs, so there could be a chance to practice with a similar handling aircraft prior to competition day. Anyway, I digress...The (24 inch[sorry...not 40 inch...had a case of H.I.A.]) rudder and elevator were made with these counterbalancers to allow the use of standard size (and consequently lighter) servos. Every effort was made to build the plane light, so more cargo weight could be added. Competition ends today, and we're anxiously waiting for the phone call with the results...