Ive been reading the posts for a long time now and have learned a great deal. I finally got the nerve to submitt a question and look forward to the response. Ive been flying my Model Tech P-51D for over a year now. Its is powered by an Evolution .46 and all standard servos as recommended in the manual. However the finished dry weight of the airplane was 7Lbs 4oz. (The manual specs estimated the weight to be 5.8 - 6.2 Lbs.) Even so the plane flys great. No bad stall tendencies and lands relatively slow.
I decided to install a 4c and purchased an ASP .65. I installed the ASP (after having to make modifications to the motor mount and catching heck tying to get the throttle linkage around the fuel tank). With the new engine the plane will weigh around 8Lbs. Ive mounted the receiver and battery rather nicely and do not want to move them unless it will adversely affect the flight charateristics. I believe I will still have to add 4oz to the tail in order to balance it at the forward recommended CG. How much will this additional weight make and will it potentially over stress the airframe?