Many pilots determine their models' CGs by putting a finger at each marked point, while inverted for low-wings, and lifting upward. This works but is not exact because finger ends cover a broad area and have a tendency to move during the lifting process. It is also difficult to adjust the CG while holding the airplane up.

    A better way is to use the Great Planes C.G. Machine or a similar homemade product to adjust your aircraft's balance point. Most modelers set their airplanes on the CG machine to try to achieve a level balance. They look for the wings and fuselage to be level. This is not always correct; it is difficult to tell when the airplane is even, especially if the wing or stabilizer does not have zero incidence.

    Instead, try balancing the airplane so the nose points downward 10°-15° but no more. Experience has shown that this compensates for any machine inaccuracies and results in the best sport-flying CG setting.

    Small stick-on weights are normally used to adjust the balance point. However, before adding weight to the airplane, try moving the receiver and battery pack. Sometimes that is enough. If not, Prather and Great Planes offer machined nose weights that attach to the engine's crankshaft, and Harry B. Higley & Sons sells a 2-ounce safety nut.

    Some pilots think crankshaft weights may strain the engine during maneuvers. In my 35 years of using these products, I have never seen this problem and my engines usually average 500-1,000 flights on a bearing set.

    These weights also act as a flywheel and improve idle reliability. Hangar 9's Evolution engines incorporate a weighted flywheel expressly for this purpose.

    Getting the nose weight as far forward as possible reduces the amount of balance weight required. If a crankshaft weight is unavailable, or unwanted, screw the weight to the bottom front of the engine mount, across the two beams in front of the engine. Use servo screws for this purpose. A lighter airplane flies better, so make sure to put any required nose weight as far forward as possible for maximum effect.

    Because extra tail weight is "way back there," its effectiveness is magnified by the long distance. Rather than use the stick-on tape, mount the tail weight using screws. This allows later CG adjustment. Longer weight strips can be installed in the old screw holes as the CG is worked rearward in time.

    The servo screws also ensure that the weights stay where they are installed. Oil-soaked stick-on weights usually release after a few flights.  

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Now that the front-to-rear CG is set, it's time to adjust the lateral balance point.

    Why do this? Most sport and trainer aircraft have "heavy" wings. Sometimes this is because of variances in the weight of the wood used during construction, but most often the lateral imbalance is caused by the engine's muffler.

    Yes, the muffler. That necessary hunk of aluminum that hangs off the airplane on one side. Most ARFs and sport airplanes are so well balanced that the muffler's weight is sufficient to move the lateral balance away from the airplane's centerline.

    The result is that loops corkscrew off to the heavy side, even though the wings are kept level. The "heavy wing" drops during sharp pullouts. Aileron trim is required to "level" the heavy wing, but the asymmetrical drag caused by the deployed ailerons causes all sorts of problems that pull the airplane off-center during maneuvers. Aileron trim constantly changes with airspeed, making it difficult to fly straight, level lines. Stalls and spins are difficult to do well since the airplane always tries banking to the "heavy" side.

    It is possible to trim an airplane for only one airspeed at any given time, so the less trim required, the better. Laterally balance every model before the first flight. It is easy to do and takes little time.

    Thread nylon fishing line, 5-pound test works well, through the rudder/fin hinge gap just under the topmost hinge. Remove the engine's glow plug and rotate the propeller until the piston is in the middle of its stroke. The propeller should be free to move in either direction without resistance.

    Do this indoors, away from any wind or drafts. Have a helper lift the airplane's tail using the fishing line while you raise the nose by holding only the propeller. The model will "bank" into the heavy wing, usually toward the muffler side. If a helper is unavailable, position the propeller on a raised flat surface and lift the tail yourself.

    Use small- and medium-size finishing nails to achieve a neutral balance point. Tape the nails to the "light" wingtip until the airplane maintains "level flight" in your living room. Then push the nails into the wingtip, leaving roughly 1/4 inch exposed.

    If your test flights prove that the balance is incorrect, the exposed nail ends make adjustment easier. After the test flights confirm that the airplane is balanced, push the nails entirely into the wingtip, secure them with thin cyanoacrylate, and cover them with a small piece of matching plastic modeling covering.

    Try laterally balancing all your aircraft this way. You will not believe the improved flight characteristics. I have watched and flown airplanes that once wandered into other time zones during loops fly like arrows from William Tell's crossbow once the lateral balance was adjusted.