PROPER CG LOCATION FOR AEROBATICS
Model Airplane News|January 2022
If you are getting into aerobatics and are starting to perform more advanced maneuvers, it is time to discuss ways you can not only become a better pilot, but how you can also improve the flight characteristics of your airplanes.
JOHN GLEZELLIS

To be more specific, let’s review how to find the correct Center of Gravity (CG) for your aircraft. In addition, we can look at a few balancing techniques, and how you can adjust the CG without adding additional weight.

Over the years, I’ve seen a few airplanes almost crash on takeoff because they weren’t balanced properly. Ensuring that your airplane has the proper CG location plays a major role in the longitudinal stability of your aircraft. If your aircraft is tail heavy, it will be more unstable and can stall at a low flight speed. It won’t be as predictable in pitch response and can become difficult to fly. On the other hand, a nose-heavy aircraft will lose altitude once the throttle is reduced and require a higher flight speed during the landing approach than if it were properly balanced.

HERE’S HOW TO DO IT:

1. Find the Mean Aerodynamic chord (MAC) for the wing. You can draw an accurate scale wing panel with a CAD program or simply trace out the wing on some graph paper. Measure the root and tip chord lengths and then transfer these measurements.

Extend lines from the leading edge and trailing edge of the root chord by the chord length of from the tip. Then, extend the leading and trailing edges of the wingtip, with the length of root chord length. It’s important to extend the wing panel outline so you can measure the root chord length at the fuselage’s centerline.

2. Now draw reference lines forming an X to connect the ends (extreme points) of the extended lines. Where they cross is the location of the wing panel’s MAC.

3. To establish the front of the CG balance range, divide the MAC by four to find the 25% MAC point. Now divide the MAC by three and find the 33% MAC point. The distance between these two points is the CG range.

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