CG and "Static Margin"
In the last article in this series, we showed that each aircraft configuration has a "neutral point" (NP), and discussed ways of finding it using a CG calculator. If the model's CG is forward of the NP location, the model will be stable in pitch. If it's behind the NP, the model will be unstable. We also noted that CG calculators ask the user for something called "static margin" before finding the acceptable CG range. So what's static margin? Simple - it's the distance between the CG and NP, expressed as a percentage of the wing mean aerodynamic chord (MAC). For example, if your model has a 5" wing MAC, a static margin of 10% puts your CG 0.5" (half an inch) in front of the NP location. Static margin is important because it's a measure of relative stability - planes with similar static margins will have similar amounts of pitch stability. Put another way, knowing your CG is ahead of the NP lets you know your model will be stable
