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Stability Distribution
by Thomas P. Turner
One of the unique aspects of flying twin-engine and turbine airplanes is the wide range of operating weights. Even more important, utilizing more or less of this loading capa- bility means there is potentially a much wider range of centers of gravity compared to
smaller aircraft. Changes in CG location create differences in control feel, airplane performance and handling – all reflecting changes in airplane stability. This aspect of flying larger airplanes is not always explored in-depth during transition and recurrent training. Let’s look at the differences in CG-related stability distribution.
Relative Characteristics
An airplane loaded toward the forward edge of its weight and balance envelope, compared to an airplane loaded further aft, will:
• be very stable in pitch;
• tend to fly at a lower angle of attack, developing less lift;
• have higher breakout forces, requiring more control force to change its pitch attitude.
Even within the approved envelope, compared to a more forward CG condition for any given indicated airspeed an aft-loaded airplane will:
• tend to pitch upward more;
• tend to fly at a higher angle of attack, unless the pilot resists the pitch-up;
• be less stable in pitch (tend to nose up and down, and not maintain a given attitude);
• have lower breakout forces. It will take less force on the elevator to change the pitch attitude, or conversely, respond more dramatically to the same amount of control input.
18 • TWIN & TURBINE
November 2018
PHOTO COURTESY OF PAUL BOWEN PHOTOGRAPHY