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Balancing of Flight Controls
As you look up under the left wing of the VJ-21 that is hanging in the museum you will notice a strange device that is present near the left wing aileron.
Lower surface bar
A second reason such devices are used is to prevent what is called “aileron flutter” in flight. If an aileron design is subject to “flutter” this transmits a vibration into the wing structure which can result in failure or fatigue in the structure. Flutter is not a good thing and designers often use such devices to prevent flutter from occurring. This scheme of design is also known as “static balancing” and “mass balancing” of the flight controls.
There is a second method of balancing flight control systems. That approach is referred to as “aerodynamic balancing.” It is achieved by placing a portion of the flight control surface forward of the control surface hinge line as shown in the illustration.