Volmer Jensen VJ-21

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

The item appears to be a bar that is attached to the lower surface of the aileron that extends forward and has a large weight bolted to the end of the bar. When the ailerons are in the neutral position this mechanism would be flush with the lower surface of the wing thereby not offering any resistance (drag) to the flow of air. This device can be used to serve two functions in the flight control system. Since the weight that protrudes forward is in front of the hinge line of the aileron it can be used for relieving some of the “heaviness” or slow response to aileron inputs by the pilot. This gives the aileron control system a measure of static balance making it easier to move in flight.
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.