Inertia Coupling - Early History

Early History

Inertia coupling was essentially unknown before the introduction of high-speed jet aircraft. Prior to this time aircraft tended to be wider than long, and their mass was generally distributed closer to the center of mass. This was especially true for propeller aircraft, but equally true for early jet fighters as well. It was only when the aircraft began to sacrifice aerodynamic surface area in order to lower drag, and use longer fineness ratios that lowered supersonic drag, that the effect became obvious. In these cases the aircraft was generally much more tail-heavy, allowing its gyroscopic effect to overwhelm the small control surfaces.

Inertia coupling killed pilot Mel Apt in the Bell X-2 and nearly killed Chuck Yeager in the X-1A. It was also extremely obvious in the X-3 Stiletto, and flight tests on this aircraft were used to examine the problem. The first two production aircraft to overtly experience this phenomenon, the F-100 Super Sabre and F-102 Delta Dagger, were modified to increase wing and tail area and were fitted with augmented control systems. To enable pilot control during dynamic motion maneuvers, for instance, the tail area of the F-102A was increased 40%. In the case of the F-101 Voodoo, a stability augmentation system was retrofitted to the A models to help combat this problem.