the longitudinal and directional stabilities. Rolling motion introduces coupling between longitudinal and lateral motions of the aircraft. Although a typical jet aircraft has most of its mass distributed close to its centerline, and the aerodynamic forces and moments in planes which provide some stabilization (such that small fluctuations in control tend to return it to attitude equilibrium), it is important to remember that aircraft realistically always fly with a small non-zero random rate of yawing and pitching. Early history Inertial roll coupling was predicted and analyzed as a gyroscopic effect in 1948 by William Phillips who worked for the NACA. His analysis predated the aircraft that would experience the violent motions he predicted, the X-series research aircraft and Century-series fighter aircraft in the early 1950s. Prior to this time, aircraft tended to have greater width than length, 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 reduce drag, and use longer fineness ratios that reduced supersonic drag, that the effect became obvious. In these cases, the aircraft was generally much more fuselage-heavy, allowing its gyroscopic effect to overwhelm the small control surfaces. Inertial roll coupling was one of three distinct coupling modes which followed one another at Mach 3.2 killing pilot Captain Mel Apt in his first flight in the rocket-powered Bell X-2 on 27 September 1956. Inertial roll coupling had nearly killed Chuck Yeager in the X-1A three years earlier. The roll coupling study of the X-3 Stiletto (first flown in 1952) was extremely short but produced valuable data. Abrupt aileron rolls were conducted at Mach 0.92 and 1.05 and produced "disturbing" motions and excessive accelerations and loads. The first two production aircraft to experience inertial roll coupling were the F-100 Super Sabre and F-102 Delta Dagger (both first flown in 1953). The F-100 was modified with a larger vertical tail to increase its directional stability. The F-102 was modified to increase wing and tail areas and was fitted with an augmented control system. To enable pilot control during dynamic motion maneuvers the tail area of the F-102A was increased 40%. In the case of the F-101 Voodoo (first flown in 1954), a stability augmentation system was retrofitted to the A models to help combat