Inertial coupling

With inertia coupling is referred to instability in aircraft whose mass is concentrated around the longitudinal axis in connection with an insufficient directional stability .

It appeared for the first time in the Mach 2 technology demonstrator X3 Stiletto , but has not yet been recognized as such. It had fatal effects in the series of crashes of the early North American F-100 Super Saber, here the wings and the vertical stabilizer had been shortened for the highest possible speeds and the fuselage lengthened. The shortened fin and the long fuselage led to a coupling of roll and yaw moments (turning-roll moment). As a countermeasure, the wingspan and rudder were increased, effectively avoiding the inertia coupling. The inertial coupling becomes noticeable as an uncontrolled tumbling movement around all three axes, which can quickly lead to overloading of the structure. Sufficient directional stability, tip tanks at the wing ends or aileron dampers and a low-lying horizontal stabilizer counteract it. The Dutch Roll poses a further stability problem.