High-performance military aircraft normally have ejection seats that allow a pilot to eject from an aircraft along with his seat in an emergency. Emergencies requiring an ejection can occur at virtually any airspeed. Ejection from a high-performance military aircraft at high speeds imposes a great deal of stress on the pilot, primarily due to the aerodynamic drag on the pilot. In fact, the aerodynamic drag on a pilot ejecting at very high airspeeds can even decapitate the pilot or sever his arms or legs.
In order to control the effects of aerodynamic drag, modern ejection seat technology includes propulsion and stabilization systems which control the angular orientation of the ejection seat as it decelerates. However, these propulsion and stabilization systems create their own adverse stresses on the pilot. More specifically, the propulsion and stabilization systems must act quickly enough to orient the ejection seat before it allows the aerodynamic drag to injure the pilot. Yet rapid changes in the angular orientation of the ejection seat apply rapid roll rates which exert very high lateral loads on the pilot's head.
Injuries to pilots resulting from aerodynamic drag and high lateral forces resulting from modern ejection seat propulsion stabilization systems might be avoided by continuously restraining movement of the pilot's head and limbs while he is flying the aircraft. However, restraining the pilot's head while he is flying a high-performance military aircraft is not practical for a number of reasons. First, it is necessary for the pilot to continuously look around for both hostile and non-hostile aircraft. In fact, the pilot must even periodically check his six o'clock (i.e., rear) position to be sure that an enemy aircraft is not engaging him from behind. Thus, the pilot must be able to freely move his head about. Second, the optimum angle of the head is not the same in both flying and ejecting conditions. When the pilot is flying the airplane, his head should be tilted forward in a comfortable position to place the pilot's head at a prescribed angle in order to permit proper operation of the head-up display in the cockpit. In contrast, during ejection, the head should be aligned with the spinal column so that acceleration of the ejection seat during ejection does not cause the head to be thrown forward. Thus, it is not possible to provide both safe ejection characteristics and optimum flying characteristics by fixing the position of the pilot's head.
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