Since the Germans developed the ejection seat in World War II, a countless number of pilots have been saved by this technology. With current fighter technology becoming faster and more agile, the ejection seat pushes the pilot’s body in excess of 20G’s, bordering the limitation of the human spine which is 25G’s.
With the inevitable development of the hypersonic cruise vehicle, considerations must be taken into account on whether it is possible for a pilot to eject at hypersonic speed.
When assessing current ejection systems, it is known that the ejection seat is ineffective in clearing a tail-plane safely at altitudes of 20km without passing human biomechanical limitations. This is due to the high drag forces developed from the seat design.
After considering human limitations and hypersonic conditions, one can develop an ejection system that increases the likelihood of survival for the pilot in such demanding conditions.
The geometries used in the conceptual hypersonic vehicle design, which includes the parabolic curve and the wedge, have been assessed with Newtonian plate theory to determine which of these geometries can allow for a safe hypersonic ejection for a pilot. From the analysis, the asymmetric wedge of 14 degree half angle generated a drag coefficient of 0.1176, which has shown to be most effective in clearing the tail-plane at both test altitudes of 16.8km and 18.3km. The exit velocities are of 20m/s and 25m/s respectively.
As the Newtonian plate theory gives an estimation of what might be expected, the aerodynamic characteristics of the most effective geometry were assessed with the oblique shock theory. From the oblique shock theory, the 14 degree half wedge developed a drag coefficient of 0.273. It was found that the geometry failed to allow the pilot to clear the tail plane at an altitude of 16.8km and exit velocity of 20m/s. However, the geometry successfully cleared the tail-plane while at an altitude of 16.8km with an exit velocity of 25m/s, and, at an altitude of 18.3km with an exit velocity of 20m/s.