By Gareth Evans
Although the concept of hypersonic flight has been around for a surprisingly long time, it is no simple matter to turn that idea into a functioning reality capable of travelling at more than five times the speed of sound – over 3,836 miles per hour, or a staggering 1.7 kilometres a second. The physics of the airflow alone places massive demands on airframe design, not least the generation of temperatures in excess of 1,500oC that will melt conventional aircraft materials. At relatively low hypersonic speeds, the molecular bonds in the air itself vibrate, changing the aerodynamic forces acting on the surface of the aircraft; faster and those bonds are torn apart, producing an ionised, electrically-charged plasma envelope around the vehicle. It is clearly not a design-challenge for the faint-hearted, but in the light of the announcement of a recent major test success, the hypersonic air force may no longer be quite so far away.