The significance of Mach 1.4

Ron Ayers

The target for the BLOODHOUND SSC project is to get as close as possible to 1000 mph, and exceed that figure if we can. Now to set a new record, the F.I.A procedure is that we must complete two runs in opposite directions within one hour. The average speed of the two runs is taken as the speed achieved. It is clear from this that, at least in one direction, a maximum speed significantly in excess of 1000 mph must occur in order to achieve the 1000 mph two-way average. My performance model shows that we may even have to peak at 1050 mph in order to achieve the 1000 mph average, and so the car is being designed with a maximum speed potential of 1050 mph.

The speed of sound is not constant, but varies with temperature. At 15 deg. Centigrade, typical of the temperatures we experience while record breaking, the sonic velocity is 761.2 mph. Thus at this temperature the car will need to travel at 1050/761.2 = 1.379 time the speed of sound. That is, it will need to travel at M = 1.379. If the ambient temperature is lower, the speed of sound is also lower. For instance, a Mach number of 1.4 would be reached if the car peaks at 1050 mph at a temperature of 7 degrees C.

At ground level, and at these high Mach numbers, the aerodynamic forces on the vehicle are huge. They also change as the vehicle accelerates because the increased speed not only increases the aerodynamic forces, but the changing Mach number also changes the flow pattern around the vehicle. Furthermore, designing a jet intake that works equally well from M = 0 all the way up to M = 1.4 is a formidable challenge.

These and related subjects will be discussed in detail as the project progresses.