Ambience: Jet Aircraft

When engineers think about the speed of a plane, they relate it to the speed of sound. Iâ€™m Jim Metzner and this is the Pulse of the Planet. Paul Reukauf is a Project Manager at Dryden Flight Research Center who works with hypersonic aircraft.

â€œIn aircraft speeds, we talk about three different speed regimes. RegimeI mean that speed range. Subsonic regime is from 0 to the speed of sound, so from zero to about 700 miles an hour or so. Supersonic regime is from 1.2 times the speed of sound up to about 5 times the speed of sound, and then, hypersonic regime is everything above that. We use the speed of sound to define these speed regimes for aircraft because the mathematical equations that you use to calculate the performance of aircraft engines change in these different flow regimes, for instance, subsonically is like driving your car. The airplane takes in air and adds fuel to it and burns it and creates thrust, which would drive the wheels on your car. When youâ€™re going supersonically, the vehicle creates shockwaves. So, once youâ€™re going faster than the speed of sound, then anything moving at those speeds creates shockwaves, which make it change the mathematical relationships that you use to define performance of the vehicle. Vehicles moving at 3,500 miles an hour or faster are considered to be in the hypersonic regime. And hypersonically, again, the mathematical equations change because youâ€™re going so fast that you actually measure the reaction of the molecules of the air hitting the vehicle to calculate performance of the vehicle.â€

Weâ€™ll hear how hypersonic aircraft propel themselves in future programs. Pulse of the Planet is made possible by the National Science Foundation, with additional support from NASA. Iâ€™m Jim Metzner.