Recently, intense research has gone into the development of planes that can fly at hypersonic speeds, approximately five times or more than the speed of sound. At these speeds the properties of air change radically; there is a rapid increase in temperature associated with the air flowing at such speeds along a plane's surface. The U.S. Air Force is working to develop an aircraft that could travel at 13,000 mph (21,000 kph), a speed that would generate temperatures greater than 3,500°F (2,000°C).
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.