The cruise missiles so often used to destroy ISIS installations and other enemy targets descend like a flash out of the sky, traveling up to 600mph as they approach unsuspecting terrorist compounds, hideouts, and ammo storage facilities. But the impressive speed at which a cruise missile is propelled will seem like a proverbial stroll in the park when an awesome new generation of hypersonic “birds” take flight as an operating Air Force weapon system.
Scramjet is short for Supersonic Combustion Ramjet. Ramjets have been around since shortly after World War II, but haven’t been practical for much because they don’t work at low speed. They have to be launched by something, usually a rocket, because the produce no thrust until they reach about half the speed of sound. Then they can fly very efficiently, but usually only up to about Mach 3.
A ramjet has been referred to as a “flying stovepipe,” because it is essentially a tube with no moving parts. Its internal shape is what makes it work. At high speed, it takes in air and immediately slows it to subsonic speeds before it reaches the combustion chamber. In the combustion chamber, it burns steadily, and has been likened to “lighting a match in a hurricane and keeping it lit.”
To go even faster, the design must be changed; but it still has no moving parts. The modified internal design no longer slows the incoming air. Ignition is at full super-sonic speed, thus the name Supersonic Combustion Ramjet, or Scramjet. Air entering the front never slows down. This design has been tested at least as fast as Mach 5.1 and can probably eventually reach Mach 16. We’re not testing one that fast, yet.
The X-51 Waverider Scramjet Missile
X-51 was really a proof of concept test. It showed that you could get a scram jet engine, launch it off an aircraft and it could go hypersonic. It was able to go more than Mach 5 until it ran out of fuel. It was a very successful test of an airborne hypersonic weapons system,” Endsley said.
The speed of sound at sea level in dry air at 20 °C is 768 mph. This is referred to as Mach 1. The fabulous X-51 Waverider test missile in the picture flies Mach 5.1, or almost 4,000 mph. In time, it should be good for a lot more than fast missiles.