The X51A Waverider, a U.S. Air Force experimental “scramjet” aircraft, achieved a top speed of nearly five times the speed of sound in its record-breaking first test flight Thursday. The Boeing X-51A made aviation history with the longest-ever scramjet-powered hypersonic flight. Air Force officials said the X-51A scramjet propulsion record can be compared to the leap from propellers to jet engines after World War II. Aviation engineers say scramjet propulsion will eventually replace current technologies.
X-51A Waverider flight test
For the scramjet test, The X51A Waverider, about the size of a cruise missile, was strapped to the wing of a B-52 bomber. A rocket booster was attached like a cash advance to bring the aircraft up to the hypersonic speed required for the scramjet engine to function. Aviation News reports that at 50,000 feet over the Pacific Ocean, the Boeing X-51A was dropped from the mothership and the booster quickly accelerated the Waverider to Mach 4.5. The X-51A ignited and the scramjet powered the aircraft for about 200 seconds as it reached a 70,000-foot altitude and an approximate speed of Mach 5.
Scramjet propulsion allows the Boeing X-51A to fly without wings. The Register reports that the Waverider actually surfs on the sonic shockwaves trailing back from its nose. Normal jet engines, which force air into the combustion chamber with compressor blades, can’t run past the hypersonic barrier, which is considered 5 times the speed of sound. Ramjet engines brought to hypersonic speed by a booster simply scoop the air in. However, ramjets have to slow the flow of air to subsonic speeds to keep from blowing out the flame in the combustion chamber. The X-51A scramjet engine (short for “supersonic combustion ramjet”) has a supersonic combustion chamber.
Scramjet engines: the future of aerospace
The 200-second Boeing X-51A flight test set a duration record for an aircraft powered by a scramjet engine. CNET News reports that the air-breathing scramjet engine, when eventually perfected, promises to radically advance aeronautic technology. Because scramjets use oxygen from the atmosphere, scramjet powered vehicles won’t need to carry huge tanks of liquid oxygen or hydrogen like rockets used today. Scramjets also use less fuel. The Boeing X-51A could usher in an era of cheaper rocket launches for the next generation of space exploration. On the dark side, scramjet engines could also propel military missiles to their targets at a speed impossible to defend against with today’s technology.