It really is the stuff of sci-fi stories and high-tech dreams - a light, sleek, black, insanely supersonic aircraft that can whisk passengers across the globe or into space, all the while using little fuel and emitting barely any pollution compared to today's airplanes, space shuttles and rockets. It's a "gee whiz, wouldn't it be great" idea for an engine that has scientists, aviation enthusiasts and space buffs excited and aerospace manufacturers curious.

How it Works

Reuters news service wrote, "The plane's hypersonic concept is so simple that it was first imagined by 17th Century visionaries, and its Œscramjet' engine design - which one scientist likened to 'keeping a match lit in a hurricane' - is so complicated that it took engineers more than 40 years to achieve."

In March, NASA successfully flew the X-43A at seven times the speed of sound making it the fastest, air-breathing powered aircraft in the world. Even the SR-71 only flies at Mach 3+. Developed as part of NASA's Hyper-X program to explore alternative propulsion systems for hypersonic speed (speeds over Mach 5), the X-43A features an air breathing scramjet engine. Many industry experts are hoping it will become the next powerplant to send business travelers around the world in a matter of hours and astronauts into space.

The X-43A combines the power of rockets with the flexibility and controllability of conventional aircraft. While rockets have limited throttle control and must carry heavy tanks of liquid oxygen for fuel combustion, the air breathing scramjet (short for supersonic combustion ramjet) is quite maneuverable with its lifting body wing design. There's no need for huge oxygen tanks strapped onboard. It simply draws in oxygen from the air similar to a turbine engine.

Although the pressure (density of the air) changes, the percentage of oxygen in the air remains the same (about 20 percent) up to 70,000 feet. One source foresees that an Earth-to-orbit mission vehicle might need oxygen tanks onboard, but less than what a space shuttle requires.

According to Cornell University, "Both ramjets and scramjets [remember scramjets are a supersonic combustion ramjet] operate on the same basic principle as a jet. As the plane flies, air flows through the engine and is compressed. Fuel is added to the compressed air and the mixture is ignited. The expanding gases are shaped and directed by the engine's nozzle and propel the plane forward." (See the NASA illustration below.)

Unlike jet engines, which can overheat at about 2,500 mph, there are very few moving parts to wear out on the highly efficient scramjet engine. Since it doesn't require heavy oxygen tanks, the aircraft's weight is dramatically reduced thereby allowing increased range and payload capacity.

Recent Testing Successful

A Cornell whitepaper on scramjets points out that "Ramjets are a proven technology, used on the SR-71 Blackbird spy plane. The Blackbird also has normal jet engines, used to accelerate it up to Mach 3, the speed at which its ramjets become operational.

"While a jet engine uses fans to compress the air, ramjets and scramjets rely on the forward motion of the vehicle alone. Ramjets and scramjets can produce no static thrust; the vehicle must already be moving fast enough to compress the air before these engines can operate."

In its current configuration, the X-43A is unable to reach altitude on its own. During testing, the 12-foot, wedge-shaped X-43A rested like the tip of a sword on a modified Pegasus booster rocket, which was nestled under the right wing of a B-52B. Once at an altitude of about 40,000 feet, the unit was dropped from the B-52 and the rocket boosted the X-43A to 95,000 feet over the Pacific Ocean. Once separated from the rocket booster, the unpiloted X-43A fired its engine for 10 seconds, performed maneuvers during a glide and splashed down in the ocean.

The Hyper-X program, which is being conducted jointly by the Langley Research Center, Hampton, Va., and the Dryden Flight Research Center, Edwards, Calif., is expected to test at least one more model-like X-43 aircraft but at speeds near Mach 10. Each test aircraft, three in all, features slightly different oxygen intake designs. In June 2001, the very first X-43A was lost after releasing from the B-52.

Others Eye Scramjets

ATK (Alliant Techsystems) served as the system prime contractor on the X-43A program - manufacturing the engine, airframe and fuel systems in addition to integrating the vehicle in preparation for flight. ATK and NASA are not the only ones eyeing scramjet technology.

In January, the U.S. Air Force Research Laboratory (AFRL) selected Pratt & Whitney and Boeing Phantom Works to "explore the air-breathing system-level potential of scramjets through multiple flight tests that will begin in 2007-2008."

According to Pratt & Whitney, the company ground tested an actively cooled, hydrocarbon-fueled scramjet engine. "During numerous runs at Mach 4.5 and Mach 6.5 conducted September 2002 through June 2003, the ground demonstrator engine, known as the GDE-1, reliably produced significant net positive thrust."

Hypersonic flight has been a major research activity at the University of Queensland's Centre for Hypersonics in Australia for over 20 years. In July 2002, they tested their own scramjet in much the same way that NASA flew the X-43A. Called HyShot, the Aussie scramjet program was such a success that the university research team - the first in the world to successfully flight test a supersonic air-breathing scramjet engine received an Australian Research Council grant of $1.8 million to continue their work.

Promising for Aviation

The scramjet's ability to deliver remarkable power at a very low weight and with few moving parts means the engine is likely to become a staple in the aviation industry, especially for long-range, high-altitude flying. Imagine getting from New York City to Tokyo in just over an hour or from Chicago to Paris in just under an hour. Once the scramjet details are worked out, we'll be flying across the globe as casually as though we were heading two states over for a family vacation. At that point, engineers will be on to even better things such as the matter-antimatter propulsion system, another amazing, sci-fi-like concept currently being studied by scientists around the world.

Next ==>  part 2     part 3    (pdf files)


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