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scramjet powerplants

scramjet powerplants Higher, further, faster, carry more. These have always been the goals of aircraft designers from the very beginning of aviation history. Even today engineers and researchers attempt to build aircraft that will be able perform better. Throughout the history of aircraft design, the main limiting factor has been the performance of power plants. This is still going on today as we attempt to build engines that allow superior performing aircraft. Scramjet engines offer one potential solution to this problem. By the end of World War II we had the technology to build airframes that would fly higher, go further, faster and carry more, but there were no power plants available to power such aircraft. With the introduction of the jet engine aircraft took an enormous step forward. Although the jet engine offers a multitude of advantages over jet engines, there are still limitations. One of these is that jet engines have a limited operating speed. A speeds much higher than Mach 3 the turbine engines, with rotating blades and other moving parts are unable to stand the stress and pressures associated with high speed flight. Rocket power has been used in some applications. Some of these include experimental aircraft such as the X-15. Rocket power is also used in spacecraft as the main means of propulsion. Rocket powered aircraft must carry a supply of hydrogen and oxygen. The requirement to carry large supplies of fuel severely limits the payload capabilities of the ship. In addition it is cost prohibitive for most operations. Commercial transportation is out of the question. Ramjet engines offer some improvements, but are still speed limited. A ramjet engine works in a similar manner to a turbine engine, but there are no moving parts. Instead of using a compressor section to produce high-density air, the forward speed of the aircraft is used to compress the air. The air is then slowed to subsonic speed through a reverse venturi. Fuel is ignited and creates thrust is a fashion similar to that of a turbine engine. (Ramjet/Scramjet...) Scramjet is the name given to a supersonic compression ramjet. It operates in a similar manner to a ramjet, however the air passing through the engine maintains supersonic speed. The scramjet uses hydrogen fuel, just like a rocket engine, but is does not require an onboard supply of oxygen. Instead it uses the oxygen available from the large quantity of air taken in by the engine inlet. This allows a scramjet powered aircraft to fly at hypersonic speeds (above Mach 7) without some of the disadvantages of rocket engines. Because the scramjet does not require a supply of oxygen, many of the problems associated with rocket power are eliminated. Payload can be increased, allowing the aircraft to be much more useful. It can be operated much more economically as well. Scramjets have the potential to be safer than rocket engines. Rockets carry a dangerous mix of explosive hydrogen and fire promoting oxygen, while scramjets carry only hydrogen. There are several barriers to the implementation of scramjet powered aircraft. The amount of testing that can be done in a laboratory is limited. Therefore expensive and time consuming field research is required. Another problem associated with scramjets is the supersonic flow of air around, through and out of the engine. Shock waves are generated by the structure of the engine. Due to the speed of the aircraft and the nature of the shock waves, they tend to pile up in one area. This leads to enormous pressures on the airframe and engine components. The heat resulting from such high speed travel is another problem that must be considered. There have been several tests preformed using scramjet technology. The first of these actual tests was performed by the Defense Advanced Research Projects Agency and Gasl Inc. in New York. They launched a 4-inch diameter miniature scramjet from a gun to achieve a speed of Mach 7.1. The scramjet successfully provided a positive thrush to drag ratio for 25 milliseconds. This was a significant test because it was the first time scramjet technology was tested in actual flight as opposed to a wind tunnel test. It should be noted however, that the test engine did not use hydrogen, as the operational scramjets will most likely do. Instead ethylene was used because is enabled a larger quantity of fuel to be used on the test projectile. Using ethylene also eliminated the need to regulate fuel pressure. Early attempts failed because the projectile broke up under the 10,000g force exerted when the gun was fired. (Phillips, E. 2001) There have since been attempts at airborne scramjet aircraft. NASA’s X-43A is a scramjet powered test vehicle. The X-43 is a 12 feet long unpiloted aircraft. It is designed to be carried to an altitude of 20,000 feet by a B-52. At that point it is released and a rocket powers the X-43 to an altitude of 100,000 feet. The scramjet is ignited, data is recorded and the aircraft descends into the ocean. During the first testing of the X-43 problems arose with the Pegasus booster rocket and the ship had to be destroyed. All evidence points to the booster causing the problem, not the test vehicle. There are two X-43s remaining and hopefully further research will be conducted. (NASA prepares for…) Success of the scramjet could lead to affordable hypersonic travel. An aircraft capable of speeds up to Mach 25 could make the trip from New York to Tokyo in less than 2 hours. This would drastically change international travel. Scramjet power would also be a superior means of military transportation. The applications could range from large transport aircraft to scram powered missles. With the proper funding and research a scramjet powered vehicle could be reality in the near future. Bibliography:

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