Official Nasa Communication 95-69

Michael Mewhinney May 16, 1995 Ames Research Center, Mountain View, CA (Phone: 415/604-3937) RELEASE: 95-69 NASA TESTS NEW NOISE REDUCTION JET EXHAUST NOZZLE NASA's Ames Research Center, Mountain View, CA, is testing an advanced jet exhaust nozzle designed to reduce noise produced by a 21st century High Speed Civil Transport (HSCT) without adversely affecting the plane's takeoff performance. The tests are part of NASA's High Speed Research Program, which is evaluating technologies needed for development of a 300-passenger supersonic transport that is both economically practical and environmentally acceptable. "The commercial success of the next-generation HSCT depends upon its ability to satisfy mandated community noise regulations governing aircraft operations," said project manager Brian Smith, an Ames aerospace engineer. As proposed, the HSCT would be capable of flying at Mach 2.4 (2.4 times the speed of sound) and have a range of 5,000 to 6,000 nautical miles. Envisioned to fly long distances over water, the HSCT could reduce the Los Angeles to Tokyo flight time from about 10 hours to only four. The expected date for beginning service is 2006. The High-Lift Engine Aeroacoustics Technology (HEAT) tests are being conducted in Ames' 40-by-80-Foot Wind Tunnel in cooperation with Boeing Commercial Airplane Group, Seattle, WA; McDonnell Douglas Aerospace, Long Beach, CA; General Electric Aircraft Engines, Cincinnati, OH; and Pratt & Whitney, Hartford, CT. The 19 weeks of tests will continue through May 26. "These tests will provide critical information needed to evaluate the suitability of ejector-type suppressor nozzles for the HSCT," said Michael Dudley, assistant manager of Ames' High Speed Research Office.

"There are three technical challenges to overcome in order to build a supersonic transport," Smith said. "The first is to make the HSCT quiet on takeoff and landing. We want the HSCT to be at least as quiet as a conventional subsonic jet transport." The second challenge is to ensure that the sonic boom created during supersonic flight does not adversely affect people or wildlife. "As a result, when operating supersonically, the HSCT will probably only fly over water or land where the sonic boom is not detrimental to the environment," Smith said. The last challenge has aerospace engineers studying how to reduce pollution produced by turbojet engines operating in the stratosphere. During the HEAT tests at Ames, engineers are concentrating on the first of these three challenges. Working with NASA's Langley and Lewis Research Centers as well as the aerospace industry, project engineers are testing a mixer-ejector nozzle on a semi-span conceptual model of an HSCT. Developed by General Electric, the exhaust nozzle is designed to reduce the HSCT's noise during takeoff and landing without adversely affecting its performance. The semi-span, 13.5 percent scale model is comprised of a wing and half-fuselage of a Boeing "Reference H" concept supersonic transport. The model will be wind tunnel tested at speeds of up to 300 knots (345 miles per hour). "The Reference H model is the configuration being used for a variety of HSCT studies by the High Speed Research Program," Smith said. "It incorporates the latest aerodynamic features that Boeing brings to the table and is representative of current HSCT designs." The 42-foot-long aircraft model is mounted on a four-foot high sound-absorbing platform called a splitter plate. The platform is insulated with ten inches of acoustic foam to absorb noise generated by a propane-powered jet engine simulator developed by Boeing and NASA. A pair of microphones mounted on traversing struts beside the platform and four microphones suspended from the wind tunnel's ceiling enable engineers to measure jet noise at

different speeds, flap configurations and angles of attack. The mixer-ejector nozzle is mounted on the trailing edge of the model's semi-span wing. The nozzle has large air intakes which act like giant vacuum cleaners. During the wind tunnel tests, cool air flows over the model and through the nozzle's air intakes, where it mixes with hot air from the jet simulator. "This cools the exhaust and reduces the velocity without affecting the thrust," Smith said. "The net effect is that we can maintain the same thrust while reducing the jet's velocity and hence the jet noise when the aircraft is taking off with 300 passengers," Smith said. "HEAT is the first test to accurately measure the effects this nozzle has on the noise and performance of the aircraft," Smith said. "This is important from an environmental standpoint, because if the nozzle causes the aircraft to develop less lift, the only way to compensate is to take off at a higher angle," Smith said. "That requires more thrust and more thrust means more noise," he added. "What we want is an efficient airplane that can take off at a low angle of attack with high ratios of lift to drag," Smith said. "Low drag means less thrust, and less thrust means less noise." -endNASA press releases and other information are available automatically by sending an Internet electronic mail message to [email protected]. In the body of the message (not the subject line) users should type the words "subscribe pressrelease" (no quotes). The system will reply with a confirmation via E-mail of each subscription. A second automatic message will include additional information on the service. Questions should be directed to (202) 358-4043.