Machine Design

Looking Back — Quieter F-18s | Betters Turbofans | No-Magnetism Sphere

10 YEARS AGO — 1992

Quieter fighter jets: A new method of quieting U.S. Navy F-18 fighter-jet engines has been developed by a professor at Florida State University, Tallahassee. Noise is reduced by siphoning off some of the air traveling through the engine and forcing it, at high pressure, through multiple microjets that fan around the exhaust. The small jets of highpressure air hitting the large stream of relatively low-pressure jet exhaust cuts noise. Even more noise is suppressed by forcing liquid, such as water or an aqueous polymer, through the microjets.

Tests so far show a 5-dB reduction, with 6 dB representing a 50% reduction. Researchers hope to achieve a 10-dB noise reduction by year’s end.

30 YEARS AGO — 1982

Turbofan looks good in test cell: A turbofan engine being developed for use in British transport aircraft and potential use in U.S. aircraft, passed ground tests at the Air Force’s Arnold Engineering Development Center. Four different configurations of a 6,700-lb thrust Avco Lycoming ALF502R-3 turbofan were tested for 84 hr at conditions simulating flight at speeds from zero to 620 mph and at altitudes from sea level to 40,000 ft. Performance improvements due to modifications were validated, and the engine’s compressor stall margin was determined at 23 different flight conditions and power settings.

50 YEARS AGO — 1962

Permeable sphere detours magnetic fields: Fluxtank, a two-piece test enclosure that shields out magnetic interference, reroutes all flux lines through its skin. Made from Allegheny Ludlum’s highly permeable Mumetal, the device should be a big help to scientists developing instruments to measure the faint magnetic fields encountered in space. First use for the new sphere was in calibrating and testing a magnetometer that will measure a field 100 million times weaker than that generated by a child’s play magnet, according to the designers Marshall Laboratories, Torrance, Calif. Top of the sphere (not shown, but constructed like the bottom) is lowered over the enclosure when the tank is in use.

© 2012 Penton Media, Inc.

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