A history and description of Stealth Aircraft Emily Ranquist Aircraft Propulsion 12/17/2015 Background • Stealth means being as close to undetectable as possible: • IR Signature • RCS • Visibility • Noise • Most stealth technologies have evolved due to war • Developments such as IR guided missiles and RADAR have pushed the need for stealth aircraft World War I • Start of Stealth • German experimentation with cellon and Fokker III • British experimentation with silenced engine on SS class airship World War II • 1934-1939: RADAR developed by 8 countries • US, UK, USSR, Japan, Germany • June 1943: German Project “Chimney Sweep” • Horten Ho 229- “The First Stealth Bomber” • First to experiment with Radar Absorbent Materials (RAM) • Used wood, carbon impregnated resins • Northrop study • Reduced Radar detection by 37% Radar Absorbent Materials • Wood, cloth, plastic, fiberglass • MUCH lower radar reflectivity than metal • A-12 and SR-71 used “Ironball Paint” • Absorbs radar beam and converts to heat • Today, dielectric composites with ferrite particles are used • Nearly invisible to radar Vietnam and Cold War • 1974: DARPA’s Have Blue Project • Competition between Lockheed and Northrop to research levels at which an aircraft is ‘undetectable’ Lockheed’s Have Blue • Lockheed Have Blue became precursor to F-117 Nighthawk • Northrop encouraged to stay together • Start of the first concepts of B-2 Spirit • First real studies on Radar Cross Section and IR signature reduction Northrop’s Tacit Blue Radar Cross Section (RCS) • Hypothetical area required to intercept transmitted power from radar source and scatter signal isotropically back • Depends on material, size, shape and orientation Reducing RCS • Angled Surfaces • Allow for high incident angles • High reflection angles • Flatter surfaces • Any surface normal to wave will reflect directly back • Flying Wing Design • Smoother surfaces • Rough surfaces scatter in every direction Infrared Signature Infrared Signature Carbon Dioxide Water Vapor Infrared Signature • Accounting for hot parts • Put the engine inside the fuselage or wing • Serpentine inlet to hid engine face • Active Cooling • Running fuel or coolant alongside engine or exhaust pipe • Accounting for exhaust plume • Mix cool air inside of exhaust stream • Non-circular tailpipe to reduce area of plume • Accounting for airframe • Run coolant along leading edge during supersonic flight Recent Years • 1996: Bird of Prey • Technology Demonstrator • Researched methods of reducing visibility • 1997: F22 Raptor • Fighter that must also have stealth capability • Focus on unmanned systems • RQ-180- start of LRB program • Boeing Phantom Ray, X-45 Visibility •Active Camouflage • Uses fluorescent panels or LEDs to cover aircraft surface • Changes color to surroundings • Paint Schemes • Paint underbelly to match the sky • Bird of Prey painted to reduce visibility of any identifiable component on aircraft Noise • Most stealth aircraft use turbofans • Avoid sonic boom by being incapable of traveling at high Mach • Two exceptions are Horten Ho 229 and A-12 • Required high speeds • Similarly, most lack afterburners • Reduces speed and IR signature • Some fighters, such as F-22 Raptor are equipped with them • Putting engine inside wing also muffles the noise Conclusion • Stealth aircraft designs change with advances in technology • Almost all new aircraft are inspired by older aircraft • Horten Ho – B-2 Spirit • Have Blue – F-117 Nighthawk • A-12 – SR-71 • Future may hold advances in visibility and noise, mainly unmanned systems Emily Ranquist Aircraft Propulsion 12/17/2015.