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FAA Sonic Boom DC.Pptx Fixing the Sound Barrier Three Generations of U.S. Research into Sonic Boom Reduction … and what it means to the future Presented at the FAA Public Meeting on Sonic Boom July 14, 2011" Outline" • Perspective# –" Concorde & The U.S. SST# –" Recent interest in supersonic civil aircraft# •" Sonic boom basics# •" Progress in Sonic Boom Minimization# •" What$s happening now# •" Looking forward# 2 Perspective" Concorde U.S. SST Cruise Speed #Mach 2# Cruise Speed #Mach 2.7# Takeoff Weight #400,000 lbs# Takeoff Weight #675,000 lbs# Payload #100 passengers# Payload #274 passengers# First Flight #1969# Program Start #1965# Commercial Service #1976-2004# Program Cancelled #1971# 3 Perspective" Concorde, U.S. SST faced many challenges# …Leading toOne the FAR of the prohibiting largest supersonic was… SONIC commercial BOOM! flight over U.S. 4 Interest in Supersonic Flight has not Diminished" Supersonic cruise aircraft offer significant mobility improvements in the Future Air Transportation System ! Supersonic flight over land will enable a revolution in transportation … " … up to 50% reduction in cross country travel time" … improving personal productivity and well-being# … moving time-critical cargo, including life-saving medical supplies # … enhancing homeland security through rapid transportation of critical responder teams# 2010" 2020" 2030" Supersonic Civil Aircraft with increasing capability will be enabled if technology and environmental barriers can be overcome! 5 Sonic Boom Basics" •"Speed < Speed of Sound (< Mach 1)# •" Speed = Speed of Sound # •" Speed > Speed of Sound # •"Pressure Disturbance (sound) = Mach 1# > Mach 1# precedes aircraft# •" Aircraft Speed = Speed of •" Aircraft precedes pressure Pressure Disturbance# disturbance # •" All disturbance reaches an observer instantaneously# Sonic Boom is NOT the sound of an aircraft “breaking the sound barrier” Sonic Boom is created as long as the aircraft is flying faster than Mach 1.0 6 Sonic Boom Basics" Multiple disturbances (“shock waves”) near aircraft •"Disturbances Merge •"Signal lengthens •"Noise attenuates •" Sonic Boom is 3-Dimensional •" Large “Carpet” of ground is exposed as aircraft flies •"Two disturbances remain •" Noise is reduced at the edge of •"Signal has a characteristic “N” shape the carpet •"Called an “N wave” boom “signature” 7 Sonic Boom Basics: The N-Wave" 2 1 Measured Sonic Boom !P 02 -11 -20 .. To the same scale 0 0.1 0.2 0.3 0.4 Time, s -1 0.2 -2 0.10 10 20 30 40 50 60 Measured SubsonicOverpressure !p Takeoff Flyover !P 0 -0.1 Duration Rise Time! -0.2 0 10 Factors20 30in N wave40 annoyance50 60 Time, s 8 Sonic Boom Research in Supersonic R&D Programs" Current Mach: 1.2-2.0 SizeIntegration of Low Efforts TOGW 100,000- 300,000 lbsSonic Boom Boom Design NASA, FAA & Payload: 8-100 Passengers Indoor Noise Impact 3rd Generation Industry Atmosphere Effects DARPA Mach: 2.4 SizeBenefit of Small Size Quiet We are doing TOGW 100,000 lbs SonicLow Boom Design Supersonic Payload: 20,000 lbs Flight Validation of something! Platform Boom Shaping 2nd Generation 80-90’s Mach: 2.4 Shaping Benefit High-Speed TOGW 750,000 lbs Low Boom Design Can we do something? Research Payload: 300 Passengers Community & Wildlife Impact 1st Generation 60’s-70’s Mach: 2.0 -2.7 Sonic Boom Basics Concorde TOGW 400,000 - 675,000 lbs Community Impact Payload: 100 -234 Passengers Can we live with it? U.S. SST Shaping Concepts 9 Practical Approaches to Sonic Boom Reduction -1! “Boomless” Flight " If Aircraft ground speed < Speed of Sound at the ground (~760 mph)… 60 Boom can “refract” and not reach M cutoff the ground BOOMS OBSERVED 40 NO BOOMS ALTITUDE, OBSERVED KFT 20 Boom Region 0 1.0 1.1 1.2 1.3 1.4 MACH “Caustic Line” Rumble sound, rapidly decaying Ground 10 Practical Approaches to Sonic Boom Reduction -2! Minimization Through Aircraft Shaping" Control Strength and Position of Disturbances Disturbances do not Fully Merge Shocks Coalesce into “N-wave” Shaped Boom at the Ground Minimum Overpressure Minimum Initial Shock 11 Noise Reduction from Sonic Boom Shaping" A A = 1.3. psf B Rise Time B/A Sullivan 1990! 12 Practical Application of Boom Shaping Concept" George & Seebass 1969! Darden and Mack, 1979! Area Distribution! F-Function! Ground Signature! 13 Experimental Validation of Boom Reduction Concepts" • Scale model tests in supersonic wind tunnels# 14 Key Step in Validation of Theory" Design … Through Ground Measurement of Booms from Modified and Unmodified F-5Es! Shock Thickening Adjusted Ground Boom Signature Comparisons 1.4 Demonstrate 1.2 M = 1.40 1.0 h = 32 kft. Tanh 1/P Modification 0.8 0.6 Shaped Boom 0.4 0.2 0.0 P - psf Propagation in ! -0.2 -0.4 SBD-24b F-5SSBD@ 12,700 lbs. ! -0.6 F-5E @ 11,200 lbs. -0.8 F-5E! Real -1.0 -1.2 -1.4 Atmosphere…! 0 10 20 30 40 50 60 70 80 90 100 Time - msec Noise Acceptability 15 Shaped Sonic Boom Demonstrator (SSBD)" F5-ESSBD loaned WTM-2 Near-Field by US Pressures Navy# Extensive design effort using most ! o M = 1.367, CN = 0.132, h/L = 1.5, = 0 0.04 up to date computational methods # 0.03 0.02 0.01 0.00 local freestream -0.01 P / -0.02 local P " -0.03 Euler - 24b WTM-2 @ MFR = 0.76 -0.04 24b4 WT Data @ MFR = 0.76 - 0.80 - Rdg. 143 (P3) -0.05 24b4 WT Data @ MFR = 0.76 - 0.80 - Rdg. 157 (P4) -0.06 35 40 45 50 55 60 65 70 75 Along Track (Model) - inches Wind tunnel validation of design# Engineering, fabrication & flight clearance for research aircraft # 16 Theory Validated!" First-Ever Shaped Sonic Boom Recorded 27 August 2003! Signatures recorded during SSBD back-to-back data flights in the Edwards AFB supersonic flight corridor early morning! Flight conditions: !! !Mach 1.36+, ! !Altitude 32,000 ft! Design Mach: 1.4 Shock Thickening Adjusted Ground Boom Signature Comparisons 1.4 1.2 M = 1.40 1.0 h = 32 kft. Tanh 1/P Modification 0.8 0.6 0.4 0.2 0.0 P - psf ! -0.2 -0.4 SBD-24b @ 12,700 lbs. -0.6 F-5E @ 11,200F-5SSBD lbs. -0.8 -1.0 -1.2 F-5E -1.4 0 10 20 30 40 50 60 70 80 90 100 Time - msec 17 Impact of Boom Shaping on Noise" Low Boom signatures are achieved by Potentially more than 35 dB(a) of applying shaping to smaller aircraft! Reduction!! ~2000x less sound intensity! 18 Research on Boom Acceptability! How do We Determine What is Low Enough?" • Sophisticated boom simulators# •" Greatly improved reproduction of sonic boom noise# –" Consistent, repeatable test conditions# •" Study elements of boom that create annoyance# –" Goal: Understand how annoyance is related to spectrum, level, rattle, vibration# 19 How do We Study Low Sonic Boom?" •" Current aircraft cannot generate low booms during straight and level flight# •" Sonic boom is generated during supersonic dive of an F/A 18 aircraft # •" Long propagation distance, significant attenuation# •" Boom amplitude observed at house is adjusted by Subsonic moving dive location relative to the house# Boom Amplitude .1-.5 PSF (5-25 Pa)# Boom Loudness 60-80 PLdB# Subsonic House Ground 10 to 20 miles 20 Research in Realistic Environments" Subjective Reaction# Structural & Acoustic Response# •" Dive maneuver creates new research opportunities # •" Realistic, varied structures and environments# –" Living & working conditions# •" Test conducted in approved supersonic Small & Large flight corridors# Structures# 21 Flight Validation is a Critical Next Step" •" Full scale, complete validation of design tools & techniques# •" Develop understanding of the full spectrum of atmospheric effects# •" Validate acceptability measures in realistic situations# •" Gather data on public reaction to low noise sonic boom# –" Communities without prior experience of sonic boom exposure# Boeing F-16XL Based Design Gulfstream Clean Sheet Design 22 Summary of Sonic Boom Research" Past Research" •" Basics of sonic boom creation, propagation and impact are well understood# –" Effects on structures, terrain and animal life are minimal# –" Human response is primary consideration# •" Several practical reduction approaches have been identified# –" Flight below the cutoff Mach number# –" Shaped booms# •" Theory, design approaches and benefits have been validated# –" Analysis, ground experiments, simulation, flight tests# Current Research Focus" •" Understanding impact of booms heard by people indoors# –" Transmission of the boom sound into a house/building# –" Effects of rattle and startle# •" Understanding effect of atmosphere, operations & realistic ground environments# •" Full integration of boom reduction into aircraft design# –" Shaping the aft portion of the signature# –" Engine exhaust jet effects# –" Simultaneous design for low boom, high efficiency, light weight, etc# 23 Expanding Design Knowledge" •" New target signatures# •" More sophisticated analytical and design tools# •" Multiple disciplines considered simultaneously# –" Boom, efficiency, takeoff and landing noise, etc.# "$% " Shaped Loudness Equivalent to: Start Cruise 0.30 psf N-wave End Cruise #$% 0.23 psf N-wave # Overpressure (psf) # %# "## "%# &## &%# '## '%# ! #$% ! " 24 Future Vision" Efficient, Affordable Supersonic Flight…..# Thank you for your attention! … with little or no sonic boom noise 25 .
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