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 • Whatʼs 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

-2 .. To the same scale 00 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 TOGW 400,000 - 675,000 lbs Concorde Community Impact Can we live with it? U.S. SST Payload: 100 -234 Passengers 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.

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" Shaped Loudness Equivalent to: Start Cruise 0.30 psf N-wave End Cruise #$% 0.23 psf N-wave

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Overpressure (psf) # %# "## "%# &## &%# '## '%#

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! " 24 Future Vision

Efficient, Affordable Supersonic Flight…..

Thank you for your attention!

… with little or no sonic boom noise 25