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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

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SLIDE 1

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

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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
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Perspective

Cruise Speed Mach 2 Takeoff Weight 400,000 lbs Payload 100 passengers First Flight 1969 Commercial Service 1976-2004 Cruise Speed Mach 2.7 Takeoff Weight 675,000 lbs Payload 274 passengers Program Start 1965 Program Cancelled 1971 Concorde U.S. SST

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Perspective Concorde, U.S. SST faced many challenges

…Leading to the FAR prohibiting supersonic commercial flight over U.S.

One of the largest was… SONIC BOOM!

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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

Supersonic Civil Aircraft with increasing capability will be enabled if technology and environmental barriers can be overcome

  • 2010
  • 2020
  • 2030
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Sonic Boom Basics

  • Speed < Speed of Sound (< Mach 1)
  • Pressure Disturbance (sound)

precedes aircraft

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

  • Speed = Speed of Sound

= Mach 1

  • Aircraft Speed = Speed of

Pressure Disturbance

  • Speed > Speed of Sound

> Mach 1

  • Aircraft precedes pressure

disturbance

  • All disturbance reaches an
  • bserver instantaneously
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Sonic Boom Basics

  • Sonic Boom is 3-Dimensional
  • Large “Carpet” of ground is

exposed as aircraft flies

  • Noise is reduced at the edge of

the carpet

  • Disturbances

Merge

  • Signal lengthens
  • Noise attenuates

Multiple disturbances (“shock waves”) near aircraft

  • Two disturbances remain
  • Signal has a characteristic “N” shape
  • Called an “N wave” boom “signature”
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Sonic Boom Basics: The N-Wave

Rise Time!

Overpressure !p Duration

Factors in N wave annoyance

Measured Sonic Boom Measured Subsonic Takeoff Flyover

10 20 30 40 50 60

  • 2
  • 1

1 2

.. To the same scale

0.1 0.2 0.3 0.4

  • 2
  • 1

1 2

!P Time, s

10 20 30 40 50 60

  • 0.2
  • 0.1

0.1 0.2

!P Time, s

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60’s-70’s Concorde U.S. SST

Mach: 2.0 -2.7 TOGW 400,000 - 675,000 lbs Payload: 100 -234 Passengers

Sonic Boom Basics Community Impact Shaping Concepts

Sonic Boom Research in Supersonic R&D Programs

80-90’s High-Speed Research

Mach: 2.4 TOGW 750,000 lbs Payload: 300 Passengers

Shaping Benefit Low Boom Design Community & Wildlife Impact Size Sonic Boom DARPA Quiet Supersonic Platform

Mach: 2.4 TOGW 100,000 lbs Payload: 20,000 lbs

Benefit of Small Size Low Boom Design Flight Validation of Boom Shaping Size Sonic Boom Current Efforts NASA, FAA & Industry

Mach: 1.2-2.0 TOGW 100,000- 300,000 lbs Payload: 8-100 Passengers

Integration of Low Boom Design Indoor Noise Impact Atmosphere Effects

1st Generation 2nd Generation 3rd Generation Can we live with it? Can we do something? We are doing something!

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Practical Approaches to Sonic Boom Reduction -1
 “Boomless” Flight

If Aircraft ground speed < Speed of Sound at the ground (~760 mph)… Ground Boom can “refract” and not reach the ground

60 40 20 ALTITUDE, KFT 1.0 1.1 1.2 1.3 1.4 NO BOOMS OBSERVED BOOMS OBSERVED MACH M cutoff

“Caustic Line” Rumble sound, rapidly decaying Boom Region

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Practical Approaches to Sonic Boom Reduction -2
 Minimization Through Aircraft Shaping

Shocks Coalesce into “N-wave” Control Strength and Position of Disturbances Shaped Boom at the Ground

Minimum Initial Shock Minimum Overpressure

Disturbances do not Fully Merge

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Noise Reduction from Sonic Boom Shaping

Rise Time A B A = 1.3. psf B/A

Sullivan 1990!

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Practical Application of Boom Shaping Concept

George & Seebass 1969! Area Distribution ! F-Function ! Ground Signature ! Darden and Mack, 1979 !

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Experimental Validation of Boom Reduction Concepts

  • Scale model tests in

supersonic wind tunnels

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Key Step in Validation of Theory

Demonstrate Shaped Boom Propagation in Real Atmosphere…

Design Noise Acceptability

Shock Thickening Adjusted Ground Boom Signature Comparisons

  • 1.4
  • 1.2
  • 1.0
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 10 20 30 40 50 60 70 80 90 100

Time - msec !P - psf

SBD-24b @ 12,700 lbs. F-5E @ 11,200 lbs.

Tanh 1/P Modification

M = 1.40 h = 32 kft.

F-5SSBD F-5E

… Through Ground Measurement of Booms from Modified and Unmodified F-5Es

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Shaped Sonic Boom Demonstrator (SSBD)

N

  • 0.06
  • 0.05
  • 0.04
  • 0.03
  • 0.02
  • 0.01

0.00 0.01 0.02 0.03 0.04 35 40 45 50 55 60 65 70 75

Along Track (Model) - inches "Plocal / Plocal freestream

Euler - 24b WTM-2 @ MFR = 0.76 24b4 WT Data @ MFR = 0.76 - 0.80 - Rdg. 143 (P3) 24b4 WT Data @ MFR = 0.76 - 0.80 - Rdg. 157 (P4)

F5-E loaned by US Navy Extensive design effort using most up to date computational methods

  • Wind tunnel validation of design

Engineering, fabrication & flight clearance for research aircraft

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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

Shock Thickening Adjusted Ground Boom Signature Comparisons

  • 1.4
  • 1.2
  • 1.0
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 10 20 30 40 50 60 70 80 90 100

Time - msec !P - psf

SBD-24b @ 12,700 lbs. F-5E @ 11,200 lbs.

Tanh 1/P Modification

M = 1.40 h = 32 kft.

F-5SSBD F-5E

Design Mach: 1.4

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Impact of Boom Shaping on Noise

Low Boom signatures are achieved by applying shaping to smaller aircraft

  • Potentially more than 35 dB(a) of

Reduction!

  • ~2000x less sound intensity
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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

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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

moving dive location relative to the house

Boom Amplitude .1-.5 PSF (5-25 Pa) Boom Loudness 60-80 PLdB

House Ground

Subsonic Subsonic 10 to 20 miles

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Research in Realistic Environments

Structural & Acoustic Response Subjective Reaction Small & Large Structures

  • Dive maneuver creates new research
  • pportunities
  • Realistic, varied structures and

environments

– Living & working conditions

  • Test conducted in approved supersonic

flight corridors

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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

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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

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Expanding Design Knowledge

  • New target signatures
  • More sophisticated analytical and design tools
  • Multiple disciplines considered simultaneously

– Boom, efficiency, takeoff and landing noise, etc.

Overpressure (psf)

! " ! #$% # #$%

"

"$% # %# "## "%# &## &%# '## '%#

End Cruise Start Cruise

Shaped Loudness Equivalent to: 0.30 psf N-wave 0.23 psf N-wave

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Future Vision

Efficient, Affordable Supersonic Flight…..

… with little or no sonic boom noise

Thank you for your attention!