An Overview of the Rotorcraft Noise Model RNM

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An Overview of theRotorcraft Noise Model (RNM)

• David A. Conner
• Aeroflightdynamics Directorate (AMRDEC), U.S.
  Army AMCOM
• Casey L. Burley and Michael A. Marcolini
• NASA Langley Research Center
• Juliet Page, Ken Plotkin and Micah Downing
• Wyle Laboratories

Environmental Noise Session International
Military Noise Conference Baltimore,
Maryland April 24-26, 2001
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Rotorcraft Noise Model
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Rotorcraft Noise Model (RNM)
Purpose Provide capability to determine noise
impact due to terminal area operations

• Requires sound hemispheres for different
  operating conditions as input data base (measured
  or predicted)
• Desired flight profile provided as input (i.e. x,
  y, z, airspeed, nacelle angle as function of
  time)
• RNM interpolates between hemispheres and
  propagates to the ground
• Multiple (10 max) sound spheres (geometry
  specified by user)
• Tones and/or broadband
• Metrics specified by user
• Output is flat earth noise footprint (input to
  ACNIM if desired)
• Generic methodology applicable to
  rotorcraft/aircraft

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Experimental Determination of Sound Hemisphere

• Linear microphone array perpendicular to flight
  path
• Acoustics measured continuously

• Directivity angles and ranges are calculated

• Range vectors are translated to a single point
• Resulting surface defines the ground contour
  coordinates

• Hemisphere radius selected
• Range vectors determine sound field coordinates

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Propagation Algorithms

• Similar analytical techniques as used in NASAs
  Aircraft Noise Prediction Program (ANOPP).
• Validated through many years of testing
• Propagation model accounts for
• Spherical spreading
• Atmospheric air absorption
• Ground reflection and attenuation
• Doppler shifting
• Phase differences between direct and reflected
  rays
• Propagation model assumes
• Acoustic ray paths are straight lines
• No wind present
• No attenuation due to barriers or other forms of
  terrain

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Moose Jaw Noise Trials

• NATO/CCMS (Committee on the current Challenges of
  Modern Society) flight test conducted at CFB
  Moose Jaw, Saskatchewan, Canada, June 1998.
• Participating Countries Canada, Denmark,
  Federal Republic of Germany, Netherlands, Norway,
  Switzerland, United Kingdom, United States
• Purpose
• NATO 1) develop an international standard for
  measuring and analyzing helicopter noise, and 2)
  define a common database format that will be
  adopted as the international standard by the NATO
  countries.
• Langley To acquire a rotorcraft acoustic data
  base for 1) Validation of Rotorcraft
  Noise Model (RNM), and 2)
  Distribution of the noise hemispheres with public
  release of RNM version L1.0

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Moose Jaw Noise Trial
Bell 412 Griffin
Noise Footprint
Microphone Array Configuration
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Moose Jaw Noise Trials Comparison of Measured and
Predicted Noise Footprints 6 Approach at 41 KIAS
Direction of flight
Measured
RNM Prediction
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Development of Noise Abatement Flight Procedures
Rotorcraft Noise Model (RNM)
Predicted Noise Footprint
Assessment of Flight Procedures in
Vertical Motion Simulator
Measured Noise Footprint for Quiet Approach
with Acceptable Handling Qualities
Finalization of Flight Procedures in XV-15
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RNM Prediction Comparison with XV-15 Measured
Footprint
Increasing levels
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Planned RNM Enhancements

• Improved interpolation techniques
• Urban canyon effect
• Maneuvers
• Optimizer

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Concluding Remarks

• RNM provides a useful tool for
• Low noise operating procedures development
• Environmental impact assessments
• Current users
• U.S. Army, Navy, Marines and Air Force
• U.S. Rotorcraft Industry
• Canadian Defence Forces
• Uniquest
• The final report of the Helicopter Noise
  Prediction Subcommittee of the NATO CCMS will
  recommend adoption of RNM as the standard code
  for environmental studies.

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Obtaining RNM

• Written request is required
• Must sign a software usage agreement
• Contact David A. Conner at
• d.a.conner_at_larc.nasa.gov
• 757-864-5276