The FOOTPR and RADIUS computer programs implement state-of-the-art mathematical models for predicting levels of noise generated by existing or proposed aircraft. These programs can be used to calculate Federal Aviation Administration (FAA) noise-certification levels, airport-vicinity noise footprints, and levels of noise generated during climb and en route. FOOTPR and RADIUS originated in research at Lewis (now John H. Glenn) Research Center in the year 1981. Since that time, seven jet-noise models, four fan-noise models, a fan-noise-suppression model, and second core and turbine-noise models have been added to these codes, and a ground-reflection model already in the codes has been enhanced.

FOOTPR computes histories of noise at various observer stations (usually on the ground) for an aircraft flying at a specified set of speeds, orientations, and coordinates. These time histories are in the forms of spectra, overall sound-pressure level (OASPL), perceived noise level (PNL), and tone-weighted perceived noise level (PNLT). For each source of noise, free-field noise levels are initially computed with no correction for propagation losses other than those associated with spherical divergence. The total spectra can be corrected for the effects of atmospheric attenuation, extra ground attenuation, reflection from the ground, and shielding by the aircraft. The corresponding values of the OASPL, PNL, and PNLT are then calculated.

From the history at each point, true effective perceived noise levels (EPNLs) are calculated. Values of EPNL, maximum PNL, or maximum PNLT are thus found, as desired, for a grid of specified points on the ground.

RADIUS computes customary one-third-octave sound-pressure levels at a fixed radius at angles specified by the user. The noise-source subroutines used in RADIUS are the same as those in FOOTPR.

FOOTPR and RADIUS are batch-executed programs written in Fortran 77. No system software libraries (other than those for basic mathematical functions) are needed for execution. The current versions of these programs are executed on Unix-based computers, but they can be run on almost any computer/operating system combination that supports Fortran.

This program was written by Jeffrey Berton of John H. Glenn Research Center and Karen Kontos, Robert E. Kraft, Bangalore Janardan, and Philip Gliebe of General Electric Aircraft Engines. LEW-16576

NASA Tech Briefs Magazine

This article first appeared in the May, 1999 issue of NASA Tech Briefs Magazine.

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