Michael J. Lucas

Sonic Boom Environment Under a Supersonic Military Operating Area

A measurement program was conducted to record the sonic boom environment under a busy supersonic air combat maneuver training (ACM) arena. Simultaneous with sonic boom measurements, a complete record was made of supersonic activity. The measurements provided validation of the predicted elliptical pattern of C-weighted day-night average sound level (Lcdn) contours and demonstration of the nature of ACM sonic boom, which often includes non-W-wave signatures. Correlation of measured booms with flight activity data provided a quantitative model for prediction of LCdn contours for other similar airspaces. I. Introduction E NVIRONMENTAL assessment of sonic booms generated by supersonic air combat maneuver (ACM) training requires prediction of the C-weighted day-night average sound level (Lcdn). Initial efforts to compute LCdn contours1 were based on analysis of tracking data from an air combat maneuver instrumentation (ACMI) system, combined with simplified calculations2 of carpet booms (i.e., booms from steady level flight) for average supersonic conditions. The resultant model showed that supersonic activity occurs in an elliptical maneuver area centered between setup points used by pilots before engagement, and that LCdn contours are elliptical and aligned with the maneuver ellipse. Field validation of predictions for a new supersonic military operating area (MOA) confirmed the elliptical pattern, but measured LCdn values were at least 10 dB below predictions.3 The difference was thought to be due to the difference between carpet sonic boom footprints and the more complex footprints (described in Sec. III.B, below) which actually result from the supersonic phases of air combat maneuvers. The data collected and reported in Ref. 3 were, however, too sparse to draw general conclusions. Accordingly, a project was undertaken to measure sonic booms in a busy supersonic airspace. A 6 month sonic boom measurement program was conducted in the Lava/Mesa airspace at the White Sands Missile Range, New Mexico. This airspace is used for ACM training, primarily by F-15 aircraft from Holloman AFB. Thirty five sonic boom monitors were deployed. During the measurement period, all flight activity data for the airspace was reviewed and correlated with measured booms. A sample of ACMI tracking data was obtained for detailed analysis of particular events and to develop an understanding of how and when supersonic events occurred. Section II contains a description of the measurement program. Following completion of the measurements, statistical analyses were made of sonic booms identified with ACM activity.

Double throat pressure pulsation dampener for oil‐free screw compressors

This paper describes a recent invention at Ingersoll‐Rand for reducing the pressure pulsations in an oil‐free screw compressor. Pressure pulsation is a term used in the air compressor industry to describe the rapid change in pressure with time measured in the downstream piping of the air compressor. The pulsations are due to the rapid opening and closing of the screws as the compressed air is eject from the compressor into the piping system. The pulsations are known to produce excessive noise levels and high levels of vibration in the piping system. Reducing these pulsations is critical to achieving a quiet running compressor. This paper will describe the methodology used to analyze the data and show both computational and experimental results achieved using the pulsation dampener. A patent for this design has been filed with the US patent office.

Acoustic directivity measurements of the CH‐46E, CH‐53E, and AH‐1A helicopters

Presented in this paper are the results from acoustical measurements made of the CH‐46E, CH‐53E, and AH‐1 helicopters. Results from the test will be used to form a database of sound hemispheres that is currently under development for the rotorcraft noise model. A unique feature of the test was the use of two cranes having a tip height of 180 ft, that suspended two vertical arrays of microphones. Positioned between the two cranes was a third array of microphones located on the ground which completed the shape of a U. The helicopters flew through the center of the array with the plane of the rotor approximately inline with the cranes tips. Carried on board the helicopters was a tracking system which was time synchronized with the acoustic recording equipment. The acoustic data and the tracking data are combined in a computer program that depropagates the sound field to a sound hemisphere which preserves the directivity and frequencies of the acoustic field. A sound hemisphere is constructed for each pass th...

ROUTEMAP model for predicting aircraft noise exposure along military training routes

A model and PC‐based computer program has been prepared to calculate noise levels along low‐altitude, high‐speed military training routes. The program is designed for use by environmental planning personnel who are familiar with MTR operations and with noise, but are not necessarily expert. The program provides options for selecting general types of operations (visual or instrument navigation), aircraft types and speeds, altitudes, and nominal track centerlines. Up to 20 track/altitude/aircraft types may be defined within a 20‐mi‐wide corridor. Aircraft on each track have a Gaussian lateral distribution about the centerline. The program contains nominal standard deviations based on the type of operations, or the user may specify a site‐specific value. Aircraft noise emission levels are derived from the USAF NOISEFILE database. The program calculates Leq, Ldn, and Ldnmr, where Ldnmr is Ldn with an adjustment to account for the onset rate of MTR aircraft noise. Program output is available in tabular form or...