Public Domain Aeronautical Software (PDAS)  

This program is a solution to the problem of a shock propagating through a variable atmosphere. For an atmosphere which varies arbitrarily in the vertical direction and for a supersonic aircraft with arbitrary lift and volume distribution the computer program will give the shock overpressure and intersection points at the ground. In addition, effects due to aircraft acceleration, flight path angle and curvature and acoustical cutoff are computed and presented by the program.

The program uses the following input data:

  1. Atmospheric pressure, temperature and winds between the aircraft and the ground, and shock-ground reflection factor.
  2. Aircraft parameters such as Mach number, altitude, acceleration rate, volume and lift factors, aircraft length and weight.

The analysis is based on ray tube concepts, that is, a small segment of shock is considered to be propagating down a ray tube and its strength and location are determined along the ray path until it strikes the ground. Therefore, another input is the initial ray directions. These are specified by giving those angles, measured around the flight direction, for which computations are desired.

The computer output gives the location and strength of the shock corresponding to a selected input angle at intermediate computed points between the aircraft and the ground and also computes the location and strength of the shock at the shock-ground intersection.

This program was not released through COSMIC. I obtained the source code from a scan of the document (NASA CR-157), so there are numerous possibilities for errors in scanning. The program compiles without error and the test cases from the document run to completion. However, the results are not identical to those shown in the report, which leads me to suspect there is still a discrepancy in the program code. I would greatly appreciate any comments or suggestions. Perhaps one of you can identify a remaining error.

Public Domain Aeronautical Software (PDAS)