Investigation of Transonic Drag Computations in Aerodynamic ...

Investigation of Transonic Drag Computations in APAS
4.1.1 Program Description
Transonic drag in APAS is calculated in the subsonic/supersonic portion of the
program, UDP. UDP analysis is based on slender body theory and source and vortex
panel methods 1 . Drag calculations are performed as part of the program’s background
analysis, in which the user sets up specific runs, or flight conditions, at which the vehicle
is then analyzed. The program generates an output file which can then be used to
generate an aero-deck, which is subsequently used by the SSDL in conjunction with
POST to optimize the vehicle’s trajectory. This output file contains lift and drag
coefficients at each specified set of flight conditions, such as angle-of-attack, altitude,
and Mach number. APAS also contains commands for interactive “sub-programs” that
can be run by the user in the “foreground” of the program. The commands “wave” and
“visc” start two of these sub-programs that find the wave drag and viscous drag
respectively at user specified flight conditions of the geometry stored in the local folder.
4.1.2 Geometry Preparation
The Excel spreadsheets shown in Figures 5 and 6 were prepared in order to
facilitate geometry creation in APAS and to make rapid changes in wing size and
placement without having to create multiple configurations in APAS. APAS uses
command line prompts to input a configuration, one part at a time. Fuselage parts are
entered as sets of streamwise coordinates, the cross sectional areas at each coordinate,
and the ratio of the width of the fuselage to the height of the fuselage at each coordinate.
Jeff Miller 8