The input file for PanAir is error-prone and unforgiving. This program accepts a free-form file and creates a properly formatted input file for PanAir.
The program referred to as A502 is a pilot version of the production computer code known as PANAIR. Both PANAIR and A502 were developed by the Boeing Company under contract to the NASA Ames Research Center. The contract was funded by several agencies of the Department of Defense along with NASA Ames and Langley Research Centers.
These programs solve for the fluid flow about an arbitrary configuration at subsonic or supersonic speeds, using linearized potential flow theory. The A502 code was never intended for wide distribution and only modest efforts were made to document the input file format and explain the usage of the program. Recent developments have led to the more widespread use of A502 and the program must become available to a greater number of users. The purpose of this paper and the computer program it describes is to make the A502 version of PanAir accessible to a users in a simple fashion.
The input to A502 is described in the user's manual which is found on the disc. The input data is organized in specific columns. Editing an input file is a rather error-prone process. The PANIN program was written to enable a user to select the flow properties and all other program options by editing a short free-format file called an auxiliary file. One entry in the auxiliary file is the name of a file that contains the geometrical information. The format of this file is that of the NASA standard for wireframe geometry as described in reference 2. This file is usually referred to as a WGS file, standing for Wireframe Geometry Standard. The program reads the various items of control information from the auxiliary file and combines this information with the panel geometry in the WGS file to produce a combined file that is a properly formatted input file for PanAir.
The first and most difficult part of preparing a case for PANAIR or any panel code is the definition of the surface geometry as a set of quadrilateral panels. A variety of techniques exist for the creation of this data. A program call MAKEWGS in this collection is available for definition of simple geometries. Those familiar with the geometry programs in use at Langley may find it preferable to use QUICK or GEMPAK to produce inputs. The ultimate solution lies in the use of a Computer-Aided-Design (CAD) system that has a wireframe output option. There is a program A502WGS that will convert A502 input decks to WGS.
Once the WGS geometry file and the auxiliary file have been created and stored, the PanAir input file is created by invoking the program panin.
After the panin program has completed execution, two files have been produced. These files take their names from the data in the NAME record in the auxiliary file with extensions of .sh and .in. For example, if the record in the auxiliary file is NAME mycase, then the two files produced are mycase.in and mycase.sh. The .in file is the a502 input data.
Although a considerable effort has been expended in making the program free of errors or omissions, the user should inspect the input file and script carefully. There are many problems in forcing data to fit the fixed field format and inadvertent roundoff may result. The PRECISION keyword can be helpful, but there are many potential sources of error. The principal problem area is overflow of an output field when one is trying to keep the geometric accuracy high by printing many decimals. Two popular places for this error to occur are the x-coordinates of the trailing edges of wakes and the value of reference area. It is usually useful to scan the PanAir input file for asterisk characters.
There are many options in the PanAir input file and it would be virtually impossible to incorporate all of them in this program. For example, in PanAir you can select different reference lengths for yawing moment and rolling moment. PanIn simply asks for SPAN. And there are lots more.