Frequently Asked Questions

Some questions about Public Domain Aeronautical Software come up frequently.

How can I get a copy of the free gfortran compiler?

Go to the gfortran web site. From there, you can get a copy for Windows, Macintosh, Linux or several other platforms. The gfortran compiler is part of the Gnu Compiler Collection, and you can install the entire collection, thereby giving you Fortran, C, Java, and C++ compilers.

How can I get a copy of gnuplot?

Go to the Gnuplot Web Page for instructions on downloading and installing a free copy of gnuplot. If you use Linux, be sure to get gnuplot-x11 and not the generic gnuplot.

My old copy of the DATCOM document has missing pages. What do I do?

If you have a disc from 2012 or earlier or loaded the DATCOM reference document from this site in the past, be warned that there are missing pages. Go to fixedDatcomDocs.html to get a new copy of the entire document with the missing pages restored.

What does the variable SWAFB stand for in DATCOM?

Short answer: I don't know. Obviously, this was intended to be used for something, but it was never implemented. I have scanned the entire source code and can assure you that it is never used on the right hand side of a = statement or in a subroutine or function call. Several users have been a little worried because it appears in some examples. If anyone has any inside information, I will include it in the documentation.

What version of PanAir is distributed?

This version of PanAir is known as the ht2 version and is the last public domain version dated 1993. The Boeing Company has continued the development of PanAir, but not for public release.

Panair input is too difficult and Panin is incomplete and has errors. Isn't there an input procedure for Panair that has a graphical user interface?

People have wanted this for years, but no one has stepped up and taken on the task. There is a new company, called Hegedus Aerodynamics that is in the process of developing such a product. You may download the current version of this product from their web site.

How can I get a copy of the NASA report on the geometry of the NACA airfoil sections?

In December 1996, NASA published a new report outlining the theory behind the NACA airfoil sections. It is designated TM-4741 and you can download a copy (PDF, 293 KB) from this server.

How can I get a copy of NACA Report 1135 with Equations, Charts and Tables for Compressible Flow?

You can download a copy (PDF, 12.9 MB) from this server.

When I try to run a program, it says that I cannot open a certain file (usually a .out file). What is wrong?

The most likely reason this happens is if you are trying to run the program from the CD-ROM and have set the default drive to the CD-ROM. The problem is that the program is trying to open an output file on the default device. Now, you cannot create a new file on the CD-ROM. It is possible to run from the CD-ROM, but you must leave the default drive set to a hard disk.

I copied a file from the CD-ROM. Now, when I want to modify it, my editor says that I can't. What's wrong?

All files on a CD-ROM are read-only. Sometimes, depending on how you do the copy, this attribute gets carried over to the copy of the file. If this happens, bring up the Properties page for the file and uncheck Read-only. (Right-click to get Properties). This should never happen on Linux or Macintosh.

The program on this disc gives coordinates for NACA airfoils, but I am interested in a [... airfoil name ...]. Can you help?

The best source for help is the Airfoil Data Site.

What airfoil is used on the [... airplane name ...]?

I once started a list of airplanes and the associated airfoils. Then I ran across The Incomplete Guide to Airfoil Usage and was amazed at the depth of coverage. There are hundreds of airplanes in the list with the corresponding root and tip airfoils. I quietly threw my meager list away and now consult this page. You can all thank Dave Lednicer for maintaining this list and send him any info you may have for additions to the list.

I want to get copies of the books Fluid Dynamic Drag and Fluid Dynamic Lift by Hoerner. They do not seem to be available in bookstores. Can I get copies through PDAS?

No, not from me. But if you write

Hoerner Fluid Dynamics
PO Box 21992
Bakersfield CA 93390

you should find out the current price, etc.
I think you can order through Amazon, also.

What book should I read to learn about [... aeronautical topic ...]?

The best thing I can do is to refer you to Dan Raymer's book list. He has collected a most comprehensive list of important books for aero folks with comments, etc. His whole site is worth a visit.

Why don't you put a copy of Theory of Airfoil Sections by Abbott and von Doenhoff on the distribution?

Simple. It is copyrighted and I will get myself sued. However, you can easily download a copy of NACA Report 824. This report by Abbott, von Doenhoff and Stivers was the prototype of the book. The report has some interesting material that is not in the book. You can also download a copy of NACA Report 452 by Theodore Theodorsen with a thorough treatment of airfoil theory that overlaps much of the material in the book. You should be aware that there are many typos in the numerical tables in the three appendices to the book. There are corrected pages at this web site. Anyway, you should all buy a copy of Abbott and von Doenhoff and also print the corrected pages from this web site for any airfoil you wish to examine. The inexpensive Dover edition is a bargain among the expensive textbooks of the modern day.

How can I get a job in the aviation industry in the USA?

I get asked this a lot and I really don't have a good answer. If anyone can help me out with a reference or a web site that deals with this question, I would really appreciate it.

How can you make the best approximation of pi, using only six decimal digits?

So, what does this have to do with aeronautical engineering? Probably nothing, but I will share this way to win a free beer now and then. Most folks will answer this with 3.14159, but you can amaze them with the fact that 355/113 is 3.14159292... which is better than 3.14159, and much, much better than 22/7 which is often offered as an approximation. But, to really top them all, you can use the fact that

Sqrt(Sqrt(2143/22)) = 3.14159265...