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Public Domain Aeronautical Software (PDAS)  
How do I get a copy of gnuplot?

Go to the Gnuplot Web Page for instructions on downloading a free copy of gnuplot.
The gnuplot website seems to move from time to time, but I will try to keep this reference current. There seems to be another entry point at UCC and if all fails, just try Google on "gnuplot".

How can I get a printed copy of DATCOM?

If you intend to be a serious user of digital DATCOM, you should get the manuals for the original DATCOM. I have a DATCOM Manual page that gives you the ordering details.

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 on the CD-ROM?

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.

There are files of type .pdf that are supposed to be copies of NASA reports. How do I look at these or print them?

These are files in portable document format (PDF). To read them, you need a PDF reader. The most commonly used program is Adobe Acrobat Reader. You can download a copy from the Adobe web site. You can also purchase the entire Acrobat package from Adobe (about $200) that lets you create PDF files and convert scanned documents into PDF. The Acrobat reader, which is free, only lets you read files that other people have created. The Acrobat reader acts as a plug-in for Netscape Navigator and Microsoft Internet Explorer that let you view a PDF directly in your browser.

I see that you have some pages labelled as XHTML + MathML. What is this?

I think that MathML is the upcoming way of presenting pages on the web that contain mathematical expressions. Go to my MathML page for more information.

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

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 the NASA document server. There is a copy on the CDROM.

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 the NACA document server. There is a copy on the CDROM.

When I try to run a program, it says that I cannot open a certain file (usually a .prt 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 just received my disc in the mail and I cannot read it on my computer. What do I do now?

I assure you this is not a frequently asked question, but it has happened. Since 1997, the PDAS discs have been CD-R rather than CD-ROM and there always is a possibility that the color of the dye on the disc and the color of the laser used to read it are not entirely compatible. One year, I ran out of discs in Reno and had to purchase some blanks locally. They were pale yellow in color and two people could not read them. I have access to many different shades of CD-R blanks and I will keep making discs for you until we get a match. I think the media manufacturers and the drive manufacturers have got this pretty well sorted out now -- just in time for a new technology, namely the DVD drives. I have heard stories of incompatibilities between CD-R and DVD-ROM, although I have not had a customer with a problem - yet! All I can say is that I will work with you until we get it. In the history of this operation I have only had four discs that needed to be replaced and one of these was because the postman folded the envelope to get it into a narrow mailbox. There is an informative article on this subject in PC Magazine, 18 Jan 2000, p. 124.
[Note added 31 Oct 2004. The last problem of this sort was in 1998. I am going to drop this item from the FAQ list soon.]

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.

NASA has written hundreds, maybe thousands of flight simulator programs. Why don't you put some of these on the CD-ROM?

The simplest answer to this is that Flight Sims tend to be very graphical and this will tie the program to one platform. In addition, there are numerous commercial products that are better value to an end user than a research code from NASA. If you want a flight simulator that you can look inside and modify to your needs, have a look at the FlightGear open source flight simulator. If you want more information on commercial flight simulators for the PC, you might begin at the AvSim site or the Thirty-Thousand Feet page. There are many add-in or add-on files for setting up simulators for a particular airplane or scenery - even cockpit gauges.

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.
They now have a web site at http://members.aol.com/hfdy/home.htm

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 your disc?

Simple. It is copyrighted and I will get myself sued. However, there is a copy of NACA 824 on the disc. 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. The disc also has 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. Anyway, you should all buy a copy of Abbott and von Doenhoff; the inexpensive Dover edition is a true 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.

What does the little image with W3C in the lower right of many pages mean?

This means that I have submitted this page to the World Wide Web Consortium and it has been approved as complying with the XHTML 1.1 standard. If you have web pages, you may also check them for compliance. Just click on any of my W3C images, and you will be taken to the W3C validation web site. You simply type the URI of your web page and you will find out what HTML errors you have committed. If your page passes, then you may proudly display the W3C logo.

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. But, to really top them all, you can use the fact that

Sqrt(Sqrt(2143/22)) = 3.14159265...
Can I use my credit card to order a copy of Public Domain Computer Programs for the Aeronautical Engineer?

You may use Visa, American Express or MasterCard to charge your purchase. The cards called EuroCard that also have a picture of the MasterCard logo seem to work. You may place an order at the PDAS Store and your credit card information will be encrypted for transmission over the internet. If you want to place a credit card order by mail or FAX, include the card number, expiration date and the name on the card if it is different from that on the shipping address. If you live outside the USA, please check that your card can be used to place US orders. I occasionally get orders (usually from students) whose cards may not be used outside the country of residence.

How can one place orders from outside the USA without using a credit card?

To place an order from outside the United States, you should go to a major international bank and have them write you a check to Public Domain Aeronautical Software (PDAS) for $299 US. They will charge you the equivalent in local currency plus money exchange fees. An alternative approach is to get an International Money Order, usually through a local post office.

I want to order by credit card, but I do not feel comfortable sending my number via the internet. What can I do?

There are several options.

  1. You can call me by telephone at 831-454-9754. Unfortunately, I am often out of the office, but
  2. There is an answering machine and I am the only one who reads the messages.
  3. There is a FAX machine attached to the same number and I am the only one who picks up faxes from the machine.
  4. A clever fellow had a way to defeat the so-called 'sniffer' programs that watch for 16 consecutive digits in mail messages. He sent me three messages. The first has the first 8 digits; the second message had the next 8 digits; and the third had the expiration date. Not perfect security, but pretty good. Another idea is to spell the number in words.
  5. Regular mail in an envelope. Not the fastest, but some of these programs date back to the sixties. You have made it for 30 years without these codes - what's another 5-6 days?
  6. Reconsider your options and decide to use the PDAS store. This will use the same level of encryption that you use when you purchase from Amazon or other online merchants.
I want to use a non-postal carrier, such as UPS or FedEx. Is this possible?

The simple answer is yes. But, of course, it costs more to do that. If you are in North America or Western Europe, you have to be in an fantastic hurry, because most people receive their discs in about five days. In other parts of the world, I can appreciate that the local mail service sometimes leaves a bit to be desired. The prices vary from location to location, but expect to pay an additional $70 for air express to east Europe, Middle-east or Asia.

Why do you put a low value on the disc on the customs declaration form for non-USA shipments?

If I put the price of $295 as the value, it actually slows down the delivery. Many people, even the express carriers themselves, tell me that the value that should be declared is the cost of sending another package if this one is lost or destroyed in the mail. From this point of view, the value is the cost of the blank disc plus the envelope and wrappers - about $5 at most.

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Public Domain Aeronautical Software (PDAS)