Article: 4032 of comp.sys.handhelds
Path: jpl-devvax!elroy.jpl.nasa.gov!usc!orion.oac.uci.edu!!nelson
From: (Matt Nelson)
Subject: Airfoil Plotter for HP48sx
Summary: draws airfoils of arbitrary size
Date: 29 Oct 90
Reply-To: nelson@psroot.ps.uci.edu
Organization: University of California, Irvine

    This is for all of the R/C model airplane/sailplane enthusiasts out there,
especially if you are into designing and building.  

    Here is the latest version of my airfoil section plotter.  I needed to plot
some ribs for a glider project, and realized that I had sold my trusty HP-28s.
I quickly re-wrote my original program to run on the HP-48sx, and came up with
something MUCH prettier, and MUCH MUCH faster.  This thing is really quite
painless to use now (the 28s version was slooooow).  

    The speedup came from creating a PICT that is big enough to contain the
entire airfoil section.  The airfoil data is plotted only once, and then sent
to the printer, one screen at a time, through successive PVIEW and PRLCD
commands.  BE WARNED...  although this is a very fast way to print out large
objects, it is also a memory-hungry way to do it; for example, a 10" SD7003
required a PICT that was 131 by 832.  When I saved this PICT to the stack and
BYTESed it, it was 14,154 bytes big.  On top of that, just the data for the
SD7003 (as listed below) is 988.5 bytes long.  All I am saying is that this
program DOES use a lot of memory, but is very handy, and serves my purposes
very well; if you don't like it, feel free to use something else.  

    To use this program, simply get into the AIRFOIL directory, and hit
[AIRFOI].  It will ask for an airfoil.  Just hit the menu button corresponding
to the airfoil data you wish to use (you can hit [SD700] to try it out), then
[ENTER].  It will then ask for a chord.  Give it a number corresponding to the
desired chord, in centimeters, then [ENTER].  The program will handle other
units, and in fact presents you with the UNITS LENG menu, so you can give it a
chord size in any unit you wish.  Just be sure to give it a valid unit object
(you have to supply the underscore manually, since the calculator is in program
entry mode at this point).  You should be greeted by a "working..." message.
Point the calculator at your 82240A/B printer, and watch the airfoil section
print out.  

    The airfoil data is assumed to be in a complex vector, where each element
corresponds to a point (x,y) on the airfoil.  The points should be arranged so
that if you were to draw lines sequentially from one point to the next, you
would trace out a closed outline of the airfoil section.  The sample airfoil in
this posting, the SD7003, should help illustrate this.  For those who are
interested, the SD7003 is an airfoil designed specifically for use at very low
Reynolds numbers, such as those encountered by model sailplanes.  

    There are two parameters which control the absolute size of the printed
output.  These are the global variables ycmps and xcmps.  These represent the
number of centimeters per screen OF PRINTED OUTPUT for the y and x directions,
respectfully.  One arrives at these values by printing a screenfull of
anything, and measuring the size of the printed output in centimeters.  The
numbers supplied below are for the 82240A printer; I have never used a 'B'
version of the printer, and don't know whether these numbers will have to be
changed in order to work properly with that printer.  The only reason I left
these numbers as global variables is so that the user could have some control
over the aspect ratio of the output, without diving into the program itself.  

    Please direct any comments/suggestions/questions etc.  to: 

     Matt Nelson           internet:  nelson@psroot.ps.uci.edu
     Physics Dept.         bitnet:    mnelson@uci
     University of California   phone:     (714) 725-2629
     Irvine, CA 92717