Barrowman for Unix

by Andreas Müller

Barrowman's method allows a rocketeer to compute the center of pressure of a rocket based on its dimenions, thus it becomes possible to predict stability of larger rockets where the swing test is not practical. However, most such software runs on Windows only, making it inaccessible to all those who don't want to do business with a convicted monopolist.

This is where the barrowman programm enters. Using a very simple command line interface, the center of pressure of any rocket that is decomposable into sections as described in the Barrowman report can easily be computed. To compute the center of pressure for the WRak, our weather rocket (see one would simply type the command

barrowman -v nosecone conic length:260 diameter:87 \
	transition length:15 diameter1:87 diameter2:79 \
	cylinder length:465 \
	transition length:87 diameter1:79 diameter2:102 \
	cylinder length:1137 \
	finsection length:390 a:390 b:140 diameter:102 s:171 m:210 n:4 \
	transition length:68 diameter1:102 diameter2:47
Within less then 10ms, the programm would produce the following summary of the rocket and computation of CP:
the rocket consists of the following parts:
      /\       length:  260.000
      \/       length:   15.000
      ||       length:  465.000
      /\       length:   87.000
     |  |      length: 1137.000
    #|  |#     length:  390.000
      \/       length:   68.000
total length: 2422.000000
C_n =     42.671
X_n =   1999.802

The programm also contains help which also explains how to specify fins:

usage: ./barrowman [ -d ] [ -v ] <section_specification>...
  -d   turn on debug mode
  -v   verbose mode: display additional info about the rocket
section specifications have the following formats:

    nose|cylinder|transition|finsection [ nosetype ] name:value ...

the nosetype argument is only required for a nosecone section
the allowed additional parameters in name:value format depend
on the type of section being added. Only the 'length' parameter
is required and common to all section types. A cylinder section
does not have any parameters except the length.

Nosecone parameters:
valid nosetype strings: conic|ogive|parabolic
   diameter    = diameter at base of nosecone

Transition parameters:
   diameter1   = forward diameter
   diameter2   = rear diameter

Finsection parameters: Fins are assumed to be trapzoidal with parallel
sides parallel to the axis of the rocket
   n           = number of fins
   a           = length of fin at airframe
   b           = length of fin at outer tip
   m           = shear: distance between leading edge at base and at tip
                 of fin projected to the axis of the rocket
   diameter    = diameter of the fin can
   s           = radius of outer tip of fin
approximate graphic representation (fin filled with *, airframe with .):
      ^   |.....:.....+        
      |   |.....:.....|\        ^
      |   |.....:.....|*\       |
      |   |.....:.....|**\      |
      |   |.....:.....|***\     |m
length|   |.....:....a|****\    |
      |   |.....:.....|*****\   v
      |   |.....:.....|******|
      |   |.....:.....|******|b
      |   |.....:.....+-__***|
      v   |.....:.....|    ^-+
                :      s

barrowman is free software available under the GNU General Public License. The current version is 0.9, it can be downloaded here:

© 2005 Dr. Andreas Müller, Beratung und Entwicklung