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 http://rockets.othello.ch) 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 diameter2:47Within 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>... options: -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 .): : diameter <---------> : ^ |.....:.....+ | |.....:.....|\ ^ | |.....:.....|*\ | | |.....:.....|**\ | | |.....:.....|***\ |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: http://rockets.othello.ch/barrowman/barrowman-0.9.tar.gz.