THREE MODEL ROCKET PROGRAMS: ALTITUDE, STABILITY TRACKING

By Burton L. Craddock


STABILITY
The program STABILITY calculates the stability of model rockets with 0-3 conical
transitions of the body and with 1-3 sets of fins. Each set of fins has either 3
or 4 fins. The program can handle the stability calculations for model rockets
from one-stage models to three-stage models. Stability can be an aid in
designing stable model rockets.

The first group of input data is the nose length and the nose base length. The
nose base length is rocket diameter at the nose base. The rocket nose is the
front part of the rocket. The rocket dimensions in this program are expressed in
millimeters. 

TRANSITIONS
If there are any transitions, enter the input data for 1-3 transitions. The
input data for each transition is the transition front diameter, the transition
rear diameter, the transition length, and the length between the nose tip to the
transition front.

FINS
The next group of input data is the fin data for 1-3 set of fins. The data for
each set of fins consists of the number of fins, radius of the body at the fins,
and the fins' dimensions.

The following is a description of the fin dimensions for fins with four sides.
These measurements are required for the program. 

The fin root chord is the fin edge, or side, in contact with the rocket body.
The fin tip chord is the fin edge with no endpoints in contact with the rocket
body. The fin semispan is the perpendicular line distance from a line through
the root chord and the tip chord rear endpoint. The midchord length of a fin is
the distance from the midpoint of the fin root chord and the midpoint of the fin
tip chord. The fin root to tip LE sweep is the distance parallel to the body of
the root chord frontal endpoint and the tip chord frontal endpoint. The nose tip
to fin chord distance is the distance between the nose tip and the root chord
frontal endpoint. 

For delta fins with three edges, the input for fin tip chord length is 0 and the
input for the midchord length is the distance from the midpoint of the fin root
chord and the fin tip corner.

CENTER OF GRAVITY
The next input data is nose tip to center of gravity distance. The center of
gravity is found by balancing the rocket model with a loaded motor installed for
each stage on a narrow edge.

NOSE SHAPE
The last input data is a menu selection of three nose shapes. The three nose
shapes are ogive, cone, and parabola. An ogive nose shape is similar to a
parabola but has a tip that is sharply pointed instead of rounded like a
parabola.

READOUT
The output includes the normal force, the moment, and the center of pressure for
the transitions, fins, and total rocket; the stability margin in distance from
center of gravity and in calibers for the total rocket; and the stability as
unstable, questionable, or stable.

After the output results, the user has the option of running the program again.



Gazette, June 1994