Jim Barrowman’s approach was to divide the rocket up into sections, as shown at left, and to calculate the CP parameters for each section. By combining all the elemental CP’s, one can derive the overall CP.

At angles near zero (assumption 1), the following formula gives the normal force acting on the rocket:

                        N = CNα.1/2 ρV2.α.Ar

where:    N = normal air pressure force acting on the

                        rocket

               CNα = dimensionless coefficient related to the             shape of the rocket

                1/2ρV2 = dynamic pressure

                 α = angle of attack

                 Ar = body reference diameter (usually  taken at base of nosecone)

So the idea is to calculate the individual values of N for each section of the rocket, using known CNα’s for certain shapes. Another of Barrowman’s key assumptions is that, at angles of attack (α) close to zero, the contribution of the force on the body is so small as to be negligible.

To break up the rocket and do the analysis, Barrowman used CNα to represent normal force (instead of N), and used subscripts as follows: n = nose, cs = conical shoulder, cb = conical boat-tail and fb = fins in the presence of rocket body. Lastly he used the term

_

X (pronounced X bar) to mean distance from a reference point, this being the tip of the nosecone.

 

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