Week 16: The Barrowman Method

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Back in Week 7 we said CP had to sit behind CG for a stable rocket — but how do you actually calculate where CP is before you ever build the rocket? That question didn't get a rigorous, practical answer until the 1960s.

History

Rocketry needed to grow up from careful craftsmanship into rigorous, predictive engineering — being able to calculate stability on paper, before cutting a single piece of balsa or cardboard.

Forces

The Barrowman method estimates CP by adding together the aerodynamic contribution of the nose cone and each fin, based on their shape and position along the body.

Math

CP ≈ nose contribution + fin contributions, each weighted by shape and position along the body — a multi-term sum rather than a single simple formula.

Advances

James Barrowman developed and published this method while working at NASA, giving hobby and professional rocketry alike a reliable way to predict stability before flight.

Key Date

The Barrowman equations were published in 1966.

Safety Note

This is the math behind the Week 7 stability check. That ≥1 caliber margin only means something if CP was calculated accurately in the first place — Barrowman's method is how.