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The stability triangle

Stability triangle formula

Abbreviations

sg
Gyroscopic stability factor
sd
Dynamic stability factor

Explanations

The dynamic stability conditionGo to formula can be expressed in an alternate way. leading to a very illustrative interpretation of bullet stability.
In using a quantity s, according to the above definition, the dynamic stability condition takes a very simple form (see above formula). This means that for a bullet to be gyroscopically and dynamically stable, a plot of s vs. sd has to remain completely within the stability triangle (green area in the figure below).
Stability triangle


The red areas are regions of gyroscopic stability but dynamic instability: either the slow mode oscillation (left area) or the fast mode oscillation (right area) get umdamped.

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