Polar moments and ballistic properties of tri-foil penetrators

Early design tools for tri-foils involved the use of ersatz structures for analysis purposes. This paper presents a method that employs the actual shape to calculate the polar moments of inertia relative to a rod of equal cross sectional area. The method also degrades at its extrema into two logical shapes for this calculation, namely the circle and the equilateral triangle. A ballistic test was performed on a tri-foil having an effective aspect ratio of 14. Performance comparisons with a rod of aspect ratio 16 shows the ballistic performance of the tri-foil to be of the same order but marginally poorer. Systems considerations using tri-foils could make the tri-foil more attractive than the rod.