Resolving the Orientation of Cylinders and Cuboids from Projected Area Measurements

Report No. ARL-TN-0759
Authors: Richard Saucier
Date/Pages: May 2016; 44 pages
Abstract: The FATEPEN model predicts the penetration of a mass striking a target plate for a variety of shapes, including cylinders and cuboids—among others. Crucial to the use of the model is a good estimate of not only the mass and velocity but also the impact orientation in terms of pitch, yaw, and roll. Yaw cards and orthogonal X-rays can provide estimates of the impact projected area,but the model makes use of the impact angle, which is defined to be the minimum angle that a face makes with the target plate. This report addresses this issue by calculating the pitch-yaw-roll rotation sequence that will bring about the orientation at impact from orthogonal projected area measurements. It is shown that the impact angle is uniquely determined in the case of cylinders, but that is not the case for cuboids. Furthermore, for cuboids multiple impact angles for the same projected area measurements can lead to significantly different FATEPEN predictions. This leads to the conclusion that cylinders and not cuboids should be used for FATEPEN validation.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2016