Getting to the meat, now.
The aero cap construction differs from the style
Phil Knox and
Brett Herndon produced for their trucks. Where they set up either a continuous straight line, or gentle arc from the top of the cab to tailgate level, the report author used a "compound" design to maximize storage space under the cap:
From Construction of Test Apparatus - Miscellaneous (p.11)
Quote:
Two main alternative cap profiles were established.
Design #1 is a design with two main angles, alpha & beta: alpha remains constant at 15 degrees with the horizontal, since covered volume was desired to be a maximum. Thes particular angle was chosen because it is the largest turning angle that can exists without [flow] separation. This is as stated by Dr. Walter M. Presz Jr., Western New England College.
Beta angle is the controlling factor in Design #1. This angle can vary between 0 and 12 degrees with the horizontal.
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Design 1, fixed 15 degree alpha angle, variable beta angles
Design 2, fixed 8 degree beta angle, rounded termination