Determining aircrew helmet size design requirements using statistical analysis of anthropometric data.

Traditionally, the number of aircrew helmet size rolls has been determined using head length and breadth for specified percentile ranges of a target population. Helmet mounted display technology will require taking the third dimension (pupil-vertex height) into account. Using data from "An Anthropometric Survey of 2000 Royal Air Force Aircrew, 1970/1971," the three head dimensions of length, breadth, and pupil-vertex height were plotted for each subject. A minimum number of helmet sizes was calculated to achieve a reasonable quality of fit. The 93.5% of subjects grouped around the population mean was the largest fraction which had a reasonable quality of fit while using nine sizes. Attempts to fit a larger percentage would require either a large increase in the number of sizes or a relaxing of fitting quality.