Thermal comparison of aircrew clothing aboard OV-10 aircraft.

Thermal evaluation of aircrew clothing in the field usually involves conditions which make it difficult to distinguish clothing effects from other, confounding factors. This paper reports a field study designed to solve this problem. The question concerned possible heat stress effects caused by adding an oxygen mask, an anti-g suit, or both to the usual clothing worn by pilots of OV-10 (twin turboprop) aircraft during 20 hot-weather flights (actual experimental temperatures of Tdb = 28-38 degrees C, rh = 18-20%). The four test ensembles were flown simultaneously, allowing side-by-side comparison to compensate for variations in flight profile and weather. Subjects (n = 10) encountered noticeable heat stress in flight, with rectal temperature = 37.4-37.6 degrees C, skin temperature = 35.0-35.5 degrees C, and weight losses = 2.1-2.4 kg. There were no measurable differences among the four clothing outfits, indicating that the anti-g suit does not present a heat stress problem. The mask and anti-g suit did contribute to aircrew discomfort as their impermeable materials prevented evaporation of sweat and caused 100% skin wetting in covered areas. Under these dry, desert conditions, the body was apparently able to compensate for the loss of evaporative surface area.