THERMAL STUDY OF ANTI-G ENSEMBLES ABOARD F-16 AIRCRAFT IN HOT WEATHER

Continuing advances in the performance of new fighter aircraft have en gendered requirements for more sophisticated protective clothing and l ife support systems. A major goal is prevention of acceleration-induce d loss of consciousness. The USAF's Advanced Technology Enhanced Desig n G-Ensemble (COMBAT EDGE) increases acceleration tolerance by providi ng positive pressure to the oxygen mask; the work of pressure breathin g is reduced by adding a counter-pressure bladder over the chest. Howe ver, the addition of impermeable layers over the chest reduces the are a available for evaporation of sweat. This study was designed to deter mine whether COMBAT EDGE (CE) was demonstrably hotter than standard su mmer flight clothing (ST) during F-16 sorties in hot weather. Eight ma le pilots served as volunteer subjects, each flying missions at 1430 a nd 1745 h on two consecutive days, one day with CE and the other with ST. Data were logged at 1-min intervals for rectal temperature (Tre), skin temperatures at the chest and thigh (Tch and Tth) and air tempera tures outside the clothing at the same two sites (Tach and Tath). The weather was stable over the 4 d of data collection with highs of 34-36 degrees C and simultaneous dewpoints of 19-23 degrees C (relative hum idity 35-45%). The mean Tach was stable at 28 degrees C in flight, whi le individual means for Tath ranged from 22 to 25 degrees C. The lower value and greater variability at the thigh reflect its proximity to t he air conditioning vent. Despite the differences in air temperature, Tch and Tth remained in the range 34-36 degrees C throughout the fligh ts. Statistical analysis by ANOVA showed no significant effect due to the suit worn (CE vs. ST). The Tre tended to rise during preflight act ivities and the first half of the flight, and values during three flig hts reached or exceeded the 38 degrees C threshold recommended as the upper limit for core temperature in crews of high-performance aircraft . Post-study questionnaires showed that the pilots felt that CE was ho tter than ST; the failure to demonstrate objective differences may be due in part to the variability of conditions inherent in field studies . The finding of continuously warm skin temperatures and undesirably e levated Tre confirm the growing evidence that advanced aircrew clothin g imposes a high degree of thermal isolation which makes cockpit air c onditioning a poor means of facilitating aircrew comfort.