Chapter 6 TEST OA SERVICE EQUIPMENT AND TECHNIQUES 6.1 EFFECTS ON AIRCRAFT IN FLIGHT During Castle, Wright Air Development Center (WADC) continued their studies of the overpressures, gust loading, and thermal effects on aircraft in flight. A B-36D, pre-~ viously used on Ivy and Upshot-Knothole but with additional instrumentation and a white- painted underside, was flown in close proximity to all Castle shots. A B-47, previously utilized on Ivy and also additionally instrumented, participated in all shots but Shot 5. The ultimate objective of the program was the establishment of operational and design criteria concerning nuclear-weapon effects on delivery aircraft, both current and future. Data on both thermal and blast responses at input levels that were to approach the design limits of the aircraft were to be obtained for the B-36. The B-47 project had as its par- ticular objective the determination of the effects of a megaton-yield-range nuclear device upon a B-47B positioned to receive the predicted-maximum thermal radiation. The important characteristics of a nuclear detonation, with respect to aircraft, are nuclear and thermal radiation and the air-blast wave. At ranges critical for a B-36 with regard to thermal] and blast effects of weapons in the megaton-yield category, it had been previously shown that nuclear radiation effects due to proximity, envelopmentin the cloud, or fallout were negligible. The irradiance from the fireball varies with time and is characterized by a fast rise to a peak followed by a relatively slow decrease to zero. Radiant exposure for the B-36 in the Castle tests was expressed as: Q=Cc Ww e“KD = 36 W .-0.000D os D* (6.1) Where: Q = radiant exposure on a surface normal to the radiation, cal/cm? W = total yield of source, kt K = atmospheric attenuation coefficient, (10° feet)! D = distance between source and receiver, 10° feet C =a constant based upon thermal yield and attenuation measurements The relationship between the temperature rise of the thin skin (commonly used in aircraft) and radiant exposure was given by: AT (6.2) = QaL cosi =O Gpt Where: AT = change in temperature, F « = absorptivity coefficient 73