686 



MECHANICAL DESIGN AND PACKAGING 



1400 



1.0 1.5 2.0 



MACH NUMBER 



Fig. 13-2 Stagnacion Air Temperature vs. Flight Speed and Altitude. 



earth's surface. Since, however, the factor of transmissivity of solar 

 radiation through the earth's atmosphere is a variable, it is feasible and 

 conservative to consider the maximum solar radiation constant of 429 

 Btu/ft^/hour to obtain for all design conditions, ground operations as well 

 as flight conditions. Therefore, the actual rate of heat transfer to the 

 aircraft or body skin by solar radiation (resulting in an increase of internal 

 compartment temperatures) is the product of the solar radiation constant, 

 the absorptivity of the body surface, and the surface area. For purposes of 

 calculation, the surface area used should be only that area exposed to the 

 sun's rays. The temperature effects of solar radiation should be added to 

 the effects of aerodynamic heating and equipment heat in order to establish 

 the total temperature of the compartment housing the electronic equip- 

 ment. Solar radiation is a large percentage of the total load for that phase 

 of the equipment life concerned with ground operation. This is especially 

 true during the nonoperating phase of the equipment, since the total 

 compartment ambient temperature is then determined by the effects of 

 solar radiation. 



