13-3] TEMPERATURE 683 



component parts. The design philosophies and environment requirements 

 are set forth in documents known as military specifications (MIL Specs). 

 The documents also establish procedures for testing airborne equipment 

 under simulated and accelerated environmental conditions. 



Types of information contained in the military specifications, and listed 

 therein under the heading "Requirements," are environmental tests, 

 modification of test limits, test facilities, test measurements, and sequence 

 of tests. Listed under "Test Procedures" are tests of reliability in face of 

 temperature and altitude, vibration, shock, humidity, salt spray, explosion, 

 sand and dust, fungus, and acceleration. 



Recommended materials, parts and processes are sometimes outlined in 

 the military specifications in order to achieve optimum space, weight, and 

 interchangeability and still allow the designers to meet the performance and 

 environment requirements. Methods of mechanical locking, fastening 

 devices, structural mounting of component parts, electrical connections, 

 wiring, etc. are included in order to aid designers in creating products that 

 can resist the imposed environmental conditions. 



The major documents that outline the general philosophy of the design 

 and testing of airborne electrical equipment are: MIL-E-5400A(ASG), Gen- 

 eral Specification Electronic Equipment (aircraft); MIL-T-5422C(ASG), 

 Aircraft Electronic Equipment, Testing Environmental; MIL-E-5272A, 

 General Specification for Environmental Testing, Aeronautical and 

 Associated Equipment; and MIL-E-8189A, General Specification for 

 Electronic Equipment, Guided Missiles. Other applicable specifications 

 defining detail requirements of items such as equipment mounting bases, 

 vibration and shock mounts, electrical connectors, installation of wirings, 

 etc. are all referred to in the above-mentioned specifications. 



Military specifications are necessary in order to obtain uniformity of 

 design, high reliability, operation and maintenance suitability, economy, 

 manufacturability, and weapon compatibility. Conformance to the 

 specifications will aid in achieving an optimum airborne electronic system 

 which is required to operate while being subjected to the various environ- 

 mental conditions. 



13-3 TEMPERATURE 



Plainly the performance of an airborne radar system will be affected and 

 limited by the temperature of its components. This is also true of the other 

 equipment installed in the aircraft, and indeed, of the aircraft itself. 

 Temperature has an important effect upon the materials problem. The 

 variation in structural properties of metals and plastics with temperature 

 (see Fig. 13-1) may have to be considered in designs for installations in 

 high-speed aircraft. More critical, however, are the characteristics of the 



