680 MECHANICAL DESIGN AND PACKAGING 



electronic packaging design, it is so evident that it requires little discussion. 

 Practically all design is influenced by space and weight limitations, and the 

 packaging of an airborne radar is no exception. The available space, 

 generally well defined by the airframe designer, is invariably so small as to 

 require a considerable amount of ingenuity of the equipment designer if he 

 is to fit it in while meeting all of the other requirements. Weight limitations 

 are equally important. In an airborne application anywhere from 5 to 20 

 pounds of airframe, engine, and fuel weight are required to support each 

 pound of payload. This ratio — defined as growth factor — increases with 

 the speed and altitude for which the aircraft is to be designed. For space 

 vehicles, growth factors from 50 : 1 to 100 : 1 are common. In a particular 

 application the radar designer should be thoroughly familar with the 

 trade-offs between the weight of the radar equipment and the performance 

 of the weapons system. The specification "as light as possible," while 

 laudable in intent, is not a sufficient incentive to design ingenuity. 



13-1 THE INFLUENCE OF ENVIRONMENT UPON DESIGN 



An airborne radar which contributes to the control of guided missiles 

 often is installed in high-performance aircraft operating at extreme speeds 

 and altitudes. It must perform reliably according to specifications in spite 

 of acoustic noise, vibration, heat, and other adverse environments. Failure 

 of a single component of the radar to operate satisfactorily when subjected 

 to the environment of a mission may mean failure of the aircraft to accom- 

 plish its task. Thus the design of an airborne radar, like the design of other 

 military equipment, must enable it to survive the undesirable conditions 

 imposed by the various environments encountered during its life. The 

 information presented in this chapter includes a description of the various 

 categories of environment, some of their adverse effects upon the equip- 

 ment, and some of the design principles that will assist in obtaining 

 optimum performance from the electrical equipment. An extensive 

 treatment of guided missile design in the expected environment is to be 

 found in the volume Aerodynamics^ Propulsion, Structures, and Design 

 Practice (see Bibliography at the end of this chapter: item 1 under Books). 



Environment, for the purposes of this chapter, may be defined as the 

 aggregate of all the external conditions and influences affecting the life and 

 performance of an equipment. It may be classified by type and condition 

 as was done in Paragraph 1-9, i.e. as the physical environment and the 

 airjrayne environment. The elements of the physical environment likely 

 to cause difficulty include temperature, pressure, humidity, precipitation, 

 salt spray, radiation, sand, dust, etc., while those of the airframe include 

 dynamic forces, acoustic noise, explosion, etc. During its life, the equipment 

 will be subjected to the many rigors of flight conditions, as well as takeoff 



