13-1] THE INFLUENCE OF ENVIRONMENT UPON DESIGN 681 



and landing, both while operating and while secured. The life of the 

 equipment also spans the conditions of manufacture, testing, storage, 

 transportation, handling, maintenance, and possibly shipboard operation. 

 An environment or envelope of environments is associated with each of 

 these conditions. Thus while the flight conditions are most important, all 

 conditions must be considered when the critical design values are selected 

 for the various types of environment. For example, mechanical shocks 

 received during ground handling and transportation may exceed in severity 

 any shocks imposed by the aircraft in which a radar is ultimately installed. 



The environment classifications mentioned above are closely related to 

 two categories called natural environment and induced environment. The 

 natural environment includes the influences which would be present at a 

 point in space before the arrival of the aircraft. These ever-present factors 

 include ambient wind, temperature, pressure, density and other specific 

 properties of the atmosphere, solar radiation, humidity, salt spray, and 

 moisture in other forms. The effects of these factors will be discussed in 

 detail in this chapter. There are also several types of natural environment 

 which must at some time be considered by the designer of an airborne radar, 

 but do not warrant a detailed discussion here. Among these are sand and 

 dust. The induced environment is the aggregate of the conditions and 

 influences (affecting an equipment) generated by the vehicle in which the 

 equipment is installed. One of the most troublesome examples of induced 

 environmental conditions affecting an airborne radar is the temperature 

 resulting from aerodynamic heating. Other examples are acceleration loads 

 from aircraft maneuvers, acoustic noise, vibration and shock, and nuclear 

 radiation. In most respects, an airborne radar actually lives in the induced 

 environment which is, therefore, the one of chief concern. 



The induced environment is, of course, influenced by the natural environ- 

 ment in which the aircraft flies. For example, the shock and vibration 

 acting on the equipment may be influenced by wind gusts and air density. 

 In a piece of electronic equipment cooled simply by ram air, the tempera- 

 ture of the air entering the equipment is roughly the temperature of the 

 ambient or "natural" air plus the temperature rise incident to compression 

 of the air entering the plane. 



The location of airborne electronic equipment in its parent aircraft has an 

 important effect upon the severity of the environment which it must with- 

 stand. The types of environment that change significantly in magnitude as 

 a function of location in the aircraft are temperature, vibration, shock 

 acceleration, acoustic noise, and (if present) induced nuclear radiation. 

 A designer has a very limited opportunity to locate the units of an airborne 

 radar so as to take advantage of this effect. For example, in the case of an 

 AI radar the indicator and controls have to be in the cockpit, the antenna 

 in a particular place, depending upon the type of target, and weight and 



