712 MECHANICAL DESIGN AND PACKAGING 



introduces disadvantages similar to those of a pressurized system. The 

 placing of a grounded shield between the conductors and the careful use of 

 insulation techniques between terminals is sometimes of advantage. 

 Smooth surfaces and rounded edges on conductors will help to eliminate 

 any tendency toward excessive voltage gradients. 



Protection from the damaging effects of this environment can be met 

 satisfactorily by known conventional methods. The challenge lies in 

 evaluating each of the methods for its effect on an overall system with 

 regard to the electrical, mechanical, structural, and thermal requirements. 



13-12 MAINTENANCE AND INSTALLATION 



Another major influence upon packaging design is the necessity of 

 providing for efficient maintenance and easy installation. Although the 

 designers make every effort to promote reliability, it is evident that 

 maintenance requirements cannot be altogether eliminated. 



Maintenance^ the practice of keeping equipment in a state of full effi- 

 ciency, generally may be divided into preventive maintenance and repair. 

 Both are dependent upon checking and testing. It is important that 

 maintenance interfere with aircraft availability as little as possible, and 

 that it require a minimum of work space and manpower. It is also desirable 

 that the required inventory of parts and tools be as small as possible. 

 Good packaging promotes these objectives mainly by minimizing the effort 

 and skill required to gain access to all parts of the radar. 



Application of several principles can assist in reducing the maintenance 

 problem. The approach to all subassemblies and components should be 

 reasonably direct. It should be possible to remove any major unit of the 

 radar without first removing adjacent units. Within any subassembly 

 (except throwaway units) it should be possible to replace any component 

 without disturbing others. Subassemblies should be light enough to be 

 handled safely by one man; their removal and replacement should require 

 no more than two hands. Alignments should be positive: shimming and 

 other difficult adjustments are undesirable. Test points for checking should 

 be visible and accessible. 



Although it is advantageous for mounting fasteners to be easily remov- 

 able, it must be remembered that the primary function of fasteners is to 

 fasten securely in spite of all environmental hazards. Reliability in 

 fasteners must never be sacrificed to obtain quick-release features. 



The use oi plug-in subassemblies is an important packaging technique and 

 has several good features for maintenance and installation. In this type of 

 design, the radar is built up of a number of comparatively small assemblies. 

 The interconnecting wiring of such an assembly is brought out from a 

 multicontact connector which is rigidly mounted to the chassis in a fashion 



