134 THE DEVELOPMENT OF WEAPONS SYSTEM REQUIREMENTS 

 100 



90 



> 

 o 70 



o 

 ^ 60 



40 



4 6 8 10 12 14 16 18 20 22 



RANGE (n.mi.) 



Fig. 2-52 The Probability of Conversion After Lock-on. 



The discerning reader will note that a trade-off analysis could be made 

 between lock-on range and look-angle. For example, a longer lock-on range 

 would allow a smaller look-angle. When space in the aircraft nose is at a 

 premium, it may be easier to increase lock-on range than to provide large 

 look-angles. In addition, the derived look-angle specification (67°) is 

 pessimistic. At the aspect angle at which look-angle is critical {d = 75°) a 

 lock-on range of 10 n.mi. yields a conversion probability of 100 per cent. 

 This reduces the vectoring probability requirement for this attack from 

 95 per cent to 78.5 per cent. The look-angle requirement corresponding to 

 this vectoring probability may be read from Fig. 2-36 as 53°. This is quite 

 a significant relaxation of requirements and illustrates the advantages to be 

 gained by examining the interrelationships among the system factors. 



In summary, the lock-on requirements are established by the head-on 

 attack situation, and the look-angle requirements are establised by the 

 beam aspect approach situation. These requirements are: 



Required lock-on range 



Required look-angle 



10 n.mi. with 90 per cent cumulative 

 probability 



±53° in azimuth and elevation 



The look-angle capability must be provided in both azimuth and eleva- 

 tion because the aircraft will roll to angles approaching 90° during the 

 conversion and vectoring phases. 



