186 



TARGETS 



for each of a series of 3-seconcl intervals. A plot is 

 made of P2 against range d on log log coordinates. 

 As might have been anticipated from equation (45), 

 in Chapter 2, it is foimd that a Ime with a constant 

 slope of —4 passes through the average of the IB- 

 second interval maximum points, although the 

 individual points fluctuate \\'idely. The value of a 

 corresponding to this line is calculated. 



The resulting value of a still cannot be called an 

 average value because the maximum value of a 

 has been used for each point. Consequently these 

 values of a-, sulDstituted into eciuation (45) in Chap- 

 ter 2, cannot be expected to give the average value 



of P2, or to give observed maximiun ranges. How- 

 e^-er, it is found that if the A'alues of cr thus computed 

 are reduced 40 per cent, they give correct results. 



These empirical cross sections are relatively mde- 

 pendent of \va\'elcngth. This result may bv inter- 

 preted to mean that a plane in motion behaves more 

 or less like a collection of specularly reflecting sur- 

 faces oriented at random, as equation (21) indicates. 



Attempts have been made to develop formulas 

 giving operational cross sections as a function of 

 some large feature of plane design, such as wing 

 span or length of fuselage, but these attempts have 

 not been successful. 



