194 



REFLECTION AND TRANSMISSION OF RADIO WAVES 



fuselage is so large relative to the echoes from other parts of the aircraft 

 that it predominates over them and a relatively small amplitude variation 

 results. 



Fig. 4-16 shows a 5-second sample for the B-45 twin jet bomber, taken 

 for an approach run in which the aspect varied by 2|°. Here the approach 

 to the Rayleigh distribution is poor, the range of amplitude variation being 

 much more compressed. However, a 5-second sample at another aspect, 

 in which the aspect angle varied 4|° (Fig. 4-17) shows a much closer 



0.01 0.5 5 20 40 60 80 90 95 p 98 99 99.5 



PERCENTAGE OF TIME THE VALUES EXCEED THE ORDINATE 



Fig. 4-16 Cumulative Amplitude Distribution of B-45 Echo, Approach Aspect; 

 Small Range of Aspect Angle. 



approach to the Rayleigh distribution. From an examination of data taken 

 over a wide range of aspects, it was concluded that samples in which the 

 azimuth of the B-45 varied by more than 4° gave a satisfactory fit to the 

 Rayleigh distribution. 



Fig, 4-18 shows a set of distributions for the F-51 single-engine propeller- 

 driven fighter. Although the lower amplitudes follow the Rayleigh distribu- 

 tion quite well (on 9380 Mc/sec the lower levels were lost in the noise at 

 the range of the measurements plotted in this figure), there is a pronounced 

 upswing at high levels above the values expected from the extension of the 



