To safely withstand the operating requirements, a t/d ratio of 0.58 

 or larger would be used. Since the minor diameter is to be as large as 

 possible and commercial acrylic sheets come in thicknesses up to 4 inches 



t/d = 0.58 



The largest minor diameter would be 6.9 inches. 



The elevation, h, (see Figure 2) of the viewport in the flange is 

 another important aspect of the total viewport design. Using a t/d ratio 

 of 0.58 on the abscissa of Figure 14, a value for the ordinate is obtained 



from Figure 14 6, „ ^„„^ . , ^ „„„ 



,, , , > -1^ = 0.0021 inch per 1,000 psi 



(free boundary) d 



It is recommended by the authors that the viewport be elevated five 

 times the analytical (free case) displacement 



0021 

 h = 56, = (5) [ ' ^^ ) (6.9) (2,000) = 0.145 inch 



For safe operation of the viewport, a minimum elevation of 0. 1 5 inch 

 should be used in this particular design to insure adequate distance to the 

 end of the conical surface, again recognizing the fact that any significant 

 elevation above this achieves nothing (stress distribution remains the same) 

 and, in fact, only adds additional flange material (i.e., weight) to the vehicle. 

 Figure 19 provides for the use of a safety factor in designing conical 

 viewports. Safety factors are utilized when a designer cannot control all of 

 the many extraneous variables during fabrication and service that might 

 affect his original design. In view of the in-depth research for both the 

 structure and the material properties contained in this report, and the 

 reproducibility of commercial Plexiglas, the authors feel that a safety factor 

 of 1.5 is more than adequate, if all other design recommendations contained 

 herein are followed. 



ACKNOWLEDGMENT 



Mr. John McKay conducted the experimental tests and reduced the 

 experimental data used in this study. 



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