F • CONVECTIVE HEAT TRANSFER IN GASES 



required to carry the same load for buckling. According to Fig. F,20a 

 it is apparent, from a tension-load standpoint, that titanium is most 

 suitable all the way up to about 800°F, above which stainless steel would 

 be preferable. On the other hand, from a plate-buckling standpoint. Fig. 

 r,20b shows that aluminum alloy is preferable up to a temperature of 

 about 600°F, titanium is most suitable up to about 900°F, after which 

 stainless steel would be desirable. At any rate, regardless of loading con- 

 dition, it may be concluded that titanium should be the most useful of 

 the three metals between about 600°F and 900°F. (Mach number ranges, 

 corresponding to full boundary layer temperature rise from an ambient 



400 800 1200 1600 



Temperature, °F 



Fig. F,20b. Effect of temperature on the weight ratio 

 for the same buckling load for various metals. 



temperature of — 60°F, are also indicated in Fig. F,20b.) At higher tem- 

 peratures, say 1500°F, other heat-resistant alloys must be considered. 

 For example, Hastelloy C is a recently developed high temperature, 

 nickel-base alloy which has good inherent section properties and there- 

 fore may prove suitable for the design of the main structure of high 

 Mach number vehicles. Because the temperature of a body is greatest 

 at the nose as well as at other protruding parts, it may be necessary to 

 use an insulating material of low structural value, such as a ceramic, in 

 those regions, especially when such regions may be backed up with suf- 

 ficient supporting structure. The leading edges of wings may be treated 

 likewise. 



Calculation of skin temperature. In the engineering calculation of the 

 skin temperature of a high speed vehicle, the usual assumptions are: 

 (1) the skin is so thin that the temperature gradient in the skin normal 



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