1. Reference 16;Since
2. The aerothermochemical analysis was conducted for a typical lifting entry vehicle with a wing loading parameter, W, of 200 and a lift to drag ratio, CLS (L/D), of unity. Figure 25 shows the low Reynolds number aerodynamic convective heat transfer utilizing the non-conservative and inappropriate high Reynolds number theory. Note that gross errors result in heat transfer predictions when low density, viscous effects are not considered. The surface temperature response for the JTA nose cap is shown in Figure 26. Both RVA and PT-0178 nose caps showed comparable surface temperature responses. All three materials reach the same maximum surface temperature of 42000R. For the PT-0178 nose cap, a computation was also made at a station one radian downstream of the stagnation point utilizing the reduced downstream heat flux shown in Figure 25. In this case, the maximum surface temperature reached 390O0R. The over-all lower temperature level at this station has a significant effect upon the surface recession as may be seen in Figure 28.
3. The location of the critical lifting entry times for subsequent stress analysis was determined utilizing the identical approach followed for the ballistic entry study. By reviewing the transient behavior of the four thermostructural parameters, defined in Equations (9) through (12)for each concept, entry times of 104 and 2000 seconds were judged to be critical. Since both the pressure and radial stresses are small for the hemispherical nose cap configuration, Equation (16)was utilized for determining the circumferential stresses at the two critical entry times of 104 and 2000 seconds.
4. For effective use of any one of the materials involved in this study as a leadlng edge component of a glide re-entry vehicle, further characterization of the reaction rate controllea oxidation mass loss over a wider temperature range is required. The graphite-refractory compound composite has afiaracteriatlca quite different from the bulk graphites and Plber reinforced graphltes and has exceptionally good oxidation resistance In the temperature range 3100-330O0F. The development of a heat and mas8 transfer theory for this composite is needed t o enable meaningful flight predictions to be made of the material behavior during glide reentry conditions. The investigation of a wider range of ballistic entry missions than was involved in this study is needed t o identify desired materials characteristics which, in turn, would be most helpful in the development of bodies with optimized properties. This is more applicable t o graphites than most other materials since graphite la easily fabricated into shapes having any one set of properties of a large range of property combinationa. Finally, characterization of the physical properties of graphite (and carbon), including phase diagram work, at temperatures above 500O0F l a needed for reliably assessing the suitability of graphites for heat shield and other high temperature applications.