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A limited experimental investigation has been conducted to confirm the existence of exhaust backflow from a cluster of three widely spaced nozzles operating in a near-space environment and to determine pressure and heat- transfer coefficients in the region washed by the backflow. Experiments were conducted in a 61-foot-diameter vacuum sphere using a sine solid-propellant rocket motor and a reflection plate. The reflection plate was used to simulate the interference planes that would normally exist for a cluster of three nozzles. Data were obtained for nozzle spacings of 8.02 and 17.05 nozzle exit diameters for pressures which simulated a nominal altitude range of 3.2 x 109(exp 5) to 1.8 x 10(exp 5) feet. The pressure data indicated that the backflow was super- sonic for several nozzle exit diameters ahead (upstream) of the nozzle exit plane and that the flow over small-diameter thermocouples in this region was in the free-molecule region. Average heat-transfer coefficients obtained for small-diameter cylinders (thermocouples) in this region were on the order of 1 x 10(exp -4) Btu/sq ft-sec-degrees R.
An investigation was conducted to determine the effect of temperature and composition on alloy softening in group VIA metals Cr, Mo, and W alloyed with Re. Results showed that alloy softening was similar in all three alloy systems occurring at homologous temperatures less than 0.16 and at Re concentrations less than 16 atom percent. Rhenium content required to produce a hardness minimum diminished rapidly in all three systems with increasing test temperature. The similarities in hardness behavior in these three alloy systems suggesat common softening mechanism which may arise from lowering the Peierls stress.