A program has been conducted at the NASA Lewis Research Center to evaluate methods of providing thrust modulation for solid-propellant rockets by varying the nozzle throat area. Three of these methods were evaluated in a cold-flow rig over a pressure-ratio range from 10 to 150. In one of these methods (throat injection) throat-area variation was obtained by injecting air at the nozzle throat perpendicular to the primary flow. The other two methods used physical blockage and are re¬ferred to as the throat insert and the elliptical throat.nThe injection configuration produced a maximum reduction in effec¬tive nozzle throat area during the investigation of 14 percent at an injection flow ratio of 0.33 (i.e., secondary to total flow);no meas¬urable losses in thrust ratio were evident at or near design pres¬sure ratio. The throat-insert and the elliptical-throat configurations produced an area reduction of the order of 50 percent. For these two configurations as the nozzle throat area was reduced about 35 percent at or near design pressure ratio the thrust ratio decreased about 0.02. Larger thrust-ratio reductions were encountered at nozzle pres¬sure ratios considerably below design.
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