Efficiency of Supersonic Nozzles for Rockets and Some Unusual Designs

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Abstract
The paper describes experimental work that has been carried out over a number of years to find an efficient rocket-nozzle shape that could be manufactured simply. Experiments have been conducted with nozzles generally of 1/2-inch diameter throat discharging air to atmosphere from reservoir pressures in the region of 900 lb. per sq. in. and the thrust reaction and discharge rate have been measured. The air flow within the nozzle and the issuing jet have been examined photographically. The apparatus used and the experimental techniques are fully described. The investigation has determined the best design for simple nozzles of conical divergence and found these to have a thrust efficiency of some 96 per cent. Suitable entry radius and divergence angle are recommended and the effect of machining errors, of obstructions in and near the nozzle and of operating at incorrect pressure ratios have all been considered experimentally. In the course of this study, a number of unusual designs has been considered. These include annular nozzles, a variable thrust-nozzle, and a nozzle designed to be mounted at the front of a rocket. These unconventional nozzles all have some special feature which makes them particularly suitable for certain requirements. The paper gives data on all the nozzle-design details investigated and an attempt has been made to relate the observed thrust-losses in conical nozzles to a simple theory. Throughout the research and in presenting the results, the requirements and interests of the rocket-motor designer have been kept in view.

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