Design and analysis of a double nozzles small thrust difference measuring device

Double nozzles small thrust difference measuring device and its accessory facilities are presented, which can be used to study the effects of nozzle contour on the thrust performance of small thrust rocket engine. The reference nozzle and the testing nozzle are set coaxially in reverse directions in the measuring device. The small thrust difference between the two nozzles can be obtained by measuring the structure strain caused by the thrust difference. Theoretical analysis of the measuring device was made with simplified models. Theoretical formula of the measuring device sensitivity coefficient was deduced. Based on the formula, key parameters were designed and reasonable sensitivity coefficient was determined. The theoretical formula can be used to guide the design of the test system. The results of the validation experiment show that the small thrust difference which is only several Newtons can be obtained, and the calibration curve has good linearity. The relative expanded uncertainty of the thrust difference is about 0.5% compared with the reference nozzle thrust in the experiment. Further more, the relative expanded uncertainty will be smaller when the ratio of the thrust difference to the reference nozzle thrust is smaller. The measuring device can be applied to the experiment study for nozzle performance analysis and optimization design.