All Choked Up

Overview

All Choked Up: The Effect of the Convergent Section Half-Angle on the Thrust of a Cold Gas Rocket continues my investigation of cold gas rocket nozzles. Rockets and Nozzles and Thrusts, OH MY (RNTOM, Sigrest 2016) determined the optimum nozzle divergent half-angle, α=20˚. This is different than accepted rules-of-thumb (12˚-18˚), and provides the engineer with greater choice when optimizing nozzles for thrust and length/weight. All Choked Up validated the findings of RNTOM and investigated the effects of the convergent section half-angle, θ. Nozzles were machined from Delrin, and a test apparatus was built to collect real-time chamber pressure and thrust data. The experiment consisted of five trials for each nozzle (θ = 15°, 20°, 32°, 45°, 50°). The results showed θ = 50˚ produced the most thrust, which did not support my hypothesis that 32˚ was best. Rocket nozzle design theory predicts no correlation between convergence angle and thrust. All Choked Up disproves this theory. All Choked Up showed a positive correlation between convergent angle and thrust; and, the widest angle, θ, (which produces the shortest nozzle) produced the greatest thrust. All Choked Up, together with RNTOM, showed significant savings in nozzle length/weight can be achieved with an increase in thrust when compared against the accepted rules-of-thumb. RNTOM, as validated in All Choked Up, shows that with a 27% reduction in divergent section length/weight there is only a 5% reduction in thrust. By increasing the convergent section θ from 32° to 50°, an additional length savings of 14% can be achieved with a 9% increase in thrust, which counteracts the slight decrease in thrust from the wider divergent half-angle.

Competition history

• AJAS 2018 Category not listed

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