Design and development of the Phoenix-1B hybrid rocket.

Abstract

In August 2014, South Africa’s first university-based hybrid rocket, Phoenix-1A, was launched at the Overberg Test Range near Cape Agulhas. The vehicle suffered nozzle and parachute failures during flight which, together with a reduced oxidiser load, reduced the nominal design apogee of 10 km to 2.5 km. The aim of this research was to improve on the design and performance of the prototype demonstrator and thereby develop a workhorse hybrid sounding rocket, named Phoenix-1B, to serve as a reliable platform for future hybrid rocket research at the University of KwaZulu-Natal (UKZN). Analysis of Phoenix-1A shortcomings served as the starting point for the new design, which utilises a paraffin wax and nitrous oxide propellant combination. The focus of this research was the propulsion system, with specific attention being paid to the nozzle and injector designs. In addition, an aerodynamic study was applied to the 1 m long ¾ parabolic nose cone and four tapered swept fins. Final design of the aluminium oxidiser tank and combustion chamber bulkheads incorporated finite element analyses to ensure an operational safety factor greater than 1.5. The oxidiser tank and combustion chamber assemblies were pressure tested to 80 and 60 bars respectively. A key output of the present work is an analysis of the effect of aluminium loading in the paraffin wax fuel grain, which indicated a potential rocket mass reduction of 23 kg when transitioning from a pure paraffin grain to one containing 40% aluminium by mass. The analysis also indicated that combustion temperature rises with aluminium loading, increasing from 3300 K for pure paraffin to 3600 K for 40% aluminised fuel. Consequently, an iterative transient thermo-structural analysis was conducted on the nozzle, resulting in an optimised design able to sustain the higher operating temperatures as well as mitigate the risk of failure as seen with Phoenix-1A. The final manufactured composite nozzle has a throat diameter of 32 mm, an expansion ratio of 6.38, and a length of 156 mm. The nozzle has a steel casing which provides structural support to the silica phenolic insulation and graphite throat insert. A two phase CFD analysis, coupled with analytical mass flow rate models, was used to configure the axial injector and reduce the potential for combustion instabilities associated with the nitrous oxide flow. The Phoenix-1B motor has a design thrust of 5 kN to propel the fully loaded vehicle, with a mass of 70 kg, a length of 4.3 m and a diameter of 164 mm, to an altitude of 16 km.