The goal of University of Queensland's hybrid rocket team for 2005 was to study the regression behavior of Perspex (PMMA) and Poly Vinyl Chloride (PVC) in order to optimize the performance of the hybrid rocket and eventually lead to a flight version. In 2005, the team successfully conducted 13 hybrid rocket firings, gathering data for 11 of these tests. In addition, paraffin wax fuel has been developed for testing on the test rig, and moulding method for the paraffin wax production was also perfected. The mould is capable of producing paraffin wax fuel grain up to 800mm in length. Paraffin formulation containing 20% graphite powder was found to improve the toughness and shear strength of the wax sufficiently to withstand chamber conditions. The improved ignition system has achieved 100% success rate of firing. Tangential injection system was also tested, though due to low oxidizer flow rate it was unsuccessful.
The data gathered from the tests had allowed for an accurate PVC regression model to be developed. The regression rate formula for PVC was found to be ŕ= 1.436 x 10-5 G0 0.72. Longer fuel grains had lower regression rates, but also lower oxidizer to fuel (O: F) ratio and higher specific impulse. The regression rate was observed to be constant across the length of the fuel grain for fuel grains with large length on diameter (L/D) ratio and short bum times, bur varied for smaller L/D ratio and longer bum times. The experimental optimal O:F ratio for PVC fuel grain has been isolated into a region between 3 and 4.1. Maximum thrusts of 370N for PVC (test1) and 290N for PMMA (test 4) had been achieved. The theoretical regression rate for PMMA was found to be grossly overestimated. The regression rate formula for PMMA was found to be ŕ = 1.1 x 10 -4 G0 0.3. PMMA and N2O combination was observed to produce higher combustion temperatures than the PVC and N2O combination. In addition, 37second long bum test of PVC was conducted. The regression pattern information gathered would help assist in the development of flight versions as flight durations were likely to be in the region of 30 seconds.
Overall, the project could be considered as a success. The initial goals of studying the regression behavior of PMMA and PVC were achieved, along with the development of paraffin wax fuel. The quantity and quality of data gathered as well as the lessons learnt would benefit future teams as they strive towards developing a flight vehicle.