Vanderbilt Aerospace Club

14 January 2012

Sub Scale Rocket Launch

As per simulation, a H170 motor would provide ideal parity with the full scale rocket in terms of 'g level' at launch, and the rail exit velocity. We were interested in testing out the integrity of the engine harness and the ability of the team to work as a unit. The parachute was set for motor ejection.

Ground level winds were low (less than 10 mph). The rocket cleared the launch pad well, but caught the side wind immediately, implying that it did not have sufficient launch rail exit speed. The launch rail was sufficiently long (8') compared to the rocket size (4'), so we do not attribute the inadequate exit speed to it. Inadequate rail exit speed rail can have deleterious consequences on the rest of the flight as rocket trajectory and stability would be altered drastically. Fish tailing just while leaving the launch pad is a clear indication that the rocket is leaving at a much lower speed than predicted, and is catching the side winds. An analysis of the expected and the actual drag characteristics of the rocket have been detailed. The altitude reached was 672' as opposed to a predicted 876'. After careful analysis we have determined that the vehicle drag was not completely accounted for in the simulation. The main culprit seems to be the engine pylon drag and an aerodynamic design will address the problem. We intend to make the modification for the actual full scale rocket.

Based on the experience of another launch, combined with the fact that this was a quick burn motor, the parachute ejection burnout delay was left at 14 seconds. While a previous flight with a lighter rocket established parachute deployment at 400', the model rocket failed to deploy the parachute at a reasonable altitude due to a longer delay, and as such landed in the bushes. Luckily, the DAQ board and the payload were recovered for further analysis. The team should have lowered the delay by 4", but was lucky to recover data for further analysis.