Impulse Calculation of Model Rocket Engines

IMPULSE CALCULATION OF MODEL ROCKET ENGINES FROM EXPERIMENTAL DATA In order to provide the engineering freshmen with a hands-on experience to teach them important physical and calculus concepts, a model rocket thrust test stand was designed and integrated with a data acquisition system. The purpose of the experiment is to show how impulse is calculated experimentally. The thrust test stand features a precise load cell and a flexure load frame that ensures that only the thrust from the engine is measured. The design of the stand is horizontal to avoid errors caused by the change in engine mass during combustion. The test stand was designed and built by a graduate student so that students in the introduction to engineering course can conduct their own experiments using model rocket engines of various sizes. The data from the load cell is collected and analyzed using a stand-alone data acquisition unit and LabVIEW software. The user obtains burn-time (x) and thrust (y) data. Integrating the resulting curve y(x) yields the impulse (N-sec) using an embedded MATLAB program invoked by the GUI used to run the entire experiment. Students have enjoyed conducting experiments using the new apparatus. They have observed different impulse values for successive tests using ostensibly identical engines. This, in turn, partially accounted for different maximum altitudes reached by the same model rocket. The primary educational benefit of the experiment comes from using the downloaded test data and processing the data manually as a team project. Students learned how to directly calculate the impulse by writing code both in Excel and Matlab to calculate the area under the thrust versus burn-time curve. Hence, students were able to understand and apply the concept of integration as they were analyzing data obtained from a real event. The concept of “area under the curve” and its importance in engineering became clear to all of them early on, even before many of them have taken calculus. For the above set of activities, a students’ attitude assessment survey was designed, implemented, and analyzed. Overall, students felt this was a very exciting and a worthwhile learning experience that taught them the concept of integration and variability in experimentally acquired quantities. Students also claimed that this learning experience enhanced their Excel skills while introducing them briefly to Matlab software and its capabilities.