The agenda for Friday was mostly concentrated on finishing our rockets in preparation for the static firing on Saturday morning. The propellant had cured overnight and was ready for final motor construction. Let’s review what happened on Rocket Motor Design Class – Day Three.
The first thing done this morning was to remove the wooden dowels from the center of each cartridge. This was done easily as the dowels had wax paper and shipping tape as a barrier to the propellant. As you can see in the picture to the right, the propellant had expanded as it cured.
In this picture, John Wickman is demonstrating how to cut back the unwanted propellant. He also had us carve out concave depressions into each end of the cartridge. This cavity will encourage the hot gases burning near each cartridge edge to be funneled back into the combustion core. This will help mitigate any burn-through danger to the motor casing at these transitions.
Once the cartridges were trimmed they were connected end-to-end with a heavy rubber tape. This tape serves to hold the cartridges in place and also provide another barrier to a motor case burn-through.
The motor is now ready to be assembled. A PVC end cap was drilled and tapped for a connector. This connector will be attached to a pressure transducer that will measure chamber pressure during the static testing tomorrow.
The propellant cartridges were inserted into the motor casing. The nozzle that was prepared on Wednesday was then cemented onto the end of the motor casing. Notice in the picture above that silicon rubber was placed around the perimeter of the nozzle housing and the throat of the motor. This is to prevent the burning gases from touching any of the PVC.
Motor Structural and Thermal Analysis
We took a break from the motor construction and discussed motor structural analysis. Items covered in this lecture included where to place measurement tools, how to measure stress, and strength of materials.
Heat analysis started with the explanation of the different types of heat transfer; conduction, convention, and radiation. John explained how each impacts the performance and soundness of each part of the rocket motor. The computer programs THERM and CHEM were also covered.
We finally were taught how to build a composite propellant resister igniter. This igniter consists of a resistor that is embedded in composite propellant. When current is supplied to the resister, it heats up and lights the composite propellant. This propellant then ignites the rocket motor propellant.
The motor is ready for static firing. Looking forward to it on Saturday.