After deciding to launch a high altitude solid motor test rocket to reach SEB's goal of reaching space with a liquid bipropellant rocket, we realized that we had to manufacture and characterize custom propellant grains to achieve the altitudes required to successfully test high Mach structures and high altitude recovery and avionics. This test stand design is a result of the need to test a large P-impulse class experimental rocket motor during a static fire to qualify the motor for flight. This project served to adapt our motor casing and data acquisition hardware with the infrastructure of the Friends of Amateur Rocketry (FAR) test site and perform a static fire that would give us confidence in the accuracy of our simulations and the performance of our propellant grains for a flight vehicle.
This test stand was designed to (1) safely execute a full duration static fire of the motor without putting personnel or equipment in danger, (2) obtain accurate test data on thrust, chamber pressure, and temperature over the course of a nominal burn, and (3) be easily manufactured, transported, and assembled given its massive size. The overall assembly was broken down into multiple subassemblies to ease manufacturing and integration.
All CAD was done in Autodesk Inventor.
Support Structure: The main support structure assembly of the test stand design consisted of strut channel and elbow strut channel brackets due to its relatively low cost, widespread availability, and reliability under high stress conditions. The support structure was then mounted to the large horizontal test stand at FAR.
Thrust Transfer: The main subassembly of the test stand design was the thrust transfer, which served to collect thrust data and secure the back of the structure to the large horizontal test stand at FAR. Load cells were fastened between the two thrust transfer plates, with the front plate transferring the thrust generated by the motor to the load cells. A wide conversion plate was attached behind the back thrust transfer plate to mount the thrust transfer assembly to the large hardware on the test stand at FAR.
To mount the casing to the thrust transfer at the back of the stand, I designed a circular mount that would fasten to the existing radial bolt pattern on the forward end of the motor casing, in addition to mating the ring on a different axis to the front thrust transfer plate. The entire casing was also mounted along linear rails using vibration-damping U-bolts. The linear slides kept the motor secure, while providing minimal interference with the thrust measurement as the slides only produced a negligible friction force.
Nozzle Retention: The nozzle retainer assembly was used to keep the motor constrained from the forward end if the forward closure of the motor failed and the motor produced thrust in the opposite intended direction. Using a simple assembly of two plates and gusset L-brackets, we constrained the motor from the forward end without any axial force applied to confound thrust measurements.
Because of the simplicity of this design, the entire test stand was transported down to FAR in the Mojave Desert in a small sedan, and integration of the propellant grains, motor casing, and sub-assemblies at FAR was completed within a few hours.
The static fire went smoothly, recording an average thrust of approximately 6500N and a total impulse of roughly 49,000 Ns. This data correlates to a projected HAD flight vehicle altitude of 110,000 feet (33,500 meters) and maximum velocity exceeding Mach 3.