Rocket Team Status Update
Rocket Team Status Update
April 02, 2015
The Rocket Team is currently on schedule with the main rocket built, the certification rocket built and bench testing being conducted. Once the testing is completed, final assembly of the rocket parts will be done to get the rocket ready for launch. Launch is tentatively scheduled for April 18th. On April 11th the smaller of the two rockets constructed will be launched at a SEVRA event to attain a Tripoli level I & II rocketry certification. This is necessary to launch the main rocket on April 18th.
Work done by the propulsions team includes manufacturing methods testing, fuel production, combustion testing, nozzle manufacture, and nozzle redesign. Manufacturing testing took place before fuel manufacturing began. This consisted of cooking an inert fuel where the Potassium Nitrate oxidizer was replaced with Sodium Chloride in the same mass ratios as the fuel mixture. These tests revealed that in order to make a homogenous mixture which could be molded easily, it is necessary to heat the mixture at a higher temperature than what is minimally necessary to cause melting of the Dextrose. The sample batch which was made at a lower temperature did not melt fully and was difficult to work with when melting occurred. During these tests, the mixture was exposed to an open flame which showed that the dextrose fuel was resistant to overheating. The dextrose tended to decompose, rather than burn in the presence of excessive heat. Tests involving a dry mixture of the Potassium Nitrate and Dextrose confirmed this result, even in the presence of the oxidizer. When exposed to an open flame, prolonged expose to the flame source was necessary to obtain ignition of the mixture. This is desirable from a safety standpoint while manufacturing fuel to know that there is a large margin between melting and ignition of the fuel.
The fuel mixture was heated in a heavy bottom metal pot over a scientific hot plate and stirred throughout cooking with a silicon spatula. The constant stirring was necessary to prevent hot spots and premature caramelization of the dextrose which would negatively impact fuel performance. After the mixture was fully melted and homogeneous, the fuel was poured into casting tubes around a metal mandrel and then compressed to eliminate air gaps in the propellant. Burn samples were performed on fuel samples where the fuel components were blended down to a finer grain size compared to where the fuel components were not modified. It was shown that the fuel which was not blended to a finer grain size burned more rapidly and more completely. The unmodified fuel mixture was a lighter color after heating which indicates that less decomposition of the fuel occurred. It is possible that reducing the grain size of the oxidizer without modifying the fuel could further improve burning properties.
Burn tests showed that the fuel mixture gave off tremendous amounts of smoke but burned rather slowly. The mixture will burn faster at higher pressures. Ignition with open flame was inefficient and could not get the entire fuel sample to ignite rapidly which was necessary for use in a motor. A comparison test showed that a similar size fuel sample will burn more completely and rapidly when ignited with black powder.
The nozzle parts were machined by the Batten Model shop and assembled for testing. The nozzle received from the shop was damaged during its manufacturing and as a result will be unfit for testing. An improved design with a thicker throat area was sent to the shop on Monday the 30th and will be ready by Wednesday 8th. In an attempt to appease concerns, the new nozzle will be constructed from 1018 steel.
Work done by the avionics team includes avionics bay redesign and manufacture, avionics, vibration analysis, and bench testing. A redesign of the avionics system has been done, and construction of the bay is complete. The electronics system has been installed, wired, and continuity checks were done to ensure the system operates properly. The hardware required for programming the altimeters has been received and the team will download the software and begin programming the altimeters for dual-deployment. The software also allows the team to upload flight data that will be used to validate the performance of the rocket.
The finished avionics bay has been modeled in Autodesk Inventor, and was used to perform vibration analysis through Autodesk Simulation Mechanical. Modal analysis was first conducted and used inputs of a 5 pound mass load representing the stacked weight of the rocket above the avionics bay and 25 frequency points to analyze the expected frequency through the model. These results were then loaded into the Random Vibrationanalysis tool and given frequency and acceleration inputs which constitute the needed power spectral density values for analysis. The vibration force was applied axially along the length of the avionics bay. The displacement results show the deformation in the normal direction to the axially applied load, which is the direction the avionics bay bends during frequency oscillations. These results showed that the maximum displacement of the part under loading would not exceed 0.01738060 inches displacement during the frequency values being considered. Based on the findings, the Avionics bay is considered acceptable for use in this model rocket from the vibration data. It is not expected to experience the damaging vibrations leading to excessive displacement, during oscillations.
Bench testing of the payload and parachute recovery system have been accomplished. Prior to testing, calculations were performed to predict the amount of black powder necessary to produce the required force to separate the rocket. Ejection charge size testing was performed using information obtained from the calculations to ensure the rocket separates properly, with enough force to eject the payload and parachute recovery system. There were four tests performed, with varying black powder charge amounts, before determining a quantity that would most effectively separate the rocket during flight.
Work done by the avionics team includes a small scale model submittedto the Batten Model shop, acquiring a small scale model for subsonic testing, and rerunning the CFD analysis with the new fin design. An inventor scale model of the rocket was made andthe drawing and work order was submitted to the machine shop for fabrication. This scale is planned to be used in the supersonic wind tunnel. A member of SEVRA (Southeastern Virginia Rocketry Association) donated a smaller model of the team’s rocket that can be used in the subsonic wind tunnel. The fin designs were changed requiring new runs of the CFD analysis to be done. Runs from Mach 0.1 to 0.7 have been completed, but divergence is occurring at higher Mach numbers. The inventor model is currently being modified slightly to prevent divergence. Schlieren imaging and flow visualization using smoke and a laser wall will be done in the subsonic wind tunnel.
Future work to be done includes manufacturing more fuel, manufacturing the nozzle to the new design specifications, conducting FEA on the new nozzle, finishing the test stand, conducting a test burn, conducting subsonic and supersonic wind tunnel testing, finishing the CFD analysis reruns, and performing the certification launches.