Highlights of recent developments on the DoubleSShot project --------------------------------------------------------------------------------------- - On January 4th, Rick Maschek test fired the 89mm (3.5”) K-rocket motor with DD-slot grains once again, this time fitted with 4 grains (it had previously been fired with 2 grains). The test firing was conducted at the FAR site, with the motor mounted on the horizontal test stand. Ignition of the motor occurred promptly, and burned well for the expected duration. Near the end of the burn, the motor casing suffered a burn-through near the nozzle, where maximum heating was expected. Upon disassembly, the 1/8” (3mm) cardboard thermal liner was found to have been fully burned away. Good pressure readings were recorded over the full duration of the burn. The maximum chamber pressure was about 1260 psi (8.7 Mpa), which was significantly higher than expected. Two hypotheses are being looked into. Partial blockage of the “sliver catcher” by liner debris may be responsible for the higher pressure. Another possibility is “rotation” of one or more of the four DD grains, at some point during the burn, that may have partially restricted the flow. For expediency, it had been decided that he four grains would not be bonded together as a single grain. A misalignment of 90 degrees could potentially cause a restriction of the flow channel. To eliminate this possibility in the future, all grains will be aligned and bonded together. Illustration of two grains misaligned: http://sugarshot.org/downloads/dd-slot_misaligned.pdf Sliver catcher: http://sugarshot.org/downloads/dscn0887a.jpg Sliver catcher with grain support: http://sugarshot.org/downloads/dscn0886a.jpg Newly made bulkhead with removable ignition plug: http://sugarshot.org/downloads/dscn9516a.jpg http://sugarshot.org/downloads/dscn9519a.jpg Panoramic view of the motor under full thrust: http://sugarshot.org/downloads/4-grain_dd_motor_test_image1.jpg Video of the test firing will be posted soon. (photos courtesy Rick Maschek) - The pressure data from the Dec.21st test firing of the K-motor with 2 DD-slot grains has been compiled and plotted, and compared to the design curve. The resulting comparison shows good correlation and marks a promising step forward in validating this particular grain geometry. Pressure curves: http://sugarshot.org/downloads/k-motor-2grain_pressure_curves.jpg -A regular Avionics telecon was held this past Sunday. Participants were Chris King, Hans Olaf Toft, Richard Nakka and Mattias Lampe. This was a relatively short session, as limited progress had been made over the past few weeks due to the holidays. However, Hans did have some positive progress to report. Hans stated that he finally had success with figuring out the Telemetrum software code. As such, it should be feasible to modify the code to suit our needs with respect to trajectory calculations and in particular, estimating point of apogee. The next telecon will be held on January 19th. -Vicente Alvero has made good progress on preparing the prototype Pyro Separation Device (PSD) for testing. The original igniter design proved problematic, so this was replaced with a miniature R/C airplane “glow plug” which worked out very well. There were some fit-up problems that are in the process of being overcome. The fit-up issues were a result of manufacturing as well as design deficiencies, which are in the process of being rectified. The first test of PSD operation with a live charge resulted in only one of the six arms being withdrawn due to excessive friction. A fix is being implemented and a repeat test will be done in the near future Glow plug for the PSD igniter: http://sugarshot.org/downloads/glow_plug_ex.jpg Test of glow plug with crimson powder charge: http://sugarshot.org/downloads/glow_plug_test_firing.mov Video of first live test of PSD: http://www.youtube.com/watch?v=7-aiVf9mZ8k Vicente describing fit-up issue with the piston arms: http://sugarshot.org/downloads/psd_demo1.mov Fit-up improved when joint screws removed: http://sugarshot.org/downloads/psd_demo2.avi (videos courtesy Vicente Alvero) -The “DoubleSShot Pyrotechnic Separation Device (PSD) Prototype Operating Manual” has been uploaded to our documentation page: http://sugarshot.org/documentation_old.html -Ben Brockert has posted some further information on numerical approaches and material selections relating to SS2S nosecones: http://sugarshotsolidworks.wordpress.com/2013/12/22/numeric-analysis-of-nose-cone-heating-first-steps/ -Richard Nakka, with help from brother Blair Nakka, conducted further testing of the prototype de-spin system. Earlier, test runs had been performed with an aluminum flywheel. A steel flywheel with twice the angular moment of inertia was recently fabricated in order to get comparison data. The more massive steel flywheel (1 kg) proved challenging to secure to the motor shaft. The high torque resulted in slippage of the delrin flywheel mandrel. This was overcome by using a set screw tightened against a flat milled in the motor shaft. Several runs were made this past weekend with both flywheels. Data was gathered using a digital wattmeter to measure power input to the electric motor (which drives the flywheel). The initial spin of the simulated rocket body was 330 RPM (achieved by using a power drill). A higher spin was also attempted (550 RPM) but the flywheel was unable to bring the body to a full stop. Digital wattmeter reading: http://sugarshot.org/downloads/wattmeter_run4.jpg Steel and aluminum flywheels: http://sugarshot.org/downloads/2-flywheels.jpg Power curve for one of the runs: http://sugarshot.org/downloads/despin_run1_plot.jpg Energy curves for all of the runs: http://sugarshot.org/downloads/despin_runs_summary_e.jpg - Chris North, has become our newest Bronze Donor, kindly making a donation of $25. http://sugarshot.org/sponsors.html#Donors Coming soon…! http://sugarshot.org/downloads/tool-o-rama.jpg (graphic courtesy Knut Gangåssæter) Every donation brings us closer to our goal of reaching Space. Please make a donation today. http://www.sugarshot.org/sponsors.html#Donors --------------------------- -Sugar Shot to Space is on facebook. Check us out. http://tinyurl.com/2exr92k