Held on Saturday, August 12, 1995 at the HALO Rocket Motor Test Facility
The following text was taken, with permission, from an article by Tim Pickens, which was published in the September-October 1995 issue of the Southeastern Space Supporter, newsletter of HAL5.
The seventh Project HALO rocket motor test day was held on Saturday, August 12. That old baseball superstition --- about bringing bad luck for mentioning no-hitter during a no-hit game --- struck Project HALO, not once, but twice!
While setting up the first test, a member (who will remain anonymous) noted that Mother Nature had been kind to us so far, and that all our tests had been held in fair weather. Within a half hour, Mother Nature taught us a lesson with a downpour even Noah would have appreciated! The path between the barn and the test site, mostly dirt from recent excavation, turned into thick, sticky mud. Although the rain stopped, for the rest of day we felt like World War I infantry. Man, did we get exhausted!
We were to test five HALO hybrid motors, this time with a longer burn time, 6 seconds instead of the usual 3. We were also to test two hybrid motors made by James Mitchell of Tennessee.
The HALO motors were all designed to deliver a total impulse of 2000 lb-sec. The planned 6 second burn time would allow us to measure the regression rate of the asphalt propellant, as well as other pertinent data for later analysis.
Our objectives for the day would be to increase our motors efficiency or specific impulse (Isp), to test our new flight-capable aluminum motor casing, to test our new plug valve design, to measure the flow characteristics of our new motor injector, and to test our motors ability to survive a 6-sec burn.
We first tested a motor in a standard steel casing (as in the past). The first test was primarily to see if the Isp and oxidizer-to-fuel (O/F) ratio would deliver the required performance.
The test would use an all-asphalt motor with a 1-inch core diameter and an 11-inch length. The test proceeded very well, with good ignition, and a burn time of 6 seconds. All hardware appeared unharmed. Nozzle wear was minimal. The motor yielded an average thrust of 161 lb and an Isp of 203 sec.
Next up, after a lunch break, was an all-asphalt motor with a 1.25-inch core diameter and an 11-inch length. This motor would be placed in a light-weight aluminum casing, similar to what would be used for an actual flight. Like the steel pipe used previously, the aluminum casing had pipe threads on each end to accommodate our current nozzle and injector end-caps.
The test had good ignition --- the new plug design was working very well! After 4 seconds into the test, fire erupted from the side of the casing, located just above the nozzle in the post-mixing combustion chamber. We immediately aborted the test. Aside of the casing, no damage was caused to the test stand, property, or personnel. Prior to the burn through, the motor yielded an average thrust of only 150 pounds and an Isp of 200 seconds.
Post-test analysis revealed that the casing threads (which reached almost to the post-mixing chamber) locally weakened the casing. Once heat burned away the carbon-phenolic mixing tube, it quickly melted the locally thin aluminum, creating a hole by which flame could pass through. The hole grew to two inches wide and one inch high, before the test firing was aborted.
One solution to the problem is to use snap rings (already used for Genes motor) instead of pipe threads. Another is to insert either an ablative or flame-resistant liner inside the carbon-phenolic mixing-chamber tubing. Both solutions will probably be implemented.
With an obviously damaged aluminum casing, we decided to return to using our sturdier steel casings. Three more HALO motor were successfully test fired, and all-but-one ignited on the first attempt. The only ignition failure followed immediately after a member remarked At least the new ignitors are working well. (Baseballs no-hitter curse strikes again!)
The third test involved an all-asphalt motor with a 1.25-inch core diameter and an 11-inch length. A completely successful 6.0 second test yielding an average thrust of 154 pounds and an Isp of 192 seconds.
The fourth test involved an all-asphalt motor with a 1.25-inch core diameter and a longer, 12-inch length. Another successful 6.0 second test yielding an average thrust of 175 pounds and an Isp of 182 seconds.
The fifth test involved an asphalt-with-aluminum motor with a smaller, 1-inch core diameter, but still a 12-inch length. Again, another successful 6.0 second test, yielding an average thrust of 171 pounds and an Isp of 184 seconds. So far, no significant performance gains have been achieved by adding the aluminum powder to the asphalt.
James Mitchell had driven a long way to attend this event, and we were all determined to test-fire his motors, despite the hot, muggy weather, and the mud - which by then was on everyones nerves (and clothes). Chris Pickens came to rescue again with some delicious, home-made ice cream. Just what us weary infantrymen needed!
James, previously came down from Tennessee to test home-made solid motors (the J, K, and L-class motors mentioned in the last newsletter). He had expressed an interest in creating a hybrid motor, but using PBAN rather than asphalt as the propellant. Steve Mustaikis and I gave him the critical design information, such as the injector area, grain length, core diameter, and nozzle dimensions.
James first test, performed just after sunset, involved an all-PBAN motor with a 1-inch core diameter and an 12-inch length. A successful 4.0 second test yielding an average thrust of 114 pounds and an Isp of 168 seconds.
James second test, performed at night following a dinner break, involved a PBAN-with-rubber-and-charcoal motor with a 1-inch core diameter and an 12-inch length. A successful 6.0 second test yielding an average thrust of 129 pounds and an Isp of 202 seconds.
This is extremely good for a first timer! James has also had a very good success rate with solid motors. He builds all his own hardware and is quite a machinist. He has offered his services to Project HALO for building some hardware that we cannot do locally because of time.
It was the end to another good day at the HALO Rocket Motor Test Facility. The group agreed not to purposely test-fire motors at night again, not only for safety reasons, but also out of courtesy to the neighbors of Herman and Chris Pickens.
Overall, the performance was very good for all these tests. Ignition was excellent, startup looked good, and our Isp was above 200 seconds --- which is very good for asphalt fuel grain with a N2O oxidizer. Steve has done an excellent job in his mathematical modeling of the chemical combustion for the asphalt-and-N2O combination.
The next test day is scheduled to start at Noon on Saturday, October 21. Based on the results of several rocket design reviews, we will be scaling up our propulsion system in order to improve the vehicle propellant mass fraction. The new design should yield a thrust of 340 pounds and a 10 second burn time, for a total impulse of 3400 lb-sec.
For more information on Project HALO, contact HALO Project Manager Yohon Lo at (256) 658-2043 or via E-Mail at: firstname.lastname@example.org.
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This file was last modified on Saturday, 15-Apr-2017 13:19:40 EDT