by Dave Nordling, Secretary, Reaction Research Society
The RRS had our last launch event of the year this Saturday, December 7, 2019, at the Mojave Test Area (MTA). We were hosts again to the Los Angeles Police Department (LAPD) Community Safety Partnership (CSP) and this time with 99th Street Elementary.
The RRS has been reworking some of our rails including our trusted and reliable alpha rail launcher. Months of use had slowly built up uneven layering of zinc-sulfide on the rail surfaces making loading difficult but protecting the steel surfaces from the slow corrosion of the dry salt lake bed just a few miles away. Osvaldo did great work in giving our alpha rail launcher a new lease on life. Thanks also to Russell Hoffing and his kids for helping out with the installation before the event crew arrived.
The winter seasonal rains have arrived a little early to southern California, but the weather began to clear today just before we started. The winds were very low which was excellent for launching rockets. From the washing action of the rain this week, the loose sand drifted into a vein-like pattern over the harder sand below which gave the ground a slightly “Martian” quality. It was cool but not cold and a great day for a launch.
We had a minor problem from the rainwater gathering in the bunker. It wasn’t more than an inch or two deep, but on a cool December morning, it would be a miserable place for our guests. The RRS was grateful to some of the Friends of Amateur Rocketry who let us borrow a small sump pump to pull the standing water out.
We gave the students the standard safety briefing about how to avoid the dangers at the site. We also gave them a live demonstration of how the micrograin zinc and sulfur powder burns in the open showing the brilliant yellow color. Larry Hoffing had also prepared a small sample of solid composite propellant made with ammonium perchlorate and an iron oxide accelerant.
Larry Hoffing and his grandsons had a few model rockets to try out at the event. After setting up the launch wire and clamping the smaller 6-foot long 1010 rail to a suitable rigid and weighted base. Winds were very light all day so we had few problems from the elements.
Larry flew a classic Estes model, Big Bertha, which is always a crowd-pleaser. This vintage model design is slowly powered at take-off by a C6-3 commercial motor then gains traction after its fins start working. It has flown to couple hundred feed then at apogee made a nice parachute recovery.
The high-powered fiberglass bodied rocket launched on a 1010 C-rail was boosted by a vintage Flight Systems F6-7 motor, but failed to move vertically up the rail by more than a couple of feet before settling nicely on the launch pad with an impressive 6-inch exhaust flame. It will be back to the drawing board for that model with the possible addition of a more powerful G-sized AP motor or a H-sized hybrid. The students at 99th Street Elementary witnessed the launch, but the biggest part of the event was yet to begin.
The ten RRS standard alpha rockets from the students were already loaded the night before. A last minute addition of another alpha painted by their teacher was included. Osvaldo showed me his latest propellant loading approach that minimizes external powder contamination on the person loading. Using zinc-sulfur is simple, but it has it’s own problems. Many of our spouses and friends are not pleased with the persistent odor of brimstone (raw sulfur) on our clothes upon our return to the city. Osvaldo has known this problem for years and found a simple method of blocking the migrating propellant dust using a simple pillowcase shield. He has also improved the mating funnel and with a steady light bouncing of the propellant tube on a wood block, the propellant tube can be filled with its 3.2 pounds of zinc-sulfur mixture.
Our alpha launch operations were conducted a little differently at this event. Osvaldo did the loading at the rails, while I was manning the launch switch in our observation bunker with everyone else safely under cover. By California law, the person on the launch switch is the pyro-op in charge. With our experienced team doing road and air space checks before each firing, we had a good safe launch and a lot of fun.
We had ten alpha rockets plus one extra painted by the teacher for this event. All of them looked really sharp with bright colors easy to spot when recovered from the desert floor. 99th Street Elementary really enjoyed the five weekly classes and were very exciting to have the last class at the Mojave Test Area to see real demonstrations of rocket propellants and the micrograin powder in each of the rockets propelling them into the gray sky one by one.
Most of the alpha flights were perfect. The flight times were consistent and given the low winds we could hear the whooshing return and the thump on nearly every one to confirm impact.
We had one particularly troublesome flight which is a rarity with the RRS standard alpha after all of the years spent perfecting that design. The second rocket sputtered and hesitated a lot before taking off slowly from and rails and flopping back to the ground. No obvious cause was found on that rocket, no unusual burn pattern or melting and the propellant tube seemed intact. After inspecting the rocket more thoroughly upon its recovery just a few feet from the launch rail, it was clear that the nozzle mounting screws must not have been installed. No damage was seen to either the propellant tube or the nozzle. The nozzle throat was in tact which indicates it must not have been present to choke the fiery exhaust flow. This also explains the profound lack of thrust, but yet even without a nozzle the micrograin rocket was able to generate enough pressure to lift itself out of the rails. The nozzles often fit very tightly into the propellant tubes which might have been how someone could have failed to notice the missing attachment screws during transport to the launch pad. This is quite an error which will not be repeated.
We said goodbye to our visitors and prepared to clean up the site. In the winter months, the sun sets quickly so we didn’t have a lot of time to search for the alphas. Frank had a lot of luck finding six of the eleven launched that day. Some of the parts can be reused with a little work.
We’ll surely discuss the results of the launch event at the next RRS monthly meeting which is next Friday, December 13th. Also, we’re already planning the next MTA launch event which will happen in January. We are expecting more launches in this next year, 2020. Thanks for reading!