The UCLA Project Prometheus had reserved the RRS MTA for Saturday, July 17, 2021, for another round of static fire testing of a nitrous oxide hybrid motor on our vertical test stand. Dave Crisalli was the pyrotechnic operator in charge for that day and recorded the successful static fire. The footage will be posted on the society Instagram page soon.
This summer semester test would demonstrate UCLA’s student designed and built custom hybrid motor. Average thrust was around 300 lbf with a maximum value of 349 lbf. Total impulse recorded was 2044 lbf-sec (in the M-motor range). UCLA shared a few pictures from the event.
Success on the stand……starts with good testing in the lab
This was another great example of a university team success thanks to careful design, lab testing, training, planning and smart, in-the-field engineering. The RRS is glad to offer our facility and technical advice. The RRS looks forward to working with UCLA again soon.
For teams seeking to schedule the use the RRS MTA, please contact the RRS president, Osvaldo Tarditti. Always include a full project description such that the society can accurately evaluate your request.
The Reaction Research Society held a launch event at the Mojave Test Area mainly to support the UCLA Prometheus team for a static fire test of their high powered hybrid motor. UCLA chose one of the largest nitrous oxide hybrid motor designs, the M1575, made by Contrails Rocketry. Dave Crisalli was the pyrotechnic operator in charge for this event. I was his apprentice for the hybrid static fire.
There were three main activities at this event. The first was the UCLA Rocket Project making their preparations to launch their ethanol and LOX vehicle from the Friends of Amateur Rocketry (FAR) site from the 60-foot rail. FAR is just to the south of the RRS MTA where the UCLA Rocket Project had twice in one day static fired their 750 lbf liquid propellant rocket engine just four weeks earlier on 05-01-2021.
Weather conditions were ideal with winds being nearly still for most of the morning. This makes little difference for the hybrid motor static fire testing at the RRS MTA which was the second project by UCLA. Wind would factor heavily in the flight of the UCLA’s liquid rocket.
The third planned activity for UCLA was a series of model rocket flights from several high school teams mentored by UCLA graduate and undergraduate students. Still winds made for easier recovery of the first rockets launched that day.
UCLA Prometheus team prepares for static fire at the RRS MTA on 5-29-2021Dave Crisalli gives the MTA safety briefing for the event in the loading area where the model rockets were assembled for flight.UCLA graduate students conducted the model rocket launches from just west of the large test stand at the MTA
UCLA at the end of each Spring Quarter conducts a launch event where student groups build small rockets with egg payloads using single and dual-stage vehicles with model rocket class motors (G and under). UCLA graduate students and Professor Mitchell Spearrin were leading this event.
It is good experience for beginners and experts alike to build and fly model rockets., The RRS has it’s own such internal program called the Yoerg Challenge which is to motivate all members to build and fly a model rocket kit at least once from the RRS MTA. The RRS is known as an experimental society and not limited to the model rocket code, but we are also fully supportive of all forms of propulsion as long as it is safely conducted and compliant to the regulations set by the state of California.
As the UCLA hybrid rocket team was making their system checks, they discovered a problem in their nitrous filling system and valve commands. During this diagnostic period, some of the RRS members went to the nearby FAR site to see how the UCLA liquid rocket preparations were progressing.
UCLA’s liquid rocket set on the 60-foot rail launcher at FAR. The team preparing the vehicle for erecting, loading then flight.RRS members from left to right, Bill Inman, Waldo Stakes, John Wells and Manuel Marquez, inspect the UCLA liquid rocket on the 60-foot launcher deployed at the FAR site.A few last minute fixes and the rocket was made ready.The liquid rocket sits on the rail before raising it for launch.UCLA’s rocket is in position getting ready to clear the area for propellant loading and pressurization operations.
Some of the RRS members remained at the FAR site to witness the launch. After two years of design, planning, build and world pandemic, the UCLA team liquid rocket launch was an amazing success. Due to the relatively low winds that day under clear skies, recovery was made just under a mile away. Preliminary data from telemetry confirmed a new university team altitude record of 22,000 feet. It was an amazing sight to witness from the observation bunker at the RRS MTA.
UCLA’s liquid rocket had a perfect launch on 5-29-2021 setting a new altitude record of 22,000 feet by a university team. Photo by Xavier Marshall, RRS.
The UCLA Prometheus team had corrected their initial electrical problem and began the series of procedural checks to familiarize the new members of the hybrid rocket team. Some minor adjustments of the motor mount alignment was necessary before getting into test.
The UCLA Prometheus team makes some adjustments to better align the hybrid motor in the vertical skid mounted to classic I-beam at the RRS MTA.The nitrous oxide K-bottle sits inverted in the sloped stand to allow the liquid to flow from the port. Some nitrous oxide bottles come with an internal siphon line to avoid having to invert the container. The bottle is also being chilled with ice to keep the oxidizer sufficiently dense and improve performance in hot-fire.The top bulkhead of the hybrid motor is attached to the load cell for thrust measurement. A pressure transmitter is tapped into the nitrous oxide volume to further gauge performance.The high-powered hybrid motor by Contrails uses four 1/4-inch fill lines and a single smaller vent line from the same floating injector at the mid-point insideDave Crisalli (right) inspects the hybrid motor on the test rails before the firing UCLA Prometheus team tracks their written procedures as they progress to hot-fire in the old blockhouse.
The hybrid motor firing proceeded without further problems and resulted in a spectacular test meeting expected performance. Continuous thrust levels over 600 lbf were recorded but data analysis is still ongoing.
The hybrid motor at startup.The UCLA hybrid motor at full thrust. Chamber pressure was over 1000 psia.
The team had a second hybrid motor grain ready for another firing so they proceeded with disassembly and inspection of the parts. The floating injector seals were still in good condition but the graphite nozzle having survived many prior hot fire tests did not survive that day’s test. Although the throat was in good condition, the inlet taper had cracked requiring a replacement the team did not have.
The top half of the floating injector with its internal siphon tube protruding up to near the top bulkhead.The floating injector being removed from the lower half containing the spent fuel propellant grain.The floating injector was removed after hot-fire and the dual O-ring seals were inspected. Seals were ok for re-use.The nozzle assembly did not pass inspection after the first and only hot-fire on 05-29-2021.The graphite nozzle fractured at the inlet taper from the first and only firing that day.
UCLA Prometheus was pleased with the results from the single firing and will proceed with integrating the motor into their flight vehicle for a launch from FAR on June 19, 2021. The RRS will hold an event at the Mojave Test Area on this same Saturday for member projects and will observe the flight from our northern vantage point.
UCLA avionics team conducted a few tests on the GPS tracking module that will fly on their vehicle in June 2021.
In the last hours of the day, after most of the UCLA liquid and hybrid teams had cleared the area, packaged and carried away their trash, packed their equipment and departed the RRS MTA and FAR sites. The UCLA avionics team remained at the MTA to conduct another series of tests on the GPS tracking system. The society was glad to support this diligence which will help assure success in one of the most important aspects of rocketry which is data acquisition from telemetry. If there is no data, it didn’t happen.
For any group interested in using the RRS MTA for their propulsion related projects, download one of our Standard Record Forms from our RRS.ORG website and submit this request to the RRS president. The society has had a long relationship with UCLA and USC, but we are also supportive to any amateur, professional or academic groups wanting to learn from test.
Based on the recent lacking performance of the Contrails H222 nitrous oxide commercial hybrid motor, a pair of static fire tests were conducted to improve the ignition and severance of the nylon fill line. The latest of these static firings was conducted at the Friends of Amateur Rocketry site south of the RRS MTA on 4-17-2021. This was done for simple convenience since I was unable to attend the MTA launch event in the week prior. Mark Holthaus and John Newman oversaw my static firing and offered good advice. Fellow RRS member, Dmitri Timohovich, joined me that day and brought his four channel firing box to conduct the remote fill and fire operations of the hybrid.
Dmitri connects the fill manifold to the nitrous oxide bottle at FAROrange fill and firing box for the hybrid motor Fill, drain and firing circuit for a Contrails hybrid rocket motor. The separate vent solenoid valve hasn’t been added. Weight scale is also a separate feature and not necessary for operation.
Nylon is one of the stronger polymer tubing materials which can handle the 900 to 1200 psig nitrous oxide pressure when flow is supplied from the solenoid valve controlled manifold. The problem is that this strength makes it difficult to quickly and cleanly sever the Parker NBR brand, 3/16” OD fill line allowing the nitrous oxide to flow against the fuel grain while getting reliable ignition.
The original ignition method as designed by the manufacturer is a small resistor in place of an electric match and the use of a Pyrodex pellet which is essentially a pressed cylinder of black powder. The first flight attempt of the nitrous oxide hybrid rocket used this method but was not successful.
Contrails Rocketry, H222, 38mm, 16-inch high powered nitrous oxide hybrid motor
Earlier builds of the hybrid motor used electric matches and small scraps of composite propellant grain for a swifter and hotter ignition. The first two flights showed evidence of the fill line remaining connected. A better means of ignition and fill line severance was needed.
February 2021 launch of the hybrid motor in Larry’s 3-inch rocket body. It is clear that a hot plume is exiting the nozzle but the sharp arc to the north seems to indicate that the fill line is still attached.
The composite propellant is an ammonium perchlorate, aluminum powder and HTPB binder mixture with some red iron oxide used as an accelerant. These scraps were from RRS member, Larry Hoffing’s, small solid motor that he unsuccessfully tested at the MTA in 2019.
The Contrails H222 motor was mounted upside down due to the lack of a proper motor retainer feature. The static firing was the primary purpose which resulted in a feeble puncture of the filling line and no subsequent ignition.The aft end of the hybrid motor mounted for static fire at the RRS MTA on 3-20-2021Failed ignition resulted from the 3-20-2021 static firing. Disassembly revealed an excessive amount of electrical tape and an uneven burn around the fill line circumference was the most likely cause. Previous solid propellant grain motor test in 2019 was a failure, but the remaining tailings from the casting were useful in boosting the ignition power in prior hybrid motor tests
The last static test at the MTA failed to achieve ignition and only created a small tear in the fill line without achieving ignition of the grain. The composite fuel grain fragments were getting clean ignition but the electrical tape wrapping method I used failed to adequately focus the high temperatures to getting clean ignition and severance of the black nylon fill line.
At John Newman’s suggestion, we used a small ring of composite propellant grain at the forward end inside the hybrid high-performance (HP) fuel grain. These were made from a 22mm cylinder that was cut to a 3/4-inch length and drilled out to a 3/8-inch hole size which is roughly twice the diameter of the black nylon filling line passing through. This larger hole would allow the electric match head to be in close contact with composite propellant ring. As the solid propellant charge burns it focuses the tremendous heat of combustion on the nylon fill line causing it to soften, extrude and cleanly sever.
John Newman uses his lathe at his shop to gently machine fuel grains for custom applications.The ring of 22mm diameter composite propellant grain fits within the head-end of the hybrid fuel grain and can be pressed flush to the edge. A 3/8-inch hole is run through the 3/4” long segment to allow the nylon fill line to pass through with enough room for the electric match head Floating injector (left) with the nylon fill line pushed into the Parker push-to-connect fitting. Composite propellant grain is pressed in flush to the edge and electric match head can be seen beofre it is secured to the fill line to get the proper position when the motor is assembled Snap ring, graphite nozzle and steel nozzle washer finish the motor grain assembly inside the 16-inch aluminum body of the H222 modelThe complete motor assembly clamped into the unistrut holding fixture. The clear vent line at the head end must protrude to the outside to give a visible and audible indication when the oxidizer volume is filled with liquid before committing to firing.Dmitri Timohovich makes adjustments to the clamps holding the hybrid motor in place. Peak thrust is just above 200 lbf according to the official thrust curve data for this H222 model.Four channel firing box sits at a safe distance from the static fire test stand.Dmitri Timohovich (left) and Dave Nordling (right) pose next to the unistrut mounted static fire mounting of the Contrails Rocketry H222 high-powered 38mm hybrid motor ready for testing at the FAR site on 4-17-2021
With everything in place, we called over the pyrotechnic operators in charge for this FAR event. After inspecting the connections and describing the fill and fire procedures, we were authorized to begin the short filling process.
Successful ignition of the hybrid motor at FAR
The hybrid motor was loaded, fired, reloaded and fired again. Both times stable ignition was achieved and the fill line dropped out of the motor as expected. We had to abort the initial second firing as visual confirmation of the nitrous oxide completing fill was not apparent. Given the hybrid motor has a small weep hole in the head end of the motor means that given time the nitrous oxide will leak out safely. The clear 1/8” acrylic vent line had become tangled in the unistrut obscuring the liquid plume. Trimming the acrylic vent line helped to keep the tip more visible on the second and last firing that day.
Cheap and simple, the 3-inch Little John from Mad Cow Rocketry
The next step will be to purchase a 75mm rocket body able to integrate the 16-inch long, 38mm standard hybrid motor inside. The 3-inch Little John rocket from Mad Cow Rocketry was selected and should arrive soon. With luck, the rocket can be built and ready for 1010-rail launched flight at the next RRS MTA event on 5/1/2021.
The RRS is thankful for the support of FAR at their facility for this static fire. Dmitri and I conducted a safe dispoal burn of the scrap propellant. I was able to acquire a few more propellant ring segments for subsequent tests of the hybrid in flight. Later, we plan to revisit the Pyrodex black powder charges with the electric resistors as the initiator. It is not clear if this will be as effective as the high temperature composite grains and an electric match, but it is worth a try.
