The Reaction Research Society met on September 11, 2020, by teleconference. Several members called in from out of state. After calling the meeting to order and the reading of the treasurer’s report, we began to discuss events to come and those in planning.
MTA WORK EVENT 10/3/2020
The next event at the Mojave Test Area will be on Saturday, October 3rd. This will be a work event to repair our large adjustable rail launcher, remove tumbleweeds and brush from around our site, fix the two cut strands of barbed wire at our front gate, clean off corrosion from several areas and also potentially replace the bent panel on the vertical thrust stand. Osvaldo is leading the work event and all members are encouraged to come out. In addition to bringing sunscreeen, proper desert attire and footwear, bringing work gloves will be very useful.
As with all events at the MTA, social distancing and facemasks are required by all attendees at this event. Newcomers must request permission to attend and sign our indemnification waiver in advance of their arrival. See our website for these forms and submit them to the RRS president.
At this same event, we may also have a few launches if members are ready to do so. Dave Nordling was appointed to be the pyro-op in charge for this day. Wolfram Blume had planned to attempt his first flight of the two-stage Gas Guzzler to verify the staging and recovery systems. The nitrous-oxide hybrid motor is also ready for another launch attempt at this event.
Bill Inman also plans to join us at the MTA to conduct some tests of his solar concentrator to be used with his next generation steam rocket still in build.
NEW RESTROOM FACILITY AT THE MTA
Last year, the executive council set priorities for improvements at the Mojave Test Area. At the top of the list was building a new restroom facility which would offer our guests greater comfort than the current facility.
Larry Hoffing and Dave Nordling have begun to approach potential contractors willing and able to build a modest facility at our site. No formal proposals have yet been received yet but the society expects to have more to share in the coming month. With the hot summer months receding and the cooler temperatures of autumn approaching it is a perfect time to begin this project.
Given our modest budget, we are asking for donations to help the society make this much asked for and much needed improvement. Donations to the RRS are tax deductible as we are a registered 501(c)3 educational non-profit group in California. Our Paypal link is one our website and if there are any questions please contact the RRS president or any member of the executive council.
2021 RRS SYMPOSIUM
It was recommended that we try to set a firm date for the 2021 RRS Symposium with the Ken Nakaoka Community Center on a Saturday in late March. Although it is not certain if the symposium can be held, preparation for the symposium can take many months. Frank was going to see if a tenative date could be established only for planning purposes. If COVID-19 restrictions in Los Angeles were lifted to allow our symposium, we would have little time for advanced planning. There’s liitle to lose in scheduling the event and postponing if it becomes necessary.
Contact the RRS secretary with questions. Next meeting will be held virtually on October 9, 2020, 7:30pm. Contact the RRS secretary for details.
On July 25, 2020, the Reaction Research Society held its first launch event at the RRS MTA since the start of the pandemic. Our pyrotechnic operator in charge that day was our society president, Osvaldo Tarditti. I was his backup. We also had Jim Gross come out for the event who has been our pyro-op in charge at many of these events.
We observed social distancing as best as we could and everyone was wearing a mask. Protective equipment is normally required for loading operations and keeping our people spread apart only makes good sense. The heat (107 F) was significant but everyone was largely prepared to endure the exhausting environment. We had a few glitches in the launch process which can happen at any event. It is times like these that make patience and planning very valuable.
We held a short safety briefing before beginning launch operations. I reviewed the natural and man-made hazards at the MTA, underscored the importance of hydration, the buddy system and montioring each other and ourselves for hest exhaustion. We had a lower turnout as this was a private society event and with the heat we sought to run through the micrograin launches in one straight series holding the hybrid rocket flight for last. After the safety briefing, Larry performed a propellant burn demonstrstion then we adjourned to the observation bunker while the pyro-op’s began to ready the micrograin rockets in the rack. John Krell assisted me with the rack loading and arming process.
We had four micrograin rockets and the hybrid rocket for this launch event. There were three alpha rockets with slight differences in their design. John Krell had built three avionics payloads, one for each, to capture the trajectory data (acceleration and barometric pressure) so that an apt comparison could be made. We also had an avionics package and recovery sytem (parachute) built into the beta by Jerremy Hoffing, son of Larry Hoffing. The hybrid rocket would be last in the series,
Bill Inman came to the launch event to both spectate the launch of the micrograin and hybrid rockets and also examine portions of his launch rail unit from his Scalded Cat steam rocket project. He has already begun planning a newer steam rocket design.
This segment talks about the three alphas we built and flew to compare two design changes. The three designs were:
standard alpha with three-foot propellant tube, plain carbon steel nozzle
standard alpha with three-foot propellant tube. ceramic coated nozzle
longer alpha with four-foot propellant tube, ceramic coated nozzle
Among these three designs, we were examining the effect of the ceramic coated nozzles which used a proprietary coating process used on automotive engine pistons and exhaust pipe interiors in the racing industry. Specialized Coatings was the company providing the service which we have used before. The coating was proven in a prior alpha flight in 2017, but the nozzle was misplaced and lost after photos were taken at the event. A repeat test was warranted to not only provide photographic evidence but also to cut-up a nozzle to see how the coating survived. It is likely that a ceramic coated nozzle can survive multiple firings before erosion sets in.
The other variable explored was to change the length of the propellant tube and thus increasing the propellant available. Past projects have explored using longer propellant tubes, but this project would bring flight data for direct comparison. To achieve maximum altitude, a second ceramic coated nozzle was used. Just based on the time of flight observed from the observation bunker, the four foot alpha remained aloft for at least four more seconds. John Krell took some video like a few others did. We may be able to estimate the trajectories if we fail to recover the data from one or all of the alphas.
BETA WITH RECOVERY SYSTEM
The beta rocket used at the launch event had a recovered nozzle which had some minor erosion. This was sufficient for this flight. The two features were the parachute recovery system and the avionics package to record altitude data.
The beta was the first micrograin rocket ready for flight and thus it was loaded into the box rails built for the beta. This beta design differed from the standard design by having a straight coupler meaning that the aluminum payload tube was the 2.0-inch diameter as the 2.0-inch DOM steel propellant tube. Because of cost, betas are produced in smaller and less frequent batches. This sometimes leads to more variations in the design. With a little more part production, we can achieve greater consistency between betas.
The typical aluminum coupler design flares out to a 2.5-inch aluminum payload tube. The standard design better fits the box rail launcher which was made with a 2.5-inch bore. The standard payload tube size would have offered more room for packaging the recovery system. Nonetheless, Jeremy was able to fit everything together and the beta propellant tube was filled and made ready.
The 2.0-inch rocket did lay properly inside of the quad-rail launcher, but the sloppy fit was a little concerning. We had considered using a sabot to fill in the gap, but no practical solution could be made. The solid steel rails would contain the rocket but the concern was whether the avionics switch would get bumped into the off-position. To avoid this, a small block of wood was used to lift the beta high enough to clear the switch near the top of the payload.
The first launch attempts resulted in no firing. After re-checking the cabling and my hookups, no error was found. Second attempt also had the same negative result. To expedite the launch process we proceeded with the alpha launches.
After the alphas flew, we re-tried the beta rocket with a dual-igniter for redundancy, the first electric match was found to be defective. This time after some initial trouble with the battery, on the third attempt we got ignition.
SECOND FLIGHT OF THE HYBRID ROCKET
A new rocket body was built to hold the same Contrails H222 nitrous oxide hybrid motor flown earlier. this year. Larry Hoffing did a lot of work building a new rocket body from scratch. It’s boat tail was fitted to accept the 16-inch long, 38mm casing of the Contrails H222 model. Osvaldo built in the parachute recovery system and all parts of the rocket fit well together at the RRS MTA. I changed the location of the vent tube and routed the line to the outside trimming the excess away once the rocket was vertical and captured in the 1010 rail. A lot of this preparation was documented on the RRS Instagram page.
The Contrails H222 motor is a very simple design made for reloading and re-use. The designs are built to common metric standards used in model rocketry. Using the smallest size, 38mm, for a first hybrid project made sense as we would learn the practical things necessary for a successful launch. It also was a size very close to the micrograin rockets that the RRS commonly uses.
The Contrails design is very simple and easy to assemble with the right tools and lubricants. The interior of the 16-inch long motor is divided into two parts, one for filling with nitrous oxide liquid supplied under pressure and the other holds the inert plastic reloadable fuel propellant grains and a graphite nozzle. The two volumes are separated by a dual O-ring sealed piston called the floating injector.
The motor uses a snap-ring retention method for securing the graphite nozzle plug in the aft and another snap ring is used to keep the vented top plug in place. The internal pressure of the nitrous oxide liquid holds the floating injector down against the fuel grain. The injector consists of a stainless steel Parker push-to-connect plastic tube fitting. The ignier is designed to break the filling line inside of the motor releasing the flow of nitrous oxide and providing ignition nergy to start the combustion of the plastic fuel grain in the presence of newly streaming oxidizer flow. It is a very simple and impressive system. Contrails also sells kits and replacement parts to replace those that wear out.
Last launch attempt successfully demonstrated the motor assembly, motor integration into our first rocket body and loading process. The remote actuation of the nitrous filling line and separate electric ignition circuit required a two-channel firing rig which operated well as expected. The flaw in the first aunch was failing to quickly and cleanly sever the thick-walled nylon fill line.
The nitrous bottle was recharged with liquid and secured to an I-beam. The valve manifold was attached and after a quick tightening was free of leaks. We secured the electrical and fluid connections to the rocket and ran our control lines back to the old blockhouse with all of our observers in the safety of the observation bunker. Osvaldo and I conducted all operations with care. Then the first problem struck.
We couldn’t get the fill solenoid to open. This was first thought to be the battery. In past summer events the heat can degrade the battery. We had several no-fire conditions which led us to suspect the battery health. For the beta, the fault was a broken lead on the electric match. Running a voltmeter showed a little weakness of the battery but 12-volts was showing on the needle. We moved one of the cars closer to the blockhouse to use its battery but the solenoid still wouldn’t open. Given, the late hour in the peak of the afternoon, we scrubbed the launch attempt and safed and disconnected the fluid and electrical system.
The bottle pressure was reading very high that day and although the vessel and plumbing is amply rated for the 1400 psi reading on the gauge. By weight, the bottle wasn’t overfilled, but the heat of the day certainly brought the pressure up. The solenoid valve was bought as part of an assembly sold by a different supplier. With no labelling or marking on the solenoid, there is nothing to identify the manufacturer or model number. A couple emails were sent to the seller but no information on the valve make and model has been given. The internal design and operating limitations of this 12 VDC normally closed solenoid valva is unknown but it is possible that the high pressure against the seat was too much for the solenoid to overcome. Chilling the bottle or simply venting the bottle to lower the pressure might have helped. More tests of the solenoid valve will be done to verify its functions and perhaps some careful disaasembly of the valve may reveal markings to identify it. We are also considering building our own simple solenoid valve fill and drain assembly once the right parts can be specified.
It was a long day but very worthwhile. We hope to have another launch event soon. The results of the day’s events will be discussed at the August 14, 2020, monthly meeting which will be held by teleconference.
The RRS held a launch event on Sunday, March 1st, 2020, at the Mojave Test Area. It was a brisk morning with steady winds that occasionally slowed enough for a safe launch.
This launch event was originally for a university static fire and a few member projects. The university had to reschedule but we had sufficient interest from our own projects so we held the event.
The weather was a concern with passing storms and rain predicted earlier in the week. But as often happens, the weather shifted for the better on launch day with winds staying low enough to launch most of our projects.
Wolfram has been working for a few years on his Gas Guzzler ramjet rocket. He is just now entering the first system flight tests to demonstrate the staging and recovery systems. He filled his ramjet with water in place of the gasoline to have a representative weight.
Wolfram was able to load his booster on to the 1515 rails with good alignment. His upper stage had some alignment problems due to using a different prototype for this initial flight. After some examinations on the pad, he pulled his rocket stages back to the Dosa building for internal adjustments to assure a clean fit between the booster and upper stage.
The next launch was Keith Yoerg’s high powered rocket, Charlie Horse. He used an I-350 Smoky Sam motor and had a dual-deployment system with a GPS tracker built in. The flight was smooth off the rails but the trajectory data seemed to show a steady wind pushing west to east. He reached an apogee of around 4000 feet. Recovery wasn’t a problem as his rocket landed just a hundred yards east of the RRS MTA.
Wolfram returned his rocket to the pad but accidentally dropped the second stage breaking a piece of the ramjet plastic cowl on the concrete below. With this significant disruption of the aerodynamic surface, he was forced to abort the flight and rework this part. He was also going to check some of the other parts in his assembly for this long-awaited first flight. It’s important to not rush a project and wait until all is ready for a successful flight.
The next flight was to be the hybrid rocket that Larry, Osvaldo and I have been working. The Contrails H222 motor was safely loaded from last month and after some improvements to the vehicle body for better parachute recovery functions, we felt we were ready.
The winds were still favorable so we proceeded with clearing the area and making our electrical connections back to the old blockhouse. With just a handful of people and the lightweight vehicle, the old blockhouse was sufficient for our operations that day.
The nitrous bottle was refilled from the prior week and the manifold was plumbed to the vehicle tank. With the opening of the nitrous bottle, remote operations could begin. The time of tanking the small 38mm H-motor tank was not precisely known, but was not expected to take very long given basic calculations of the available flow rate. As expected, the tank volume primed within 15-20 seconds. We waited a full minute as we were initially unsure of whether the full volume was filled with liquid. After spotting a jet of liquid escaping from the vehicle body vent, we were assured that the hybrid motor was ready to be ignited.
Osvaldo conducted the firing operation after a short five-count. The resistor and Pyrodex charge ignited after a slight delay for the resistor to heat up sufficiently. The motor seemed to reach full thrust quickly and leave the rail as expected from the thrust curves from this commercial motor.
The vehicle was spotted tumbling after leaving the rails leading us to believe the rocket was not properly balanced. More detailed calculations would have been beneficial, but from initial estimates and the heavier recovery system in the extended rocket body, it was believed the rocket would be stable enough.
Examination of Osvaldo’s high speed camera footage from the hybrid flight revealed the reason for the vehicle tumbling. Some of the frames show that the nitrous fill line remained attached to the rocket during launch and even after clearing the rails. The fill line did snap loose in the flight at some point, but it was supposed to completely sever at ignition. This imparted a significant torque to the vehicle leading to a tumbling and short trajectory back to ground.
Worse, in my rush to get the hybrid loaded on the rails and made ready for filling operations, I forgot to arm the recovery system. This is a classic mistake and one that I could have easily avoided.
At least, the other issues with the flight limited the distance the rocket travelled. The rocket was recovered just north of the 1010 launch rail still within the bounds of the MTA. The rocket landed on its nose breaking it and significant body tube damage was sustained. After disassembling the hybrid motor from the body, we opted to scrap the rocket body and rebuild a new one for the next flight. The fill and fire operations were successful and the equipment we built worked fine.
The Contrails H222 motor parts survived well. We were able to easily remove the motor assembly and disassembled the parts for inspection. The graphite nozzle showed very little ablation and will be reused. None of the parts had heat damage. The fuel grain didn’t exhibit much ablation as compared to the other unburned grains we had. The burn duration in flight seemed to be similar to what is shown on the thrust curve, but this should be reviewed against the flight footage.
More review of the flight footage will be necessary to better understand how the hybrid motor operated. We are considering changing the ignition method to use an electric match and maybe a shape charge that would better ignite the hybrid motor.
We are considering building a static testing rig for the hybrid motor to verify some changes we intend to try with the ignition. There will be more on this subject in later reports.
Larry Hoffing had built a custom composite solid rocket motor using a spent casing from a commercial solid motor. This simple end-burner grain also had a custom-made nozzle. Larry had suspended his experimental motor a length of metal piping threaded on our large adjustable box rails that is still undergoing refurbishment.
Unfortunately, Larry’s motor design was not successful and rapidly overpressurized scattering both end caps and propellant grain fragments across the desert floor. No fires resulted from this static firing failure and no serious damage was done to nearby structures used for this demonstration.
The last launch attempt was Keith Yoerg’s smaller model rockets using the tiny B and C motors. The winds became stronger as the day progressed and by that time sustained wind levels were too high for any launch particularly for such a small vehicle. These rockets would be saved for a later event and Keith began examining his Charlie Horse rocket and its camera footage.
It was a good day for the RRS to have a launch event exclusively for our member projects. We plan to hold more of these events for both universities and our membership very soon.