August 2020 virtual meeting

Posted on August 16, 2020 by Dave Nordling

By Dave Nordling, Reaction Research Society

In the absence of our secretary, I took a few notes from the meeting. This is what I recorded. Contact the RRS secretary for updates and corrections.

The Reaction Research Society held its monthly meeting by teleconference on August 14, 2020. Our monthly meetings are always held on the 2nd Friday of every month. We’ve had a lot of success with holding our meetings remotely and we will likely continue for the next coming months to continue our commitment to safety in light of the pandemic. Our membership is in regular contact with our community which has allowed us to promote and hold events including our first launch at the Mojave Test Area (MTA) on July 25, 2020. You can read the details in the firing report posted on this website.

Our members are doing well and thus far no one has reported being infected with COVID-19 which we hope continues to be the case. Frank is in regular contact with the Los Angeles Police Department’s (LAPD) Community Safety Partnership (CSP) but under current circumstances, the next school event may not be until next year. Options are being considered on how to continue our educational programs while maintaining social distancing.

The August 2020 RRS meeting held by teleconference.

REVIEW OF THE 7/25/2020 LAUNCH EVENT OPERATIONS

The first topic was the recent launch event we held on July 25th at the Mojave Test Area for the first time since the start of the pandemic. We had some difficulties in operating under the summer heat (106 Fahenheit at the peak) but this is nothing unusual for this time of year. Many of us were well prepared for the hot sun with our hats, sunscreen and iced beverages and chilled water. We also did a good job of watching out for each other. Still, the heat was responsible for leaving all but one of the micrograin rockets downrange. It also underscores the importance good planning, coordination and putting safety over all other considerations. We had several mis-fires which we were able to resolve, but maintaining discipline during the event proved to be a larger challenge. The launch protocols will be explained more thoroughly in the next safety briefing. The meeting highlighted that every member and pyro-op attending the event holds a joint responsibilty for the safety of all and it starts with self-discipline and patience by all.

Getting the beta rocket ready in the launcher on 7/25/2020 and setting the camera

We also discussed proper protocols such as announcing the pyro-op in charge well before the event and the necessity of providing detailed information about the intended operations to the pyro-op in charge in advance. Most of the planned projects were well understood as they were micrograin rockets and the previous hybrid rocket attempted at the last launch event.

DATA REVIEW OF THE STANDARD ALPHA FLIGHT OF 7/25/2020

The only micrograin rocket to be recovered from the launch event of 7/25/2020 was the standard alpha with plain steel nozzle. John Krell has been developing progressively better and more powerful avionics payloads designed to fit the narrow confines of the RRS standard alpha payload tube. John was able to spot and recover one of his payloads and process the flight data captured that day. The avionics payload was intact after being extracted from the desert floor including the solid-state data chip. John was able to recover the data and accurately reveal the huge acceleration of the RRS standard alpha with unprecedented accuracy. A peak acceleration of 114 G’s was recorded at roughly 0.3 seconds just before tail-off and burn-out at 0.4 seconds from launch. I was able to screen capture his plot below.

John Krell’s presentation of the data from the one recovered alpha ( to date).

The second plot shows the velocity derived from the accelerometer readings in the half-second which captures burnout at 0.4 seconds. Burnout velocity was measured at 670 feet/second which is consistent with prior data and trajectory predictions. The alpha is subsonic but travels at substantial speed from the swift acceleration. Given the high air temperature that day, 106 Fahrenheit, the speed of sound was 1165 ft/sec. The altitude of burnout was determined to be 130 feet which is consistent with prior flight data and high speed video footage.

Trajectory plot of the standard alpha flight from 7/25/2020

The third plot was made for the whole flight of standard alpha from the 7/25/2020 event from launch to impact at 35 seconds. Given the roets were impacting 2000 to 3000 feet downrange, the sound delay matches with the time to impact witnessed in the observation bunker. The maximum altitude was just over 4,400 feet based on the barometric pressure measurements using the 1976 standard atmosphere model. Base atmospheric pressure reading at the start of the flight shows the elevation of alpha launch rail platform is 2,048 feet.

Trajectory of the standard alpha flown on 7/25/2020

John Krell has really accomplished something with these custom avionics packages. He has been mentoring some of our other RRS members and the society encourages other members to build and fly their own payloads to spread the knowledge.

John Krell and Bill Behenna discuss avionics payloads

The society hopes to recover the other two alphas and the beta for further data analysis. Both of the unrecovered alphas from this last launch event had ceramic coated nozzles which should not erode. This should result in a more ideal performance as the throat area will not open up. The actual effect of this design improvement can best be assessed with recorded flight data. Also, we hope to compare the trajectory of the four-foot propellant tube with the standard length. Lastly. if the beta is recovered with recorded flight data, we may be able to assess its performance in unprecedented detail. The society hopes to report this flight data soon.

IMPROVEMENTS TO THE NITROUS OXIDE FILL/DRAIN MANIFOLD

The failure to launch the second build of the hybrid rocket was discussed at the August 2020 meeting. After discussing the launch procedures and corrective actions followed during the attempt to launch the nitrous oxide hybrid at the MTA with Osvaldo (the Level 1 pyro-op in charge) and racing experts at Nitrous Supply Inc., Huntington Beach, California, the cause of the fill valve’s failure to open became clear.

nitroussupply.com

In the racing industry, these normally-closed direct-acting solenoid valves are commonly used to open the flow of stored nitrous oxide bottles against the full supply pressure in the storage bottle. These are called “purge solenoid valves” among racers because it is this solenoid valve that opens the flow of nitrous oxide which displaces or purges out the air in the engine lines during the race. Buying these 12-volt DC high pressure solenoid valves from racing suppliers is much cheaper given they are made in greater numbers for the racing industry. (~$120 each versus $400+ each from reputable solenoid valve manufacturers).

In researching common designs for normally closed (NC) solenoid valves, the excessive heat of that day simply created too much inlet pressure against the internal valve seat for the electromagnetic solenoid coil to overcome and open the flow path. 1000 psig is likely the limit to reliably open these valves according to advice given by Nitrous Supply Inc. who has decades of practical experience at racing tracks around the country using purge solenoid valves for an application nearly identical to the needs of hybrid rocketry fill and drain operations. The ambient temperature at the MTA on launch day was creating a bottle temperature of 1400 psig accordling to the bottle pressure gauge and the separate pressure gauge in the manifold when the bottle was opened. This is well above the 900 psi recommended pressure range seen by marking on the gauge. The bottle, valve body and fittings are rated for these higher pressures, but opening mechanism of the solenoid valve was not.

A color-coded example of direct-acting normally closed solenoid valve is below. Blue shows the high pressure fluid path which is holding the seat down along with some assistance from an internal spring only for low inlet pressure conditions. With current applied to the electromagnetic solenoid (Orange), it pulls up on the moving armature (in red) which then allows the fluid to slip past the seal and through the flow control orifice when commanded open. Only a slight amount of movement is necessary to lift open the valve. However, if the fluid inlet pressure is too great, the solenoid can not provide enough force to lift and open the seal, therefore the valve stays shut.

Example of a direct-acting normally closed (NC) solenoid valve courtesy of M & M International (UK) Limited with color added to distinguish key parts.

To understand the relationship between pressure and temperature of the nitrous oxide you must consult the vapor pressure curve for nitrous oxide. This set of data points spans between the triple point and critical point of any pure fluid. NIST provides accurate data to generate such a curve.

webbook.nist.gov

The critical point of any pure fluid is where the distinction between gas and liquid phases disappears. This is not necessarily hazardous but it does mark a fundamental change in fluid behavior. The critical point of nitrous oxide (N2O) is 1053.3 psia and 97.6 degrees Fahrenheit according to Air Products company literature. This means the nitrous oxide conditions in the bottle at the launch (1400 psig as read on the gauges with an fluid temperature of 106 Fahrenheit or more) was well in the supercritical range, but again, this is only hazardous if the pressure vessels and plumbing connections aren’t able to safely contain the pressure. If the solenoid valve could have been opened, the pressure drop would have returned the supercritical fluid back to normal conitions and would flow dense liquid into the rocket when the fluid naturally chills down from the expansion.

Both the bottle pressure gauge and the manifold pressure gauge read excessively high on that hot summer day.

Keeping the bottle pressure below 1000 psia means controlling the external temperature of the bottle to a lower temperature. Below is a tabulation of state points along the vapor pressure curve for nitrous oxide (N2O) for common ambient temperatures. You can see that small shifts in ambient temperature can greatly affect the vapor pressure of the pressurized liquid. Keeping nitrous oxide under pressure is the key to retaining its denser liquid state. As long as the tank pressure is above the vapor pressure at that fluid temperature, you will have a liquid phase in the tank. If the pressure on the fluid drops below the vapor pressure, the liquid will begin to boil away.

30 F, 440.05 psia
40 F, 506.63 psia
50 F, 580.33 psia
60 F, 661.71 psia
70 F, 751.46 psia; liquid density 48.21 lbm/ft3, vapor density 0.1145 lbm/ft3
80 F, 850.46 psia
90 F, 960.09 psia
97.6 F, 1053.3 psia; density 28.22 lbm/ft3, CRITICAL POINT
Molecular weight = 44.01 lbm/lb-mol

Vapor curve for nitrous oxide over ambient temperature ranges

At first, it was thought that there wasn’t sufficient current from the lawnmower lead-acid battery we use. The summer heat can cause batteries to fail, but even after switching to a car battery, the failure to open was the same. Having a 12-volt solenoid requires greater current to actuate the solenoid valve, but it is a common standard for automotive grade parts which can be less expensive yet reliable. A current draw of 15 Amps over the long cable runs of a few hundred feet can be taxing to the firing circuit battery. This was not the cause of the problem, but it is a regular concern making sure sufficient voltage and current is available to both ignition and valve control.

To exclude outright failure of the solenoid valve, Osvaldo brought the unit home, allowed it to cool to room temperature then dry-cycled the valve from a battery to see if it still actuated. This simple test was successful and the filling valve in our nitrous oxide manifold continues to operate. At the next launch attempt, we will be prepared to chill the nitrous oxide supply bottle with an ice bath if necessary as was originally suggested at the prior launch event. Keeping the bottle pressure in an appropriate pressure range for fill operations is dependent on controlling the fluid temperature (60 to 90 F) under extreme heat or cold environments.

In researching purge solenoid valves, a second 12 VDC normally-closed valve was found and purchased. Nitrous Supply Inc., was out of purge solenoid valves but offered many alternative suppliers in the Los Angeles area. After some searching, I selected a high flow purge solenoid valve sold by Motorcycle Performance Specialties (MPS) Racing in Casselbury, Florida, for the purge solenoid valve used for venting our nitrous oxide manifold. The control panel is already equipped with the second command channel to open the vent from the blockhouse should it be necessary in launch operations. A schematic illustration is provided in this article.

mpsracing.com

Normally-closed 12 VDC purge solenoid valve from MPS Racing in Florida used for nitrous oxide applications including car and motorcycle racing.

The previous drain solenoid valve equipped with the nitrous manifold I bought was not deisgned for the full bottle pressure in the manifold so it quickly failed during initial checkouts. A manual valve was used in its place to carefully bleed out the remaining pressure in the line after the main bottle valve was tightly closed. This second solenoid valve will be used for draining the nitrous in the event of a launch scrub. Although the Contrails hybrid motor already has a small orifice and vent tube at the head end of the nitrous tank to provide slow release of pressure buildup, it is better to have a remote option to quickly depressurize the vehicle if the need arises.

Fill, drain and firing circuit for a Contrails hybrid rocket motor

With some re-plumbing of the nitrous oxide manifold to include the new vent solenoid, a soap-bubble leak check would be needed to prove the system before use. Given the significant overhanging weight of two solenoid valves, it may be wise to mount both valves on a separate plate structure to avoid excessive bending loads on the bottle connection. Design changes like this will be considered in preparation for the next launch event.

PYROTECHNIC OPERATOR TRAINING SESSION BY FRIENDS OF AMATEUR ROCKETRY

Mark Holthaus of the Friends of Amateur Rocketry (FAR) organization is offering an online training session for those interested in becoming licensed pyrotechnic operators in the state of California. The event requires registration on the FAR website and a fee paid to FAR ($10) to attend this two-hour introduction to the licensing and application process to be held on August 26th.

Classes

Friends of Amateur Rocketry website for indicating interest in pyro-op classes

Amateur rocketry in California is controlled by the same laws governing fireworks which require licensing by a state exam. The application forms and guidelines are available through the Office of the State Fire Marshal in the state of California (CALFIRE).

https://osfm.fire.ca.gov/divisions/fire-engineering-and-investigations/fireworks/

This training course for pyro-op applicants is another example of FAR and the RRS partnering to help the cause of amateur rocketry. The RRS, FAR and Rocketry Organization of California (ROC) last year met to create a joint set of recommendations to help CALFIRE improve the definitions used to govern amateur rocketry when CALFIRE they were seeking input from rocketry organizations. It is to the mutual benefit of the whole rocketry community and the public that there be more licensed pyro-op’s in amateur rocketry to both increase awareness of state laws and improve the culture of safety in our hobby and professions.

This FAR training course only serves to provide applicants with basic guidance on how to begin the application process and prepare to take the examination. Members of FAR, the RRS, ROC and any other amateur or model rocketry organization are welcome to apply. Several members of the RRS have already applied as the society continues its campaign to grow our ranks of licensed pyro-op’s at all three levels.

Completion of this training course does not substitute for any part of the pyro-op application process set by CALFIRE. As each applicant is required to pay their own fees including fingerprinting, they must also provide five letters of recommendation from licensed pyro-ops at or above the level of license being sought. After this class, each applicant must formally request these letters from state licensed pyro-ops in writing. For a licensed pyro-op to offer a letter of recommendation to an applicant, they must be willing to endorse their skills, knowledge and character to the state of California based on their personal experience with that individual. This is done through active participation at launch events through rocketry organizations having licensed pyro-ops leading their operations. Apprenticing, studying and attentiveness are all ways that a pyro-op can get to know an applicant personally and thus build confidence that the applicant is ready to have the responsibility of being licensed in rocketry. A letter of recommendation is given solely at the discretion of the licensed pyro-op which means their standards and expectations may vary significantly from others. It is important to establish a working relationship with both the society and the specific pyrotechnic operator over several projects to demonstrate skills and learn best practices through active participation.

As the RRS has more licensed pyro-ops than FAR at this time, this training course will be successful if both organizations support it. Some of the RRS pyro-ops have already offered their support as this means more people will need to become active with the RRS and conduct their projects at the MTA.

ROCKET LABORATORY AT THE COMPTON AIRPORT

Keith Yoerg announced that there is a tentative plan to create a rocket laboratory in a hangar at the Compton Airport, Although, the hangar will be used from time to time to store or service light aircraft, there is a great deal of working space which will help the RRS continue their liquid rocket project already underway. Several members of the RRS are also active with civil aviation and are members of Chapter 96 of the Experimental Aircraft Association (EAA 96). The EAA has generously supported the RRS over the last two years and we hope to continue and expand this partnership.

NEXT EVENT AT THE MOJAVE TEST AREA

The RRS has been planning the next event at the Mojave Test Area which will be dedicated to repairing some of our facilities including the adjustable rail launcher damaged in solid rocket launch explosion in August 2019. The consensus at the meeting was that we should not to return to the MTA for a formal launch event until the seasonal temperatures decrease from the excruciating desert summer. October 3rd was selected for this work event, Our hope is the weather will be cooler and we can accomplish more on that day. We may also take some time to search for more rockets planted downrange from past launch events.

The RRS may also conduct a few static firings or even a launch if member projects are ready. All such proposed hot-fire and launch activities must be proposed to the RRS president and the selected pyro-op in charge for that day. Some of our member projects such as Wolfram Blume’s Gas Guzzler two-stage ramjet and my second-build of the high-powered hybrid rocket are both still works in progress and may be ready for the early October launch date. Larry Hoffing has been working on an improved solid motor chemistry which he may want to test at the MTA.

The RRS is available for private events before that time, but one must make their request to the RRS president as usual. Some have indicated interest in returning to the site for just a few hours to recover more rockets downrange. Its our policy that at least two members be present for any excursions to the MTA and the RRS president must be notified in advance.

IN CLOSING

Some topics were not able to be covered including the overview of the new RRS Constitution as it gets ready for administrative membership review. Also, facility improvement plans at the RRS MTA including new restroom facilities and blockhouse should be discussed.

The next RRS meeting will be held by teleconference on September 11, 2020 as it is unlikely we will be permitted to return to the Ken Nakaoka Community Center by then. We hope everyone continues to stay safe during these days of the pandemic and try to stay in touch as we are planning another event at the MTA for October 3, 2020.

If there are any questions, please contact the RRS secretary.

secretary@rrs.org

MTA launch, 2020-07-25

Posted on July 26, 2020 by Dave Nordling

by Dave Nordling, RRS.ORG

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 surveys the upper half of his launch rail made from electrical conduit for the three-finned steam rocket he built.

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.

Bill Inman captures a launch from his cell phone camera from the MTa observation bunker.

THREE ALPHAS

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.

Converging part of an alpha nozzle with the ceramic coating

Diverging part of the alpha nozzle with a ceramic coating.

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.

The four foot alpha rocket payload is being loaded.

The four foot alpha rocket sits in the alpha rails with the beta rocket in its own rail launcher behind it.

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.

Beta rocket with a classic Dosa-style fin can.

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 used beta nozzle sits next to the Dosa-style fin can

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 ignition wiring of the beta with the dual igniters is rechecked by Osvaldo. The beta is propped up on a chunk of wood to clear the payload switch. There was a concern that it could accidentally switch off.

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.

The beta under repair in the old blockhouse.

Two burst disks with two electric matches.

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.

Still capture of the beta rocket at the 7/25/2020 launch event

A massive smoke plume from the beta just a fraction of a second after 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 second fllight of the hybrid rocket sits on the 1010 rail.

The hybrid rocket sits on the 1010 rail positioned for flight

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 H222 motor slipped into the rocket body awaiting the retaining ring. The igniter is taped against the nylon filling line going up the nozzle, fuel grain and up to the floating injector fitting.

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.

Cross-sectional illustration of the Contrails hybrid rocket motor

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.

Top bulkhead fitting with an orificed vent line in the top, snap ring is installed and removed with a special tool.

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 floating injector with the 3/16-inch nylon fill line inserted. The Parker brand push-to-connect fittings are used for this application.

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.

Nitrous bottle with the filling manifold

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.

Nitrous oxide bottle courtesy of Nitrous Supply Inc. in Huntington Beach. The fill-drain system with remote operated solenoid valve.

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.

IN CLOSING

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.

Lovking up the gate at the end of the day.

Scalded Cat Steam Rocket Project Report

Posted on June 20, 2020 by Dave Nordling

by William J. Inman, Reaction Research Society

Editor’s Note: This article was originally published in the March 2001 issue of RRS News, an RRS print magazine. It is reprinted here on June 20, 2020, for the RRS.ORG website with permission from the author and from the RRS. Copyright belongs to the author and the RRS.

Some of the products mentioned in the article are still available and links to the company website are provided solely for the reader’s convenience but does not constitute an endorsement of any product by the RRS.

William J. Inman’s Scalded Cat Steam Rocket Project

STEAM ROCKET THEORY

Water has the ability to hold and store a tremendous amount of energy in the form of heat. Unlike more conventional propellants that store their energy chemically, the steam rocket, or hot water rocket as it’s known, relies on the amount of heat stored in the water. Two other properties of water that make the steam rocket work so well are the vapor pressure developed as the water is heated beyond it’s “normal” boiling point and that when released it will expand to 1700 times the volume it occupied in the liquid state. It can be heated to 700 degrees Fahrenheit (at 3200 psi) before it reaches it’s critical point. Power increases with heat, but so does pressure, so the farther up the scale it goes the stronger the tank needs to be to withstand the pressure. Optimum performance is a balancing act between power of higher pressure and the weight of a stronger tank. Obviously, the tank should be made of the strongest, lightest weight, heat resistant material available… Titanium would undoubtedly be the ultimate if cost were no object.

Vapor pressure of water at increasing temperatures up to critical point of 705 F.

In the nozzle, the water starts flowing as it enters the convergent section. The venturi principle causes the local pressure to drop as velocity increases through the nozzle, and as pressure drops, the water starts flashing to steam. This steam, as it expands, continues to accelerate in the divergent section. The percentage of water that actually becomes steam depends on the amount of stored heat in the water. The temperature will drop all the way to the ambient boiling point at the nozzle exit, being converted to kinetic energy in the form of jet velocity. This velocity can exceed Mach 2 in a well-designed nozzle. As the water level in the tank drops, it boils, keeping the volume above it filled with steam, maintaining the equilibrium. This also consumes some of the heat in the tank, so the tank pressure will drop about 25% during the course of the discharge.

THE ROCKET

The “Scalded Cat” Motor

At the time I started this project, I knew much less about steam rocket theory than I do now. The motor was based on a piece of surplus 4-inch diameter, type 316 stainless steel, schedule 10 pipe that I found. Wall thickness was 0.120 inches and the burst pressure as stated by the supplier was 4000 psi. I got a pair of stainless steel domed end caps and had them welded on, then a hole bored in the center of one and a 1-inch threaded stainless steel pipe fitting welded in for the nozzle attachment. Three steel fin-mounting tabs were welded to the nozzle end of the tank and a flange for mounting the payload section was welded to the other end. Compared to the 45 pound welding oxygen cylinder I used for most of my static testing, this was a lightweight tank, but at 24 pounds, it’s still pretty heavy for a flight tank. To take advantage of its strength and to partially offset its weight, I ran it at higher pressures than most previous steam rockets that I read about. The flight on December 2, 2000, was at 1500 psi tank pressure (610 degrees Fahrenheit). Theoretical specific impulse (Isp) at this heat is around 75 lb-sec / lb.

Welded-on steel fin mounts with nozzle screws into the bottom tank head.

The nozzle was machined aluminum with a 3/8-inch throat; a figure I arrived at because I wanted a throat area of 0.110 square inches. There was a curved convergent section who’s curve radius was 12 times the throat diameter, then the divergent section had a half-angle of 10 degrees (20 degrees between the walls) and an expansion ratio of 18.3 to 1. This made the exit diameter 1.600 inches. The throat was 1/2-inch long to give a pair of O-rings on the plug a place to seat.

The fins were 0.085-inch thick aluminum and were bolted to the steel fin tabs at the bottom of the tank by running machine screws through the fins and screwing them into the threaded holes in the tabs. The fins extended beyond the back of the tank and also bolted to tabs on the fiberglass boat-tail to help secure it. The boat-tail also had a ring at the back end that slipped over the nozzle to keep it straight.

Boat tail with aluminum fins bolted into the welded steel fin attach points. Nozzle retention points at the nozzle.

The payload section mounting flange was a piece of stainless pipe 1/4-inch smaller in diameter than the tank and 0.030-inch thinner. It was 3-inch long with three semi-circular notches cut in one end leaving three “pedestals” that were welded to the top of the tank. This reduced the steel to steel contact and hopefully the heat transfer rate from the tank to the flange. A total of six holes, three sets of two, were drilled and tapped in this flange for the mounting of the payload section adapter.

Vehicle Specifications

Length = 7.5 feet

Diameter = 4.5 inches

Weight (filled) = 53.2 lbs.

Water capacity = 8.5 liters / 2.25 gallons (80% full)

Operating temperature = 610 degrees Fahrenheit

Tank pressure = 1500 psi

Calculated tank yield point = 1800 psi

Estimated peak thrust = 297 lbs.

Thrust duration = 4.75 seconds

Estimated power = 5500 Newton-seconds, “M 1155”

Propellant mass fraction = 35%

Parachute (tank) = PML, 84-inches

Parachute (payload) = PML, 54-inches

Electronics = Adept ALTS2 and Blacksky AltAcc2

Deployment charges = 3 (redundant)

Charge igniters = 4 (redundant)

Bridle (shock cord) = Kevlar “muletape”

Fins = 3 (aluminum)

Nozzle throat area = 0.110 square inches

Nozzle expansion ratio = 18.3

Divergent cone taper = 20 degrees between walls

The Payload Section Adapter

This part was used to provide a slip-fit mount for the composite payload section while helping isolate it from the heat. It bolted to the mounting flange with six machine screws and extended 6.5 inches up beyond the end of the flange so the area in contact with the payload section would not be touching a hot steel surface on the other side. I needed something strong, heat resistant, a poor heat conductor, and made of a material I could work with. The only epoxy I could find that claimed to be good to 600 degrees Fahrenheit was J-B Weld, so it was thinned with lacquer thinner and used as the laminating resin for a Kevlar structure.

The top end of the tank and the mounting flange and eye-bolt. The payload section is in front of the motor. Notches in the Kevlar ring are to minimize contact with the payload tabs.

Looking down into the electronics bay. The plywood ring with ends of two “T-nuts” are visible with silicone “form-a-gasket” on the inner edge. AltAcc is mounted to the airframe (left) while a brass charge canister is inserted into the gas baffle for the backup charge (right). When the lid is installed, the altimeter and the other two canisters fit in between this other equipment (a close fit!).

J-B Weld – Adhesive Products

A J-B Weld and Kevlar ring was epoxied to the outside as a stop to keep the bottom edge of the payload section 1.85 inches above the upper edge of the steel flange. A Kevlar and J-B Weld “floor” or bulkhead was added to put another heat barrier between the tank and the payload section. Cellulose insulation was stuffed into the area between the tank and bulkhead.

The Payload Section

For this section, I used an 18-inch length of 4-inch phenolic tubing from LOC Precision with several layers of fiberglass wrapped around it.

LOC Precision – Rocket Kits and Accessories

I was concerned about the heat from the tank damaging it so I added 2-inch of Kevlar and J-B Weld composite to the bottom where it was closest to the metal flange. The bottom 11-inches of the payload section was open and housed the 84-inch PML parachute. The Kevlar “muletape” shock line was attached to a 3/8-inch eye-bolt in the top of the tank. Above this section was a 1/2-inch plywood bulkhead that housed a black powder charge and expansion chamber / stainless steel gas baffle section. There were two igniters in this charge, one connected to the Adept ALTS2 altimeter and the other to the Blacksky AltAcc2 accelerometer. These were to be triggered by the “main” event switches on the two electronic devices to blow the chute out if the 54-inch pilot chute hadn’t already deployed it. I did this for a backup system in case the payload section got soft and sticky from the heat and didn’t slide off easily as planned.

The whole steam rocket assembly with nosecone, payload and the metal propellant tank to hold the water propellant load.

There was a compartment above the bulkhead where the altimeter and accelerometer were housed. The three canisters for the powder charges were also in this compartment, blowing their gases through the bulkheads into the gas baffles. The canisters were 1/2-inch brass pipe nipples with 3/8-inch plugs inserted in one end with pipe threads, sealed with Teflon tape. The igniter wires were inserted through holes in these plugs and sealed with 6-minute epoxy. The AltAcc was attached to the inner wall of the airframe in the usual manner and the ALTS2 was attached to a piece of aluminum box tubing that was epoxied to the removable lid of this compartment.

The compartment lid was also 1/2-inch plywood with a 3/8-inch eye-bolt attached to it’s center and a gas baffle compartment on each side of the eye-bolt. The underside of this lid had a ring of Permatex “blue” silicone form-a-gasket where it sealed to the mounting ring. There were also two threaded holes, one at the base of each gas baffle, for the brass change canisters to screw into. Four stainless steel #6 machine screws held the lid to the mounting ring, which was made of 1-inch plywood epoxied to the inner wall of the airframe tube. “T”-nuts embedded in this built-up ring distributed the load from the screws. On the 3/8-inch eye-bolt was the Kevlar “muletape” shock line to the 54-inch PML pilot chute.

The Nosecone and Parachute Arrangement

The nosecone was a 4-inch LOC Precision unit with a wrap of 1.8 ounce Kevlar on the inside of the neck to help reinforce it after the bottom had been removed to gain access to the interior space. A 3-foot length of Kevlar “muletape” was attached to the inside of the tip of the nosecone by having a loop go around an aluminum cross-rod inserted through holes on each side of the nosecone tip. This whole assembly was then encased in a solid mass of epoxy, then the cross-rod cut off flush with the outside surface of the nosecone. On the other end of this line was a loop sewn in with Kevlar thread from Edmund Scientific. The 15-foot main shock line and parachute shroud lines were all attached at this point. The main shock line had accordion folds sewn into it with Kevlar thread. The stitches were not heavy duty so they would break when a load was applied. The first six folds had a single stitch holding them, the second set of six folds had a double stitch, the third set had a triple stitch and the fourth had a quadruple stitch. The idea was that the singles would break first, letting out 3 inches of line out at each break and adding tension. Then the doubles would start breaking, increasing tension and still letting out 3 inches per fold. By the time all the stitches were broken (which they were), hopefully things would be slowed down enough to keep the final shock from being too severe. (Kevlar does not stretch.) The 25-foot line from the tank to the 84-inch parachute was stitched up in this same manner.

Accordion folds were sewn into “muletape” Kevlar bridle line. Breaking the stitches allows the line to lengthen while adding increased tension and slowing the rate of separation, reducing shock when the line pulls tight.

The “recovery module” was built onto a 1/2-inch plywood disc that also served as the electronics compartment lid. The two gas baffles on the left of the disc with an eye-bolt between them are reinforced with Kevlar. The two brass change canisters (the far one is behind the altimeter) can be seen with the igniter wires in their end plugs. The Adept altimeter is bolted to a piece of aluminum box tubing.

The first flight of the Scalded Cat used the nose cone tot the left.

THE GROUND SUPPORT EQUIPMENT

The Launch Tower

Somehow I got the bright idea to build a tower with six longitudinal tubes of 1/2-inch electrical metal tubing (EMT). There would be one on each side of each of the three fins, just far enough apart to let the fin pass without binding. The reason was so I could pop rivet the three burner shrouds to these tubes, allowing each shroud to cover the entire tank surface between fins. “U” shaped strap steel brackets were welded to each set of tubes to hold them together and allow the fins to pass through. The three “U” brackets were held together by other pieces of steel strap welded to the outside corners, making a triangle shape at each of these brace points. The braces were spaced every 47-inches along the length of the 25-foot tower. For the real support, three lengths of 1-inch EMT were welded to the outside of the points of these “triangles”, also running the full length of the tower. In retrospect, diagonal cross braces should have been used and the second set of 1/2-inch tubes should have ended right above the tank where there was no longer any need for them. Anyway, it worked well enough. Three guy wires ran from the 12-foot point to anchors in the ground and another three ran from the 24-foot point to a second set of anchors 2 feet past the first set. Turnbuckles on all six ends made adjustment precise and easy.

The tower could be raised and lowered by pivoting on a stand which was a 3/4-inch galvanized pipe sitting in mounts on two 37-inch high welded steel “A-frames”. A flat attachment point was welded to two of the 1-inch EMT main supports and “U-bolts” went around the 3/4-inch pipe and through holes in the flats. To raise it, a couple of guys would get under the top end, raise it over their heads and start walking towards the base. After it was raised a certain amount, a third guy would start pulling a rope tied to the 12-foot point. A bolt on the bottom of the lower tower extension went through the base to hold it in position while the guy wires were being adjusted, and then help lock everything together.

The detached lower tower extension with the plug/release mechanism sitting in its notches. The release lever arm is sticking out in back. The fiberglass-covered styrofoam steam deflector is epoxied into the bottom. The hole in the flat bottom plate on the right is to bolt it to the plywood base.

The lower tower extension was a 17-inch piece of 7-inch diameter well casing with slots and access holes cut in it. A bottom plate was welded on for a place to bolt the plywood base, and three 3/8-inch headless bolts were welded to the upper end to bolt to the bottom of the tower. There was a fiberglass-covered styrofoam steam deflector in the bottom of this piece to direct the steam flow away from the electric actuators and the gas valve.

The Tower Base

This was what the tower sat on and what held all the peripheral ground support equipment. It was a 30-inch square piece of 3/4-inch thick plywood with two galvanized “Telespar” box sections bolted along the bottom of two opposite edges. These box sections were 36-inch long so they protruded 3-inches past each end of the plywood. Each of these four ends had a hole drilled in it to accept a 5/8-inch steel hold-down stake. The two welded “A-frame” tower supports bolted to the edges of the plywood base and had cross-bracing on the back side. A pipe coupler was welded to the top of each of these “A-frames” so the 3/4-inch tower support pipe could slide through.

A bracket to hold the release actuator was attached to one side of the tower and a bracket to hold the gas valve actuator was attached near the back of the lower tower extension. Then there was a third bracket to hold the clamp that secured the gas manifold near the back edge of the base. The plywood was thoroughly primed and painted to ward off the effects of the elements and the steam blast.

The Nozzle Plug / Release

Based loosely on the release mechanism designed by Bob Truax for his steam rockets in the 1950’s and 1960’s, this multi-talented device serves several purposes. First, it plugs the nozzle throat so no water or steam will escape before it’s released. Second, it provides a connection to the pressure gauge so it can be monitored during heating. Third, it has the integral clamping system that holds the rocket on the plug until released, and (provide) the means of releasing it.

The central plug is machined out of steel and has a long narrow taper to the 3/8-inch tip that goes into the nozzle throat. This tip is 0.60 inches long and has two O-ring grooves to accept Parker fluorocarbon or “Viton” O-rings to make the seal. The part below the taper is threaded with 7/8-inch bolt threads. A hole is drilled through the center to provide access to the tank pressure.

The plug/release mechanism locked onto the nozzle (boat-tail removed). The brass fitting connects to a steel brake line to the pressure gauge. Rotating the release cam (holding the red bars out) allows the bars to pivot off the nozzle.

The bottom end of the plug is drilled and threaded to accept a 1/8-inch brass pipe fitting. This fitting is an adapter that allows a 5/16-inch automotive steel brake line to be used to connect the pressure gauge, which sits on the tower’s 3/4-inch support pipe on the end facing the blockhouse.

A support structure with three “spokes” is built around a 7/8-inch nut that screws onto the plug. The “spokes” are steel box tubing long enough to reach past the wall of the lower tower extension and sit in the bottom of three dedicated notches in the extension. Each of the spokes has a rectangular hole cut in it’s top and bottom to allow a smaller piece of square steel bar to pass through. This bar is pinned to the spoke by a 1/4-inch bolt running through it crossways, allowing it to pivot. When the three bars are brought together at the top, they contact the tapered outer walls of the nozzle like fingers.

Below the structure with the spokes and bars is a cam plate made from a round piece of 1/8″ steel sheet welded to a bored-out 7/8-inch nut that slips onto the plug. Three equally-spaced half-round notches are cut into the edge of this plate. The spacing between the plate or cam and the “spokes” structure is adjusted with washers between the two. When adjusted correctly, the “cam” edges of the plate will hold the bottom edges of the three bars out at a distance that positions the other end of the bars so they hold the nozzle firmly onto the plug, with the O-rings seated in the throat by “gripping” the tapered outer walls like fingers holding a knob. Rotating this cam by pulling on an attached lever arm with a 12-volt DC electric linear actuator allows the bottoms of the three bars, or fingers, to fall into the three notches, pivoting around the 1/4-inch bolts and releasing the nozzle from it’s grip. A 7/8-inch “keeper nut” with a nylon insert is screwed onto the plug below the cam and give it something to ride on and keep the spacing so it turns freely but doesn’t have excess play.

The Burners and Gas Delivery System

At the bottom of the tower are three sheet metal burner shrouds that are as long as the tank (48 inches). In the bottom of each of these shrouds is a 30,000 BTU propane gas log lighter for a fireplace attached by two “U-bolts”. There are adapters for flexible appliance gas lines on each burner to attach to the manifold. The manifold is a 1/2-inch pipe nipple and “L’s” on each side, creating three points to attach the flex-lines. A clamp with three notches fits over these three lines at the manifold, holding it to the plywood base. On the other end of the feed nipple is a brass ball valve with a union on the other end. The rubber hose from the propane bottle is connected to the manifold at this union.

Launch tower erected with the power cables running back to the blockhouse, propane bottle to the right feeding the burners

Attached to the ball valve is an aluminum extension that is painted bright red so the valve position can be determined visually from the blockhouse. Also attached to the valve handle is the end of a 24-volt DC electric linear actuator attached to the control panel in the blockhouse. This actuator is used to open and close the gas supply to the main burners.

Electric linear actuators used in the launch process.

4.5-inch pressure gauge with a red plate behind it for easier visibility.

Sheet metail placed around the three burner shrouds for better heat retention. Propane torch igniters seen at the bottom. Steam pressure gauge is reading tank pressure.

Three small handheld propane torches are positioned around the base of the tower pointed up into the shroud burner areas. These act as pilot lights for the main burners should they need to be turned off and then back on again. They also add additional BTU’s to the heating effort but don’t put out enough to maintain heat (and pressure) by themselves.

The Control Devices and Panel

Pressure is monitored visually by watching a 4.50-inch diameter pressure gauge with binoculars from the blockhouse. Heating is controlled by a gas valve in the line to the main burners. A 24-volt DC linear actuator is attached to the handle of the gas valve and opens and closes it by pushing and pulling. It is wired to a double pole-double throw (DPDT) toggle switch on the control panel so that pushing it one direction opens the valve and pushing it the other direction closes it. It is a three-position momentary switch so releasing it allows it to spring back to the center “off” position. The power comes from two 12-volt batteries wired in series in the box. The control panel is actually the lid of the battery box.

The directional control switch and “launch button” are located under the safety flap on the control panel. Both the 24-volt system cord to the gas valve actuator and the 12-volt system cord to the launch actuator extending from the right side of the box.

Launch is initiated with another electric actuator, this one a 12-volt DC unit, also wired through a DPDT toggle switch in the battery box. Three 12-volt batteries wired in parallel power this actuator. One lead goes through a momentary red pushbutton switch wired in series with the DPDT switch. The DPDT is a two position, one for extend, the other for retract. This allows the cam to be rotated back to the “reset” position easily, which is good because we had to move it back and forth once to release the rocket for it’s maiden flight. The red “launch” pushbutton and the DPDT toggle switch controlling the direction of the release actuator are both under a spring-loaded safety flap made from an outside electrical box outlet cover.

Another view of the control panel with cable feed-through glands. Use of 12-gauge extension cords works well.

To connect the control box to the actuators at the pad, color-coded 12-gauge extension cord is used. Two 25-foot cords were bought, one yellow, the other blue with an orange stripe. Yellow is for the 24-volt gas valve actuator while blue-and-orange is for the 12-volt release actuator. These 25-foot cords were cut a few feet from the “female” end and attached to their respective switches in the box with the ends dangling outside a foot or so. The other long piece was wired to the actuators with the “male” end like a regular power cord on any appliance or power tool. Two 100-foot cords with the same color coding bridged the distance from the blockhouse to the pad.

THE MAIDEN FLIGHT

Setup and Preparation

The tower base already leveled and staked down on launch day and the tower was waiting nearby. The guy wire anchors were driven in at the pre-determined and marked spots and the peripherals were all attached to the base and tower. The igniters and deployment charges were already set up earlier in the motel room so once it was time to start the heating, the altimeter and AltAcc were turned on. After the tower was raised vertical and secured, the burners were lit and the AltAcc armed. We did not time the heating, but it went fairly quickly once a piece of sheet metal was wrapped around the tower at the position of the heaters. It was carefully bent so the fins would pass inside it during launch. When the pressure reached 1400 psi and then launch hopefully at a point where it had dropped to 1350 psi, the target pressure. Instead, the pressure continued to climb to 1500 psi, where it stayed until launch.

Bill Inman makes a minor adjustment to the fins of his steam rocket, the Scalded Cat

“Team Steam” shortly before the launch. From left to right: Jeanne Hoover, Bill Inman and Tim Clifford.

The Flight

When the release actuator was retracted, nothing happened. This had happened before, but when checked again during my last static test, it worked fine. Here we were sitting at 1500 psi with the release cam turned and the rocket just sitting there. So I had Tim Clifford, my partner and launch officer, switch the directional control to “reset”, work the actuator, then flip it back to “launch” and try it again. This time, after a couple seconds of hesitation, it took off on the most beautiful plume of steam I’ve ever seen. From the blockhouse it is not possible to visually follow a rocket very far into it’s flight through the small windows, so we just stood there listening to the roar as the sound came from farther and farther away. Finally, it stopped and for a brief moment there was no sound, until there was some cheering from the bunkers. The command was given over the P-A system to “quiet down”, and to “listen for an impact”. A few seconds later there was cheering again, and this time a more irritated repeat command was given only to be answered by shouts. “What was that?” … “A paraachute?” … “Two parachutes?” … “O.K. Keep an eye on it and stay under cover until the heavy piece is down.”

Launch of the Scalded Cat at approximately 2:30pm, December 2, 2000. Not the clearest view of the launch from behind the weathered blast windows of the blockhouse.

Another view of the steam rocket launch, photo courtesy of Richard Butterfield

Knowing it was under canopy was the best feeling of all. I have seen so many rockets crash because of recovery system failure that it makes that part especially critical. There was also the satisfaction of knowing that along with being the first successful steam rocket launch in the 57-year history of the RRS (at that time in the year 2000), it was also going to be one of the very few RRS flights to make a soft landing under parachute. I was able to squeeze out through the blockhouse door enough to actually see the parachutes coming down in the southwestern sky, the tank falling slightly faster than the payload section.

Jeanne Hoover stands over the safely recovered motor.

Post-Recovery Examination

The only damage found was where the ring at the base of the boattail got broken in two spots from being driven into the ground from the weight of the tank. Otherwise, everything was all right and the altimeter was reporting 4,479 feet. That evening, Bill Seiders was kind enough to download the AltAcc on his computer. It showed a maximum acceleration of 128 feet per second (4 G’s) to a velocity of 506 feet per second (345 MPH), a coast time of 15 seconds, and a peak altitude of 4,400 feet.

Blast pattern after the steam rocket launch. Very little equipment damage after the launch.

Editor’s post-script: Bill Inman has decided to rejoin the RRS after being away for many years. We enjoyed talking with him at our virtual meeting on June 12, 2020. He spoke by teleconference as we are still unable to hold our meetings in person at the Ken Nakaoka Community Center in Gardena, California, due to the COVID-19 restrictions from the city of Los Angeles. Bill has decided to start a new steam rocket build based on the many lessons learned over the years and we hope he’ll teach some of us how to make this unique form of rocket fly.

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