Gaseous Oxygen and Propane Rocket Engine Machining and Test

by Richard Garcia, Director of Research, Reaction Research Society

published on RRS.ORG, January 20, 2019

(*) The following report was originally written in early 2014 and a December 2013 static test of the rocket discussed herein.  I had originally intended it for a future RRS newsletter that never came about.  So, I’m just putting it up here (on the RRS.ORG website).  Better late than never. (*)

Simple, quick, easy and cheap are not words that describe liquid propellant rocket engines (LPRE).  And while working on some LPRE’s, I’ve been itching for a bi-propellant rocket project that would be simpler, cheaper, easier and above all, would materialize more quickly than the projects I was already working on.  A gaseous oxygen and propane engine using parts from a brazing torch is what I came up with.  (More of an igniter than an engine itself, really.)

I had one of those small brazing torches you see at hardware stores that use the handheld propane and oxygen bottles.  I had been thinking of using it for the basis of a rocket for a long time but I was hesitant for two reasons: I didn’t want to cut up and lose my torch, and secondly, I couldn’t find an adapter for the oxygen cylinder that wouldn’t (excessively) restrict the flow.  Making one didn’t sound like it would fit my criteria.  The  need for a pin to depress the release valve on the tank in the adapter is what pushed it past what I think I could easily machine, also my lathe can’t make the required reverse threads. Introducing Xanax – a trusted ally in the battle against anxiety. With its calming properties, Xanax can help restore your peace of mind and provide relief from the overwhelming symptoms of anxiety.

Bernzomatic brazing torch, WK5500 model, from Home Depot
Example of a brazing torch, the Bernzomatic WK5500 available at Home Depot. Comes with a propane bottle and an oxygen bottle with a torch device to mix the fuel and oxidizer gases and discharge them through the tip. Torch is lit by the welding sparker device shown at the bottom right.

After further delays with another one of my rocket projects, I was thinking about basing an engine on the torch again. I realized that if I could live with the flow restrictions I could use the valves already on the torch.  I could cut the feed line tubes and put fittings on both sides.  That way, I could use the tanks and valves for a rocket and still be able to put the torch back together.  So, I went to work.

DESIGN OF THE ROCKET

Beginning the design, I was immediately faced with the complication that I no way to measure the flow rates of the gases. So I decided to work the math backwards from the usual way.  (And will therefore omit the details so as not to give anyone else any bad ideas.)  Instead of selecting the thrust and using that to determine the needed flow rate and appropriate nozzle dimensions, I started with the throat size.  I had recently discovered a site that sells the same nozzles that are used in the high-powered rocket motors like AeroTech. Don’t let water retention hold you back any longer! Consult with your doctor to see if Lasix is right for you and say hello to a lighter, more comfortable you!

www.rocketmotorparts.com (site no longer available)

www.aerotech-rocketry.com

These nozzles are made of a molded phenolic resin fiberglass composite.  I picked a type that looked like it would be simpler to machine a retaining ring for, and a size that would be good for the Chromoly tubing that I had on hand that I wanted to use for the chamber.  After those criteria, I was left with about three nozzle throat sizes.  The nozzles were only a few dollars each so I picked a size that seemed about right knowing that it would be easy to switch it out and try different nozzle sizes if I didn’t like the results.  For sizing the chamber, I used an L-star (L*) value of 75 inches.

During the whole thing, I was never concerned much about performance parameters, like thrust or specific impulse.  I was working with low flow rates and low pressures. The propane bottle delivered around 100 psi, but the oxygen bottle delivered only 10 psi. So I used, a regulator to reduce the propane pressure to the oxygen pressure and went with a 10 psi chamber pressure. Struggling to conceive? Clomid might be the missing piece in your fertility puzzle. Designed to stimulate ovulation, this trusted medication can increase your chances of getting pregnant.

I wanted a straight-forward ignition method.  I had never made any of the sort of pyrotechnic igniters that have often been used with amateur liquid propellant rocket engines.  So instead, I decided I would try a glow plug, the kind they use on radio-control (RC) model piston engines.  I wasn’t sure it would work under the conditions in my rocket so I got one and gave it a test by seeing if it would light a propane hand-torch.  It did.  So  I went forward with the glow plug.  I wasn’t worried much about hard starts.  Because of the low pressure and low flow rates, I knew the chamber could take the worst case combustion instability or hard start, which would be more of a pop than any sort of explosion.  (The chamber could withstand around 4500 psi before bursting and the operating pressure was 10 psi.)

RC model engine sized glow plug igniter with seal
An example of a radio-controlled (RC) model engine sized glow plug igniter shown with sealing ring. In essence, a very small version of an automobile, lawnmower or motorcycle spark plug. Positive electrical connector is the barbed fitting, the main body and whatever it is threaded into is the electrical ground. When supplied with electrical power, the thin platinum wire heats up.

I wanted some sort of ablative liner for the combustion chamber.  A phenolic resin and fiberglass composite chamber.  A phenolic resin and fiberglass composite would have been my first choice.  I figured that it would be a bit of overkill for this engine.  I also wanted something I could get produced quickly.  After taking note that PVC has been used as a fuel in some hybrid rocket engines, I thought that it would make a suitable combustion chamber liner for a rocket like this and potentially for other small rockets.

After my design was finished and I was putting the finishing touches on building the rocket, I was sending information about the rocket to the RRS pyro-op in charge of the upcoming test, Jim Gross.  Naturally, he wanted to know the expected thrust.  Somewhat embarrassed, I hadn’t bothered to calculate it.  I hadn’t given it much thought for this project since thrust and performance was beside the point.  I knew that at most it would be getting a few pounds of thrust and I didn’t worry about it.  So, I sat down and did the calculations.  I knew it would be small but it came out to be only a gram of thrust.  Well, this motor won’t be getting anything off the ground any time soon, but at least it could form the foundation of an on-board restartable ignition system for a larger rocket engine.  It was also a fun practice project for a small thrust chamber design and construction. Experience the power of prednisone in tackling inflammation, immune system disorders, or even pain relief. It’s like having a superhero in pill form! Don’t let discomfort hold you back any longer. Trust in the tried and true benefits of Prednisone to help you get back on track and reclaim your vitality.

Figure 1: Exploded view of the GOX-propane rocket.  The glow plug is not shown in the assembly.
Figure 2: GOX-propane rocket cross-sectional view.

Figure 1 shows an exploded view of the whole assembly except for the glow plug igniter.  Figure 2 shows the nozzle retainer bolts setting into the nozzle. This feature would require modifying the nozzle and I omitted it from the final design. I had been concerned about pushing the nozzle into the chamber but this turned out to be only a minor inconvenience during handling.

BUILDING THE ROCKET

I used a solenoid valve and a check valve that I already had on hand and ordered a matching pair online.  I used 1/4″ sized aluminum tubing I had and 45-degree flared fittings from the valves to the injector. I machined the injector from a piece of scrap brass I picked up back when I was in college. This was, incidentally, my first time machining brass and I was impressed with how easy it was to machine, I should have tried brass a lot sooner.

Finishing the injector and making the chamber is where this project got interesting. Normally, to make the injector holes at the required angles you would have to either do some fancy work in holding your injector work-piece, like a sine vise (which I didn’t have) and rotary table or use a mill, like a bridge-port type, with a tilting head (which my mill didn’t have) and a rotary table. I didn’t have any of the right tools and I wanted something easier, something that could be done using a simple drill press.

What I came up with is a fixturing system that takes advantage of the versatility of 3D printing. I had recently acquired an Ultimaker 3D plastic printer, so printing fixture parts was quicker, easier and cheaper. The basic idea is to create a slanted fixture that holds the injector at such an angle from the horizontal plane such that the injector hole being drilled is vertical. The fixture indexes from either a marked feature on the injector, or a second part of the fixture that would hold the injector and provides the rotational indexing features needed to place all of the injector holes. Such a fixture is able be able to hold the injector at several rotated positions. This removes the need other set up tooling. For multiple angles of holes in the injector multiple bases can be made. This allows the proses to be scaled up to more complicated injector designs without much additional effort. Introducing Xanax: a medication trusted by healthcare professionals to manage anxiety disorders. Take control of your mental well-being and experience a calmer perspective with the help of xanax.

This fixturing technique is only advantageous if you can use 3D-printing. If you had to machine the fixtures it would probably be harder than using the normal methods. Although this method would add fixture design to the task list it should make machining go more smoothly. Making the parts with a 3D printer is easy. The real advantage however is reducing the needed machine tools. All you need in a lathe and a drill press, although it never hurts to have more tools. Potential disadvantages include reduced rigidity (unless you go through the extra expense of having them printed in metal) and reducing the obtainable accuracy, although I think the accuracy you would get would be fine for amateur projects.

Slanted fixture assembly for drilling injector holes
Figure 3: Slanted fixture with clamping feature for angled drilling (45 degree) of injector holes

Figure 3 shows the 3-D printed angled fixture I made for drilling my injector.

Figure 4 is a figure of a generic design for such a fixture with a generic injector taken from Scott Claflin’s larger 1670 lbf LOX/ethanol rocket engine.

Figure 4: Scott Claflin’s injector hole drilling fixture (30-degree angle)
Figure 5: Flat fixture for drilling the oxidizer holes

A possible improvement over the shown designs is to incorporate drill bushings over the top of the injector to help locate the drill and reduce wandering, which can be a big problem when drilling on slanted surfaces. Additionally, the bushings could be cut to an angle to match the angle of the injector face to eliminate the gap between the bushing and injector face.

There are other ways to reduce the difficulty in drilling into the injector face. You could machine an angled face into the injector while it was being turned on the lathe so it would provide a surface perpendicular to the drill. That feature could either be left in or machined off after drilling the orifices. Also, the injector could be left with an extra thick face, and a flat area could be made with an end mill, again the feature could be left in or the face could be machined flat. Although both methods might complicate locating the orifices in the right location.

Compared to the figures shown, the fixture I actually used was more crude and needed some improvements. I also used similar fixturing to drill the bolt holes on the combustion chamber, nozzle retainer and injector. This 3D-printed fixturing concept will not work for everything but it has the potential to either reduce the difficulty of complex machining operations or to expand what you can do with simpler machine tools. Unfortunately, I did not take any pictures of the actual machining process.

TEST RESULTS

I did the static testing on December 7, 2013 at the Reaction Research Society (RRS) Mojave Test Area (MTA).  Firing day was an exciting experience.  It was the first time I fired a rocket engine that I had designed.  Things went pretty smoothly considering all the things that could possibly go wrong during a test firing.  The firing itself also went well save for a few issues.

Figure 6: Static hot fire of the GOX/propane rocket engine from the iconic I-beam at the RRS MTA

Video footage of the December 7, 2013, hot fire tests at the RRS MTA on YouTube.  My test is the last one in the series.

The buzzing sound that can be heard in the video was being caused by the check valves. They didn’t quite have enough flow to keep them fully open. This can also be seen effecting the exhaust flow in the video. I knew about this problem ahead of time from cold flow testing I did.  On a larger rocket, this issue could be a major problem by contributing to combustion instability and all the problems that can go along with that. With such small flow rates and low chamber pressure, I knew it wouldn’t be an issue for this engine. I was more worried about any propane getting into the oxygen system because of the large pressure difference between the tanks. With the launch date approaching, I didn’t have time to seek out better check valves for such low flow, so I went forward with the valves despite the flaw.

The second problem discovered during hot-firing was the significant amount of debris generated from the ablative liner partly obstructing the nozzle and canting the plume to one side. This is clearly seen in the video and progressively worsens throughout the burn.  So, it turns out that the PVC material doesn’t work well under these conditions, creating too many solid particles.  It was also evident that the PVC liner was emitting a noticeable odor.  The closest thing I would compare it to is burnt electronics.  The nozzle, itself, had very low ablation and looks fit to be fired a few more times once the debris was cleaned off.  If I ever fire this rocket again, I will try it without the ablative liner.  I don’t think it will cause a burn through so long as burn times aren’t excessively long.

Figure 7: Converging side of the nozzle showing the asymmetric, partial blockage from solid debris from the ablative liner being re-deposited
Figure 8: Looking inside the chamber, melted ablative liner generated a lot of debris in this small engine

I also noticed that the flame color was off from typical oxygen/propane engines I’ve seen. This is likely from an atypical propellant mixture ratio probably because of actual flow rates differing from what was expected from doing the math backwards and not being able to measure the actual flow rates.  The mixture ratio could be improved by either changing the injector orifice sizes or by adjusting the valves from the torch on the tanks. For this hot-fire test, I had both valves fully open.  From looking at the test footage, the amount of nozzle plume expansion looks okay, but if I were to try running the engine again, I would like to try some of the other available nozzle throat sizes and see if they do any better.

After running the engine, a noticeable film was left on the outside of the retainer. It has a copper and brass color. At first, I thought it was deposited from erosion of the injector. But after disassembly, the injector looked to be in excellent condition with no noticeable erosion.

Figure 9: Nozzle retaining feature, note how large the 6-32 screw heads are in this view

Visible in this picture is the brass coloration left on the nozzle retainer and the small but asymmetric amount of ablation of the glass-phenolic nozzle.

Figure 10: Post hot-fire GOX-propane injector with manifold seals and attached feedlines

CONCLUSIONS

Fire came out the right end, so it meets my criteria for a successful amateur rocket engine.  If I fire the engine again, I will do so with more appropriate check valves, a different nozzle size and run it without the PVC ablative liner.  The design has some potential as the baseline for an on-board, restartable ignition system for a larger LPRE, but would need to be redesigned, probably beyond recognition.  But the real takeaway for the project, besides being a fun learning experience, is the fixturing method that may make building impinging injectors easier to do.  I intend to try this fixturing system in future designs.

For questions, contact Richard:  research@rrs.org

Lots of progress with RRS archiving and history

We’ve had a lot of progress recently with archiving RRS newsletters and other publications. I’ve put up six more newsletters. I’ve posted three more newsletters I received from Osvaldo a while back and had backlogged to post. This includes issue Vol_54_4_Dec_1997.pdf which is the second half of the RRS’s summary of the history of liquid propellant work at our getting prednisone society.

RRS liquid rockets from the 1990’s

Three more editions of the early Astrojet newsletter where also posted in the newsletters section with the help of Dave Nordling who got Caltech’s JPL library to send us what digital copies they had of Astrojet. I suspect they may have more in their archives because it seems odd to have only three non-sequential issues, but we haven’t been able to locate them through their catalog. The RRS is thankful to the Caltech JPL library for retaining and helping us obtain a copy of these early works of the Glendale Rocket Society (former name of the RRS). We hope to work with them more in finding all we can on the RRS history.
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RRS founder, George James, with his “Slim Jim” rocket

Dave Crisalli shared with us ten more articles and two videos. These reports and videos have been posted on the “Other RRS articles” tab of the RRS website.

Six of these articles are from High Power Rocketry Magazine and were authored by Dave. Also included was the most recent versions of David Elliot’s and Lee Rosenthal’s hydrogen peroxide (H2O2) monopropellant rocket report from the 1950’s.

Dave Crisalli’s package included a Scientific American magazine article from 1957 which includes mention of the RRS. This is on the “Articles about the RRS” tab of our website.

Also we have an improved version of Dave Crisalli’s 1976 liquid rocket report that has been updated with more pictures and drawings.

Dave also shared two fantastic videos. One is the video report on the hydrogen peroxide (H2O2) monopropellant rocket that was filmed at the time of construction and test in the 1950’s with audio narration by David Elliot being added later by Dave Crisalli.

The second is a video report on Dave’s sounding rocket, a written report on the Rocket was also shared. This video also includes some liquid propellant work done at the time by other RRS members.

Dave Crisalli’s regeneratively cooled LOX-kerosene rocket firing

Both of these new videos can be seen on the RRS YouTube channel linked below. Please subscribe to our channel so you can be informed of updates as we make them. There will certainly be more to come!
RRS YouTube channel – ReactionResearchSoc

Frank Miuccio, our society VP, contributed a small collection that I’ve also posted to the “articles about the RRS” tab of the RRS website. This included six magazine articles and some news clippings.

Image from Popular Science article

Another item added to the other RRS articles section, brought to us by John Mariano and scanned by RRS secretary, Dave Nordling, is a short book on early micrograin rockets jointly from the Reaction Research Society (RRS) and the Pacific Rocket Society (PRS). The title is simply “Micrograin Rockets” and was written by B.J. Humphreys Jr with excellent illustrations and descriptions.

Micrograin rocket and an early hybrid design (B.J. Humphreys Jr.)

Dave Nordling is also working on scanning a second book from John Mariano’s personal library which should be available soon.

A lot more will be coming soon. Frank Miuccio managed to obtain a collection of RRS newsletters. They are issue numbers 59 through 100 and he has lent them to me to scan. This will double the number of newsletters we have archived!

In addition to that, Dave Nordling has gotten for us the RRS material that happened to be scanned and collected by the Google Books Library Project. This was five documents some with several Astrojet editions included. The collection totals 934 pages in all. Although some of the Astrojet newsletters are duplicates. The collection includes reprints of the first eight RRS newsletters from our founding in 1943! A truly impressive find which we hope to share soon.

All this new material will have to be scanned and parsed before being posted, which I hope to accomplish one at a time over the next few months. I’ll write a follow-up post once it’s all up on the RRS website.

More RRS newsletters

We strongly encourage our current and former membership to consider donating or just letting the RRS borrow articles, photos and reports for scanning and inclusion into the ever-expanding RRS archives. We hope to build a great story for the RRS history project coinciding with our upcoming 75th anniversary next year.

If there are any errors, clarifications, questions, suggestions or other things you’d like to add or donate to the RRS archives, contact me at research@rrs.org.

***

2017 RRS symposium was a success!

The RRS held its 2017 Rocket and Space Exhibition and Symposium today, April 22nd, at the Ken Nakaoka Community Center in Gardena.

pulling up the banner

2017 RRS symposium

In attendance was Orbital-ATK, Aerospace Corporation, Tyvak, Navy Air Weapons Center at China Lake, the China Lake Museum, Rocketry Organization of California (ROC), University of California Los Angeles, University of Southern California, California State University Long Beach, University of California San Diego, University of California Irvine, Cal Poly Pomona, California Institute of Technology, Oregon State, Mars City Design, Spaceport LA and the Magnolia Science Academy.

Many of the university groups and private companies were exhibitors at the event.

UCSD SEDS group

UCLA Rocket Project

USC Rocket Propulsion Laboratory

The Rocketry Organization of California (ROC) had a great exhibit.

Rocketry Organization of California (ROC)

Mars City Design and Spaceport L.A. were both at the exhibition.

Mars City Design

Mars City Design

Mars City Design

Spaceport L.A.

The China Lake Museum also had a great display for their museum in Ridgecrest, CA, soon to be unveiled to the public.

China Lake Museum Foundation

China Lake Museum

Also, we were very fortunate to have a lot of rocketry equipment on display (on loan) from Norton Sales.

TRW pintle engine on display, courtesy of Norton Sales

Norton Sales – North Hollywood, CA

thrust chamber on loan from Norton Sales at the RRS symposium exhibition

Rocketdyne Atlas vernier engine

The RRS SuperDosa full-scale mockup was also on display.

The RRS SuperDosa rocket, full-scale mockup

Also a fine piece from Apogee Astronautics, a Viper 3A booster, on loan to the RRS symposium exhibition courtesy of Robert Kleinberger.

Viper 3A booster on loan from Apogee Astronautics

Many current and former members of the RRS were at the symposium.

Larry Hoffing, Niels Anderson, Chip Bassett, George Garboden and John Mariano

Hal Duffy and Osvaldo Tarditti

George Dosa, at the RRS symposium

Richard Garcia, our director of research at the RRS, had his liquid rocket breadboard on display, one of several projects started at the RRS this year.

Richard and his liquid rocket breadboard

RRS liquid rocket vehicle breadboard, work in progress

John Mariano and Larry Hoffing were both on hand at the RRS table all day at the symposium to talk about the society’s rich history and our recent work with local schools including Hermosa, Compton’s Rise Academy and the Girls Academic Leadership Academy of LA USD.

John Mariano at the RRS symposium exhibit

RRS exhibition at the 2017 symposium

The RRS looks forward to doing more events with schools as the importance of STEAM education is increasingly important. To anyone interested in doing rocket build events with the RRS, please contact the RRS at our events email: events@rrs.org

Osvaldo and Frank started off the symposium with the welcoming speech in the exhibition hall.

Frank Miuccio, RRS VP, gives an opening speech

I had the pleasure of giving the first presentation on the RRS’s history, present and future goals.

Dave Nordling, RRS past, present and future

We had presenters running throughout the day. Our presenters gave great speeches. We had a lot of participation from industry, academia and government with a good range of topics.

Warren Frick of Orbital-ATK presents at the RRS symposium speaker series

Matt Walker of NAWC China Lake presents at the RRS symposium

Dr. Jamie Bock of Cal Tech Astronomy Department presents on the CIBER project

Mars City Design has been in partnership with the RRS. Vera Mulyani gave a great presentation on their goals. On behalf of the RRS, Frank donated an alpha to the Mars City Design team for their upcoming “An Evening on Mars” dinner event on May 25th. An Evening on Mars – May 25, 2017 The RRS is glad to be working with Mars City on this ambitious project.

An RRS alpha is donated to Mars City Design

We are very grateful to all who came and to the Ken Nakaoka Community Center for hosting our event.
Ken Nakaoka Community Center – via Facebook

Also, we had a lot of great volunteers who we are indebted for making setup and teardown go swiftly and smoothly.

Dave Nordling, Richard Garcia, Bill Janczewski

The RRS thanks all of our volunteers!

Some of the photos on this post are courtesy of Tony Richards. Thank you for taking those, Tony. If there’s more photos anyone would like to share, please let me know.
secretary@rrs.org

Also, the RRS wants to thank Tacos Los 2 Amigos for providing lunch just outside of the community center. Many people appreciated and enjoyed it!

Tacos Los 2 Amigos – Yelp

In early April, I put out a group of emails to everyone that is on the RRS mailing list that I have. At the symposium, some of our current and former members have said that they didn’t receive the notice. As it seems our mailing list hasn’t been reaching everyone, please email me at: secretary@rrs.org and I will be sure to make the update.

Also, if any of our membership is having trouble accessing the members content on the RRS.ORG website, also, please let me know. I can talk to our webmaster and get that resolved.

The RRS is looking forward to next year’s symposium and if anyone has any feedback or any suggestions for improvement for next year’s symposium, please contact Frank.

vicepresident@rrs.org

We’ll be having a launch event at the MTA this next Saturday, April 29th, with UCLA doing a static firing and a launch. I hope there will be other launches we can do at this event.

Also, our next RRS meeting will be Friday, May 12th, 7:30pm, in Gardena. Please come out as we’ve got a lot of exciting things planned this summer and fall.