March 2018 meeting

The RRS held its monthly meeting on Friday, March 9, 2018 at our usual location at the Ken Nakaoka Community Center. We got a timely start at 7:31pm. After the reading of the treasury report, we proceeded to discuss the agenda items.

The first item is the release of the Astrojet newsletter. We’ve sold the first twenty copies already. Copies are $10 each and proceeds go to benefit society activities in this 75th anniversary year. The RRS’s newsletter hasn’t been in print for nearly 20 years. The RRS is very proud to offer a tangible token for the public’s reading pleasure. The RRS is grateful to member Bill Janczewski for making a very professional looking newsletter to commemorate this milestone year for our society.

75th anniversary issue of the Astro-Jet is now on sale for $10/copy.

The second item on the agenda was to get an update on the on-going RRS educational event with the students at Florence Joyner Elementary supported by the growing and successful LAPD CSP program. The program that started in February is going well and the students were able to visit the California Science Center as part of the five session program. The rocket build was completed today and the painting will commence on Saturday. Frank had the students make the paper tube rockets for use with the air launcher. The launch event at the MTA was rescheduled to April 7th. The forum has also been updated with this change.

Flo Jo Elementary students visit the California Science Center with the RRS

Frank has compiled a lot of educational materials from the many Powerpoint presentations over the last few classes, but the amount of material is getting pretty large. Some work should be done to pare down the content to have a greater impact to our younger audience. Also, Frank has bound the information in a booklet which might make for a fine publication as we refine our content with the great questions we get from the students.

For the third agenda topic, we discussed the progress on the RRS symposium. All is going very well and our speaker list is nearly fully confirmed. We held our first teleconference and will hold the next one on Tuesday, March 13th to continue the many planning activities left. 116 free tickets on Eventbrite have been sold already. Frank has been putting out flyers to local high schools such as Redondo Beach, Torrance, and Gardena. We ask all members to download the flyer and spread the word to colleagues, friends and other fans of rocketry both past and present.

The RRS 75th anniversary symposium will be Saturday, April 21st, 2018 and will have speakers and exhibitors from academia, industry and government agencies on topics related to professional and amateur rocketry. If there are any questions, please contact Frank Miuccio our society vice president and symposium coordinator.

At the symposium, the RRS would like to show photos of people and projects throughout our long history. We have received a lot of great items from members past and present and we encourage everyone to contribute whatever they can to the on-going RRS history project. In particular, photos, articles or stories from the 1970’s and 1980’s are of particular interest to us as we have little from this time period.

I am happy to lead this project and hope to give a nice montage to display before all of our symposium attendees and also invite people to write articles describing their experiences and past projects with the RRS. It is through storytelling that the RRS history is kept for future generations to learn and appreciate those that have come before us. Please email the RRS secretary if you have anything to share for the RRS history project.

On the next agenda topic, we discussed the possibility of moving the meeting start time to 7:00PM. The purpose was to try to have more time to discuss the growing activities at the RRS. The RRS is growing and the meeting time is important. After some discussion, it was decided to keep the meeting time at 7:30PM. The meetings will start on time and discussions will have to stay on the topics of the agenda. Many people come from great distances, but if other topics want to be discussed they can be done before the meeting starts.

For the next topic, a lot of progress was made on the horizontal thrust stand that will be used at the MTA on the small concrete slab just in front of the old blockhouse at the MTA. I had the load cell adapter pieces made and they fit quite well. Many thanks to Matt Moffitt of CNC Specialty Machining in Huntington Beach.

adapter blocks made for the S-type load cell

The horizontal thrust stand will go out to the MTA on the April 7th launch event, but this will be only for final fit checks. Osvaldo is also helping with getting the last mating hardware pieces to complete the set.

load cell adapter matching a standard alpha payload tube

The main frame pieces were welded, but we will not be able to use the thrust stand at the next launch event until the foot plates are aligned and welded. Many thanks to Jim Shirley of Shirley Design and Custom Fabrication in Huntington Beach for his welding skills. I hope to complete the thrust stand and have it ready to static fire alpha rockets at the next launch event after April 7th.

main structure of the horizontal thrust stand to be used for alphas at the RRS MTA

Richard spoke briefly about the progress he’s made to date on his liquid rocket vehicle build. The RRS standard liquid rocket will be the result of a few builds and a lot of testing to arrive at what will be a practical and effective standard design. Richard has built his thrust chamber with a G10 fiberglass internal liner insert and a graphite nozzle. Richard found a good supplier of fiberglass tubes and pipes that are sold in convenient 5-foot lengths.

Richard’s liquid rocket thrust chamber with fiberglass interior wall liner

Richard’s design also includes a pintle-type of injector which is in the works. We hope to see more details when he finishes this piece in the coming month or so.

The last agenda topic was about that fact that we are flying a lot of alphas, but few of them have payloads besides the smoke grenade which works well to help spotting them in flight at apogee. I have looked into making flight speed sensor and my parachute system. I am hoping this will be a semi-regular topic in future meetings.

A future topic for next month’s meeting will be to discuss the pyrotechnic operator’s exam. Licensing is done by the California Fire Marshall’s office and it is an important qualification to have. The RRS is working to get more members trained to help us expand our rocketry activities at the MTA and help us expand knowledge about safety in our hobby.

The meeting adjourned at 9:03pm. The next RRS meeting on April 13th will likely be spent working on the final details of the RRS symposium which will take place 8 days later at the same Ken Nakaoka Community Center in Gardena, Saturday, April 21, 2018.

If there is anything from the meeting that I missed or misstated, please let me know. I am also trying to keep the email list updated. Please let me know if anyone isn’t getting the meeting notices.

November 2017 meeting

The RRS held its November monthly meeting at the Los Angeles Cleantech Incubator in downtown Los Angeles. Our regular location at the Ken Nakaoka Community Center in Gardena was closed for Veteran’s Day on Friday, November 10th.

Los Angeles Cleantech Incubator (LACI)

Meeting topics included the upcoming launch event with the kids from the Imperial Courts neighborhood. This event was postponed to November 18th and was greatly anticipated as the kids worked hard and learned a lot in the five-week program put on by the RRS events team with the help of the LAPD CSP program.

Imperial Courts students prepare their paper rockets for launch

The program included a tour of Los Angeles Air Force Base at the SMC Heritage Center with Lt. Col. Alec Porter where the kids got to build and launch paper rockets.

Paper rockets at LA AFB with the Imperial Courts RRS class

USC Impact News has been documenting the whole Imperial Courts class program including the launch event at the MTA. The RRS looks forward to seeing their finished program at the end of the semester this December 2017.

The programs with LAPD CSP have been very successful and another program with Florence Griffith Joyner Elementary School is in the works for early next year.

The RRS symposium is in the planning stages for the upcoming 75th anniversary symposium on April 14, 2018. Several invitations to presenters and exhibitors have been issued and more are in the works. Frank Miuccio is leading the symposium again and we hope to have an even grander event for the public on this special occasion.

The Astrojet newsletter still needs submissions! We have had several interested parties, but no submittals have been received.

Please! Submit your drafts to the RRS secretary right away.

The Astrojet newsletter was the original publication started by the RRS when it was founded by George James in 1943. We thought it fitting to issue this one-time edition of the Astrojet for our 75th anniversary on January 6, 2018. It will be available in print only and the funds collected will support the RRS in our anniversary year events. Issues will be available by mail to our membership and other interested parties for a cost of $10 per issue.

Nominations of next year’s officers for the RRS took place at the meeting which is our normal custom. Voting by the administrative membership is underway and the results of the elections will be announced at the December 8th meeting. The meeting will be at the Ken Nakaoka Community Center in Gardena, as usual at 7:30pm.

Please let me know if I have missed or misstated anything in this post. See you at the next meeting.

RRS standard alpha rocket

Some time ago, I was asked to explain in more detail about the RRS standard alpha rocket. Although it has been frequently referenced, some of our general audience may not be familiar with the many aspects of the alpha. Therefore, I have decided to devote an entire article to this subject.

Alpha rocket iso view

This standard design at the RRS has been a common beginner’s rocket in our amateur rocketry society. We use it in our build events with schools, offer it as an experimental testbed for universities and also for our members to conduct their own experiments. It has a long history with the RRS and we still continue the tradition of building these rockets as it is a nice platform for experimentation and introducing newcomers to amateur rocketry.

RRS president, Osvaldo Tarditti, holds a pair of alphas

A similar “Ft. Sill alpha” rocket design was mentioned in the 1960 book, Rocket Manual for Amateurs, by Bertrand Brinley. Over the years, there have been changes made to the alpha design, but this article describes what has become the RRS standard in the alpha rocket design. I have been told that the 1-inch alpha design was created as a smaller and cheaper-to-fly design from the 2-inch beta design.

The alpha is a single-stage rocket consisting of a 3-foot length of 1.25″ outer diameter (OD) drawn-over-mandrel (DOM) steel tubing to hold the propellant. It is often erroneously referred to as a 1-inch rocket, which is more of a relative size measurement. The propellant tube has four trapezoidal sheet steel fins welded at their edges near the bottom such that the rocket fits with the launcher rail design at the Mojave Test Area (MTA).

the RRS launcher rails for four-finned rockets,
beta launcher is shown

Once ready, the alpha rockets are top-loaded into the rails and the pyrotechnic operator (pyro-op) in charge hooks up the igniter wires once we go into a launch mode.

RRS alpha sitting in the rails

launch rails for the alpha as viewed from above

The propellant tube has a bolted bulkhead at the forward end sealed with an O-ring. With good tolerancing, we’ve had no leakage from this joint and the four 1/4″ fasteners have sufficient retention under the brief ~1000 psi chamber pressure surge during combustion. This solid aluminum 6061-T6 bulkhead is installed first into the top of the propellant tube to begin loading the powdered propellant from the aft end.

coupler and bulkhead piece for the alpha

alpha bulkhead loaded and bolted in

The powdered propellant is loaded using a metal funnel a little at a time and gently and periodically bouncing the tube against a wood block to help settle out any air gaps. Many different improvements to increasing the packing density have been tried by the society over the years, but the society uses no special method for increasing the packing density of the micrograin propellant in most of our launches today.

Alpha tube loaded with micrograin propellant

Next the nozzle is loaded with a thin plastic burst disk (or diaphragm) with two tiny through holes to thread in an electric match (e-match).

electric match and burst disk

An e-match is a common pyrotechnic device used to initiate larger reactions with propellants. An e-match is two thin-gauge wires with a segment of nichrome heating wire bridging them. Covering the nichrome wire is a small amount of pyrogel compound that creates a brief high temperature flame once the match is given sufficient current. The e-match is single-use as the tiny wire is destroyed after ignition.

an Estes rocket igniter or e-match, shown as an example

With the burst disk sitting on top of the nozzle facing inward to the propellant, the e-match is packed into the propellant with the thin wire leads running to the outside. The burst disk sits inside the propellant tube held behind the nozzle closing off the propellant powder in the rocket. Although the zinc/sulfur micrograin propellant is fairly insensitive and stable, the e-match has sufficient energy to ignite the micrograin propellant behind the burst disk.

loaded propellant tube with nozzle and burst disk ready for attachment

The use of a linen-filled Micarta burst disk is not only for practical reasons of holding the propellant inside the tube after the tube is turned right-side up, but it helps build up the chamber pressure after the first few moments after ignition. The burst disk is designed to sacrificially break under the elevated pressure created from initial ignition from the e-match. The thickness of the burst disk is carefully chosen to not over-constrain the initial pressure rise in the propellant tube on ignition. The burst disk fragments then quickly exit the nozzle as the rocket takes off leaving the lead wires behind.

alpha nozzle bolting into the bottom of propellant tube

nozzle loaded on to propellant tube with e-match wires sticking out

Above the coupler is the payload tube. The standard alpha design uses a 1.75″ OD, 0.065″ wall, aluminum 6061-T6 tubing. The standard design calls for an 18-inch payload tube length, but shorter versions have been flown with 12-inch lengths being common in some of our school launches.

Nose cones have been made from wood, Delrin plastic and from solid aluminum. The RRS standard alpha design uses a tangent ogive shape which has been more of a traditional choice. Nose cones sometimes have hollow space inside for more payload capacity, although solid nose cones have also been used. The aluminum nose cones are fairly light and are very damage resistant compared to the plastic nose cones that mash from impact or the wooden ones that shatter. Aluminum nose cones have been re-used in subsequent builds after some turning and polishing.

12-inch payload tube with aluminum nose cone

Instruments are flown in the payload section and although space is very limited in these small rockets, smaller chips have increased the number of measurements possible (altimeters, cameras, barometric pressure sensors…). Smoke tracers have been used in recent events with increasing success. This helps in spotting the direction of flight and where to start looking to recover the rockets after impact. In these flights, we have a second set of ignition wires running to the rocket to first light the smoker before lighting the motor.

vented payload tube with smoke grenade inside, wooden nosecone

The alpha is a solid fueled rocket by what is called a micrograin propellant. The zinc and sulfur fine powders are one of the earliest solid propellants used in amateur rocketry and was invented by RRS founder, George James. The RRS standard mixture is 80% zinc and 20% sulfur by weight. Different ratios have been tried in the society, but this is our standard. Although a low performer among today’s solid propellants, it is inexpensive, simple to find, comparatively stable and quite fast once ignited.

zinc powder

sulfur powder

micrograin combustion demonstration at MTA

The zinc and sulfur powder constituents are separately measured and weighed then added to the 30-pound capacity metallic mixing drum. The mixing drum has internal metal baffles to speed up mixing as it is rotated on an electric motor driven rolling carriage.

metal baffled mixing drum with the zinc and sulfur, before mixing

electric motor driven mixing rolling carriage used for micrograin propellants

alpha launch 03-25-2017

The empty weight of the alpha is 3.65 pounds. Measured after propellant loading, the alpha fully loaded is 6.55 pounds. The calculated propellant load would be 2.90 pounds.

Specific impulse of the zinc/sulfur micrograin is quite low, 32.6 seconds. With an ideal combustion temperature of 2,600 degrees Fahrenheit, despite best efforts in packing, a significant part of the powdered propellant falls unburned out of the nozzle from the rapid acceleration even as the propellant is combusting. The rocket is supposed to operate as an end-burner with a 90 inch per second burn rate measured in many tests. Although most rocket groups no longer use the micrograin, the RRS maintains the tradition and it is hard to beat for simplicity.

The burnout time is about 0.8 seconds and burnout velocity is subsonic (roughly 600 ft/sec). Apogee for the alphas have been estimated at 5,500 feet based on the flight times (35 to 38 seconds) from launch to impact. Despite the long history of launching the alpha, some of these performance figures haven’t had many recorded measurements. The RRS is working on making systems to take better measurements, not only for the alpha, but for any of the rockets we build and test at the MTA.

If there are any questions about anything in this article or there is anything more you’d like to know about the RRS standard alpha, feel free to post a comment on our forum.