August 2017 meeting

The RRS met for our monthly meeting Friday, August 11th, at the Ken Nakaoka Community Center in Gardena. We were well attended, but got a late start. After the usual reading of the treasurer’s report, we began the meeting with the first agenda topic.

Frank has been talking with several groups interested in doing alpha build events including the LAPD wanting to serve another set of students in another housing project in Watts. The Watts event at the MTA was very successful and we discussed what went well and what could be improved.

We discussed getting a shared server for running RRS members to run applications related to rocketry. Frank and Chris are looking into options but haven’t found anything yet. Many of us use cloud services to store our files, but the RRS ought to discuss data storage options that can be better accessed by our membership. This topic is on-going.

The RRS history project continues. We received a set of RRS newsletters from Bill Claybaugh (thank you, Bill!). Richard Garcia continues to scan the newsletter stacks he has. We are still interested in getting reports, newsletters and anything else relevant to our history.

Bill Claybaugh was also kind to donate one of his 3-inch nozzles with a graphite insert to the society. In time, we will receive Bill’s propellant test rig which I look forward to examining and using at the MTA.

Bill Claybaugh’s three-inch nozzle

side view of three-inch nozzle with graphite throat

The RRS has made contact with our founder, George James, and some of the other early members of the society. We hope to schedule interviews and help to document as much of our history as we can in advance of the 75th anniversary symposium, April 14, 2018. The RRS is working on a list of our officers going back through the many years to the beginning starting with George James. We appreciate the help we’ve got so far, but there’s still a lot of work to do.

The next launch event at the MTA will likely be in the latter part of September. Some of the potential events with schools will be in October. There is significant interest in the RRS having a launch event for the several members interested in launching their own alphas. Many of our new members, Alastair, Bill, Angel and now Drew, have expressed interest in launching their own alphas. Myself and Larry will likely try to put something together as I continue to work on the parachute system for the alpha.

The council will update our membership once the next launch event at the MTA can be organized and set.

We had hoped to look at the footage from the keychain camera mounted to the fin on LAPD’s alpha rocket. The camera was recovered and the data was good, but Osvaldo did not have the opportunity to edit the footage. Alastair also had some video footage he took from the 7-22-2017 Watts launch event at the MTA, but he was still editing. We decided to push this item off to next month.

We discussed timer chips and other methods of switching on payloads right at launch. I brought my wood block breadboard and worked with Richard to resolve some issues with my circuit not firing. Osvaldo built a cotter-pin based spring-loaded switch that he mounted inside a segment of the alpha payload as an example. The society continues its efforts to learn more about what works with payloads and what doesn’t. I discussed my idea to attempt a flight speed sensor with a pair of barometric pressure sensing chips. Osvaldo said he’d drill a hole in the tip of an aluminum nosecone for the stagnation port.

We adjourned late at 9:22pm. In the future, we need to watch the time spent on each agenda topic. I would suggest we bring a simple battery-powered 6-inch wall clock into the meeting room so all people can more easily keep better track of time without pulling out their phones.

The topic of issuing membership cards and developing a better system of tracking dues collections was not addressed and will also be pushed to the next monthly meeting.

Our next meeting will be Friday, September 8, 2017.

If there is anything I missed or misstated, please let me know.
secretary@rrs.org

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 platform 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.

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.

***

MTA launch event, 2017-07-22

The RRS hosted a launch event on Saturday, July 22, 2017, with the students of Jordan Downs, sponsored by the Los Angeles Police Department’s (LAPD) Community Safety Program (CSP) at our Mojave Test Area (MTA). This launch event was the final part of the educational program put on by the RRS. The event was very successful as we fired 10 student alpha rockets and one more alpha from LAPD.

RRS sign at the MTA entrance

It was a typically hot day (105 F / 41 C) for late July at our private test site the Mojave Desert, but everyone was well prepared. Some even brought umbrellas which was a great idea to stay out of the sun’s rays. The misting fan we bought from Home Depot seemed to work well in the observation bunker. Home Depot was also very kind to donate water misting bottles for this event which helped tremendously in keeping people cool. RRS treasurer, Chris Lujan, was also very well prepared for the event as he saved me with a cold water bottle just after launch. Looking after each other is what we do.

RRS VP Frank Miuccio talks with students from Jordan Downs

Larry addresses the Jordan Downs students at the MTA

Our pyro-op in charge was Dave Crisalli and he gave our safety briefing before we got started. The students were well prepared and seemed to get a lot from it. New RRS member, Alistair Martin was nice enough to film some of the briefing.

Alistair films the burn demonstration

We also gave a propellant burn demonstration after the safety briefing to give everyone an appreciation for the power of the chemicals commonly used in amateur and professional rocketry. I have a still of the sample composite grain below. I took a video of the composite burn and will have it posted on our YouTube channel very soon.

sample composite grain sitting in the cage

Larry and Osvaldo had already loaded the rockets the night before so we could get the event started as quickly as possible. The rockets were safely stored in our old blockhouse ready to go.

Each of the students had painted their rocket with a unique pattern and color scheme to better help identify them later. The photo below is from just after the build event.

Jordan Downs alpha rockets painted and ready

Dave allowed me to assist on the pyro-op duties including rail loading and connecting for firing. As promised, we worked quickly to call out each one as they were loaded in the rails. Dave and I worked very efficiently to get each one off swiftly and safely.

The LAPD rocket was the 11th one in the series. It had a few special features including a smoke tracer in the payload section and a tail-fin mounted camera.

LAPD’s alpha rocket

LAPD payload with red smoke tracker inside

LAPD’s alpha rocket, tail fin camera

The LAPD rocket was able to be recovered shortly after launch thanks to the smoke tracker. The nose cone wasn’t able to be recovered but the camera on the tail fin remained in tact. We have had good luck with one of these keychain cameras in the past. Although the camera imparts a spin on the rocket, the flight is very stable. Once the footage is downloaded, and depending on the quality, the RRS will post it on our YouTube channel. It should be a lot of fun to see (fingers crossed).

YouTube – RRS channel

The specific brand of smoke tracker used was “Enola Gaye”. Given the success of the flight, the RRS should certainly use more of this product in the future. There has been some discussion to increase the number of holes in the payload section to allow more of the smoke product to escape throughout the flight.

Dave Crisalli with the recovered LAPD rocket

Due to the summer heat, the students of Jordan Downs didn’t go downrange to search for their rockets after the launching was over. However, Frank was able to locate and recover (dig up) one from the event.

Frank in the Dosa Bldg. just before going out to search for rockets

The RRS thanks LAPD officers Acuna, Plascencia and Terrazas

The RRS is grateful to all of the parents and adults who supported the event with us. Also, the RRS is grateful to LAPD officers, Acuna, Plascencia and Terrazas, for their help in making this event a big success.

Osvaldo receives Cert of Recognition

University of Southern California (USC) and RRS president, Osvaldo Tarditti, were glad to receive a certificate of recognition from L.A. City Councilman, Joe Buscaino of the 15th district for putting on this event with the students of Jordan Downs in Watts. It is with gratitude that the RRS accepts the certificate and we hope to work again with the students of Jordan Downs and other groups in the city.

As for my own rocket which would have been the 12th alpha launched, an electrical problem with the timer forced me to pass on launch. Although each part of the circuit seemed to work individually when I tested them the night before, the fully integrated system failed the demonstration at the site. Working with Richard and with some more time, I can resolve the issue, improve the design a little, and fly the parachute system in the alpha at the next launch event.

Dave’s alpha parachute deployment system, still in work

UCLA was also at the MTA to continue their work on their liquid rocket project. UCLA proceeded after the Jordan Downs launch, but had an electrical problem which prevented their scheduled cold flow testing. UCLA hopes to reset their efforts and be back at the MTA for more testing in late August.

Chris, Richard and I discussed making some rocket candy (sugar/KNO3) at the MTA loading area, but it seemed that there wasn’t enough time to get things started. With most of the resources already on hand, we’ll wait for the next event for Chris to cook a small batch of this classic amateur rocketry compound for demonstration purposes.

If any one has any pictures or video of the event that they’d like to share on the RRS website. Please send them to me at secretary@rrs.org
Or comment to this posting below.

For more information on the RRS educational programs, please contact us at:
events@rrs.org

Also, if I have missed or misstated anything, please let me know. Our next monthly meeting will be August 11th at the Ken Nakaoka Community Center in Gardena, CA.
secretary@rrs.org