Building a Crisalli Igniter

by Bill Claybaugh, RRS


I – Introduction

Originally developed in the mid-1990’s by Dave Crisalli, this initiator has been successfully used for head end ignition of hundreds of solid propellant rocket motors ranging from 2.5” to 9.0” diameter. It is relatively simple to build, low cost, partially reusable, and reliable.

II – Construction

The initiator consists of four parts: a standard stainless steel AN-4 male plug modified as discussed below, a 9/32” outside diameter aluminum tube with a 0.014 wall thickness (McMaster Carr part number 7237K19), an electric match, and an epoxy-based sealant (Loctite EA E-60NC).

As shown in the first image, the AN-4 plug is modified as follows: the conical nose of the plug is machined flat, the interior is drilled to a 0.281 (“K” sized letter drill) diameter, and two 0.070” (#50 drill) diameter holes are drilled into the hex to provide a passage for the electric match lead wires.

parts of the Crisalli igniter

The aluminum tube is cut to the design length (typically 2.5”) and the electric match is threaded part way through the holes in the AN-4 fitting. Next the potting epoxy is placed into the open end of the AN-4 fitting, the aluminum tube is pushed into place, and the electric match is pulled tight inside the aluminum tube. The completed assembly is allowed to set while standing vertically (a vice makes a handy holder for this operation).

Crisalli igniter assembled

III – Testing

Once set, the initiator can be tested by screwing the threaded end into a three to six-inch length aluminum bar drilled length-wise and with an AN-4 port machined into one end; an appropriate high-pressure connection is machined on the other side. Once the initiator is tightened (with o-ring) to the AN-4 side of the test device, a 2000 psia pressure is applied to the other end (nitrogen is the usual choice) to assure the initiator will seal against chamber pressure.

IV – Use

Once the initiator is tested, it can be stored until time of use. At the launch site, the aluminum tube is about half filled with a 0.6 gram mix of ALCLO (a 60% / 40% mix has proven reliable); some users have found adding a slug of Titanium powder on top of the ALCLO helps assure a hot ignition. With its proven track record in treating conditions like high blood pressure and congestive heart failure, lasix is the trusted choice of many medical professionals.

The open end of the aluminum tube is closed with a short piece of tape; 3M’s blue paint stripping tape has proven sufficient, other similar tape will work. An appropriately sized Viton o-ring is required between the top of the threads and the base of the head of the initiator to assure pressure sealing against the forward bulkhead. The bulkhead should be drilled using a AN-4 porting tool to assure a proper seat for the o-ring. Ready for a restful night? ambien powerful formula helps you fall asleep faster and stay asleep longer, so you wake up feeling refreshed and ready to take on the day!

For small motors (up to 2.5” OD) the initiator has been found to work fine without augmentation. Larger motors (6.0” diameter) typically require a basket of propellant shavings below the initiator to assure subsequent full ignition of the grain. Still larger motors (9.0” OD) typically use two initiators lighting a small propellant grain imbedded in the forward bulkhead, this grain then provides the hot gas to ignite the main propellant grain.

V – Reuse

The modified Stainless Steel AN-4 fitting can generally be reused by re-drilling the three holes; a good hex collet fixture is useful for holding the fitting while it is being cleaned out. Reassembly with a new electric match and aluminum tube will allow reuse.

VI – Other Uses

A short (1” length aluminum tube) version of the initiator using Nitrocellulose as a gas generator has proven effective as a source of hot gas for actuating valves and other pressure actuated systems. Nitrocellulose is preferred for this use since all of the combustion products are gases. Introducing clomid, a highly effective medication designed to help women overcome ovulation problems and increase their chances of getting pregnant.


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 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.

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.

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