Building a Crisalli Igniter

Posted on July 29, 2022 by Dave Nordling

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.

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).

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.

MTA Launch Event, 2022-07-21

Posted on July 27, 2022 by Dave Nordling

by Chris Kobel and Larry Hoffing, Reaction Research Society

On Tuesday, July 19, 2022, 31 interns from various departments within Aerospace’s Engineering Division gathered in the Building D8 cafeteria to construct mid-power rocket kits. The kits were based on the LOC Precision company’s HyperLOC-160 model kits which utilize a 1.6” diameter airframe, plywood fins, and a 29mm motor mount, along with other requested custom modifications. Under the tutelage of Aerospace Corporation, Astrodynamics department retiree, Chris Kobel, along with his son James (both RRS members), VDID’s Isaac Goldner, Jeff Lang and his son Chase, and the Propulsion Science Department’s, Andrew Cortopassi (former RRS secretary and member), the interns successfully constructed the kits over a 2.5 hour period, while discussing various aspects of aerodynamics, propulsion, stability, recovery, and construction techniques. A second session was held the next day for three interns who couldn’t make the first session.

On Thursday, July 21, 2022, approximately 35 interns left Aerospace early in the morning on chartered buses and made the journey to RRS’s MTA facility in the Mojave Desert. They were accompanied by the Aerospace Corporation build team, along with VDID’s Jerry Fuller and Sophia Martinez as well as Carah Fukumoto from University Relations and Recruiting. The RRS treasurer, Larry Hoffing, acted as the Pyrotechnic Operator in charge for the event.

Under calm and clear skies, but with increasing temperatures reaching a high of 106 degrees Fahrenheit, approximately 45 flights were made, mostly successful. A new 5-rail launch pad provided by Aerospace Corporation was paired with the RRS MTA’s Cobra Wireless firing control system to handle the rocket flights. A few of the early flights indicated some slight instability which was addressed by adding ballast to the nose cones of the rockets (using desert sand!) moving the center of gravity (CG) forward to increase the margin of stability. The sight of some rockets were lost as they departed the launch wires in a somewhat sideways direction out over the desert or on a direct trajectory towards a blazing sun.

Jeff Lang and Chris Kobel with the five station launch rail system built by Aerospace

A demonstration flight of Aerospace’s C-LINK technology was marginally successful as the booster performed flawlessly, but the payload separated incorrectly and ended up powering into the ground.

Following the launch activities, the interns were treated to a terrific launch at the Voyager restaurant at the Mojave airport, welcoming the cool air-conditioning and ice cold drinks. Overall, it was a long and hot day, but a very successful outing with an enthusiastic response from the interns.

MTA Work Events, July 2022

Posted on July 21, 2022 by Dave Nordling

by Dave Nordling, President, Reaction Research Society

The society has been planning and working on a restroom facility for many months. This creature comfort has been the most requested improvement and this month it has come closer to being a reality at our humble site.

The society held two weekend work parties with the primary purpose of placing the restroom container at the concrete pads poured a few months earlier. The society prides itself on launch events but there are times when our volunteers must step up and do the mundane and arduous tasks of maintenance even on the hottest months of the year. We are grateful to members, Dimitri Timohovich, Osvaldo Tarditti, Larry Hoffing, Keith Yoerg, Bill Inman and new members Rushd Julfiker and Joe Dominguez for spending their day with us in the 108-112 degree heat of summer over the weekends of July 9-10 and July 16. While not all tasks were accomplished, we did achieve a great many things.