75 & 98mm RMS™ Reload Kit Grain Bonding Advisory

smart-grid-update-1312pg

Received from AeroTech:

Dear AeroTech/RCS Dealers and Customers,

Over the past 26 years we have accumulated and examined a great deal of in-house test data and customer field experience with the RMS Reloadable Motor System™. In addition, the development of new products such as the recently-released Super Thunder™ 98mm reloads have required us to test the limits of the system, pushing it to generate performance numbers previously unheard of from AeroTech products.

During this testing, development and use we have discovered certain motor configurations that have benefitted from bonding the propellant grains into the liner prior to firing to achieve enhanced reliability. Not only does it prevent movement of the grains toward the nozzle during acceleration and the differential chamber pressure experienced during startup (which can cause a CATO if the aft propellant grain collapses under pressure and plugs the nozzle), it appears to greatly reduce instances of “tunneling” where hot gases penetrate the spiral gaps in the propellant casting tubes, causing the propellant to burn on the outside of the grain that is normally inhibited by the tube.

Therefore, we are advising all our customers to bond the grains of the following reload kits into their liners with Elmer’s Glue-All Max™. This is a polyurethane glue with minimal foaming and expansion to prevent the liner from cracking during cure, and has a long working time. The bonding process itself takes only a few minutes after which the glue should be allowed to cure overnight before use.

The reload kits affected by this advisory are:

75mm
K1000T, L1520T, L2200G, M1500G, M1780NT

98mm
L1500T, M2400T, L2500ST, M4500ST, M1845NT, M2100G, M2500T, M2000R, M6000ST, N2000W, N3300R, N2200DM

If you have any of these reload kits in your possession, we strongly advise you to bond the grains into the liner prior to flight for maximum reliability. All new production lots of these reload kits will now include a copy of the grain bonding instructions along with the standard assembly instructions.

A copy of the grain bonding instructions will be posted on the AeroTech website in PDF format –

AeroTech Grain Bonding Instructions

Working Your Way up the Alpahbet

alphabet

We have a saying in hobby rocketry, “Work your way up the alphabet.”  It is highly advisable to fly smaller rockets before trying to design, build, and fly an M powered rocket.  There are myriad subtleties that can cause serious problems.

As a general rule, if you aren’t sure something is right, don’t risk flying it.  Ignoring some detail that isn’t understood or hasn’t been handled has a name.  NASA calls it “Go Fever”.  The Challenger disaster is but one result.  (Proving that even groups with LOTS of experience and numerous smart people can “screw the pooch”.)

Both NAR and Tripoli’s certification programs align with this path as well.  Requiring that you start with smaller class motors, and then work your way up to bigger (and some would say) better things.

Contests are a great way to remind us about this general rule.   At our club, Northern Colorado Rocketry, we have a very popular “Alphabet” contest.  Each entrant starts with an A motor rocket then with a successful flight the contestant moves to a flight with a B motor rocket, and then so on, and so on up through the alphabet.  If there is a failure in any flight then they start over at A, again.  This contest goes on for the calendar year. The flyer with highest motor class takes the prize, and in the event of a tie, then the total impulse burned is the tiebreaker.

Amateur rocketry is one of the best hobbies to continually learn, grow, and expand your interests.  There’s basically no limit to what you can do – Just look at Elon Musk, he’s now talking about going to Mars.  I bet he started with an Estes A motor.