Joe, Chris, and Charlie were back again at LDRS this year with the Talon 12, this time on a P motor. (Their novel of a build thread is here on TRF. It’s required reading.) The basic design of the motor is the same one that I worked up for our two stager at USC, and flown again (with different propellant) in the Turbo Encabulator and Del Grande. For effect, we switched back to the purple flame propellant in the Talon, and it looked great under power, as seen in this photo by Ray LaPanse:

Unfortunately, though motor operation was nominal, the rocket shredded just at the end of the burn (as has happened once before with this motor, in another rocket). Full details on the propellant and configuration (and a flight video) are below.

This is mostly from the document submitted to the TRA Class 3 committee, as submitted, with a few tweaks for web posting.

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The Talon 12 motor is a six-grain motor in standard 0.25” wall, 6″ diameter hardware. It has been successfully fired three times before – once at Balls in 2008, and twice at the Mojave Test Area under the jurisdiction of the Reaction Research Society. The Balls flight is shown in Figure 1a, and the latest MTA flight is shown in Figure 1b.

The propellant is an AP/HTPB-based system, with 82% solids loading, 6% metals, and a pinch of CuO catalyst. The two flights in Figure 1 are uncatalyzed, however motor performance was nearly identical to that of the catalyzed mixture on the first flight, and purple flames are cool.

The motor physical design consists of six grains. The nozzle throat diameter is 1.600”, with an expansion ratio ε of 4.75. This gives a port-to-throat area ratio H of 1.56, giving an aft-to-head pressure ratio Φ = 0.917, which implies a nozzle entrance Mach number of 0.416. This low Mach number, combined with a low startup mass flux of 1.86 lbm-in^-2-sec⁻¹, implies very little erosive behavior at motor startup.

Internal ballistics analysis was performed using a lumped-parameter method, which is reasonably accurate on small motors such as this. The results of this simulation are shown in Figure 2. Isp was calculated assuming constant C^∗ with η_C^∗ = 1 and no nozzle cosine losses (all optimistic assumptions), and a constant external pressure of 13.24 psi, as is standard at the Lucerne Dry Lake flying site.

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Overall, I’m fairly pleased with this motor’s behavior. It’s a good, reliable geometry for a baby P, and the 0.25″ wall hardware, though heavy, is somewhat “standard”, so liners and casting tubes are easily available, and it’s quite robust. In the future, I think the nozzle throat can safely be tightened up further to provide extra Pc and expansion ratio, for some additional thrust and better η_C^∗. I couldn’t be present during the buildup of the motor, so some of the issues took a little doing to hammer out – John DeMar helped out with speccing the o-rings, and Chris/Charlie/Joe did the insulation disks, liner sizing, final grain trimming, and motor assembly. Thanks to all of you for putting up with me while I was away, and having the patience to get the motor together and in the air again. Any day a P flies is a good day!

Here’s video of the liftoff and subsequent shred, taken by Dave Griffith:

Posted June 20, 2010 in Tests & Flights. Add Comment / Trackback