Aerotech I357

TDK I300

OH YEAH. The one drawback was that this motor was not nearly as loud and generally “nasty” sounding as the higher pressure one. This was down at a Kn of 180, and operation was completely smooth, coming up to pressure and shutting down cleanly. I like this a lot. I have a 54/1050 and two 38/640s of this stuff ready to go next…

I’ve been working on a new blue formula as of late. Consider this the first “official release”. It was conceived in January, first fired in April, and first fired with data last weekend. It’s a smokeless variant of the typical blue I’ve flown in the past — 1% CuO, 2% Al — with the goal of getting something “Blue Thunder“-like. The story of the first flight is up in a blog post on OurPlanet.

First reactions from the flight were: (1) Not quite as fast as Blue Thunder, but certainly nice nonetheless, and (2) Oh my, look at that flame separation. Data from static testing showed that this burn was only at ~570 PSI, but the flame stands off nicely, even at low chamber pressures. It turns out to be about as fast as Kosdon fast, at least per the data. Here’s a typical curve from a Loki 38/480 firing:

Delivered Isp is somewhere around 200 sec, so nothing too special — just another “knob” propellant to add to the fray. Formula and rate data after the jump.

“SA Blue” (named such as I envisioned doing this in a C-slot for a Standard Arm I’m building) is 2% Al 400, 1% CuO, 80% solids with all 200 mic AP. Pretty much as simple as you can make it. But I like how it performs; not much to no slag on the nozzle, and a lot tamer than high CuO formulations (Amarillo Blue, I’m lookin at you…). Initial data says r = 0.0175P_c^0.42 (P_c in PSI) with a theoretical C* of 4632 ft/sec, safe to run between Kn = 200 and 300 in most situations. Maybe one day I’ll try it in a 2550 — right now it looks like just over 900 PSI and a 1.8 sec burn. L1500 anyone? Maybe after it’s better characterized…

The motor worked well, although the rough deployment at apogee caused the casing to be kicked and subsequently damaged upon landing. A new one is ready to go on the lathe, though, so no worries.Lessons learned:

• Use a stronger motor retainer — 6″ hardware is heavy, no matter what Todd says.
• Forward insulation is a good thing — the bulkhead of the motor got a little toasty and actually melted in one spot. It’s now in the BURP bin. Apparently the larger hardware produces more heat than can be carried away (volume goes up by the cube, surface area by the square…) so this makes sense, as we haven’t seen this on smaller motors, and the aluminum content of this propellant wasn’t inordinately high (5%).
• Aft insulation disks work great — we used 1/16″ G10 on top of the nozzle carrier to protect it from the same fate the bulkhead suffered.
• Nozzle carriers work great, too — this motor had a nozzle made from a 3.75″ diameter chunk of graphite for the nozzle insert, held in place by an aluminum nozzle carrier. We expanded the exit cone into the nozzle carrier a bit, which surprisingly wasn’t harmed by the exhaust flame one bit. I still don’t understand why it doesn’t melt — maybe the flow velocity is so high that it doesn’t have time to heat soak the part. Either way, carriers work. Save a graphite tree and use them. CAD drawings forthcoming.