Side by Side Comparison

I fired two motors this past Saturday. One was an AP based motor and the other was a KNO3 based motor. Both motors were of approximately the same total impulse, but it wasn't really a fair comparison. The KNO3 motor used Xylitol for the fuel. I first heard about this sugar on Scott Fintels web site, and it was available at the local Whole Foods store. It has a low melting point and casts very nicely, the problem was that the grains took a long time to cure, weeks in fact. Anyhow, the propellant in the AP motor is fully characterized and the propellant in the KNO3 motor not so much. The side by side comparison is still interesting to watch though.

Composite motor class

I took part in a composite motor class this past weekend. The class was taught by Dave Reese and was conducted at the Friends of Amateur Rocketry site. The class was a lot of fun and full of lots of useful information. Dave is currently a student a USC and I'm sure that he is very busy but despite this he did a great job organizing and conducing the class. The motor that we prepped propellant for was based on standard high powered rocketry hardware of which I have none, so I made some hardware based on drawings that I found on the Loki Research website. The hardware worked really well; I like the simplicity of the Loki design. Here is a video of the class motor that I static tested, I didn't have any instrumentation partly because I didn't want to risk any equipment on untested hardware and a propellant that I don't have much experience with, but mostly because I've been so busy lately that I just didn't have time to get anything together in time. The design/propellant is pretty well characterized though. The thrust produced should have been in the neighborhood of 90lbs with and Isp of around 185-190.






The Paul Breeds of Unreasonable Rocket were also at the site. Paul senior was flying an RC helicopter loaded with telemetry to gain information for their Lunar Lander Challenge quest.

Composite Propellant Class

Later this month I'll be participating in a composite propellant class at the FAR site. The class is being taught by Dave Reese. Dave's a student at USC and was involved with this awesome project flown at the RRS some time ago. Photo by James Davidson.





Here is a picture of some of the 38mm hardware that I made myself for the class. I only had to buy the tubing. I bought enough for three casings for under $30. I had enough "scrap" pieces laying around for the bulkheads and nozzles.

Nozzle From Recent Static Test

After cleaning up the motor after last weekends static test I noticed distinctly copper coloration to the nozzle. I have noticed this to a lesser degree in the past few static tests that I've conducted. I attributed it to the copper tubing that I have been using for the pressure gauge. It didn't really make sense because that tubing is upstream of the exhaust flow so it seems like any copper from the plumbing would be pushed towards the gauge, not the nozzle. There are two significant differences between this test and the others. The first is that in this firing the nozzle appeared to get much hotter than the other nozzles that I have noticed this copper coloration in, the other is that in this nozzle there appears to be little globules of copper colored material that have been driven out of the surface of the of the nozzle. the thing that I can't figure out is that these nozzles are made of 12L14 steel, which is made up of Iron, Carbon, Manganese, Phosphorus, Sulfur, and Lead. So where does the copper coloration come from?

Static Test

This past Saturday I participated in a sugar propellant class at the Friends of Amateur Rocketry (FAR) facility. Brent Dougherty did a nice job presenting a general overview of how to safely work with and cast sugar based propellants. Thanks to the FAR guys Kevin, Mark, Ted and the others for letting us use the site. They have done an amazing amount of work on the site, including a massive vertical test stand (I don't remember what it's rated for).



As part of the class I fired an L-class KNO3/Sorbitol demonstration motor. The firing went well and good data was collected. This is a simplified set-up from what I've used in the past and it worked well. I'm planning on making some adjustable steel brackets that mount with bolts rather than the cargo straps. Here is the set-up:




In the picture taken just after the firing you can see the nozzle glowing red hot, once I got the motor torn apart and cleaned, everything appeared to have survived the firing just fine. The gauge measuring thrust began to register data about a tenth of a second or so before chamber pressure began to be recorded. I suspect that the pressure port was briefly clogged by the igniter initially. After tearing the motor apart I found a glob of melted plastic that used to be the soda straw that held the BP.

Terrapin Nozzle

One of my all time favorite small sounding rockets has to be the Terrapin. Click here to see my earlier Terrapin post including pics and launch footage. Developed at the University of Maryland in the Mid '50s, it is a study in simplicity. It was a two stage vehicle that used existing motors, fins welded directly to the motor case, a zero length launcher, and had tremendous performance. One of the cooler pieces of Terrapin hardware has to be the nozzle from the booster. The booster was a modified Deacon motor. Here is a photo of another one of my favorite small rockets that used two Deacon motors for the initial boost. I have been doing some 3D modeling recently so I did a model of the Terrapin nozzle. I found a drawing of the Terrapin in Small Sounding Rockets which is a great book with a lot of drawings and photos. I wish the illustration quality was a little better, but I highly recommend it to any one interested in rockets/rocketry. The Terrapin nozzle appears to have been of all steel construction. It also appears to have had an O-ring seal between the nozzle and the casing liner and another between the nozzle and the casing. Retention appears to have been through a number of small roll pins (not shown in renders) I would love to see what one of these nozzles looked like after firing. Any additional info., photos, or corrections are welcome.
Anyway, here are the renders:

Nozzle Cross Section

Here is a render of the new nozzle for the camera rocket. This render shows the much shorter that usual convergence section, this was done in an effort to reduce overall weight while still keeping the rest of the nozzle fairly "beefy".