2.375" Motor

Well November went by and I didn't get much done on the new motor. I did do a little testing with Erythritol based propellant. My first attempt was a little surprising given the fact that others have expressed that the combination is really easy to work with and cast. I found that the Erythritol based propellant "froze" quickly once removed from the heat source. Casting was challenging at best. I think there may be at least a couple of different factors at play. In my initial attempt I used a stainless steel pot which has thin walls and not much ability to retain heat. The other possible factor is the brand that I used. In contrast to the pure white Erythritol that other experimenters are using the brand that I have seems to have a hint of color which means that it may have some contaminant that is affecting it. I don't think that the quick freezing of the propellant is something that could not be overcome, but since I tend to cast out at the RRS facility where it's difficult to escape the wind and sometime surprisingly cold weather. Since I have around 50 lbs. of Sorbitol I decided to try an alloy of fuel consisting of 50/50 Sorbitol/Erythritol. This combination cast very well and was cured enough to remove from the mould after about 1.5 hours. A test strand had a burn rate that fell right in the middle of KNSB and KN/ER, so I'm expecting motor performance to be roughly the average of the the two fuels. Expected chamber pressure is expected to be around 1250psi.
The first image at the bottom is a sample segment of KN/ER, the middle image is a segment of KN/ER/SB, and the top image is a frame of the test strand burn test of the KN/ER/SB.
The RRS Christmas party/launch where I was expecting to test this motor was canceled this year so I'm hoping to find some time between Christmas and New Years to test.

Casting Tools

I haven't had much time lately, but the 2.375" motor project is moving along. The 2.375" motor project...hmmm. I have never a given a motor or rocket project a name. I usually refer to them by color, some key feature, or size like the orange and black rocket, or the camera rocket, or the 2.375" motor. I think I'll try and come up with a name for this motor, maybe something from Norse mythology since the high L/D of the design makes me think of the motor of one of my favorite sounding rockets the Loki dart.
I should be ready for the first test firing which is tentatively scheduled for early December. I modified the one existing casting set-up that I had for the original 2.375" motor to accommodate the slightly smaller diameter casting tube size. That set-up worked well in the past. The t-handle is removed during casting so it doesn't get in the way. Once the propellant is cured the handle is used to unscrew the mandrel from the base which pushes it part way out out of the propellant segment making mandrel extraction pretty easy.
The other two are simple hardwood bases coated with epoxy to maintain dimensional stability and keep them from absorbing the grease which will be used to keep the propellant from sticking. The coring rods are Delrin, which I haven't used before. Apparently Delrins thermal expansion properties allows them to basically fall out of the propellant once fully cooled. Basically the coring rod takes longer to return to ambient temperature than the propellant allowing the rod to shrink a bit more than the propellant.

Ares x-1 Launch

There is some good video of this morning Ares launch. The second video as some cool camera angles. Everything apparently went as planned, I guess the payload seperation wasn't as dicey as it looked.

2.375" Motor Updated

I changed the design again. I decided to optimize the it for KNER propellant by adding two additional segments. The additional propellant brings the motor up to a solid L-class motor and the chamber pressure sims. at right about 1000psi. I'm hoping to have an opportunity to test fire it for the first time in early December

Update: I updated the SRM output to correct a mistake. I had been using the wrong grain OD.

2.375" Motor Update

I've completed a couple of the wooden pyrogen canisters. I also ran a new SRM simulation with KNER propellant. The result of switching from KNSB to KNER is that the burn time basically doubles and the chamber pressure is cut to about half. The drop in chamber pressure results in a bit of a drop in Isp, but for my first KNER test I'm fine with that. A sugar motor this size with a four second burn time should be pretty cool and at this point the purpose of this test is to get some experience with KNER and test the pyrogen design.

2.375" Motor Update

I've been talking with Magnus from AIR recently about this motor and he has convinced me to use erythitol based propellant. I first heard about erythitol on Scott Fintel's site and the biggest attraction seemed to be ease of casting as well as a decent Isp even at relatively low chamber pressures. One of the other attractive things that Magnus has pointed out to me recently is that it functions well in a motor with a high L/D. Click here to see Magnus' latest motor that utilizes nine segments and has an L/D of around 15. One slight drawback is that it's hard to ignite, but from a safety stand point this is actually a good thing.
I'll keep the length of the motor the same for now, but in the future I could conceivably lengthen the casing and add two propellant segments without any additional changes and increase the total impulse by about 36%. The resulting increase in Kn would increase the chamber pressure, but it should still be well within the design limitations of the casing and the closures.

Rather than using a hotter igniter, I have decided to add a simple pyrogen cannister to aid in ignition. The design is a small wooden cup that will have a KN/SU/RIO propellant cast into it which will be ignited by a "standard" BP igniter. For added safety, the igniter will be inserted through a NPT plug fitting that can be screwed into the bulkhead just prior to testing. The cup will have a burst diaphragm attached to help ensure a quick ignition of the pyrogen grain.

Wood may not seem like the best choice, but I used a wooden disk in the original design to insulate the bulkhead and it was reusable a surprising number of times with just a bit of refurbishing each time.

Reaction Research Society, 1958

I just noticed that the RRS website has a pdf of a 1958 Popular Mechanics article reporting on the activities of the society. It's fun to think what it would be like to have been alive at some point in history, whether it be in the midst of the "space race" or some other time. It's nice to see that while much has changed since 1958, the essence of what the RRS and other similar organizations stood for then still exists today. Whether it's medium or small size companies competing with big ones, or organizations that not only encourage but facilitate education and experimentation, or small organized efforts like SStS, the spirit of competition, exploration, and experimentation is alive and well. No need to travel back in time.