Sunday, November 29, 2009

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.


Ben Brockert said...

Hey Randy,

Kevin of FAR sent this out in his last announcement:

"The RRS did not have a Christmas party last year nor are they having one this year. I might be kind of fun for FAR to at least have an afternoon cookout/dinner on the afternoon of 19th before it gets cold and dark that evening. The students will be partying and it would be a perfect time. Let’s not make it a big deal, just burgers and hotdogs and such. Try and bring a little bit of food or fixings along with your rockets!"

The 19th is also the next general launching day, with four or so projects on tap.

Kevin is kevin [at] litepanels [dot] com, if you want to shoot him an email about flying then.

The EGE said...

I recall reading about this guy adding a small percentage of antifreeze to their homebrew fuel... that should help with your freezing problem, and also apparently adds a bit of red to the flame.

linky link

Randy Dormans said...

Thanks for the info Ben, I'll send Kevin an email.

As I understand it Antifreeze or (Ethylene glycol) is added to reduce the viscosity of the propellant mix to make it easier to pour. The problem I was experiencing was that when the ER based mix was removed from the heat source and began to cool it hardened...quickly. I'm not sure the two are necessarily related. For now the Erythritol/Sorbitol alloy seems to be working well so I'll test that, but thanks for the info.