nozzles

[Greg O'Bryant]

I static tested my end burner yesterday. It had mixed results. I really expected it to cato but to my suprise it didn't. I calculated the KN ratio based off of assumptioms from burn rate data so I was a little worried. Anyway the motor had a nozzle throat of 1/8 of an inch and the burning surface of the propellant grain was 1 inch in diameter. It should have had a total burn time of about two seconds. When I fired it it went up to presure for about a second, and then blew out the remainder of the propellant grain, becuase I didn't have anykind of forward plug in it. This is OK becuase I was interested in figuring out if the KN ratio was calculated right. The total burn time was just over a second, and eventhough I don't have anyway of measuring thrust it had a strong burn. If it were in a rocket or on a stick it would have flown. I used a clay nozle that showed some erosion so next time I will try a steel washer. Last I just had a question. I have noticed that it easier to cast the propellant in a heated metal tube. I wanted to know if anybody has ever used a reusable metal grain inhibitor like copper water pipe?
thanks

[Zippiot]

I used a copper water pipe for a while, but I made the engine too large and the power scared me. It seems to work fine BUT every website says donnot cast the fuel inside the motor case, as the metal case is likely to shrink and crack the brittle porpellant during cooling. A possible solution is to cast it in a paper tube inside of the copper tube, the paper will not expand (if thick enough) so when the copper tube shrinks back down it wont crack the propellant.

[Zippiot]

I am going to head down to tap palstics today or tomorrow and buy some casting epoxies. I will make a cast of the phenolic nozzle that came with my aerotech reloadable, this way I can re-cast them using a myriad of stuff and play with my sugar rockets confidentally knowing that the nozzle works (only on composite propellant I am sure, does anyone know the dimesions of the 29mm aerotech reload and if it will support candy fuel?)

I'll get up pics of the process hopefully. I plan on testing many different types of nozzle material aswell as composing my own mixes!

I got
anchoring cement (gotta watch for the expansion in my casting)
rock hard water putty
graphite flakes
carbon fiber
fiberglass
ground up kitty litter
a few other things

Ill prolly make a mix based on water putty and mix in some carbon fiber and fiberglass for rigidity, of course I will also use a washer to help prevent erosion so maybe I can make a reloadable motor outta it!

We already know that water putty doesnt expand and it can be used as a sugar fuel nozzle, my main question is will the nozzle made for composite motors work at all in a sugar motor or will my casting need modification?