Monday, May 13, 2013


It been almost exactly one year since I started this motor...far too long.  SStS has been going very slowly and in spite of some recent progress, I suspect that the the way forward will continue to be a slow progression.  Back when I started getting really involved with amateur rocketry thirteen years or so ago, I was designing, making, testing, and flying much more frequently.  I think in those early days, once I joined the Reaction Research Society there was so much excitement in going to the launches.  The first event that I went to included zinc/sulfur, LOX/kerosene, HTPB, and sugar .  Within the next few months I saw many more of those and added steam, HTP, and a variety  of hybrids, good times.  I don't know that I can get back to that level of activity anytime soon, but Theo definitely enjoyed the desert, the rockets, and the people so we should make a point to go more than once a year.  With that in mind I'm making a conscious effort to finish the TR-1 motor ASAP.

Here is the next part to be made. 

This is a fairly heavy motor, but it won't matter.  With 1000 lbs of thrust there is no doubt in my mind that it will get itself off the ground when it's time to.  The purpose is to build something relatively simple and at low cost, and to sharpen my skills before moving on to a larger project that I've been toying with for the past 10 years or so.  There is some excess material in this design, so the part could go through a weight reduction process, but there is really no point for a static test.


Ben Brockert said...

Hey Randy,

Looking at the print of the overall engine, what's the reasoning behind the long straight throat in the nozzle? It's a feature I've seen in quite a few homebuilt solids, but not one I've seen an explanation for.

If you look at nozzle design guides in Sutton or H&H, they all suggest a rounded entry and a small radius to the exit cone. The throat is then linearly very small, no straight to it at all.

I understand making the throat as two cones is easier on a manual lathe, but the straight between the two cones just adds weight, drops nozzle efficiency (as much as 10%), and increases the total heat flux into the nozzle.

Randy Dormans said...

Hey Ben,
It's mostly because of my limitations as a machinist. What I try to do is draw the inlet as a rough guide. I don't have a way to machine a radius so I get the convergent roughly to shape, then I work the "corners" down a little at a time, and finish by grinding to as smooth a radius as I can get. In the end I should end up with no real flat area in the throat. You can kind of see it in this smaller nozzle that I made.
I'll try to get some better pictures of this nozzle as I go along. Thanks for the input!

Ben Brockert said...

Aha, I see. Thanks for the explanation, and good luck with the motor!