Tuesday, September 2, 2014

TR-1 Motor update

We finished the bulkhead and nozzle. The nozzle has been done for a while but still needed the holes for the retaining screws drilled and tapped.

We also ordered some casting tubes from Uline. Four inch ID tubes with a wall thickness of 0.080".  I also intended to order some sorbitol and looked around online for the brand that I use to use, Now Foods, but I was surprised that it appears to have been discontinued. I'm sure there are other sources but am hesitant to try a new brand but I've noticed a significant difference in casting with other brands. After giving it some thought I decided to switch to Dextrose.  It's a bit of a change but propellant produced with Dextrose versus Sorbitol has a slightly higher burn rate which is good for a boosted dart.  It's also about half the cost which doesn't hurt.  I don't need to change the motor design as it was a bit conservative to begin with. The dextrose will result in a slightly higher chamber pressure but still well within safe limits. I bought the dextrose from Lucky Vitamin.  It's the monohydrate form of dextrose so 9% of its mass is water.  This isn't an issue as most, if not all, can be driven off during casting.  It is important to account for this when weighing out to assure the correct ratio.

No comments: