Monthly Archives: January 2013

Boilerplate midbulkead

After the previous work on the midbulkhead, I was told that the specifications I’d been working from had changed. So I dumped all that and designed a boilerplate version instead.

boilerplate bulkhead-Study 1-Results-Factor of Safety1.analysis

PDF of print. And yes, it now has four holes, but I haven’t renamed it. It’s made out of a 0.75″ plate of plain carbon steel, and weighs 5.11 lb, compared to 1.31 lb for the 7075/PMMA laminate proposed in the last post.

Rick Maschek asks, You say “I remain not a fan of this overall approach.” Reasons and or suggestions for something different?

There’s a saying that “An engineer is someone who can do for a dollar what any fool could do for two.” At this point we’ve definitely spent a metaphorical three dollars in time and effort on the midbulkhead concept. The best approach to it, since its function is just a check valve, would be to make a check valve. It’d be a bit more complex, but would be easily reusable and easy to test.

More generally, a two burn sugar motor is never going to go to space, the stated goal of the project. A two stage rocket is the way to go and is superior in almost every way. It would require relatively little R&D compared to the four dollars that’s been spent on the two burn concept so far.

If it turns out that it isn’t possible to build a sugar motor large enough to be a first stage for a two stage rocket due to the propellant’s physical characteristics, then it similarly wouldn’t have been possible to do a two burn rocket of the same size. Time spent trying to figure out the two burn architecture is time wasted until it’s been demonstrated that it’s possible to even get one burn of sufficient impulse.

Sandwich bulkhead thinned down

Regarding the latest design, Richard asks, “can the edges be modified to fit with the space shown in the attached sketch?”

richards question
(original PDF: MBH CSD interface detail)

Short answer: no. I reduced the thicknesses as low as I could go and still get reasonable factors of safety. It is thinner, but it’s still not half an inch thick at the edge.

three hole laminate
(as a PDF: three hole laminate)

Further, the retainer ring will have to be machined after a couple complete sandwiches have been made, to find out how thick the final part is including adhesive.

There’s also the question of how it’s sealed into the midbulkhead. I didn’t add an o-ring gland. I expect silicone would work, as long as the parts are kept at a relatively constant temperature.

I remain not a fan of this overall approach.