Hello again, Jetexeers. I'm more of a propellant mixer than an aeromodel builder, and I'm about to embark on an experiment making tiny Jetex-type 'wick' (fuse). Who will donate a few small swatches of thin, flexible, strong, very white tissue paper that we can nitrate to create small swatches of pure nitrocellulose (NC). Like some wag on a Supreme Court once said (about porn), "I can't describe it, but know it when I see it."
What we're looking for are just a few, thin swatches of plain tissue paper, sized to fit a regular mailing envelope. That will be sufficient quantity for these tests (a few sq inches, at most). Ideally, it will be "strong" (resistant to tearing), very white (without color additives), very thin (for rapid nitration through and through), and without too much coarse, embedded fiber.
For the tests, the tissue will be cut into sections of 2-in x 2-in (before nitration), so larger patches aren't needed.
If you have a wee bit of such tissue that you can donate, kindly let us know and mail the envelope to:
Jetex Propulsion Lab (JPL)
Rocket Science Institute, Inc.
PO Box 1102
Mojave CA 93502 USA
I'll be sure to let you know what becomes of your tissue samples!
When I interviewed Bert Judge, a head honcho at Wilmot Mansour in the fifties, about the original Jetex pellets and fuse, he made the point that Jetex fuse (or wick) had a copper wire core so that the heat of combustion was conducted through the Jetex nozzle (diameter about 1 mm) and keep on going.
So a fuse with a paper core, or, like Rapier fuse, no apparent core at all, may not work with a metal motor (the Rapier nozzle/orifice is ceramic).
Has anyone whittled down a Rapier fuse and see if it will carry on burning through a Jetex nozzle? Worth a try I think before we go too far!
Dr Zigmund, who makes our Rapiers, did make an experimental batch of Jetex fuse. This was copper cored, burned OK, but was, alas, too thick for your average Jetex nozzle.
Thanks Roger, I absolutely agree with your observations. For Jetex nozzles, and passing around the gauze and curling over the pellet, methinks copper-wire embedded flexible fuse is essential (unless one turns to either ignition priming or hot metal probes, electric or otherwise). Any way you look at it, Jetex fuse is bound to be both fragile and delicate, even when freshly-made. Nevertheless, fools rush in where ....
(In case my previous post wasn't clear, I've no intent to attempt a paper or powder-train fuse for Jetex. The NC product from the tissue paper will be used as a laminate, with NC-dope, for ignition primer testing. Jetex pellets, even when fresh with fresh fuse, worked best with a nice coil of 'wick' on the pellet, to better achieve a flat burning surface area. Jetex pellets, at best, tended to burn into a somewhat cone, or dimple-shaped grain surface, sometimes worse due to poor across-the-surface ignition in the beginning.)
Jetex 'wick' has much in common with Rapier fuse strips, though I've not made a chemical analysis. Both are extruded, and both have a substantial content of NC, along with DICY as a plasticizer and burn-rate modifier. It will be down the road a bit, and I do intend to at least attempt "mass production" of a few feet of copper-wire core, NC with DICY 'wick' of at most 1.0-mm diameter.
Will 1.0-mm fuse fit the Jetex 50 comfortably, Roger? Anyone with a micrometer and coil of wick at hand?
Rapier ignition is another matter, in my mind, and I'll share my thoughts on that separately.
Best wishes to one all this new week in our world!
I have been selling a few Jetex 200's that I acquired a few years back that had been modified to have electrical ignition from a terminal mounted in the backplate. This led to a resistance wire inside that must have ignited the pellet directly, or, more likely some Jetex wick placed in the usual position. I assumed that the original inventor had a multi-200 powered model and was seeking simultaneous ignition. I wonder if it worked. Here is a photo of one of them: