I had 1 set of Geo Sat LV SRB nose & nozzle sets (that I could find). So I did a quick silicone rubber mold and resin cast them out of Alumalite. They are hollow because I rotationally molded it by hand, but they still need some hollowing out. They are a bit heavy, but I am TRYING to make this thing about 8-10oz so it will NOT go too high on a D12-3 or Quest D8-(?). I will look to get 400 feet or so on boost.
If you have not glued yet and have the time..... try mixing micro-balloons with the Alumilite. I did that for my 1/72 model's SRB noses, SSME nozzles, and OMS pod aft ends (with the thruster arrays). Hollow-cast. Now, I did not use a machine to rotate them, I rotated them by hand. For the noses and SSME nozzles, I held the molds almost sideways, tilted a little so the resin would not pour out. The microballoons thickened the resin enough that with some practice I could get some pretty consistent results and of course for the SRB noses it did not matter what they looked inside (unlike the SSME's). BTW - I used Vac-form for the SRB aft skirts and nozzles, main OMS pods, plus a few other bits (I cast the pieces for the four hold-down structure details on each aft skirt then glued them to the vac-formed skirts).
I found there was an optimum ratio beyond which too much microballoons would be too thick to flow quite enough for the rotation by hand to work well. And also the more microballoons, the more fragile the parts were. I then had to balance against the ratio mix, or making the parts a little thicker. That might be an issue with the SRB nozzles, but then you might find it practical to cast the nozzles with little to no micro-balloons, while the rest of the SRB aft skirt assembly did use a decent mix with microballoons. OK, so making up separate molds would be a hassle, but take your existing mold, do a light mix for the aft skirt, but cast everything, then cut off the nozzle. Then cast a sturdier nozzle, casting he whole mold if need be, and trim off everything that is not the nozzle.
Hmm, wait, If the SRB’s are going to be on the glider, then there is no need to worry about landing damage for the SRB nozzles.
Just remember, this is an R/C glider, and you do not really want to be adding a lot of extra mass if you can help it. That is why you will be using really light radio gear to begin with. You would not use an ultra-light receiver and servos, then throw in a 110 mAh nicad pack, would you? no, becasue you want ot save the weight. And even though this is not for contest flying, and is for sport flying, the lighter it is, the better it flies. So the longer everyone gets to enjoy seeing it flying.
BTW- you had mentioned if you needed the weight of the SRB nozzles in the tail for balance? Why wouldn’t you locate the R/C gear in the right spots to make it balance right? I know that can be somewhat tricky in mid-build, and always needs some tweaking when completed. But you can usually get it into a good ballpark range and tweak with battery location, and if you are far off, receiver location too.
Yeah, and what KILLS me now is that I have enough micro RC equipment to choke a whale... Back then I couldn't afford squat! What was a Cannon Super Micro servo back in the 80s? Like $40? Now you can get smaller ones for $5!
Would you believe.... just $59.95 for a servo, and merely $120-130 for a 2-channel Super-micro receiver? In 1980? Well, possibly $49.95 for the servo, I am not totally sure or might be thinking of a later price increase. I do think that a 4 or 5 channel receiver was $150. I think a package deal for a 2-channel flight pack (one 2-ch receiver, 2 servos, and one 110 mAh nicad pack) was at least $220, NO transmitter. Recently I tied to find info on the old Cannon gear, but could not Google anything useful (Cannon and R/C bring up a lot of hits for model Tanks, and Bill Cannon R/C not a lot better). And I thought I had some papers here, in an old cardboard box a system came in, but it had other stuff, like a manual, but no prices and no specs like masses. But IIRC from memory the receiver was .54 oz., servos .47 oz., and 110 mAh Ni-cads about 1.1 oz. And yet that was totally revolutionary in early 1980 when it first came out, and was till the early 1990’s. Actually I still have some, including the later “ultra-micro” gear (I do not recall masses for those, I'd have to weigh them).
- George Gassaway