Launched... and Wrecked

September 28, 2008

As described here, I launched the Navigator at the SPARC club launch in St. Peters, Missouri yesterday. I tried it with a B6-4, and the boost was straight and pretty, but the delay was evidently too long... it arched over and was coming down when the ejection charge fired. I used a long non-elastic shock cord in an attempt to avoid the "Estes dent." This was a mistake. The chute fouled in the fins and did not open properly, and the rocket came in ballistic. Here is where I discovered how much stouter those Semroc (Centuri sized) body tubes are... the damage at the forward end of the rocket was quite minimal. The ST-7 wasp waist section bent in two places, and I'll need a 4" piece of tube to fix it (which I have already ordered from Semroc). The Navigator will fly again. I have finally created a fleet page entry for this rocket, here.

Primed and Glued Together

September 21, 2008

Over the last several days, I've been doing the priming, filling, and sanding procedure. As noted, I've been working on this rocket in two pieces for easy handling. Tonight I decided the finish is smooth enough to glue up the pieces. There will be at least some spot priming after the join, so I thought I'd do a little touch-up sanding first. While working on the tail section, I discovered a thin crack in one fin along the upper dowel. Dang. I dripped a little thin CA on the crack, carefully pulled it open to allow the CA to wick in, then left it to dry a few minutes. It all sanded out smooth. Probably will need a little more sanding after the next (last?) coat of primer is on. The Join: I brushed slightly thinned filler just under the transition lip of the top section, then applied yellow glue inside the upper end of the tail section. I quickly glued the two sections together, checking the lug alignment by eye first and then with a rod. The filler squished out of the joint, which was my intent; it was much easier to get the filler inside the joint before assembly than it would have been afterward. I wiped the excess filler off and set the rocket aside to dry on the launch rod. Upon rechecking, I find that the lugs aren't 100% perfect, but they don't bind on the rod so I don't think I'll try to change them. It's a bit late anyway...

Almost Ready to Prime

September 17, 2008

Last night I applied the epoxy fillets, attached the hub half-discs, and brushed some thinned filler on the tail section's spiral grooves and into the dowel-to-fin joints. Tonight I sanded the filler, put fresh fillets on the hub halves, and put a launch lug on each section. On the top section, I attached the lug to the aft end of the ST-10 just above the transition, while on the tail section I installed the lug beside one half-disc. When I glue the top and tail together, I'll have to be careful to align them. I took the picture at right (click it for a larger view) with the two sections slipped together. I won't actually glue them until after I have primed and sanded enough times to get it all smooth; then I'll just have to fix up the joint. I figure it will be easier to work on the tail section without the awkward weight of the top section attached to it.

Some More Progress Is Made

September 14, 2008

Well, I've made a little more progress. Last night, I glued the baffle into the top of the ST-7 tube, as explained above, and then glued the extra baffle plate into position. I also sanded the now-dry (and, happily, warp-free) fins smooth. They'll need work after the primer is applied, no doubt, but this initial filler application will reduce the number of coats of primer I have to apply.

Tonight I finished the fins:

Glued the top ST-10 tube into place (I had attached the 6 foot shock cord, made from tent "rope," on a previous occasion) and installed the nose cone:

Cut out the six "hub" pieces from 1/16" balsa:

and, at last, attached the fins: Attaching the fins cost me some more of my dwindling hair. I've never before used a set of fins that (a) had such a short fin root relative to the fin span, and (b) had such inconvenient leverage against the joint (due to the forward curve). The leverage issue should be irrelevant in flying configuration, as the dowels and hubs should hold everything in place. However, I can tell you right now that I'll be applying epoxy fillets! I won't be working on the Navigator tomorrow; probably Tuesday, I'll glue on the hubs and possibly apply the epoxy fillets. I doubt I'll attach the top and tail sections together until after the fins are 100% solid.

I Got A Little More Done...

September 11, 2008

Well, I got some more done tonight. I built a baffle (see picture at right) which I will glue into the top of the ST-7 tube about a coupler-length down from the top; the baffle has two plates, and a third plate will be glued over the top of that tube (the centering ring flush with the top should make that easy). I considered papering the fins, but instead I brushed thinned Elmer's wood filler over the fins. I could only do one side at a time, and by the time the fins were dry enough to do the other side, they were visibly warping. This wasn't unexpected, though. As soon as the second application was dry enough to handle, I accordion-folded some newspaper and put a fin in each fold; after making sure they were stacked neatly, I put the whole collection under a pile of books. I'll have to wait until tomorrow to know for sure, but I believe this will work fine. I have also brushed thinned filler over the spiral grooves in the middle ST-7 and upper ST-10 tubes; I won't do that to the lower section of ST-10 until I have the fins installed, to avoid possible adhesion problem. After the filler dries and is sanded smooth, I'll sand the slots for the spokes a bit larger (they are too tight by design) and cut and glue the spokes in place. A second application of filler to the joints will smooth that part out, and then I'll attach them to the body tube with yellow glue. The spokes will "float" (be unattached) at the inner end at this point; after the glue is entirely dry, I'll glue on the 1/16" balsa half-circles that will form the hubs. When all of this gluing is done and dry, I expect I'll probably mix up some slow-setting epoxy for fillets. I need to remember to install the lower launch lug (beside one of the hubs) before applying the epoxy fillets. The lower section will be fully assembled before I attach it to the upper section; the last thing to go on the airframe will be the upper launch lug, which I expect I'll need to place at the lower edge of the upper tube. Lots left to do...

The Fins Arrive, and Much Progress Is Made

September 8, 2008

I got my "CARE package" from Carl today (see the picture at right, click it for a larger view). TWO sets of laser-cut fins (well, I did ask him for pricing for two sets) and he charged me NADA. I just can't believe it. So a big THANK YOU to Carl, for doing them, and to Sheryl for suggesting I ask him.

So I started on a set of fins. First, I carefully cut one set of fins free (see picture). I sanded the mating edges (only) of the pieces to remove the slight bevel from laser-cutting. I didn't want to be too aggressive, and as a result I may have gone too easy on them; but I'm drying them pressed under a pile of books to keep them from warping, and I'll paper them in a few days for added stiffness.

Here is a picture of the one fin I hand-made, and one of Carl's. Now, I did leave mine a bit large to allow for sanding three of them to the same size and shape, and thus it would have looked better finished than it does here; but I'd likely be a bit frazzled by the time I got all that done. This is much easier, and will look better too.

I assembled the engine mount, made the paper transitions, and did the preliminary assembly of the middle part of the airframe. The transitions will be glued down with white glue (I've had transitions buckle when using yellow glue) and allowed to dry completely before attaching the upper and lower body tubes. I went ahead and installed the engine mount in one of the ST-10 tubes, which obviously will become the lower sustainer tube. I didn't bother to take a picture of that (nothing to see there). I used yellow glue to install the engine mount; the centering rings were a bit loose in the outer tube, and I'm wondering now if the yellow glue will dimple the outer tube. If it does, I'll mix up some epoxy to glue the three body tube sections together, so I don't dimple them there also. Everything has to dry a while now; I have a family get-together tomorrow, so I won't be able to work on it again until Wednesday at the earliest.

The Parts Arrive

September 6, 2008

Today I received my first package from Semroc, being all the parts of the Celestial Navigator except the fins. The parts layout is visible to the right (click the picture for a larger view). The ST-10 tubes are 9.5" long, and the ST-7 is 18". I plan to sink 1.5" of the ST-7 into the ST-10 tubes at each end, leaving 15" of ST-7 between them. I will make 1" long paper transitions for each end, so actually only 13" of the ST-7 will be exposed. I may build and install a baffle in the top of the ST-7 tube. Of course, I'll anchor the shock cord through the upper centering ring. I prefer the "Turanko tail" in general, with the aft engine mount centering ring flush with the end of the body tube. However, I have been doodling with the idea of a booster for this rocket, so I'll set the aft ring an inch or so into the ST-10 to allow room for a coupler. I cut out and assembled one fin, and it cost me some of my hair (and I have little left to lose). Then I got a PM from Sheryl at Semroc, offering Carl's services... ... now I'm waiting for the laser-cut fin set he is sending me. When I get one of THEM put together, I'll post a picture. Semroc should be SemROCKS. Insanely good service, and nice people to boot.

Project Begins

September 3, 2008

This will be my first truly homebrew design. I've always been a kitbasher; even my beautiful (and sadly missing) Dawn Star was bashed from a Patriot and a Baby Bertha. About the only original rocket in my fleet is my Phoenix, which was more an accident than a planned design. That ends now. I've just received notice that my parts order has shipped from Semroc, including two 9.5" ST-10 tubes, an 18" ST-7 tube, an 18mm engine mount for the ST-10, appropriate centering rings to allow me to mate the ST-7 to the two ST-10's, and a medium-length ogive cone to cap it off. The final fins will each consist of three of the large sections and one of the small. The notches are to accept small dowels, which will be covered at the other end with half-circle "hubs" made of 1/16" balsa (not shown on the template since the main fin parts are 3/32" balsa). The dowels I'm using are actually birch skewers I picked up at the local grocery store; 100 for $1.00. Probably 2/3 of them aren't good enough to use on a rocket, but those will be fine for stirring epoxy etc. I'm posting my fin template, to show how the fin parts can be cut from a 4" wide sheet of balsa. The template is 150 dpi. I just took the first completed fin out from under the books I pressed it with (to prevent warpage as it dried) and I can see I'll have to do some sanding to get the right curvature. I'll wait until the other two fins are done before doing the sanding; that way, I should be able to make them all match.

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