Ah--it was an unintentional Einsteinian "red card/blue card" experiment (where one side is red, the other is blue, and observers are asked which color the card is--and both are right, despite giving diametrically opposed answers). Yes, all of the slab-like equipment housings will protect the boat tail well, and:

That Mars Lander's shroud (I'm sure APRO *doesn't* stand for "Aerial Phenomena Research Organization" in this case :-) ) almost looks big enough to need flat stiffening rings as well as ribs.

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NAR #54895 SR

origin of the name

Thank you. That picture is reminiscent of some of the ones in the Estes educational booklets (the ones showing rocket clubs' range set-ups, with pennant banners).

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NAR #54895 SR

The control fins rest on... what I shall call "servo platforms", because that sounds real official-like.

Each numbered item corresponds to an attached picture.

1) Strips of 1/8" x 1/2" balsa are covered on one side with Sharpie

2) Pieces of 1/16" balsa are then glued on top of the Sharpie (later I realized it was thicker than necessary, and built some new pieces with 1/32" balsa instead)

3) Using a piece of 220 grit sandpaper wrapped around a 3/4" PVC coupler, I hollow out each piece on the side with the thin laminated piece. The black Sharpie shows when I've gone the correct depth, and ensures that all four pieces are symmetrical and consistent.

4) The points are then cut away.

5) The points are beveled down slowly and carefully with 400 grit sandpaper. The image shows one piece held onto a piece of BT55 illustrating the good fit.

6) Small pieces of 1/4" x 1/2" balsa are sanded to what I think is the shape of the rear of the platforms. Hard to tell from pictures exactly. If I'm wrong don't tell me!

7) The pieces are then attached to the ends of the previous pieces. Later I realized I should have mounted the end pieces *underneath* the others, to ensure a flat top surface. Oh well!

8) The pieces are then mounted to the tail end of the BT.

You can't see it in the last picture, but the four pieces are not particularly well-aligned. This annoyed me sufficiently that I ripped off the two worst of them and built new pieces and installed them more carefully. The new set is still not perfect but much more acceptable. If I were starting again I could do a much better job, having learned what I have learned. But I am not starting again.

This almost completes these assemblies, but not quite. Still a bit more to do!

Attached Thumbnails

               

Constructing each main fin (i.e. the long ones in the middle of the rocket) is a mini-project unto itself. I experimented with a few possible techniques before settling on this one.

The fins are very long (about 10" long, only 1" high), span three of the body bands, and have straight "skirts" along the roots rather than typical fillets. My goal was to recreate the fin profiles as closely as possible.

Once again, each step corresponds to an image [argh, they attached out of order for some reason. Oh well, you get to figure out which is which]

1) The fin cores are cut from 1/16" balsa. To get 10" with the grain oriented correctly, two pieces are cut somewhat oversize and glued together. I try to get one good clean root edge; the other will be cut.

2) The fin shape is traced on the wood core

3) Here's the cut piece. It is very flimsy and delicate at this point, and not nearly flat. Not to worry.
Also the cutouts for the body bands are a bit oversized; they'll be hidden under the skirts so don't need to be precise. Finally, note that one little piece that broke off the end, that happened on three of my four fins. Just glued it back on, no biggie.

4) The skirts are implemented with 65 lb cardstock. First I created a template for cutting them, which include some score lines for folding.

5) Here's a piece, fully cut out and folded. We'll need 8 of these.

6) TBII is applied to the cardstock. Care is taken to avoid getting glue on the skirts.

7) The piece is (carefully!) applied to the fin, and clamped for a few minutes so the glue grabs. Then the second piece is glued onto the other side, and the whole thing is clamped to a piece of aluminum angle. When dry, the finished sandwich is very stiff and straight as an arrow.

8) Repeat x 4. Here's the finished set.

As far as I can tell these came out great. The test will getting them mounted properly. That will come quite a bit later.

Attached Thumbnails

               

Even laminating 1/16" sheet balsa fins with just typing paper or computer printer paper (it's 20 pound bond paper, if I recall correctly) makes them amazingly strong, as long as the glue is spread on thinly and evenly, and the "sandwich" fins are pressed between glass sheets or something similar. Using card stock "facing sheets," as you're doing, would yield even stronger laminated fins.

__________________
Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

These are most likely called Actuator Fairings. They enclose the actuators for the tail control fins.



I suspect they call these the wings. General missile naming convention is canards are forward of the CG, wings at the CG, and tail fins aft of the CG.

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No glass sheets or heavy books required...

My standard method of finishing fins now is to use regular printer paper and white glue... The SECRET is apply as THIN of a layer of glue AS POSSIBLE to the paper... I basically squirt a little on the paper and then spread it as widely, thinly, and rapidly as possible with a fingertip, then press the pre-shaped and airfoil-sanded fin directly down onto the glued paper surface, turning the fin around and applying another large super-thin spot of glue on the opposite side of the fin leading edge, then folding the paper over the LEADING EDGE of the fin, holding the paper taut, and then using the round end and barrel (opposite the felt tip end) of a Sharpie marker to burnish the paper down tight to the fin surface, and squeeze any excess liquid glue out of the space between the fin and paper, burnishing from the center of the leading edge toward the trailing edge, tip edge, and root edge of the fin, and finishing by burnishing the paper over the edge of the fin and down onto itself, in effect "sealing" the fin into the paper much like how those food vacuum bagger things work to seal meat or foods in between a couple layers of plastic air free and sealed around the edges. Let the fin dry overnight, then cut around the fin with scissors to within a quarter inch or so of the tip, trailing, and root edges to remove excess paper, then use a SHARP hobby knife to "shave" the paper down to expose the tip and root edges of the fin and down *almost* to the trailing edge of the fin, just shy of the wood itself-- leaving an extremely thin ribbon of paper along the trailing edge to encapsulate the fin (if possible-- if the paper gets shaved down to the wood no biggie-- the process works anyway). The leading edge is encapsulated by a full wrap of the paper held flush down both sides of the fin, strengthening the leading edge and preventing any possibility of a loose seam allowing airflow to 'rip the paper off' the fin in flight.

Works terrific... on one build I had an upper stage go "cruise missile" in the wind and ended up smacking into the ground horizontally at high speed under thrust, completely shearing the fin off the tube.

Thanks to the use of a double glue joint with yellow wood glue, the fin didn't just snap off the tube-- the glue joint held. It had to physically rip the outer layer of the paper tube off for the fin to separate, so the tube failed, NOT the glue joint. When the glue joint exceeds the strength of the materials being joined, what's the point of trying for "stronger"??? At any rate, the tube itself did not fail until after the fin had impacted a hard clod of dirt hard enough to completely crush and destroy the outer 1/4 of the span of the leading edge about halfway back along the tip edge of the fin, but due to the papered fin, the rest of the fin was COMPLETELY UNDAMAGED... I COULD have merely 'done surgery' on the fin, replacing the outer forward 1/4 of the tip/leading edge corner and fixed the fin, but I merely cut out a new fin, sanded it to shape (airfoiled it) and then encapsulated it in paper again, cut the remains of the old fin away from the section of paper tube it ripped off the outiside (essentially the fillet area) and glued it back onto the outside of the tube, then glued the new fin over it and refilleted and sanded it down once it was all dry, and shot a little paint over it. Good as new.

When the strength of your joints exceed the strength of the base materials, you don't need to make them any stronger than that...

Later! OL J R

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If I need fins to be stronger than balsa sealed with normal fillercoat/sanding Sealer, I use basswood, plywood, or G10.
No messy paper, thanx.

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I normally paper with Avery label paper and get excellent results. In this case, the skins are structural and required something more rigid.

I'll bet I could have gotten away with 1/32" balsa in the core, but I'm not interesting in building a new set of these (this is already my second set, sort of).