Note: This is a slightly shortened, edited version of Ted's article with fewer pictures.  Visit Ted's site for all the pictures.

Backround

 My plans are to certify in '99, either at Whittakers or a NOVAAR club launch in northern Virginia. Rather than go from D's to H's in one long jump (and missing the fun along the way), I decided I'd better get more experience with midpower rockets, experimenting with construction techniques as I go.

 Beginnings

 I knew I wanted to do a 2.6" airframe (BT-80), and considering another upscaled Yellow Jacket seemed appropriate. After 'imagineering' several ideas over the next couple of weeks, the final design was set down on paper, and then put away so as to get a fresh look at it in the future. A month or so later, I pulled out the design, looked it over, made some changes, and finalized it.

 Features:
2.75x upscale Estes Yellow Jacket
BT-80 body tube (2.6")
Three 24mm motor mount cluster
Through-the-wall, to-the-motor-mount fins *
Mid-body separation
Anti-zipper design with ejection baffle *
All-balsa fins, strengthened with laminated bond paper *
Home-made decals *

 * - new techniques for me

 Considered but rejected for this bird was a removable motor mount system that would allow different engine configurations. I figured that there was enough new stuff in this design, and the removable system could wait for another rocket.

 Construction

 First step was calculating the upscale measurements. Since the NC-80 nosecone I had was much shorter scale-wise than the original, I added length to the body tubes to make up the difference. The rocket looks a little different, but it's close enough for me.

 Once the body tubes were cut to length, spirals were filled with Elmers' Fill-n-finish and sanded. The nosecone joints were also sanded and made ready to prime. Then the upper pieces and nosecone were set aside for awhile because the motor tube/fin assembly was going to take some time to do right.

 I cut three centering rings from 1/8" balsa for the cluster motor mount. To ensure that things would be strong enough, I laminated bond paper to each side of the rings with thin CA. This little trick adds a *lot* of strength to balsa. After drilling out the motor tube openings, some careful work with a dremel sanding drum trued up the holes.

 Engine hooks were added to the motor tubes (9" long BT-50), and here is where I made a possible mistake (in hindsight); I added engine blocks to the tubes. This will make it difficult, if not impossible to fly anything larger than Estes 'D' engines in this rocket. Clustering composites is tricky and maybe I won't ever *want* to, but the option might've been nice. Time will tell.

 After soaking the motor tubes in thin CA (for durability), I assembled them to the front and middle centering rings. The middle centering ring sits at the top of the fin tabs, providing that much more strength to the completed assembly.

 Next I cut the slots for the fins into the body tube. Measure carefully, but don't be overly worried about neatness, since the fin fillets will cover small mistakes. I just used an x-acto with a brand new blade to make the cuts; make several light passes and it goes pretty smoothly.

 On to the fins. The Yellow Jacket has fairly large fins, so I considered many alternate ways to do them. What I finally decided on was to use 1/8" balsa laminated with thin CA and bond paper. This was not the easiest method, but hey, it's a learning project.

 Since the fins were larger than the width of my balsa, I carefully cut the fin template to fit 4" wide balsa. (see figure 1) This became the "top" two thirds of each fin. The rest of each fin was cut out of the remaining balsa using the rest of the template. Amazingly, I got all three fins (six pieces) out of a single piece of 36"x4"x1/8" stock. Then I carefully edge glued the fin pieces together using yellow glue, and weighted them down between wax paper for a day. When dry, I lightly sanded the glue lines and joints until smooth.

Next came fitting the fins/motor mount assembly into the bottom body tube. Careful sanding and checking allowed everything to fit together nicely, with the fins nestling into the valleys between motor tubes. Yellow glue drizzled into place and allowed to dry over the next couple of days made this entire unit rock-solid. The last step was to glue the rearmost centering ring into position, butting up to the bottom of the fin tabs, and applying yellow-glue fillets to the fin/body joint (on the outside).

 First step to finishing the fins was to cut six fin templates from bond paper. I cut the fin tabs off of the templates, then trimmed 1/4" from each template. I wasn't sure how the thin CA would react with the yellow glue joints running along each fin span, so I also cut the templates in half there. (see figure 2) In effect, each fin side was laminated with two separate pieces of bond paper. A generous amount of thin CA was applied to the fin and spread quickly with a scrap balsa 'edge'. The paper was applied and the CA soaked through as the paper was squeegeed to the surface with the scrap balsa. The trick was to use plenty of CA, because gluing down edges later was more difficult than getting it all down in the first place.

Do this in an area with plenty of ventilation, those CA fumes are strong!

 Here I ran into another problem; I ran out of CA. After checking local sources, I decided to try some CA available at a nearby model train store. Turned out to have a completely different chemical composition, and although it worked (sorta), it was ugly and needed a *lot* more effort to finish adaquately. Very very expensive too. I finally bit the bullet and drove many miles to the nearest rocket shop for *real* CA to finish the fins.

 Once everything was dry (I waited overnight), I started laying Elmers' Fill-n-Finish onto the fins where the paper edges met bare wood, including the gap along the wood glue joint. Letting it dry a couple hours, followed by light sanding, and then repeating the process a couple more times let me get the fins smooth. Not perfect, but not too bad.

 Now I started building the fin fillets. Using generous amounts of Fill-n-Finish to build them up, followed by careful *light* sanding, the YJ fins almost appear to 'melt' into the body tube. Once the fillets were done, I painted thin CA over the Fill-n-Finish to toughen it up, rounded the fin edges, and did the final shaping and sanding on the fins.

 1/4" launch lugs were aligned and fastened with yellow glue. One near the bottom of the rocket, and one right below the mid-body separation line, very close to the CG. I filleted the lugs with Fill-n-finish and thin CA too.

 The bottom third of this rocket took 95% of the construction time. One last thing goes into the bottom section, and that's the ejection baffle/anti-zipper coupler. For this, I cut four bulkheads from 1/8" balsa and sanded them to fit inside a BT-80 body tube coupler. Two bulkheads were glued together with the grains at a 90 degree angle; this became the top of the baffle. Four 3/8" holes were drilled around the perimeter of it, and a hole was drilled in the middle for an eyebolt attached with fender washers and nuts. This top baffle was glued inside the top of the coupler with yellow glue and filletted well on both sides. Once it was dry, thin CA was soaked into the bulkhead for added durability.

 The middle bulkhead was drilled with a single 3/4" hole in the center, soaked with CA, then coated with a heavy layer of yellow glue before attaching to the inside middle of the coupler.

 The bottom bulkhead is drilled with holes around the outside edge (like the top) and soaked with thin CA before attachment. Since this bulkhead takes the brunt of the ejection particles, I gave it a good thick coat of yellow glue on the bottom face.

 The completed baffle/coupler was glued halfway into the bottom tube/fin section.

 The original plans for the anti-zipper design had the shock cord running from the bottom coupler, up through the body tube, and fastening to the nose cone. I decided to do it slightly differently. Another bulkead was made (two actually, laminated together like the top of the baffle), and a second eyebolt was attached facing downwards. No other holes were drilled. This bulkhead was glued into place at the top of the uppermost body coupler. Before gluing the coupler in permanently, I attached a quick-link and an 8' length of 1/2" elastic shock cord. A 24" nylon parachute from Recovery Technologies is used. I bought a yellow one to go with the rocket.

 The nose cone is friction fitted *and* has it's own 'emergency' shock cord attached in the Estes 'paper sandwich' style. This allows about a 12" payload section at the top end of the rocket. Next time though, I'll run the shock cord to the nosecone. The upper shock cord will be a pain to replace the way I did it, if it's ever necessary. 

Finishing

The entire rocket was sprayed with 3 coats of primer, followed by a light sanding, then 3 more coats of primer with sanding between coats. The top section was measured, masked off, and painted with gloss black Krylon. This was allowed to dry for about a week. The bottom section was then painted with Krylon Safety Yellow and also allowed to dry for about a week.

 I used a photocopier to enlarge the original Yellow Jacket decal set (stripes and the bee logo) to the correct scale, then scanned the logo into the computer. Using Paint Shop Pro, I cleaned up the logo and saved it to a .tif file. The stripes were measured and scaled, then drawn using MS PowerPoint. The logo file was added to the page, and CP and identification info was created as well. The one change made to the stock decals (besides scaling) was the "YJ-324" plate added to the stripe set. The page was then laser printed onto decal paper from Tango Papa decals (highly recommended) and oversprayed with clear glosscoat. When dry, the decals were cut apart and applied in the standard way. After the decals dried overnight, I gave the entire rocket a couple of light coats of glossy clearcoat.

 The paint scheme and logo decals are not perfectly scale; the black comes too far down the tube, and the 'bee' was made a bit smaller to compensate. It looks good enough to me, I'm happy with it.

 Stats and Flight Report

 Final ready-to-fly weight came out to just over 20 ounces. The CP of the Yellow Jacket is even with the top of the fin root (derived using VCP), and the loaded CG is just below the mid-body separation joint. This gives the YJ-324 better than a 2 caliber stability margin, and will allow the use of larger and heavier motors without needing much (if any) nose weight.

 First flight of the YJ-324 was at the NOVAAR sport launch on 24 October, 1998, in Manassas, VA. Three Estes D12-5's were prepped and loaded into the motor mount tubes. The solar igniters were placed in such a way that all three igniters had one leg twisted together in the middle, and two of the igniters had the second legs twisted. This allowed me to use one clip on one leg of the igniters (3 twisted together), and a simple clip-whip to the other legs (2 twisted together and 1 single).

 The second flight was a disaster. See the section below; Death of a Rocket (pictures are there too).

 Summing Up

 Building this rocket accomplished my primary goal; to learn new techniques necessary for mid-power and high-power rocketry. I'm not going to get any experience with bigger motors with the YJ-324, but other winter rocket projects can help there. Overall, this is an impressive looking rocket, and fun to fly. Now I need our local craft store to run more of those 50% off coupons (triple-D clusters for less than $5.00 a launch).

 Materials and Resources

 Tango Papa Decals email: BakerTom@aol.com

 Granddad's Hobby Shop phone: 703 - 426 - 0700
5260-A Port Royal Road fax: 703 - 426 - 0702
Springfield, VA 22151-2113

 Recovery Technologies phone: 602 - 915 - 0915
4807 W. Purdue Ave.
Glendale, AZ 85302 web: WWW.INFICAD.COM/~DAVEF