Brief:
Single stage Centuri Classic circa '73 - '81. Upscaled for 24mm motor C & D.

Construction:
Stats Original Upscale:

• Length 18 in 23.4 in
• Diameter (Inside) 1 in 1.3
• Fin Root L 2 7/16 3 1/8
• Fin Topline Length 2.25 3 in (close enough)
• Fin Trailing Length 2 in 2 19/32nd
• Vane Width 3/8 in ½ in
• Vane Length 7.75 in 10 1/16th
• Nose Cone L 5 inch 6.4 inch (6.5 scale)
• Body Tube L 13 inch 17 inch (16.9 scale)
• Engine Mount 18 mm 24 mm

Parts list:

• Body Tube ST-13 17 inch
• Nose Cone BNC1364 6.4 inch
• Engine tube BT-50 2.75 inch
• Centering Rings CR5055 Fiber
• Tube Coupler c55 2 inch
• Engine Hook standard 2.75
• Fin Stock (3 Fin) 3/32 basswood
• Vane Stock (3 Vanes) 1/16 basswood
• Tether 400lb Kevlar® 24”
• Shock Cord ¼ inch Sewing Elastic 30”
• Metallic Bands ½ inch shiny gift wrap bow
• 15 " Ripstop Parachute with locking Snapswivel

The upscale called for a body tube length of 16.9 inch and a nosecone of 6.5 inches. I chose the BNC-1364 for its length at 6.4 inch. Although it was not the right shape, it was reasonable to add 1/10th inch to tube length to keep length to scale. A closer shape match would have been the pointy BNC-1353 Secant Ogive, but adding 1.2 inches more tube might have changed the look too radically.

Parts supplied by SEMROC. Parachute home made (another review maybe?)

Building

Scaling this rocket should have been easy, rotate the kit templates, print to 130% scale on printer and cut. But something didn’t look right. When I printed it up, the vanes were too short. Luckily I had the original Kit to measure against. The drawn Fiber fin template in posted plans measure in at 7 17/32 . The actual kit measures 7 ¾, calling for 10.075 inch upscale length. I cut the vanes to 10 and 1/16th inches, scale to my original Nomad Kit. Vane width on the kit was approx 11/32 finished. I chose to use ½ inch width 1/16th thick basswood, available from my local craft store AC Moore. After trimming to scale, I rounded the edges removing about 1/16th inch.

I tested the scale of the printed template for the fins against the original model and they were on the money. They were printed at 130% and cut from 3/32 basswood. I tried using 1/16th basswood for the fins, but they just didn’t feel sturdy enough. Rather than risking fin flutter or shearing, I went with the 3/32 stock. This also provided a stronger joint with the glue rivet method.

Templates

After marking up the body tube with a standard fin marking guide, I drew the lines for 3 fin and vane alignment, adding a mark for lug mounts centered between two of the vanes. I also measured up from the rear end a position around the tube for the rear end of the vanes. This measurement was attained by measuring the fin root of 3 1/8 inch and adding another 1/3 inch for spacing, up from ¼ inch on the original.

With the tube marked, I printed out 3 Centuri Fin Guides on heavy stock 5x7 index cards. I cut out the size 13 center and cut out the fin guides to ½ inch length. I pushed the fin guides along the length of the body tube spaced about 4, 8 and 12 inches from the rear of the tube. I set the vanes against the body tube with three fin guides supporting along the length of the vane and tacked the position with C/A near the fin guides. The tube was laid on its side with the index cards supporting it on a flat surface. They set perfectly and were next treated to Elmer’s Pro-bond, a thin fillet pressed into the joint with a finger pass. Do not use the super glue at the front or rear contact points as these points have the highest shearing stress. The vanes were not riveted because I was going to install a baffle ejection. As it turned out I did not use the baffle. A few launches will judge this decision. When the vanes were absolutely dry and set, they were sanded by hand to bevel/round the edges. A small strip of sandpaper pinched between the thumb and forefinger drawn along the vane length makes a great bevel on this thin stock.

Engine Mount

This was fun as I had to improvise a little. I built the mount in a 2 inch section of C55 coupler tubing. I know its not the same diameter, but I have tons of CR5055 and this tubing worked well with it. The Bt-50 engine tube was used with a thrust ring, engine hook and Kevlar® tether attached, mounted in the forward centering ring. The coupler stock was glued to the other CR and allowed to dry. After drying, the CR was notched to accommodate the engine hook. All interior joints were reinforced liberally with Pro-bond. When glued together, they made a nice mount, albeit a little narrow in diameter. This was solved by using an index card as a shim, glued inside of the rear of the ST-13 body tube. One wrap around gave a perfect fit for the mount assembly, which was glued just past flush, to allow for the engine hook retracting. The engine hook was set directly opposite the launch lug alignment line. (Say that five times fast!!!)

Fin Prep and Mounting

The basswood fins were exceptionally smooth after a few passes with 150 grit sandpaper. I used my rotary tool ($9 attachment piece designed for mower blade sharpening) to bevel the outside edges to 45 degrees. Very quick work with the small drum sander bit.

Using the rotary tool, with another of the over a zillion pointy bits available, I made 1/16 rivet holes slightly staggered along the fin guide lines. These holes went through the engine mount as well. With the tool out and buzzing, I made rivet holes for the Launch Lug standoff mounts ½ inch long starting at 6 ¼ inch and 10 ½ inches from the rear body tube. The mounts were scaled to their template at ¼ inch high ½ inch long and cut from 3/32 basswood with the grain aligned parallel to the leading edge. The fins and mounts were glued on and set with the help of another fin guide, cut to accommodate them. A light brushing with thinned Elmer’s white glue gave a smooth workeable surface, prepared for finishing with a light sanding. Two ½ inch Launch lugs were trapezoid cut, sanded along their mounting line and glued flush with the leading edge of the standoff mounts with Pro-bond.

Nosecone

Every time I grudgingly have to wait for something to dry, I remember I have a nosecone to finish. The BNC-1364 was smooth and clean, but I debated sanding the tip to a narrow point to match the original. Close enough won out and I started with a liberal brushing of wood hardener. After letting it dry for two days over the boiler, I sanded off a few excess resin beads and gave it a wood filler rub. Another light sanding with 220 grit and it was ready for a diluted Elmer’s over-coating. This really bonds the filler and leaves a liquid smooth finish. By the time I am ready to give it a last sanding, the final fillets were drying on the vanes and fins and the project is about complete.

Finishing

This usually takes months, only because I usually start another project first. This time I had a forecast of 50 degree weather (in the middle of January?), so I was motivated to git’er done. Test fits and CG/CP confirmation, I was ready for paint. The quality of the body tube eliminated the need for tedious spiral filling, so the first light coat of Krylon white primer was without blemish. A few glue marks were noted and promptly ground or sanded away. Krylon Gloss White went on smooth and light for three coats. I coated each third of the project horizontally from the top, with one fin pointing down. Any overspray would gather in the fin and vane fillets, giving it that “dipped” look.

Chromed bands and Specifications Plate

The Decaling was pretty straightforward. I had originally wanted to build a 1:1 clone so I had redrawn the NOMAD decals long before I bought the ST-13 tube. Based upon the scans in the online plans, I used MSPaint to straighten, refine and clarify some of the details. It came out remarkably good, even perfect when viewed enlarged. Some cutting and pasting would fit the decals on one sheet of 8x11 Bel inkjet paper. The chrome metallic bans that encircle the tube and vanes at the standoff mounts were too cool to not include. After searching for materials to use, I settled on a large chrome look gift-wrap bow. It was ¾ inch wide with paper backing and did not react adversely to clear acrylic gloss spray. I trimmed it down to ½ inch to match the standoff mounts and used brush on C/A one section at a time. I used painters tape below the final position to mark the line, only you have to remove it as you affix the ribbon or the c/a might set the tape as well. Pressing the ribbon to the tube as you go around will assure a good set. As it happens, a full length of ribbon (separated by staple marks from its bow shape) made it around the tube and vanes. It looked so nice I decided to give the Spec Plate a try. I drew up a black decal with white transparency and altering lettering for placement over a chrome tape 1 1/8 x 1 ½ square. It looks mint.

The completed decal work and specification "sticker" were covered with a healthy over-coating of Krylon Crystal Clear.

Flight:

I had eagerly waited to see this bird fly. My opportunity came with a "quickie" up at the local elementary school field before school resumes. Limited spacing and lots of trees, and I did not want to go branch fishing that day so I made an impromptu 18 mm adapter for the 24mm mount. I packed it with a C6-3, hoping it would clear the launch rod. Although this bird comes in at around 116 grams without an engine, it is lighter than my Redstone that performs well on a C6-3.

Leaving the rod there was a pronounced whiplash effect, and I immediately feared the worst as the bird made a quick turn toward the trees. She climbed at about 70 degress only reaching a guestimated 350 feet. Deployed its 15 inch rip-stop parachute and drifted back within a hundred feet of the pad. I had thought I lost possibly the forward or rear lug, but there was no damage at all. The build included (2) 3/8in lugs but I had to launch from 1/8 rod due to paint build-up. That was not a good idea as the rod I used was 36" but a little on the flexible side.

Its second voyage was on a C11-5 off the 3/8 rod and it was far nicer. Noticed a little weather-cocking in what I thought was only a light breeze, but the bird still made it up to about 450 ft before the ejection. From my angle it was a little quick on the deployment as she was still at the lowest part of an apogee arc, or still weather cocked and climbing.

The third voyage I had to go for it on a D12-7. It scared the crap out of me. Winds were barely noticeable when she left the rod and did what can only be described as a "hip-check" move. That's what it looked like, almost a fishtail, only it recovered straighter. This little hiccup must have taken some of the steam out of her because she climbed only to about 500 ft. and I had expected way more. I think the engine weight may be the root of my problem. The CP was about 1.5 inches behind CG with the C6-3(and adapter). Got a little tighter with the C11 and I assumed the D12 was about the same weight. Could the chute have shifted rearward from launch inertia tipping the scales a little too much?

I quit, thankful that I had not damaged her.

I will be launching again soon with a little nose-weight to see how that goes.

Summary:
Great build, the outcome made me feel like a craftsman, although I am far from one. Good decal work was icing on the cake.

Other:
Plug all launch lugs with easily removable objects, like popcorn or spitballs, before painting. The fin alignment template was the best thing I could have done. Printed on identical 5x7 index cards, they will force the alignment to be true from vanes to fin.