NC-50 (generic ogive type)
BT-50 - 5" long
BT-50/BT-55 transition (had a plastic one leftover from some Estes kit)
BT-55 - 7.5" long
BT-55 - .5" long
BT-5 - 9" long (need 4 of these)
Elastic shock cord - .25" x 30"
Elastic shock cord - .125" x 8"
1/16" balsa fin stock
1/8" launch lugs - .5" long (need 2)
EB-5 engine blocks (I sawed the ends off of expended mini-engine casings) need 4 of these
Cut the BT-5s to length and glue together in pairs. When dry, glue the pairs together, making sure everything is straight and the ends are even. Fillet with Fillnfinish. Pick the most even end, and glue the engine blocks in.
Cut the half-inch BT-55 ring and test fit before gluing in place. The bottom of the ring will sit about 1/8" from the ends of the BT-5s. When ready to glue, spread four fairly wide lines of glue inside the ring. Insert the clustered BT-5s, so that the glue is between the tubes. Now rotate the cluster inside the ring so that the glue is pushed up into a fillet shape along the tubes. Add more glue to the other side of the tubes.
Cut the 7.5" BT-55 and glue the clustered BT-5s into it the same way you did the lower ring. The BT-5s should go into the BT-55 about an inch or so. Make sure everything is straight.
Make a putty from tissue soaked with yellow glue. Stuff this mess into the gaps between the BT-5 boosters and the long BT-55. Let it dry, check for openings, and add more putty if needed. Leave the gaps around the lower ring open.
I built the rocket to separate at the transition. Tie the end of the 1/8" shock cord to the upper (smaller) end of the transition and add a drop of white glue to the knot. Thread the cord through the BT-50, then tie the other end to the nosecone (another drop of white glue on the knot). Use a wrap of masking tape to fit the transition, BT-50, and nosecone together tightly, so even if it does separate, itll stay in one piece.
Make an Estes style shock cord mount and glue the quarter-inch shock cord into the BT-55 tube. Make sure its deep enough not to interfere with the transition shoulder. Tie the other end to the transition.
Cut out the fins according to the template, airfoil and finish as desired. Sand and/or cut a shallow notch along the bottom half inch of the fin root to accommodate the lower ring on the booster. Go slow and test fit often. Glue the fins on, one along each booster tube, with the bottom of the fin even with the bottom of the ring.
Glue a lug onto the lower ring, into a fin root. Glue the second lug directly above it at the bottom of the upper BT-55 tube. Make sure they are lined up correctly.
Painting and Detailing
The Saturn III is very clean and uncluttered as described. There are plenty of details that could be added such as exhausts, antennas, conduits, etc.
I sealed, sanded, and primed as usual, followed by a solid coat of white. After letting it dry for several days, I added the roll patterns by cutting squares and rectangles from a roll of ¼" pinstriping bought at a local auto store. Some rub-on lettering supplied the numbers on the lower booster support ring, and NARTS has decals with the vertical United States available.
Friction fit the four motors. Insert wadding and parachute as usual and socket the upper stage into place.
See the diagram for how I wire the igniters together. Ive never had a motor fail to light with this setup. Make sure the igniters have a good amount of pyrogen on them before installing them. Also, make a couple of good sets of wire whips (see diagram). Reliability is the key for igniting clusters.
As always with clusters, use a 12V launcher to make sure you have enough power to fire all the igniters.
The Saturn III made her maiden flight at NARAM, and flew perfectly. She made several more flights throughout the week without a hitch. Ive only flown it with A3-4Ts installed, Ill probably try 1/2A3-2Ts some time when we fly at a smaller field. I havent tried it yet, but Id think this would also fly acceptably on a pair of A3-4Ts or A3-10Ts in opposite motor tubes, with plugs in the unused motor tubes.