After building the Red Spike in RockSim, I took the original images provided on the website and sized them to fit the BT-80 nosecone. I printed out several copies to use as templates and guides. The first thing in the build was to cut the base of the nosecone off leaving a 1” shoulder. Then, I cut the BT-80 and BT-60 to size and build the engine mount. Next, I installed the six centering rings evenly spaced on the last 4” of the BT-60 and glued the BT-80 over them (see the RockSim file). I then constructed and installed the BT-60 baffle in the top of the main body tube (should have done that first!) and the engine mount into the other end.
Next I worked on the wing pods. I cut the BT-5s and BT-20s to size and glued the nosecones into the BT-5s. I installed the centering rings around the BT-5s and inserted them into the BT-20s leaving 4” hanging out one end, giving the other end a sort of “ramjet” look. In hindsight, I should have planned the location of the centering rings a little better as you will see later.
Finally it was time to work on the fins. In the image, the fins are strangely shaped and the rear fins are very thin at the top. I printed a copy of the image full-size, and cut out the fin parts and used them as a template and cut the fins out of 1/8” balsa. I wasn’t comfortable with just gluing the fins to the body tubes and pods, so added extra length to the top and bottom to make them through-the-wall. At least the rear fins are, and also where they connect into the pods. I had to notch the upper parts of the fins because of where I placed the centering rings in the pods. I don’t believe it will impact stability, but those pods are just asking to break off on landing anyway. I carefully measured for the fin slots and cut them in the main body tube and the pods. Turns out the rear fins are longer than the body tube, too, so I had to cut a notch for the interior centering ring as well! A longer engine mount tube would have avoided this problem.
After installing the rear fins, I realized I had forgotten to install the pair of centering rings to support the transitions! Oops. So I cut the rings in half and glued them onto the body tube right up next to the lower fins (offset to the cut edges weren’t lined up).
Next I re-measured the space available and used the Template Wizard (from EMRR) to print out the two transitions (one 3” long and the other ¾” long). I cut them out and dry-fit them to ensure they were the right size. With the rear fins installed I had another problem – I couldn’t properly install the rear transition! I traced the two transition patterns onto poster board. The rear transition was broken up into three oversized pieces so there would be some overlap for strength. The front transition went on smoothly and then the rear transition pieces (slotted to fit over the fins).
To complete the main body I glued the front fins (through-the-wall into the pod but not into the main body tube) and pods on and lined everything up. I chose to place a strip of 1/8” balsa under the launch lug to offset it from the rear transition just in case.
I glued a piece of shock cord into the nosecone using a standard tri-fold mount and tied that to the Kevlar cord in the baffle. Finally, I attached the 18” parachute to the shock cord.