This is a closeup of the aft mounting ring and motor tube. I call it a mounting ring instead of a centering ring because it doesn't center anything. The outside edge doesn't touch the coupler of the lower section. The terminal strip is trimmed down from a radio shack part. The timer wires are soldered to posts on the back side. The screws (BloomBolts) are threaded into 6/23 T-nuts.

Here is a close up of the fins (left) and the timer compartment internals (right). The PML G10 fins are laminated with 3/32 plywood to add stiffness and the airfoil shape. I used a 3" disc sander and had no problems but of course they aren't perfect.

The timer (Olsen) is mounted on a plywood board and held off 1/2 inch with spacers. Behind the timer circut board you can see the 1/4 ID aluminum tube that slides over the all-thread rod. The alum. tube is bonded to the wood board. This allows the board to be slid in and out of the timer compartment. Quick disconnects are used on the wires to the timer.

The altimeter is housed in a coupler with one bonded bulkhead (left) and one which is removable (right end). On the left airframe section you can easily see the threaded coupler nut and washer in the perforated bulkhead. An eyebolt is threaded into the opposite end of the coupler nut.

Also visible is the ring of phenolic coupler material which can be seen down by the perf. bulkhead. When the altimeter bay is threaded into the BT it stops when; The threaded rod bottoms out in the coupler nut; The bulkhead of the altimeter bay hits the phenolic coupler ring section; And the BT airframe (white) makes contact with the BT band (white) on the altimeter bay. (which needs 3 3/16 holes)

*credit to Stu Barret for the original design of this style altimeter bay

It's about 8 feet tall when all put together. I plan on a first flight May 7th at our local club launch. An I300 in the booster and a G80 in the top half will keep it under 5000 feet out at Monroe. Later in May, in Oregon, I'll let it air out a bit more on an I300 to I161 or so. Then, down in Blackrock, why not a J350 to J350?