Design goals:
Rocket will require:
This includes:
No difficult or critical construction steps.
From top to bottom:
Fairly basic: the ring is drilled to mate with the Aeropack retainer. The sunken nuts are dremelled (cut-off wheel then grind stone) flush with the retaining ring. The nuts are set in place with a epoxy, then waxed on the fore end to prevent future epoxy from seeping onto the threads.
Picture 1 is a trial layout of the booster components. The main load-bearing component is the double centering ring above the fins. The fore coupler is also designed to be load-bearing.
Picture 2 shows the MMT ready for insertion into the booster body tube. After insertion, holes are drilled through the body wall, and epoxy mixed with 1/32" glass fiber is injected to lock the internal centering rings in place. Each internal ring has approximately 1 centimeter of epoxy matrix above and below it.
The TTW fins are inserted, and held in place using a piece of elastic cord. Masking tape covers the small gaps between the fins and fin slots. After checking for alignment, the internal fore edge of the fins are locked in place by pouring epoxy and 1/32" into the assembly from the aft end. Note the coupler tube in the motor tube: it's used to keep drips out of the motor tube. After this expoy has cured, holes are drilled between each of the fins, the rocket is inverted, the aft thrust ring is set in place, and epoxy is injected to secure it in position. The masking tape is removed and a visual inspection shows all fins are locked in place fore and aft.
Epoxy and 1/32" are now injected into the fin can holes. This forms the internal fillets for the fins (12 internal edges requiring 6 epoxy applications.) The external fillets are made simultaneously by masking the fin ends, then pouring epoxy and colloidal silicia into the channels.
I leave a 3mm lip on the coupler. This will be sanded down later to mate with the internal coupler in the main airframe. I drill a 3/8" hole in the coupler bulkhead: this will pass the booster recovery harness to the upper airframe.
The fore altimeter housing: a short length of 3" BT provides the fore seal for the altimeter section.
The rear altimeter housing ring has holes for securing the altimeter section to a 4" bulkhead drilled with ejection gas vent holes.
The airframe recovery system is webbed to the inside of the alitmer housing outer wall, and epoxied (colloidal) to the fore and aft centering rings.
Fore and aft views of the almost completed altimeter housing. Three steel screens separate the ejection charge compartment from the upper airframe
recovery components.