For projects Odyssey,Therion, and Raziel, the team has iterated a removable fin can designed such that the outer tube can be slid on and off the fin can itself. For Therion, the fins themselves are removable. Specs and pictures are below.
Therion:
Therion's fin can is much heavier and sturdier than that of an L1 or small L2. Materials included:
- Phenolic motor mount tube
- Aluminum centering rings, thick enough to screw into the airframe (archived designs available in the EPDM (Depreciated))
- Carbon fiber airframe
- Aluminum thrust plate
- Carbon fiber/foam sandwich panel fins
The airframe of the removable fin can was slotted and drilled using a mill (see notes on fin alignment in How to: Build a Fin Can).
To assemble the fin can precisely, we followed this complicated process:
- Slide the fins into the slots in the centering rings, allowing for the appropriate spacing of the centering rings
- Slide the motor mount into the centering rings
- Slide the airframe over the fins, then screw the centering rings in place
- Remove the fins, now that the centering rings are aligned, and use a pencil with a long, thin tip to mark the edges of the centering rings on the phenolic tube
- Unscrew the centering rings and gently remove the airframe, trying not to disturb the centering rings
- Make sure the alignment marks are legible
- Mix enough Proline (an adhesive similar to epoxy) according to the package directions to attach the centering rings to the motor mount
- For each centering ring, move the centering ring out of its marked off area and cover the part of the marked off section nearest to the centering ring with a layer of Proline (plenty to stick, but not enough that it will ooze. Some will spread when you move the centering ring over the current layer).
- Move the centering ring back to its location and spin it in order to evenly coat the tube and the ring.
- Add a fillet of Proline around the centering ring, trying to avoid the sections where fin supports will be placed (a Dremel can be used to remove dried proline)
- Use a hairdryer to heat the Proline until it becomes tacky or completely hardens.
- Repeat process for next centering ring, to make sure it is still aligned. Repeat for any other centering rings.
- The fins were sandwiched between aluminum supports, which were epoxied to the centering rings. Place one or two of these between the centering rings, test with a fin, and mark their location.
- Place epoxy where the supports attach, and fillet around the supports. Repeat for next set of supports.
Once the fin can has been assembled, it is stored in four parts - the airframe, the fins, the hardware, and the motor mount. To assemble these pieces, put screws through the fin supports, threaded inserts in fins, and place a nut on the other side of the fin support. Slide the airframe over the motor mount/fin assembly. Place screws through airframe into centering rings (15 screws in total for Therion, excluding any for the rail buttons)
Raziel
Raziel's fin can structure is essentially the same as Therion's. The major differences are as follows:
- Aluminum parts (thrust plate, fin supports, and centering ring, all pictured below) are welded together. This is stronger, more professional, and easier to assemble. None of these parts are permanently attached to the tube; instead, they can be slid in and out of the airframe and attached with 14x 8-32 screws.
- We only have one centering ring, 10" above the thrust plate. A second centering ring is extraneous.
- Although a motor retention plate was in place with Therion, the one on Raziel serves as the second rail button mount, approxiately 3' above the thrust plate.
Raziel's lower fin can:
