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OK, I'm a fan of internal filleting. I realize that it may add weight, but I've seen how one of my fins took a hard hit (read: a heavy metal
restaurant-type chair tipped over and fell on it) that would have sheared off a surface mounted fin, and (after repairs to the damaged leading edge) will look none the worse for it.
I have a pair of split fin rockets that I'm building now. The Velociraptor, and the Raptor from Binder Designs. With the way that the fins are laid out internal filleting isn't possible. Or is it?
What I'm going to do is this:
Sand all CR so that they can be inserted over the motor tube, and inside the body tube smoothly, yet still be snug. Drill 2 or more holes into the aftmost CR and temporarily add eye bolts to allow it to be inserted into the body tube and then fished out as needed.
If I had opted for the stock configuration, I'd install the mounting equipment to forwardmost CR and use thread tightening compound (or epoxy) to ensure it stays secure.
Glue the forwardmost CR in place on the motor tube, and fillet it. Aft of the forward CR, wrap the motor tube with wax paper to prevent Epoxy drips from forming on it and preventing later CR's from being installed. Slide the assembly into the body tube taking care to ensure that it's in the correct location.
Take other motor tube and CR, and insert it into the top of the body tube, using the dowel to "pin" the motor tubes together. This will hold the motor tube steady while the epoxy cures. Apply epoxy to the back side of the Stock Motor tube to fillet it into place (and seal the rear of the motor tube assembly and prevent venting issue with the ejection charge). Allow Epoxy to set.
After epoxy has set, remove the wax paper from the motor tube, and fit the aftmost CR into place. Remove the dowel, and the spare motor tube. Wrap a small portion of the dowel with wax paper, and insert this into the motor tube to prevent epoxy from dripping into it. Apply epoxy to the front of the forwardmost CR to ensure a solid instillation and complete the seal. Allow epoxy to set.
Next, remove the dowel, and glue in the forward set of split fins, using whatever form of alignment guides you desire. You might want to temporarily use the dowel and the spare motor tube to ensure internal alignment while the fins set up. After the glue has set. Wrap the motor tube with wax paper again, sliding it up to the back of the fin tabs, again preventing accidental drips from preventing the remaining CR's from being installed. Fillet the fins, and allow the epoxy to set. Then remove the wax paper, and slide the next CR into place. Wrap the motor tube with wax paper again, and apply epoxy to fillet the CR into place.
Once that epoxy is set, remove the wax paper, and install any CR's that may be behind the second CR (ahead of the next set of fins) and then protect the motor tube with wax paper again. After that has set up, Glue in the next course of fins, and internal fillet them. Finally glue on the aftmost CR, remove the eye bolts and seal the holes created for them (I'd use bamboo skewers, chopsticks, or dowels).
restaurant-type chair tipped over and fell on it) that would have sheared off a surface mounted fin, and (after repairs to the damaged leading edge) will look none the worse for it.
I have a pair of split fin rockets that I'm building now. The Velociraptor, and the Raptor from Binder Designs. With the way that the fins are laid out internal filleting isn't possible. Or is it?
What I'm going to do is this:
Items needed:
Stock Motor Tube, and Centering Rings, any mounting equipment for the Shock Cord.
small eye bolts
Spare Motor Tube
Dowel that is wrapped with tape to match the ID of the motor tube in 3 locations. Dowel should be the length of the body tube plus a little extra to allow you to grasp it and pull it out.
Wax paper and tape
Your choice of adhesives.
small eye bolts
Spare Motor Tube
Dowel that is wrapped with tape to match the ID of the motor tube in 3 locations. Dowel should be the length of the body tube plus a little extra to allow you to grasp it and pull it out.
Wax paper and tape
Your choice of adhesives.
Sand all CR so that they can be inserted over the motor tube, and inside the body tube smoothly, yet still be snug. Drill 2 or more holes into the aftmost CR and temporarily add eye bolts to allow it to be inserted into the body tube and then fished out as needed.
If I had opted for the stock configuration, I'd install the mounting equipment to forwardmost CR and use thread tightening compound (or epoxy) to ensure it stays secure.
Glue the forwardmost CR in place on the motor tube, and fillet it. Aft of the forward CR, wrap the motor tube with wax paper to prevent Epoxy drips from forming on it and preventing later CR's from being installed. Slide the assembly into the body tube taking care to ensure that it's in the correct location.
Take other motor tube and CR, and insert it into the top of the body tube, using the dowel to "pin" the motor tubes together. This will hold the motor tube steady while the epoxy cures. Apply epoxy to the back side of the Stock Motor tube to fillet it into place (and seal the rear of the motor tube assembly and prevent venting issue with the ejection charge). Allow Epoxy to set.
After epoxy has set, remove the wax paper from the motor tube, and fit the aftmost CR into place. Remove the dowel, and the spare motor tube. Wrap a small portion of the dowel with wax paper, and insert this into the motor tube to prevent epoxy from dripping into it. Apply epoxy to the front of the forwardmost CR to ensure a solid instillation and complete the seal. Allow epoxy to set.
Next, remove the dowel, and glue in the forward set of split fins, using whatever form of alignment guides you desire. You might want to temporarily use the dowel and the spare motor tube to ensure internal alignment while the fins set up. After the glue has set. Wrap the motor tube with wax paper again, sliding it up to the back of the fin tabs, again preventing accidental drips from preventing the remaining CR's from being installed. Fillet the fins, and allow the epoxy to set. Then remove the wax paper, and slide the next CR into place. Wrap the motor tube with wax paper again, and apply epoxy to fillet the CR into place.
Once that epoxy is set, remove the wax paper, and install any CR's that may be behind the second CR (ahead of the next set of fins) and then protect the motor tube with wax paper again. After that has set up, Glue in the next course of fins, and internal fillet them. Finally glue on the aftmost CR, remove the eye bolts and seal the holes created for them (I'd use bamboo skewers, chopsticks, or dowels).