Sandhawk Fin can
Fins
The fins were cut out of 3/16 in ply.
I beveled them on my router table
on the leading edge and the outside edge.
I didn't bevel the rear edge
because I liked the look.
Because the guide tubes that attach to the lower
stage were only 9in long I had to put a CR in the middle of the fin.
I
thought at first that this would prove to be a problem but it actually helped to
line up the fins when gluing.
I cut a slot in the fin tab using a dado blade set to the correct
width(3/16).
I just clamped the fins together and
cut it in one pass on my table saw.
The fit
was perfect.
Assembly
I glued the upper CR in place on the MMT.
When dry I slipped the other 3
CRs in place.
To help align the bottom CR I put a hose clamp at the position
where it should be(1/2in from bottom).
I dry fitted the whole assembly aligning the guide tubes against a fin.
I tacked each fin down with 5min epoxy aligning it with a plumb line being sure to keep the guide tubes up against the fins.
When these dried I pulled the BT off and tack glued the CRs at the top and bottom of the fins keeping the guide tubes flat against the fins..
I then filleted all the joints between the fins,MMT, CRs and guide tubes.
In this picture you can see the black fiberglass guide tube and the brass ignitor conduit that leads up to the wood blocks where the electronics will mount.
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Tube slotting
I used the same technique for slotting the fins as I used on the Terrier. I
made a box that the tube would fit snug in. Clamped it in place and cut the
slots on the table saw.
The only thing I did different was I used a dado
blade so it was only one pass and the slot was the perfect size.
I also tried
a variation on the cutting. What I did was clamed the tube in the box and cut
1/2in slots on each side with the tube in place. What this did was marked the
position of each fin. Then I just cut one side to length and rotated the tube
90deg so the 1/2in slot lined up with the long slot and made the cut.
I
almost cut long slots on each side but figured it would weaken the box too
much.
Since the fins don't go all the way to the aft end I filled the excess slots with epoxy as I was doing the fillets. You can see them filled in this picture.
Harness attachment
I installed a U-bolt in the forward centering ring of the fin can for mounting the recovery harness.
