MIM-23B Hawk Assembly
©2007 MadCow Rocketry™
3
Ensure tailcone & ring
is clear of the fin slots
Step 4 – Fin Assembly
Step 5 – Launch Lug Attachment
Mark the CG point along the launch lug line you made in the previous step. Make sure
you measure the CG point from the tip of the nose cone and NOT the end of the body
tube. Apply a small amount of epoxy on the launch lug line about ¾” long on the CG
mark. Press one of the launch lugs into the epoxy and ensure that it is aligned with the
launch lug line previously drawn on the body tube. You can site down the tube and look
through the launch lug to make sure it is straight. Similarly epoxy the second launch lug
about 1/2” from the aft end of the body tube. Site down both launch lugs and make sure
they are both aligned. If you have a ¼” launch rod, you can use this to ensure that both
lugs are aligned properly.
After the fin tips have curred, sand
the spruce to the same thickness
of the plywood fin. Also bevel the
leading edge of the spruce to match
the sweep of the fin leading edge.
Test fit each of the fins into the
pre cut fin slots. The fin should seat firmly against the motor tube - sand each fin if
necessary. When you are satisfied with the fit, apply some epoxy to the end of the fin
tang that will contact the motor tube as well as the fin root that will contact the body tube.
Also, spread a thin layer of epoxy on each side of the fin tang.
Slide the fin into place and check the alignment. Carefully align the long forward section
of the fin with your fin alignment marks. Secure the forward section of the fin with
masking tape against the body tube. Clean any excess epoxy from around the fin joint.
Continue rechecking the fin alignment until you are sure the epoxy has set. Repeat for
the remaining fins. Note: When assembling a 4 fin rocket, sometimes it is easier to
assemble the 2 opposing fins at the same time. Make sure both fins form a straight line
when viewed from the rear of the rocket. A straight edge held on the aft end of the rocket
can help with this alignment.
Next, apply epoxy fillets to both sides of each fin. Carefully smooth the epoxy fillets with
your finger before the epoxy sets. Allow each fillet to set before rotating the airframe for
the next fillet.
Cut a length of the 1/8” square spruce just a little longer than the length of the fin tip.
Epoxy the spruce square to the tip of the fin so that it is flush with both sides of the fin.
This will act to reinforce the fin because of the hinge cutout. Repeat this step for all fins.
1/8” Square Spruce
is seated into the body tube. It’s a good idea to test fit a fin in each slot here before the
epoxy sets. Hold the body tube with the motor tube assembly down until the epoxy sets.
Make sure the weight of the motor assembly doesn’t cause it to slide out of alignment.
Using a door jam or small section of angle stock, pencil a line halfway between two of
the fins that extends from the front to the
back of the body tube. This line will be
used later to align the launch lugs.
Using the same method, pencil a line that
extends from each of the fin slots to the
forward end of the body tube. This will
help you align the long forward section of the fins.
