Momba™ Assembly
©2006 MadCow Rocketry™
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Ensure rings are clear of the fin slots
Step 4 – Fin Assembly
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. Continue rechecking the fin
alignment until you are sure the epoxy has set. Clean any excess epoxy from around the
fin joint. Repeat for the remaining fins. 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.
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.
over the forward centering ring)
Spread some more epoxy on the inside edge of the
body tube before sliding the rear centering ring into the body tube. Continue sliding the
assembly inside the body tube until the aft end of the motor tube is even with the aft end
of 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.
Step 6 – Final Assembly
Insert the largest motor you intend to fly (or simulate the weight with an substitute).
Ensure the CG is forward of the recommended CG. The CG is measured from the tip
of the nose cone. If the CG is behind the specified point, add weight inside the nose
cone by pouring lead shot into the nose cone tip and adding some epoxy.
IMPORTANT:
Screw in a screw through the plastic nose cone into the lead to hold it in place.
Grind or cut off the screw head before filling and applying the nose cone finish.
The epoxy will not stick to the inside of the nose cone and if you do not anchor
with a screw, the liftoff force will cause the weight to become dislodged causing
an unstable model.
You can also place the lead in the base of the nose cone so that it
cannot become dislodged during liftoff, but you will have to use more weight.
Step 7 – Flying Your Model
Attach the end of the shock cord and the parachute to the nose cone. You can also
attach the chute protector to the shock cord just below the nose cone. When packing
your chute, wrap the chute protector around the chute with the opening in the chute
protector facing forward. Always make sure your chute is well protected as the hot
ejection motor gasses will melt the nylon chute.
