2 ©2014
MadCow
Rocketry™
Screech™
Assembly
Screech™ Assembly
©2014 MadCow Rocketry™
3
Please make sure you read all directions and understand how to assemble your model
before you start construction. It is also a good idea to test fit each part before assembly.
Fiberglass parts still contain small amounts of mold release and other materials on the
surface that will inhibit adhesives and/or paint. It is important to clean each part prior
to assembly with a solution of 1 part rubbing alcohol, 3 parts water and a drop of dish
washing soap. IMPORTANT: do not sand any parts until after you have cleaned them -
you will embed the materials you are trying to clean making it difficult to clean.
The G10 parts will have holding tabs left over from the CNC machine. These small tabs
will need to be sanded off before assembly. Before assembling any part with epoxy,
rough up the surface to be epoxied using course sandpaper. The scratches in the G10
surface will give the epoxy something to grab onto.
Step 1 – Motor Mount Assembly
Step 2 – Insert Motor Tube Assembly into Body Tube
Test fit each of the fins into the pre cut fin slots. Because G10 thickness varies, you will
need to sand the slot to the correct width. Wrap the shock chord into a small bundle
and stuff it inside the motor tube for this next step. Test fit the motor tube assembly into
the body tube to ensure a snug fit. Sand the centering rings if necessary. When you
are satisfied with the fit, spread some epoxy on the inside of the body tube and slide the
forward centering ring of the motor assembly into the body tube.
Make sure you have
the motor assembly facing the right way!
Spread some more epoxy on the inside
edge of the body tube before sliding the rear centering ring into the body tube. Continue
Ensure rings are clear of the fin slots
sliding the assembly inside the body tube
until the aft centering rings are just clear
of the fin slots. 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 tube
doesn’t cause it to slide out of alignment.
Step 3 – Fin Assembly
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. Test fit each of the fins into the pre cut fin slots. The fin
should seat firmly against the motor tube - sand each fin or slot 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. 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 aft fins. Next, apply epoxy fillets to both sides of each fin by applying a
thin bead of epoxy at the fin-body tube joing. 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 7 – Flying Your Model
Attach the parachute to the shock cord near the nose cone. You can also attach the
chute protector to the shock cord near the parachute. 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.
Step 5 – Balancing Your Model
Assemble your model and insert the largest motor you intend to fly (or simulate the
weight with a substitute) and ensure that the CG is at least 1 body diameter in front of
the estimated CP point specified on the first page. The CP point is measured from the
tip of the nose cone. If the CG is behind the desired point, add weight inside the nose
cone by pouring lead shot into the nose cone tip and adding some epoxy.
Test fit centering rings over the motor mount tube and sand motor tube if necessary. Also
test fit the centering rings in the body tube and sand if necessary. Spread some epoxy on
the outside of one end of the motor tube and slide the ring (without the notch) until there
is approximately 1/2” of motor tube exposed. Make sure you clean the motor tube of any
epoxy so as not to interfere with the fin tangs later. After the aft ring is dry, make a mark
1/2” from the other end of the motor tube. Spread some epoxy on the motor tube and
slide the forward ring until it aligns with the mark.
VERY IMPORTANT: make sure there
is not any epoxy on the motor tube that would interfere with the fin tangs later on.
Fin
Fin Tang
1/2” Exposed
1/2” Exposed
Forward Ring Notch
Push cord in corner and
tack with epoxy
The shock cord in this kit consists
of a shorter section of Kevlar and a
longer section of nylon cording. The
two sections should be tied together
using a single overhand, ring bend
or double fisherman’s knot. The
Kevlar section will be attached to
the motor mount and the nylon
section will be attached to the nose
cone.
Wrap the end of the Kevlar shock
cord around the forward end of the
motor tube and tack in place with
CA. Make sure the cord lays flat
enough so it will not interfere with
the body tube when you slide the
motor tube inside. Apply some
epoxy to the cord to hold it in place.
Make sure the cord is secure
and will not come loose later with
ejection forces that will pull on the
shock cord.
Step 4 – Launch Lug
Mark the CP point along the launch lug line you made in the previous step. Make sure
you measure the CP 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 CP
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 2” from the aft end of the body tube (aligned with the aft end of the fins). 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.
Tie some knots in the end of the nylon section of the shock cord and lay the shock cord
onto the inside of the nose cone. Cover the shock cord with epoxy to secure it to the
inside, side or tip of the nose cone.
Step 6 – Nose Cone Assembly
