Theta 18 Aerospace Speciality Products Page 5
It is not required, but if desired, you may round or airfoil the leading and trailing edges of the fins. This
will make the fins more aerodynamic and allow you rocket to fly higher than it would if you just left the
fin edges square (the airfoiled, or “teardrop” shaped fin is more aerodynamic than a fin that is just
rounded). In either case, be sure to keep the root edge (the edge that will be glued to the body tube)
square. The tip edge may be kept square or rounded. See Figures I and J (the left example in Figure
J is a rounded fin, the right example is an airfoiled fin).
Using medium grit sandpaper, shape each fin
as desired - a sanding block may be used for this. If you don't have a sanding block, lay the
sandpaper down on a flat surface and move the edges of the fin against the sandpaper. Be careful
not to remove too much wood at one time - roughly shape one side then turn the fin over and do the
same on the other side. Continue this procedure with the medium and then fine sandpaper to further
shape and smooth the fins until you are satisfied with their appearance. Repeat with extra fine
sandpaper if desired.
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5) You will now attach the fins to the body tube. One fin at a time, apply a thin layer of glue to the
root edge of each fin and also to the body tube along the line where the fin will be attached and allow
the glue to dry. One fin at a time, apply another thin layer of glue to the root edge and firmly press the
fin in place on the body tube. Note that the bottom of the root edge of each fin should be even with
the 1/8" mark you made on the body tube (see Figure K). As the glue sets, be sure that the fin is
straight out from and parallel to the tube. Looking from the base of the model you can use the lines
drawn down the body tube as a guide to be sure the fins are straight. Repeat for the remaining fins.
As the glue sets, be sure that the fin is straight out from and parallel to the tube. Looking from the
base of the model you can sight down the lines drawn down the body tube as a guide to be sure the
fins are straight. You can also use the Fin Alignment Guide on the last page of these instructions to
help you in aligning the fins straight out from the body tube. Allow the model to rest horizontally while
the glue dries on each fin (you can download the “Rocket Caddy” from our website to make a stand
that will hold your model horizontally). Repeat for the remaining fins. See Figure L for what correctly
aligned fins should look like and an example of incorrectly aligned fins.
Correct Alignment
Incorrect Alignment
Figure L
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6) Locate the launch lug (the very small white tube). Using the same method as you used to attach
the fins, glue the lug to the body along the launch lug line you drew earlier. The bottom edge of the
lug should be at the 2 1/2" mark you made on the line. Be sure the lug is parallel to the body. See
Figure M.
