Hangar 9 J-3 Piper Cub Assembly Manual page 18

Section 6: Installing The Tail
6. Trial fit the horizontal stabilizer in place in the fuselage.
With the wing installed, check the alignment of the
horizontal stabilizer by measuring from a fixed point on
the wing to the hinge line at the tip of the horizontal
stabilizer. Both right and left dimensions should be the
same. Then sight the stabilizer alignment from the rear of
the airplane, making sure the stabilizer is exactly level
with the wing.
7. Trial fit the vertical fin in position, making sure the base of
the fin keys into the notch in the leading edge of the
horizontal fin. Then carefully check the fin to be sure it is
aligned 90° to the horizontal stabilizer.
Note: The back of the vertical fin and the back of the horizontal
stabilizer must be even with the back of the fuselage.
90°
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8. Double check the horizontal stabilizer and vertical fin
9. When you are satisfied with the alignment, carefully mark
90°
alignment. It may be necessary to slightly trim the balsa
wood on the fuselage with a sharp hobby knife to achieve
exact alignment.
the position with a pencil at the junction where the
horizontal stabilizer meets the fuselage top and bottom
and where the vertical fin meets the fuselage. The pencil
should leave a light indentation in the covering.
CONTINUED