Hangar 9 P-51 Mustang 1.50 ARF Assembly Manual page 15

Step 4
Install the hinges in the flap and slide the flap into
position. Check to make sure the flap aligns with
both the aileron and wing trailing edge. If it does not,
enlarge the first 1/4" of the hinge holes in both the
wing and flap to provide more clearance for the center
of the hinge. This will allow the flap to be positioned
closer to the wing for alignment.
Section 4: Hinging the Flaps
Step 5
Use 30-minute epoxy to install the hinges. Apply epoxy
to both the holes in the flap and wing using a toothpick.
Apply a light coat of epoxy to the hinge. Slide the flap
into position, and move it up and down to make sure the
hinges are aligned. Use tape around the division between
the flap and wing, as well as the flap and aileron, to hold
the flap until the epoxy fully cures.
Step 6
Repeat Steps 1 through 5 for the remaining flap.
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