TB 1-1615-351-23
(b) Mix polyurethane coating with polyurethane curing agent, in 1-quart container (3 parts A, 1
part B) and using paint brush, apply first layer to tip cap. Allow 2 minutes drying time between coats
when sprayed and 5 minutes when brushed until desired thickness is reached. (Figure 3-31). If spraying
thin coating using methyl ethyl ketone, (2 parts coating to 1 part MEK). Allow 24 hours curing time.
Accelerated curing time 4-hours at 140 -160F (60-71C).
CAUTION
Damage to tail rotor blade can occur while removing tape from masked
area of blade. Hold cutting knife parallel to blade surface when removing
tape.
(c) Remove masking tape by slitting coating at ridge created by the double layer of tape. Do
not scratch or gouge blade surface.
NOTE
The structure to which the polyurethane protective tape, 3M 8663, is
to be applied should be in recent overhaul or new condition. This
means that repairs have been made and the part has been primed
and painted in accordance with the appropriate technical directive
for that part.
NOTE
The rotor blade must be smooth. Any dirt inclusions or paint rough-
ness must be sanded off the surface using 400 grit sandpaper. Simply,
the surface should be at least as smooth as you can get it by sanding
with 400 grit sandpaper.
(5) Clean the surface by rinsing with isopropyl alcohol and wiping dry with clean untreated paper
towels or rags.
(6) Using a small clean rag, apply a thin coat of #86A adhesion promoter to the entire area of the
rotor blade that is to be covered with 3M 8663 PPT film. Let the 86A dry 15 minutes, prior to application
of 3M 8663 PPT film.
(7) Cut a sheet of 8663 polyurethane protective tape (PPT) to the size of the area to be covered
leaving a margin of 1/8 inch around the perimeter. This margin will later be used for application of the
edge sealant around the perimeter of the PPT sheet.
(8) Prepare a "wetting" solution as follows: To a pint sized spray bottle, add 2 drops of liquid
dishwashing detergent and 1/2 cup of isopropyl alcohol and fill the bottle with clean water. (The actual
mixture is: 75% water, 25% isopropyl alcohol and 2 drops of liquid dishwashing detergent per one liter
of solution.)
(9) Remove the liner from the sheet of PPT. Liberally spray the adhesive side with "wetting
solution" that was prepared in step #4 above. Also spray the surface of the part to which the PPT is to
be applied.
(10) Carefully position the PPT on the part. Use a plastic squeegee, starting at the middle of the
sheet, and remove the wetting solution from beneath the PPT sheet, by using long overlapping strokes.
If you should trap an air bubble, lift an edge to allow the bubble to be removed. When the edge is lifted,
respray with more "wetting solution" to insure that no air is trapped under the PPT. Use a clean rag to
mop up the excess water solution at the edges to prevent the water solution from "wicking" back under
the tape.
Change 3 3- 89
