(i) Apply patch to blade, moving patch
slightly back and forth under pressure, to seat properly
and expel air pockets in adhesive. Blend out excess
adhesive around edges.
(j) Patch may be held in place while
curing with rubber bands made from inner tube or other
(k) Refinish patch and adjacent area.
(3) Repairing blade pockets. Holes in blade
pocket skin shall be repaired, as applicable, with
aluminum tape, a bonded aluminum patch, or with
urethane foam and aluminum tape. Refer to the
applicable maintenance manual for specific repair
(4) Tip cap damage. Inspect the tip cap for
nicks, cracks, and corrosion. Check the balance weights
for security of attachment. Refer to the applicable
maintenance manual for specific repair procedures.
(5) Corrosion removal. Remove corrosion
from skin using abrasive cloth. Refer to the applicable
maintenance manual for specific removal procedures.
(6) Trailing edge voids. Any voids not in
excess of the allowable limits as shown by the applicable
maintenance manual are to be sealed with adhesive.
Blades with voids which exceed allowable limits shall be
forwarded to depot for evaluation and repair.
b. Fiberglass Blade Repair. For fiberglass repairs,
refer to the applicable maintenance manual.
3-13. Rotor Blade Painting. Main and tail rotor painting
is explained in the following paragraphs. After complete
repainting or extensive touch-up, rotor blades shall be
rebalanced in an intermediate or overhaul maintenance
facility. Refer to TM 55-1500-345-23 for detailed painting
practices and procedures.
Painting of main rotor and tail rotor blades
unacceptable vibration conditions. Strict
adherence to instructions is required to
reduce the probability of creating these
out-of-balance conditions. Care must be
exercised to apply proportionate amounts
of paint to each blade to maintain proper
Complete repainting of main and tail rotor
blades on UH-60, UH-1, OH-58, AH-1, AH-
64, OH-6, and CH-47 aircraft is normally
accomplished during blade overhaul only.
Main and tail rotor blades are individually
balanced (spanwise and chordwise) to
between blades of the same configuration.
Painting of blades in the field may cause
subsequent interchangeability problems.
a. Main Rotor Painting. Tactical and nontactical
aircraft rotor blade painting is described in TM 55-1500-
b. Spot Painting. Spot painting procedures are
described in TM 55-1500-345-23.
c. Refinishing. Refer to the applicable maintenance
manual for refinishing of rotor blades during maintenance.
3-14. Rotor Blade Alignment. Methods used to align
rotor blades are described in the following paragraphs.
a. Telescopic Method. The telescopic method of
blade alignment is done with the rotor hub and blade
assembly removed from the helicopter. The main rotor
hub and blade assembly is placed on stands which will
allow a blade to move horizontally if it needs to be
adjusted. An alignment scope is positioned on the hub
and is used to sight on the alignment screw on the blade
tip. Alignment adjustments are made by adjusting the
drag brace. Consult the applicable maintenance manual
for detailed instructions.
b. String Method. This method has been used for
about 25 years and is considered good and accurate. A
string is stretched between the alignment screws at the
blade tips. The string should cross the rotor hub at the
center of rotation. Consult the applicable maintenance
manual for detailed guidance.
3-15. Troubleshooting Procedures (Rotor Systems).
Reference applicable maintenance manual.
3-16. Helicopter Vibrations The following paragraphs
describe the various types of vibrations. Table 3-2 shows
the general frequencies into which frequencies are
Change 2 3-11