b. Mass Balance Weights (Bars). Certain
fiberglass and composite structure rotor blades contain
weights which are incorporated into or right behind the
spar. These blades are balanced during manufacture.
c. Spanwise Balance Weights. Spanwise balance
is accomplished by changing (preferably reducing) the
weight in one of two areas. Some model helicopters have
cylindrical tubes behind the spar to use as a container for
weights. On other helicopters, one-inch tape is used to
determine how much lead weight should be added to the
hollow shank of the blade attach bolt. Consult the
applicable maintenance manual.
d. Tracking Weights. Tracking weight adjustments
are made to compensate for the added weight of repairs.
The location of the repair is cross-referenced to a chart in
the maintenance manual. The chart will indicate weight
removal or shifting necessary to maintain balance.
Tracking weight adjustments are recorded on the DA
Form 2408-16, Component Historical Record. Consult
the applicable maintenance manual.
e. Trim Tabs. Trim tabs are adjusted by using a
blade bending tool which is calibrated in degrees. The
blades are raised by bending the tab up and lowered by
maintenance manual for procedures and bending limits
for the trim tabs.
3-11. Rotor Removal, Cleaning, and Inspection. Rotor
explained in the applicable Maintenance Manuals.
3-12. Rotor Blade Repair. General procedures for
metal and fiberglass rotor blade repair are described in
the following paragraphs. Refer to the applicable
maintenance manual for specific procedures.
a. Metal Blade Repair. General procedures for
metal blade repair are described in the following
(1) Negligible damage. Negligible damage
can be defined as a nick a scratch, a dent, or a gouge,
depending on the type of helicopter and the construction
of the rotor blade. The location of the damage on the
blade, i.e. top, trailing edge, root area, by the tip, also
has a bearing on being called negligible damage. Consult
the applicable maintenance manual for specific definitions
and corrective actions, if any.
(2) Damage repairable by patching. Typical
patching procedures for damaged rotors are explained in
the following steps. Refer to applicable maintenance
manual for specific procedures.
(a) Remove paint from area to be
patched. Protect core if exposed, so as not to
contaminate while cleaning.
(b) Draw a circle around damaged area
large enough to encompass damage.
(c) Cut out skin around damaged area.
This may be accomplished by using a hole saw or scribing
through skin with a sharp instrument
disturbing core as little as possible.
(e) Deburr edges of hole, ensuring skin
is free of scratches and nicks.
(f) Prepare a patch of the same type of
metal. Patch shall be large enough to overlap hole at
least 0.75 inch all around perimeter. Deburr edges of
Cleaning materials are flammable and
toxic. Avoid skin contact and breathing
of solvent vapors.
(g) Sand mating surfaces of blade and
patch, using No. 400 grit paper. All paint and primer shall
be removed from bond surface of blade. Wipe both
surfaces clean with a rag soaked in methylethylketone,
Federal Specification TT-M-261. Dry with clean cloth.
Area to be bonded shall be clean, dry,
and free of grease, oil, wax, etc. Bonding
will not hold properly on a dirty surface.
(h) Apply adhesive to bond areas of
patch and blade.