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One way of retaining track is to attach tracking
weights in front of and behind the feathering axis at
the blade tips (Figure 3-23). By adding removing or
shifting tracking weights, the repairer can move a
blade track up or down to match the track of the other
blade or blades. This causes all blades to move in the
same tip path plane.
Trim Tabs
Another method used to align the rotor blade on the
same plane of rotation is the use of trim tabs (Figure
3-24). Using tracking weights adds to building costs,
but the same results may be achieved by cheaper
methods; for example, putting a sheet metal trim tab
on the trailing edge of the blade. The trim tab is
usually located near the tip of the blade where the
speed is great enough to get the needed aerodynamic
reaction. In tracking operations the trim tab is bent
up to make the leading edge of the rotor blade fly
higher in the plane of rotation. Or it is bent down to
make it fly lower. The trim tabs are adjusted until the
rotor blades are all flying in the same plane of rotation.
TAIL ROTOR BLADES
Tail rotor blades are used to provide directional control
only. Made of metal or fiberglass, they are built
similarly to main rotor blades. Metal tail rotor blades
are made of aluminum; the spars are made of solid
aluminum extrusions, hollow aluminum extrusions,
and aluminum sheet channels. Fiberglass rotor
3-11
FM 1-514
blades are made of fiberglass sheets; the spars
are made of solid titanium extrusions. Refer to
Figure 3-25.
Metal Blades
The blade skins are formed around and bonded to
the spars, which in most cases form the leading edge
of the blades. Metal blade skins are supported from
the inside with aluminum honeycomb, ribs, and some
smaller blades which have no bracing or support
inside themselves.
3-12
Fiberglass Blades
The blade skins are formed around and bonded
to H-shaped titanium spars. The blade skins are
supported inside with aluminum honeycomb.
The space around the spar is filled with foam
plastic.
FM 1-514
Blade Balance
Spanwise
On some models spanwise balance is accomplished
by adding or subtracting washers on the blade tip.
On others the washers are added to the blade-cuff
attaching bolts.
On some models blades are balanced chordwisc by
adding weights to the tips behind the spanwise
balance screw. Other models are balanced by adding
weights to the trailing edge of the blades near the cuff
end.
Trammeling
Fully articulated tail rotor systems must be trammeled
before they are balanced. Trammeling consists
of aligning the tail rotor blades an equal distance
to one another with a 2° angle of lead to the blades.
3-13
FM 1-514
CHAPTER 4
ALIGNMENT AND TRACKING PROCEDURES
This chapter discusses procedures required for
alignment and balancing of rotor blades. Specific
procedures for aligning blades vary with different
types of helicopters. Prior to aligning blades, consult
the appropriate technical manual for specific instructions
and maximum allowable tolerance. This chapter
also includes a description of the Vibrex balancing
kit.
MAIN ROTOR BLADE ALIGNMENT
Main rotor blade alignment is the centering of the
mass (distribution of weight) of the main rotor assembly
across the center of rotation to balance it.
The alignment of the rotor system has a distinct effect
on balance because of the great weight and long aim
involved. A greater weight on one side of the center
of rotation will cause a lateral vibration. The requirement
for manually aligning the main rotor blades
applies to rigid and semirigid rotor systems only. The
fully articulated rotor system automatically aligns
itself as centrifugal force increases and pulls the
blades into a pure radial position. The most common
method of manually aligning main rotor blades is the
telescope method.
A small bore rifle telescope is the basic tool used to
align the main rotor assembly (Figure 4-1). A fixture
to hold the telescope is fitted onto the hub directly
over the center of rotation. A repairer should be
concerned with the vertical cross hair only. Ignore
the horizontal cross hair. Place a zeroed telescope in
the holding fixture and sight the vertical cross hair on
a reference point of the blade. The reference point
normally used is a rivet in the skin at the tip of the
blade in line with the feathering axis. Adjust a
misaligned rivet by moving the blade in the the hub
to bring the rivet into alignment. Align the other
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