(3), part no. 2940 thru 2950, (7HEL065 kit),
4-39. UH-1, (Series UH-1C, UH-1H, UH-1M, UH-
select the pair (set), identified as having the lowest
1L, AH-1J, TH-1G, TH-1L and AH-1G Typical),
part number (2940). Make sure each bar bears the
Tail Rotor Hub and Blade Assemblies. (See figure
same matched pair serial number and the same part
number. Trial install the matched set of bars (3),
a. Assemble the work stand and hoist support
blocks upward, between opposite blade attachment
structure as described in section III.
bolts; contacting shanks underneath the bolt
b. Place the fixture (2), recessed side down, on
heads. Do not force bars onto the shanks of the
the stand table (1) or suitable support blocks.
bolts. If bars are too short, continue the trial in-
c. Prior to installing post assemblies (4), adjust
stallation using increasingly longer bar sets
movable index pins (14) of the positioning post
(identified by matched pair serial numbers and
assemblies to proper dimension as required by the
identical part numbers) as necessary until the
rotor design configuration shown in view B of
longest matched pair that can be installed between
figure 4-21. Tighten the pin set screw (14) to
the bolt shanks without force has been precisely
maintain proper setting.
established. Once this set and length have been
d. After adjusting post assemblies properly,
determined, select the next higher part number bar
thread the post assemblies (4) into two
pair, but make sure each bar also carries the same
diametrically tapped holes of fixture (2), shown as
matched pair serial number. This is the matched
holes A in top view of fixture (view C).
pair bar set that shall be used during the balance
operations. Be certain that the pair is identified
e. Locate the pilot bushing (11), large end
down, centrally on top of fixture hub.
correctly with a matched pair serial number and the
same part number.
f. Remove or loosen nuts (16) from tail rotor
blade attaching bolts (17). Drive bolts partially out
l. Carefully lift upward on both rotor blades at
of yoke assembly to obtain an approximate 9/32-
their tips simultaneously to produce increased span
inch gap under the bolt heads as shown in view A.
distance between the blade bolts; install the
properly matched and identified pair of bars
g. Set tail rotor on fixture (2) so that blade
described and selected in paragraph k above. Then,
shanks clear posts (4); flat surface of hub is up-
release blade tips, allowing the bolt shanks to rest
ward, and inside diameter of rotor splined trunnion
firmly upon the bar ends. Move bars precisely into
fits over diameter of pilot bushing (11).
final position by pressing upward to seat block
h. Install bushing (7), flange end downward
section against rotor grip bushing face surface and
on balancing arbor (8) so that top surface of
inwardly to seat stop tang of bars against the bolt
bushing aligns with 7-¼" or 7-3/8" position on
shanks. (See view D, figure 4-21). Investigate to
arbor scale (9) depending on the yoke con-
make sure that the positioning post index sections
figuration. Figure 4-22, illustrates the difference in
are engaged in grip pitch arm holes and that the
yoke designs and it will be noted that the "Beefed-
arbor (8) with bushing (7) is tight against the rotor
up" yoke with the half-moon cut-out portion at the
bottom as shown in view A of figure 4-22, requires
m. Sight beneath the rotor hub across the
the 7-3/8" setting. View B, illustrates the yoke
positioning bar pair (3) to make sure they are in the
configuration requiring the 7-¼" setting. Lock
same plane. Correct, if required, by readjusting the
hushing in this position by moderate and uniform
index section of each positioning post on its
tightening of bushing set screws (10) using 3/32"
mounting rod an equal amount.
hex wrench (7HEL053 kit).
n. Install quick-disconnect
i. Place part no. 2586 plate (6) (accessory
(7HEL053 kit or 7A050 kit) on arbor suspension
part) centrally on top surface of rotor hub as shown
coupler and suspend entire assembly free of in-
in top view of assembly. Insert lower end of
terference. Note balance condition indicated by
balancing arbor (8) downward through plate (6),
black indicator disc at top of balancing arbor.
bushing (11) and hub of fixture (2). Seat assembly
O. For balance tolerance and application of
firmly together by pressing downward on bushing
balance corrections, refer to applicable helicopter
(7) and lock in this position by moderate and
uniform tightening of two lower fixture set screws
p. When using Tail Rotor Balance Position-
ing Kit, AA4920-8503 follow the instructions of
j. Rotate the rotor hub on fixture, positioning
paragraphs a through o except use an arbor set-
the index pins (14) of the two post assemblies (4)
ting of 7-1/8" or 7-1/4" position on the arbor
until the indexing diameters enter the pitch linkage
scale as follows: View A of figure 4-22 requires
holes in grip arms to their full depth.
a 7-1/4" setting and View B of figure 4-22 re-
quires the 7-1/8" setting.
k. From the matched sets of positioning bars
4-34 Change 1