UH-1, (Series UH-1C, UH-1H, UH-1M, UH- 1L, AH-1J, TH-1G, TH-1L and AH-1G Typical), Tail Rotor Hub and Blade Assemblies

TM 55-4920-201-14

(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

4-21).

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-" 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

hub.

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-" 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

coupling

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

manual.

uniform tightening of two lower fixture set screws

p. When using Tail Rotor Balance Position-

(12).

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