CH-37 Tail Rotor Assembly Balance Check.

TM 55-4920-201-14

be restricted to a minimum during the

4-67. CH-37 Tail Rotor Assembly Balance Check.

balance checking operation.

(See figure 4-39).

a. Assemble stand table and hoist support

g. For balance tolerance and application of

structure as shown in figure 3-3 except substitute

balance corrections, refer to applicable helicopter

part no. 2769 longer tube in place of the no. 4

manual. (Refer to appendix A).

vertical tube (2288) to provide the additional arm

height required for this application.

h. Following addition of rotor balance

corrections, carefully lower balanced assembly onto

b. Install cone (1, figure 4-39), hub upward,

work stand. Remove quick-disconnect coupling

on balancing arbor (4) so that top surface of cone

from arbor suspension rod. Rotate the part no.

hub aligns with 12--inch position on arbor scale

2769 tube approximately 30 degrees to swing hoist

(5). Secure cone in this position by tightening cone

structure away and provide working clearance.

setscrew (2) with 1/8-inch hex wrench (8, figure 1-

Remove elastic band (3, figure 4-39) from

13).

balancing arbor (41. Remove hand wheel (26,

c. Install balancing arbor (4, figure 4-39)

figure 1-13) and spacer (9, figure 4-39) from lower

downward through hub of tail rotor assembly (6)

end of arbor. Lift arbor and cone assembly out of

and hub of fixture assembly (8). seating cone firmly

fixture assembly hub.

in rotor assembly hub top cone seat.

i. In order to verify that the rotor blades

d. Position rotor hub pitch change beams so

actually were in the proper trammeled position

that their inner ends rest against sides of balancing

during addition of rotor balance correction,

arbor (4) with links vertical against sides of arbor.

reinstall scope support assembly (3, figure 4-38), as

Install suitable heavy elastic band (3) or O-ring

instructed in paragraph 4-66, steps d and e. Install

around links to hold links and pitch change beams

target assembly (17) on any blade, and install scope

in this position during balance check.

(7), part no. 2421 (7HEL056 kit), in scope wheel

e. Install spacer (9) on lower end of balancing

(8). Align scope cross-hairs (19) on alignment

arbor (4). Install hand wheel (26, figure 1-13) in

target (18) by tilting scope and rotating arbor in

bottom of arbor, and tighten wheel to clamp spacer,

rotor hub. Do not shift position of blade.

(9, figure 4-391, fixture assembly (8), rotor

j. With scope cross-hairs aligned in smallest

assembly hub, and top cone (1) firmly together.

target circle, lock balancing arbor (11) and scope

f. Install 3 / 16-inch suspension cable (13,

support assembly (3) to rotor hub with hand wheel

figure 1-131 and quick-disconnect coupling (10)

(141.

assembly on arbor suspension rod end, engage

k. Carefully transfer target assembly (17) to

suspension cable in lifting plate of hydraulic pump

next adjacent blade and reindex scope support

assembly, and hoist entire assembly approximately

assembly (3) to next 90-degree position in scope

inch off work stand. Check to insure that

support index plate (10). By tilting scope wheel (8)

suspended assembly is free from interference with

only in vertical plane, intersection of scope cross-

work stand or other objects. Observe balance

hairs (19) should fall within smallest circle of

condition indicated by black indicator disc at top

alignment target (18).

end of arbor, and apply balance corrections to rotor

l. Repeat step k to check alignment of

assembly as required.

remaining two rotor blades.

NOTE

m. Should steps i, j, k, and l indicate that

blades, after balancing, are still in their correct 90-

Due to blade span of this rotor assembly,

degree relationship, balance of the rotor may be

stability of balance indication is dependent

on complete absence of moving air

considered satisfactory. Should this check indicate

blade position was disturbed during or prior to

currents. Balance check should be per-

addition of balance corrections, realign blades 90

formed in completely draft-free area, and

degrees apart and recheck rotor assembly balance.

movement of personnel in this area should

4-64