OH-13 and TH-13 Main Rotor Hub and Blade Assembly Balance Check

TM 55-4920-201-14

Key to figure 4.17:

NOTE

Since pitch equalizer linkage insures

1. Auxiliary support block

symmetrical blade pitch variations, locking

2. Fixture assembly (2532,

pitch arms is not required.

7HEL053 kit)

3. Port assembly (2539,

e. Install balancing arbor (4) through pilot

7HEL053 kit) (2)

bore of fixture (1).

4. Tail rotor hub and blade

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

assembly

figure 1-13) and quick-disconnect coupling (10)

5. Port assembly index pin

assembly on suspension rod at top end of arbor, and

6. Plate (2586 or 2531,

engage suspension cable in lifting plate of hydraulic

accessory part, 7HEL053

pump assembly.

kit)

g. Adjust suspended height of arbor so that

7. Bushing (2533, 7HEL053

top of fixture (1, figure 4-18) aligns with arbor

kit)

scale (5) position as follows:

8. Balancing Arbor (2516.

(1) Wood-blade rotor assemblies-14-3/4-

7HEL053 kit)

inch position.

9. Arbor scale

10. Bushing setscrew

(2) Metal-blade rotor assemblies- 14-

11. Pilot bushing setscrew

inch position.

12. Pilot bushing (2530,

h. Install spacers (6) on bottom end of arbor

7HEL053 kit)

as follows :

13. Spacer (2536, 7HEL053

(1) Wood-blade rotor assemblies-spacers,

kit)

part no. 2202 and 2203 (7A050 kit).

14. Lower fixture setscrew

(2) Metal-blade rotor assemblies-spacers,

part no. 2202 and 2204 (7A050 kit).

4-35. OH-13 and TH-13 Main Rotor Hub and

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

Blade Assembly Balance Check. (See figure 4-18.)

bottom end of arbor, and tighten wheel to seat

spacers (6, figure 4-18) firmly under base of fixture

NOTE

(1). Check to insure that sensitivity setting

Additional hoist arm support height is

specified in step g has been maintained.

required for thin balance check application.

j. Hoist entire assembly approximately 1/4

To provide this additional hoist arm height,

inch off work stand. Check to insure that

substitute the miscellaneous component

suspended assembly is free from interference with

tube assembly, part no. 2769 in lieu of part

work stand and other objects, and note balance

no. 2288 tube provided in 7A050 kit.

condition indicated by black indicator disc at top

end of the arbor.

a. Assemble hoist support structure using the

part no. 2769 tube assembly (38" length) in place

NOTE

of the vertical tube no. 4 (part no. 2288) shown in

The span of the rotor blades makes it

figure 3-3.

essential that this balance check be per-

b. Center fixture (1), with sleeve (2) installed,

formed in a draft-free area and that the

on stand table assembly (1, figure 1-13).

movement of personnel in the area be held

c. Carefully lower rotor hub and blade

to a minimum.

assembly (3, figure 4-18) over top of fixture (1),

guiding rotor hub trunnion spline inside diameter

k. For balance tolerances and application of

over sleeve (2). Make certain that base of rotor hub

balance corrections, refer to applicable helicopter

yoke seats squarely on fixture base.

manual. (Refer to appendix A.)

d. Set blade pitch of rotor hub and blade

assembly (3) approximately at zero position.

4-28