OH-58 Series Main Rotor Hub and Blade Assemblies Balance Check (Cont)

TM 55-4920-201-14

m. Place rotor blades in their radially outward

h. Where not previously accomplished, install

position. Lift both blades at their tips evenly to

pitch positioning locks (4) on rotor assembly in

approach the precone angle. Maintain an outward

accordance with instructions of stop d.

load on each blade while slowly allowing them to

i. Position blade gripe to flat pitch and secure.

return to their initial hub supported condition.

NOTE

n. Loosen set screw (12) of bushing (8) and

seat bushing taper firmly in rotor trunnion bore. Do

Observe this operation in this step sequence

not retighten bushing set screw at this time.

only when rotor blade alignment is to be

Refer to applicable

accomplished.

o. Screw handwheel (13) into lower end of

helicopter maintenance manual for blade

arbor and moderately tighten to seat yoke legs

alignments requirements and procedures.

against hub surface. Maintain alignment of yoke

(1) Place yoke (9) legs upward, centrally

legs along pitch axis and seat of bushing taper into

on the top surface of rotor trunnion.

trunnion bore.

(2) Place base of bubble protractor head

p. Tighten bushing ret screw (12) to maintain

on exposed surface of yoke and align at 90O

position.

(across) to pitch axis. Adjust protractor to center

q. Position blade gripe to flat pitch and

bubble and lock.

secure. Refer to instructions contained in step i,

(3) Transfer protractor, keeping it in the

except place protractor base on top flat surface of

same transverse position, to the machined surface

yoke (9) for adjustment of bubble to indicate

of a grip adjacent to its blade retention bolt and

central.

again align at 90O to the pitch axis.

r. Attach 2266 quick disconnect coupling.

with 2264 cable (7A050 kit) to arbor. Engage

(4) Adjust and moderately tighten ring

cable ball into lifting plate of stand hoist.

nuts (7) of pitch positioning lock (4) (installed in

step d) to recenter bubble by positioning grip.

s. Hoist assembly approximately -inch

above stand table, stabilize movements, and ob-

(5) Locate clamp block section (6) of lock

serve balance indicated by black disc in top surface

to provide full length contact with rotor hub flange

of arbor shaft. Check to insure balance indications

edge and moderately tighten clamping ring nut (5).

are not affected by interferences from the stand, air

(6) Readjust grip pitch, if necessary, to

drafts or movement of nearby personnel.

maintain bubble in central position.

t. For balance tolerance and methods for

(7) Transfer protractor, keeping same

correction, refer to applicable helicopter main-

transverse position, to like location and 90

tenance manual.

alignment on opposite grip.

(8) Repeat pitch adjustment and

CAUTION

clamping operations.

Forces generated during wrenching

(9) Recheck bubble for central position

operations required for blade sweep

on trunnion (yoke) reference again on initial grip.

balance adjustment can damage the

balance indicating and adaptering

NOTE

equipment. Prior to and after ac-

Following each blade sweep adjustment,

complishing each adjustment, observe

recheck grip pitch settings and maintain at

the following process steps.

zero condition.

u. Release hoist, allowing the support fixture

j. Install yoke (9), legs down, on arbor (10).

(2) to rest on stand table (1).

Position to align yoke top flat surface (sensitivity

v. Loosen set screw (12) securing bushing (8)

setting reference) with the 15-1/8-inch scale location

to arbor (10).

and secure by tightening set screws (11).

w. Loosen handwheel (13) at base of arbor

k. Install bushing (8), knurled section up-

(10) a minimum of 5 turns.

ward, on arbor (10) and position against lower

NOTE

surface of yoke body. Lightly tighten retaining set

Blade sweep adjustment operations may

screw (12) to maintain position.

now be safely made; however, restrain

1. Install arbor, with assembled components,

rotor tilt and forces applied to pitch

downward through rotor trunnion engaging

positioning locks (4) by pitch arms.

adapter (3) and fixture (2). Position legs to align

Following the adjustment continue

with blade pitch axis and seat on top surface of

procedure as outlined below.

rotor hub.

4-37