Robinsons R66 - 18-22 Ground Checks; 18-23 Balance Adjustment

18-22 Ground Checks
NOTE
Run-up and shutdown helicopter throughout procedure as
required per R66 Pilot's Operating Handbook (POH) Section 4.
NOTE
Use the following balancing procedures in conjunction with
approved equipment manufacturer’s balancing instructions.
WARNING
Tail rotor balancing equipment must be removed for flight.
1. Prepare helicopter for tail rotor dynamic balance per Section 18-21.
2. Make a photocopy of Figure 18-7; use copy to record ground check data. Check tail rotor
balance at 99-101% RPM on ground and record data. Maximum vibration allowance is
0.2 ips (inches per second). (If using Chadwick-Helmuth system, set Function Knob on
Balancer to appropriate channel, set balancer RPM Range knob to X10, and set RPM to
231. During ground run, view tail rotor assembly target tape through Strobex and tune
Balancer by adjusting RPM dial.)
3. Adjust balance per Section 18-23 as required, record change, and recheck balance.
Repeat steps 2 and 3 as required until tail rotor balance is within limits.
4. Remove track and balance equipment. Install tail rotor gearbox output shaft cap forward,
top attachment bolt and special torque per Section 20-33. Install 0.032-inch diameter
lockwire securing cap retaining hardware and safety in pairs.
WARNING
A rotor which is smooth after balancing but goes out of balance
within a few flights is suspect and must be examined by RHC
before further flight.
18-23 Balance Adjustment
Refer to R66 Illustrated Parts Catalog (IPC) Figure 64-1. Refer to Section 64-11 for tail
rotor assembly static balance procedure.
A. Pitch Horn-to-Pitch Link Fastener (Chordwise Balance Adjustment)
Chordwise dynamic balance is achieved by varying NAS6604 bolt length and nut-side
washers on tail rotor blade pitch horn-to-pitch link fastener. Select bolt length and
washers as required to balance tail rotor assembly chordwise per Figure 18-7, and
to meet torque requirements per Section 20-30. Standard torque nut and palnut per
Section 20-32, but do not torque stripe.
B. Blade-to-Hub Outboard Fastener (Spanwise Balance Adjustment)
Spanwise dynamic balance is achieved by varying nut-side washer size on tail rotor
blade-to-hub outboard fastener. Four washers are required under outboard nuts. Select
a combination of four washers to balance tail rotor assembly spanwise per Figure 18-7,
placing largest washers closest to hub assembly. Standard torque nuts and palnuts per
Section 20-32, but do not torque stripe.
25 OCT 2010 R66 Maintenance Manual Chapter 18 Track and Balance Page 18.19