Fault Isolation; Main Rotor System Troubleshooting - MD Helicopters MD Explorer Servicing And Maintenance

1. Main Rotor System Troubleshooting

Rotor Vibrations
WARNING
The following troubleshooting procedures are a
brief summary of main rotor system faults,
which may be encountered (Ref. Table 101).
Fault
Unusual or excessive
vibration.
Vertical or lateral vibration.
One−per revolution lateral
beat in hover and cruise.
May also occur on ground
during warm up or shutdown.
One−per revolution vertical
beat. Beat may appear
throughout entire flight
regime, becoming more
pronounced at higher
airspeeds.
Autorotation rpm low.
Autorotation rpm high.
Five−per revolution or
medium−frequency beat.
Lateral feedback (beat) in
cyclic control stick with no
longitudinal.
High frequency vibrations.
Erratic track and balance
readings.
Cross−over rotor instability
High vertical, roll or pitch
vibration felt by the pilot
which occurs between
35%−40% Nr on startup or
shutdown.
MD Helicopters, Inc.
Rotorcraft Maintenance Manual
VIBRATION AND NOISE ANALYSIS

FAULT ISOLATION

Table 101. Main Rotor System Troubleshooting
Probable Cause
Main rotor blades damaged.
Main rotor hub or hub
components damaged.
Defective main rotor hub
damper.
Main rotor blades out of
track.
Blade pitch is too high
(Pitch links are too short).
Blade pitch is too low
(Pitch links are too long).
Worn pitch control bearings.
Rotor blades out of track.
Loose or defective
component in Anti−torque
System.
Incorrect azimuth to sensor
gap.
Cyclic control not centered at
low rotor speed.
Damaged flexbeam.
Troubleshooting tables should be used with
system schematics, electrical wiring diagrams,
serviceability checks and other detailed
procedures in this and other chapters of the
manual.
Corrective Action
Inspect blades.
Inspect main rotor hub
assembly.
Replace defective main rotor
hub damper(s).
Track main rotor blades.
Lengthen pitch links equally.
Shorten pitch links equally.
Replace pitch links.
Track main rotor blades.
Inspect and replace damaged
components.
Verify azimuth sensor gap.
Perform flexbeam inspection.
Perform flexbeam inspection.
18-00-00
CSP−900RMM−2
Ref. Section
62−10−00
62−20−00
62−20−00
18−00−00
18−00−00
18−00−00
62−30−00
18−00−00
64−00−00
62−30−00
62−20−00
62−20−00
Page 101
Revision 15