Description And Operation; Vibration Analysis; Main Rotor Vibration Monitoring; Notar® Anti-Torque System Vibration Monitoring - MD Helicopters MD Explorer Servicing And Maintenance

1. Vibration Analysis

Vibration analysis is accomplished using the
sensors installed on the NOTAR® anti-torque
fan and the main rotor mast base assemblies.
These sensors provide vibration levels to the
Balance Monitoring System (BMS) processor
integrated into the Integrated Instrument
Display System (IIDS).
BMS software in the IIDS records the vibra­
tion data and provides recommended adjust­
ments for correcting imbalance condition in
both the main rotor and the anti-torque fan
assembly.
A. Main Rotor Vibration Monitoring
(Ref. Figure 1)
Typical causes for main rotor vibrations are:
Mass Imbalance (weight distribution) caused
by normal wear of rotor system components or
blade replacement.
Aerodynamic Forces caused by slight
differences in rotor blade airfoil shapes, blade
twist, or erosion.
The main rotor vibration sensor provides a
vibration level signal to the IIDS. BMS
software in the IIDS uses this data to deter­
mine if the main rotor vibration levels are out
of tolerance.
BMS software also provides recommended
changes to pitch case weights, blade tabs or
pitch change links to bring the main rotor
vibration levels within tolerance. These
recommendations are based on information
stored in the IIDS related to blade tab
position, main rotor blade hub weights
installed, and pitch case weights installed.
Typically, the BMS will be able to provide
balance corrections that will bring the
vibration levels into tolerance within two
flights if the starting vibration level is no
greater than 0.5 IPS (Inches Per Second).
MD Helicopters, Inc.
Rotorcraft Maintenance Manual
VIBRATION AND NOISE ANALYSIS

DESCRIPTION AND OPERATION

B. NOTARR Anti−Torque System Vibration
Monitoring
(Ref. Figure 1)
Anti-torque fan failure modes that would be
detected by the BMS include:
Deteriorating fan blade airfoil or loss of blade
mass due to erosion.
Loose blade attach bolts or other associated
hardware.
Loss of a fan blade is not yet predictable but
the fan support structure is designed to handle
the resulting out of balance condition. The
BMS will detect anti-torque fan ``out of
balance" conditions. Maintainers will use this
as an indication to correct fan balance reduc­
ing vibration to an acceptable level of (0.15
IPS or less). Attempts should be made to
balance the assembly to the optimal balance of
(0.05 IPS).
C. Transmission and Drive System Vibration
Monitoring
(Ref. Figure 1)
Future enhancements to the BMS will include
monitoring transmission and drive system
components and engines.
D. Vibration Trend Monitoring
The critical components of the main rotor
system and anti-torque system are designed
to be replaced ``on condition". Warning of
abnormal conditions in these components will
be provided by three indications:
(1). BMS vibration monitoring trends,
(2). Normal periodic inspections,
(3). Perceptible unusual vibrations at the
pilot's station.
The BMS can be the most sensitive of these
indications giving a warning in advance of the
other detection methods. Typically the BMS
sensors will be able to detect changes in
vibrations before they become apparent to the
pilot.
18-00-00
CSP−900RMM−2
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Revision 26