Rotor Track and Balance

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Rotor Track and Balance

• .

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Overview

• Rotor Balance
• Types of Balance
• Equipment
• Installation
• Data Acquisition and Making Adjustments
• Troubleshooting

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Rotor Balance

• What is an imbalance?
• Advantages and disadvantages
• Causes of imbalance
• Other sources of vibration

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Rotor BalanceWhat is an imbalance?

• A condition where there is more weight
  distributed on one side of a rotating component
  than on the other side

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Rotor BalanceAdvantages

• Simple
• Cost efficient
• Cost effective

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Rotor BalanceDisadvantages

• Noise
• Vibration

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Rotor BalanceCauses of Imbalance

• Manufacturing tolerances
• Shimming and alignment
• Rotor track
• Static track
• Dynamic track

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Rotor BalanceRotor Track

• Static track
• Perfect track if all blades produce the same lift
• Assumes that blade twist, profile, and stiffness
  are equal on all blades
• Assumed then to give equal lift on all surfaces
  of the blade

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Rotor BalanceRotor Track

• Dynamic track
• How the rotors fly during operation
• More important to sacrifice a perfect tip path
  track for a rotor that is perfectly balanced

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Rotor BalanceOther Sources of Vibration

• Mechanical looseness
• Misalignment
• Track
• Worn bearings

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Types of Balance

• Dynamic track and balance
• Purpose of balancing
• Types of imbalance

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Types of BalanceDynamic Track and Balance

• First introduced in the late 1950s
• Operators found that virtually all statically
  balanced rotors were out of balance dynamically
  when installed.

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Types of BalancePurpose of Balancing

• Static
• Knife edge
• Suspended arbor
• Bubble balance

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Types of BalancePurpose of Balancing

• Dynamic
• Performed during operation
• All of the rotating components are balanced as an
  assembly

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Types of BalanceTypes of Imbalance

• Mass imbalance
• Distribution of the mass
• Spanwise or chordwise
• Aerodynamic imbalance
• Out-of-track condition exists

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Types of BalanceBenefits to Dynamic Balance

• Enhance comfort
• Reduce wear
• Increase safety by reducing component stress
• Lower operating costs

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Equipment

• Sensors
• Tach sources
• Vibration measurements
• Amplitude and phase

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EquipmentSensors

• Accelerometers
• Displacement sensors
• Velocity sensors

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EquipmentAccelerometers

• Measure acceleration
• Typically reported in gs
• More sensitive to higher frequencies
• Directly related to force caused by unbalance
• Used in balancing (after conversion to velocity
  or displacement)

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EquipmentDisplacement Sensors

• Measure change in position
• Typically reported in mils (.001 of an inch) peak
  to peak
• More sensitive to Low frequencies
• Directly related to movements due to imbalance
• Seldom used in balance (however, displacement
  units are often used)

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EquipmentVelocity Sensors

• Measure velocity
• Typically reported in IPS peak
• More sensitive to medium frequencies
• Directly related to energy from imbalance
• Often used in balance

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EquipmentSensor Construction
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EquipmentTach Sources

• Magnetic pickup
• Phototach

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EquipmentMagnetic Pickup
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EquipmentPhototach
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EquipmentVibration Measurements

• Amplitude and phase
• Correlation between the trigger of the tach
  source and the time until the sensor registers
  the maximum amplitude.
• The result will be a phase angle in degrees or
  time (clock angle)

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Installation

• Sensor
• Tach Source
• Tip Targets

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InstallationSensor
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InstallationTach Source
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InstallationTip Targets
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InstallationOptical Tracker

• Optical devices obsolete tip targets

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Data Acquisition and Making Adjustments

• Polar plotting
• Automated solutions
• Rotor track and balance
• Rules

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Data Acquisition and Making AdjustmentsPolar
Plotting

• IPS and phase values are taken from the analyzer
  and manually plotted on charts to obtain a
  correction.

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Data Acquisition and Making AdjustmentsAutomated
Solutions

• The analyzer is used to collect the phase and IPS
  readings then calculates a solution
• The calculated solution is then implemented by
  the user eliminating manual calculations

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Data Acquisition and Making AdjustmentsRotor
Track and Balance

• Pitch links
• Tab
• Sweep
• Tip weight
• Hub weight
• Blade chordwise weight

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Data Acquisition and Making AdjustmentsPitch
Links

• Changes the lift of the blade by adjusting the
  angle of attack at the rotor hub
• Characteristically changes the tip path plane
  throughout speed range
• Characteristically has large drag changes
  resulting in a strong effect on lateral balance

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Data Acquisition and Making AdjustmentsTab

• Changes the lift of the blade by adjusting the
  twist in the blade aerodynamically
• Characteristically changes the tip path plane at
  higher airspeeds
• Characteristically has small drag changes
  resulting in little affect on the lateral
  vibrations

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Data Acquisition and Making AdjustmentsSweep

• Changes the balance of the rotor head by
  adjusting the center of mass
• Characteristically changes the mass at all air
  speeds
• Characteristically it has little effect on the
  lift of the rotor and the vertical vibration

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Data Acquisition and Making AdjustmentsTip Weight

• Changes the mass of the rotor head by adjusting
  blade weight
• Characteristically no change to tip path plane
• Characteristically has a large effect on lateral
  vibration

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Data Acquisition and Making AdjustmentsHub Weight

• Changes the mass of the rotor by changing rotor
  head mass
• Characteristically has large effects on the
  lateral vibration
• Characteristically has no effect on tip path
  plane

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Data Acquisition and Making AdjustmentsBlade
Chord Weight

• Changes the center of gravity of the blade
• Characteristically changes tip path with changes
  in collective force
• Characteristically has large effects on verticals
• Characteristically has large effects on laterals
  at ground/hover and in letdowns

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Troubleshooting

• Polar Plotting - Human error
• Worn components
• Structural resonance

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TroubleshootingPolar Plotting

• Human Error
• The result of an adjustment increases the IPS or
  the moveline 180 degrees out

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TroubleshootingWorn Components

• A specific vibration level is achieved and
  continued adjustments result in IPS levels that
  do not change and phase angle walks around the
  chart.
• A large amount of weight added to a location
  results in no change in IPS or phase

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TroubleshootingStructural Resonance

• Unrepeatable reading
• Adjustments result in varying results
• Phase angles and IPS levels are very erratic and
  unpredictable when known good solutions are
  implemented.

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Contact
www.acessystems.com 1-865-671-2003 sales_at_acessyste
ms.com