Creating better aviation maintenance solutions... Rotor Track and Balance

Creating better aviation maintenance solutions...

Rotor Track and Balance

OverviewRotor BalanceTypes of BalanceEquipmentInstallationData Acquisition and Making AdjustmentsTroubleshooting

Rotor BalanceWhat is an imbalance?Advantages and disadvantagesCauses of imbalanceOther sources of vibration

Rotor Balance

What is an imbalance?A condition where there is more weight

distributed on one side of a rotating component than on the other side

Rotor Balance

AdvantagesSimpleCost efficientCost effective

Rotor Balance

DisadvantagesNoiseVibration

Rotor Balance

Causes of ImbalanceManufacturing tolerancesShimming and alignmentRotor track

Static track Dynamic track

Rotor Balance

Rotor TrackStatic 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

Rotor Balance

Rotor TrackDynamic track

How the rotors fly during operation More important to sacrifice a perfect tip path track

for a rotor that is perfectly balanced

Rotor Balance

Other Sources of VibrationMechanical loosenessMisalignmentTrackWorn bearings

Types of BalanceDynamic track and balancePurpose of balancingTypes of imbalance

Types of Balance

Dynamic Track and BalanceFirst introduced in the late 1950’s

Operators found that virtually all statically balanced rotors were out of balance dynamically when installed.

Types of Balance

Purpose of BalancingStatic

Knife edge Suspended arbor Bubble balance

Types of Balance

Purpose of BalancingDynamic

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

assembly

Types of Balance

Types of Imbalance Mass imbalance

Distribution of the mass Spanwise or chordwise

Aerodynamic imbalance Out-of-track condition exists

Types of Balance

Benefits to Dynamic BalanceEnhance comfortReduce wearIncrease safety by reducing component stressLower operating costs

EquipmentSensorsTach sourcesVibration measurementsAmplitude and phase

Equipment

SensorsAccelerometersDisplacement sensorsVelocity sensors

Equipment

AccelerometersMeasure acceleration Typically reported in g’sMore sensitive to higher frequenciesDirectly related to force caused by unbalanceUsed in balancing

(after conversion to velocity or displacement)

Equipment

Displacement SensorsMeasure change in positionTypically reported in mils (.001 of an inch) peak to

peakMore sensitive to Low frequenciesDirectly related to movements due to imbalanceSeldom used in balance (however, displacement

units are often used)

Equipment

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

Equipment

Sensor Construction

PEDESTAL

PIEZOELECTRICELEMENT IN

COMPRESSION

SEISMIC MASS

OUTPUT CONNECTOR AND AMPLIFIER

PRELOADSCREW

Equipment

Tach SourcesMagnetic pickupPhototach

Equipment

Magnetic Pickup

Equipment

Phototach

Equipment

Vibration MeasurementsAmplitude 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)

InstallationSensorTach SourceTip Targets

Installation

Sensor

Installation

Tach Source

Installation

Tip Targets

Installation

Optical TrackerOptical devices obsolete tip targets

Data Acquisition and Making AdjustmentsPolar plottingAutomated solutionsRotor track and balanceRules

Data Acquisition and Making Adjustments

Polar Plotting IPS and phase values

are taken from the analyzer and manually plotted on charts to obtain a correction.

Automated SolutionsThe analyzer is used to collect the phase and

IPS readings then calculates a solutionThe calculated solution is then implemented

by the user eliminating manual calculations

Rotor Track and BalancePitch linksTabSweepTip weightHub weightBlade chordwise weight

Pitch LinksChanges 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

TabChanges 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

SweepChanges 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

Tip WeightChanges 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

Hub WeightChanges 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

Blade Chord WeightChanges 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

TroubleshootingPolar Plotting - Human errorWorn componentsStructural resonance

Troubleshooting

Polar PlottingHuman Error

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

Troubleshooting

Worn 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

Troubleshooting

Structural ResonanceUnrepeatable readingAdjustments result in

varying resultsPhase angles and IPS

levels are very erratic and unpredictable when known good solutions are implemented.

Contact

www.acessystems.com

1-865-671-2003

sales@acessystems.com

Creating better aviation maintenance solutions... Rotor Track and Balance

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