Rotor Track and Balance .

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

Rotor Balance What is an imbalance? Advantages and disadvantages Causes of imbalance Other 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 Advantages Simple Cost efficient Cost effective

Rotor Balance Disadvantages Noise Vibration

Rotor Balance Causes of Imbalance Manufacturing tolerances Shimming and alignment Rotor track Static track Dynamic track

Rotor Balance Rotor 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

Rotor Balance Rotor 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

Rotor Balance Other Sources of Vibration Mechanical looseness Misalignment Track Worn bearings

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

Types of Balance Dynamic Track and Balance First 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 Balancing Static Knife edge Suspended arbor Bubble balance

Types of Balance Purpose of Balancing Dynamic 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 Balance Enhance comfort Reduce wear Increase safety by reducing component stress Lower operating costs

Equipment Sensors Tach sources Vibration measurements Amplitude and phase

Equipment Sensors Accelerometers Displacement sensors Velocity sensors

Equipment Accelerometers Measure acceleration Typically reported in g’s More sensitive to higher frequencies Directly related to force caused by unbalance Used in balancing (after conversion to velocity or displacement)

Equipment Displacement 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)

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 PIEZOELECTRIC ELEMENT IN COMPRESSION SEISMIC MASS OUTPUT CONNECTOR AND AMPLIFIER BASE PRELOAD SCREW

Equipment Tach Sources Magnetic pickup Phototach

Equipment Magnetic Pickup

Equipment Phototach

Equipment Vibration 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)

Installation Sensor Tach Source Tip Targets

Installation Sensor

Installation Tach Source

Installation Tip Targets

Installation Optical Tracker Optical devices obsolete tip targets

Data Acquisition and Making Adjustments Polar plotting Automated solutions Rotor track and balance Rules

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.

Data Acquisition and Making Adjustments Automated 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

Data Acquisition and Making Adjustments Rotor Track and Balance Pitch links Tab Sweep Tip weight Hub weight Blade chordwise weight

Data Acquisition and Making Adjustments Pitch 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

Data Acquisition and Making Adjustments Tab 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

Data Acquisition and Making Adjustments Sweep 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

Data Acquisition and Making Adjustments Tip 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

Data Acquisition and Making Adjustments Hub 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

Data Acquisition and Making Adjustments Blade 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

Troubleshooting Polar Plotting - Human error Worn components Structural resonance

Troubleshooting Polar Plotting Human 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 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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