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Rotor Track and Balance Only????
Agenda
• History of Rotor Track and Balance.
• Vibration Requirements Increasing.
• Using the Tools You Have.
• Cost Savings.
History of Rotor Track and BalanceFlat Track and GO!
History of Rotor Track and Balance (Cont.)
And the Maintenance Manual Said “Try the Pitch Link. If that does work Try the Tab!”
History of Rotor Track and Balance (Cont.)
And Jim Chadwick Said “There has got to be a better way”
And an Industry was BornAnd an Industry was Born
History of Rotor Track and Balance (Cont.)
Computer Based Track and Balance
Computer Based RT&B
• SUGGESTIONS– Always do all changes requested or enter in
changes performed.– No track and balance equipment will ever help
if the adjustments are not performed correctly.• Verify that the adjustment is performed on the
correct blade
– Verify Equipment Installation
Computers are Stupid - They only know “OFF” or “ON”
Vibration Requirements Increasing• WHY?
– Safety– Cost Savings– Because the tools currently have the capability.
• Manufacturers Increasing Requirements• Increased Flight Regimes (S-76
125Kias,145KIAS,155KIAS)(Bell 407)
• Increase in complexity
• More Limits, More Regimes, More …..
• Scheduled Vibration Level Checks
More Vibration Requirements
• Other requirements AS-350/355 Driveshaft hourly requirement BELL 407 Flywheel, FRAM Dampener Turbomeca
400 Hour Vibration Check• Manufacturers put out limited freq chart as
Aid to troubleshooting
Tail Rotor Ground Balanced
Tail Rotor Vertical and Lateral Ground Balanced
Tail Rotor Vertical and Lateral Ground & Flight Balanced
Safety
US Marine Corp H-46 Rotor Head Bearing Failure• Squadron Pilots had complained about an unusual vibration.
Aircraft was put in a functional test flight mode and vibration analysis performed. The below spectrums show that both the forward and aft rotors tripped the 1 per alarms indicating a balance problem. The trend shows a significant increase in 1 per vibrations with several trend points. The crew decided not to perform any maintenance actions and assumed that it was “JUST” that the aircraft needed balanced and it could wait until scheduled maintenance. 7.5 flight hours later one of the forward head Horizontal Hinge pin bearings failed which resulted in a violent 1 per that forced an immediate shut down. Further inspections revealed a crack in the forward transmission mounting structure which we have yet determine if this is collateral damage or preexisting damage. Components are on their way to Cherry Point for analysis.
• NOTE: The Maintenance Manual requires an inspection and RT&B exercise anytime the rotors trip the 1 per alarms.
Fwd Rotor Lateral Spectrum
H-46 Data Prior to Failure
Fwd Rotor Lateral Trend
Horizontal Hinge Pin Bearing Failure
Fwd Transmission Mounting Structure Crack
H-53E Swashplate
H-53E - Good Bearing
H-53E - Bad Bearing
Bearing Harmonics
Using the Tools You Have
• Using Spectrum to Detect– Detecting Imbalance– Misalignment– Mechanical Looseness– Resonance
Imbalance
• Signs of Unbalance– Vibration Occurs at 1 per Rev.– Amplitude Increases with Speed. – Phase or Clock angle is stable .
Aircraft Data - Ground
Ground 4.3 IPS’s
Aircraft Data After HSS Change
All regimes wellbelow limits
Questionable Adapter Balance
ExcessiveGrinding
ExcessiveGrinding
Misalignment
• Characteristics of Misalignment– High Levels at 2X Shaft Speed (Elliptical Orbit)
– Fore/Aft Readings are High
– Fore/Aft Measurements are 180 Deg out of Phase
– No Raised Noise Floor
1X
2X
3X
AXIAL
MH-53J Engine Driveshaft
• Detected After Routine Maintenance• Plot is of Average Vibration Level of Each Flight for
the Driveshaft
Shaft Bearing changed during phase inspection
Bearing reinstalled correctly
SH-60B IGB Misaligned Gears
Mechanical Looseness
• Loose Bolts, Structural Frame Cracks, Wear Between Bearing and Supports
• Raised Noise Floor• Phase or Clock Angle is Unstable
.5X
1X
2X
3X
RADIAL
S-61N TRDS Structural Crack
Per Flight Averagesof
Tail Rotor Drive Shaft 1P
S-61N TRDS Structural Crack
Dramatic Increase in 1/P and 2/P levels as RPM
Decreases
S-61N TRDS Structural Crack
1P 2P3P
Resonance
RESPONSE
FREQUENCY
NATURALFREQUENCY440KHz.
TUNING FORK"A" FREQ.=440KHz.
100 200 300 400 500 600
SPECTRUM ANALYZER
Resonance / Natural Frequency
• Frequency that an object will vibrate when excited. Frequency will not vary with RPM.
• Fn = 2*PI*f k/m– Where k = Stiffness and m = mass
• Guitar Strings, Tuning Forks, Aircraft ground Resonance, Absorbers, Hammers, etc ….
Aircraft Data - H46 High Speed Shaft
Extremely High Vibe atResonance frequency
Note 1 per is in limitsG-meter would have missed this resonance
Aircraft Data After HSS and Adapter Change
No resonance
Damaged Sensors Due to HSS Resonance
H-46 Mixbox Gear Resonance (Waterfall)
Cost Savings
Cost Savings Through:
• Vibration Reduction• Continuous Monitoring• Reduced Maintenance Time by Aircraft Hardwiring
Vibration Reduction
P3: US Navy,1 Year Prop Vibration Reduction
Systems Tracked:1. Reduction Gear Box2. Valve Housing3. Fuel Leaks/Tanks4. HF Radio5. VHF Radio6. APS-115 Radar7. ASA-70 Display8. TD Amp9. Doppler10. Average for all Systems
1 2 3 4 5 6 7 8 9 100
50
100
150
200
250
300
1 2 3 4 5 6 7 8 9 10
BEFORE
AFTER
Effect on MFHBF During Study
Major System
AVERAGE MFHBF DOUBLED FORALL SYSTEMS!
Results of Initial Squadron Trial
Measure Effect of Vibration Reduction to 0.15 IPSTotal Failures Before/’After Prop Balance Decreased by 22.8 PercentMaintenance Man Hours Per Flight Hour Decreased by 11.5 PercentTotal Maintenance Man Hours “O” Level Decreased by 19 PercentTotal Maintenance Man Hours “I” Level Decreased by 16 PercentFlight Hours Per Maintenance Action Increased by 4 Percent
Continuous Monitoring
US Air Force Record of Cost Reduction and High ROI
Fleet size = 47 AFSOC MH-53J
Aborts per month pre VMS 23.5 per month post VMS 14.1Aborts per month saved 9.4
Aborts per fleet prevented per year12 months x 9.4 aborts = 112.8 aborts/year
2 flight hours lost/abort112.8 x 2 hours x $3,500/hour = $789,600 saved per year
VMS - Vibration Monitoring System
Aircraft Hardwire Savings
• Manufacturers Requirements Are Increasing.– Some Aircraft are coming from Factory Hardwired for Routine
tasks (S-76, EC-135)
• Savings From;– Reduced Installation / Removal time
– Equipment Life increases (most damage comes from removal and installation)
– More Frequent analysis performed
– Overall Safety improvements
Conclusions
• Rotor Track and Balance has Changed
• Vibration Requirements are increasing
• Significant Cost Savings are available