rotor track and balance only????. agenda history of rotor track and balance. vibration requirements...

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