Transcript angel2

Rotor Track and Balance
Only????
Agenda
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•
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History of Rotor Track and Balance.
Vibration Requirements Increasing.
Using the Tools You Have.
Cost Savings.
History of Rotor Track and Balance
Flat 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 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
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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.
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NOTE: The Maintenance Manual requires an inspection and
RT&B exercise anytime the rotors trip the 1 per alarms.
H-46 Data Prior to Failure
Fwd Rotor Lateral Spectrum
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
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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 well
below limits
Questionable Adapter Balance
Excessive
Grinding
Excessive
Grinding
AXIAL
3X
2X
1X
Misalignment
• Characteristics of Misalignment
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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
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
2X
RADIAL
3X
.5X
1X
Mechanical Looseness
• Loose Bolts, Structural Frame Cracks, Wear
Between Bearing and Supports
• Raised Noise Floor
• Phase or Clock Angle is Unstable
S-61N TRDS Structural Crack
Per Flight Averages
of
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
2P
3P
Resonance
SPECTRUM ANALYZER
NATURAL
FREQUENCY
440KHz.
RESPONSE
TUNING FORK
"A"
FREQ.=440KHz.
100
200
300
400
FREQUENCY
500
600
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 at
Resonance frequency
Note 1 per is in limits
G-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
Results of Initial Squadron Trial
Measure
Total Failures Before/’After Prop Balance
Maintenance Man Hours Per Flight Hour
Total Maintenance Man Hours “O” Level
Total Maintenance Man Hours “I” Level
Flight Hours Per Maintenance Action
Effect on MFHBF During Study
Effect of Vibration Reduction to
Decreased by 22.8 Percent
Decreased by 11.5 Percent
Decreased by 19 Percent
Decreased by 16 Percent
Increased by 4 Percent
Systems Tracked:
1. Reduction Gear Box
2. Valve Housing
300
BEFORE
AFTER
3. Fuel Leaks/Tanks
250
200
4. HF Radio
150
5. VHF Radio
100
6. APS-115 Radar
50
7. ASA-70 Display
0
8. TD Amp
Major System
9. Doppler
AVERAGE MFHBF DOUBLED FOR 10. Average for all Systems
ALL SYSTEMS!
0.15 IPS
Continuous Monitoring
US Air Force Record of Cost Reduction and High ROI
Fleet size = 47 AFSOC MH-53J
Aborts per month pre VMS
per month post VMS
Aborts per month saved
23.5
14.1
9.4
Aborts per fleet prevented per year
12 months x 9.4 aborts = 112.8 aborts/year
2 flight hours lost/abort
112.8 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