top 3 causes of aircraft vibration
TRANSCRIPT
Top 3 Vibration Causes
VIBRATION• Effects• Causes• Terminology• Detection• Correction• Examples• Tips
Vibration EffectsBearing Wear
Vibration causes increased maintenance• Accelerated component failure• Engine / motor failure
Bearing life reduced by third power10x increase in load = 1000x decrease in life
Sliding Wear
Generally varies linear with load
@1 IPS (Inch per Second variation), 7800 RPM, engine experiences 2G oscillation, variation of .001 in.
Industry standard is vibration less than 0.1 IPS; 10x reduction in vibration is 10x reduction in wear rate.
Vibration Effects
Cowling cracks
Vibration Effects
Exhaust Cracks
Vibration Effects - Pilot Comfort
Cause: 1) Mass Imbalance
Center of Rotation vs. Center of Gravity
Why?• Manufacturing defects• Installation error• Propeller damage• Moisture / corrosion• Maintenance / paint / repair
Cause: 1) Mass Imbalance
Cause: 1) Mass Imbalance
Center of Rotation vs. Center of Gravity
• Manufacturing defects• Installation error• Propeller damage• Moisture / corrosion• Maintenance / paint / repair
Cause: 1) Mass Imbalance
Center of Rotation vs. Center of Gravity
• Manufacturing defects• Installation error• Propeller damage• Moisture / corrosion• Maintenance / paint / repair
Cause: 1) Mass ImbalanceCenter of Rotation vs. Center of Gravity
• Manufacturing defects• Installation error• Propeller damage• Moisture / corrosion• Maintenance / paint / repair
Cause: 1) Mass ImbalanceCenter of Rotation vs. Center of Gravity
• Manufacturing defects• Installation error• Propeller damage• Moisture / corrosion• Maintenance / paint / repair
Cause: 2) Aerodynamic Imbalance
Blade track
Cause: 2) Aerodynamic ImbalanceBlade track
Cause: 2) Aerodynamic Imbalance
Blade pitch
Cause: 2) Aerodynamic Imbalance
Blade pitch
Cause: 2) Aerodynamic Imbalance
Blade shape
Cause: 3) It’s Complicated
• Compression• Spark• Fuel flow• Worn bearings • Intake / Exhaust variances• Vibration isolators• Torsional absorbers• Gearbox• Aerodynamic interaction
TerminologyIPS – Inches per Second (Velocity)
1 per – Rotates at Prop / Rotor RPM (Once Per Revolution)½ per – Every other rotation, 4 - stroke2 per – Twice per rotation (Two Blade)3 per – Three per rotation (Three Blade)
Vibration Correction – 1 PerInstall Equipment
Measure the 1-per Vibration
• Warm up the engine
• User averaging to optimize signal
• 2090RPM
• 0.88IPS @ 258
Vibration Correction – 1 Per
Realign blade with phototach
Vibration Correction – 1 Per
Add / Remove Weight
• Leave prop clocked
• 258 degrees in the direction of prop rotation
• 50 grams per IPS starting point
• Remove weight at 258 or add at 78
• Rerun, usually takes 2-3 cycles
Vibration Correction – 1 Per
Final Reading
Vibration Correction – 1 Per
Vibration Correction - TroubleIf it doesn’t work, something is typically wrong
Phase angle changing
Vibration Correction - TroubleIf it doesn’t work, something is typically wrong
New IPS and angle each run
Vibration Correction – Advanced
DynaVibe GX Balancer and Analyzer
• AutoBalance
• TruePhase Measurement
• Spectrum Analysis
• TotalVibe
• Reporting
Vibration Correction – Advanced
AutoBalance
Setup Screen
• Owner / Engine Info• Blade Location• Direction of Rotation• Phototach Location• Accelerometer Location• Weight Addition Locations
Vibration Correction – Advanced
AutoBalance
• Polar Chart• RPM• IPS and phase
• Generates Split weight mass amounts and location
Vibration Correction – Advanced
Spectrum
Long-Ez
1-per
2-per
2.6 – per
Vibration Correction – Advanced
Spectrum
Long-Ez
½ per - rough
1-per
2-per
Vibration Correction – AdvancedSpectrum
½- VW - started at 0.7 IPS
Vibration Correction – AdvancedSpectrum
Kitfox IIIVery large 3 perRough engine shows 1.5 per
crank
½ crank
Vibration Correction – AdvancedSpectrum Crank
1.5 Crank
½ Crank
Left engine has ½ per crank vibration, bad cylinder
Right engine has a 1.5 per crank, bad mag
Vibration Correction – AdvancedSpectrum
Vibration Correction – AdvancedTotal Vibe
Aircraft Resonance
Magnitude vs. RPM
Rotax 912 Setup
Mount two DynaVibe accelerometers on the engine.
Rotax 912 @ gearbox
Gearbox Vibe spectrum shows a slight propeller imbalance (1per < 0.2 IPS).
Gearbox Vibe spectrum shows a ½ per crank (1.2per of 0.3IPS) indicating carbs need balanced.
Rotax 912 @ Right Carb
Analysis reveals a “2-per” vibration.
Additionally there is a 2.43 per vibration caused by the front-back variation in airflow.
These two frequencies together cause a low frequency 7hz rumble that shakes the airplane. (beat frequency)
Rotax 912 as RPM changes
Tips• FAA Advisory Circular 20-37E
• Verify propeller bolt torque on wooden propellers every 25 hours at oil change, or when changing environments
• 1.20 IPS requires static rebalance
• 0.003 inch crank run out can cause 0.6 IPS
• Typical Problems:Fiberglass back platesUnbalanced spinnersBlade Pitch
Vibration Correction – Helicopter
Vibration Correction – Helicopter
Equipment Costs• DynaVibe Classic– RPM, 1 Per IPS & Angle– $1495
• DynaVibe GX2– AutoBalance, Spectra, TotalVibe– 2 Accelerometers at the same time – DynaTrack, Strobe, Highspeed– $3995