uh-1h main rotor blade fatigue

8/7/2019 UH-1H Main Rotor Blade Fatigue

1/24

UH-1H MAIN ROTOR BLADE FATIGUE

by

Patrick Conor, Alan James, Michael Hollis

Defence Technology AgencyNew Zealand Defence Force

Auckland


2/24

PRESENTATION OUTLINE

BACKGROUND

BLADE CRACKING

GRIP PAD DISBONDING

BLADE INSPECTION

NDI RESULTS

CAUSAL FACTORS

IN-SERVICE MANAGEMENT


3/24

UH-1H MAIN ROTOR BLADE (MRB) FATIGUE

BACKGROUND

RNZAF AIRFRAME AVERAGE TSN APPROX 10,000 HRS

US ARMY HOLD TYPE CERTIFICATE

MAIN ROTOR BLADE SAFE LIFE 2,500 HRS (US ARMY SPECTRUM)

RNZAF MAINTENANCE iaw US ARMY MANUALS

RNZAF FREE OF SERIOUS MRB PROBLEMS SINCE 1965


4/24

!

""""####"$"$"$"$

MEDIUM UTILITY HELICOPTER ROLE

Location of flight operations in 2000 - 2001:

NEW ZEALAND

EAST TIMOR

BOUGAINVILLE

ANTARCTICA


5/24

DEFECT INDICATION NZ3816, EAST TIMOR 2001


6/24

%

Grip Plate(Aluminium)

Grip Pad

(Steel)

Toughenedepoxy adhesive

BLADE CONSTRUCTION

D-spar

Bushing

ADHESIVELY BONDED METAL LAMINATE STRUCTURE


7/24

&

$''($''($''($''(

FRACTURE SURFACE

CHORDWISE C/S

Fatigue crack limits


8/24

)

GRIP PAD DISBONDING

FATIGUE CRACK

SAW CUT

TIP

L.E.

UNDER-SURFACE

OF CRACKEDBLADE

GRIP PAD REMOVEDAND BLADE CUT UPFOR FRACTURE

SURFACE ANALYSIS


9/24

*

$+$+$+$+

RESULTS OF DESTRUCTIVE TESTS

TWO MRB CLASSES

Early-Model Blades

- MODERATE DISBONDS AT 2,500 HRS

Recent Blades

- SIGNIFICANT DISBONDS AT 1,000 HRS

- MANY BLADES IN SERVICE


10/24

DAMAGE ASSESSMENT

GRIP PLATE CRACK GROWTH RATE WAS RAPID

CRACKS CONCEALED BY GRIP PAD

CRACKING PRECEDED BY GRIP PAD DISBONDING

SAFETY PREDICATED BY DISBONDING

SO,

MANAGE SAFETY BY MONITORING DISBOND ONSET

(SAFETY BY INSPECTION)

PRESCRIBED INSPECTION CAREFUL VISUAL CHECK


11/24

,$',$',$',$'

DISBONDING FOUND IN ABLADE REJECTED FOROTHER REASONS AFTER

1100 HRS IN SERVICE -

- LARGE DEFECT WAS NOTDETECTED BY EITHER:

BONDLINE VISUALINSPECTION (IN A LABENVIRONMENT)

OR,

COIN TAP-TESTING

Grip Plate

(Aluminum)

Grip Pad(Steel)


12/24

EXISTING INSPECTION METHODS DID NOT PROVIDE ADEQUATEMEASUREMENT CAPABILITY

PERFORMANCE OF AVAILABLE INSPECTION METHODSFOR MEASURING GRIP PAD DISBONDING

INTERPRET

- DIFFICULT TOULTRASONIC TEST

- FAILEDCOIN TAP TEST

- UNRELIABLEDYE PENETRANT

- UNRELIABLEVISUAL

RESULTMETHOD


13/24

NEW INSPECTION TECHNIQUE

- BONDLINE COMPLIANCE -


14/24

!

'$''$''$''$'

STRAIN GAUGE MECHANICAL DISPLACEMENT

1 23 4

5 67 8

9 10

0

54.4

5

95.9

75

0

100

200

300

400

500

600

700

Microstrain

Strain Gauge NumberBending

Moment

(metre.kg)

BONDLINE COMPLIANCE

RESULT WITH

MULTIPLESTRAIN

GAUGES

BONDLINE

LOAD


15/24

$'$'$'$'

BLADE GRIP PAD EDGE STRAIN vs TIME SINCE NEW

0

200

400

600

800

1000

1200

1400

1600

0 500 1000 1500 2000 2500

TIME SINCE NEW (Flying Hours)

Max.

Strain(uS)


16/24

%

OPTIONS TO KEEP FLYING

1. BUY MANY NEW BLADES AND REPLACE VERY EARLY

- VERY EXPENSIVE

- IMPOSSIBLE SUPPLY PROBLEM

2. ADOPT SAFETY BY INSPECTION

- DEFINE SAFE DISBOND SIZE

- DETECT AND MONITOR SUB-CRITICAL DEFECTS

- USING THE STRAIN NDI METHOD


17/24

&

-"$-"$-"$-"$

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120 140

Delaminated Area (cm2)

Max

TE

Strain(uS)

DISBOND

RUNAWAY

LIMIT

BLADEQUARANTINELIMIT


18/24

)

CAUSAL FACTORS


19/24

*

'$,'$,'$,'$,

# ./011/2.342526247.15

0

500

1000

1500

2000

2500

A-FS11396

A-FS11421

A-FS11423

A-FS12014

A-11392

A-FS11365

A-FS11068

A-FS11416

A-FS11413

A-7619

A-6715

A-FS11343

A-6712

A-FS11347

A-FS12062

A-FS11415

A-11376

A-FS11271

A-FS11243

A-FS11449

A-FS11385

A-FS11419

A-11928

A-FS12026

A-FS12061

A-FS12584

A-9144

A-FS11349

A-FS12008

A-FS12768

A-FS12767

A-FS12007

A-FS12708

A-FS12874

A-FS12060

A-11389

A-FS12769

A-FS12051

A-FS12869

AMR01288

A-FS12797

A-FS12890

A-FS12921

A-5031

A-FS12866

A-FS12770

A-FS12828

A-FS12923

Blade

BladeT

SN

(hours)

0

200

400

600

800

1000

1200

1400

1600

Strain->

Ice Hrs

Hrs NZ

Hot &WetHrs

Strain 1

RNZAF DATA

Analysis by S/Ldr M Going


20/24

MB

P

Resultant Horizontal Shear

Resultant Horizontal Shear

Steel Grip Pad

Adhesive

Bond Line

Outboard Up

MAIN ROTOR BLADE ATTACHMENT FITTING

Aluminium Grip Plate

ADHESIVEPEEL

- LOAD TRANSFER


21/24

HIGH PEEL STRESS INTHE ADHESIVE

DEMANDING LOADS

SPECTRUM?

FEA: ADHESIVE STRAIN IN Z-AXIS

FATIGUE?

Analysis by S K Campbell (DTA)


22/24

####,',',','

SAFETY BY INSPECTION

STRAIN NDI FOR DISBOND MONITORING

CONTINUOUS ANALYSIS OF RESULTS

REDUCED BLADE LIFE CONFIRMED

INSPECTION METHOD IMPOSES ANUNAVOIDABLE MAINTENANCE PENALTY


23/24

THE BLADE WAS AFFECTED BY AN EXCEPTIONALLY LARGEFATIGUE CRACK

- THE HELICOPTER WAS SAVED BY CONSERVATIVE DESIGN

- MULTIPLE LOAD PATHS

- REDUNDANT STRUCTURAL ELEMENTS

- FLIGHT SAFETY IS NOW MAINTAINED BY BONDLINE STRAININSPECTION

- THE INSPECTION IS BASED ON EXHAUSTIVE ANALYSIS OFIN-SERVICE DEFECTS

SUMMARY


24/24

!

Acknowledgements

RNZAF

Wing Commander D C Howard

No. 3 Squadron Maintenance FlightRNZAF Base Auckland Technical Support Unit (ATSU)RNZAF Base Ohakea Technical Support Unit (OTSU)

DTA

Mr S K CampbellMr I P Gatehouse

Bell Helicopter Textron Incorporated

uh-1h main rotor blade fatigue

Documents