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CLASSIFICATION
UNCLASSIFIED
– Approved For Public Release
Helicopter Airframe Fatigue Spectra
Generation
By Luther Krake
Presented by John Vine at FATIGUE 2014
Melbourne, Australia
5 March 2014
Background & Objective
DSTO has undertaken a project to improve its fatigue
analysis and fatigue testing capability for helicopters.
H-60 airframe being used as a test bed
Fatigue analysis for design or in-service life management
typically starts with the Design usage Spectrum (DUS)
– consists of an ordered sequence of flight and ground regimes and their
durations
What data does DSTO have to generate fatigue spectra?
– H-60 DUS description
– Australian Black Hawk flight test data
Helicopter Airframe Fatigue Spectra
Generation
Purpose:
– To generate flight-byflight fatigue
sequences consistent
with DUS.
What are the fatigue
drivers?
3
The Spectrum Generation Process
MH-60S DESIGN
USAGE
SPECTRUM1
SEQUENCE
REGIMES
ASSIGN FLIGHT
LOADS DATA
BLACK HAWK
FLIGHT STRAIN
SURVEY DATA2
SCALING
TRUNCATION
FURTHER
PROCESSING
1.
2.
‘MH-60S Dynamic Component Fatigue Substantiation’, SER-521877, Sikorsky, 2009.
‘Joint USAF-ADF S-70A-9 Flight Test Program, Summary Report’, A-6186, GTRI, 2001
ETC
MH-60S Design Usage Spectrum (DUS)
Why use DUS?
– No OLM data, no whole flights; hence, need to build spectra up
from pieces
– Choice (today)
45-45-10 composite spectrum:
– 45% Vertical Replenishment (VERTREP)
– 45% Armed Helicopter (ARMED HELO)
– 10% Airborne Mine Countermeasures (AMCM)
Worst case spectrum:
– Occurrence rates for the most damaging manoeuvres are set at
the highest rates anticipated in service
123 conditions in total, consisting of:
– 83 ‘basic’ (non mission specific)
– 40 mission-specific
MH-60S DUS
Regime Sequencing: Process Overview
STEP 1: GENERATE BASIC FRAMEWORKS FOR ALL FLIGHTS
INSERT TAKE-OFFS & LANDINGS
INSERT GROUND REGIMES + ROTOR ENGAGE/SHUTDOWNS
INSERT TRANSIENT REGIMES, CLIMBS & DIVES
STEP 2: REFINEMENT & COMPLETION
INSERT MISSING REGIMES
DELETE ADJACENT DUPLICATES
SMOOTH LEVEL FLIGHT ACCELERATIONS/DECELERATIONS
DISTRIBUTE TIME FOR STEADY-STATE CONDITIONS
ASSIGN GW PRORATES
Regime Sequencing: STEP 1
TAXI TURN
LANDING
TAKE-OFF
TAXI
ROTOR ENGAGE
Insert landings, take-offs, ground regimes +
rotor engage/shutdowns:
TAXI
LF 0.4VH
STDY CLIMB
LF 0.4VH
LF 0.6VH
E&R 30 RT
30 TRN RT
E&R 30 RT
LF 0.6VH
LF 0.6VH
E&R PPD
STDY PPD
E&R PPD
LF 0.6VH
LANDING
TAXI TURN
Insert transient regimes, climbs & dives:
TAKE-OFF
Regime Sequencing: STEP 1
ROTOR ENGAGE
TAXI
LF 0.4VH
STDY CLIMB
LF 0.4VH
LF 0.6VH
E&R 30 RT
30 TRN RT
E&R 30 RT
LF 0.6VH
LF 0.6VH
E&R PPD
STDY PPD
E&R PPD
LF 0.6VH
LANDING
TAXI TURN
Basic framework but needs further refinement:
TAKE-OFF
Regime Sequencing: STEP 1 Complete
ROTOR ENGAGE
TAXI
LF 0.4VH
STDY CLIMB
LF 0.4VH
LF 0.6VH
E&R 30 RT
30 TRN RT
E&R 30 RT
LF 0.6VH
LF 0.6VH
E&R PPD
STDY PPD
E&R PPD
LF 0.6VH
LAT REV LF
LF 0.6VH
LANDING
TAXI TURN
Insert missing regimes (e.g. control revs, sideslip,
etc):
TAKE-OFF
Regime Sequencing: STEP 2
ROTOR ENGAGE
TAXI
LF 0.4VH
STDY CLIMB
LF 0.4VH
LF 0.5VH
LF 0.6VH
E&R 30 RT
30 TRN RT
E&R 30 RT
LF 0.6VH
LF 0.6VH
E&R PPD
STDY PPD
E&R PPD
LF 0.6VH
LAT REV LF
LF 0.6VH
LANDING
TAXI TURN
Smooth level flight accelerations/decelerations:
TAKE-OFF
Regime Sequencing: STEP 2
ROTOR ENGAGE
TAXI
LF 0.4VH
STDY CLIMB
LF 0.4VH
LF 0.5VH
LF 0.6VH
E&R 30 RT
30 TRN RT
E&R 30 RT
LF 0.6VH
LF 0.6VH
E&R PPD
STDY PPD
E&R PPD
LF 0.6VH
LAT REV LF
LF 0.6VH
LANDING
TAXI TURN
Delete adjacent duplicates:
TAKE-OFF
Regime Sequencing: STEP 2
ROTOR ENGAGE
TAXI
LF 0.4VH
STDY CLIMB
LF 0.4VH
LF 0.5VH
LF 0.6VH
E&R 30 RT
30 TRN RT
E&R 30 RT
LF 0.6VH
E&R PPD
STDY PPD
E&R PPD
LF 0.6VH
LAT REV LF
LF 0.6VH
LANDING
TAXI TURN
Delete adjacent duplicates:
TAKE-OFF
Regime Sequencing: STEP 2
ROTOR ENGAGE
TAKE-OFF
LF 0.4VH
STDY CLIMB
LF 0.4VH
LF 0.5VH
LF 0.6VH
E&R 30 RT
30 TRN RT
E&R 30 RT
LF 0.6VH
E&R PPD
STDY PPD
E&R PPD
LF 0.6VH
LAT REV LF
LF 0.6VH
LANDING
TAXI TURN
Distribute time for steady-state conditions:
TAXI
Regime Sequencing: STEP 2
ROTOR ENGAGE
Regime Sequencing Example
Flight Loads Data Assignment
Purpose:
– To assign flight loads data to each regime in the
sequence.
Method:
– Identity candidate Flight Strain Survey (FSS)
data files based on regime name and GW
– Rank candidates WRT selected flight state
parameters in order to minimize
unrepresentative load changes between regimes
– Adjust ‘actual’ durations to match ‘nominal’
durations (steady-state regimes only).
Black Hawk FSS Data
Major flight strain survey
conducted in 2000 at the Army
Research & Development Unit
(ARDU), RAAF Edinburgh, South
Australia.
Over 250 parameters measured,
including:
– 51 flight state & control system
parameters
– 217 airframe strain gauges
– 18 airframe accelerations
– 16 GW/CG loadings
– 65 productive flight test hours
Sample Single Flight Spectrum
Black Hawk Main Transmission Support Beam (cabin roof) located
strain gauge
Sample 100 Hour Block Spectrum
Summary
DSTO has developed an automated means of
pseudo-randomly generating helicopter fatigue
spectra.
Currently using Black Hawk FSS data and MH60S DUS but could be adapted to use other
data.
Initial emphasis is on creating as realistic ‘raw’
spectrum as possible.
Next Steps:
– Make the spectra usable for analysis and test
purposes via truncation and further simplification.
Acknowledgements
Mr Phil Jackson and Mr Rob Boykett (DSTO)
Mr Nam Phan, Naval Air Systems Command
(NAVAIR), United States Navy (USN)
Dr Arvind Sinha, Helicopter Systems Division
(HSD), Defence Materiel Organisation (DMO)

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