Transcript COMET AIRCRAFT_Group 6.ppt

COMET AIRCRAFT
Fatigue Failure
Group 6
THE COMET - BACKGROUND
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De Havilland
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Engines
Aircraft
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Standard piston engines before 1929
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First commercial airline using turbojet
engines
THE COMET - BACKGROUND
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Passenger flights began 1952
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London – Johannesburg flight time from 40hrs
to 23hrs
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Comet deemed a success
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Fully pressurised cabin
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Quiet & smooth flight
Flew 28,000 passengers in first year
Human Factors
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British v’s Americans
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Politics, time, market pressures
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3 years testing, not 7
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BOAC concerns over fatigue
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Fleet in service before testing
INITIAL ACCIDENTS
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1952 – Accident on take off
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Blamed on pilot error
1953 – Failed to gain altitude
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Initially blamed on pilot error
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Subsequently found to be design flaw in wing
Calcutta accident – plane disintegrated
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Blamed on tropical storm
INITIAL ACCIDENTS
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1954 - Comet explodes over Mediterranean
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Flights Suspended & recovery of wreckage
Design modified:
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Shields between engines and fuel tanks
However ... 2 months later ...
Yet another accident
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Comet flying from Rome disappeared
Wreckage retrieved from the sea
The Real Problem
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Investigation began
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Large water tank
= cabin loading
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Wings flexed by hydraulic
jacks
= flexing due to wind load
The Real Problem
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Sudden pressure drop
at equivalent of 9000
flight hours
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Corners of square
windows – high stress
concentration
Stress Concentrated at
Windows
The Real Problem
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Navy recovers 70% of
wreck & confirms test
results
METAL
FATIGUE
Lessons Learned
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Unforeseeable possibilities – 1st jet airliner
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Fatigue failure
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Minimising stress concentrations
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Materials for specific situations
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New aircraft testing
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Testing to simulate ‘real life’ conditions
Redesigned as Comet 4
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First scheduled trans-atlantic service
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113 produced
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Production ceased 1968
Finally …
Thank You