Transcript Comet aircraft.ppt

Comet aircraft
Fatigue failure
Group 6
Background
 de Havilland
– Jet powered aircraft
– Comet became first commercial jet airliner
 First prototype flew 27th July 1949.
Background
 Passenger flights began 1952
 Tokyo – London flight time from 85 to 36
hours
 Comet deemed a success
– high pressure refuelling
– hydraulic actuation of control surfaces
– air-conditioned cabin.
Things go wrong
 Soon after introduction, Comet 1 ran into
difficulties. A string of accidents followed
 March 1953, Comet CF-CUN
– Crew killed during takeoff
 May 1953, Comet G-ALYV
– Plane disintegrates mid-air
 January 1954, Comet G-ALYP
– Plane explodes and crashes into sea killing all on board
Things go wrong
 All Comet 1 aircraft subsequently withdrawn from
service
 Design modified and re-enters service. However…
 April 1954, Comet GALYY
– Ran into difficulty 30 mins into flight and crashed
 12th April 1954
– Certificate of airworthiness removed from Comet
Investigation
 Crashes initially assumed due to
unfamiliarity of pilots with new aircraft
 De Havilland knew there could be problems
with take-off performance and was relying
on pilot skill to over-ride this
 Weather also blamed
 Evidence showed the aircraft suffered a
catastrophic explosion of the fuselage
Causes of Failure
 Extensive testing gave
the following reasons
for failure:
– stresses of 315MPa at edge of rear
ADF window and bolt hole around
window of 70MPa stress at the bolt
position
– New technology introduced new
load cases (high altitude flight for
turbojet engines requiring cabin
pressurisation)
Causes of Failure
 Main cause of failure determined to be...
Fatigue failure
Lessons Learned
 Revision in estimates of safe loading strength
requirements of airliner pressure cabins
 Discovery that stresses around sharp-cornered
cut-outs around pressure cabin apertures were
considerably higher than had been appreciated
– future jet airliners feature windows with rounded corners
 Different materials used for specific situations
 New testing methods
Technological Outcomes
 Full-scale testing of aircraft structures
utilised in future aircraft.
 Better understanding of fatigue testing
achieved
 Concept of ‘one-bay’ crack tolerance in
fuselage probably formulated
Re-design
 Modifications made to design of aircraft and the
Comet 4 re-entered service October 1958
 Opened trans-Atlantic route with 80 passengers
 A few weeks later Boeing 707 flew same route
with 120 passengers and a safer, more flexible
design engine
 The loss of 6 years to the Comet problems
instrumental in losing the lead in future jet
transportation to the US
 Only 113 produced
 Production ceased 10 years after redesign
 Thank you!!