Vipac Engineers & Scientists Ltd was awarded the contract for the acoustic design, analysis
and test of the composite centre and outer flaps for the Lockheed C130J transport aircraft.
Working closely with the Australian prime contractor (responsible for overall design and
production) Vipac was responsible for the analysis of the acoustic loads and structural
response and for the acoustic qualification testing.
The flaps located in the propeller slipstream are subjected to an intensive acoustic field. Composite material, graphite fibre reinforced epoxy, is being employed due to its superior acoustic fatigue performance compared to conventional aluminium semi-monocoque construction, to satisfy a demanding service life requirement in excess of 30,000 flight hours.
The analytical activities included the development of a set of acoustic loadings to simulate the propeller noise field excitation and an advanced dynamics finite element model (FEM) of the wing flaps. The coupling between the set of wing flap modes and the acoustic excitation was calculated from which the structural response was estimated.
An integral part of the programme was the establishment of appropriate acoustic fatigue criteria
obtained through testing of elemental coupons under random input spectrum. Further testing was
performed on structurally representative articles to verify damping characteristics and techniques
for both acoustic and structural modelling. Final acoustic design qualification was achieved through
full scale testing of both flaps (larger outer flap was abbreviated) in a reverberation chamber.
To achieve a practical test duration to simulate 30,000 flight hours, an acoustic test level above
146dB was employed.