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Flt Lt Chris Kourloufas

Topic: Managing Composite Structural Integrity Hazards – A RAAF F/A-18A/B Case Study

Presented by: Flight Lieutenant Chris Kourloufas, Defence Aviation Safety Authority, Melbourne

Abstract

The Royal Australian Air Force (RAAF) F/A-18A/B ‘Classic Hornet’ is a twin engine fighter aircraft introduced into service in 1983 to replace the Mirage III in the tactical fighter role. The Classic Hornet is a multi-mission aircraft with extensive air-to-air and air-to-ground capabilities. Boeing (formerly McDonnell Douglas) designed the aircraft, with Northrop as the prime sub-contractor, to United States Navy (USN) design specifications. The airframe was designed to achieve 6,000 hours under a safe-life philosophy. Contemporary high-strength aluminium alloys are the primary structural materials. However, high-performance Carbon Epoxy composites are used in the vertical and horizontal tails, wing skins, trailing edge flaps and access doors and dorsal covers. Numerous full-scale fatigue tests were conducted during the design and production phases to validate the fatigue life of the structure.

A hazard to the airworthiness of Classic Hornet Inner Wing – potential disbonding of the ‘Step Lap Joint’ area, is being identified and analysed (figure 1).

Fig 1. Area of Interest: Classic Hornet Step Lap Joint Source RAAF Kourloufas

Fig 1. Area of Interest: Classic Hornet Step Lap Joint

The root cause of these disbonds is likely to have stemmed from contamination during surface preparation process at manufacture. The performance of composite structure and in particular, bonded joints is highly sensitive to the process controls in place at the time of wing build. Disbonds are susceptible to growth in-service but techniques to reliably model this growth are not at an implementation stage of readiness. The RAAF is working to establish the condition of the fleet via NDT (Phased Array Ultrasonic Inspection) as a matter of priority. The RAAF has seen a higher incidence and new configurations of defect indications compared to international fleets, which is being managed closely by the Defence Aviation Safety Authority.

The Phased Array NDT technology will also be presented and briefly compared to conventional Ultrasonic Testing (UT). The practical application of the technology to the Inner Wing Step Lap Joint will also be described, along with reporting capabilities and defects detected. Further, the analysis and interpretation of inspection results will be discussed as well as the management strategies applied to findings. Finally, opportunities for collaboration and research will be outlined to meet RAAF certification/management requirements.

Keywords: Contamination; Disbonding; Damage growth.

Presenter’s resume

Chris Kourloufas, ME(Aerospace), MS(Aeronautics and Astronautics), BE(Aero) Hons joined the RAAF as an Aeronautical Engineering Officer in 2009 and is now Flight Lieutenant, F/A-18A/B Structural Integrity, Defence Aviation Safety Authority. Previous positions include: PC- 9A Structural Integrity; F/A-18A/B Component Maintenance.

Flt Lt Kourloufas is also presenting a paper in the Peer Reviewed Stream on  Effect of Saltwater Absorption/Desorption Cycling on Strength of Carbon Fibre/Epoxy Composites. Go to this abstract …