Projects

Project Air 5376 Ph 3 – F/A-18 Hornet Upgrade

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Phase 3 - Background

Hornet Upgrade (HUG) Phase 3 adds no new capability to the aircraft and is essentially a structural refurbishment program that is required in order for the Hornet fleet to reach its Planned Withdrawal Date (PWD). Similar to other fighter aircraft, the Hornet suffers from fatigue cracks that increase in size and numbers as load stresses are applied throughout the life of the aircraft. Indeed it is not uncommon to have thousands of small fatigue cracks evident at the end of an aircraft's life. As the Hornet is a United States Navy (USN) aircraft, it has been designed using a safe life philosophy. In effect, this philosophy means that the aircraft will exhibit a number of fatigue cracks, none of which should reach critical crack length prior to retirement of the aircraft. Optimally, all areas of the structure should be 'worn out' at about the same time and the jet withdrawn from service.

When the Hornet was initially acquired the structural fatigue life of the F-18 A/B was specified at 6 000 hours based on a USN nominated design usage spectrum developed from historic operational data. However, only when the aircraft entered service were the true capabilities of the Hornet revealed, and actual fatigue usage spectra differed markedly from the design spectra such that the 6 000 hour life was no longer relevant. In service, the RAAF rate of fatigue accrual is higher than that of the USN. Much of the USN fatigue usage is dominated by carrier catapult take-offs and arrested landings, which create great stresses on the undercarriage and fuselage. RAAF fatigue usage exhibits higher G and sustained G loadings that have a greater effect on the centre fuselage and wings.

In order to address this looming problem the RAAF, in collaboration with Canada, initiated a fatigue test program, known as the F-18 International Follow-On Structural Test Project (IFOSTP) to determine the safe (fatigue) life of the aircraft and identify modifications to ensure the continued safe operation until PWD. The results of the IFOSTP show that both RAAF and Canadian Forces Hornet fleets will require major mid-life structural modifications to meet their respective Planned Withdrawal Dates (PWDs). To address both the fatigue and corrosion related structural degradation on the RAAF fleet, a multi-staged Structural Refurbishment Program (SRP) has been initiated. This multi-staged SRP forms the basis of HUG Phase 3.

HUG Phase 3.1

The HUG Phase 3.1 project comprises the first stage of the SRP, and includes approximately 22 discrete structural modifications on all aircraft within the fleet. Modification design, prototype activities, low rate initial production program and modification kit manufacture has been sole-sourced to L-3 Communications MAS Canada (L-3 MAS). The production installation program to date has been conducted by Boeing Australia Limited and BAE Systems Australia, with L-3 MAS providing engineering support. Production installation on the remaining aircraft is being conducted under new contractual arrangements. All modifications are being undertaken at Williamtown (NSW, Australia), with the exception of the prototype modification installation on one aircraft, which was undertaken at L-3 MAS facilities in Mirabel, Canada.

HUG Phase 3.2

The HUG Phase 3.2 project follows on from the HUG Phase 3.1 project and represents the second stage of the SRP. HUG Phase 3.2 is the larger and more complex stage and involves some additional “Delta” discrete structural modifications (on the majority of aircraft) and the centre barrel replacement (CBR) on select aircraft. The centre barrel is the primary load bearing structure in the fuselage for withstanding the loads induced by the wings. Essentially, the centre barrel is comprised of three major bulkheads to which the wings are attached.

Further analysis on the centre barrel fatigue locations has been conducted by Defence Science and Technology Organisation (DSTO) in conjunction with ASI-DGTA and QinetiQ. The results of the analysis enabled extension of the intervals before some of the modifications need to be incorporated, subsequently decreasing the number of aircraft required to undergo CBR. The number of aircraft requiring CBR depends on fleet Planned Withdrawal Date, aircraft rate of effort and fatigue life accrual rate. Based on these considerations the project office has completed modelling leading to the decision to conduct CBR on a total of ten aircraft.

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Timings

HUG Phase 3.1:

• Prototype activities – completed Jan 2004.
• roduction installation (including low rate initial production) – commenced Apr 2004 with completion expected in 2012.

HUG Phase 3.2:

• Delta Modification Prototype activities – completed in May 2005.
• Delta Modification Production installation (including low rate initial production) – commenced Jan 2006 with completion expected in 2012 (conducted in conjunction with HUG Phase 3.1 installations).
• CBR Prototype activities – commenced Feb 2006 with completion in Jan 2008.
• CBR Production installation (including low rate initial production) – commenced Feb 2007 with completion expected in 2010

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Contact

Director
Tactical Fighter Project Management Unit
Group Captain Ian Nesbitt
Tactical Fighter Systems Program Office
RAAF Base
Williamtown NSW 2314
Telephone: (02) 4928 6901
E-mail: Ian.Nesbitt@defence.gov.au

Last reviewed: July 2009