Hornet SRP delivers a winner

The Hornet structural refurbishment program has delivered some strong wins for both industry and the R&D communities in Australia and Canada.
While some Defence projects have been taking heavy hits from the Auditor-General, who now has his own problems, as well as from media critics and others, there are projects which have been outstanding successes.

One of these is Air 5376, the multi-phased F/A-18 Hornet upgrade (HUG) program, especially the more recent Phase 3 which is now seeing the fleet undergo a Structural Refurbishment Program (SRP) under Phase 3.1, commonly referred to as SRP1, with a number of aircraft to later undergo the replacement of centre barrels and adjacent structural components under Phase 3.2.

Although it was only in November 2003 that Defence Minister Robert Hill announced approval of the $230 million structural upgrade to extend the life of the F/A-18's airframe, this aspect of the HUG program had its genesis in the International Follow-on Structural Test Program (IFOSTP), a Canada-Australia joint project, initiated in 1989, that has become one of the longest-running international programs, producing billion dollar savings in military aircraft fleet management and life extension, as well as demonstrating new fatigue testing techniques and new methods for fatigue load reduction.

The IFOSTP team members comprised the National Research Council of Canada Institute for Aerospace Research, (NRC-IAR), the Department of National Defence (DND), L-3 MAS, DSTO's former Aeronautical and Maritime Research Laboratory (AMRL) and the Royal Australian Air Force.

The collaborative arrangement came about because both countries, having purchased F/A-18 aircraft and used it in ways that were different from the original design specifications, discovered there were indications that the airframe would wear out before reaching its design service life of 6,000 hours.

IFOSTP was the largest and most complex test undertaken by NRC-IAR and that organisation was subsequently hired by DND to work with the Australians to develop a detailed understanding of the fatigue mechanisms involved, as well as methods to extend the useful life of the aircraft through advanced structural repair schemes and non-destructive testing techniques. The resulting data, combined with fatigue life management initiatives, has been effective in extending the safe operating life of the fleet by up to 25 percent, with potential savings to the ADF of more than $1 billion.

(So impressed was the International Council of the Aeronautical Sciences (ICAS) by this international collaborative research effort that in 2002 it awarded the Canadian Institute for Aerospace Research and AMRL the prestigious ICAS-von Karman Award.)

Initially designed and tested by McDonnell Douglas (now Boeing) for service with the US Navy, the fatigue life of the F/A-18 aircraft had never been determined for Australian or Canadian conditions. Under the collaborative arrangement, Australia's DSTO tested the rear fuselage and tail assembly, while Canada tested the centre fuselage and wings.

And it was here that Canadian IFOSTP technicians made an important early discovery. They found small cracks in the bulkhead walls of a test aircraft - where the wings are attached. Five planes underwent further tests to confirm the findings. Three of the five showed signs of cracking and as a result fifteen CF-18s were temporarily removed from flying status so that bulkhead modification work could be done. The problem was that while these cracks had been forecast by the US Navy, they were occurring earlier than anticipated.

The cracks were tiny, the longest was only about two-thousandths of an inch, and while they did not pose any flight safety risk, they were an economic risk in that if not repaired, in a worst case scenario, the entire bulkhead would have to be replaced at a cost of some $3 million. The find was also significant because, by using the test aircraft as a fatigue-life benchmark, it was now possible to determine which planes would reach the point where cracks could occur and when.

Aircraft in both Australian and Canadian fleets are equipped with load monitoring gauges to measure accumulated fatigue, so they can be compared to the test plane. Thus the aircraft selected for the Phase 3.1 modification show those levels of fatigue at which point cracks are expected to develop.

Under SRP1 it was necessary for the structural modification process to be developed and a prototype installation of the modifications carried out. This was completed in early 2004. The project then shifted to a low rate initial production (LRIP) program involving six aircraft. This provided an opportunity for further validation of the modification designs and installation processes, ahead of the mature production program. Additionally, the LRIP program was where knowledge and skills transfer occurred in the form of training of maintenance and modification teams.

To undertake the structural refurbishment program the Hornet Industry Coalition (HIC) was formed, comprising three companies with specific expertise in Hornet aircraft support. Boeing Australia Limited is the prime contractor for the HIC, with BAE Systems Australia and L-3 MAS Canada as subcontractors/team members. The partnership between the companies has seen L-3 MAS develop the HUG Phase 3.1 modifications in Canada, prototype the installation of the modifications, manufacture and supply the modification and tooling kits, and provide on-going engineering support.

L-3 MAS was also responsible for training its Australian industry partners in the modification installation process with Boeing Australia and BAE Systems Australia now responsible for the production installation program. With the completion of the prototype and LRIP programs, the aircraft delivered by Boeing Australia on 15 July was the first production aircraft delivered. On 25 July the second production aircraft was delivered, this time from BAE Systems Australia, and four weeks ahead of schedule. Ten aircraft are now being modified across the contractor venues at RAAF Williamtown.

The entire RAAF fleet of 71 F/A 18 Hornet aircraft will be modified with most completed by December 2008 although it is anticipated that SRP1 production will not wind down until after another three or four years.

And what are the 'modification installations' developed by L-3 MAS for the remediation of fatigue-affected airframes? L-3 MAS has significant expertise in structural design and analysis, aircraft fatigue management and has had major involvement with all the CF-18 engineering support programs and developed the structural component modification and repair 'installations' for both the Canadian and Australian F/A-18 structural refurbishment programs.

Shot peening using glass or ceramic beads has proved very effective in preventing the type of crack initiation revealed by the structural test program in key locations of the aircraft. Based on its research AMRL developed a rework process offering the potential of repeatedly restoring the fatigue life of critical locations on the F/A-18 aircraft. A feature of the process is the requirement to polish surfaces prior to peening to obtain maximum benefit from the peening operation.

Peening is now a standard localised rework treatment on the F/A-18 and is used on numerous structural components with the biggest change being the progression from glass to ceramic bead peening. Ceramic bead peening is now used on all RAAF aircraft where localised peening is performed. To ensure complete coverage, a layout ink is used on the area to be peened which allows improved assessment of the area coverage. The area is peened twice to ensure saturation and coverage.

A robotic shotpeening technique was developed by L3 MAS for the CF-18 where the objective was to reach inside the aircraft and conduct a consistent shot-peening operation that could be certified to military aviation standards in various hard to reach areas. Using computer aided techniques, L-3 MAS modelled the environment, programmed the shot peening paths, and interfaced the process with systems to perform off-line programming of complex robot motions The robotic peening system has been implemented on the CF-18 program but no decision has yet been made on its use in the Australian program.

Successfully extending the fatigue life of the RAAF F/A-18 Hornets through the Structural Refurbishment Program is the result of the extraordinary level of research cooperation between Australia and Canada, the dedication of the scientists, engineers and technicians involved and now the very valuable collaboration of the Hornet Industry Coalition team members, Boeing Australia, BAE Systems Australia and L-3 MAS of Canada. The RAAF can be proud of their initiation and management of this program. We suspect the next phase, the replacement of centre barrels on 15 or so aircraft, will be handled equally expeditiously by the same parties.

By Tom Muir, Canberra