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Healing wounded wings

With more operational flying hours than any other military fleet in the world, the Canadian Forces (CF) has become industry experts and teachers at keeping older Hercules aircraft aloft – lessons other air forces, as well as the manufacturer, are drawing from.

The Canadian aircraft are a mix of 32 E and H models, acquired between 1973 and 1992, and have flown a combined total of over a million miles. Most of the fleet is under some form of restriction and five of the aircraft had been taken out of service. At the current operational tempo, another aircraft will drop out of service every four or five months.

While the CF await word on a contract for 17 new C-130J-30 aircraft from Lockheed-Martin, they still face the task of keeping many of the existing aircraft in the air. The long term plan is to have the current 13 CC130 H model aircraft available for a search and rescue (SAR) role from about 2010 to 2017, although LCol Bruce Cooke, the Canadian Forces Weapons System Manager, Transport and Helicopter, could not be definite about when the C130-J would come into service to allow that to happen.

“Rightly or wrongly, we’ve assumed that the aircraft will be delivered as of 2010, assuming that the contract is going to be signed, hopefully in the next three or four months,” LCol Cooke said, adding that the CF would then need time to bring the aircraft to Final Operating Capability.

In the meantime, the key maintenance challenge to Hercules airworthiness is centre wing cracking, which has proved to the main limiting factor of the aircraft. Until recently, LCol Cooke said, Canada and most other Hercules operators tracked wing life by actual flying hours. But that has changed dramatically.

“About five years ago, we found aircraft that were coming in with some exceptionally odd cracks and failures in key components of the structure of the centre wing box, and we said, ‘this seems to be a little premature from what Lockheed had said, based on their wing durability test,’” he recalled.

With a disconnect between the expectations Lockheed-Martin had created based on Hercules wing testing and the reality of what they were seeing, engineers sent their findings to both the manufacturer and the United States Air Force (USAF).

“USAF said, ‘Canada, holy cow, where you found small cracks we found whopping cracks’, so we were able to alert the world that we have some funny things happening on the wing that are occurring a little quicker than Lockheed originally envisioned,” LCol Cooke said.

It was clear that just looking at flying hours is not a good way to track wing life, because it is not the hours but the actual flying that puts stress on the wing. A new measurement called Equivalent Baseline Hours (EBH) was developed.

“Equivalent Baseline Hours is a very simple equation. It just takes your flying time of the wing, multiplies that by a severity factor and that gives you the EBH,” LCol Cooke explained.

There are some limitations to EBH as it is currently used. Not only is every type of flight different, Hercules operators use different severity factors. Taking SAR missions as an example, LCol Cooke looked at the reasons behind the difference. “The United States Air Force might say their SAR missions are going to take longer to reach altitude and spend a shorter time on station. So their mission mix is a little different and they might say that they actually fly a little harder when they’re down low – ‘we experience more yank and bank than you folks’ – so the severity is different,” he said.

There can be a 10% to 20% variation between EBH, “but it’s as close to a Rosetta Stone as we can get, and we have now proposed to Lockheed this year – and the USAF has agreed with this – that we are now going to refine EBH such that countries that want to compare apples with apples are going to start actually tracking individual aircraft, and we are going to cone out with a common severity factor approach,” he said.

Because SAR missions have a relatively high severity factor, the Canadian Forces will be monitoring wing usage closely, with the goal of bringing all the H model CC130 wings to approximately the same number of Equivalent Baseline Hours at the projected retirement date of 2017.

Dedicated onboard sensors, global positioning systems and flight data recorders have the potential to bring more certainty to wing sustainment programs by supplying more data to calculate Equivalent Baseline Hours. “Lockheed is already taking the lessons learned and they’re incorporating it in their J model. The J model has sensors on board that allows for fatigue measurement and they’re always updating those,” LCol Cooke said.

Looking at Canada’s contribution to Hercules endurance, LCol Cooke said, “we have taken the time to develop a capability with industry; we have taken the time to produce very good engineers both in DND and with industry. I’m really proud to say that Canada has done a lot in trying to further the engineering.”

SIDEBAR

Canadian ingenuity
The same flying hours that have brought the Canadian Forces’ Hercules aircraft to the limits of their endurance have created an opportunity for Canadian business to meet the challenge of extending the lives of an estimated 700 aircraft in the worldwide Hercules fleet.

Under its ‘Herc 2020’ banner, Edmonton-based SPAR Aerospace (L-3 SPAR) is refurbishing C-130 center wings for the Royal New Zealand Air Force, using its own processes and tooling. The Canadian Forces manage rather than replace CC-130 wings under the Wing Availability and Sustainment Program. LCol Bruce Cooke said SPAR has developed their own solutions based on Canadian inspection and improvement experience. “They’ve applied that and taken a different approach where they have gone with the New Zealand Air Force and said, ‘we are going to rebuild the wing.’”

While one part of the Canadian aviation industry is demonstrating an indigenous capability to refurbish existing wings, the Canadian Forces are working with Cascade Aerospace as the prime contractor to manage the existing Hercules fleet, under a performance-based contract. With a consortium of companies called ‘Herc Solutions’, Cascade offers a range of Hercules engineering solutions from Abbotsford, British Columbia.

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