By Marsha Childs and Frank Taormina
FRCSE Public Affairs

Jacksonville, Fla.—Fleet Readiness Center Southeast (FRCSE) has pioneered a repair solution to fix F/A-18 Hornet internal wing cracks thanks to the collective creativity of its innovative workforce.

The wings of a Hornet, not unlike those of a bat, are covered with a durable skin to protect the underlying structure or “bones.”

When the wings become damaged, it makes flight risky at best for the military aviator. Stress corrosion cracking is the main culprit, typically caused by water intrusion from condensation occurring in the operating environment.

The Hornet’s inner wings are comprised of a series of aluminum spars, the main structural components held together by metal ribs. Spars are placed at right angles to the fuselage—the body of the plane—to carry flight loads and the weight of the wings while on the ground.

When wing spars develop cracks three inches or longer, they must be repaired or replaced. Cracks are detected visually or using nondestructive inspections such as film or real-time X-ray and ultrasound screenings.

Small wing spar cracks were first observed in 2004 at Fleet Readiness Center Southwest (FRCSW) in San Diego. The two depots joined forces to X-ray 40 wings on Hornets undergoing maintenance and repairs at both facilities.

Based on those findings, two types of repair methodologies were developed: the skin-on and the skin-off repair.

Skin-on repairs are used for cracks three to six inches in length. The wing’s composite covering is kept intact. The wing fasteners are removed and the holes are “cold worked” by pulling a steel mandrel, shaped like a baseball bat, through the holes usually aided by a hydraulic gun.

The mandrel compresses and changes the molecular structure of the material. This process increases the material’s density and installs a residual stress field for added strength.

Skin-off repairs are used for cracks seven inches or greater. The wing’s covering is removed and the defective spar or section is replaced.

During a routine wing inspection in January 2008, FRCSE artisans detected a 12-inch crack in the inner number four intermediate wing spar, a fissure much too large to repair. The challenge lay in finding new replacement parts, not available from the Navy or from the original manufacturer, the Boeing Company.

The creative team decided if they could not buy the parts, they would build them, more than 50 in all. These included not only the spars but also the fixtures, formers, ribs, straps and a whole host of tools and tooling systems to support the repair.

Overhaul and Repair (O&R) Shop Supervisor Buster Hathcock said, “It was important to make sure a repair of this magnitude was economically feasible. We knew that once we completed the first spar, future spar repairs would go much quicker, so it turned out to be a win-win.”

The Tool Engineering and Computer Numerically Controlled (CNC) Programming Branch Head Bill Sowell and his team created prototypes for the parts using computer-aided design files supplied by Boeing.

The artisans use a 3-D prototype printer to “grow the part.” The resin and powder model ensures the part’s proper form, fit and function without the expense of fabricating a metal component only to later find a design flaw.

Aerospace Engineering Technician Phil McLane authored the draft Repair of Repairables (ROR) guidance for the Hornet’s inner wing repair. The document includes installation inspection requirements along with processes and procedures for the rework.

The ROR guidance is also being used by other Navy facilities and Boeing. McLane said the guide explains, “This is what you are going to do and this is how you are going to do it.”

He credits Process Engineer Carol Brooks, the project manager, for her strong support. “We take Phil’s requirements and create the tooling and equipment to make the process work,” Brooks said.

Mechanical Engineering Technicians Michael Smith and Mitch Maxson designed the prototypes of fixtures and tooling to support the rework. They not only designed new parts, but in some cases they improved the design of existing ones.

Maxson recognizes the enormity of the project and the many contributions of personnel throughout Naval Air (NAVAIR) Systems Command. “It is a work in progress as some of the tooling isn’t in existence yet. As you find more problems you develop more tooling to solve them. It is a group effort,” he said.

Before any repairs could begin, CNC Tool and Die Shop machinists John T. Martin and Clifford Shinskie had to construct a wing fixture designed to provide structural stability and prevent warping. This was a critical step in the process.
//More//

By June 2008, the Machine Shop had fabricated the first-ever replacement wing spar using a five-axis milling machine. Following final inspection and approval, the piece was sent to the Plating Shop for finish coatings and on to the Paint Shop.

In early August, sheet metal artisans Bill Anlage and Wayne Lamar removed a six-foot section of the damaged inner spar and spliced the replacement section to the existing structure.

Because of this innovative maintenance solution, the grounded F/A-18 Hornet was returned in November 2008 to its custodian, the Air Test and Evaluation Squadron (VX-9) in China Lake, Calif.

Test pilot and FRCSE F/A-18 Production Officer Cmdr. Mitch Conover who deployed to Iraq from May 2008 to March 2009, knows all too well what a grounded plane can mean for troops on the battlefield.

“It throws a wrench in your operational flow and it can put troops on the ground requiring close air support in jeopardy,” he said.

The expertise of many trades was needed to accomplish this unprecedented restoration. The FRCSE workforce identified and targeted a major repair issue and tackled it head-on.

With five intermediate wing spars currently in production, the FRCSE Industrial Business Office sees the potential for establishing new business opportunities. The facility now has the capability of manufacturing spars and most of the accompanying parts needed for repairs.

Business Management Specialist Larry Hanks is working with Boeing on the Fleet Integrated Readiness Support Team (FIRST) project. When finalized, FRCSE will fabricate the repair parts and supply them to Boeing.

In turn, Boeing will prepare wing spar kits to include the spars and other milled parts from the depot, as well as additional items such as fuel tubing needed for the repair. The kits will be returned to FRCSE to enhance production capabilities and streamline efficiency.

“Anything that brings in work for the depot is good for us,” said Hanks. “It is also great for the Fleet.”

FRCSE continues to lead the way in the maintenance and repair of military aircraft. Its enhanced responsiveness and agility to meet Warfighter needs is critical to the maritime mission.

//USN//

Contact Judy Alexander at 904-790-4835 for photos.
CAPTIONS

09-037B:
FRCSE Machinist Scott Orr fabricates a wing spar segment on Sept. 10, only the second to be fabricated at the facility. (Photo by Vic Pitts)

09-037F:
Mechanical Engineering Technicians Bryan Berry (left) and Jamie Rupert (right) conduct a laser inspection on a milled aluminum wing spar. (Photo by Vic Pitts)

09-037G:
Sheet Metal Mechanics Wayne Lamar (left) and Bill Anlage (right) splice in a wing spar section on an F/A-18 Hornet. (Photo by Vic Pitts)

09-037H:
O&R Supervisor Buster Hathcock (left) and Aerospace Engineering Technician Phil McLane (right) use a three-dimensio