# New forging dies and organic manufacturing improve aircraft wing spar support

/ Published March 10, 2017
Richmond, Va., 
In 2014, Warner Robins Air Logistics Complex, Robins Air Force Base, Georgia, and the F-15 Eagle System Program Office identified a critical requirement for the F-15 C/D model aircraft wing spars.  The spars, a critical structural component within the aircraft’s wing, were showing stress cracks. 

Air Force engineers performed a fatigue test.  The part failed the test, which led to a requirement for a recurring inspection of the spars using a depot-level ultrasonic procedure.  Engineers implemented a design change to the intermediate spar in production that eliminated the stress concentration responsible for initiating the crack; however, there was no retrofit program for earlier wings. 

So new wings going forward were fine; but how would technicians retrofit earlier wings?

At the time the stress failure was found, 84 C/D models were in service with the early spar configurations. Engineers were also losing confidence that the inspections were adequate to reliably identify and protect the fleet from the cracks.

Based on potentially inadequate inspections and aircraft flight hours with early configuration spars, Air Force engineers assessed the risk as serious and changed the depot inspection to a more intrusive, but highly reliable bolt hole eddy [electric] current procedure to be done during depot overhaul.

Over the past several years, technicians with the 572nd Commodities Aircraft Component Repair Squadron at the ALC performed spar repairs because the detected cracks were minimal in size/complexity, and new spars were often unavailable, said Gregory Noble, chief, Planning and Support Division, Customer Operations Directorate, Defense Logistics Agency Aviation at Warner Robins, Georgia.

“Spar supportability reached a crisis due to the lack of new spars while the severity of cracks was increasing,” said Noble.  With the increased severity of cracks, repairs became increasingly unlikely and the lack of replacement spars would critically effect wing overhauls.

Anticipating serious support challenges, DLA Aviation’s Planning and Support team aggressively pursued various support options with original equipment manufacturers, existing support contracts and partnering with the ALC’s 402nd Commodities Maintenance Group for organic manufacturing of the spars.

DLA Aviation Sustainment Specialist Clifton Ducre submitted organic manufacture requests for 10 each of the right intermediate spar in December 2014 and 10 each of the left intermediate spar a month later. The 402nd CMXG quoted a delivery schedule of 660 days. DLA Aviation awarded the organic manufacturing contracts to the Air Force in February and March 2015, respectively.  Based on the known requirements plus demand forecast intelligence provided by the F-15 SPO, the quantities of 10 each were sufficient to support maintenance requirements until commercial sources could be qualified.

Awarding the contracts was just the first step in the process.  The organic manufacture of the spars also required a specialized die forging for which there was no substitute and which had a substantial acquisition lead-time.  Air Force personnel worked with the original equipment manufacturer and the WR ALC Procurement Office to get permission to use forging dies for the required titanium forgings and to buy the forgings.  The forgings were delivered to Robins Air Force Base in January 2016 but required additional modifications before they could be transformed into wing spars.

The forged billet provided is a solid metal form of titanium. Although formed to resemble the needed spars, the forgings required additional milling to become a usable intermediate wing spar. 

Artisans from the 402nd  Maintenance Support Group and CMXG engineers converted a 5-axis Olympia milling machine, a machinethat can move a part or a tool on five different axes at the same time, to mill the approximately eight-foot spar from the forged titanium billet. 

The complex milling took roughly 400 hours and required many machine adjustments during the process to ensure that the part remained in tolerance and was manufactured correctly on the first run said Ronald ‘Mark’ Johnson, deputy director, 402nd CMXG.

The maintainers and engineers were critical in this effort, said David Foskey, 573rd Squadron director.  “If the part was one-fourth an inch longer, engineers could not have finished it on the Olympia machine,” he said.

With additional in-house support, through non-destructive inspection and coordinate measurement machine programming, Britni Miller, 573rdCommodities Manufacturing Squadron flight chief, noted that this was a total team effort.

“The 573rd CMXG Metrology Lab inspects first articles to ensure that they meet the specifications required for the finished product,” said Miller. “Spot checks are done based on the quantity of parts ran because over time, the machinery that produces these individual parts can shift slightly, become dull, or lose alignment in a way that causes problematic differences. The CMM is utilized as it can be programmed to inspect the parts bringing a high degree of repeatability and reproducibility.”

On Feb. 6, the 402nd CMXG successfully completed the required Form, Fit, and Function testing/inspection of the first right intermediate spar required under the contract terms.

The F-15 SPO Engineering office approved the test and Melinda “Mindy” Stahl, chief, Material Management , Commodities Aircraft Component Repair Support Branch, Customer Operations Directorate, DLA Aviation completed receipt documentation to allow the installed spar to remain on the wing after testing. 

With the successful completion of the right spar, 402nd CMXG personnel will now move forward with the organic manufacture and testing of the first left intermediate spar.  And, DLA will stand by to receipt the approved spar into the supply system so that it can be placed on the aircraft.