173rd Fighter Wing structural innovation helps keep aircraft aloft

  • Published
  • By Master Sgt. Jefferson Thompson
  • 173rd Fighter Wing

For years, structural maintainers have emerged as artisans of sorts, creating parts by hand, meticulously shaping them from custom wood forms and delicate hand-tool work.

They gently tap away with a small hammer, slowly giving shape to a sheet of aircraft-grade aluminum so it will slide into the tight confines of an F-15 Eagle fuselage with an expected tolerance of .005 of an inch.

This is necessary because of the thousands upon thousands of parts that make up an F-15C, many of them don’t exist in the supply system any longer—they haven’t for decades.

“It’s a 50-50 shot when you need a part, that it’s out there,” said Master Sgt. Paul Allen, 173rd Fighter Wing structural maintenance technician.

One such part is a fairing rib, a semi-circular part originally stamped from a sheet of aluminum with three-dimensional relief. It’s a part that sustains damage in refueling operations when the boom cracks into the aircraft—a somewhat common occurrence—creating an ongoing demand for fairing ribs.

Allen and his structural maintenance co-workers make new ones. First they cover the part with tape, then carefully cut away a section to give them a rough pattern for the new part, and then trace that part on a new piece of metal. Once traced, they cut it from the sheet with hand-tools and file it to match, or as close as they can get. Allen says it’s really not possible to get to .005 of an inch this way—the acceptable tolerance for this part.

Now this flat piece of metal needs to be formed, so they carefully hammer it to shape around a mold. First, they tried a hard plaster cast, but it cracked when they hammered the sheet metal against it. They got it done though, as they have for years now—27 man-hours later.

Today, emerging technology can shorten that process to seven hours.

It begins with a better way to assess the part’s exact dimensions—enter a brand new scanning arm with a mounted camera and an attached computer, which can map a part perfectly rendering it in three dimensions. A mold is created using the same software and printed using the brand new 3-D printer located not five feet away. This printed part takes the place of the wood mold.

“We’re definitely using innovation to save time and money,” said Master Sgt. Joshua Fuhrer, shop supervisor. “If you think about carving a tool from wood, that’s something that goes back to the 1950’s, now we are printing parts in a matter of hours and that’s cutting edge.”

And this mold is very strong. Printed from a carbon filament, it proves vastly more durable than a wood mold.

The team relies on that strength to utilize another piece of time-saving technology, a “smash-box.” It’s something Tech. Sgt. Michael Jordan brings to the shop from his experience at Rogue Aerospace Engineering, the company he runs specializing in helicopter repair and part fabrication when he’s not wearing the uniform on drill weekends.

The “smash-box” is a reinforced steel box, lined with a thick rubber mat and closed with a reinforced “lid,” also made of steel. The rubber used is very high durometer and does not easily deform, it’s difficult to make any indentation in it even with, for example, a screwdriver. But when placed in a 100-ton press, that same rubber flows around the mold in a nearly fluid state, which shapes the accompanying part perfectly—every time.

“Being able to reproduce the parts and get the same outcome every time is very valuable,” Jordan said. “For the Air Force, not just the F-15 fleet.”

The reason he says it represents value to the Air Force is because once a part is printed and mapped those files can be transferred to another unit when they need to replace the same part.

Allen envisions a near future when units will share these files frequently creating a platform within the community of Air Force structural maintenance, capitalizing on the initial effort being “crowd-sourced” across the fleet and beyond. He goes on to say he doesn’t see a reason why it should be confined to career field or service, and it may likely be beneficial to the whole of the Department of Defense.