Bemidji shop resurrects WWII planes, flaws and all

Scanning a P-47's full wing
Stefan Hokuf scans the full wing of a P-47 at the AirCorps facility in Bemidji in October. The wing's aluminum skin will have to be replaced thanks to spending 70 years in the jungles of Papua New Guinea. Scanning the wing allows the team to record its shape before starting the rebuild.
Courtesy of John LaTourelle | AirCorps Aviation

The P-47 Razorback fighter plane in Erik Hokuf's shed is in terrible shape.

Missions over the South Pacific during World War II wore the hefty plane out by 1944. It was decommissioned by the U.S. Government and abandoned in Papua New Guinea, a rotting marker of old conflicts.

What's left rests in pieces in Hokuf's shop. He owns AirCorps Aviation in Bemidji, a company that rebuilds WWII airplanes.

The Razorback spent the better part of the last century in the jungle, but Hokuf says it will fly again. When it does, he says it will be perfect, just as it rolled off the assembly line, down to one-seven-hundredth of an inch.

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"We'll replicate every piece," he said. "Even the flaws. That's the dream."

That level of perfection is possible thanks to a new piece of machinery the shop just bought called a HandySCAN from Creaform, a Canada-based manufacturer.

Some 3,000 pieces of the Razorback will have to be replaced. The dimensional nuts and bolts are easy to buy in bulk. But many are more complicated. Only a few dozen P-47s are still flying, fewer still of the early Razorback model.

Scanning a wingtip
Stefan Hokuf uses the new HandyScan 3-D laser scanner to build a 3D model of this P-47 wingtip at AirCorps Aviation in Bemidji.
Courtesy of John LaTourelle | AirCorps Aviation

The puzzle is getting ahold of parts to replace the ones ruined by 70 years in the jungle.

"In this business," Hokuf said, "sometimes we're dealing with the very last of something."

Instead of shelling out for those rare pieces, Hokuf's team borrows them from museums and collectors around the world and builds replicas. Before the scanner, that meant 40 hours with a slide rule and engineering software building a digital 3-D model, then piping that model into a series of computerized milling machines.

The scanner will cut that time drastically, generating a much more accurate 3-D model in just a few minutes.

Hokuf brought in HandySCAN technician Frank Pare to show his team of engineers how to the scanner works. Pare demonstrated on a pristine P-47 wingtip on loan from an aeronautics museum.

"Just move slow and steady," Pare said, "like you're spray painting."

Preparing a P-47 wing tip
Steve Wold, Stefan Hokuf and Frank Pare set up a P-47 wing tip at AirCorps Aviation. They'll use a new HandyScan Laser scanner to make a 3-D model of the piece, then build a new one for a rebuild.
Courtesy of John LaTourelle | AirCorps Aviation

He held the scanner like a barcode reader in the grocery store checkout line, casting a hatchwork of red laser lines down onto the shaped aluminum. It works by triangulating those lasers and mapping the data in a complex computer program.

"It acquires about half a million points per second," Pare said, moving the scanner slowly above the wing.

As he moved a model grew on the screen of a nearby laptop — exact down to the dimple in each rivet, and the tiny blemishes stamped by factory workers more than 70 years ago.

Steve Wold said the scanner marks the culmination AirCorp's search for the fully accurate rebuild.

As Pare demonstrated the machine, Wold strolled around the hulking P-47 pointing out the damage.

"You can see here where fishermen cut out chunks of the skin for lures," he said. "Someone signed their name over there on the wing."

Before the scanner arrived, it was his job to draw each of the borrowed replacement parts. His models guided Hokuf's milling machines and the metal workers. It's a difficult thing to get just right.

"I lay in bed at night wondering," he said, "Did I get every angle just perfect? Is it exact?"

Hokuf's whole company is built on that obsessive drive for perfection. Most of his planes are purchased as hulks by wealthy collectors from around the world. They pay Hokuf for the rebuild — it's the same story with the P-47.

Hokuf doesn't like getting too specific about the cost of his projects, but he's employed 24 people for four years in Bemidji, and only rebuilt two full planes. It's an expensive process, but a very accurate one.

A 3D model is seen on screen.
In just a few minutes, the HandyScan scans a perfect 3-D model of the P-47 wingtip. It's accurate down to one-seven-hundredth of an inch.
Courtesy of John LaTourelle | AirCorps Aviation

The AirCorps team is almost done with a P-51 — a beautiful warbird glistening with polish and new paint. That paint has the same chemical makeup as the original, though there's better material available. Even the inside of the aluminum skin is printed with the same lettering left by the original 1940's era manufacturing process.

The wiring is the same cotton and rubber coated copper used in WWII. A shuttered factory had to be reopened to make the stuff.

Rushed assembly line workers during WWII accidentally put a handful of blue stained rivets into the fuselage. The AirCorps workers counted those blue rivets and made sure the same number were mixed into their rivet guns.

"Anal-retentive is a workable term," said Chuck Cravens, "but we prefer 'exacting.'"

Cravens is the AirCorps resident historian. He said the crew always tried to get the little details right but never before had the tools to fully achieve their goal.

The obvious question is why. Why obsess over tiny details no one will see once the plane is done? Why buy a $40,000 laser scanner to exactly replicate ancient flight technology?

"I think of it like this," Cravens said, "We're rebuilding these planes for their story. If we aren't exact, we're writing fiction."

When the P-51 is finished and rolled away, work on the Razorback will start in earnest. Hokuf says it will take two or three years, then be flown to Minot for a new home with the Texas Flying Legends collection.

Now that he's switched out his slide rule for the laser scanner, Wold won't have to lay awake and night and worry.