Restoration specialist brings grounded warbirds back to active flight status

May 2013 - There’s nothing quite like the guttural growl of a vintage P-51 Mustang when the pilot opens the throttle and turns on the generator to “wake her up.” In the spirit of its fiery equine namesake, the plane surges against the brakes, its muscular body vibrating as prop blades slice the air and its V-12 Rolls-Royce Merlin engine roars to life. The pilot “S” turns the plane for visibility as he taxis into position. With the throttle at 2,300 rpm and the stick pulled back as far as it will go, the pilot must complete a number of pre-flight steps in quick succession. Opening the throttle to 40 in. of manifold pressure lifts the tail. As the throttle crosses 55 in., the plane’s sleek, metal body takes to the sky.

For award-winning restoration artist and fabricator Mike Vadeboncoeur, takeoff is a moment of truth—the ultimate test. Owner of Midwest Aero Restorations Ltd., Danville, Ill., Vadeboncoeur and his crew specialize in the painstaking job of disassembling and rebuilding World War II-era warbirds to original condition, right down to the last rivet, label and wire marking identification. But the work doesn’t stop there. They also restore the airplanes to modern FAA flight standards and safety regulations. A single project can take several years before the  aircraft is ready for its test flight. Over the last two decades, Vadeboncoeur has finished seven P-51 Mustang projects.

“The first time I completed a Mustang and watched it take off was actually pretty emotional,” recalls Vadeboncoeur, who was then 29 years old. Reaching that phase of a project can be nerve-racking, he says, because you are hoping everything will go well. Before a test flight, the Midwest Aero crew performs many landing gear retraction tests and ground engine runs to make sure the engine is operating within normal parameters. They also conduct safety inspections, check fluid levels, and ensure each bolt is properly torqued, secured and safety wired/cotter pinned. “But there is only so much ground preparation you can do before you have to take her to the skies,” he says.

Early roots

An F-6D Mustang (a later P-51 variant) called Lil Margaret was Vadeboncoeur’s first project, earning him both the Gold Wrench and Grand Champion awards in 1993 at the Experimental Aircraft Association’s Fly-In Convention in Oshkosh, Wis. It also prompted him to start Midwest Aero the same year. A graduate of the Spartan School of Aeronautics, Tulsa, Okla., Vadeboncoeur’s work for the University of Illinois Aircraft Maintenance Facility as a master sheet metal mechanic gave him a strong foundation in metalforming. But he says his passion for restoring World War II-era planes actually began when he was a boy. “A plane ride with a friend of my dad’s captured my imagination,” says Vadeboncoeur. “When I was 12 years old I became intrigued with the show ‘Baa Baa Black Sheep’ based on World War II ace Pappy Boyington and his squadron of Marine fighter pilots. From there my fascination with World War II aircraft accelerated rapidly and influenced my choice of career path.”

For his customers, most of whom are private individuals, Vadeboncoeur says the Mustang’s popularity is tied to several factors. “The plane has beautiful lines,” he says. “Among all the World War II fighters, it’s the most distinguished looking. The plane’s beauty plus its dynamic performance and remarkable legacy only enhance its status among collectors and history buffs.” Interest in the Mustang also fueled a growing demand for restoration and maintenance, a trend that first emerged in the 1980s.

To better understand Vadeboncoeur’s enthusiasm for restoring Mustangs and his customers’ obsession with owning and flying the airplanes, one has to consider the circumstances that gave birth to the warbird. 

In 1940, the British Purchasing Commission contracted with North American Aviation, today part of the Boeing Co., to build the P-51, which provided critical air cover to bomber squadrons that were open to attack during dangerous daylight bombing raids. “The prototype was designed, developed, produced and flown in just 117 days,” says Vadeboncoeur.

The first Mustang, designated P-51A, was equipped with an American-made motor. But the Allison engine lacked power above 15,000 ft., limiting the aircraft’s capability and relegating it to photo reconnaissance missions. Refitting the P-51B with a V-1650 Rolls-Royce Merlin engine more than doubled the aircraft’s service ceiling and allowed the plane to dominate the skies. “The Merlin’s two-stage, two-speed supercharger was a game changer,” says Vadeboncoeur. “The added horsepower combined with the Mustang’s aerodynamically efficient airframe made it unstoppable.” The aircraft was adopted by the U.S. Army Air Corps after the 1941 bombing of Pearl Harbor.

As a long-range fighter, the Mustang used bomber formations as bait to entice and engage enemy aircraft but was equally adept at low strafing runs. Subsequent P-51 C and D models also featured the Merlin engine. Eight different versions were produced altogether. The spunky muscle plane’s ability to easily repel and dispatch the enemy is credited with turning the tide of the war in favor of the Allies. The Truman Senate War Investigating Committee rated the Mustang as “the most aerodynamically perfect pursuit plane in existence.”

Congress created the U.S. Air Force in 1947 and all of its P-51 Mustangs were redesignated F-51. When the Korean War started in 1950, the Air Force still had 1,804 F-51 Mustangs in service. They flew 62,607 combat missions before the emergence of the fighter jet. Following that, the remaining Mustangs were scrapped or sold to foreign military. The last active Mustang was retired by the Dominican Air Force in 1984. Today there are 293 surviving P-51 Mustangs with 169 considered airworthy. 

Fabrication challenges

“These planes are living pieces of history that need to be preserved so we can show them to the next generation,” says Vadeboncoeur. “But it takes fabrication to bring them to life. You can’t call up the factory and order new parts—you have to make them.”

Vadeboncoeur admits the task, at times, seems insurmountable. He uses production manuals from the 1940s as a starting point. “During World War II, government funds supported mass production of parts for these planes,” he says. “We don’t have that advantage today. The tools themselves also can be costly.” During the 1940s, a steam-powered drop hammer or press was used not only to shape metal into heavy steel parts and thin metal stampings but also to produce hand tools. Other manufacturing processes included stretch forming and hydroforming. “We don’t need hundreds or thousands of parts,” Vadeboncoeur adds. “We may only need five parts. Our challenge is figuring out how to fabricate both the tools and the parts. We have to make them right and make them economically.”

When Midwest Aero takes possession of a customer’s Mustang, the first step typically is to open up the plane, remove its systems and take it down to its basic aluminum structure. The paint is removed and the structure inspected for corrosion and metal fatigue. Special attention is given to the longeron, a longitudinal structural component of the aircraft fuselage. “North American Aviation had issues with heat treating these components in the 1940s,” Vadeboncoeur says. “As a result, items like the longeron and extruded stringers and angles tend to have what we call inner granular corrosion. On most of our aircraft we change these components out.”

Midwest Aero fabricates its own fixtures out of welded steel tubing and thick aluminum plate. The fixture holds the aircraft in perfect alignment while the crew examines the fuselage and structural parts. Without its skin the P-51 becomes a light structure that can easily be twisted. “Riveting new skins to the plane’s skeleton is what gives the plane its structural strength,” says Vadeboncoeur. “The fixture, which sits atop a laser-leveled table, maintains the aircraft’s center alignment while we attach major components like the skins, wings and tail. Without that fixture, structural pieces could be slightly off, causing the frame to be twisted and the airplane to fly crooked.”

In addition to making its own tools, Midwest Aero is equipped with standard items like press brakes, shears, shrinking and stretching machines, mill lathes and small forming hammers. If Vadeboncoeur needs to hand form a part, he’ll make a tool for it and form the part in a dead soft condition. The part is then sent for heat treating to bring the component back to T4 condition for airworthiness. “One of the benefits of the Mustang being so popular is that there are a few companies that have tooled up to produce some of the more complicated parts,” says Vadeboncoeur. “Sometimes it’s easier for us to buy some of the parts we need, although there isn’t a lot of complexity involved with the P-51 compared to some of the other World War II types.”

Vadeboncoeur’s current project, a P-51D, is scheduled for test flights early this summer before making its maiden flight in July at EAA AirVenture Oshkosh 2013. The P-51D was originally introduced in 1944 and became the most famous of the Mustang versions. Sporting the now signature tear drop canopy and a more powerful (1,790 hp) Packard Merlin engine, the fighter plane could travel 437 mph and carry a total of six .50-caliber machine guns.

The road to restoration

Midwest Aero’s P-51D sat dormant for many years as an outdoor display in Uruguay. The plane suffered from widespread corrosion. “Once we removed the paint and evaluated the structure, we were able to determine which pieces needed to be replaced versus repaired,” says Vadeboncoeur. “The interior was reprimed and painted to bring the plane back to its original colors. During World War II they used a chromate primer to protect the aluminum. We match the color of the World War II primer but use a modern product because we feel it increases the longevity of the plane.”

Although new longeron assemblies, ribs and other key components were fabricated, the crew’s goal is to use as much of the original material as possible. “As long as the new parts are properly fabricated, it’s not difficult to marry new material with old,” Vadeboncoeur says.

Midwest Aero sources 2024 T3 aluminum in 4 ft. by 12 ft. flat stock. The shop also buys sheets in varying thicknesses. Specifications call for 0.080-in. material at the front of the fuselage and 0.040-in. material closer to the tail.

“If we have a good candidate skin, we’ll use the original skin as a pattern by laying it over top of the new metal to pick up the holes,” Vadeboncoeur explains. “We use shears to cut and trim the material to fit. Some of the skins are longer and don’t follow straight lines. In those cases, we use the shear to cut the skin as close as possible to the desired measurement then sand and file it for a perfect match. It’s very labor-intensive.”

The exterior skin of the plane’s body is then flush riveted. Aluminum more than 0.040 in. thick is machine countersunk. Skins less than 0.040 in. thick are subjected to a dimpling process, which forms the shape of a countersink without removing any material.

The wings are treated in a similar fashion. Once all of the skins are riveted up and the plane is structurally sound, the crew begins fitting the aircraft with components that were removed at the start of the project.

“How much of the skin is fabricated from new aluminum depends on what the customer wants,” Vadeboncoeur says. “If he wants a high-polish exterior, old material won’t lend itself to that because 1940s metal has too many scratches and dents. On an airplane that will carry a paint scheme, you can get away with using older skins. Our P-51D will be painted so it has a combination of both new and original skins. The goal is always toward making the aircraft fly at the end of the day, so we strive to make the plane as authentic and safe as possible.”

Midwest Aero uses a combination of sheet metal rolling, hand forming and shrinking to fabricate the aircraft’s side cowling, which surrounds the exhaust stacks and is made from stainless steel. “Stainless is our least favorite metal to work with,” Vadeboncoeur says. “When you are used to working with aluminum, it’s like going from butter to ice.”

The company outsources the compound fairings or fillets—the curved components that produce a smooth profile and reduce drag at the wings and tail. “These are complicated, beautiful pieces that must be Yoder-hammered,” says Vadeboncoeur. “It’s a true art form that requires a craftsman who can hammer with minimal marks. Fit-up also can be challenging, requiring us to stretch or shrink the piece to fit before we polish it. We use a similar process on the cowling that encloses the engine.”

Midwest Aero is in the process of painting the fuselage of its current P-51D project before performing the electrical work required in the cockpit. The crew finishes as much of the work as possible with the cockpit and wings before mating the wings to the fuselage, reinstalling the engine and making the landing gear functional.

In addition to fabrication work, Midwest Aero is known for the authenticity it brings to each project. “We go to extra lengths to make each aircraft authentic because we are literally bringing history back to life,” Vadeboncoeur says.

Mark of authenticity

No detail, regardless of how small, is overlooked. In 1940, manufacturers used a metal marking technique to identify material, size and other specifications, as well as the manufacturer’s name. The stamps ran in red lettering every 8 in. along the aluminum sheets that were assembled on the aircraft. The red ink would bleed through the yellow paint so the marks remained legible. “We replicate that process on our Mustangs,” says Vadeboncoeur.

Today’s aviation hardware is cadmium-plated in an iridescent gold color called CAD 2. Typical 1940s hardware was plated in a straight silver color called CAD 1. Midwest Aero orders new hardware and sends it to a certified aerospace plating facility for replating to CAD 1 specifications. The company also pays special attention to its wiring. “Wire from the 1940s had a brown woven cloth covering,” says Vadeboncoeur. “We take new wire and have it cloth-covered to look just as it would have in World War II. Then we hot stamp the wire with the proper marking. We also found a World War II specification for a dye process for bolts. During the 1940s, manufacturers would Magnaflux hardware lots. If a certain number of bolts passed inspection, the entire hardware lot or batch was dyed orange. We recreate that dye and use it on our hardware to replicate that look.”

While Midwest Aero is committed to authenticity, the company is looking to the future for tools and technology that support its metalforming requirements. “As a fabricator you have to keep an open mind to consider resources, technology and people that can help you accomplish your task,” says Vadeboncoeur. “New computer technology is coming online that has the potential to help us make tools and parts more efficiently and cost-effectively. There are pourable mold materials that can help lower tooling costs and 3-D printing that is changing the way prototypes are made. We’re not engineers but we’re very interested in learning how these techniques could make our lives as restoration specialists easier.”

Like his airplanes, which are a mix of both old and new materials and metalforming methods, Vadeboncoeur hopes to do more than just preserve history. “I have young people on my crew along with older, experienced fabricators,” he says. “True art work is taking flat pieces of metal and welding them in such a way that they look like one piece. In addition to making history live again through these planes, I also want to engage the younger generation and excite their interest in learning the fabrication skills we’ve developed over the years for forming and shaping metal.” FFJ

 HOW THE MUSTANG GOT ITS NAME

Ever wonder how the P-51 Mustang came by its moniker? Legend has it an anonymous member of the British Purchasing Commission, influenced by his love of Zane Grey westerns, bestowed the name Mustang on the nimble fighter. Grey, considered the father of the Western novel, wrote more than 60 adventure novels painting an idyllic view of the American frontier that also featured wild horses, or mustangs.  The U.S. Army Air Corps gave the aircraft its P-51 designation—P for pursuit—along with the name Apache. However, the name Mustang stuck and was later officially adopted. 

Like the P-51, the staying power and endurance of the mustang horse and its Spanish descendants is legendary. As such, the link between horseflesh and metal-skinned machine, created by the etymology of a shared name, bears a closer look. The Spanish mustang is a direct descendant of horses first brought to the New World in the early 1500s by Spanish explorer Don Hernando Cortes. Carrying orders from the king of Spain to conquer North America, Cortes and his conquistadores hit the shores on highly trained, intelligent mounts. History records that Native Americans fled thinking “each horse and man was one evil monster.” Cortes is said to have sent word back to the king stating, “Horses were our salvation. After God, to the horses belonged every victory.”

The breed’s progeny became the original American Indian warhorses, buffalo ponies, pony express mounts and cow horses. As these horses spread across the West, some broke free and ultimately became known as mustangs, stemming from the Spanish word mesteño, which means wild or stray.

The versatility and strength of the breed, honed in the wide-open stretches of the Wild West under nature’s brutal hand, has produced a hardy horse with the aptitude to deliver superior performance in almost any equine field. The mustang horse is famous for its accomplishments on the ground but its aluminum namesake, the P-51 with its string of airborne firsts, is undoubtedly the most famous warbird in history. 

Superior speed, long-range endurance and agile maneuverability gave the P-51 unparalleled skills as an interceptor, ground attacker and reconnaissance aircraft. It was the first single-engine plane in Britain to penetrate Germany, the first to shadow heavy bombers and the first to wage a successful large-scale sweep against all enemy fighters. The P-51 Mustang’s legacy of helping to win a world war makes its name somehow appropriate, and in the aftermath of Cortes’ words about victory, somehow prophetic.

For more fabricating photos on the P-51, check out our Facebook gallery.

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