Double take

“Truthfully, the preparation is so time consuming that it seems wasteful to go through all that trouble just to produce one or two actual airframe parts,” said Carlo Cilliers, AOPA’s resident “airplane whisperer,” a technical advisor at the AOPA Pilot Information Center who, in his spare time, has built two award-winning aircraft from blueprints. “The idea was to build two airplanes side by side and gain some efficiency in the process.”

Cilliers, an airframe and powerplant mechanic with inspector authorization, teamed up with Rick Van Lehn, a recently retired Boeing 777 captain and devoted tailwheel pilot, to create a pair of Hatz Classic biplanes from plans. The two are longtime friends and hangar neighbors at AOPA’s home base of Frederick Municipal Airport in Maryland.

They also hoped to use their combined buying power to get package deals on engines, propellers, and avionics, and they shared shipping and other costs, too. The two builders and pilots also have some complementary skills. Cilliers, a master machinist, is a metal-bending magician. Van Lehn has a home woodworking shop, and the Hatz design uses wood extensively in its construction.

"We're not here to please the purists; we're here to please us." -Carlo Cilliers“We knew we could help each other out,” Van Lehn said. “Carlo could take the lead on most things, and I could help in a few other areas.”

The Hatz Classic appealed to Cilliers for two reasons. First, the low-and-slow flying, open-cockpit biplane was vastly different from the speedy, sleek, efficient Bushby Mustang II he’d already built and flown. (The Mustang II won a Bronze Lindy at EAA AirVenture in Oshkosh, Wisconsin, in 2016.) Second, the Hatz has a reputation for being difficult.

“I wanted to challenge myself and learn some new skills,” Cilliers said. “I wasn’t looking for something easy. The idea of a collaboration appealed to me, too.”

Neither Cilliers nor Van Lehn had flown a Hatz when they embarked on the project. And the idea of flying at all seemed far away when Cilliers picked up the first steel tubes that they’d eventually shape and weld into two identical fuselages.

He brought the long pieces home with the ends protruding from his beater Toyota pickup, a red rag serving as a warning flag for other drivers. Once there, he placed them in the garage next to a TIG welder.

“I’ve always loved welding,” Cilliers said. “It’s something I look forward to.”

Purely emotional

John Hatz designed and built the first biplane bearing his name in Wisconsin over an eight-year period beginning in 1959. His original CB-1 first took to the air in 1967, and it was meant to be a low-tech, low-speed, fun flying airplane powered by an economical 100-horsepower Continental O-200 engine. Later, the Hatz Classic included many refinements and could accommodate a larger engine, the 150-horsepower Lycoming O-320 engine among them.

Hatz biplanes had appealing touches such as a rounded tail and turtle deck reminiscent of larger, far more expensive, radial-engine Waco biplanes that had captured the imagination of pilots since the 1930s. In 1986, a Hatz biplane built by Rich Hansen raised the design’s profile when it won Grand Champion honors at EAA AirVenture.

About 150 Hatz biplanes have been built and flown over the years, and the Hatz Biplane Association sells plans for them, not kits.

Cilliers and Van Lehn made one big departure from the Hatz norm in their choice of engines. They decided early on to use a Rotec R2800 radial from Australia, a nine-cylinder, 150-horsepower engine selected for purely romantic reasons.

“There’s just something uniquely appealing about a radial-engine biplane that’s indescribable,” Cilliers said. “Most of my decisions involved in building an airplane are practical and technical. The choice of this radial engine was purely emotional.”

The two builders worked together, mostly at home workshops, for the first two years of construction producing an inventory of sub-assemblies. Their strategy of building side by side moved into high gear while fabricating the wood wings.

There were eight wings to make in total, and their learning curve was steep at first. It generally took each of them about one full day to make a single rib. But they soon streamlined their process into a slow-motion assembly line.

“It took us about a month to get the first wing together,” Van Lehn said. “It only took us a few days to do the last one.”

Aesthetic eye

The most difficult piece to fabricate was also the one that sets their airplanes apart: a metal speed ring that encircles the radial engine.

Contrary to its name, the speed ring doesn’t make the airplane fly faster. But it sure improves the looks, and Cilliers, the metal perfectionist, wanted it to be a gleaming work of art.

“I’d never used an English wheel before,” he said of the painstaking, frustrating-to-use, medieval-looking apparatus that, in the right hands, can pound a flat piece of metal into a smooth, complex shape. “But I kept at it and kept at it until I was satisfied with the result.”

Cilliers discarded his first couple of attempts before finishing the two that adorn both the airplanes now.

“We had very few remakes during the construction process,” Van Lehn said. “But the speed rings had to be done more than once to meet Carlo’s standard.”

Cilliers and Van Lehn have very different styles.

Cilliers jumps into each task and is comfortable with improvisation. He likes action and often figures things out along the way.

Van Lehn is a planner. He looks before he leaps.

They also learned a great deal about each other. Cilliers will keep working as long as there’s ginger beer to drink. Van Lehn relies on a variety of rock music from Spotify for motivation.

“You get to know a person’s thought patterns and personality when you build airplanes together,” Cilliers said. “Rick has an aesthetic eye and he’s got a sense about the details that make an airplane look good. I don’t have that kind of sensibility.”

The two made most of their big decisions through consensus. They both wanted radial engines and bought them new as a pair. They also wanted Dynon glass-panel avionics even though the modern instruments are anathema to biplane purists.

“The glass panel was actually a no-brainer,” Cilliers said. “We’re right next to the Washington, D.C., airspace so you want to know exactly where you are all the time. And modern avionics are lighter and far more reliable than old analog gauges. We had to have glass panels, even if meant the purists would disown us.”

They also weren’t focused on winning awards from judges who often place a heavy emphasis on historical accuracy. They wanted to build airplanes that they could enjoy flying on a regular basis.

“We’re not here to please the purists,” Cilliers said. “We’re here to please us.”

Exceptional craftsmanship

Cilliers set a goal of flying his Hatz to EAA AirVenture 2022 and worked furiously throughout the spring and early summer of that year to get his airplane ready to fly to the July event.

Van Lehn was a senior airline captain making long international trips at the time, so he put his project on hold while Cilliers surged ahead.

One of Cilliers’ last tasks was upholstery, and he took that on himself, even though he’d never done anything remotely similar.

“I bought an industrial sewing machine and a couple of [leather] hides and disappeared into the basement,” he said. “It’s amazing what you can learn on YouTube. The result wasn’t masterful, but I had fun doing it. Upholstery wasn’t as daunting as the English wheel, but it was still daunting.”

The first flight for Cilliers’ Hatz took place in May 2022, on the same day that the airplane received its airworthiness certificate.

A local pilot with extensive biplane and tailwheel experience made the initial flight, yet it didn’t go exactly as planned. The Rotec engine developed a major oil leak soon after takeoff, and the airplane trailed a steady stream of white smoke as it circled over its home airport.

When the airplane landed 20 minutes later, it had lost more than half its engine oil. Cilliers got busy addressing and repairing the problem, a blown oil seal, and subsequent test flights went smoothly. The airplane flew straight and true with obedient flying characteristics.

Cilliers began flying the airplane himself and tweaking its rigging until it flew “hands-off.” Stall characteristics were gentle and benign, and positive-G aerobatics were obedient and unsurprising.

“I’d never flown a taildragger that was so completely blind in the landing attitude,” Cilliers said. “That took some getting used to. But the airplane handles delightfully. It has the same Clark Y airfoil as a Piper Super Cub, and it flies like one. Even the airspeeds are almost identical.”

At the end of the FAA-mandated 40-hour test period, Cilliers flew the airplane to EAA AirVenture with longtime friend Claudius Klimt, with whom he had built and flown an AirCam. There, it was awarded a Bronze Lindy for exceptional craftsmanship.

Van Lehn’s airplane flew for the first time the next spring once he’d retired from airline flying. And unlike the smoky, abbreviated first flight of Cilliers’ airplane, this time the engine operated normally.

Since then, Cilliers continued to make improvements to his Hatz, and when he brought it back to EAA AirVenture in 2023, it won even higher honors, a Silver Lindy.

For you, by you

In sum, it took Cilliers and Van Lehn four and a half years to build their airplanes side by side. Was that quicker, more efficient, or less costly than doing so independently would have been?

Cilliers says he’s pretty sure it was, although he kept no real records.

“I think the second airplane went about 30 percent faster,” he said. “But I don’t log the hours I spend building airplanes because I just enjoy it so much. The bottom line that I had a fantastic time on this project, and having a partner made it better.”

For Van Lehn, the Hatz was the first and only airplane he’s built, and he doubts he ever would have started without the more experienced Cilliers encouraging and leading him throughout the long process.

“Building an airplane is something I’ve long wanted to do,” he said. “But doing it from plans is a huge job, and I probably wouldn’t have taken it on by myself.”

Now that their airplanes are finished, the two hangar neighbors have a long list of friends to take for invigorating, open-cockpit flights throughout the Mid-Atlantic region. They also expect to attend local aviation events, particularly those that involve turf runways well-suited to biplanes.

And although the two airplanes were built side by side from the same materials, they’re not identical. From the exterior paint to the interior dimensions, each airplane has small modifications that reflect its builder. And that makes flying them a singular experience for each builder/pilot.

“Flying an airplane that you’ve built is different because you know every weld and every glue joint,” Cilliers said. “Ergonomically, the airplane is highly customized because it was made for you and by you. There’s nothing else quite like it.”

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