Airplane Almost No One Knows, Part One

Ask a hundred pilots to name a plans-built open-cockpit biplane and most will land on the Pitts, the Starduster, or the Skybolt. Very few will say “Hatz.” The design has been flying since 1968, has won more than two dozen Lindy awards at Oshkosh, and is administered today by an active international association — and it remains, by any fair measure, one of the least-known homebuilts of its era. That obscurity is not a knock on the airplane. It is a consequence of how the Hatz came to exist and how it has been passed hand to hand ever since: never marketed hard, never turned into a factory kit business, kept alive instead by a small community of builders who found it, built it, and told a friend.

This is the first of two parts. Here I trace where the airplane came from — the man who designed it, the airplane he was chasing, and the chain of people who kept his drawings in circulation after he was gone. Part two covers the family the design has since produced and what it takes to build one today.

The Man And The Airplane He Wanted

John Hatz was a flight instructor, airport manager, and A&P mechanic from the Merrill and Gleeson area of northern Wisconsin. He owned an OX-5-powered Waco 10, a 1920s open-cockpit biplane, and he loved the way it flew — but not what it cost to feed, maintain, and keep in the air. Around 1957 he began sketching an airplane of his own: a two-seat biplane with the look and handling of the grand ships of the 1930s, sized and powered so an ordinary person could build it and fly it without a large-displacement engine or a large bank balance.

Hatz stated the goal plainly in his own design notes: “a two place with generous wing area — enough to make flying a pleasure on as little as 85 HP,” and “a straight-forward design with simple details and a minimum of time-consuming jig work.” Those two sentences explain almost everything about the airplane. The generous wing area — 178 square feet on a 25-foot span, a flat-bottom Clark Y airfoil, the same section Waco used and the same one under the wing of the Spirit of St. Louis — is what lets the airplane fly well behind a small engine. The simple details and minimal jig work are what put it within reach of a first-time builder working alone in a garage.

He built it the way the Wacos were built: a welded 4130 steel-tube fuselage and tail, spruce wing spars with wood truss ribs, and doped fabric over all of it. He gave it tandem seats with dual controls, bungee-cord landing gear, and a small shelf in the front cockpit for an overnight bag. It was not fast and it was not aerobatic in any serious sense. It was a pleasant, honest airplane meant to be flown low and slow on a Sunday afternoon, and it did that job on as little as 85 horsepower, exactly as designed.

The work took most of a decade. Sources put the design-and-build span at roughly eight to eleven years, spare time only, and the prototype flew in the spring of 1968. It was powered by a small Continental — most accounts say 85 hp, a few say 65 — and that engine gave the airplane its name. CB-1 stands for Continental Biplane, first design. Hatz’s daughter had a name of her own for it. She called it “Happiness,” and the name stuck to the prototype.

A note on the record here, because the sources do not fully agree and I would rather flag it than smooth it over. Most accounts, including EAA’s fiftieth-anniversary retrospective, put the first flight in the spring of 1968. Aeropedia dates U.S. Experimental Amateur-Built certification to April 18, 1968, with first flight the next day. AOPA’s 2024 feature says 1967. The weight of the evidence favors 1968; I note the 1967 claim rather than bury it (EAA Hangar Flying; Aeropedia; AOPA).

Why Almost Nobody Sold It

The central fact of the Hatz story — the one that explains its obscurity — is that John Hatz had no intention of going into the plans business. He built the airplane for himself. There was no company, no advertising, no booth at Oshkosh selling drawings. For most of a decade the CB-1 existed as exactly one airplane, admired by the people who saw it and unavailable to everyone else.

That changed because of one man. Dudley R. Kelly, an engineer from Versailles, Kentucky, and the owner of a de Havilland Gipsy Moth, saw the Hatz at the Antique Airplane Association fly-in at Blakesburg, Iowa, in 1977 and recognized what it was: a genuinely buildable modern biplane with no plans behind it. Kelly convinced Hatz to let him produce proper drawings.

What Kelly did next is the reason the airplane survived at all. He hand-drafted a full set of plans directly from Hatz’s prototype — measuring the actual airplane, recording weight-and-balance data and flying-wire dimensions, and drawing a full-scale wing-rib template so a builder could lay a rib out one-to-one on the drawing itself. These were not marketing drawings. They were a working set produced by someone who understood that the viability of a homebuilt design depends on the quality of its plans. Kelly and Hatz shared the plan-sales profits for several years, and Hatz eventually transferred the rights to Kelly.

There is a detail in those drawings worth pausing on, because it tells you what kind of plans they are. Kelly drew the wing rib full-scale, one-to-one, so a builder could lay the actual spruce and cap strips directly over the drawing and build the rib on top of it — no scaling, no interpretation, no room to introduce error in the most repetitive structural task in the airplane—the work of someone building for other builders, not for a catalog. It is also, in a small way, why so many Hatz wings have come out right in garages and hangars where the builder had never built an airplane before.

So, from the beginning the Hatz was propagated not through a company but through a person — first Hatz, then Kelly — who took it on essentially as a labor of conviction. That pattern, one committed individual carrying the design forward at a time, repeats through the entire history of the type. It is why the airplane has never been famous and why it has never disappeared.

John Hatz did not live to see most of what his design became. He died in 1989, at 64, in a car accident. Recognition came late: Wisconsin inducted him into its Aviation Hall of Fame in 2024, thirty-five years after his death and fifty-six years after his airplane first flew.

The Airplane Finds Oshkosh

An amateur design becomes visible in one place above all others: the flightline at Oshkosh, where the best-built examples win Grand Champion and Lindy awards and featured in Sport Aviation. The Hatz’s national profile can be traced through those awards, and the breakout came in 1986, when Rich Hansen’s Hatz — an airplane he called “Tizzy Lish” — won Grand Champion at Oshkosh. Hansen was not a one-time builder; he went on to build three Hatz biplanes over his life, which tells you something about how the type takes hold of the people who build it.

The wins kept coming. Steve Lund’s Hatz, modified to take a vintage Kinner radial, was Grand Champion at Oshkosh in 1992. Over roughly the next three decades, Hatz-family airplanes accumulated more than two dozen Lindy awards at AirVenture — an extraordinary record for a design that was never seriously marketed. The awards did not make the airplane a commercial product. They made it a known quantity among the people who care about open-cockpit biplanes, which is a smaller world, and exactly the world the Hatz lives in.

That world is not confined to the United States. A French builder, Michel Pallier, spent 13,000 hours over 22 years building a CB-1 — from age 22 to age 44 — and was recognized in 2024 as Grand Champion Plans-Built at the Euro Fly-In in France, then awarded the FAI’s David Faulkner Bryant Diploma in October 2025. There are Hatz biplanes flying in Switzerland, Australia, Canada, and New Zealand. The design’s reach is genuinely international; its numbers everywhere are small.

How Many, And Who Keeps Track

Nobody knows exactly how many Hatz biplanes have been built, and the honest answer is that the sources disagree. Jane’s All the World’s Aircraft and Wikipedia put CB-1 construction at roughly 150 as of the early 2010s. AOPA’s 2024 feature independently says, “about 150 Hatz biplanes have been built and flown over the years.” A Swiss builder-history site says more than 200 across all variants; another photo archive says over 100; EAA’s fiftieth-anniversary piece says more than 100 are currently flying. The spread reflects the reality of amateur construction over more than five decades: builds that were started and never finished, airplanes registered and then sold, and no single authority counting heads. Put the total somewhere in the low hundreds and you are close enough.

Tracking that scattered fleet is the work of the Hatz Biplane Association, a nonprofit volunteer organization whose stated purpose is to educate the public about the history and construction of the Hatz and its variants and to keep the design flying. The Association publishes a quarterly newsletter, The Hatz Herald, runs an online builder forum, and issues serialized plan sets. Annual membership is $25, due each January, and it comes with the newsletter and a roster of fellow builders — “Hatz Nutz,” in the group’s own phrasing — so a builder in one region can find another nearby.

The Association is small and it is unmistakably a community rather than a company. Its 2024 officer list runs from a president in Peshtigo, Wisconsin, through four U.S. regional directors to a director for Europe in Switzerland and one for the Pacific in Australia. Its flagship gatherings are the Pietenpol/Hatz Reunion at Brodhead, Wisconsin — hosted with EAA Chapter 431, and run again July 17–20, 2025 — and AirVenture at Oshkosh. At Brodhead the group holds its membership meeting, hands out completion plaques to builders who finished airplanes that year, and makes small charitable donations: in 2024, $500 each to EAA Chapter 431, the Kelch Aviation Museum, the Vintage Aircraft Association, and a youth hangar project.

The organization’s own history mirrors that hand-to-hand character. It grew out of a West Coast Hatz club, became the American Hatz Association around 1999, and is now simply the Hatz Biplane Association — the same design, carried by successive volunteers as the earlier caretakers aged out or passed on. When Dudley Kelly died in 1998, his widow, Thelma, kept selling plans for a time before the Association took over distribution; the group’s mission statement still names its purpose as the “perpetuity” of the Hatz and its variants, which is an unusual word to find in a mission statement and an accurate one here.

That is the texture of the thing—a few hundred people, spread across four continents, who chose the same airplane and organized themselves to help each other build it, fly it, and pass it on. The plaques at Brodhead and the four-figure donations to a local aviation museum say more about why the Hatz has survived than any specification sheet.

What Comes Next

The design John Hatz drew for himself has since branched. Dudley Kelly produced a simplified version under his own name. A Texas builder named Billy Dawson refined the airplane into something closer to the 1930s Wacos that Hatz had admired, and won Grand Champion with it. A Wisconsin builder named Mark Marino reengineered it to fit within the Light-Sport rules so a Sport Pilot could fly it, and builders since have hung small radial engines on the nose — including the 124-hp example in these pages — for the sound and the look of a bygone era.

Those variants, what separates them, what it costs, what it takes to build one, and how to get the plans in 2026, are the subject of part two of this story. In addition, we’ll have builder’s stories and comments, along with more fine photos of the Hatz biplanes.

---

This feature first appeared in the 2026 September Issue of KITPLANES magazine.