On the morning of May 4, 1928, a cream-colored monoplane was positioned into a south wind at Curtiss Field on Long Island, New York. The pilot was Leonard Warden Bonney, 44 years old, an experienced aviator who had learned to fly from Orville Wright himself in 1910 and held Fédération Aéronautique Internationale license number 47. The aircraft he climbed into that morning was unlike anything that had ever flown — or, as it would prove, would ever fly successfully. It was his life's work, his dream crystallized in corrugated aluminum and hydraulic tubing and an obsessive love of birds. It was the Bonney Gull.
The Gull took off successfully into the south wind. It climbed to perhaps 100 to 150 feet. Then it wobbled, fishtailed, nosedived, and struck the ground. The cream-colored aircraft broke apart on impact, its wings outstretched like a mangled gull. Leonard Bonney was killed.
He had spent four years and more than $83,000 — some accounts say closer to $100,000 — building a machine that flew for less than a minute. But the ideas embedded in those folded, articulated, hydraulically-controlled wings would outlive him by decades. They are still flying today, in fighters and carrier aircraft and variable-sweep bombers that their designers may not know owe a conceptual debt to a man who kept pet seagulls on Long Island in the 1920s.
The Man Who Studied Gulls
Leonard Bonney's credentials as an aviator were impeccable. He had flown with the Wright Exhibition Team as early as 1910 — those barnstorming pioneers who toured America demonstrating powered flight to a public that still found it miraculous. He served in the First World War with operational experience. He had instructed students in the most unforgiving of all aviation activities: flight training, where a moment's error kills both teacher and pupil. He was, by any measure, a man who understood aircraft.
Which makes his decision in the mid-1920s all the more remarkable. Despite twenty-five years of evidence that the Wright brothers' approach — rigid wings, separate control surfaces, braced structures — was the right way to build flying machines, Bonney looked at the birds and decided humanity had been doing it wrong.
He began keeping and studying live seagulls, observing how they managed lift, roll, and braking. He noted the gull's extraordinary two-to-one lift-to-weight ratio. He experimented, adding weights to captive gulls to understand the relationship between wing shape, loading, and performance. He became convinced that variable wing geometry — wings that changed shape in flight as a bird's do — was the key to genuinely efficient flight, and particularly to the short takeoff and landing performance that conventional fixed-wing aircraft of the era conspicuously lacked.
In 1925 he began building models. In 1926 he began the full-scale aircraft, working with the Kirkham Company of Garden City, New York — a firm with its own engine manufacturing capability. He tested his ideas in the wind tunnels at MIT and the Daniel Guggenheim School of Aeronautics at New York University. He had the Gull registered under the special designation K-1783, receiving a temporary special-class license because no existing certification category could accommodate its unorthodox design.
The Aircraft: What It Was
The Bonney Gull was a low-wing cantilever monoplane with side-by-side seating for two, dual controls, and an upholstered cockpit enclosed by a large streamlined greenhouse canopy. Construction was primarily of corrugated duralumin — the aluminum alloy used in Junkers and Ford Trimotor airframes. It was powered by a 180-horsepower Kirkham radial engine in the nose. The landing gear used single streamlined struts with independent braking and a large, steerable, fully faired tail wheel.
In silhouette, it was not dramatically unusual — contemporaries compared its profile to the Alexander Bullet, a sleek low-wing monoplane of the era. The highly tapered, swept-back wings with pronounced dihedral and large tapered tail surfaces gave it an undeniable elegance. The tail used small vertical stabilizers with large elevator surfaces that, remarkably, could reportedly be swept back and dimensionally compressed in flight to reduce their area — emulating the way a bird fans or closes its tail feathers.
But the wings were where Bonney's genius — and his doom — resided.
The Wings: A Decade Ahead of Their Time
The Bonney Gull's aluminum wings did everything except flap. They incorporated:
- Variable angle of incidence — the entire wing could pivot at the root from the normal 10-degree angle to 45 degrees, driven by hydraulic actuators. At 45 degrees, the wings spilled their lift entirely and acted as an aerodynamic brake, shortening the landing roll dramatically. This was the VSTOL concept Bonney was pursuing.
- Automatic variable camber — the wing profile could change shape in flight, flattening for high-speed cruise (as a gull flattens its wings in level flight) and cambering more deeply for slow-speed approaches.
- Variable dihedral — the wing's anhedral/dihedral angle could apparently be altered in flight, though the mechanism for achieving this was sufficiently complex that later observers found it difficult to reconstruct from the surviving documentation.
- Swept outer pinions — the outer wing sections could sweep both forward and aft by 20 degrees, functioning as ailerons for roll control. Differential sweep — one pinion forward while the other swept aft — produced banking. This is precisely the concept later used in variable-geometry aircraft like the General Dynamics F-111 and the Grumman F-14 Tomcat, though those aircraft swept both wings together rather than differentially.
- Folding for storage — the wings could fold rearward from 10 degrees to 45 degrees for ground transport and storage. This feature anticipated the folding-wing carrier aircraft that Grumman would develop a decade later, beginning with the F4F Wildcat.
All of this was controlled by what Bonney described as "a minimum amount of central controls" — a remarkably optimistic description of what was in fact an extraordinarily complex hydraulic system. The inboard wing sections incorporated large flaps. The tailwheel was steerable. Even the conventional aileron — the standard roll-control surface that every other aircraft designer of the era took for granted — was entirely absent. Bonney had eliminated it, replacing its function with the differential sweep of the outer pinions.
"In appearance the Bonney Gull resembled an Alexander Bullet in bird-drag. A low-wing, cantilever monoplane with a two-place cockpit, it was filled with intricate mechanical and hydraulic devices, including a wing-folding mechanism that presaged that of later Grumman fighters." — HistoryNet
The Ideas That Were Right
It is fashionable, and tempting, to dismiss the Bonney Gull as an eccentric folly — a brilliant man's fatal obsession with a biological analogy that doesn't translate to engineering. That verdict is unfair to the ideas themselves.
Consider what Bonney got right:
Variable incidence is used today on virtually every large airliner's horizontal stabilizer to provide trim authority. The Vought F-8 Crusader used variable incidence for the main wing — raising the wing's angle of incidence for takeoff and landing while keeping the fuselage level — solving the carrier approach visibility problem elegantly. Bonney conceived this in 1926.
Variable sweep — wings that change their geometry in flight — became the defining feature of supersonic combat aircraft from the late 1960s onward. The F-111, F-14, B-1 Lancer, and the Soviet MiG-23 and Su-24 all use variable sweep to reconcile the conflicting demands of low-speed handling and high-speed performance. Bonney used differential sweep for roll control rather than symmetric sweep for speed range, but the underlying insight — that a wing's sweep angle need not be fixed — was his.
Wing folding for carrier storage became standard on US Navy aircraft from the late 1930s onward. The Fairey Firefly, the Grumman Hellcat, the Vought Corsair — all used folding wings. The Bonney Gull folded its wings in 1928.
Aerodynamic braking using the wings themselves — rather than separate flaps or drag chutes — is used in modern fly-by-wire aircraft through spoiler deflection. Bonney's wing-rotation-to-45-degrees concept was crude compared to modern spoiler systems, but the intent was identical.
The Bonney Gull was not wrong about where aviation needed to go. It was wrong about how to get there in 1928, with the hydraulic and structural engineering technologies of 1928, with a 180-horsepower engine, and — most critically — with a test flight that attempted to demonstrate all of these features simultaneously on the first outing.
The Flight, and the Silence After
Accounts of the fatal flight differ in some details. The aircraft made a successful takeoff — that much is agreed. The cream-colored Gull climbed away from Curtiss Field and reached altitude. Then something went wrong in the complex hydraulic symphony of the wing controls, and the aircraft became uncontrollable. It nosed over and dove into the ground.
A fragment of eyewitness description, preserved in a Long Island early fliers' club newsletter decades later: the aircraft broke apart on impact with its wings outstretched like a "mangled gull" — an image that manages to be both terrible and strangely fitting for a machine that had spent four years trying to become one.
Leonard Bonney was killed on impact. His silent financial partner, identified in surviving correspondence only as Knapp — possibly the source of the "K" in the aircraft's registration K-1783 — lost his investment. The aircraft was destroyed. No second prototype existed. The project ended the morning it began.
Both prototypes of the contemporary R-40C fighters — the XP-55 Ascender and one XP-56 Black Bullet — survived to reach museums. The Bonney Gull left nothing but photographs, a surviving scale model of uncertain ownership, test reports from MIT and NYU wind tunnels, and the memories of a handful of men who watched a cream-colored machine fold its wings for the last time on a Long Island morning in 1928.
Bonney Gull — Technical Profile
| Characteristic | Specification |
|---|---|
| Designer / Pilot | Leonard Warden Bonney (FAI license No. 47) |
| Builder | Kirkham Company, Garden City, New York |
| Registration | K-1783 (special temporary class license) |
| Configuration | Low-wing cantilever monoplane, pusher-free tractor layout |
| Seating | 2 side-by-side, dual controls, upholstered |
| Engine | 1 × 180 hp Kirkham radial piston engine |
| Wingspan | 40 ft 3 in (12.27 m) |
| Length | 22 ft 7 in (6.88 m) |
| Takeoff weight | 1,984 lb (900 kg) |
| Construction | Corrugated duralumin (aluminum alloy) |
| Cockpit | Streamlined greenhouse bubble canopy |
| Landing gear | Conventional fixed, streamlined struts, independent brakes, steerable faired tail wheel |
| Wing incidence range | 10° (normal cruise) to 45° (braking / storage) |
| Outer pinion sweep | ±20° forward and aft (used for roll control — no ailerons) |
| Wing folding | Full rearward fold for storage / transport |
| Variable camber | Automatic; hydraulically actuated |
| Variable dihedral | Yes (mechanism not fully documented in surviving records) |
| Tail surfaces | Gull-like; elevators could be swept back and reduced in area in flight |
| Estimated cost | $83,000–$100,000 (1927–28 dollars) |
| Wind tunnel testing | MIT; Daniel Guggenheim School of Aeronautics, NYU |
| Number built | 1 (destroyed on first flight) |
| First and only flight | May 4, 1928 — Curtiss Field, Long Island, New York |
| Outcome | Fatal crash; designer killed |
| Legacy technologies | Variable incidence (F-8 Crusader), variable sweep (F-111, F-14), carrier wing folding (Grumman fighters), aerodynamic spoiler braking |