It looks like someone strapped wings and two open cockpits onto a beer keg and pushed it off a hill. Short, fat and hollow, the Stipa-Caproni is routinely voted one of the ugliest aircraft ever to actually fly. And yet this 1932 Italian oddity quietly sketched out an idea that powers nearly every airliner you have ever flown on.

Behind the barrel was a genuinely brilliant man and a genuinely brilliant — if drag-soaked — idea.

An engine inside a barrel

The designer was Luigi Stipa, and his concept had a name: the “intubed propeller.” Instead of hanging a propeller out in the breeze, Stipa shaped the entire fuselage into a tapered tube — a venturi — and put the propeller and a 120-horsepower de Havilland Gipsy III engine inside it. The duct squeezed and accelerated the airflow before it left the back of the aircraft, using Bernoulli’s principle to wring more thrust out of the same engine. In other words, the whole aeroplane was one big ducted fan.

The execution was charmingly low-tech: mostly wood, a mid-mounted wing, and two crew sitting in tandem in a little hump on top of the barrel.

Did it actually work?

On 7 October 1932, test pilot Domenico Antonini took the flying barrel into the air — and the physics held up. The intubed propeller really did improve the engine’s efficiency, just as Stipa had calculated. The airfoil-shaped interior of the duct generated extra lift, giving the aircraft a remarkably low landing speed of just 42 mph and a healthy rate of climb. It was even noticeably quieter than its contemporaries.

There was, however, a fat problem — literally. That barrel of a fuselage created so much aerodynamic drag that it cancelled out the efficiency it had won, and the Stipa-Caproni topped out at a leisurely 81 mph. Italy’s air force took one look and politely declined.

The barrel that predicted the jet

Here is the twist that turns a punchline into a footnote in aviation history. Stipa’s intubed propeller is, in essence, an ancestor of the ducted fan — and, by extension, of the turbofan engine that hangs under the wing of almost every modern jet. The Kort nozzle developed in 1934 leaned on the same principles, and more than a few historians trace a direct conceptual line from this wooden barrel to the high-bypass engines of today.

Period footage of the original survives, and it is worth a watch — there is something hypnotic about that stubby tube hauling itself into the sky.

A flying barrel, reborn

The idea refused to die. In Australia, the firm Aerotec Queensland built a three-fifths-scale replica, and in October 2001 pilot Bryce Wolff coaxed it into two short hops of around 600 metres, climbing to about six metres — behaving, witnesses said, much as the original had seventy years earlier.

The Stipa-Caproni never won a contract, never broke a record, and never lost its place on every “ugliest aircraft” list ever written. But it was right about something important long before anyone else was. Sometimes the silliest-looking machine in the room is the one quietly seeing the future.

Sources: Wikipedia; Vintage Aviation News; HistoryNet; Flight Journal.