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The aircraft built and tested in the 1950s and 60s had tilting wings so it could hover and land like a helicopter but fly forward like a plane.

The Canadair CL-84 Dynavert was part helicopter, part airplane and a complete flop.

The aircraft built and tested in the 1950s and 60s had tilting wings so it could hover and land like a helicopter but fly forward like a plane. Canadair killed the CL-84 program after it failed to find a buyer, and the aircraft was forgotten.

But now a Swiss aviation company has revived the design, with a modern spin. Dufour Aerospace’s Aero 3 is based on the CL-84′s aerodynamic shape and concept, but burns fuel and electricity to power an eight-seat aircraft.

Dufour aims to have hybrid gas-electric versions of the plane, a cheaper and more efficient alternative to air ambulances and rescue helicopters, on the market by 2025.

The company has secured letters of intent to purchase for about three years production of the Aero 3. Dufour is eyeing a possible Canadian manufacturing facility in addition to a European base, Thomas Pfammatter chief executive officer of Dufour, said from Zurich.

“The principle has become useful again,” said Erin Gregory, the curator at Canada Aviation and Space Museum in Ottawa, where one of the two remaining CL-84 sits on display.

“It stands out because it is an odd-looking airplane, for sure,” Ms. Gregory said.

A test aircraft by Dufour takes flight in August, 2020.Reuters

The Aero 3 will cost between US$2.5-million and US$5.4-million, and operate at a cost of about US$1,500 an hour. A typical helicopter can cost several millions of dollars, and cost US$20,000 an hour to operate. Every hour in the air requires four hours of maintenance on the ground.

Dufour in 2015 became one of the first to build an all-electric stunt plane, the Aero 1, and is making a pilotless version of the Aero 3.

To design the four-engine Aero 3, Dufour engineers studied flight data, NASA research papers and other publicly available information on the Canadair CL-84, which died in 1974 after the U.S. military decided not to place orders.

“It is a known aerodynamic concept proven by pilots, many dozens of them, who flew that aircraft in the sixties,” Mr. Pfammatter said by phone. “Aviation is so difficult and you have so many unknowns that you want to limit your risks. There is so much material out on the tilting aircraft data, how they fly and how they behave in which conditions.”

The CL-84 was among several tilt-wing aircraft developed in the 1950s and 60s.

“There are quite a few examples,” Ms. Gregory said, “some that never flew, some that made a couple of test flights but didn’t go very far, others that were kind of failures out of the gate.”

“The idea was to try to get something that would have all the benefits of a helicopter without the limitations of the helicopter, and then all the benefits of a fixed-wing aircraft without the limitations of requiring an airfield,” Ms. Gregory said.

The CL-84 was a failure, but not at first.

Canadair built four CL-84s and flight-tested three of them. The design was liked by pilots and tested extensively by the U.S. military, which was looking to use the CL-84 for troop transport and gunships in the war in Vietnam.

Two crashed because of mechanical failures. And by the early 1970s, the U.S. switched tactics in the war. It began dropping bombs from high, rather than intensifying the ground war by bringing in soldiers on helicopters.

The U.S. walked away from the CL-84 in 1974. With no other potential buyer, the aircraft was scrubbed.

Today, a CL-84 sits flightless in the Ottawa aviation museum, an aluminum embodiment of the dream of flight, past and – possibly – future.

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