The Mirage 4000 was one of the first aircraft to incorporate carbon-fiber composites to keep down weight — and was probably the first to feature a fin made of this advanced material. Thanks to its light structure and powerful engines, it had a thrust-to-weight ratio that exceeded 1:1 in an air-to-air load-out.

On its sixth test flight, the French warplane reached 50,000 feet and Mach 2 in three minutes and 50 seconds. The Mirage 4000 would have been agile, long-ranged and able to haul an impressive arsenal. Its capacious nose could have held an advanced long-range radar.

But the French air force didn’t want it. Iran — another potential customer — suffered a revolution and Saudi Arabia, also on the look-out for a heavy fighter, opted for the F-15. Despite its obvious potential, the Mirage 4000 failed to find a customer, which was an enormous blow for Dassault, as the company had privately funded the type’s development.

Kamov V-100:

Kamov’s long flirtation with twin, wingtip-mounted rotors led to some truly startling ideas. One was a vast, C-130-size transport. At the other end of the size spectrum was the V-100, an extremely fast battlefield helicopter that Kamov tinkered with in the 1980s.

As well as the unusual rotor configuration, the V-100 was to have a single pusher propeller that the designers expected would give the aircraft a top speed of around 250 miles per hour— a whole 70 miles per hour faster than the U.S. Army’s AH-64, itself no slouch.

Armament that Kamov considered for the V-100 included two 23-millimeter cannons or a single 30-millimeter weapon … and even the huge Kh-25 air-to-ground missile. In the end, Soviet authorities considered the design too risky. It never flew.

Yakovlev Yak-43:

Russia, and the Soviet Union before it, often stands accused of stealing U.S. aircraft concepts and technologies. In reality, there’s a give and take — as well as similar design solutions resulting from parallel teams working to solve similar problems.

That American firm Lockheed Martin bought data from Russia’s Yakovlev regarding the short-takeoff, vertical-landing propulsion system of the Yak-41 fighter is pretty notable. The Yak-41, impressive though it was, was merely a stepping stone to the formidable Yak-43.

The Yak-43, work on which began in 1983, would have been faster and more versatile than the Anglo-American Harrier. It’s possible the Yak-43 would have matched the performance of the MiG-29. The tumultuous, post-Soviet transitional period that made the collaboration with Lockheed possible also killed the Yak-43, but its DNA lives on in Lockheed’s F-35B jump jet.

BAe P.125:

The United Kingdom’s deep expertise in stealth technology is not widely known. Britain pioneered radar-absorbent material for aircraft, worked on reduced radar-observability for nuclear warheads in the early 1960s and was able to create a world-class stealth testbed in the form of the Replica stealth-fighter demonstrator.

Prior to Replica in the 1980s, British Aerospace developed an aircraft concept so advanced that it remained classified until 2006.

The BAe P.125 study was for a stealthy supersonic attack aircraft to replace the Tornado. It was to be available in both a short-take-off and vertical-landing variant and a conventional version. The conventional variant would have featured a central vectored nozzle, The STOVL version would have had three vectoring nozzles.

In some ways, the P.125 was more ambitious than Lockheed Martin’s later F-35 is. The aircraft was to have no pilot transparencies, with the reclined pilot instead viewing the world through synthetic displays.

It is likely that this formidable interdictor would have been even less visible on radar than the F-35 is, although the absence of planform-alignment is noteworthy. Despite its 1980s vintage, many of the P.125's low-observable features are reminiscent of today’s latest fighters. Others, such as its unorthodox wing design, are unique.

BAe quietly dropped the project when Britain joined the F-35 program in the 1990s.

This piece first appeared in WarIsBoring here.