Runways are undesirable locations for military aircraft.

Being tied to miles of concrete gives jet aircraft a built-in vulnerability as well as restricting their flexibility. At sea, it is extremely difficult (and dangerous) to operate aircraft from the pitching deck of an aircraft carrier with its limited amount of deck space.

So, it is hardly surprising that designers have made great efforts in trying to produce vertical take-off-and-landing (VTOL) aircraft able to operate like helicopters. But creating such an aeroplane is exceptionally hard. These almost inevitably doomed projects have put some fascinating shapes into the sky. Demonstrating how fiendishly hard it is to develop a ‘jump jet’, is the fact that only three on this list of ten made it into service!

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10: VFW VAK 191B

As with several aircraft on this list, the £192 million VAK-191 was an entry in NATO’s huge competition for a supersonic VTOL strike aircraft. The propulsion system, developed with the help of Rolls-Royce, used a Rolls-Royce/MAN Turbo RB.193 (similar to the Pegasus engine of the Harrier in concept) and two lift jets. The aircraft had an internal weapons bay.

When the NATO requirement was scrapped (after being technically won by the British Hawker P.1154), the VAK-191 flew on for research purposes as part of an ambitious US–West German fighter project. When this project was also canned, it was hard to justify the project, and the VAK-191 was axed by the West German government in 1972.

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10: VFW VAK 191B

The best feature of the VAK 191B was the simple-to-implement propulsion system, using the Harrier’s approach of steerable jet thrust, plus two fixed lift-engines. It was a neat configuration, with much higher fineness-ratio than the tubby Harrier. The Fineness Ratio is the ratio of the length of a body to its maximum width, and a higher fineness ratio will be a skinnier aircraft better suited to high-speed flight.

Its worst features were its low thrust-to-weight ratio and its small wing, so wing-borne landing would have been tricky and its manoeuvrability extremely poor. It made a successful flight, but it would have needed substantial development to become an effective operational system. The requirement eventually became irrelevant and was filled by the Tornado.

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9: ‘The Pentagon Easychair’ Ryan X-13 Vertijet

One way approach to vertical take-off and landing was the ‘tail-sitter’. The X-13 was more successful than its turboprop tail sitting brethren but was championing the wrong approach. This plane featured a Rolls-Royce Avon turbojet engine.

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9: ‘The Pentagon Easychair’ Ryan X-13 Vertijet

In an attempt to promote the aircraft, the X-13 once crossed the Potomac River and landed at the Pentagon, but it didn’t do much good as the military decided that it didn’t need the capability at the time.

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8: Lockheed XV-4 Hummingbird

Intended as a target-spotting aircraft for the US Army, this is probably the worst aircraft on this list in terms of its effectiveness. The vertical lift came from thrust being vectored downward through multiple nozzles, but the thrust generated was far less than expected, which is perhaps why the concept moved from vertical to merely short take-off.

It was however the first real first demonstration of an ejector-augmentor VTOL propulsion system, in the XV-4A An ejector-augmentor is a device for increasing the thrust of a primary propulsive nozzle through the clever use of fluid dynamics. This seemed like a free lunch but proved disappointing.

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8: Lockheed XV-4 Hummingbird

Vertical take-off was obtained by channelling the engine flow down through multiple nozzles, augmented by a flow of cold air. Subsequently, four lift jets plus a propulsion engine were added for the XV-4B. XV-4A had a relatively pedestrian top speed of 518 mph.

The ejector-augmenter propulsion system produced a thrust-to-weight ratio of only 1:04 – totally inadequate. Both the Hummingbird prototypes crashed, one killing the test pilot. The XV-4A was essentially a failure; the XV-4B propulsion system occupied the whole fuselage, leaving little opportunity for an operationally useful load.

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7: Yakovlev Yak-38 ‘Forger’

The much-maligned Soviet Yakovlev Yak-38 ‘Forger’ was only intended as an interim aircraft and shouldn’t be judged too harshly. Also, considering it is one of only three Vertical Take-off and Landing fast jets to have actually entered service, it deserves a little more respect.

This equivalent to the British Sea Harrier, but with a higher maximum speed, served the Soviet Navy from 1976 to 1991 and served in the Soviet–Afghan War. It laid the foundation for the fast, agile and considerably more impressive Yakovlev Yak-41.

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7: Yakovlev Yak-38 ‘Forger’

The whole thing was a neatly ‘packaged’ concept with two lift-engines plus a cruise engine with thrust-vectoring for landing. It featured an automatic ejector seat that would launch the pilot free from the aircraft (without his consent required) if certain parameters were exceeded, an approach later adopted by today’s F-35B stealth fighter.

The Yak-38’s worst feature was its vulnerability to any lift-engine failure in the hover, hence the need for an auto-ejection seat. Other than the Harrier and the Lockheed Martin F-35B Lightning II, it was the only crewed VTOL to enter service, with a total of about 200 produced. It also had a poor range and load-carrying ability.

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6: Ryan XV-5A Vertifan

The perky little Ryan XV-5A was built to answer the US Army’s need to research technologies required for a close-support aircraft. Attempts to develop it into a combat rescue capability were not encouraging, however; in trials, a dummy was ingested by one of the wing fans. The idea of using a lift-fan for vertical flight is still in practice today, and can be seen on the F-35B.

Its best feature was its novel fan-in-wing lift system which showed the benefits of moving large volumes of air more slowly. These produced three times the thrust that would have been provided by a conventional nozzle. But it was also its worst feature as the novel fan-in-wing lift system – with its complex doors above and below, and nose-fan for balance and control – proved difficult to manage, particularly in transition.

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6: Ryan XV-5A Vertifan

The aircraft was difficult to control, with poor low-speed handling and suffered from poor acceleration. It might possibly have worked, but it is doubtful whether the resulting combat rescue system would have been more effective than the rugged Bell UH-1 ‘Huey’.

Sadly, this challenging aircraft project suffered multiple fatal crashes killing several test pilots.

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5: EWR VJ 101

Heinkel and Messerschmitt teamed up with Bölkow to produce this six-engined, rather sexy, monster. Unlike other aircraft featuring small jets, this does not feature a larger main engine, so it’s alarming to think what would happen in the event of an engine failure. The design was in many ways like the never-completed Bell XF-109.

A test rig, called the Wippe (see-saw), was built in early 1960 to test the propulsion system. This rather comical-looking machine simple consisted of a simple cockpit on a horizontal beam. The lift engine was mounted at the centre of the beam. Its British counterpart was the earlier Rolls-Royce Thrust Measuring Rig, nicknamed the ‘Flying Bedstead’ (and was the first VTOL aircraft).

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5: EWR VJ 101

It had a six-engine control system in jet-borne flight integrated to its throttle (providing collective thrust-modulation), stick and rudder, with roll control by differential modulation of tip-mounted engine thrust and yaw control by differential wing-nacelle tilt. Pitch control by simultaneous differential thrust from two nose-mounted lift engines and the four wingtip-mounted engines.

Sadly, for this promising design, use of an afterburner on the tip engines resulted in ground erosion and hot-gas ingestion problems. The propulsion and control system worked, and it reached a speed of Mach 1.14 (1408 km/h), which was an impressive achievement. Significant developments were proposed for operational aircraft against changing requirements, which were first met by the F-4, then the Typhoon.

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4: Dornier Do 31

As with the Royal Air Force, in the early 1960s the Luftwaffe became concerned about the vulnerability of aircraft operating from large airbases. The British developed and eventually deployed the Harrier; the Germans, in a frenzy of innovation, developed and flew – but did not put into service – two potentially supersonic VTOL fast-jets and even a big VTOL transport, the Do 31.

They also experimented with a zero-length launch system for the Starfighter, the ZELL. As a production aircraft, the Do 31 was envisaged as supplying tactical, logistic support to the fast jets, itself using as forward-operating bases the airstrips on which the ZELL Starfighters were expected to land using arrester gear.

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4: Dornier Do 31

But it turned out that the tactical and logistic support of forward air operations could be well supported by another aircraft that was in development at the time – the Fiat G.222. This has now been developed into today’s C-27 Spartan, which offers similar payload-range performance to the Dornier 31E, albeit with short take-off and landing rather than VTOL capability, and at a fraction of the cost, risk and complexity of a production Do 31.

The Dornier Do 31 was an impressive answer to a question that shouldn’t have been asked. Technical progress and ambition had run ahead of operational analysis, resulting in flawed requirements. There’s no reason why this would not have worked, but short take-off utility and cargo aircraft provide a simpler and more rugged solution if the VTOL operational requirement is relaxed.

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3: Yakovlev Yak-141/41/43/201 series

The USSR was often accused of stealing US aircraft concepts and technologies, but in reality, it was a case of give and take, as well as similar design solutions resulting from parallel teams working to solve similar problems. That US company Lockheed bought research from Yakovlev on the propulsion system of the Yak-141 is notable (the idea had also been explored earlier by US company Convair).

The Yak-141’s best feature was its swivelling rear thrust-vectoring nozzle, and impressive maximum speed of Mach 1.4, far faster than the Harrier. Its worst feature what its use of afterburning for vertical flight, resulting in deafening noise, ground erosion and the potential for sucking in highly heated air into the air intakes causing engine problems.

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3: Yakovlev Yak-141/41/43/201 series

The programme was halted in 1991 due to economic conditions in the Soviet Union, but it would have been an impressive operational capability had development been continued. The Yak-141, impressive though it was, was merely planned as a stepping stone to the formidable Yak-43 fighter, which was never made.

The Yak-43 would have been far faster and more versatile than the Harrier, with a performance comparable to the MiG-29. In the 1990s, Yakovlev studied a more advanced stealthy version, the Yak-201, which would have been loosely analogous to the US F-35B Lightning II.

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2: Lockheed Martin F-35B Lightning II

The F-35B is the STOVL variant of the F-35 stealth fighter family, and is a very impressive piece of engineering. The F-35B was the first supersonic jump jet to enter service – a highly impressive feat after more than fifty years of failed attempts by some of the world’s greatest designers.

Vertical flight comes courtesy of the Rolls-Royce Integrated Lift Fan Propulsion System (ILFPS). This combines a shaft-driven lift fan and a Three Bearing Swivel Duct Nozzle (3BSD) which is essentially a jet nozzle that can bend like the mouthpiece of a drinking straw to steer the thrust downwards. There are also two ‘roll posts’ which extend like arms from the engine and provide thrust under the wings.

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2: Lockheed Martin F-35B Lightning II

The F-35B Lightning II has been adopted by the US Marine Corps, Italy, the United Kingdom and ordered by Japan, Singapore and South Korea. Thanks to its impressive sensor suite and pilot-machine interface (including an advanced helmet) the F-35B affords its pilots unprecedented levels of situational awareness as well a high degree of radar stealth.

The F-35B has about 30 per cent less internal fuel than the conventional take-off and landing (CTOL) F-35A, due to the weight and volume of the STOVL systems. Because of this the F-35B is the shortest ranged of the F-35 Lightning family.

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1: Harrier

No surprises for guessing the No. 1 spot. The Harrier was the first operational Short Take-Off/Vertical Landing strike fighter, and the aircraft for which the nickname ‘jump jet’ was coined (and strictly speaking, the only one that can be described as such). Key to the Harrier’s success was the simplicity of the propulsion concept.

The engine’s thrust is steered through four movable nozzles. Unlike rival concepts, the wing and engine did not need to be swivelled for vertical flight, nor did it depend on extra lift engines (which were a weight burden in forward flight) or a specialised landing pad.

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1: Harrier

The Harrier was a lower-risk brother to the aborted P.1154, and was initially funded partly by the US Army (which was keen to develop an in-house fixed-wing close-support force) and partly privately, as British companies were then prohibited from developing manned military aircraft (as they were deemed obsolete).

The first-generation Harrier entered service with the RAF on 1 April 1969. Its final operator was the Indian Navy (pictured), which operated it, in Sea Harrier guise, until 2016. In British and American service, the Harrier was replaced by the bigger and more sophisticated Anglo-American Harrier II from the 1980s onwards. The Harrier II also serves with Italy and Spain.

Follow Joe Coles on Substack, Twitter X  or Blue Sky. His superb Hush-Kit Book of Warplanes is available here.

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