The VJ 101C, a groundbreaking supersonic aircraft, was a collaborative effort by the German consortium EWR, consisting of aerospace giants Messerschmitt, Heinkel, and Bölkow.
This advanced jet utilized a dual propulsion system, combining lift and lift/cruise mechanisms, and was powered by six Rolls-Royce/MTU RB.145 turbojet engines. Two of these engines were strategically placed in tandem behind the cockpit, while the remaining four were grouped in pairs within rotating nacelles at the wingtips.
In the VJ 101C’s second experimental model, the X2, a significant enhancement was made to the wingtip engines. These engines were fitted with afterburners, boosting their thrust capability from 2,750 pounds to 3,650 pounds each, thus markedly increasing the aircraft’s performance capabilities.
The EWR VJ 101 was a pioneering German jet fighter, designed for vertical takeoff and landing (VTOL) capabilities, using a tiltjet mechanism. Dubbed “Versuchsjäger” (German for “Experimental Fighter”), the VJ 101 was among the early V/STOL designs with the potential to reach Mach 2 speeds.
In the 1950s, as global interest in VTOL aircraft surged, Germany’s Federal Government called upon its rejuvenated aviation industry to explore VTOL aircraft designs. Responding to this, German engine maker MAN Turbo, in collaboration with Britain’s Rolls-Royce Limited, began developing a suitable engine in 1960.
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Concurrently, German aircraft companies Heinkel, Bölkow, and Messerschmitt conducted independent studies, eventually uniting to form EWR. This joint venture focused on creating a supersonic VTOL fighter aircraft, later named the VJ 101 D.
The Federal Ministry of Defence (BMVg) was impressed enough to commission two experimental prototypes to showcase the design’s capabilities.
These prototypes, known collectively as the VJ 101 C and individually as X-1 and X-2, underwent a comprehensive five-year testing program. The goal was to develop the VJ 101 as a replacement for the German Air Force’s Lockheed F-104G Starfighter interceptors.
However, the project faced significant hurdles due to evolving requirements from the BMVg, shifting the aircraft’s role from an interceptor to a more versatile fighter. This change necessitated a substantial alteration in performance specifications. By 1968, the development of the VJ 101 was ultimately discontinued.
Rapid Advances in Jet Propulsion
In the 1950s, advancements in jet propulsion, notably in higher thrust and smaller engines, fueled optimism about the feasibility of vertical takeoff and landing (VTOL) aircraft in Western Europe and the United States.
This period saw the initiation of several VTOL programs in Britain, France, and the U.S., and West German aviation companies were eager to join this technological trend.
Following the lifting of the post-World War II restrictions on German aircraft development in 1957, companies like Dornier, Heinkel, and Messerschmitt, resumed operations and were encouraged by the German Federal Government to explore VTOL technologies and conceptualize designs.
These German firms embarked on developing VTOL interceptor designs, aiming for performance on par with contemporary interceptors like the Lockheed F-104G Starfighter. Concurrently, the German Federal Ministry of Defence (BMVg) advocated for the consolidation of these competing companies, delaying development contracts to encourage collaboration.
Parallel to these efforts, German engine manufacturer MAN Turbo was contracted by the BMVg to research VTOL-specific engines, which led to a partnership with British engine giant Rolls-Royce Limited in March 1960.
This collaboration, under a 10-year contract, aimed at leveraging Rolls-Royce’s jet engine advancements and establishing a joint development framework to minimize production overlaps and harmonize key decisions.
The partnership’s first project was the Rolls-Royce/MAN Turbo RB153 turbofan engine, a light single-spool turbojet initially modeled after the Rolls-Royce RB108 engine for sustained supersonic flight.
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Early interest in adapting the RB.153 for VTOL applications led to the development of specialized models like the RB.153.17 and RB.153.25 lift engines.
However, by December 1961, shifts in the BMVg’s VTOL priorities necessitated significant engine modifications, redirecting focus from the RB.153 to the development of the Rolls-Royce RB145 engine.
Heinkel and Messerschmitt, each with their own preliminary VTOL designs (Heinkel He 231 and Messerschmitt Me X1-21 respectively), joined forces with Bölkow by 1959 to form EWR. This joint venture aimed to create a supersonic fighter aircraft, the VJ 101 D.
The envisioned production model of the VJ 101 D was to be powered by the Rolls-Royce/MAN Turbo RB153 engine, equipped with thrust deflection technology. In late 1960, EWR presented this concept to the German Federal Ministry of Defence (BMVg), who subsequently ordered two experimental prototypes to assess their potential as interceptors.
These prototypes, designated as the VJ 101 C, differed from the initial concept by using the lighter RB145 turbojet engine in swivelling nacelles. Development, however, faced challenges, notably a change in the BMVg’s requirements from an interceptor to a more versatile fighter.
This change demanded adaptations for longer low-altitude endurance among other performance factors. The VJ 101 C merged elements from Bölkow, Heinkel, and Messerschmitt’s designs, resembling the American Bell XF-109 in its configuration of paired swivelling nacelle engines at the wingtips. Additionally, two lift jets in the fuselage aided hovering flight.
A significant feature of the VJ 101 C was its electronic flight control system, a pioneering ‘fly-by-wire’ setup. This system was crucial for maintaining control during hover and transition phases, involving collaborative developments by Honeywell and Bodenseewerk.
Initially, two-channel control systems were used, but testing indicated a need for three-channel systems to handle hardover failures, making it the first to operate throughout all flight ranges with thrust-vector control. Even after the project shifted from being a potential F104G Starfighter successor, it remained valuable for its contributions to flight control technology.
EWR also built a test rig, the ‘Wippe’ (seesaw), for preliminary control system tests. This simple structure featured a basic cockpit on a beam with a centrally mounted “lift” engine. A subsequent “hover rig” with three Rolls-Royce RB108 engines simulated the final aircraft’s engine placement.
Starting in May 1961, tests began on a telescopic column, leading to a successful “free flight” in March 1962. Further testing with a cloth “skin” to mimic the fuselage and wings demonstrated satisfactory control under various conditions.
VJ-101C Test Flights
Two prototype aircraft, designated X-1 and X-2, were developed. The X-1 was equipped with six RB145 engines: two installed vertically in the fuselage for lifting, and four in swivelling nacelles, each capable of 2,750 lbf thrust.
The X-2 featured an enhancement in its swivelling engines, fitted with afterburners to achieve a wet thrust of 3,840 lbf each, aiming to reach a design speed of Mach 1.8.
Despite the nacelle engines producing sufficient thrust for steady hovering, the need for a smooth transition from dry thrust to reheat led to the requirement for vertical takeoff capability under reheat. This necessitated a short reheat pipe for adequate ground clearance.
The reheated engines had a two-position nozzle for reheat and non-reheat modes, and an adjustable inlet duct with an auxiliary air intake for low speeds or hovering.
The X-1 achieved its first hovering flight on 10 April 1963 and transitioned from hover to horizontal flight on 20 September 1963. Showcased at the May 1964 Hannover Air Show, the X-1 completed 40 aerodynamic flights, 24 hover flights, and 14 full transitions.
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It notably broke the sound barrier, a first for a vertical takeoff aircraft, but suffered a crash due to an autopilot defect on 14 September 1964. On 29 July 1964, the VJ 101 C achieved Mach 1.04 without afterburner.
The X-2’s inaugural flight occurred on 12 June 1965, successfully transitioning on 22 October 1965 with a new autopilot system. Unlike the X-1, the X-2 was equipped with afterburners. However, by 1968, the project was discontinued, and the planned Mach 2 interceptor VJ 101 D was never completed.
The VJ 101 C X-2 is now exhibited at the Deutsches Museum in Munich. While the VJ 101C didn’t advance to production, other supersonic VTOL fighter aircraft projects of the era, like the Mirage IIIV and the Hawker Siddeley P.1154, faced similar outcomes.
The operational success of the Harrier jump jet and later the Lockheed Martin F-35 Lightning II demonstrated the potential of VTOL fighters.
VJ-101C Single Seater
In 1966, it was decided to scale down the VAK 191B program to a purely experimental project, reducing the number of prototypes to three. By 1968, Italian partners withdrew from the collaboration, but prototype development proceeded.
The first prototype was unveiled on 24 April 1970, and after preliminary captive tests, it made its maiden flight on 10 September 1971, delayed by about three years from the initial plan. The subsequent months saw the other two prototypes taking flight. Following the merger of VFW and Fokker in 1969, the prototypes were branded as “VFW-Fokker”.
The VAK 191B bore a notable resemblance to the BAE Harrier, a design similarity driven by the use of a vectored-thrust engine with four rotating nozzles.
Positioned at the aircraft’s center of gravity for balance, this engine dictated the high-mounted position of the wings, which featured a 48-degree leading-edge sweep. The wings were equipped with ailerons and single-piece flaps, the latter also serving as effective airbrakes.
Plans were in place for manufacturing a single-seat interceptor, known as the EWR VJ 101D, which would have significantly varied from the initial research prototypes. It was designed to maintain VTOL capabilities using a series of Rolls-Royce/MAN RB.162 lift-jets located in the fuselage.
The primary propulsion was to be provided by two Rolls-Royce/MAN RB.153 turbofans situated in the rear fuselage, utilizing thrust deflection for maneuvering and control. However, this particular model of the aircraft never reached the production stage.