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RFB X-114
RFB X-114
RFB X-114
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The RFB X-114 was a ground-effect craft, designed chiefly to operate over water but capable of flight at higher altitudes where required, carrying five or six passengers or freight along coasts and capable of surveillance duties. One was evaluated by the German military in the late 1970s, but no orders followed.

Key Information

Design and development

[edit]

The RFB X-114 Aerofoil Craft was an experimental ground-effect vehicle intended to work over water, with the ability to fly out of ground effect when required. It was the last of three such aircraft designed by Alexander Lippisch in the 1960s and early 1970s. The low powered, two-seat proof of concept Collins X-112[1] was followed by the RFB X-113, structurally and aerodynamically refined, but still low- powered.[2] The much larger X-114 seated six or seven and had a 149 kW (200 hp) engine.[3]

All three were inverse delta aircraft, that is, they had a wing that was triangular in plan, but with a straight, unswept leading edge.[1] Combined with strong anhedral, this layout produces stable flight in ground effect.[4] Specifically, it is claimed that it is stable in pitch and also that it can fly in ground effect at altitudes up to about 50% of its span, allowing it to operate over rough water. This contrasts with the lower aspect ratio square wing of the Ekranoplans, which leaves ground effect at only 10% of span, limiting them to the calmer waters of lakes and rivers.[5]

The weight of the X-114 was more than twice that of the X-112, the next heaviest of the series, but all three shared the same control systems. At each wing tip there was a long, flat bottomed float reaching forward about 2.5 m (8 ft 2 in) beyond the wing's leading edge,[6] with short, outward leaning winglets in line with that edge and fitted with ailerons. At the rear the fuselage swept upwards to a conventional fin and T-tail, the latter carrying elevators. On the water's surface, the floats stabilised the X-114 and, in combination with the strong anhedral, held the fuselage well clear of the water. The X-114 had a pod type fuselage, projecting forward as far as the floats. Seating, in rows of two, accommodated six or seven under multi-section glazing. The pod extended rearwards to about one quarter root chord, its rearmost part unglazed and forming a streamlined pylon for the separately podded, 149 kW (200 hp) Lycoming O-360 flat-four engine. A drive shaft ran rearwards from the engine within a conical fairing to a shrouded, five bladed pusher configuration propeller mounted near mid-chord.[3][6]

Though primarily intended for over-water flight in ground effect, the X-114 could also be flown out of ground effect over obstructions like trees, peninsulas, or waterfalls. It was also equipped with conventional landing gear, with small wheels retracting into the floats and a tailwheel on the fuselage at the wing's trailing edge, which could be lifted up to lie along the fuselage bottom where it began the upward slope to the tail. It is not clear if this lightweight gear allowed land based take-offs and landings,[3] or if it simply acted as beaching gear, allowing the X-114 easy access from water to land-based facilities.[6]

The X-114 began its trials with the German Ministry of Defence in April 1977. At some stage it was fitted with downward angled hydrofoils mounted to its floats with the aim of decreasing take-off speed, but they proved to have the opposite effect by decreasing the ram air pressure. They also called for care on landing, pulling the craft rapidly into the water if their angle of attack was negative. Despite completing its test programme satisfactorily, no production order was received and the sole prototype was the only X-114 built.[6] It was finally lost in an accident. Though Lippisch died just before the X-114 test programme began, his concept was further developed in the Airfish series of ground effect vehicles,[6] which continued in operation until at least 2012.[7]

Specifications

[edit]

Data from Jane's All the World's Aircraft 1978-79.[3]

General characteristics

  • Crew: One
  • Capacity: Five or six passengers
  • Length: 12.80 m (42 ft 0 in)
  • Wingspan: 7.00 m (23 ft 0 in)
  • Height: 2.90 m (9 ft 6 in)
  • Empty weight: 1,000 kg (2,205 lb)
  • Max takeoff weight: 1,500 kg (3,307 lb)
  • Powerplant: 1 × Lycoming IO-360 flat four, 150 kW (200 hp)
  • Propellers: 5-bladed ducted pusher configuration

Performance

  • Cruise speed: 150 km/h (93 mph, 81 kn) in ground effect. Out of ground effect, estimated: 200 km/h (124 mph; 108 kn)
  • Range: 2,000 km (1,200 mi, 1,100 nmi) approximately, in ground effect
  • Endurance: 20 hr, in ground effect

References

[edit]
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RFB X-114

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from Grokipedia
The RFB X-114 was an experimental developed by Rhein-Flugzeubau (RFB), a affiliate, in the 1970s as part of a series of wing-in-ground (WIG) effect prototypes designed primarily for efficient operations over water while retaining the ability to transition to conventional flight at higher altitudes. It combined features of aircraft and , gliding on an air cushion over surfaces like water or land, with an unsinkable design constructed from reinforced (). Intended for both military and civilian uses, such as amphibious transport, the X-114 aimed to meet requirements like the U.S. Navy's for a 100-knot (approximately 185 km/h) amphibious craft. The project originated from the work of aeronautical engineer Dr. , who had previously developed the X-112 hydro-wing in 1963 at Collins Radio Company and the X-113 prototype tested between 1970 and 1972. After Lippisch founded the Lippisch Research Corporation in 1966, RFB took over construction of the X-114 as the third in the series, with development focusing on enhancing —reportedly about 50% lower than comparable conventional —through WIG operation. The design incorporated retractable for operations on both land and water, addressing limitations of earlier WIG vehicles restricted to calm conditions. Key features included an inverted for superior lift in ground effect, a compact central cabin seating up to six passengers, a assembly, stabilizing winglets, and a rear-mounted pusher propeller driven by a small-output . With a length of 12.8 meters and a of 7 meters, it achieved a maximum speed of around 180 km/h in ground effect and could reach altitudes up to 800 meters (about 2,600 feet) for free flight. Initial trials commenced in spring 1977 over the , where the single demonstrated promising performance in rough waters and generated interest from the West German Ministry of Defense. Despite these successes, no production orders followed, and the project was abandoned, with the prototype later lost in an ; factors contributing to its failure remain unclear but may include economic challenges and lack of commercial viability.

Development

Background and predecessors

After , , renowned for his pioneering delta-wing designs such as the Me 163 rocket-powered interceptor, shifted his focus toward innovative ground-effect vehicles, or wing-in-ground (WIG) craft, during the late 1950s and early 1960s while working in the United States. Employed at Collins Radio Company, Lippisch explored ekranoplans—vehicles that exploit the aerodynamic cushion formed between the wing and a surface like water—to achieve enhanced performance, drawing on his expertise in tailless and delta configurations. This transition was motivated by the potential to address limitations in conventional aviation and maritime transport, particularly for operations over water where traditional aircraft faced high drag and ships were slow. The initial small-scale demonstrator in this lineage was the Collins X-112, a two-seat experimental craft designed by Lippisch and first flown in 1963. Built primarily of balsa wood to test basic principles, the X-112 featured a reverse-delta wing with significant anhedral and a , achieving speeds up to 124 km/h during tests that confirmed its in ground effect. Key findings highlighted the design's ability to maintain control and efficiency at low altitudes, with ground effect contributing up to 35% of total lift through minimized shifts in the center of . In 1967, following Lippisch's retirement from Collins in 1964, the patents for this concept were sold to the German firm Rhein-Flugzeugbau GmbH (RFB), which advanced the work. RFB developed the X-113 as a single-seat test craft, constructed with for improved durability and first flown in October 1970, with testing continuing until 1974. Powered by a 40 hp engine, the X-113 provided critical insights into ground-effect stability, demonstrating pitch stability and the ability to operate effectively over rough surfaces at altitudes up to 50% of its . These prototypes underscored the rationale for : exploiting ground effect to reduce induced drag and achieve lift-to-drag ratios as high as 20:1, enabling higher efficiency for short-range compared to conventional or . Such vehicles promised applications in civilian passenger and freight services, as well as roles like , by allowing speeds over 100 knots with significantly lower fuel consumption—potentially one-fifth that of standard —while maintaining amphibious capabilities. Lippisch remained actively involved in refining these designs until his death on February 11, 1976, from heart and lung ailments in , just prior to the commencement of testing for the larger X-114. His foundational contributions laid the groundwork for subsequent developments, emphasizing the inverse delta wing's role in achieving stable, efficient flight in proximity to the surface.

Design and construction

The RFB X-114 was manufactured by Rhein-Flugzeugbau GmbH (RFB), an affiliate of based in , , representing the third iteration in Alexander Lippisch's series of wing-in-ground (WIG) effect vehicles following the X-112 and X-113 prototypes. The primary design goals centered on achieving amphibious operations over water surfaces, enabling transitions to conventional out-of-ground-effect flight for versatility, and providing capacity for five to six passengers or equivalent freight loads in a compact configuration. Design initiation occurred in the mid-1970s, with the project drawing from the scaled-up foundation of the X-113 to enhance payload and operational range while maintaining efficiency. The single prototype's assembly was completed by early 1977 at RFB facilities. Construction emphasized a lightweight glass fiber-reinforced plastic () sandwich structure for the hull and wings, incorporating RFB's patented tube system of sealed square profiles to promote unsinkability and corrosion resistance essential for repeated water contacts and amphibious landings. The prototype achieved its first flight in April 1977, validating fundamental airworthiness and ground-effect performance during initial tests over water.

Testing program

The initial test flights of the RFB X-114 prototype were conducted over the waters of the in , commencing on April 15, 1977. Test pilot Dr. Volkmar Wilckens performed the maiden flight, focusing on validating the vehicle's ground-effect operations at heights up to 50% of the wingspan (approximately 3.5 meters, given the 7-meter span). These early sorties confirmed the basic aerodynamic principles derived from Alexander Lippisch's earlier designs, demonstrating safe takeoffs from water and sustained flight in close proximity to the surface. Subsequent performance validations highlighted the X-114's stability within ground effect, its smooth transition to conventional out-of-ground-effect flight, and its capability for amphibious landings on water. The prototype exhibited reliable handling during these maneuvers, with the reverse configuration providing inherent pitch stability and resistance to porpoising over waves. Handling characteristics were generally favorable, though tests revealed limitations in maneuverability when operating very near the surface, where wave disturbances could induce minor oscillations requiring pilot input. Data collected during the testing program underscored significant efficiency gains from ground effect, including an estimated 20-30% increase in at low altitudes compared to free-air conditions, which contributed to reduced induced drag and overall fuel consumption approximately 50% lower than comparable conventional . Detailed logs indicate around 25 starts accumulating 7.5 hours of , to assess structural integrity and system reliability. These results affirmed the viability of the airfoil boat concept for both civilian and potential applications.

Design

Aerodynamic configuration

The RFB X-114 employs an planform with forward-swept leading edges and a low of approximately 1.5, optimized for enhanced low-speed stability and ground-effect efficiency. This configuration, scaled and refined from the predecessor X-113, incorporates significant anhedral of 15° to 19° along the , promoting inherent stability during operations close to the water surface. In ground effect, the X-114's proximity to the —typically maintained at 10-25% of the mean aerodynamic chord—generates a dynamic air cushion beneath the wing, augmenting lift by up to 35% through surface-induced pressure and suppressing to reduce induced drag. This mechanism elevates the from 8 in free flight to 20-25 during low-altitude cruise, enabling efficient operation over with minimal power input. Wingtip end plates further enhance this effect by confining airflow and minimizing lateral spillage. The design features a assembly with a and horizontal stabilizer for longitudinal and . Control surfaces include winglets at the tips for lateral damping, elevons along the trailing edges for combined pitch and roll control, and a on the for yaw. Hull integration features a stepped lower structure that supports hydrodynamic planing during water takeoffs and landings, ensuring a smooth aerodynamic transition to flight mode while accommodating amphibious operations on varied surfaces.

Propulsion and systems

The RFB X-114 utilized a single Lycoming IO-360 air-cooled flat-four engine rated at 150 kW (200 hp), mounted in a rearward to drive the system. This engine choice provided reliable power for the experimental ground-effect vehicle's operations over water and in free flight. The pusher layout contributed to improved propeller clearance during low-altitude ground-effect flight. The engine powered a rear-mounted pusher propeller. This configuration enhanced the craft's ability to maintain stable operation close to the water surface while minimizing drag. The fuel system supported extended missions with a capacity enabling roughly 20 hours of flight , benefiting from the vehicle's low consumption—approximately 50% less than comparable conventional due to ground-effect efficiencies. Provisions for operations over included amphibious capabilities, though specific refueling adaptations were not detailed in primary development records. Avionics were kept minimal for the , focusing on basic (VFR) instrumentation suitable for test flights over controlled areas like the . Flight controls employed hydraulic actuators for precise handling of the reversed and stabilizing surfaces, with the electrical system drawing power from the engine's to support essential functions.

Structural features

The RFB X-114 features a blended wing-body layout optimized for low-drag ground-effect operations and inherent , with an overall length of 12.80 m and wingspan of 7.00 m. This configuration integrates a reverse with anhedral into the central body, forming a streamlined catamaran-style hull with supporting floats to facilitate efficient transitions between water and air. The employs a glass fiber-reinforced (GFK) sandwich construction, utilizing composites for the skin over a lightweight internal structure, which provides an excellent strength-to-weight ratio and resistance to marine corrosion. This material choice, pioneered by RFB in prior prototypes, enables durable performance in amphibious environments while maintaining structural integrity under repeated water contacts. Amphibious operations primarily rely on the hull's hydrodynamic shape for water takeoffs and landings, supported by an optional detachable retractable for land use; pilot and crew access is provided through a forward canopy. Safety provisions include built-in flotation from the sealed tube framework, rendering the craft unsinkable even if damaged, along with emergency egress facilitated by the canopy design.

Operational history

Military evaluation

The RFB X-114 underwent military evaluation by the West German Ministry of Defense between 1977 and 1980, primarily to assess its suitability for amphibious operations over water. These tests built on initial developmental flights over the Baltic Sea in spring 1977, conducted under a Federal Ministry of Defence order dating back to 1967, focusing on ground-effect performance in operational scenarios. Key findings highlighted the X-114's effectiveness in low-altitude over-water missions, achieving a cruise speed of approximately 150 km/h in ground effect while demonstrating inherent stability due to its reversed delta-wing configuration and air-cushion capability. It exhibited 50% lower fuel consumption compared to conventional comparable , enhancing efficiency for extended patrols, and showed potential for low signature operations owing to its low-flying profile. However, limitations were noted in single-engine reliability for critical missions and insufficient range for prolonged operations beyond coastal zones, restricting its versatility against more established platforms. Overall outcomes were positive regarding the vehicle's efficiency and stability for niche maritime roles, validating the Lippisch-inspired airfoil boat concept for military applications. Despite this, no production contracts were awarded, attributed to high development costs and competition from advanced helicopters and that offered greater operational flexibility during the late era. The evaluations continued through the late , though exact end dates are not documented. They concluded without advancing to , marking the end of the X-114's military assessment phase.

Prototype loss

The sole prototype of the RFB X-114, registered as 9829 and bearing serial number V1, was constructed in the mid-1970s as an experimental wing-in-ground (WIG) effect vehicle developed by in collaboration with designer . This aircraft, intended for amphibious operations with the capability to transition out of ground effect, underwent initial flight trials starting in April 1977, demonstrating successful performance during tests conducted for the West German Ministry of Defense starting in April 1977. The was ultimately destroyed in an during the testing phase in the late 1970s, with no specific date or detailed circumstances publicly documented. The was written off as a , marking the end of active development for the X-114 program. The loss of the only existing , combined with insufficient funding and lack of orders despite prior evaluations, prevented the construction of a second or continuation of the project. Data and insights gathered from the preceding test flights contributed to broader advancements in WIG vehicle concepts, influencing subsequent designs in the field.

Specifications

General characteristics

The RFB X-114 accommodates a crew of one pilot. It has a capacity for five or six passengers or an equivalent freight payload of approximately 500 kg. The vehicle's dimensions comprise a length of 12.80 m, a wingspan of 7.00 m, and a height of 2.90 m. Key weights include an empty weight of 1,000 kg and a of 1,500 kg. The X-114 is powered by a single Lycoming IO-360 piston engine rated at 150 kW (200 hp) driving a rear-mounted .

Performance

The RFB X-114 demonstrated a cruise speed of 150 km/h while operating in ground effect. Range capabilities extended up to 2,000 km in ground effect. Takeoff and landing were conducted on water, emphasizing the vehicle's amphibious nature and reliance on calm water conditions for optimal operations.

References

  1. https://1000aircraftphotos.com/Contributions/Visschedijk/10307.htm
  2. https://www.airhistory.net/photo/238098/9829
  3. https://worldaviationato.com/en/airplane-ground-effect/
  4. https://nationalinterest.org/blog/buzz/rfb-x-114-could-have-been-revolutionary-plane-heres-why-it-flopped-162553
  5. https://eaglepubs.erau.edu/introductiontoaerospaceflightvehicles/chapter/hovercraft/
  6. https://escholarship.mcgill.ca/downloads/70795b34z.pdf
  7. https://apps.dtic.mil/sti/tr/pdf/ADA430859.pdf
  8. https://findingaids.lib.iastate.edu/spcl/manuscripts/MS243/MS243.5.html
  9. https://www.britannica.com/biography/Alexander-M-Lippisch
  10. https://www.researchgate.net/publication/341621991_The_design_of_a_four-seat_reverse_delta_WIG_craft
  11. https://apps.dtic.mil/sti/tr/pdf/ADA361836.pdf
  12. https://www.sciencedirect.com/science/article/abs/pii/S1270963820311573
  13. https://www.frontiersin.org/journals/aerospace-engineering/articles/10.3389/fpace.2022.975158/full
  14. https://asmedigitalcollection.asme.org/fluidsengineering/article/140/7/071104/383627/Ground-Effect-on-the-Vortex-Flow-and-Aerodynamics
  15. https://www.sciencedirect.com/science/article/abs/pii/S1270963818311957
  16. https://www.ayrs.org/repository/AYRS%20126.pdf
  17. https://www.recreationalflying.com/forums/topic/38733-oddball-experimental-or-one-off/page/13/
  18. https://www.airhistory.net/aircraft/16176/RFB-X-114
  19. https://forums.x-plane.org/forums/topic/316154-who-wants-a-wig-rfb-x-114-wing-in-ground-effect-craft/
  20. https://edition.cnn.com/travel/article/caspian-sea-monster-ekranoplan-ground-effect-vehicle
  21. http://fdra-aereo.blogspot.com/2024/12/ekranoplano-rfb-x-114.html
  22. https://forums.x-plane.org/files/file/25256-x-114-wig-lippisch-1970-v1031/
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