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.

Design and development

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 was followed by the RFB X-113, structurally and aerodynamically refined, but still low- powered. The much larger X-114 seated six or seven and had a engine. All three were inverse delta aircraft, that is, they had a wing that was triangular in plan, but with a straight, unswept leading edge. Combined with strong anhedral, this layout produces stable flight in ground effect. 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 The aspect ratio of a geometry, geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side—the ratio of width to height, when the rectangl ...

square wing of the

Ekranoplan A ground-effect vehicle (GEV), also called a wing-in-ground-effect (WIGE or WIG), ground-effect craft/machine (GEM), wingship, flarecraft, surface effect vehicle or ekranoplan (), is a vehicle that is able to move over the surface by gaining su ...

s, which leaves ground effect at only 10% of span, limiting them to the calmer waters of lakes and rivers. 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 beyond the wing's leading edge, with short, outward leaning winglets in line with that edge and fitted with

aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement aroun ...

s. At the rear the

fuselage The fuselage (; from the French language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as wel ...

swept upwards to a conventional fin and T-tail, the latter carrying

elevator An elevator (American English) or lift (Commonwealth English) is a machine that vertically transports people or freight between levels. They are typically powered by electric motors that drive traction cables and counterweight systems suc ...

s. 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, 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 In aeronautical and naval engineering, pusher configuration is the term used to describe a drivetrain of air- or watercraft with propulsion device(s) after the engine(s). This is in contrast to the more conventional tractor configuration, wh ...

propeller A propeller (often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon a working flu ...

mounted near mid-chord. 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 Conventional landing gear, or tailwheel-type landing gear, is an aircraft Landing gear, undercarriage consisting of two main wheels forward of the Center of gravity of an aircraft, center of gravity and a small wheel or skid to support the tail ...

, with small wheels retracting into the floats and a tailwheel on the fuselage at the wing's

trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 1997. ...

, 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, or if it simply acted as beaching gear, allowing the X-114 easy access from water to land-based facilities. The X-114 began its trials with the German Ministry of Defence in April 1977. At some stage it was fitted with downward angled

hydrofoil A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains sp ...

s 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 In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relat ...

was negative. Despite completing its test programme satisfactorily, no production order was received and the sole prototype was the only X-114 built. 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, which continued in operation until at least 2012.

Specifications

References

{{Lippisch aircraft Ground-effect vehicles RFB aircraft 1970s German experimental aircraft Single-engined pusher aircraft Aircraft first flown in 1977 T-tail aircraft Ducted fan-powered aircraft