Broadband Stealth May Drive Taranis Design

By Bill Sweetman
Source: Aviation Week & Space Technology
February 17, 2014
Credit: BAE Systems

BAE Systems' Taranis unmanned combat air system demonstrator is designed to defeat new counter-stealth radars, and may use thrust vectoring as a primary means of flight control and an innovative high-precision, passive navigation and guidance system, an AW&ST analysis indicates.

Taranis is a blended wing-body shape with no tail surfaces, like most UCAS designs for wide-band, all-aspect stealth. It has a triangular top-mounted inlet and 2-D V-shaped exhaust nozzle. The underside is flat, with visible outlines representing weapon-bay doors. Panels under the leading edge point to provision for a dual-antenna radar like a smaller version of that fitted to the B-2 bomber. The demonstrator may be designed so that functional weapon bays and sensors can be installed for a follow-on program.

The Rolls-Royce Adour engine is mounted low in the center fuselage, behind a serpentine duct. Two small doors are visible on either side of the raised centerbody, and are likely to be auxiliary inlets used at low speeds. The weapon-bay outlines are on either side of the engine and the forward-retracting main landing gears are outboard of the weapon bays. The demonstrator's gear comes from the Saab Gripen.

The wing leading edges are highly swept to reduce head-on radar cross-section at all wavelengths. The double-V trailing edge is swept more acutely than on most blended wing-body UCAS designs. Unlike the Northrop Grumman X-47B or the Dassault-led Neuron, there are no short-chord wing sections or short edges: The shortest edge is more than 11 ft. long.

This most likely indicates Taranis is designed to avoid detection by very high frequency (VHF) early warning radars such as those being developed by Russia and China as counter-stealth systems (AW&ST Sept. 2, 2013, p. 28). VHF radars can detect some stealth shapes with wing and tail surfaces close in size to their meter-range wavelengths. When that happens, radar scattering is driven by “resonant” phenomena not affected by the target's shape.

Taranis's flight controls are intriguing. There are two large elevon surfaces on the trailing edge, with deep “cat-eye” cut-outs at both ends: These prevent formation of right-angle shapes when the elevons move, and are large because the surfaces are thick. Outboard of the elevons are upper and lower “inlay” control surfaces, set into the wing surface.

The elevons will provide pitch and roll force. The inlay surfaces can act as roll spoilers and speedbrakes, and differentially for yaw control. (Similar surfaces were used on the upper side of the X-47B.) But the inlay surfaces are non-stealthy when open, so they must mainly be used at low speeds, including take-off and landing. The one-piece elevons cannot provide yaw input that is independent of pitch or roll. There is no visible source of yaw control, which points to the use of thrust vectoring.


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