ISNE Bélos

ISNE Bélos
Belos in prototype camouflage
Role	air superiority fighter
National origin	Willink
Manufacturer	Institoúto Stratigikón Naftikón Erevnó
First flight	7 June 2021
Introduction	Q2 2025
Status	In development
Primary user	Willink
Produced	2025-
Number built	12

The ISNE Bélos is a sixth-generation air dominance fighter in development by Willinkian defense contractor Institoúto Stratigikón Naftikón Erevnó. The Bélos is designed to replace aging fourth-generation aircraft (the Questarian Dauntless and Shrike) and augment the multirole Bantam in Willinkian air service, as well as replace the F/A-77 Kovas/Havenfighter as the primary air dominance fighter in Willinkian use; the latter is to be adapted to a multirole/strike role. Initially conceptualized in 2014 as ISNE worked on missile block and cockpit support system updates for the Havenfighter, the Bélos undertook its first flight in 2021, and is scheduled to reach initial operation in early 2025. In air defense, the Bélos is intended to out-class its regional competitors and legacy platforms such as the Project 352 Nukefighter, Supermarine Sea Kestrel (Libertyfighter), and F-23 Helios (Setofighter).

Development

ISNE, under its anglicized trade name Strategic Naval Research Institute was a development partner with ARES Group on the F/A-77 Kovas, also known as the Havenfighter, being tasked with cockpit support systems and weapon system integration generally , one of two Willinkian manufacturers involved with the project alongside Gloucester Aviation. Further, in Willinkian examples of the aircraft, ISNE took on a greater role in systems integration, translation of software into native Willinkian, as well as designing a large percentage of the dedicated missile platforms carried by the plane in Willinkian service. Thereafter, it maintained an important localized role in maintenance and service upgrades, having close access to the production process, as well as test-bed aircraft to prototype and integrate new systems. In 2014, amid system upgrades intended to integrate the new Cheiron Block II SRAAM, ISNE started conceptualizing a successor craft to the Kovas, based on feedback from Willinkian pilots operating the platform, as well as their own experience with the plane's electrical and cockpit management systems.

Generally, the Kovas is a highly regarded platform by pilots, capable of (arguably) best in class maneuverability, stability at both low and high speeds, a complex, effective, powerful sensor suit, and possessing high survivability. However, several persistent issues were identified: the modular dual-layer RAM system required frequent inspections and replacements, especially in harsh environments like naval operations; at speeds above Mach 1.5–1.8, the Kovas RAM and composite materials over its lifespan tended to degrade due to aerodynamic heating, reducing stealth performance; the Kovas struggled with heat dissipation due to its powerful radar and engine, leading to IR detection risks and operational inefficiency; and the Kovas skin panels were designed for specific operational wavelengths, limiting adaptability to emerging threats with different radar bands or advanced detection methods. Combat experience with the aircraft demonstrated that the diamond wing and large canards of the Kovas would exacerbate drag and airflow disruption at slow speeds, reducing stability in dogfights or low-speed engagements or at extreme angles of attack. Finally, over time, as systems were upgraded (e.g., avionics, sensors, weapons), the airframe's weight and radar cross-section (RCS) would increase, negatively impacting its stealth profile and agility; the "future proofing" of the Kovas was under increasing strain with improvements made in machine learning and computing power, stressing the power supply systems in an already complex, electrically demanding aircraft.

Design

Aerodynamics

The Bélos sought to improve lift-to-drag ratios while maintain low observability, opting for a cranked-kite wing layout. The aircraft retains a similar rear layout to the Kovas, opting for a v-tail with "humped" engine integration into the fuselage. The Bélos mounts diamond-shaped canards as frontal control surfaces. This cranked-kite-v-tail-canard configuration was selected for its high AoA performance, excellent post-stall maneuvering, excellent yaw and pitch controls, and adaptability to both supersonic and subsonic regimes. At high speeds, the cranked-kite wing reduces wave drag, while at low speeds, canard-assisted vortex lift improves control and stability for landing or dogfighting. The combination of cranked-kite wings and canards ensures excellent longitudinal stability, even in scenarios where the aircraft's center of gravity shifts (e.g., as fuel is expended or weapons are deployed). The V-tail reduces cross-sectional drag while maintaining effective control authority for pitch and yaw, particularly important during high-speed flight. This configuration strikes a balance between stealth, maneuverability, and efficiency. Compared to other configurations, it offers superior multi-role performance by blending stealth optimization with aerodynamic versatility, enabling operations in high-threat environments against advanced radar and missile systems. The inclusion of canards and V-tail enhances agility and control, making it a more robust platform for high AoA and post-stall maneuvers. While it may not achieve the extreme stealth of a tailless design or the simplicity of a conventional wing-tail configuration, it is a well-rounded choice for scenarios demanding both survivability and dominance in contested airspaces.

The Bélos is set up in a configuration reminiscient of the Saab Viggen; its wings mounted nearly flush to the lower fuselage, minimizing the frontal radar cross-section (RCS) by reducing exposed edges and surfaces; above-wing engine intakes, mounted on the lower half of the fuselage and blended into the body line via a leading-edge extension; and canards mounted on the intakes above the wing. The loss of airflow beneath the aircraft, particularly during low-speed, high-angle-of-attack (AoA) conditions by the wing placement is mitigated by intake and canard placement generating vortex lift at high AoA. This layout blends stealth, high-AoA stability, better lift-to-drag ratios, and superior airflow control to the airframe.

Aerodynamically, the positioning of the engines and V-tail imposes specific challenges and opportunities. The "humped" engine integration creates a broader fuselage cross-section, which slightly increases drag, while also improving lift by contributing to the lifting body effect of the fuselage itself. Furthermore, the outward placement of the V-tail stabilizers enhances yaw and pitch stability by increasing the moment arm relative to the center of gravity. This configuration synergizes well with the diamond-shaped canards and cranked-kite wing, as the canards improve maneuverability and stability at high angles of attack, while the cranked-kite wing offers strong lift-to-drag ratios and low-speed stability. The V-tail's upward and outward angling also contributes to minimizing interference with the airflow over the wings and canards, ensuring smoother aerodynamics overall.

In terms of systems integration, the positioning of the V-tail and engines impacts the internal structure and layout of subsystems. The outward V-tail placement allows for more streamlined heat and airflow management around the engines, improving thermal dissipation and reducing the risk of thermal hotspots that could compromise stealth or operational efficiency. However, this arrangement requires precise engineering of control linkages and structural reinforcements to handle the aerodynamic loads transferred through the extended stabilizers during high-speed or high-G maneuvers.

Stealth

The Bélos employs a multimodal approach to stealth. Its cranked-kite airframe with frontal aspect optimization minimizes radar cross-section (RCS) while maintaining excellent aerodynamic efficiency. The V-tail and carefully blended canards are sculpted to reduce radar returns from all critical angles, leveraging anisotropic materials that scatter radar energy in controlled directions. Its contoured air intakes with boundary-layer diverters are seamlessly integrated into the fuselage, designed to reduce radar exposure while maintaining efficient airflow and minimizing turbulence. The airframe's leading-edge extensions and blended contours work in tandem with structural radar-absorbent material (RAM), ensuring broad-spectrum radar absorption across the X-, S-, C-, and Ku-bands.

The Bélos’ use of structural RAM, woven directly into the thermoplastic-polyamide composite skin, represents a generational leap in Willinkian stealth materials. Unlike traditional stealth coatings, prone to degradation under environmental or operational stress, the carbon-nanotube-based RAM is integral to the airframe itself, providing greater durability, thermal management capabilities, and broad-spectrum radar absorption. Anisotropic elements further enhance this capability, reducing scattering from exposed surfaces such as wing leading edges, canards, and V-tails. Advanced thermal management subsystems, including metallic foam heat exchangers and loop heat pipes, dissipate heat generated by radar absorption and high-speed flight, preserving the aircraft’s thermal signature and reducing infrared visibility.

From a subsystem perspective, the Bélos incorporates active electronic countermeasures (ECM) that exploit advanced signal processing to detect, jam, or deceive enemy radars. Paired with its stealth-optimized propulsion system, including variable-cycle engines with thrust vectoring, the Bélos can operate at supercruise speeds without compromising stealth. The exhaust nozzles, integrated with plasma suppressors and advanced turbine cooling, minimize infrared and radar visibility while maintaining high thrust efficiency. Additionally, the Bélos’ mission systems and sensor suites are designed for low observability, employing stealthy apertures and emitters while ensuring robust situational awareness through data fusion and passive sensor arrays.

Materials

Material engineering was a prime interest in the project, given the experience with the RAM systems of the Kovas. The Bélos employs cutting-edge materials to ensure superior performance in the high-stress environments characteristic of modern aerial combat, prioritizing thermal management, structural integrity, and stealth. Ceramic matrix composites (CMCs) are integrated into high-heat regions, such as engine nozzles and leading edges, due to their exceptional heat resistance, low density, and durability at temperatures exceeding 1300°C. These materials outperform traditional aluminum-titanium alloys, which are prone to thermal fatigue, offering lightweight strength ideal for sustained supersonic operations.

The airframe and structural components rely on thermoplastic-polyamide composites (principally PEEK), reinforced with carbon fibers, to create lightweight yet tough skin panels. These composites, fabricated through additive manufacturing, enable the formation of monolithic, seamless panels that eliminate radar-reflective seams, fasteners, and joints while enhancing damage resistance and operational flexibility. Nanostructured titanium-aluminum alloys are selectively used in high-stress areas such as wing spars and fuselage frames, offering unparalleled strength-to-weight ratios and compatibility with surrounding materials, reducing fatigue under extreme aerodynamic loads.

To address the Bélos’ thermal signature and operational heat loads, an active thermal control system combines loop heat pipes and metallic foam heat exchangers. These systems ensure even heat distribution across the airframe, reducing infrared detectability while improving system reliability during prolonged supersonic or supercruise flight. High-temperature radar-absorbing coatings mitigate traditional stealth degradation caused by heat buildup, ensuring consistent low observability even under extreme conditions. Advanced coatings also offer multi-spectral absorption, targeting both radar and infrared frequencies, while resisting erosion and environmental wear.

The Bélos opts to incorporate structural radar-absorbent material (RAM) woven directly into the thermoplastic-polyamide composite skin of the aircraft, rather than being sprayed, painted, or affixed. By embedding carbon-nanotube-based RAM into the skin itself, the aircraft achieves an inherent radar-absorptive capability that eliminates the need for traditional external RAM coatings. This structural RAM exhibits broad-spectrum absorption, effectively countering radar systems operating across X-, S-, C-, and Ku-bands, as well as lower-frequency systems increasingly used in early warning applications. The carbon nanotubes, renowned for their exceptional conductivity and electromagnetic properties, are finely tuned to dissipate radar energy through magnetic and dielectric losses, converting it into heat. To manage this thermal load, the RAM incorporates heat-dissipating properties, leveraging the Bélos' thermal management system to disperse the heat uniformly, preventing hotspots that could compromise performance or stealth.

Additionally, anisotropic materials are strategically woven into the structural RAM at critical points, such as the leading edges of wings, canards, and intake lips, as well as the V-tail surfaces. These materials guide radar energy along controlled paths, redirecting it away from the emitter and preventing backscatter. This design significantly reduces the radar cross-section (RCS), particularly at oblique angles where scattering is most likely. Unlike traditional RAM coatings, which may degrade under environmental stressors or high speeds, the structural RAM is inherently bonded to the aircraft's skin, making it exceptionally durable and resistant to delamination, erosion, or wear caused by extreme temperatures, supersonic flight, or adverse weather conditions.

The benefits of this approach are manifold. First, the weight savings achieved by eliminating separate RAM coatings improve overall performance, including range, agility, and fuel efficiency. Second, the durability of structural RAM reduces maintenance demands, minimizing downtime and life-cycle costs compared to aircraft requiring frequent reapplication of external coatings. Third, the seamless integration of RAM into the Bélos’ skin ensures uniform stealth across the airframe, with no weak points susceptible to radar detection. The broad-spectrum absorption also allows the Bélos to remain stealthy in the face of modern multi-frequency radar systems, including advanced active electronically scanned array (AESA) radars and low-frequency over-the-horizon systems.

Powerplant

The Bélos is powered by twin variable-cycle engines, designated internally as the Xiphos-Aether Mk.IV propulsion system. This system outputs roughly 80,000 lbf of thrust. These engines represent the cutting edge of Willinkian aeronautical engineering, combining adaptive-bypass technology, fluidic thrust vectoring (FTV), transpiration cooling, and advanced materials such as nanostructured titanium-aluminum alloys and ceramic matrix composites (CMCs). Each subsystem is meticulously crafted to ensure the platform achieves superior stealth, agility, fuel efficiency, and durability under extreme conditions.

At the heart of the Xiphos-Aether Mk.IV engines lies an adaptive bypass system, permitting three operational cycles the engines can switch between: high-bypass for subsonic fuel efficiency, medium-bypass for transonic maneuvering, and low-bypass for supersonic thrust. This system enables the Bélos to supercruise—sustaining speeds of Mach 1.8–2.2 without afterburners—while maintaining fuel efficiency superior to legacy designs like the F-22’s Pratt & Whitney F119. The engine's bypass ducts are embedded with additively manufactured metallic foam heat exchangers, which efficiently dissipate thermal loads, allowing the engines to operate for extended periods without overheating. This subsystem is critical for enabling extended patrol missions, long-range interception roles, and survivability in contested environments where fuel and thermal management are paramount.

The combustion process is governed by a Staged Combustion Assembly (SCA), which utilizes rich-quench-lean (RQL) combustion techniques. This staged combustion process ensures complete and efficient fuel burn across a range of operational demands. During low-power settings, the system employs a lean mixture for fuel economy, while high-power settings rely on a richer burn to maximize thrust. The quench zone, located between the two combustion stages, rapidly cools the flame to minimize nitrogen oxide (NOx) emissions, a significant advantage in reducing the Bélos’ heat signature. The SCA is reinforced with CMCs, which provide heat resistance up to 1,800°C, ensuring durability and reliability under high thermal stresses during combat maneuvers or prolonged supersonic flight.

To manage extreme turbine temperatures, the engines employ a transpiration cooling system. This system uses micro-perforated turbine blades through which cool air flows, creating a protective boundary layer that prevents heat buildup. This cooling innovation extends the lifespan of critical engine components while supporting the Xiphos-Aether Mk.IV’s capability to sustain high-speed flight for extended durations. The rotor and stator assemblies of the low-pressure compressor (LPC) and high-pressure compressor (HPC) are constructed from nanostructured titanium-aluminum alloys. These materials provide exceptional strength-to-weight ratios, enabling the LPC and HPC to compress airflow with high efficiency, supporting the variable-bypass system’s adaptive needs.

The inlet ramps of the engines feature adaptive geometries that precisely control airflow to the compressors. These ramps adjust to compress air efficiently at supersonic speeds while minimizing shockwaves and turbulence. Their stealthy faceted design deflects radar energy away from detection systems, seamlessly integrating with the Bélos’ overall low-observable profile. During transonic and subsonic flight, the ramps optimize airflow to maintain efficiency, ensuring that the engines operate at peak performance across all flight regimes.

The Xiphos-Aether Mk.IV engines incorporate fluidic thrust vectoring (FTV) technology, eliminating the need for complex mechanical actuators that might compromise the Bélos’ stealth profile. The FTV system uses streams of compressed air injected strategically into the exhaust plume to redirect thrust. This allows the Bélos to achieve extreme agility at high angles of attack (AoA) and improves its ability to recover from stalls or execute complex post-stall maneuvers. The system is particularly advantageous during dogfights or evasive actions, offering unparalleled maneuverability while maintaining a smooth, stealthy profile. The rear nozzles are axisymmetric with stealth enhancements, incorporating serrated trailing edges and advanced coatings to minimize both radar and infrared signatures. The nozzles also feature variable-area geometries, allowing them to expand or contract based on thrust requirements. This adaptability not only improves propulsion efficiency during takeoff, supercruise, and combat but also enhances the engines’ ability to dissipate heat, reducing their thermal signature. The rear nozzles are coated with heat-resistant RAM materials, further enhancing their stealth capabilities by absorbing radar energy and minimizing reflective surfaces.

Compared to the Kovas, the Bélos benefits from superior efficiency at subsonic speeds, greater thrust at supersonic speeds, and extended endurance in loitering scenarios.