e-20 pontus | NAVAL aew&c
The E-20A Pontus is a four seat, twin turbojet powered, subsonic, long range active radar and passive electronic surveillance aircraft. It is designed for carrier operations with a compact airframe and spotting factor that features an unconventional high aspect-ratio nonplanar joined-wing geometry.
Active phased-array conformal radar arrays are integrated into the wings in a double triangle or "diamond" planform without the parasitic drag and extra weight penalties of a radar dome above the fuselage. Unlike a conventional dorsal rotordome (e.g., E-2 Hawkeye, E-3 Sentry, etc) that must look out over an aircraft's wings and tail the conformal radar arrays are not obstructed by any part of the airframe or by engine pods, and as they are non-rotating can provide continuous surveillance.
The joined-wing additionally offers a clean aerodynamic configuration that is ideally suited for carrier operations with a relatively high lift-to-drag (L/D) ratio and excellent flying qualities, superior wind-over-deck (WOD), gust alleviation and flutter suppression, and high stall and post-stall performance. Turbofan engines of high fuel economy provide efficient cruise and loiter performance for long periods of detection, combined with in-flight refueling for extended mission endurance, and high dash speeds to rapidly reach station areas.
The E-20A is powered by a pair of General Electric TF34-GE-400B non-afterburning, high bypass, axial-flow turbofan engines mounted in nacelles extending on pylons either side of the centre-fuselage. For easy maintenance the cowlings of the engine nacelles have large access doors, and are secured to the pylon by only four bolts for easy removal and replacement of the complete powerplant. Developing 9,275 lb/f (41.25 kN) in static takeoff thrust at Sea Level on a standard day and with a bypass ratio of 6.5:1 the TF34 power units are a highly efficient design that offer the highest thrust-to-weight (T/W) ratio and lowest specific fuel consumption (SFC) in their class. A low noise signature and low vibration improves ride comfort in the cabin for reduced crew fatigue during long patrols. The engines are fitted with cascade vane-type thrust reversers and have been updated with technology borrowed from the F414-GE-400 powerplant including lightweight ceramic matrix composite (CMC) turbine blades for increased component life, and a dual-channel full authority digital engine control (FADEC) system that provides improved reliability and operability, reduced maintenance and increased life in harsh rapid cycle carrier operational environments.
The redesigned engine core comprises six major sections for easy maintenance and component repair or replacement: (1) a forward-mounted single stage bypass fan driven by (2) a 4-stage low pressure (LP) turbine, providing supercharged ram air to (3) a 10-stage high pressure (HP) axial flow compressor for engine combustion, anti-icing, seal pressurisation and bleed air, that is driven by (4) a 2-stage air-cooled high pressure (HP) turbine, (5) a flow through annular combustor that ignites the fuel/air mix, and (6) an externally-mounted accessory gearbox. The fuel system consists of integral fuel tanks with bladder-type fuel cells in the belly (lower lobe) of the fuselage, a single-point pressure refuelling/defuelling point aft of the starboard main gear bay, and a fuel dump vent at the extreme rear of the fuselage. A retractable inflight refuelling (IFR) probe operated by electric drive motor is fitted to the upper centreline allowing probe-and-drogue air-to-air refuelling for extended range and loiter endurance.
The aircraft electrical system comprises four generators producing 115/200VAC, three phase, 400Hz power that is distributed by six AC electrical buses, and secondary DC power from two transformer rectifier units (TRU) supplying 28VDC at 200A to two DC electrical buses. The primary electrical sources are two engine-driven 75 kVA integrated drive generators (IDG), consisting of a constant speed drive (CSD) directly coupled to an engine accessory gearbox, and supply AC power to electrics, hydraulics and pneumatics and DC power via the power inverters to avionics. Mission systems, including the radar, as well as engine air start, ground air conditioning and preflight electrical power is supplied by an Auxiliary Power Generation System (APGS) enclosed within a fireproof compartment in the lower front fuselage. The APGS consists of a General Electric T700-GE-401C front-drive turboshaft engine developing 1,890 shp, an accessory gearbox, and two oil-cooled 170/255 kVA permanent magnet (PM) brushless generators. The powerplant inducts air from scoop-type ram-air intakes at the root of each forward wing and has a downward facing forced-air cooled exhaust. Standby instrument and emergency flight power in case of a total electric failure is provided from two rechargeable Ni-Cad battery packs supplying two redundant DC battery buses, one integrated into the APGS starter system and the other a backup system. A scoop-type ram air turbine (RAT) with its inlet at the base of vertical fin drives a 15 kVA generator to provide emergency electrical and hydraulic power to essential systems only.
The environmental control system (ECS) utilises bleed air taken from the engines using the boot strap cycle, or from APGS-driven compressors, to provide breathable air, cabin pressurisation, air conditioning, windshield defogging/deicing and avionics cooling (via heat exchangers), engine inlet and wing anti-icing, aircrew anti-g suit inflation, fuel transfer and fuel line cleaning. The crew is supplied 93% enriched oxygen by a On-Board Oxygen Generation System (OBOGS) that uses zeolite molecular sieve oxygen concentrators to filter out nitrogen, while nitrogen-enriched air for fuel tank pressurisation and fire and explosion suppression is provided by a separate On-Board Inert Gas Generating System (OBIGGS) using air separation modules to remove oxygen from processed air.
The main electro-hydraulic system includes primary flight control actuators, landing gear actuation, nose gear steering, thrust reversers, leading/trailing edge flaps, wing fold mechanisms and arrester hook. The tricycle forward retracting landing gear are equipped with carbon disc brakes on single wheel main gear and twin-wheel steerable nose gear. The nosewheels attach a catapult launch bar and retracts fully into the forward fuselage, while the main gears retract into wheel wells either side of the centre fuselage on foldable struts. Two-stage oleo-pneumatic (air-oil) shock absorbers dampen the powerful impact force from repeated carrier landings.
The E-20A has a fail-safe semi-monocoque/stressed skin fuselage fabricated mostly from injection moulded bismaleimide (BMI) themoset resin infused carbon prepreg, a highly durable carbon fibre resin matrix composite with qualities including high modulus strength, high stiffness, high impact resistance, superior fatigue and corrosion resistance to survive the harsh salt air/sea water environment, and low radar cross-section (RCS). Primary structure consists of integrally stiffened sandwich panels of the abovementioned carbon fibre/BMI prepreg that cover the fuselage and wings, and internal structure including longerons, stringers, frames, formers, wheel wells, pressure bulkheads, window frames and internal wing spars and ribs that are moulded from toughened carbon fibre-reinforced epoxy unidirectional prepreg tape. A keelson structure with two parallel beams runs the full length of the fuselage to stiffen and strengthen the airframe by distributing the repeated loadings of catapult launches and arrested landings. The vertical fin is built from carbon fibre skins over an aluminium honeycomb core.
Astroquartz silica fibre (99.99% pure fused silica) is used in the nose radome and radar transparent windows in the wings that lie flush with aircraft skin to preserve unbroken outer mould lines. Secondary structures comprise resin-bonded carbon-fibre reinforced plastic (CFRP) honeycomb used for access door covers, landing gear doors, flight control surfaces, engine pylons, and engine cowlings, and carbon fibre/Nomex honeycomb in floor panels and firewalls. Wing leading edges are constructed from high impact resistant and high melt temperature polyether ether ketone (PEEK) thermoplastic polymer matrix prepreg. Titanium beta alloy is used in cockpit bulkheads, landing gear struts and the A-frame arrester hook, and aluminium alloy forgings and glass-fibre reinforced plastic (GFRP) for interior fittings. Cockpit canopies and sensor windows are constructed from Zone 1 optical quality fusion bonded polycarbonate transparencies coated in a indium-tin-oxide (ITO) conducting film that provides, along with other thin-film dielectric coatings in the cabin and avionics bays, radio frequency and electromagnetic wave shielding.
The fuselage has a blunt rounded nose, a club-shaped profile that tapers to the rear, and oval cross-section providing maximum internal volume for main fuel tanks and mission electronics. A crew of four are accommodated in dual-tandem side-by-side arrangement within a pressurised and air conditioned forward cabin featuring large windows that provide unobstructed panoramic vision. Crew board the aircraft from an entry door/ladder that folds out from the port side of the forward fuselage hinging down to reveal integral access steps. An internal passageway runs through the cabin interconnecting all crew stations and aft mission avionics bay, allowing crew to move freely throughout the aircraft to troubleshoot avionics systems, switch seats, etc.
The aircrew comprises a flight crew of one pilot and a mission crew of three tactical officers who are seated on forward-facing, upward-firing Martin-Baker Mk.16L zero-zero (zero altitude, zero speed) ejection seats. A rigid seat survival kit (RSSK) is fitted into each seat bucket that packages an inflatable one-person life raft and survival equipment. The crew can eject individually (self eject) or using a command ejection system (group eject). The latter extracts all four crew members together in a staggered sequence beginning with the two back seaters, with automatic retraction of their keyboard trays before ejection, followed 0.5 secs by the two front seaters. The crew eject through frangible sections of the overhead canopy enclosures along laterally separated trajectories to avoid colliding with each other or any ejection hardware.
The E-20A has a high lift/low drag aerodynamic configuration with paired single-spar folding wings as lifting surfaces consisting of aft swept front aerofoils of positive dihedral and forward swept rear aerofoils with anhedral, that are joined at 40° sweep at the tips and the mindpoint of a swept-back vertical fin. The twin engines are placed in the void between the wings on the aircraft's centre of gravity (cg). The front aerofoils are lower than the rear aerofoils, with the aft wing serving as both a horizontal tail and support strut to the front wing for resisting aerodynamic bending loads. The wings are locked together in a diamond-shaped planform during flight and separate at mid-span to fold upwards and inwards into a compact spot factor to fit aircraft elevators and for efficient stowage in hangar bays.
The joined-wing configuration offers the same performance as a classical cantilever wing aircraft of twice the wing span for a similar total wing area, with improved low speed/high angle of attack (AOA) performance that is comparable to a delta wing of similar wing span. Other features include lower structural weight as the wing box structure eliminates torsion bars with only a rib/spar and skin structure, higher structural strength and stiffness by the self-reinforcement of the aft wing bracing the front wing, and improved characteristics including lower induced drag from the lighter wing structure, reduced trim drag, low vortex drag, low wave drag due to favourable transonic area distribution, a higher lift coefficient, less flutter tendency and improved stability.
Flight control surfaces consist of full-span slats, elevons and flaperons on the front wings and elevators on the rear wings that operate in a variety of combinations of pitch, roll, direct lift and direct side force control; and upper and lower rudders on the vertical fin for yaw control. The controls provide excellent handling qualities at various flight conditions (low speed, high speed, stall, post-stall, crosswind, high altitude and low altitude) and manoeuvres such as push pull, minimum time to bank, aircraft trim, and one engine inoperative (OEI). The wing fold mechanisms and flight control surfaces are electrically signalled and electro-hydraulically actuated by low mass Moog actuators supplied by double-hydraulic/double-electric (2H/2E) power distribution systems that feature two primary electro-hydraulic channels and two backup electrical circuits for dual redundancy.
The aircraft is flown by a quadruple-redundant, fly-by-light (FBL) control architecture using FireWire-based MIL-1394 (SAE AS5643) Fibre Channel optical data buses, a fault-tolerant three-axis stabilised, dual-redundant full authority digital flight control system (DFCS) that operates flight controls, landing gear, nose gear steering and thrust reversers, and a dual-redundant four-axis digital autopilot system and automatic carrier landing system. An integrated modular avionics (IMA) architecture comprising four flight management system (FMS) computers distributed between redundant forward and aft avionics bays contains real-time computing modules based on commercial-off-the-shelf (COTS) quad-core PowerPC processors. The computers generate nonlinear, multichannel control laws with full flight envelope protection for the complex joined-wing aerodynamics including relaxed static stability (RSS) augmentation, automatic gust alleviation and flutter suppression.
The pilot is seated to port and the combat information officer (CIO) to starboard in the front cockpit, and the air controller and radar operator interchangeably at identical stations in the rear cockpit. The pilot's instrument panel has a wide field-of-view head-up display (HUD) and up-front control panel (UFCP) with LED character display, hands on throttle and stick (HOTAS) controls with centre flight stick column, rudder pedals/toe breaks and left or right swappable throttle quadrant, standby instruments and control panels in side consoles, and three head-down displays (HDD): a centre 8 x 8-inch situation display (SD) flanked by two 6 x 6-inch multi-function displays (MFD). The CIO has an upper UFCP and four HDD: three side-by-side 6-inch MFD above a centre 8-inch SD, with a 5 x 5-inch multi-function control and display unit (MCDU) in a side console with 16 function keys, 12 line-select keys and 40 alphanumeric keys, for accessing avionics and mission information. The rear cockpit provides two identical stations for the air controller and radar operator consisting of an upper 19 x 19-inch tactical situation display (TSD) above two 9.5 x 9.5-inch multi-function touch displays (MTFD), and a stowable/foldable integrated control system (INCSO) tray with rugged full-travel backlit keyboard and trackball controller. All displays uses high energy efficiency, low heat generating LED backlit active matric LCD (AMLCD) colour displays, and are driven by PowerPC display processors and integrated by Fibre Channel network switches.
The primary mission sensor is the Synergy Electrodynamics E/APY-03(V) Watchpost Conformal Airborne Early Warning Radar (CAEWR), a ultra high frequency (UHF) band (NATO C-band, IEEE P-band) solid-state electronically scanned array (ESA) multimode three-dimensional pulse-Doppler radar. Operating at a peak radiated power of 160 kW and cruise altitude of 10,688 m (35,000 ft) it provides full-time wide-area surveillance coverage of a 13,750,832 km³ (3,299,000 cubic mile) volume of airspace, with a full radar look-down range to the horizon of 436 km (235 nautical miles) and look-up range of 1,112 km (600 nm).
High performance radar signal processors (RSP) and radar data processors (RDP) enable the system to simultaneously detect, identify and track up to 3,000 air and surface targets and compute continuous multiple intercept vectors on up to 300 tracks - a capability to hold 50% more tracks at twice the range of its nearest peer the E-2D Advanced Hawkeye. The system employs a number of techniques to achieve this including operating in the low band 300-600 MHz spectrum to counter low observable (LO) airframe structures and ship superstructures, interleaving of air-to-air, maritime and littoral/over-land detection modes, duty cycle pulse compression waveforms for high range resolution, high pulse repetition frequency (PRF) waveforms and constant false alarm rate (CFAR) algorithms to descriminate targets from clutter, noise and decoys, and for anti-jam and moving target indicator (MTI) filtering, low sidelobes, sector blanking and frequency agile waveforms to resist jamming, and Doppler beam sharpening (DBS) techniques for three-dimensional high resolution imaging.
The radar system consists four fixed high radiated power ultra low sidelobe conformal non-load-bearing antenna (CNLA), one each integrated into the structure of a single-spar wing on their leading or trailing edges, that provide a huge 55.74 m² aperture size of very high gain sensitivity for detecting small air and surface targets at long range. Each array is an end-fire antenna that electronically scans a sector 120° in azimuth and ±120° in elevation, with all four arrays in the diamond wing planform providing full instantaneous 360° spherical look-up/look-down scan coverage without any interference or blind-spots from being masked by aircraft structure. The arrays are fixed to the internal wing structure on stiff graphite epoxy beds so that aerodynamic moments and wing flexing does not interfere with the rigid antennas. The antennas are populated with thousands of low cost transmit/receive (T/R) solid-state radiating elements capable of multi-channel digital beamforming (DBF) and electronic steering of multiple simultaneous low probability of intercept (LPI)/low probability of detection (LPD) transmit and receive radar pencil beams. Gallium nitride on silicon carbide (GaN-on-SiC) monolithic microwave integrated circuit (MMIC) beamforming networks feed the phased-array antenna and front-end VME-based multi-channel digital receiver/exciter (DREX) modules. An Identification Friend-Or-Foe (IFF)/secondary surviellance radar subsystem is integrated into each antenna to provide positive identification of cooperative targets.
Tightly integrated with the prime radar system is the Synergy Electrodynamics AN/ALQ-232 Integrated Radar/Communications/Signals Intelligence and Analysis System (RICASSO), a fully automated electronic support measures (ESM) system that provides signals intelligence (SIGINT) over a wide range of frequencies from HF through K-band (0.03 to 40 GHz) including pulse-Doppler radar i.e. electronic intelligence (ELINT) and communications intelligence (COMINT), from surface-ship, submarine, airborne, and land-based emitters. It can passively detect, identify, characterise and track emitters at extended ranges in very dense radio frequency (RF) environments, with a digital direction finding (DF) subsystem providing high accuracy bearing information. Signals are collected by conformal broadband dipole antenna and wide-open-amplitude monopulse DF antenna that cover all four quadrants of the aircraft for high spatial resolution. The RF front-end consists of high dynamic range wideband superheterodyne search and intercept receivers and the back-end processing system electronic signal processors (ESP), digital correlators and preloaded emitter libraries that identify non-cooperative targets. RICASSO produces high quality tactical information that can be processed by traffic analysis algorithms to map enemy electronic-order-of-battle (EOB), and can fuse raw sensor data (range/rate for radar, identification/bearing for ESM) for improved positional accuracy of tracks.