The Hawkeye has been flying in various forms for more than 40 years - and the latest variant promises much more. Why is it so durable?

When it comes to longevity, there are few programmes that can trace their lineage as far as the Northrop Grumman E-2C Hawkeye, successor to the W2F-1 prototype first flown 43 years ago. The airborne early warning (AEW) aircraft has progressively evolved from the E-2A to the E-2B, through a succession of different E-2C variants starting in the 1970s to the latest Hawkeye 2000. Work is due to start next month on the Advanced Hawkeye, representing the most far-reaching development and one that will keep the type in US Navy service beyond 2020.

Externally, today's E-2C Hawkeye 2000 and tomorrow's Advanced Hawkeye differ little from the aesthetically ungainly, but robust, twin-turboprop design that has populated USN carrier flightdecks since 1963. The navy once considered an all-new replacement in the form of the Common Support Aircraft, which would have also replaced the E-2's cargo-carrying sister, the C-2 Greyhound, and the Lockheed S-3 Viking, but it proved too expensive to develop.

"The key is a great legacy platform that is hard to improve on. It's already carrier qualified and it would cost a huge sum of money to redevelop that," says Tom Williams, Northrop Grumman vice-president AEW programmes. Internally, Advanced Hawkeye will represent essentially a new aircraft, encompassing a new radar system, including antenna, coupler, processors, transmitters and receivers, along with redesigned cockpit, improved communications and mission avionics and uprated power generation.

The USN is budgeting $2.1 billion for system development and demonstration (SDD) of the Advanced Hawkeye over the next nine years, about half of which will be expended on the radar modernisation programme (RMP).

Northrop Grumman Integrated Systems has given prime responsibility for the radar to Lockheed Martin Naval Electronics & Surveillance Systems, which is teamed with Raytheon and Northrop Grumman Electronic Systems (ES), supplying the receiver and transmitter modules, respectively.

The RMP reflects today's much broader USN AEW mission, which is no longer focused solely on the traditional blue water domain, but encompasses joint operations in littoral and overland environments, where clutter cancellation and increased jamming are major design drivers. The decision was made to go for a hybrid, mechanically rotated, electronically steered, solid-state UHF antenna. The system incorporates space/time adaptive signal processing enabling the radar to rotate mechanically to provide 360° coverage, while simultaneously electronically scanning critical areas and maintaining continuous target track updates.

Radar improvements

Compared to the much shorter-wavelength X-band systems associated with other active electronically scanned array (AESA) systems, it is claimed Advanced Hawkeye's UHF system will be much less vulnerable to atmospheric attenuation and better able to detect small radar cross-section targets. This is balanced against the AESA's narrower beamwidth and superior accuracy, which better lends itself to automatic target recognition capabilities. "UHF frequency is a trade driven by a number of considerations such as power, clutter, weather and platform real estate," says Mark Hartnett, Lockheed Martin AEW programme manager.

A UHF AESA (UESA) radar is the subject of an Office of Naval Research (ONR) technology programme and could provide Advanced Hawkeye with a follow-on system to the RMP, but the challenge is getting it into the aircraft. Whereas X-band radars feature multiple transmit/receiver modules in the antenna itself to minimise signal loss, UHF's longer wavelength is less susceptible to cable loss, but requires larger individual transmitter and receiver modules that can only be accommodated inside the aircraft. Although this reduces antenna weight and makes for easier maintenance access, there is the issue of space inside a compact carrierborne platform such as the E-2C.

The UESA system requires 27 transmit modules. This is down from 54 originally, but is still more than the 18 elements that make up the RMP. Weighed against this is Hawkeye's 7.3m (24ft)-diameter rotodome, home to the APS-145 UHF radar and the future L-3 Randtron ADS-18 RMP antenna, which the navy wants to keep to avoid expensive aerodynamic design changes. This limits the size of non-rotating phased-array antenna that can be accommodated, which in turn has an impact on power output and detection range. Reducing the number of transmit and receive modules without improved efficiency will only further reduce antenna gain.

"UESA is not part of the programme of record and it is several levels down in terms of maturity. However, we're working closely with ONR to derive a benefit from anything they develop that can be incorporated into Advanced Hawkeye. The system is being designed to insert other elements of other advanced technologies as they advance and reach the right state of maturity, but they need to mature before we can consider them," says Bob Labelle, USN E-2 programme manager.

The RMP system, in addition to 18 channels for radar, will have three more elements for IFF integration and other functions, all fed through a 21-channel rotary coupler. RMP will operate in one of three primary modes, full mechanical rotation at about 6RPM, a slower mechanical rotation with electronic beam steering, and a stopped radome with full electronic scan. The RMP is billed as offering almost twice the detection range of the APS-145, in addition to superior near-land/overland performance.

An early engineering version of the RMP's antenna, transmitter, receiver and rotary coupler have already been flown on a Lockheed Martin NC-130H testbed at the USN's NAS Patuxent River base. The aircraft is devoid of any radar workstations; the data instead is recorded on board for later analysis on the ground. The navy is planning 24 flights in the initial phase and will use the aircraft again around mid-2005, re-equipped with a more representative development system, as a lead into flight testing of two Advanced Hawkeye SDD aircraft starting in 2007.

The Advanced Hawkeye/RMP effort builds on the earlier improvements made to the E-2C under the Hawkeye 2000 programme, which included new advanced indicator control set (ACIS) workstations, mission computer and Lockheed Martin ALQ-217 electronic support measures in place of the Litton ALR-73 passive detection system, which is now difficult to support.

As a result of advances in processing power and the additional capacity needed for RMP, Advanced Hawkeye will need a new mission computer. Consolidating the display processors into the mission computer cabinet to cut weight is being considered, but this would mean new off-the-shelf displays in place of ACIS workstations.

Structurally, the aircraft remains unchanged, aside from an upgraded centre fuselage to accommodate the additional weight of the RMP, which will feature producibility improvements such as machined bulkheads. The centre fuselage, along with the cockpit and empennage attack points, have been mapped with Catia design software, but the USN and Northrop Grumman have resisted making any material changes. "We could have gone to an all-composite design and saved weight, but this would have needed a lot more time and money to get re-qualified," says Jim Culmo, Northrop Grumman, Advanced Hawkeye programme director.

New displays

New large flight instrument and tactical displays are planned for the Advanced Hawkeye in the first major upgrade of theE-2/C-2 cockpit in 30 years, other than navigation improvements made to the E-2C Group 2 and Hawkeye 2000 versions. The notional cockpit would be centred on three 430mm (17in) multifunction displays.

"We're adding the capability to display tactical information in the front, in essence adding a fourth operator by emulating at the co-pilot station what's in the back," adds Culmo.

The new cockpit is also intended to further improve the aircraft's precision with the introduction of integrated satellite/inertial navigation, in support of better radar-tracking accuracy and to ensure compliance with the global air traffic management (GATM) system. Other additions will include new traffic collision avoidance and terrain avoidance systems, together with 8.33kHz-spacing VHF communications and protected instrument landing system for operations in Europe. Four companies are bidding to supply the integrated cockpit - Honeywell, L-3, Northrop Grumman ES and Smiths Aerospace.

Northrop Grumman is expected to decide soon on this and around 30 other work packages that are being competitively proposed. These include a new IFF, more powerful 170/225kVA generators, improved liquid cooling for the radar and a modular communications system based initially on the ARC-210, with later provision for the Joint Tactical Radio System. The USN has studied re-engining Advanced Hawkeye with more-efficient 3,725kW (5,000shp) class turboprops in place of Rolls-Royce T56-427s.

No spare cash

Among the engines examined are the R-R AE2100 and Pratt & Whitney Canada PW150, but with the addition of GATM-compliant systems having already inflated the cost of SDD, there appears to be no spare cash for a new powerplant. "The study and other work ongoing at the time led us to the conclusion that the current engine meets all the performance requirements. However, we're studying it to see if we can generate some cost savings over the life of the aircraft, if we invest in a new engine," says Labelle.

Advanced Hawkeye, irrespective of engine choice, will feature a new composite eight-blade propeller that is in the works for Hawkeye 2000 and the C-2 transport. The Hamilton Sundstrand NP2000 is based on the Ratier Figeac six-blade propeller on the ATR 42/72-500. Vibration problems early in flight test at Patuxent River have pushed back initial fielding of the NP2000 until later this year or early next year.

The USN is planning other improvements to the E-2C outside the Advanced Hawkeye programme. These include the addition of onboard oxygen generators; provision for probe-and-drogue inflight refuelling, for which Israel Aircraft Industries holds the design drawings, and the addition of the Block 2 co-operative engagement capability (CEC). The Raytheon CEC Block I system fitted to Hawkeye 2000 has just been deployed to sea for the first time aboard the aircraft carrier USS Nimitz heading for the Gulf.

CEC represents the navy's first step towards network-centric warfare with the creation of a C-band sensor network providing USN surface vessels and aircraft with a single integrated air picture and the ability to engage threats at extended ranges. The Block 2 version now being offered is intended to be lighter and less expensive than the present system, which on the E-2C adds 320kg (145lb) in the form of a large belly-mounted phased-array antenna, a data distribution system and processor.

Wider role

"CEC gets us data we need to perform a host of different roles as the ears and eyes of the fleet. It makes the E-2C a pivotal node in the network, allowing it to acquire and deliver data, process and manipulate data and serve in a command and control capacity," says Williams. The aircraft's potential for performing a wider role was highlighted by the Afghanistan conflict, during which the need for AEW became secondary to co-ordinating and controlling allied fighters and deconflicting airspace use.

Northrop Grumman envisages the Advanced Hawkeye's longer-term role broadening to take in battle management through the fusing of onboard and off board intelligence, surveillance and reconnaissance sensor data from manned and unmanned air vehicles, and providing targeting and weapon release authority. A separately funded research effort to that of Advanced Hawkeye has been to give the aircraft a role in theatre missile defence. The navy has already tested a Raytheon infrared search and track sensor on an E-2C to detect missiles in the boost phase and identify launch locations.

With the multi-year production run of 21 Hawkeye 2000s for the USN starting to wind down from this year, Northrop Grumman is negotiating a follow-on purchase of eight more aircraft over four years to help plug the gap and provide continuity for subcontractors until work starts in 2008 on the first four Advanced Hawkeyes. These would comprise four TE-2C trainers devoid of mission avionics and four more Hawkeye 2000s, two of which would be modified into Advanced Hawkeye SDD test aircraft. This will leave Northrop Grumman short of the minimum rate of four aircraft a year needed to sustain its St Augustine, Florida, plant. The hope is that international sales will make up the shortfall.

The USN intends to buy 75 Advanced Hawkeyes, with an initial operational capability targeted for 2011, but could order more if it follows though with plans to replace the Hawkeye 2000 and possibly expand to eight the number of aircraft assigned to each carrier air group to support a 24h, seven-day operational tempo.

There is growing international interest in Advanced Hawkeye, including from the UK. "We're looking at what is exportable and not and if there are architectural changes to allow future sales to countries asking for the latest and greatest," says Williams.

Source: Flight International