Over the past decade, the focus for US carrier-based aviation has shifted from the deep ocean and superpower confrontation to the shoreline and overland operations. This is reflected in a changing mix of aircraft on carrier decks.
Grumman's A-6 Intruder long-range strike aircraft has been gone from US Navy flightdecks for a decade and its F-14 Tomcat, designed to defend carrier battlegroups against Soviet bombers, was retired in 2006. Lockheed's S-3 Viking, intended for blue-water anti-submarine warfare, will follow in 2009.
By 2020, the carrier air wing will have been reshaped around its new role in littoral warfare. In place of A-6s, EA-6s, F-14s and S-3s, there will be two main types: the Boeing F/A-E/F Super Hornet (and electronic-attack EA-18G Growler) and Lockheed Martin F-35 Lightning II strike fighters. But there will be one long-familiar shape still on the deck - Northrop Grumman's E-2 Hawkeye.
While it looks little different externally, the E-2D Advanced Hawkeye (AHE) now under development has a capability well beyond the E-2's original role as a radar picket. The aircraft's mission includes battle management and control over land, and theatre air and missile defence for naval forces operating close to the shore.
When it entered service in 1964, the E-2A was the US Navy's first purpose-designed carrier-based airborne early warning aircraft. The Hawkeye's airframe has served well, but its contents have changed many times over the years. The E-2C became operational in 1973 and has had several upgrades, culminating in the current production Hawkeye 2000 (HE2K).
The E-2D began as a radar upgrade, but evolved into a complete revamp of the Hawkeye to tackle obsolescence issues and emerging missions. The heart of the AHE is a new Lockheed Martin APY-9 solid-state radar, but the upgrade includes a digitally designed airframe, open-architecture
mission system, integrated glass cockpit, digital engine controls, more power and cooling, and expanded communications.
Northrop was awarded the $1.9 billion E-2D system development and demonstration contract in July 2003, and flew the first of two development aircraft, Delta One, from its St Augustine, Florida plant in August 2007. The second aircraft, Delta Two, flew in November. Delta One is assigned to flying qualities and performance testing, while Delta Two is the main mission-system test aircraft.
The familiar outline of the E-2D disguises the fact that the fuselage and centre wing structure are redesigned to reduce weight and increase strength, with more machined parts. The outer wing panels and four-tail empennage are unchanged, but reworking an airframe designed 50 years ago using today's three-dimensional design tools was a challenge.
After just two flights, Delta One was grounded to inspect hydraulic lines for chafing caused by vibration. Although the hydraulic lines were designed using CATIA, there were concerns about chafing and a requirement to inspect a sample set of hydraulic lines was established before flight testing began. This revealed several instances of chafing, leading to a decision to inspect all the lines.
Risk of chafing
Some 160 hydraulic lines - about 17% of the total - were found to have some risk of chafing, but less than 1% required redesign and replacement. Most issues were fixed by adjusting clearances and moving clamping points, but work took longer than expected and delayed the E-2D's return to flight to late September, affecting the start of radar testing.
The new APY-9 radar has a solid-state silicon carbide-based transmitter with higher power for extended range, and digital receivers to increase sensitivity. The surveillance envelope of the UHF radar is about 250% larger than the E-2C's.
A new L-3 Randtron antenna combines controllable mechanical rotation with the ability to scan the beam electronically in azimuth. This allows the beam to dwell on targets, to increase sensitivity, and look back to update tracks. The antenna can be slowed or stopped to stare in one direction.
The APY-9 uses space-time adaptive signal processing to reduce ground clutter and, compared to the E-2C's Lockheed APS-145 radar, provides "true overland capability" and the ability to detect smaller targets, says US Navy programme manager Capt Randy Mahr. This enables the E-2D to perform the littoral mission, including detecting and tracking ballistic and cruise missiles launched from land.
Inside the E-2D is a fibreoptic network and new operator workstations with large colour flat-panel displays. The mission computer is the same as in the upgraded Hawkeye 2000. This provides an open hardware architecture and will allow the move to an open software architecture at a later stage.
In a major change, one of the three 430mm (17in) LCDs on the new flightdeck can display mission information, enabling the non-flying pilot to act as a fourth operator. This will help the E-2D's crew cope with its expanded mission, and will become important when the Hawkeye receives in-flight refuelling capability for the first time. Development will begin this year, leading to flight tests in 2009 on an E-2C. In-flight refuelling will double the Hawkeye's mission endurance.
As well as a beefed-up structure and higher gross weight, the AHE has upgraded cooling and uprated generators. The Rolls-Royce T56-427A turboprops introduce full-authority digital engine control that provides an automatic power reserve for single-engine operation and integrates control of the eight-blade Hamilton Standard NP2000 propeller.
Carrier testing
Flight testing of the Advanced Hawkeye will continue at St Augustine to the end of 2008, when the aircraft will transfer to the US Navy test centre at Patuxent River, Maryland for carrier testing and sea trials in 2009-10. Delta One is focused on air vehicle testing, and is working towards certification for instrument flight operations.
Delta Two has been undergoing installation and integration of the radar system. The first radar flight test is expected in early February. The radar has been undergoing rooftop testing at Northrop's Bethpage, New York facility to gather data for validation in flight, says Mahr.
Northrop will deliver the last two E-2Cs in 2009 and is under contract to build three pilot production E-2Ds, to be used for operational evaluation beginning in 2010. The original plan for four-pilot aircraft was cut back because of cost increases, principally on redesigning the airframe and integrating the glass cockpit. The US Navy plans to buy a total of 75 E-2D Advanced Hawkeyes to replace E-2Cs on carriers decks beginning in 2011.
Northrop Grumman is about to begin radar testing on an improved E-2 Hawkeye that will enable the US Navy to move closer to the shore and operate over land
Source: Flight International
