E-2D Hawkeye

The Northrop Grumman E-2 Hawkeye is an American all-weather, carrier-capable tactical airborne early warning (AEW) aircraft. This twin-turboprop aircraft was designed and developed during the late 1950s and early 1960s by the Grumman Aircraft Company for the United States Navy as a replacement for the earlier, piston-engined E-1 Tracer, which was rapidly becoming obsolete. The aircraft's performance has been upgraded with the E-2B and E-2C versions, where most of the changes were made to the radar and radio communications due to advances in electronic integrated circuits and other electronics. The fourth major version of the Hawkeye is the E-2D, which first flew in 2007. The E-2 was the first aircraft designed specifically for its role, as opposed to a modification of an existing airframe, such as the Boeing E-3 Sentry. Variants of the Hawkeye have been in continuous production since 1960, giving it the longest production run of any carrier-based aircraft.

The E-2 also received the nickname "Super Fudd" because it replaced the WF (later E-1) "Willy Fudd". In recent decades, the E-2 has been commonly referred to as the "Hummer" because of the distinctive sounds of its turboprop engines, quite unlike that of turbojet and turbofan jet engines. In addition to U.S. Navy service, smaller numbers of E-2s have been sold to the armed forces of Egypt, France, Israel, Japan, Mexico, Singapore and Taiwan.

Grumman also used the basic layout of the E-2 to produce the Grumman C-2 Greyhound cargo aircraft.

Development

Background

Continual improvements in airborne radars through 1956 led to the construction of AEW airplanes by several different countries and several different armed forces. The functions of command and control and sea and air surveillance were also added. The first carrier-based aircraft to perform these missions for the U.S. Navy and its allies was the Douglas AD Skyraider, which was replaced in US Navy service by the Grumman E-1 Tracer, which was a modified version of the S-2 Tracker twin-engine anti-submarine warfare aircraft, where the radar was carried in an aerofoil-shaped radome carried above the aircraft's fuselage.Godfrey 1977, pp. 7–8.

E-2A and E-2B Hawkeye

In 1956, the U.S. Navy developed a requirement for an airborne early warning aircraft where its data could be integrated into the Naval Tactical Data System aboard the Navy's ships, with a design from Grumman being selected to meet this requirement in March 1957.Swanborough and Bowers 1976, p. 244. Its design, initially designated W2F-1, but later redesignated the E-2A Hawkeye, was the first carrier plane that had been designed from its wheels up as an AEW and command and control airplane. The design engineers at Grumman faced immense challenges, including the requirement that the aircraft be able to operate from the older modified s. These vessels were built during World War II and were smaller than modern carriers, being later modified to allow them to operate jet aircraft. Consequently, various height, weight and length restrictions had to be factored into the E-2A design, resulting in some handling characteristics which were less than ideal. However, the E-2A never operated from the modified Essex class carriers.

The first prototype, acting as an aerodynamic testbed only, flew on 21 October 1960. The first fully equipped aircraft followed it on 19 April 1961 and entered service with the US Navy as the E-2A in January 1964.Taylor 1976, p. 291. By 1965, the project had accumulated so many development issues that it was cancelled after 59 aircraft had already been built. In particular, difficulties were being experienced due to inadequate cooling in the closely packed avionics compartment. Early computers and complex avionics systems generated considerable heat and could fail without proper ventilation. These issues continued long after the aircraft entered service. At one point, reliability was so bad that the entire fleet of aircraft was grounded.

After Navy officials had been forced to explain to Congress why four production contracts had been signed before avionics testing had been completed, action was taken; Grumman and the US Navy scrambled to improve the design. The unreliable rotary drum computer was replaced by a Litton L-304 digital computer and various avionics systems were replaced – the upgraded aircraft were designated E-2Bs. In total, 49 of the 59 E-2As were upgraded to E-2B standard. These aircraft replaced the E-1B Tracers in the various US Navy AEW squadrons.

E-2C Hawkeye and upgrades

Although the upgraded E-2B was a vast improvement on the unreliable E-2A, it was an interim measure. The US Navy knew the design had much greater capability and had yet to achieve the performance and reliability parameters set out in the original 1957 design. In April 1968, a reliability improvement program was initiated. In addition, now that the capabilities of the aircraft were starting to be realized, more were desired; 28 new E-2Cs were ordered to augment the 49 E-2Bs that would be upgraded. Improvements in the new and upgraded aircraft were concentrated in the radar and computer performance.

Two E-2A test machines were modified as E-2C prototypes, the first flying on 20 January 1971. Trials proved satisfactory and the E-2C was ordered into production. The first production aircraft performed its initial flight on 23 September 1972. The original E-2C, known as Group 0, consisted of 55 aircraft; the first aircraft became operational in 1973 and serving on carriers in the 1980s and 1990s, until they were replaced in first-line service by Group II aircraft. US Navy Reserve used some aircraft for tracking drug smugglers. The type was commonly used in conjunction with Grumman F-14 Tomcat fighters; monitoring airspace and then vectoring Tomcats over the Link-4A datalink to destroy potential threats with long range AIM-54C Phoenix missiles.

The next production run, between 1988 and 1991, saw 18 aircraft built to the Group I standard. Group I aircraft replaced the E-2's older APS-125 radar and T56-A-425 turboprops with their successors, the APS-139 radar system and T56-A-427 turboprops. The first Group I aircraft entered service in August 1981. Upgrading the Group 0 aircraft to Group I specifications was considered, but the cost was comparable to a new production aircraft, so upgrades were not conducted. Group I aircraft were only flown by the Atlantic fleet squadrons. This version was followed within a few years by the Group II, which had the improved APS-145 radar. A total of 50 Group II aircraft were delivered, 12 being upgraded Group I aircraft. This new version entered service in June 1992 and served with the Pacific and Atlantic Fleet squadrons.

By 1997, the US Navy intended that all front line squadrons would be equipped, for a total of 75 Group II aircraft. Grumman merged with Northrop in 1994 and plans began on the Group II Plus, also known as the Group II / NAV upgrade. This kept the same computer and radar as the Group II while upgrading the pilot avionics, such as replacing the mechanical Inertial Navigation System (INS) with a more reliable and accurate laser Ring Gyroscope-driven INS, installing dual Multifunction Display Units (MFCDUs) (vice one in the Group II) and integrating GPS into the weapon system. A variant of the Group II with upgrades to the mission computer and CIC workstations is referred to as the MCU/ACIS, these were produced in small numbers due to production of the Hawkeye 2000 soon after its introduction. All Group II aircraft had their 1960s vintage computer processors replaced by a mission computer with the same functionality via modern computer technology, referred to as the GrIIM RePr (Group II Mission Computer Replacement Program, pronounced "grim reaper").

Another upgrade to the Group II was the Hawkeye 2000, which featured the same APS-145 radar but incorporated an upgraded mission computer and CIC (Combat Information Center) workstations (Advanced Control Indicator Set or ACIS and carries the U.S. Navy's new CEC (cooperative engagement capability) data-link system. It is also fitted with a larger capacity vapor cycle avionics cooling system. Starting in 2007 a hardware and software upgrade package began to be added to existing Hawkeye 2000 aircraft. This upgrade allows faster processing, double current trackfile capacity and access to satellite information networks. Hawkeye 2000 cockpits being upgraded include solid-state glass displays and a GPS-approach capability. The remaining Hawkeye Group II NAV Upgrade aircraft received GPS approach capability, but did not get the solid-state glass displays.

In 2004, the E-2C's propeller system was changed; a new eight-bladed propeller system named NP2000 was developed by the Hamilton-Sundstrand company to replace the old four-bladed design. Improvements included reduced vibrations and better maintainability as a result of the ability to remove prop blades individually instead of having to remove the entire prop and hub assembly. The propeller blades are of carbon fiber construction with steel leading edge inserts and de-icing boots at the root of the blade.

E-2D Advanced Hawkeye

Once considered for replacement by the " Common Support Aircraft", this concept was abandoned. The latest E-2 version is the ''E-2D Advanced Hawkeye'', which features an entirely new avionics suite including the new AN/APY-9 radar, radio suite, mission computer, integrated satellite communications, flight management system, improved T56-A-427A engines, a glass cockpit and aerial refueling. The APY-9 radar features an active electronically scanned array (AESA), which adds electronic scanning to the mechanical rotation of the radar in its radome. The E-2D includes provisions for the copilot to act as a "Tactical 4th Operator" (T4O), who can reconfigure his main cockpit display to show radar, IFF, Link 16 (JTIDS)/CEC and access all acquired data. The E-2D's first flight occurred on 3 August 2007. On 8 May 2009, an E-2D used its Cooperative Engagement Capability system to engage an overland cruise missile with a Standard Missile SM-6 fired from another platform in an integrated fire-control system test. These two systems will form the basis of the Naval Integrated Fire Control – Counter Air (NIFC-CA) when fielded in 2015; the USN is investigating adding other systems to the NIFC-CA network in the future.

The APY-9 radar has been suspected of being capable of detecting fighter-sized stealth aircraft, which are typically optimized against high frequencies like Ka, Ku, X, C and parts of the S-bands. Small aircraft lack the size or weight allowances for all-spectrum low-observable features, leaving a vulnerability to detection by the UHF-band APY-9 radar, potentially detecting fifth-generation fighters like the Russian Sukhoi Su-57 and the Chinese Chengdu J-20 and Shenyang J-31. Historically, UHF radars had resolution and detection issues that made them ineffective for accurate targeting and fire control; Northrop Grumman and Lockheed claim that the APY-9 has solved these shortcomings in the APY-9 using advanced electronic scanning and high digital computing power via space/time adaptive processing. According to the Navy's NIFC-CA concept, the E-2D could guide fleet weapons, such as AIM-120 AMRAAM and SM-6 missiles, onto targets beyond a launch platform's detection range or capabilities.

Deliveries of initial production E-2Ds began in 2010."Northrop Grumman's E-2D Advanced Hawkeye Program Demonstrating Continued Success"
. Northrop Grumman, 9 December 2009. On 4 February 2010, Delta One conducted the first E-2D carrier landing aboard USS ''Harry S. Truman'' as a part of carrier suitability testing. On 27 September 2011, an E-2D was successfully launched by the prototype Electromagnetic Aircraft Launch System (EMALS) at Naval Air Engineering Station Lakehurst. On 12 February 2013, the Office of the Secretary of Defense approved the E-2D to enter full-rate production. The Navy plans for an initial operational capability by 2015. In June 2013, the 10th E-2D was delivered to the Navy, with an additional 10 aircraft in various stages of manufacturing and predelivery flight testing. On 18 July 2013, Northrop Grumman was awarded a $113.7 million contract for five full-rate production Lot 2 E-2D Advanced Hawkeye aircraft. On 13 August 2013, Northrop Grumman was awarded a $617 million contract for five E-2Ds until full-rate production Lot 1. On 30 June 2014, Northrop Grumman was awarded a $3.6 billion contract to supply 25 more E-2D, for a total contracted number of 50 aircraft; 13 E-2D models had been delivered by that time.

In December 2016, an E-2D flew for the first time fitted with an aerial refueling capability. This feature will allow the aircraft to double its time on station to five hours and increase total mission time from four to seven hours. The refueling modification will start being built into the 46th plane (out of 75 planned) for delivery in late 2020 costing an additional $2 million per aircraft and the Navy plans to retrofit the feature on all previous Hawkeyes for $6 million per plane.

Design

The E-2 is a high-wing airplane, with one Allison T56 turboprop engine (5250 shp rating) on each wing and retractable tricycle landing gear. As with all carrier-borne airplanes, the E-2 is equipped with a tail hook for recovery (landing) and the nose gear can attach to a shuttle of the aircraft carrier's catapults for launch (takeoff). A distinguishing feature of the Hawkeye is its 24-foot (7.3 m) diameter rotating radar dome (rotodome) that is mounted above its fuselage and wings. This carries the E-2's primary antennas for its long-range radar and IFF systems. No other carrier-borne aircraft possesses one of these. Land-based aircraft with rotodomes include the Boeing E-3 Sentry, a larger AWACS airplane operated by the U.S. Air Force and NATO air forces in large numbers. The similarly placed stationary radome of the E-2's piston-engined predecessor, the E-1 Tracer, also mandated the E-2's adoption of a modern version of Grumman's ''Sto-Wing'' folding wing system, preventing the folded wing panels from making contact with the E-2's rotodome.

The aircraft is operated by a crew of five, with the pilot and co-pilot on the flight deck and the combat information center officer, air control officer and radar operator stations located in the rear fuselage directly beneath the rotodome.

In U.S. service, the E-2 Hawkeye provides all-weather airborne early warning and command and control capabilities for all aircraft-carrier battle groups. In addition, its other purposes include sea and land surveillance, the control of the aircraft carrier's fighter planes for air defense, the control of strike aircraft on offensive missions, the control of search and rescue missions for naval aviators and sailors lost at sea, relaying radio communications, air-to-air and ship-to-air. It can also serve in an air traffic control capacity in emergency situations when land-based ATC is unavailable.

The E-2C and E-2D Hawkeyes use advanced electronic sensors combined with digital computer signal processing, especially its radars, for early warning of enemy aircraft attacks and anti-ship missile attacks, controlling the carrier's combat air patrol (CAP) fighters, and secondarily for surveillance of the surrounding sea and land for enemy warships and guided-missile launchers and any other electronic surveillance missions as directed.

Operational history

US Navy

The E-2A entered U.S. Navy service in January 1964 and in April 1964 with VAW-11 at NAS North Island. The first deployment was aboard the aircraft carrier during 1965.Godfrey 1977, p.8.

Since entering combat during the Vietnam War, the E-2 has served the US Navy around the world, acting as the electronic "eyes of the fleet".

In August 1981, a Hawkeye from VAW-124 "Bear Aces" directed two F-14 Tomcats from VF-41 "Black Aces" in an intercept mission in the Gulf of Sidra that resulted in the downing of two Libyan Sukhoi Su-22s. Hawkeyes from VAW-123 aboard the aircraft carrier directed a group of F-14 Tomcat fighters flying the Combat