As a "military tent in the clouds", early warning aircraft have become an important part of the air power of many countries and regions around the world.
Early warning aircraft is a kind of special aircraft, with early warning, command, electronic warfare, air control and other functions, can effectively enhance the battlefield perception ability, has become a recognized combat power multiplier.
From the end of World War II to the present, early warning aircraft have been developed for nearly 80 years. In its development history, the research and development of almost all AWACS models in the world will involve the interaction between the two important systems of aircraft platform and airborne radar system.
E-2C AWACS
The special aircraft platform includes a special platform and a general platform, the former such as the E-2 series of early warning aircraft, the fuselage is specially developed for this type of early warning aircraft; The latter, such as the Boeing 737, is based on the existing aircraft platform and adapted to the relevant special equipment.
However, whether it is a dedicated platform or a general platform, throughout the world's many early warning aircraft that have been praised by the industry, they are led by the aircraft development unit, with the airframe platform as the main line, the airborne radar and avionics system that meet the development requirements are selected, and the design optimization is realized through the integration of the airborne system and the aircraft platform.
In the whole life cycle of the airframe platform, the airborne radar system will be continuously upgraded with the advancement of science and technology to adapt to the requirements of different users at different times. The work that runs through it is also inseparable from the good cooperation and balance between the aircraft platform and the airborne radar system.
Therefore, in the process of early warning aircraft development, the main manufacturer is generally an aircraft design manufacturer. Only aircraft manufacturers can coordinate various system suppliers, including airborne radar suppliers, integrate resources, and ultimately achieve an excellent early warning aircraft.
The E-2 AWACS is marketed worldwide.
In the E-2 series of early warning fuselages, which were once marketed worldwide, these characteristics are vividly reflected.
Integrated design of aircraft and early warning equipment
Design work for the E-2 series of early warning aircraft began in 1956. At that time, the U.S. Navy asked Northrop Grumman to develop a carrier-based early warning aircraft that could be deployed on the deck of an aircraft carrier and maximize its detection capabilities.
In order to meet this demand, NOGE, as the main contractor, designed the E-2 series of early warning aircraft after comprehensively considering the indicators and design boundaries of the airborne radar system and the carrier-based aircraft platform at that time.
The E-2A early warning aircraft conducting the first landing test.
E-2 early warning aircraft using a specially designed airframe platform, in the overall design, KNOG company comprehensively considered the deployment requirements of the aircraft carrier platform, radar system design parameters, crew division and composition and other factors, the layout, weight, stability and even flight attitude of the E-2 have been integrated design.
As a carrier-based early warning aircraft, the weight and size of the E-2 were first constrained by the carrier platform. After all, catapults and blocking systems can only support limited tonnage aircraft take-off and landing, and hangars and elevators have strict restrictions on the length, width and height of aircraft. These factors first determine the approximate weight and tonnage of the E-2 platform, and then determine how large and heavy radar can be installed outside the cabin, and how many workstations and corresponding personnel can be carried in the cabin.
The design of the E-2D, carrier-based early warning aircraft is strictly constrained by the deployment of aircraft carriers.
As the most important special equipment of early warning aircraft, airborne radar systems naturally need to be selected and adapted within this framework.
The empty weight of the E-2 series, depending on the model, is roughly around 14.1 (type A) ~ 19.6 (type D) tons, and the maximum take-off weight does not exceed 24.9 (type A) ~ 26.1 (type D) tons.
Under such a maximum take-off weight, the E-2 body can leave a very small weight margin for the radar, and the detection distance should be as large as possible; Therefore, the radar system used by the E-2 chose the largest possible antenna diameter and made greater concessions in the antenna structure and band.
The radome diameter of the E-2 reached 7.32 meters, forming a 1:3.6 ratio with the wingspan (24.56 meters). If you only consider deck operation, the E-2's antenna size is actually more room for increase than the 8.94-meter folded rear wingspan length. However, the continued expansion of the radome will inevitably bring about changes in aerodynamic shape and weight and center of gravity, which inevitably undermine the maneuverability and stability of the aircraft.
Taken together, 7.32 meters is very close to the acceptable limit of flight safety. Therefore, the E-2 has a very strict angle of attack restriction in use, and the flight attitude adopts an extremely rare nose down-down attitude.
Quite a brainstorming dedicated platform design
In addition to the requirements of aircraft carrier deployment, in order to maximize the early warning function, NORG also took a lot of effort to design and develop the aircraft platform.
In addition to conventional modification items such as weight adjustment, local structure strengthening, hydraulic gas supply and power supply, electromagnetic compatibility testing, etc., the targeted design of the E-2 on the carrier platform is mainly reflected in the tail wing.
The E-2 AWACS aircraft adopted a rare 4-tail design.
In order to avoid the tail of the radome interfering with the tail wing, and the tail wing blocking the direction of the radar wave emission, while trying to facilitate the operation of the radar system, the E-2 adopts a special 4-tail design to reduce the height of the tail and ensure sufficient tail area.
At the same time, the tail of the E-2 also uses as much fiberglass material as possible, and uses a complex dual-spindle design on the 3 rudders - which allows the E-2 to better maintain the level of the fuselage when cornering, which is conducive to radar detection.
Iterative updates are continuously made throughout the life cycle of the aircraft
Classically designed airframe platforms can often serve for decades or even half centuries, but advances in systems such as airborne radar and avionics are changing rapidly. Therefore, a good early warning aircraft product is often on top of a stable airframe platform, constantly upgrading the airborne radar system, and achieving the goal of serial development.
The E-2 series of early warning aircraft is no exception.
The early E-2A/B radars used parabolic antennas, while the later E-2C types used Yagi antennas with a longer operating wavelength (0.68 to 0.75 meters). The Yagi antenna weighs about 772 kg and weighs only 2 tons with the entire radome.
At present, the latest E-2D, the main structure of the radar antenna is still based on the enhanced design of Yagi.
In addition, due to its size, the E-2 early warning aircraft is significantly weaker than the E-3 and other models in the same period in terms of detection accuracy, reliability, and ability to cope with complex terrain environments - only technological progress can achieve leapfrog improvements in the size, weight and accuracy of airborne radar systems.
It was not until 1992 that the E-2C was equipped with an AN/APS-145 radar to achieve pulsed Doppler capabilities, which provide reliable down-vision detection of complex terrain environments.
E-2C AWACS.
The E-2, first flown in 1960, is still in service today. Over the years, the basic design of the airframe platform designed by KNOG has never changed, and the airborne radar system has undergone four major replacements - through continuous updates of equipment, the E-2D is still the world's most advanced small early warning aircraft, and it is an irreplaceable role in the field of carrier-based early warning aircraft.
E-2D early warning aircraft.
New trends in early warning systems in the future
At the beginning of the E-2 design, under normal circumstances, in addition to the two pilots, the E-2 could only carry three workstations and corresponding mission operators, responsible for radar operations, air control and combat command. This limited number of equipment and personnel also greatly limits the E-2's mission-handling capabilities, especially complex command and control tasks.
E-2A/B/B舱
In order to reduce weight and drag, the E-2 fuselage has a small diameter, a very narrow range of motion of the staff, and strong noise and vibration in the cabin, and no suppression measures have been applied.
This harsh working environment also caused the E-2's crew to become exhausted after hours of flight, and the ability to perform tasks was significantly reduced. Therefore, when the E-2 series performs continuous tasks, it is usually equipped with 2 to 3 crews in a single aircraft in order to carry out shift flights.
The effective time of the unit work also affects the improvement space of the E-2.
Due to the small tonnage of the E-2, the range and stay-at-home time (4.4 hours at 320 kilometers from the aircraft carrier) are relatively limited, but the US Navy has not considered adding aerial refueling capabilities to the E-2 for a long time, and the reason is large: the longer single flight time, although the aircraft can hold up, but the crew on the mission has not been able to hold up.
Inside the E-2C cabin.
Later, when the U.S. Navy added aerial refueling capabilities to the E-2D, one of the key points of investigation and testing was whether its crew could stick to the flight time of 8.5 to 9 hours.
In addition, with the continuous advancement of radar and electronic technology, the operators of the E-2 series aircraft have also been expanded – in particular, this expansion is not only in the cabin.
One of the important improvements of the late E-2 was to take advantage of advances in electronics to have a single driver act as a fourth operator through a glassed cockpit and high-speed data links.
At the same time, aircraft carrier ground personnel operate remotely in the rear, acting as fifth, sixth, and even seventh mission operators.
The E-2D is equipped with an AN/APY-9 radar and the cockpit has been improved to a glass cockpit.
Such changes may indicate a trend: in the future, based on the development of electronic technology, remote, intelligent and even unmanned early warning aircraft will become an important part of the future airborne early warning system, and the task operator is not on the early warning aircraft is just a beginning.
In recent years, especially after the 1990s, new small and medium-sized early warning aircraft have emerged, and the seller advantage of the E-2 has been greatly weakened, and the early hot sales scene has been difficult to reproduce.
Now, many countries around the world are developing their own shipborne early warning aircraft projects. It is foreseeable that the problems encountered by the E-2 in the development of these up-and-coming projects can be more or less unavoidable; But the delicate balance between the airborne radar system and the aircraft platform in the development of the E-2 also provides valuable lessons for later projects.