The radome is an important component of the aircraft, and since the S-band radome produced by the American company Occidental Electric was installed on the B-18A aircraft, all aircraft with radar have used the radome. Generally speaking, the radome is located at the head or back of the aircraft, such as the conical radome in the nose of a fighter aircraft, the turntable radome on the back of an early warning aircraft, the hemispherical radome of a transport aircraft, and the "nose" shaped radome in the nose of a civil aircraft.
If radar is compared to the "eyes" of an aircraft, then the radome is a "protective glass" to protect the "eyes" of the aircraft. The main function of the radome is to protect the radar system inside the radome from external damage or destruction without affecting the radar detection performance. In addition, as an integral part of the aircraft's shape, the radome also plays a role in maintaining the aerodynamic shape of the whole aircraft.
Structurally, the radome mainly includes the shell, lightning protection system, anti-static and rain erosion system, etc.
Among the relevant factors affecting the performance of the radome, the housing material has a relatively large influence. Currently, most of the world's aircraft use composite housings for radomes. With the application of various high-performance radars, the requirements of modern civil aircraft for the mechanical properties, heat resistance, electromagnetic properties and mechanical properties of the radome housing in different working environments during aircraft take-off and landing and air flight are also increasing. Therefore, composite materials with excellent properties are the best choice.
The materials used in the radome housing mainly include resin matrix, reinforcing materials and sandwich cores and other anti-static, anti-corrosion, and anti-lightning materials. The base material used to make the radome is mainly modified epoxy resin. The modified epoxy resin matrix has good mechanical properties, dielectric properties and heat resistance.
There are two main types of radome shell sandwich structure: foam sandwich structure and honeycomb sandwich structure. In contrast, the mechanical properties of foam are isotropic, while honeycomb is anisotropic. In the complex stress state, the foam sandwich structure can better meet the requirements of structure and strength than the honeycomb sandwich structure. In addition, in the process of use, because the foam is a closed-cell structure, water and water vapor cannot enter the inside of the sandwich core, compared with the honeycomb structure with open holes, it has a lower water absorption rate, reducing the cost of maintenance and inspection. The radome of China's large passenger aircraft C919 adopts the world's leading foam sandwich structure.
The composite shell is non-conductive and cannot withstand the high stress caused by lightning, which can easily cause lightning to enter the structure. Therefore, there is a circle of radial protruding metal strips on the surface of the radome, which has a good electrical lap between it and the body, providing lightning attachment points, so that the lightning current can be quickly transmitted to the metal fuselage through the shunt strip, releasing energy, and achieving the role of protecting the radome body, which is the lightning protection shunt strip.
The shunt strips are not installed randomly, their length must exceed the very front of the radar scanning envelope in the downcourse direction, and the spacing between the shunts is precisely calculated. The C919 aircraft radome adopts aluminum lightning protection shunt strip, which has little reflection of electromagnetic waves, has little impact on the wave transmission performance of the radome, and has good lightning protection performance.
During the flight of the aircraft, the radome is affected by high-speed air currents and the atmospheric ionosphere, and its surface is prone to static electricity. When static electricity accumulates to a certain extent, it will cause discharge, interfere with electronic equipment, and affect radio wave transmission. The erosion of long-term wind, sand, rain and snow will reduce the structural and electrical properties of the radome, so three layers of protective coating will be sprayed on the outer surface of the radome.
Among them, there should be good adhesion between the base coating and the cover material; The rain erosion resistant coating should have good elasticity and can play a role in anti-erosion; The antistatic coating should have a certain electrical conductivity, which can avoid the accumulation of static electricity on the radome body, so as to achieve comprehensive protection against the radome.