DEFINITION:

The knowledge of physical phenomena which contribute to the infrared radiation emitted by an aircraft in flight. Different parts of the aircraft radiate: the airframe, the exhaust jet and the motor for few aspect angles (rear part of the engine and air intake). The first aim is to have an understanding of the physical process which emits radiation in order to reduce it, if it is technologically possible. The airframe signature depends on its temperature and the radiative properties of the material. The temperature itself varies with the flight profile (altitude and speed), the material thermodynamic properties and the internal heat dissipation of electronic systems. The jet infrared signature presents a spectral emission which is characteristic of the chemical species that can be found, mainly water vapour and carbon dioxide. The radiation level is also function of the hot gases temperatures. The motor radiation can be observed for rear angle of aspect, the emission of the nozzle hot parts being partly absorbed by the hot gases in the jet exhaust. Its emission can also be perceived for very specific angle of aspect, when the first stage of the compressor is in direct view from the air intake, or through its propagation along the airduct. The control/reduction of the RCS (Radar Cross Section) of an aircraft is obtained by two main approaches: optimisation of the global or local shape and use of Radar Absorbing Materials (RAM). Modelling the RCS, by numerically solving Maxwell equations, is now a necessary way to define efficient shape modifications and materials. The chosen solutions have to be assessed by ground or in-flight measurements. Radar materials development is an important topic, as any material has to fulfil several functions, needing, for example, thermal or mechanical properties.

(Source: ACARE Domain 614)

SUBDOMAINS:

1. Material thermodynamic and optical properties.
2. Skin temperatures
3. Internal heat dissipation
4. Jet aerodynamic description, temperature, pressure and species concentration
5. Spectroscopic data base of emitting species
6. Radiative transfer computation in hot gases media
7. Multi-reflection in cavities
8. Radar Cross Section computation
9. Radar Absorbing Materials
10. Ground RCS measurements
11. In-flight RCS measurements