Stealth Technology

Stealth technology, also termed LO technology (low observable technology) is a sub-discipline of military tactics which allows an aircraft to be partially invisible to Radar or any other means of detection. Stealth technology doesn’t make an aircraft completely invisible to radar. All it can do is to reduce the detection range of an aircraft. It is similar to the camouflage tactics used by soldiers in jungle warfare.

It was in the late 1930s, when the first radar tracking systems were employed. The earliest stealth aircraft seems to have been the Horten Ho 229 flying wing. It included carbon powder in the glue to absorb radio waves. The other techniques adopted during that time included the use of Yehudi light by the RAF; the U boats (submarines) featured rubber coatings one layer of which contained circular air pockets to defeat ASDIC sonar.

Principle

Stealth technology is not a single technology. It is a combination of technologies that attempt to greatly reduce the distances at which a person or vehicle can be detected; in particular radar cross section reductions, but also acoustic, thermal, and other aspects.

While designing a stealth aircraft, the following points are to be considered:

- Reducing the imprint on radar screens / stifling radio transmissions - Turning down the heat of its infrared picture - Improved aerodynamics - Making the plane less visible. - Muffling the noise

Reducing the Radar cross-section (RCS)

Radar cross section (RCS) is a measure of how detectable an object is with radar. A larger RCS indicates that an object can be more easily detected. This is usually accomplished by

• Vehicle shape:

The possibility of designing aircraft in such a manner as to reduce their radar cross-section was recognized in the late 1930s, and it has been known since at least the 1960s that aircraft shape makes a significant difference in detect ability. The Avro Vulcan, a British bomber of the 1960’s, had a remarkably small appearance on radar despite its large size, whereas the Tupolev 95 Russian long range bomber appeared especially well on radar Another important factor is internal construction, a skin that is radar transparent or absorbing, behind which are structures termed re- entrant triangles is usually used; Radar waves penetrating the skin get trapped in these structures, reflecting off the internal faces and losing energy. Another method used is coating the cockpit canopy with a thin film transparent conductor helps to reduce the aircraft's radar profile.

In addition to all these, the design of the tail and the burying of the engine within the fuselage, or in some cases the instillation of baffles to hide the air intake turbines are also incorporated. A stealthy shape must be devoid of complex bumps or protrusions of any kind.

• Radar-absorbing material

Radar-absorbent materials (RAM), often as paints, are used especially on the edges of the metal surfaces. While the material and thickness of RAM coatings is classified, the material seeks to absorb radiated energy from a ground or air based radar station and converts it to heat rather than reflect it back. These typically consist of carbon, carbon fibre composites, or magnetic ferrite-based substance.

Flight-control surface can be made from honeycombed materials which reflect incoming radar waves internally rather than back to the radar. Radar-absorbing coatings can be applied to the surface of the body which effectively drain the energy of the radar signal.

• Acoustics

Acoustic in stealth, plays a primary role in submarine stealth as well as for ground vehicles. Submarines use extensive rubber mountings to isolate and avoid mechanical noises that could reveal locations to underwater passive sonar arrays.

Early stealth observation aircraft used slow-turning propellers to avoid being heard by enemy troops below. Stealth aircraft that stay subsonic can avoid being tracked by sonic boom. The presence of supersonic and jet-powered stealth aircraft such as the SR-71 Blackbird indicates that acoustic signature is not always a major driver in aircraft design, although the Blackbird relied more on its extremely high speed and altitude

• Visibility

The simplest of the stealth techniques used is simply camouflage; the use of paint or other materials to colour and break up the lines of the vehicle or person. Most stealth aircraft use matte paint and dark colours, and operate only at night. Lately, interest in daylight Stealth (especially by the USAF) has emphasized the use of grey paint in disruptive schemes, and it is assumed that Yehudi lights could be used in the future to mask shadows in the airframe.

• Infra-red Signature

Infra-red signatures includes An exhaust plume contributes a significant infrared signature. One means to reduce IR signature is to have a non-circular tail pipe (a slit shape) to minimize the exhaust cross-sectional volume and maximize the mixing of hot exhaust with cool ambient air.

The illustration shows the significant change in the infra-red signature of a plane when cool air is bypassed to the combustion chamber. Sometimes, the jet exhaust is vented above the wing surface to shield it from observers below, as in the B-2 Spirit.

Reducing smoke in the exhaust is accomplished by improving the efficiency of the combustion chambers.

Another way to reduce the exhaust temperature is to circulate coolant fluids such as fuel inside the exhaust pipe, where the fuel tanks serve as heat sinks cooled by the flow of air along the wings.

• Radio Frequency (RF) emissions

In addition to reducing infrared and acoustic emissions, a stealth vehicle must avoid radiating any other detectable energy, such as from onboard radars, communications systems, or RF leakage from electronics enclosures.

• Low Level Flying

Another technique used by aircraft to avoid radar is to fly at very low levels where there is a great deal of 'ground clutter', radar reflections given off by buildings and other objects. Low-level aircraft can go undetected by most radar systems. • Plasma Stealth

In this the aircraft injects a stream of ionised gas which envelopes it and makes completely invisible. Drawbacks

• Poor aerodynamic properties.

• Requires high end electronic instruments and software's.

• High maintenance cost.

• Any stealthy vehicle becomes un-stealthy even when a door or hatch opens. Conclusion:

Stealth Technology concludes its military applications in fighter Aircrafts, so that the aircrafts designed using this technology are almost invisible to Radar detection techniques and other sonar, Infrared detection methods. Stealth Technology is a step towards achieving invisibility. The first principle mainly concludes this by the reduction of RCS.