a compendium of tech stuff

Jun 20, 2012

On 5:03 PM by Lalith Varun   No comments

     Stealth or Low Observability is one of the most misunderstood concepts by the common man. Stealth aircraft are considered to be the invisible aircrafts that dominate the skies. But, in simple terms, stealth technology allows an aircraft to be partially invisible to Radar or any other means of detection. This is similar to the camouflage used by soldiers in jungle warfare. Unless he comes close to you, you cant see him. Before getting into the stealth technology, we must first know how a radar works. The radar sends out radio waves which is reflected back by any object it happens to encounter. The radar antenna measures the time taken by the wave to return and with that information it can tell how far the object is. The metal body of the aircraft is a very good reflector of radar signals, and this makes it easy to find and track planes with radar equipment.

     The goal of stealth technology is to make an aircraft invisible to radar. It is a combination of technologies.
1) The aircraft should be shaped so that any radar signals it reflects are reflected away from the radar equipment.
2) The aircraft should be covered in materials that absorb radar signals.
3) Reducing visibility and infrared signature.

     Usually conventional aircraft have rounded shape which makes them aerodynamic but it also creates a very efficient radar reflector. The round shape means that wherever the radar signal hits the plane, some of the signal gets reflected back. A stealth aircraft on the other hand has completely flat surfaces and very sharp edges which reflects the radar signals away from the radar antenna. The most efficient way to reflect radar waves back to the emitting radar is with orthogonal metal plates, forming a corner reflector consisting of either dihedral (two plates) or a trihedral (three orthogonal plates). This configuration is used in the tail of conventional aircrafts, where the vertical and horizontal components of the tail are set at right angles. Stealth aircraft use a different arrangement, tilting the tail surfaces to reduce corner reflections formed between them. A more radical method is to eliminate the tail completely. In addition to altering the tail, the engines must be buried within the wing or fuselage, install baffles in the air intakes so that turbine blades are not visible to radar. A stealthy shape must be devoid of complex bumps or protrusions such as weapons, fuel tanks etc. and they must not be carried externally. These shaping requirements have strong negative effects on the aircraft's aerodynamic properties and hence they are inherently unstable and cannot be flown without a fly-by-wire control system.

     In addition, surfaces on a stealth aircraft can be treated so they absorb radar energy and convert it into heat rather than deflecting them in other directions. Commonly used radar absorbent materials are iron ball paint and foam absorber. The simplest stealth technology is simply camouflage by using paint or other materials to blend with the environment or by resembling something else. Most stealth aircraft use matte paint and dark colors and operate only at night. With interest in daylight stealth, emphasis is on the use of gray paint in disruptive schemes. Usually planes are visible in thermal imaging systems because of the high temperature exhaust they give out. The exhaust plume contributes a significant infrared signature. This is a great disadvantage to aircrafts as they are vulnerable to missiles with IR guidance system. By minimizing the exhaust cross sectional volume and maximizing the mixing of hot exhaust with cool ambient air, IR signature can be reduced. Another way to reduce the exhaust temperature is to circulate coolants such as fuel inside the exhaust pipe.

     The stealth aircrafts cannot fly as fast or are not maneuverable like conventional aircrafts. The reduced amount of payload it can carry and its sheer cost are the major factors that sharply reduced their research and development. As air defense systems are becoming more and more accurate and deadly, stealth technology can be a decisive factor for any country over the other. Nowadays the stealth technology is being incorporated in ships, helicopters and tanks as well and in the coming years we can see many more advancements in the field of military aviation.

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