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  • STEALTH TECHNOLOGY ABSTRACT

    DEPTT. OF MECH. ENGINEERING S.S.M COLLGE OF ENGINEERING

    1

    ABSTRACT

    Stealth aircraft are aircraft that use stealth technology to make it

    harder to be detected by radar and other means than conventional aircraft

    by employing a combination of features to reduce visibility in the visual,

    audio, infrared and radio frequency (RF) spectrum. Well known examples

    include the United States' F-117 Nighthawk (1980s-2008), the B-2 Spirit

    "Stealth Bomber," and the F-22 Raptor.

    While no aircraft is totally invisible to radar, stealth aircraft limit

    current conventional radar's abilities to detect or track them effectively

    enough to prevent an attack. Stealth is accomplished by using a complex

    design philosophy to reduce the ability of an opponent's sensors to detect,

    track and attack an aircraft.

    Modern stealth aircraft first became possible when a mathematician

    working for Lockheed Aircraft during the 1970s adopted a mathematical

    model developed by Petr Ufimtsev, a Russian scientist, to develop a

    computer program called Echo 1. Echo made it possible to predict the

    radar signature an aircraft made with flat panels, called facets. In 1975,

    engineers at Lockheed Skunk Works found that an airplane made with

    faceted surfaces could have a very low radar signature because the

  • STEALTH TECHNOLOGY ABSTRACT

    DEPTT. OF MECH. ENGINEERING S.S.M COLLGE OF ENGINEERING

    2

    surfaces would radiate almost all of the radar energy away from the

    receiver.

    Reduced radar cross section is only one of five factors that designers

    addressed to create a truly stealthy design. Designers also addressed

    making the aircraft less visible to the naked eye, controlling radio

    transmissions, and noise abatement.

    The first combat use of stealth aircraft was in December 1989 during

    Operation Just Cause in Panama. On December 20, 1989 two USAF.

    F-117s bombed a Panamanian defence Force Barracks in Rio Hato,

    Panama. In 1991, F-117s were tasked with attacking the most heavily

    fortified targets in Iraq and were the only jets allowed to operate inside

    Baghdad's city limits.

  • STEALTH TECHOLOGY IN AIRCRAFTS INTRODUCTION

    DEPTT. OF MECH. ENGINEERING S.S.M COLLGE OF ENGINEERING

    3

    INTRODUCTION

    "Stealth", a buzzword common in defence circles since the early 80s,

    only became a mainstream reference in the nineties, after the second

    Persian Gulf War in 1991.Night-enhanced images of the otherworldly-

    shapedF-117s taking off in the night and striking high-value targets with

    scarcely believable precision and seeming invulnerability to thick air

    defences were widely televised and etched in the memories of TV

    viewers worldwide. The subsequent exposure of stealth aircraft and their

    participation in numerous air operations in the 90s, in combination with

    the loss of at least one F-117 in Kosovo, has peeled off some of the

    mythical cloak surrounding stealth. However, a lot of misconceptions

    about the abilities and limitations of this technology still remain, even

    amongst people in posts of high professional responsibility. It is therefore

    useful to take a broad look at how stealth works, what it can and what it

    cannot do. This article will examine strictly the application of stealth in

    air assets. Different technologies and strategies for stealth are the

    province of land, naval and underwater forces.

    First of all, although it is common to discuss the principles of stealth

    technology (also referred to as VLO or Very Low Observables

    technology) only as relevant to a narrow band of the electromagnetic

  • STEALTH TECHOLOGY IN AIRCRAFTS INTRODUCTION

    DEPTT. OF MECH. ENGINEERING S.S.M COLLGE OF ENGINEERING

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  • STEALTH TECHOLOGY IN AIRCRAFTS INTRODUCTION

    DEPTT. OF MECH. ENGINEERING S.S.M COLLGE OF ENGINEERING

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    spectrum (radar emissions), stealth as a design practice applies a wide

    range of signatures. Ben Rich, the leader of the Lockheed team that

    designed the F-117, has stated: "A stealth aircraft has to be stealthy in six

    disciplines: radar, infrared, visual, acoustic, smoke and contrail. If you

    don't do that, you flunk the course."

    That said, not all disciplines are equally important when discussing

    any given platform category. Underwater warfare will naturally hand

    dominance to the acoustic spectrum (though onacoustic sensors can and

    do exist). Land combat will emphasize visual, infra-red and acoustic

    signatures. Radar and (to a lesser extent) infrared bands dominate the

    scene of airspace surveillance, and so they have to be given higher

    priority when thinking the applications in air warfare.

    Before discussing the various techniques of reducing the radar and

    infrared signature, it is useful to understand the principles of radar

    reflectivity and how they can be exploited when one starts thinking about

    aiming for stealth in earnest.

  • STEALTH TECHOLOGY IN AIRCRAFTS RADAR REFLECTIVITY

    DEPTT. OF MECH. ENGINEERING S.S.M COLLGE OF ENGINEERING

    6

    RADAR REFLECTIVITY

    All radar systems, from an AWACS to police speed radar, work in

    the same principle: A certain amount of electromagnetic energy is

    transmitted through a directional antenna, which focuses it into a conical

    beam. When a reflective target (in radar engineering terms, anything

    observed by radar is a potential target) blocks part of the beam, that part

    of the beam is reflected in many different directions, or "scattered." If the

    scattering is fairly random, as is usually the case, some energy will be

    reflected in the direction of the radar antenna. Most radar transmits this

    energy in pulses, thousands of them every second. In the gaps between

    the pulse transmissions, the radar becomes a receiver, and the gaps are

    carefully chosen to be just long enough for the signal to make its way to

    the target and back at the speed of light1.

    The time interval between the transmission and reception of the

    pulse gives the range from the radar to the target. The radar antenna

    moves at a pre-determined regular rate, so the time at which the target

    moves in and out of the beam can be tied to the position of the antenna,

    giving the target's bearing from the location of the radar. This process has

    been considerably developed and refined in the 6+ decades since the first

    workable radars were deployed. However, it is still true that radar does

    not "see" things in the way that the human eye does. Humans see in a

  • STEALTH TECHOLOGY IN AIRCRAFTS RADAR REFLECTIVITY

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    world which is saturated with visible light, so that almost every square

    inch of it reflects some light toward us at all times; the radar only "sees"

    the energy that is reflected toward it. The radar can detect a target ONLY

    when its antenna captures enough energy to rise above the electronic

    noise that is invariably present in the receiver. (Typically, there is a

    definite signal-to-noise threshold associated with a positive detection).

    All the variables in the transmission-scattering-reflection sequence affect

    the maximum range at which this can happen. These variables include:

    The strength of the outgoing signal

    The width of the beam

    The size of the antenna

    The reflectivity, or RCS, of the target.

    The radar beam, it is important to remember, is a cone. The greater

    the range, the greater the area illuminated by the radar, and the smaller

    the proportion of the energy which will be scattered by a target with a

    given RCS. The same effect results in the scattered energy returning to

    the radar. Therefore, at a longer range, the already-reduced energy hitting

    the target is scattered over a wider area and less of it will be captured by

    the antenna. The eventual amount of energy received back by the antenna,

    even at the best of circumstances, is a very small fra

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