Stealth Plane Technology

Stealth Technology

Stealth has become the magic word in contemporary weapon systems. Contemporary work on stealth has its roots in long-standing efforts to reduce the visibility of military aircraft through camouflage paint schemes. However, as electronic sensors have replaced the eyes of pilots as the primary means of tracking other aircraft, more intricate means of defense were needed.

Often thought of simply as the use of special materials to render aircraft invisible to radar, stealth is actually a complex design philosophy to reduce the ability of an opponent's sensors to detect, track and attack an aircraft (or other platforms such as warships). Since a variety of sensors would be used in this process, design of a stealth vehicle requires careful trade-offs among different techniques. The great secrecy surrounding stealth programs is designed not simply to protect a particular stealth technology, as it is to protect the choice and mix of techniques that have been used in a specific system.

A variety of technologies are may be combined in order to make itself "invisible" to radar. These technologies include a smooth surface, "flying wing" design, radar absorbent materials (RAM), engines hidden in the body of the airplane, and electronic countermeasures (ECM). Each of these features contribute to the attempt fool enemy air defense systems. The planes low radar cross section (RCS) reduces the range at which ground-based and air-based radars can detect the aircraft. The RAM absorbs most of a radar's signal, and the aircraft's wing-shaped and rounded design redirects much of the remaining power away from the radar source. Engines are buried in the fuselage with air intake and exhaust ducts placed on the top of the aircraft in order to reduce the heat trail, and hide the jet engine's compressor blades from radar detection. ECM is a last resort attempt to confuse the radar operator through jamming and ghost imaging.

The benefits of stealth technology is inherently obvious. Especially since, 70 percent of Soviet-style air defense systems use radar detection and tracking. However, as the next section on limitations will illustrate, the other elements of air defense detection and tracking; infrared (IR), electro-optical (EO) and visual, also need to be circumvented if an aircraft is to be truly "stealthy."

Limitations

There is no one optimum stealth design, but rather each mission requirement generates an appropriate mix of techniques. Implementation of stealth is not without penalties. Some of the materials used require special and costly maintenance. The maneuverability of an aircraft can be compromised by the introduction of stealth design features. As was the case with the F-117A, each B-2 bomber will have its own covered maintenance facility, since the B-2's low observable features require frequent performance of structural and maintenance activities.

Stealth requires not only design compromises, it also imposes operational compromises. Sensors to locate targets pose a particular problem for stealth aircraft. The large radars used by conventional aircraft would obviously compromise the position of a stealth aircraft. Air-to-air combat would rely on passive detection of transmissions by hostile aircraft, as well as infrared tracking. However, these techniques are of marginal effectiveness against other stealth aircraft, explaining the limited application of stealth to the Advanced Tactical Fighter.

Aircraft for attacking targets on the ground face a similar problem. FLIR can be used for precise aiming at targets whose general location is known, but they are poorly suited for searching for targets over a wide area. A radar on the aircraft to scan for potential targets would compromise its position. In order to locate targets, stealth aircraft may rely on an airborne laser radar, although such a sensor may prove of limited utility in poor weather. A more promising approach would be to use data from reconnaissance satellites, either transmitted directly from the satellite or relayed through communications satellites from processing centers in the United States.

There are limits to the utility of stealth techniques. Since the radar cross-section of an aircraft depends on the angle from which it is viewed, an aircraft will typically have a much smaller RCS when viewed from the front or rear than when viewed from the side or from above. In general stealth aircraft are designed to minimize their frontal RCS. But it is not possible to contour the surface of an aircraft to reduce the RCS equally in all directions, and reductions in the frontal RCS may lead to a larger RCS from above. Thus while a stealth aircraft may be difficult to track when it is flying toward a ground-based radar or another aircraft at the same altitude, a high-altitude airborne radar or a space-based radar may have an easier time tracking it.

Another limitation of stealth aircraft is their vulnerability to detection by bi-static radars. The contouring of a stealth aircraft is designed to avoid reflecting a radar signal directly back in the direction of the radar transmitter. But the transmitter and receiver of a bi-static radar are in separate locations -- indeed, a single transmitter may be used by radar receivers scattered over a wide area. This greatly increases the odds that at least one of these receivers will pickup a reflected signal. The prospects for detection of stealth aircraft by bi-static radar are further improved if the radar transmitter is space-based, and thus viewing the aircraft from above, the direction of its largest radar cross section.

Several analysts claim stealth aircraft such as the ATF will be vulnerable to detection by infrared search and track systems (IRST). The natural heating of an aircraft's surface makes it visible to this type of system. The faster and aircraft flies, the warmer it gets, and thus, the easier to detect through infrared means. One expert asserts "if an aircraft deviates from its surroundings by only one degree centigrade, you will be able to detect it at militarily useful ranges." In fact, both the Russian MiG-29 and Su-27 carry IRST devices, which indicates that the Russians have long targeted this as a potential stealth weakness.

Stealth aircraft are even more vulnerable to multiple sensors used in tandem. By using an IRST to track the target and a Ladar (laser radar), or a narrow beam, high-power radar to paint the target superior data is provided.

The most basic potential limitation of stealth, is its vulnerability to visual detection. Since the ATF is 25-30 percent larger than the F-15 and