Stealth has always been an important part of military combat, but the current developments in aerial stealth technology has taken military warfare to the next level. In the military world, aircraft are usually detected with the help of various technologies such as infrared, radar, sonar and so on. In order to make an aircraft less visible to such detection methods, certain modifications need to be made to the aircraft. The stealth factor of an aircraft totally depends upon the ability of the aircraft to reflect and absorb the electromagnetic waves that are given off by a radar beacon. In other words, the design and the material of an aircraft determine how stealthy the aircraft will be.
Stealth is, however, a globally misunderstood concept. People often tend to think that stealth aircraft are invisible, which is not the case. Stealth aircraft are not completely invisible and invincible as portrayed in Sci-Fi movies. They are still detectable on the radar, but the chances are less. Even if they are detected, it is easy to dismiss their radar signature as that of a bird or even static. You may compare it to the camouflage tactics used by commandos in jungle warfare. This is what gives stealth bombers the upper hand in aerial combat. Let us have a closer look at these technological marvels.
In order to understand how stealth aircraft work, we first need to understand how a radar system works.There are basically two types of radar, namely the primary radar and the secondary radar. Both radar systems involves a ground beacon that is connected to a radar screen, such as the one shown below.The secondary radar, however, has two main components - the ground beacon and the transponder or transmitter-responder that is fitted in the aircraft. The system works on the 'interrogation' method in which the ground beacon sends out an interrogation pulse to the transponder, which in turns replies with a pulse of its own. Transponders, however, work on squawk codes, which when given to the radar controller, enables him or her to track the aircraft. Without the transponder code, a radar controller has to fall back to the primary radar, which works without a transponder.
Now, the way a primary radar works is that it sends out a ‘pulse’ or a burst of radio waves. This pulse uses air as its medium and travels through it in search of an obstacle. Once the pulse hits an obstacle in its path, it is reflected back to the beacon. The beacon then calculates the time taken by the ‘echo’ to travel back, converts this data into the distance between the beacon and the obstacle and uses it to map the obstacle on the radar screen. The direction and velocity of the obstacle are also measured by checking ‘frequency shift’ or the position of the rotating antenna of the beacon when the reflected echo is received.
The way a radar system works is quite similar to how bats navigate with the help of ultrasound. However, the radar signature of the obstacle plays a major role in its detection and this is exactly where stealth bombers differ from other aircraft. Stealth aircraft are designed in such a way that they have a very small radar signature.
The radar signature of an aircraft, also known as its radar cross section, is the measure of how detectable an aircraft is on radar. It is the amount of radio waves reflected by an aircraft. Now, in order for an aircraft to be more ‘stealthy’, its radar signature has to be drastically reduced, so that it is not detected on radar. Shown below is the radar cross section of a veteran World War II Bomber, the B-26, which had a radar cross section of 25 square meters even though it had a wingspan of 22 meters.
Ideally, the radar cross section of an aircraft is directly proportional to the size of that aircraft. The advent of stealth technology has made it possible to reduce the radar signature of an aircraft by a thousand times as compared to its size. There are a few ways to do this. One way is to install the engine in such a way that it does not give out prominent heat signatures. This can be done by strategically positioning the engine and by dispersing the heat produced by the engine through multiple small vents. Heat shields are also installed for further protection. Such absence of heat signature not only protects the aircraft from radar and infrared (IR) detectors, but it also protects the aircraft from heat seeking missiles. Other factors are discussed in the following sections.
Aviation designers had chanced upon the idea of a ‘stealth’ design at an early stage. They had seen that huge aircraft with less moving parts and abruptly angular designs produced smaller radar signatures. Then, in the early 70s, a Russian scientist named Petr Ufimtsev came up with an equation which suggested that certain 2D and 3D shapes had the ability to scatter electromagnetic radiation. With this model, it was possible to actually design a stealth structure on purpose for the first time in the history of aviation. It is seen that most aircraft, whether commercial or defense, have rounded bodies. Such shapes are the best at reflecting radar signals and achieving aerodynamic excellence. On the other hand, you might have noticed that most modern stealth aircraft have angular edges and flat surfaces. Such designs make sure that radar signals are reflected at sharp angles so that the beacon does not receive any detectable echo. This is what makes a stealth aircraft undetectable on the radar.
Most non-stealth aircrafts today have metal bodies which are great at reflecting radio signals, making radar detection easy. Using composite materials instead of pure metals for the construction of an aircraft can drastically reduce the radar signature of that aircraft. In the case of a stealth aircraft, the aircraft’s surface can be treated with special paints or gold coatings so that radar radio waves are absorbed on impact. Such special coatings are known as Radar Absorbent Material or RAM. The composition of a Radar Absorbent Material or RAM is classified information as it is used exclusively for military purposes. It is, however, believed to be wood powder or a silicon based inorganic compound. Some even claim that it is iron ball paint which has miniature iron balls which resonate when hit by radar beams and disperse most of the waves in the form of heat.
In 1975, engineers from the company ‘Lockheed’ came up with an unconventional aircraft design that was made with flat panels or 'facets'. It was seen that this design deflected almost 99 percent of radar signals away from the beacon, producing a very low radar signature. However, it was declared as aerodynamically unstable and the idea was laughed at and eventually, discarded. Critics even had a name for the design – 'the hopeless diamond'. However, better technologies were introduced later on and it became possible for even aerodynamically unstable aircraft to fly. With this advancement, the hopeless diamond became the F117 Nighthawk and in 1981, it tasted its first flight. Today, the Nighthawk is the first stealth aircraft to still be in active service.
Every great warrior has his Achille’s heel.
technology is currently ruling the skies, it will soon become obsolete as
technology has a way of evolving rapidly. For every new technology, a counter technology is always developed. Today, there are many types of radar which can detect stealth aircraft, such as the Russian 1R13. The F117 Nighthawk has been detected and eliminated in the past with the help of SAM (Surface to Air Missiles). During the Gulf war, Iraq had detected an F117, but had failed to eliminate it due to poor coordination. In the NATO war over Yugoslavia, however, an F117 was effectively shot down with the help of the triangulation method in which the aircraft’s location is trapped in a triangle with multiple radar networks. Then there is also the upcoming passive radar system which claims to detect stealth aircraft.
A stealth aircraft is traditionally known to lack aerodynamic properties. It is not as fast or maneuverable as a conventional aircraft, particularly because of the absence of the fin or the vertical stabilizer. Another disadvantage is the small amount of payload a stealth aircraft can carry. In order to maintain its stealth properties, a stealth aircraft has to carry weapons and cargo internally. Nothing can be attached to the body of the aircraft as it may increase the radar signature of the aircraft. And lastly, the cost of buying a stealth aircraft can cripple any budget. Stealth fighters are the most expensive aircraft in the world with the F-117, F-22 and B-2 costing $70 million, $100 million and $2 billion respectively. At this point, however, the benefits of owning a stealth plane far outweigh the costs.