The Tribune, Chandigarh, India

Stealth tech that makes planes invisible
Paul Singh

FROM time immemorial, everyone has the ambition to conquer the world. In this endeavour, one has to have the competent forces armed with the weapons. In good old days, the wars were fought on grounds sans strategic information about the capability of the enemy. But in the 20th century, the wars have become hi-tech. In the age of information technology, the information has become an important and vital weapon. Those who have right information, that too at right time, are the leaders in the battle field.

The information in the warfare is gathered by radar which stands for Radio Detection and Ranging. The radar has three parts viz.,transmitter, receiver and screen or indicator. The radar works on the principle of reflection or echo of electromagnetic waves which have wide spectrum ranging from gamma rays to radio waves. The transmitter sends radio waves towards the object and receives them after reflection by the receiver. These are fed to the screen. The position, speed and direction of flying objects are displayed on the screen. Thus, none of the flying objects can go undetected from the eyes of RADAR. But the scientists had been working for many years on such a technology which helps the flying objects elude the radar.

In 1990, American scientists succeeded in developing a technology called Stealth technology which means hiding the fighter planes from enemy radar. In this technology, the fighter planes are not detected by the radar. This technology can be understood in a very simple way on the basis of reflection of any radiation like light, radio, radar etc. The reflection of radiation occurs in two ways—Specular and diffuse. Whenever we see our image in a mirror, it is the result of specular reflection and this reflection is extremely identifiable. The diffuse reflection is rather different and takes place whenever one reads columns of this newspaper or the reflection on the brushed aluminium surface. The radar only works when it receives the signal after either kind of reflection.

Let us think of seeing a car with a curved chrome bumper on a sunny day. No matter where we are, we always see a tiny but bright reflection of sun because of specular reflection. Now, imagine if that bumper did not have the curved surface and rather had flat surfaces with sharp edged corners. Now, anywhere we are, we will not see any reflection of the sun from this surface. It appears that the boxy shape tends to get all the reflections go to one specific direction with almost no specular reflection. We sometimes notice that some flat truck windshields make us almost blind with the reflection but only when we are at a very specific position.

When applied to a radar, as long as the specular reflection is diverted to any other direction than coming back to the originating radar station no echo is generated and so the flying objects will become invisible on the radar screen. Some American aircraft make use of this stealth technology. This deals with avoiding the specular reflection and also minimising the diffuse reflections. This is achieved by using special coating of a paint which absorbs the radiation rather than reflecting it. These aircraft suppress both the specular and diffuse reflection, and therefore, accomplish almost invisibility on the enemy radars.

Some peculiar characteristics of stealth technology are exploited in American fighter planes e.g. the B-2 bomber, the F-117A Stealth fighter and recently F-22 Advanced Tactical Fighter. In every aircraft, the engines are noticed first of all. There is a lot of material in front of the engine intake, directly under and slightly behind the engine outlet.

The B-2 bomber engine inlets, when seen from above, have been dramatically shaped the "W" which rather look like jagged cartoon teeth. In many written sources, this "W" shape attributes to masking of infrared and radar signatures. Such a shape does not give any track of the aircraft on the radar screen.

According to reports in Popular Science I, the exotic chemicals are inserted into the engine outlet gases to remove infrared signatures and also force water molecules in the exhaust plume to break up into much finer particles. This process reduces or even eliminates the telltale contrails (white condensation seen behind the aircraft). According to another report in The World’s Great Stealth and Reconnaissance Aircraft 2, the chemical used for this feat is chloro-fluoro-sulphonic acid. It is quite toxic, if not corrosive. So its use is prohibited except for combat and recon missions.

The most fascinating feature of the stealth is, of course, its low observability (LO) on radar and negligible infrared signature. After the engine, the airframes are equally important parts which are to be dealt with. The airframes use deceptive shapes to mask their signatures. The smooth blending of the main fuselage into the wing area produces a flying wing shape when seen from above and below. The stair-step shape wings when seen from these two positions give rise to opposing reflections which aid in the cancellation of reflected radar waves. The paint and carbon composite structures enable the airframes to reduce or absorb the rediations sent by radar.

The shape of stealth aircraft is widely different from most other military aircraft. Their smooth and elliptical shape tends to look like an ovoid from rear or front with a little overall cross-section. The F-117 and the F-22 ATF both have a low height triangle appearance at front. These low cross-sectional shapes ensure a small signature from the "get-go". The LO touches such as paints and materials, the little "W" shapes all render the breaking up of the signatures either by absorption or redirection.

Future

The future of this technology is already being utilised in designing of fighter planes discussed in this article. The odd shape of F-117 is in consequence of the modeling software available at the time rather than a leap in true stealth technology. Popular Science 4 article discusses on the future Stealth requirements in the visual and infrared spectrums. It is about daylight operation. The F-22 and the Advanced Strike Fighter (in development) both are designed with daylight operation. Some methods are required for eliminating or reducing the visible light and infrared signatures of aircraft. The first method is regarding the reflected infrared surface. The sunrays on a aircraft’s wing produce long infrared event for an incoming heat seeking missile. Thus an aircraft with zero-engine infrared is still deemed fit to be intercepted. The idea is to use visual/infrared masking.

If this all sounds unbelievable and far-fetched, then imagine what a B-2 would have done to the minds of pilots in Korea or Vietnam. Who can forget the Gulf war in 1991 where the Stealth technology has displayed its manoeuvreness. We can imagine the feelings in the mind of Saddam Hussein when his subordinates had started reporting invisible aircraft dropping 2000 pound bombs right on the strategic installations. Till date, the Stealth technology eludes the radar system. It is opined that the majority of radar systems over the next 20 years will still be easily fooled by the Stealth fighter designs. But the science never comes to a standstill and it is only a matter of time before there is a more sophisticated detection system against the fighters based on stealth technology.

The writer is an Associate Professor (Physics) at HAU, Hisar.

NEW PRODUCTS & DISCOVERIES

Bacteria rid sewage of stink

HAVE you ever driven by a sewage-treatment plant and noticed a rotten-egg stink? Air-quality requirements force these plants to use devices called chemical scrubbers to eliminate malodorous hydrogen sulfide from the gases created by bacteria in sewage slurry. The process works, but it’s expensive and depends on filtering gas through toxic chemicals such as lye and bleach.

Two researchers now argue that there’s a practical, biological alternative to current odour-control systems. At a sewage-treatment plant in California, they’ve replaced several chemical scrubbers with ones using hydrogen sulfide–degrading bacteria and trickling water.

"It’s a huge step forward compared to what people thought bacteria could do," says Marc Deshusses of the University of California, Riverside. "Our findings show that for hydrogen sulfide odour control at wastewater-treatment plants, you can convert chemical scrubbers to biological trickling filters and still have the same treatment capacity much cheaper and safer."

Sewage-plant operators "would really like to get rid of the chemicals because they are corrosive and dangerous," he adds. The changeover of the first scrubber proved so successful that the California treatment plant converted additional ones to biofilters.

"In my opinion, this is very exciting work. It takes biological air treatment to the next level," says Peter Gostomski of the University of Canterbury in Christchurch, New Zealand.

Instead of using chemicals such as sodium hydroxide, or lye, and the bleach sodium hypochlorite to degrade hydrogen sulfide, the new method sends the gas over a film of bacteria growing on polyurethane foam. The microbes convert the hydrogen sulfide into odourless hydrogen sulfate, which is carried away by water trickling over the foam. Science News

The Hidden Universe

Astronomers from Cardiff University are completing the first survey ever for cosmic hydrogen, the primeval gas which emerged from the Big Bang to form all the stars and galaxies we can see today.

Since 1997 the astronomers, with their Australian colleagues, have been using two giant radio telescopes, the 64-metre diameter dish at Parkes in New South Wales, Australia, and the 76-metre dish at Jodrell Bank in Cheshire, England to build up an atlas of the heavens as mapped by cosmic hydrogen.

The survey is fundamental for two entirely different reasons. First of all the night sky, in cosmic terms, is quite bright so that structures dimmer than the sky will be invisible to optical telescopes — but not to the radio. Thus parts of the "Invisible Universe" should come to light for the first time — and they do.

Secondly, finding the gas left behind when the galaxies formed should help decode the evolution of the universe as it expands. For instance the team finds, for the very first time, infantile galaxies still apparently coming out of pristine gas. Cardiff University

UNDERSTANDING THE UNIVERSE
WITH PROF YASH PAL

When we are going upward on a mountain we are going nearer to the sun but it is becoming cold rather than hot, why?

Most hill stations are about 2 km above sea level — that is about the altitude of Shimla, or Ooty. Distance of the Sun from the earth is 250 million km. Surely, this much change in distance cannot make any difference. In any case when we go up a mountain we are not moving towards the sun at all times of the day. The reason for the lower temperature at high altitude is very different.

You must have noticed and heard that as you go up the air becomes thinner. The pressure of the atmosphere decreases. The pressure is due to the mass of the air above. At sea level this is about 1000 grams on every centimetre square. This pressure is reduced as we go higher because there is less of air on top. Around the height of Shimla or Ooty it is reduced to about 800 grams. That is reduction by one fourth. When the pressure is reduced the molecules of air move further apart. For doing so they have to work against the attraction between them. Therefore they lose energy and the air becomes cooler. This is true for most gases.

You can do simple experiments to prove it to yourself. You must have noticed that when you blow out air from your mouth, fast and with your lips compressed, the air feels cold on your hand. If, on the other hand, you breath out slowly with your mouth open the air feels warm. In the first case the compressed air is expanded while in th second case it comes out at same pressure and temperature it is inside your lungs. If your friend or your father does not spank you afterwards you can try another experiment. Just press the valve pin in the nozzle of a car or motorcycle tire and feel the temperature of the air coming out. You will find that it would be cool, if not cold. The only way we can have a stable atmosphere is to have the air get colder as we go high. This is the basic reason for it being colder on the hills. The air is thinner. There are other considerations that alter things a bit but we will let them be at the moment.

A flame has different colours at the top, the middle and the bottom. Why?

Colours arise from emissions from different constituents of the burning vapour. They are due to excitation of atoms of higher atomic levels and their de-excitation to lower energy states. Therefore they would depend on the material that is being burnt, but also on the temperature of the flame at a certain position. A flame is produced by a combustible gas being generated through heating, or supplied initially, mixing with an adequate supply of oxygen. But just this will not be able to produce the kind of flames we see. We also need gravity and the resultant convection of hot gases upwards. (This convection would be absent in a weightless situation and therefore the flames seen on earth are not possible while travelling in a satellite).

This results in a situation where the hottest part of the flame is at the top. For a gas burner, it is clearly seen that the top gives a blue flame indicating that the fuel gas has been efficiently burnt. When the burner is defective the flame tends to be yellowish, because many carbon particles are incandescent and finally escape as smoke or soot. In a candle the objective is not to produce too much heat but lot of light. Significant part of the flame glows in a yellowish orange colour. The top blue part is almost invisible. In a hurricane lamp we get a sooty colour till the chimney is put down ensuring an organised supply of air from the bottom. Then we get the bright orange flame we desire.

Your question has a deeper significance. The analysis of colours or wavelengths of light emitted by stars allows us to determine the composition and temperature of the region from where the radiation is being emitted. Indeed it is through using this method that we know the constitution of the Sun and stars.