Constantin Schlug 25/01/ :56

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Julian Joseph
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1 1 The Future of Science Fiction has arrived Stealth Technology The latest developments in Stealth Technology seem futuristic and unreal. Military vehicles look like they come straight out of science fiction movies and games. New military aircrafts look so different from what we know today, that they often get called UFOs. They can infiltrate enemy airspace and can deliver nuclear devices in a couple of hours all around the world. In addition to that a new generation of tanks becomes completely invisible to heat detecting optical sights. There is even an invisible cloak like the one from Harry Potter that is handled as the camouflage of the future. Maybe you have seen the patterns of camouflage in fashion, or in the news. Hunters, for example, wear it to merge with their environment. They don t want to be seen by their pray. Also the military, normally, wants to be unseen. They try to hide everything they can from the enemy eye. The use of camouflage, on both sides, forced the military to come up with new technologies to reveal their invisible opponents. During the Cold War this quickly started a race for technology. On the one hand the rise of new technology to reveal the invisible intruder. On the other hand the development of new devices and methods to be invisible. The so called Stealth Technology.

2 2 What is Stealth Technology? The latest development in the military hide and seek game is called Low Observable Technology, better known as Stealth Technology. When we talk about Stealth Technology, the first picture that may come to mind is the American B-2 Spirit Stealth Bomber. Maybe you have seen that unreal looking black flying wing in the news during the Afghanistan war; the US used it to bomb Al-Qaeda. With a wing span of 52 m you would expect a large radar appearance (radar cross section), similar to a B-52 bomber with a wing span of 56 m. In fact the radar cross section of the Stealth Bomber is 1000 times smaller. It is so small that it is even smaller than the radar cross section of an MiG-21, which has only a wing span of 7.15 m. Comparing these two values, the stealth bomber really becomes stealth on radar. Picture 1: Radar cross section in m 2

3 3 To be nearly, ideally, invisible to radar, sonar, infrared and other detection methods, is the goal of Stealth Technology. You can think of it as a kind of camouflage, especially designed for electronical detection methods. However stealth is not only a concept reserved for airplanes; it is also applied to submarines, ships, missiles and even satellites. How does Stealth Technology work? Stealth Technology consists of many different technologies. This makes sense, if you look at the different detection methods. The main three detection methods are: First radar detection used to detect airplanes and used in speed controls. Secondly acoustic detection mainly used to detect submarines under water and other vehicles with a characteristic sound. Thirdly thermal detection used in infrared cameras to determine the heat of certain objects. So, why has a Stealth Bomber such a small radar cross section? If you compare the B-2 Spirit and B-52, the difference in shape pops right into your eyes. The B-2 Spirit is just a flying wing. In fact it is known since the 1930s that, the shape of an airplane makes a huge difference to detectability. For example the Avro Vulcan, a British bomber from the 1960s, had a really small radar appearance despite its 30 m wing span. With today s knowledge it is known that the bomber had a stealthy shape apart from the tail. Can you believe that this large aircraft sometimes disappeared entirely from radar screens, truly amazing in comparison to the Tupolev 95. This Russian long range bomber was more than visible on radar, due to its four large (5.6 m diameter) contra-rotating propellers. In other words propellers and jet turbine blades create a bright radar image. Another example is the Blackbird, introducing radar transparent and absorbing coating. Behind the radar transparent skin is a structure that basically traps Radar Waves until they lost almost all energy. Picture 2: Radar absorbing coating

4 4 The Blackbird was a spy plane built to fly with a speed of 3,540km/h. Did you know that, it was so nicely constructed that it would leak fuel when standing in the hangar? In order to travel with Mach 3, the metal needs space to expand by a couple of centimeters. Nonetheless the leaking problem, the Blackbird was a great success for the US Government. The best way to avoid a Radar Signature is to reflect the radar waves away from the receiver. Imagine the surface as a mirror, if you can see yourself, the Radar can see the air craft. Since orthogonal shapes promote the reflection to the receiver, stealth vehicles try to avoid structures with a 90 angle such as the classical airplane tail. The best example for this is the F-117A (Picture3 lower aircraft) and the B-2 Spirit. Picture 3: Example for Radar Wave reflection The F-117A was the first airplane of its kind. The development started with a computer simulation to calculate the most invisible shape to radar. The project was called Hopeless Diamond. Imagine you had to teach that highly invisible diamond how to fly. Only with the help of computer based stabilization software was the Hopeless Diamond able to take off.

5 5 As I mentioned earlier turbine blades create a bright radar image. To avoid this, the engines have to be buried in the wings of the jet. In such a way, that the compression blades are not visible anymore. To achieve an even lower Radar Signature, airplane designers have to avoid complex bumps such as fuel-tanks and weaponry. Also they have to get rid of all kind of protrusions like the air intakes for the jet turbines. That means that every stealthy vehicle becomes visible when they open a hatch or door. Sounds a bit ironic, doesn t it? In case of the Stealth Bomber it doesn t matter. After it drops its nuclear devices its task is complete. To be acoustically invisible is especially important for submarines and ground vehicles. As you might have seen in a movie that, takes place inside a submarine. The crew turns off the engine and has to be as silent as they can, in order to stay invisible. Underwater sound waves travel very far and well. They can be detected by underwater passive sonar. In order to avoid noises the whole submarine is covered in rubber that absorbs sound. Also aircrafts, especially helicopters, are noisy as you might have experienced at a flight show. Helicopters have a unique and loud rotor noise. In order to reduce this sound, the so-called modulated blade spacing is used. This fancy name describes the fact that the rotor blades are not evenly spaced. When the rotor blades have different degrees of spacing between them, they spread the sound over a greater range of frequencies, which makes them quieter. The trickiest part about Stealth Technology is to become invisible to infrared (IR). Infrared detects the heat of an object. There are thermal driven missiles, which use infrared to lock on a target. Jet turbines act like hairdryers, they produce a lot of hot air (see picture 4).

6 Picture 4: infrared signature of a normal jet Picture 5: infrared signature of a stealth jet The easiest technique to reduce the IR signature is to use a

Another often used technique is to inject cool air into the exhaust flow. Sometimes the fuel is used as a coolant.

In case of the B-2 Spirit the wing surface is used to shield the hot exhaust stream from observers below.

6 6 Picture 4: infrared signature of a normal jet Picture 5: infrared signature of a stealth jet The easiest technique to reduce the IR signature is to use a slit shaped exhaust for the jet turbines. This minimizes the exhaust volume in cross-section and maximizes the mixing of cool and hot air (see picture 5). Another often used technique is to inject cool air into the exhaust flow. Sometimes the fuel is used as a coolant. It circulates inside the exhaust pipe and cools it down. The warm fuel is then cooled down by the cold wind stream which flows over the wings. In case of the B-2 Spirit the wing surface is used to shield the hot exhaust stream from observers below. In addition to that its exhaust outlets have the shape of slits and cool air is added to the hot exhaust mixture. In fact there is no visible exhaust stream (see picture 6). Nonetheless, as you can see, it is still visible to infrared. Picture 6: Infrared signature of a B-2

7 Latest development in Stealth technology Picture 7: Infrared signature of the PL-01 Concept The PL-01 Concept is the latest development in Stealth Technology.

7 7 Latest development in Stealth technology Picture 7: Infrared signature of the PL-01 Concept The PL-01 Concept is the latest development in Stealth Technology. It was first shown to the public in 2013 and is expected to enter service in As you can see (picture 7) the tank can change its shape in appearance to infrared cameras. If you look closely you still can see the edge of the tank. It can also choose to be completely invisible to infrared. The technique used is rather simple but brilliant. In order to become invisible to infrared, the tank has a skin made out of hexagons. Those hexagons can change its temperature. For example in a desert they act like a ceramic hob. In order to project the right temperature to them the tank has infrared sensors, which monitor the temperature behind it. Since this technology is still in development, very little is known. It can be assumed that, if this technology is a success, it will be applied not only to tanks but to every other stealth vehicle as well.

8 Picture 8: mock-up of Quantum Stealth material Imagine you could use Harry Potter s invisible cloak, a truly magical thing. There is not such a thing you think.

8 8 Picture 8: mock-up of Quantum Stealth material Imagine you could use Harry Potter s invisible cloak, a truly magical thing. There is not such a thing you think. What if I tell you there is a company called HyperStealth that developed a material that makes you totally invisible. This technology is called Quantum Stealth. Since the US Military declared it top secret for reasons of security, very little is known about the actual technology. The material is capable of bending light around the target in such a way, that the target appears completely invisible. It even makes the target invisible to infrared and removes its shadow. If you think that can t be possible and it s just a science fiction story to trick people, you might be right. But keep in mind that a lot of UFO sights around Area 51 were actually true. Well there were no aliens involved; the Unknown Flying Objects were prototypes of the F-117A and B-2 Spirit and other unknown air crafts. The B-2 Spirit had its first flight in July It took four more years for it to get revealed to the public. So be prepared for the unknown, the future of Science fiction arrived now.

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