Stealth aircrafts – The science behind the vanishing acts of fighters

Stealth the word summons images of fighter jets and bomber sneaking over  enemy lines, junking around objects while hugging the Earth to avoid detection of  batteries of radars eagle-eyed sentinels.What this project deals with is how aircraft are detected by radar, what Stealth  Technology is, the development of this technology, and the advantages of and  disadvantages of Stealth.

Stealth Technology is the technology in which a plane or other vehicle is made to  be virtually undetectable to radars and radar signals.

B-2 Spirit stealth bomber of the U.S Air Force

StealthAircraft2

How Radar Signals Are Blocked Using Stealth Technology and how a stealth air craft escapes from the clutches of the radar and radar signals which have become increasingly strong to penetrate.     Radar signals that are sent towards an aircraft that has stealth features can cause  radar signals that are sent out by a radar unit by having the signals hit a part or all of the  aircraft and what happens to those signals is that they either pass right through the aircraft or they are reflected towards another direction and this is caused because of the  Radar Absorbent Material (RAM) and in this way the aircraft can be virtually  undetectable to radar

Introduction:

Stealth refers to the act of trying to hide or evade detection. It is not so much a technology as a concept that incorporates a broad series of technologies and design features. As a concept, stealth is nothing new, having been invented by the first caveman to cover himself with leaves so that he could sneak up on a dim-witted antelope. Soldiers hid behind trees. Submarines hid under the waves to sneak up on ships, and it was submarines that first used special coatings on their periscopes to avoid radar detection during World War II.

For airplanes, stealth first meant hiding from radar. After World War II, various aircraft designers and strategists recognized the need to design planes that did not have large radar signatures (a radar signature is how big the airplane appears on radar from a specific angle and distance; it is often referred to as the “radar cross-section”). But their ability to hide from radar was limited for many years for several reasons. One major limitation was aircraft designers’ inability to determine exactly how radar reflected off an airplane.

History:

In the nineteenth century, Scottish physicist James Clerk Maxwell developed a series of mathematical formulas to predict how electromagnetic radiation would scatter when reflected from a specific geometric shape. His equations were later refined by the German scientist, Arnold Johannes Sommerfield. But for a long time, even after aircraft designers attempted to reduce radar signatures for aircraft like the U-2 and A-12 OXCART in the late 1950s, the biggest obstacle to success was the lack of theoretical models of how radar reflected off a surface.

 In the 1960s, Russian scientist Pyotr Ufimtsev began developing equations for predicting the reflection of electromagnetic waves from simple two-dimensional shapes. His work was regularly collected and translated into English and provided to U.S. scientists. By the early 1970s, a few U.S. scientists, mathematicians, and aircraft designers began to realize that it was possible to use these theories to design aircraft with substantially reduced radar signatures. Lockheed Aircraft, working under a contract to the Defense Advanced Research Projects Agency, soon began development of the F-117 stealth fighter.

An F-117 Nighthawk stealth strike aircraft

F-117_Nighthawk_Front

The Basics of the Radar

A. Echo:

There are two basic principles that are useful to understand before discussing how radar technology is used.  The first of these principles is echo.  Many understand an echo to be someone’s voice bouncing off of something and coming back to them.  This is a very accurate definition of what an echo is but it can be taken in a more broad sense to include all types of propagating waves, including light.  Someone hearing their own voice is an example of sound waves hitting a surface and then, reflecting straight back at them.  A mirror is an example of light waves being reflected back at one’s self.  Light from an external source hits a body and bounces off in several directions.  Some light waves propagate towards the mirror and then reflect off of the mirror back to that person’s eyes.

RADAR

This same exact principle applies to radio waves.  Radio waves are simply non-visible forms of light.  The idea behind radar is to transmit a radio wave and then receive the reflection from an aircraft.  The amount of time between the transmission and the reception can be used with a very accurate number for the speed of light to determine how far away the plane is from the radar station.

B. The Doppler Shift:

The second principle that is used in radar is the Doppler Shift.  One familiar case of Doppler Shift that will help to explain what it is and how it can be used in radar is that of an ambulance or car with its sirens or horn on.  The sound that you hear as the vehicle is approaching you is at a higher pitch, or higher frequency, than the sound you hear when the vehicle is moving farther away from you, see

This can be explained with the following example “Imagine that the car is standing still, it is exactly 1 mile away from you and it hoots its horn for exactly one minute. The sound waves from the horn will propagate from the car toward you at a rate of 600 mph. What you will hear is a six-second delay (while the sound travels 1 mile at 600 mph) followed by exactly one minute’s worth of sound.   Now let’s say that the car is moving toward you at 60 mph. It starts from a mile away and toots its horn for exactly one minute. You will still hear the six-second delay. However, the sound will only play for 54 seconds. That’s because the car will be right next to you after one minute, and the sound at the end of the minute gets to you instantaneously. The car (from the driver’s perspective) is still blaring its horn for one minute. Because the car is moving, however, the minute’s worth of sound gets packed into 54 seconds from your perspective. The same number of sound waves is packed into a smaller amount of time. Therefore, their frequency is increased, and the horn’s tone sounds higher to you. As the car passes you and moves away, the process is reversed and the sound expands to fill more time. Therefore, the tone is lower.”

One may ask, ‘How can this principle be used in radar?’  This Doppler shift can determine how fast an object is moving.  In radar, the transmitted radio wave discussed earlier is sent at a known frequency.  When the reflection is received, its frequency will be smaller, larger, or the same as the transmitted radio wave.  If the reflection is the same frequency then the object isn’t moving, such as a helicopter hovering in one spot.  If the reflection is at a higher frequency, then it is moving towards the radar tower and the amount of increase in frequency can be used to determine how fast it is moving towards the radar tower.  The same is true with a lower frequency reflection but in this case, the object is moving away from the radar tower.

thumb-1920-329538

C. Why Radio Waves:

If the principles of echo and Doppler Shift are used together in radar systems, then radar would be able to detect the location and the speed of an aircraft.  The previous examples used to describe these principles used sound waves.  In contrast, radar uses electro-magnetic waves instead of sound waves.  There are several reasons for this.  The first is that sound waves cannot travel as far as light without significant attenuation.  Secondly, electromagnetic echo is much easier to detect than a sound echo.

D. The Radar Cross Section:

There are multiple characteristics that determine the range of radar systems.  These variables are the peak transmitted power, wavelength of the system, a loss factor, the power of the noise within the receiver’s bandwidth, the ratio of the received echo to the amount of noise, and the radar cross-section.  The radar cross section (RCS) is the only factor that is controllable by the designers of the object under detection. For this reason, stealth designers seek to minimize the RCS of an aircraft.

radar cross section

Definition:

In order to understand stealth technologies it is helpful to understand how the radar cross-section is calculated and what it means.   “The radar cross section may be considered as the projected area of an equivalent reflector which has uniform properties in all directions.  This equivalent reflector is a sphere which will return the same power per unit solid angle (steradian) as the aircraft.”  With a sphere, the aspect angle of the radar does not affect the amount of echo energy that is received.  Thus, the energy received from an aircraft’s echo, at a given aspect angle, is compared to the surface area of a sphere that will produce the same amount of reflected energy

Aircraft designers generally describe an airplane’s radar cross-section in terms of “decibel square meters,” or dBsm. This is an analogy that compares the plane’s radar reflectivity to the radar reflectivity of an aluminum sphere of a certain size. The B-2 reportedly has a radar signature of an aluminum marble. The F-22 Raptor interceptor is roughly the same, and the F-117 is only slightly less stealthy.

 The newer Joint Strike Fighter has the signature of an aluminum golf ball. The older B-1 bomber, designed during the 1970s and 1980s, is about the size of a three-foot (one-meter)diameter sphere, whereas the 1950s-era B-52 Stratofortress, a monstrously non-stealthy airplane, has an enormous radar cross-section of a 170-foot (52-meter)-diameter sphere. The size of an aircraft has little relationship to its radar cross section, but its shape certainly does Error! compares the typical RCS values of birds and insects to typical RCS values of military aircraft.

Table 1

RCS of Various Flying Objects

Object RCS [m2]
F-15 Eagle 405
B-1A 10
SR-71 Blackbird 0.014
Birds 0.01
F-22 Raptor 0.0065
F-117 Nighthawk 0.003
B-2 Spirit 0.0014
Insects 0.001

E. Applications of Radar:

Radar has many uses in both military and civilian applications.  In the military, radar is used to detect enemy aircraft and to guide friendly aircraft.  The military also uses radar to detect above surface water vessels.  Radar can also be integrated into anti-aircraft defense systems to enable anti-aircraft artillery to be more accurate.  Radar can also be used to guide missiles to determine if they are on the correct path.

In civilian applications, radar is used in air traffic control rooms and police use radar to determine if a vehicle is traveling to fast.  Radar is also used to map out geographical locations and to observe the movement of objects in space such as planets, satellites, and debris.

Another application of radar is in predicting sort-term weather patterns such as rain, thunderstorms and even tornadoes.   There are many other applications of radar that I have not listed but from this list it is obvious that the world would be a very different place without radar.

Plasma stealth:

Plasma stealth is a proposed process to use ionized gas (plasma) to reduce the radar cross section (RCS) of an aircraft. Interactions between electromagnetic radiation and ionized gas have been extensively studied for many purposes, including concealing aircraft from radar as stealth technology. Various methods might plausibly be able to form a layer or cloud of plasma around a vehicle to deflect or absorb radar, from simpler electrostatic or radio frequency (RF) discharges to more complex laser discharges. It is theoretically possible to reduce RCS in this way, but it may be very difficult to do so in practice.

Concept behind stealth technology  

  • Non Conductive material design.
  • Shape of Aircraft
  • Other shape consideration
  • Radar absorbent paint.
  • Diffused reflection
  • Redirected radio waves

RAM deflections

RAM (Radar absorbent paint)

Radar signals that are sent towards an aircraft that has stealth features can cause
radar signals that are sent out by a radar unit by having the signals hit a part or all of the
aircraft and what happens to those signals is that they either pass right through the
aircraft or they are reflected towards another direction

RAM explained

This is caused because of the Radar Absorbent Material (RAM) and in this way the aircraft can be virtually undetectable to radar

ADVANTAGES:

  • Increased combat efficiency
  • Unopposed air strikes
  • Possibility of avoiding war
  • Weakening of opposite party

LIMITATIONS:

  • Instability of design
  • Reduced payload
  • Cost of operations
  • Reduced payload
  • Sensitive skin
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4 thoughts on “Stealth aircrafts – The science behind the vanishing acts of fighters”

  1. Increased awareness of stealth vehicles and the technologies behind them is prompting the development of means to detect stealth vehicles, such as passive radar arrays and low-frequency radars.

    Liked by 1 person

    1. People are trying to better both the technologies to compete with the other. once a radar tracks a stealth aircraft successfully and shoots it down then that aircraft is no longer safe and there is a requirement for a newer better version. 🙂

      Like

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