Introduction
Ladies and Gentlemen: From the dawn of
human civilization man has tried to gain advantage over its enemy through
gathering information and achieving surprise. One of the techniques employed in
this regard was achieved by deception employed by camouflaging and attacking
the enemy when least expected. The famous Trojan horse is the oldest documented
event where a well-guarded and unconquered city was brought to ashes just by
mere deception. This art of being invisible was taught to the humans by nature.
Like many other animal who camouflage themselves in their environment the chameleon
can change its color and very well merge with the background and deceive its
enemy. The initial technique of humans to hide them was based on the same
principles and thus the method of camouflage evolved. Over the period of
centuries this technique was very effective and resulted in gaining decisive
edge in the conflicts. With the invention of the radar and subsequent emergence
of the thermal sensors both the man and the machine were again left exposed.
Thus by the end of World War research boomed
to find ways and means to hide military hardware especially the aircrafts from
the enemy sensors. The research lead to a widely known technology called
Stealth. And even today scientists are busy in bringing about revolutions in
this technology. This brings me to the topic of my today’s presentation. Latest
trends in stealth technology and its counter measures.
Aim
The aim of this article is to appraise the
house about the Stealth Technology, its countermeasures and latest development
in this field
The sequence of my presentation will be as
flashed.
STEALTH
TECHNOLOGY
“The use of special radar absorbent
materials, flat angular surface design and other techniques to minimize the
amount of radiation reflected to a radar installation, causing an aircraft or
other vehicle to appear as a much smaller signal or not at all.”
RELATED
TERMS
Ladies and Gentlemen: Before going into
the detail of my topic I think it’s necessary to give some basic knowledge of the
related terms which I will be using during my presentation first of all is
the:-
RCS
The size of an aircraft’s image on radar is measured by
the Radar Cross Section or RCS. Imagine a metal
plate of area A square meters
held perpendicular to the beam of radar transmitter. It reflects most of the
radar energy back to the source, and thus is easily detected. It is said to
have an RCS of A square metres.
If this plate is tilted, the amount of energy reflected directly back to the
transmitter is reduced, as some of it is reflected to the sides, so the RCS is
reduced and the value will be less than A.
The concept of stealth employs the same principle, so it does not make an
aircraft invisible but rather redesigns the vehicle to reduce its
observability.
Radar
Absorbing Material (RAM)
“A material that is designed to reduce the
reflection of electromagnetic radiation by a conducting surface is called RAM”
Facet
Facets are any of the small, polished
plane surfaces of a cut gem
Scattering
Creation of Electro-Magnetic waves after
scattering from aircraft edges
History
During the World War 1, the Germans
experimented with the use of Cellon (Cellulose acetate),
a transparent covering material, in an attempt to reduce the visibility of
military aircraft. Single example is the Fokker E.III , In fact, sunlight glinting from the
material made the aircraft even more visible. Celon was also found to be quickly degraded
both by sunlight and in-flight temperature changes so the attempt to make
transparent aircraft was not proceeded with.
Nearly two decades later, a more serious
attempt at "invisibility" was tried with the Horten Ho 229 flying wing fighter-bomber, developed in Germany
during the last years of World War
In the closing weeks of WWII the US military
initiated "Operation Paperclip", an effort by the US Army to capture as much advanced German
weapons research as possible. A Horten glider and the nearly complete Ho 229 V3
third prototype airframe were secured and sent to Northrop Aviation for
evaluation in the United States, who
much later used a flying wing design for the B-2 stealth bomber.
In 1975, engineers at Lockheed found that an aircraft made with
faceted surfaces could have a very low radar signature. Lockheed built a model
called "the Hopeless Diamond”, reduced radar cross section is only one of
factors the designers addressed to create a truly stealthy design such as the
F-117 in June 1981 and B-2 in July 1989.
TYPES
OF STEALTH TECHNOLOGY
Ladies and Gentlemen: stealth technology
being used is not limited to the aircraft but it is also being used at all four
Platforms i.e.
·
Airborne
·
Satellite based
·
Land based &
·
Sea based
But I will restrict myself to Aircraft
features only and let’s discuss the design features used in Stealth
Technology:-
Design
features
The general design of
a stealth aircraft is always aimed at reducing radar and thermal detection. It
is the designer's top priority to satisfy the following conditions:-
- Reducing radar detection by
altering some general configuration (like introducing the split rudder)
- Reducing thermal emission from thrust
- Reducing infra-red and radar
detection during adverse weather conditions
Airframe
Design
The conventional airframe design is the
best platform for RADAR waves to be reflected and identified at the scope. So
in order to make the aircraft invisible to the RADAR it must be reshaped. The
first innovation in this field which found employment was the F-117 Night Hawk
with Canted Vertical Fins which deviated the RADAR waves away from their
intended path. Subsequently taking the leaf from the Nazi war machine the
United States invented the Horton of the modern era The B-2 spirit. Its wing
like shape reflects very little amount of waves back and the Radar Cross
Section is disregarded as clutter.
Faceting
Faceting is a process in which ordinarily smooth
surface of the airframe is broken up into a series of trapezoidal or triangular
flat surfaces arranged in such a way that the vast majority of the radar waves
on the aircraft will be scattered away at odd angles, leaving very little to be
reflected directly back into the receiver. On most aircraft the leading and
trailing edges are straight or near straight, so the reflected energy will be
concentrated over a narrow range of angles. By curving the leading edge as
those employed in the F-22 and the JSF, the designer arranges a method that the
reflected energy is not all returned in the same direction.
Effects
of Wing Sweep
Effects of wing sweep on RCS are shown on the
slide in front of you. The most effective out of all these is the compound
sweep, as you can see that energy reflected from compound sweep is scattered in
few chosen directions. In this slide the effect of compound sweep in RCS of
aircraft is clearly visible as energy is reflected in different directions.
Canopy
Design
One of the most troublesome cavities on an
aircraft is the cockpit. Virtually as transparent to radar energy as it is to
light, the canopy allows radar energy to reflective cockpit interior. One way
of preventing this is to apply a thin layer of gold to the canopy transparency.
This will have a minimum effect on visibility but will not be painted by the
radar as being electrically conductive surface rather than a transparency. This
technique is used on F–16, F-22 Raptor and EA - 6B prowler.
Cavities
Creation of a practical stealth aircraft
requires a meticulous attention to detail if RCS is to be minimized. Cavities
such as air intakes have high RCS. Conventional ramp – type are ideal radar
reflectors as it traps and strongly reflects radar energy. So all cavities like
inlets and exhausts are required to be redesigned to be less reflective to
radar energy. Use of half cone / cantered body, long sinuous serpentine zigzag
intakes with or without ram coating will help in reduction of re – entrant
effect.
Composites
Another RCS reduction feature of the
stealth aircraft is to use where ever possible of composite materials rather
than metal. Several types of composite type materials are now used in aircraft
construction. Radar energy striking at a composite structure has a hard job
setting up the electrical and magnetic currents which radiate energy.
Radar
Absorbing Material
Radar-absorbent
material, or RAM, is a class of materials used in stealth technology to disguise a vehicle or structure
from radar detection. A material's absorbency at
a given frequency of radar wave depends upon its composition. RAM cannot
perfectly absorb radar at any frequency, but any given composition does have
greater absorbency at some frequencies than others; there is no one RAM that is
suited to absorption of all radar frequencies.
A common misunderstanding is that RAM makes
an object invisible to radar. A radar-absorbent material can significantly
reduce an object's radar cross-section in specific radar frequencies, but it
does not result in "invisibility" on any frequency.
IR
Screening
Given present day sensor technology, IR offers the only realistic option to RADAR
for the long range detection of the target aircraft. With the growing use of IR
sensors as a radar substitute, measure must be taken to reduce the thermal
signatures of a stealth aircraft. The main sources of IR energy are hot metal
components of the engine turbine and the exhaust nozzles, which have been
heated up to 1000-1300*C. If the engine uses an after burner, the IR emissions
are increased up to 50 times. For this reason all the first generation stealth
aircraft F-117A and B-2 make use of non A/B engines. The IR signature can be
reduced by using the aircraft aft fuselage and / or vertical tail surfaces to
shield the jet pipes. The other source of IR signature is exhaust plume, which
must be cooled quickly with the cooler by pass air. The same phenomenon is
shown on the view foil and one can easily differentiate between exhaust plume
and that of mixed with cool air.
Engine
Noise
Some
stealth aircraft are subsonic.
Most of the noise created by an aircraft is because of the engine. Stealth
aircraft have anti-IR engine bay liners which are also thought to play a sound
absorbing role. It is reported that the engine noise from a taxing F-117 was
barely audible at ranges of more than a few hundred meters.
COUNTERMEASURES
AGAINST STEALTH TECHNOLOGY
Ladies and Gentlemen: To counter the
stealth technology various methods are in use. I will be talking about them one
by one.
Satellite
Based Method
The battlefield can be looked down upon
from satellites equipped with radar sensors. Although satellites would be
relatively far away from the battlefield
a couple of hundred miles away, or even more they would be able to
remain out of range of most hostile weapons, and thus would not run much risk
of being shot down, as might aircraft. Also, satellites would be able to cover
a much larger area of the battlefield, thus being in a position to locate and
track virtually all hostile stealth craft.
Longer Wavelength Radar
VHF radar systems have wavelengths comparable
to aircraft feature sizes and should exhibit scattering in the resonance region
rather than the optical region, allowing most stealth aircraft to be detected.
Despite the advantages offered by VHF radar, their longer wavelengths result in
poor resolution compared to comparably sized X-band radar array. As a result,
these systems must be very large before they can have the resolution for
engagement radar. Russian KB radar is an example.
The Dutch company Thales Nederland,
formerly known as Holland Signaal, developed
a naval phased-array radar called SMART-L,
which is operated at L-Band and has counter-stealth.
Radio
Telescope Radars
The Radio Telescope scans the sky at high
apertures with high sensitivity. Whether in the day, night or during bad
weather, radio signals from the stars reach the radar installations
uninterrupted. Since the radio map of the stars is by now very well known, it
may be assumed that if any star is not observed on the detecting screen or
output device, that particular star must be eclipsed by some aircraft flying
above the installation somewhere along the line of sight between the
installation and that particular star.
And with very sensitive radio-astronomical
equipment, virtually every part of the sky is observed to be covered with
stars! Therefore at almost every instant in time, the stealth aircraft would be
eclipsing one or another known star.
OTH
Radars
One of the most promising methods of
detecting stealth is by using Over the Horizon Radars (OTH). These radars aim at
detecting the targets which are masked from the view of conventional radars by
the curvature of earth’s surface. These radars direct a powerful sky wave
towards the earth’s ionosphere. This is refracted and is returned towards the
earth’s surface, illuminating a distant path of terrain or sea. Any target
present in this area create radar echoes which follow the reverse route back up
to the ionosphere and thus back to the receiver of the OTH radar. OTH can also
pick up scattered signals from stealth. The RADAR is dependent on the
environmental condition and for the constant detection and tracking of the
aircraft the frequency of the RADAR has to be consistently readjusted.
Bi-Static
Sanctuary Radar Concept
The other promising counter measure to
stealth is Bi-Static radar. In a normal (mono Static) radar, the receiver and
transmitter are at same location and often share the same antenna. In Bi-Static
radar, they are located some distance apart and several receivers may share a
single transmitter. The suitable location for the transmitter can be high
flying aircraft or a geostationary satellite. This technique involves radar
energy scattered by stealth in directions away from the transmitter by the
receivers of Bi-Static radar.
LATEST
DEVOLPMENTS
stealth technology has been constantly
evolving and a lot of technological advancement have been made in this field
such as
Plasma
Stealth
It has been always emphasized that stealth
is necessarily a design feature and a conventionally built aircraft cannot be
converted into a stealth aircraft. However, the Russians have developed a bolt
on kit with approximately 100 kg of weight which claims to reduce the RCS of an
aircraft by creating a cloud of plasma around the airframe. The Russians and Americans have been working
on plasma theory for very long time now but only the Russians have been able to
develop something in this regard.
The idea arose from the fact that a space
shuttle while re entering the atmosphere faces an electromagnetic blackout due
to the cloud of plasma being created around the shuttle while passing through
the ionosphere. This blackout cuts off all the radio and radar contact of the
shuttle from the ground station and it becomes invisible for this time period.
The kit when switched ON creates a layer of plasma ions around the aircraft
body. This field partially consumes electromagnetic energy of hostile radar or
causes it to bend around the aircraft. Radar energy tends to pass around a
plasma cloud rather than penetrate it, and the energy that does penetrate
interacts with the plasma charged particles, and is partially absorbed reducing
the aircraft RCS by up to 100 times. Plasma stealth is being incorporated in
the MiG-35 "Super Fulcrum / Raptor Killer".
There would obviously be some adverse
effects on the performance of the aircraft subsystems like radio transmissions,
limitations on radar emissions and other sensors, but the second and third
generation kits are being designed to take care of these problems.
Active
Cancellation
Another method under consideration for the
RCS reduction is the Active cancellation of the incoming Electromagnetic wave.
Sophisticated and complex signal processing equipment would be installed on the
aircraft. This equipment, upon receiving the EM signal would analyze the
frequency, waveform, strength and direction of the incoming wave and send a
similar but out of phase wave in the same direction, thus canceling the overall
effect. This technique is being researched by French designers and is most
likely to be incorporated on the “Rafael”.
Cloaking
Technology
Up till now the advancements in stealth
technology in electromagnetic spectrum have been discussed. Now I would
introduce a new horizon in denying visual acquisition. This advancement could
be well categorized as the camouflage technique or the Cloaking technology. One
such advancement is in meta-materials; artificially engineered structures
tailored to have specific electromagnetic properties. In particular, they can
bend light around an object, making it appear to an observer as though the
waves have passed through empty space.
A stealth technology system being
developed at Advanced American Enterprises utilizes a form of electro-optical
camouflage (referred to also as chameleonic camouflage or cloaking technology)
which, according to them renders an object, person, or vehicle 85-100%
invisible to the human eye or video camera in the visible spectrum as soon as
you flip the switch to "on", even while the cloaked item is moving.
But at the moment the operational distance is at least 20ft.
Analysis
Instability of design
Early stealth aircraft were
designed with a focus on minimal radar cross section (RCS) rather than aerodynamic
performance. Highly-stealth aircraft are aerodynamically unstable and thus rely
on onboard computers for aerodynamic stability.
Electromagnetic emissions
The high level of
computerization and large amount of electronic equipment found inside stealth
aircraft are often claimed to make them vulnerable to passive detection.
Vulnerable modes of flight
Stealth aircraft are still
vulnerable to detection during, and immediately after using their weaponry.
Since stealth payload (reduced RCS bombs and cruise missiles)
are not yet generally available
Reduced payload
Fully stealth aircraft carry
all fuel and armament internally, which limits the payload. This requires the
deployment of additional aircraft to engage targets that would normally require
a single non-stealth attack aircraft. This apparent disadvantage however is
offset by the reduction in fewer supporting aircraft that are required to
provide air cover, air-defense suppression and electronic counter measures,
making stealth aircraft "force multipliers".
Sensitive skin
Stealth aircraft often have
skins made with Radar-absorbent materials or RAMs. Some of these contain Carbon black particles, some contain tiny iron
spheres. There are many materials used in RAMs, and some are classified,
particularly the materials that specific aircraft use and are sensitive to
ambient conditions.
Cost of operations
Stealth aircraft are
typically more expensive to develop and manufacture. An example is the B-2 Spirit that is many times more expensive to
manufacture and support than conventional bomber aircraft. The B-2 program cost
the U.S. Air Force almost $45 billion.
Conclusion
Ladies and Gentlemen: Stealth is a
promising technology which gives the operator a capability to sneak in any kind
of defended environment and inflict damage to the enemy with an intensity which
was not possible otherwise. All this is achieved with minimum or zero
attrition. We, being a part of resource constraint nation might not be able to
fight out the super power’s technological advancements, but here we have to
remember that nothing is impossible in this world. Counters to stealth
technology were born the same day once the first stealth aircraft was produced.
Author Bio
Squadron Leader Ali Hamza is a retired PAF pilot with 20 years of experience, defence analyst, airpower expert, gold medallist in MSc DSS (Defence & Strategic Studies) from QAU, currently doing MPhil IR from NUML, Rawalpindi and has a keen interest in modern airpower’s role in the geopolitics at global and regional levels.
YouTube: https://www.youtube.com/@AeronautIR
X (twitter): https://x.com/AliHamzaAwan1
