| Radar is (when simply put)
radio waves thrown out into air that bounce off of objects,
return to the place of origin, and when calculated, can tell what something is, how far it is, and how fast
it's moving.
A basic,
non-foolproof formula for calculating target distance using
radar is:
target range= T/12.36 microseconds per nautical Mile
where T=Elapsed Time |
The Radar Cross
Section of a plane is basically, how much echo the plane sends
from radar. Everything has a Radar Cross Section (or RCS),
but where birds have approximately a .01 square meter RCS, the
Raptor has almost the same RCS. The B2 Bomber has a radar cross
section of .75 square meters. For the Raptor to be stealthy, the
creators had to cut down on the RCS, meaning that everything on
the plane, internal and external, had to have no echo, or as
little as possible. To accomplish this, they made many
parts of the plane with special alloys (metal mixtures) that had
little or no echo when hit by radar. The shape of the F-22
is made to have an over-all "triangular" shape, making
the over-all shape reflect radio waves in such a manner, that
they do not go back to the radar of the enemy.
Examples:
RAM, or Radar
Absorbing Material, is covering the entire fuselage of the
F-22. This material is made to absorb and kill radio waves
instead of reflect them.
The F-117 is a
prime example of scattering. The entire plane is one, large
system of triangles. It has all flat surfaces, angled to deflect
radar waves away from enemy base. The F-22 also does this,
but in a different manner. It is fairly rounded, yet on
closer observation, the over-all shape has angles to it that
scrambles the radar all over, everywhere but back to the radar's
origin.
To
be stealthy, a plane must not give off too much heat. The
heat not only makes it stand out on thermal imaging, but makes
it a prime target for missiles. The engines of the Raptor
are made to make as little exhaust and heat as possible.
The
turbulence of a plane is caused by the movement of the craft
disrupting the air around it. The shape of any stealth
plane is made so that is EXTREMELY aerodynamic, having the least
amount of air resistance. This minimizes the turbulence, and the
fuel costs, since the plane is not creating so much drag.
The less turbulence, the less likely it is that the enemy's
sensitive laser detection equipment will pick up on the plane.
Smoke Contrails
are caused when the engine(s) of a plane spurts out extra
power. Any contrail (smoke or air) is something that a
pilot does not want following his plane if he is going into the
enemy territory, after all, it is a tell tale sign of his
presence. The F-22 and many other planes were created in
such a way as to reduce this problem. Tests were once
conducted to stop or reduce contrails on planes. The F-22,
because of the super cruise ability, is able to avoid the smoke
contrail problem fairly well.
| *
"Air" (moisture) Contrails |
"Air"
Contrails are the most commonly seen type of contrail. These
come from the moisture in the air being disturbed by a
wing. When these contrails are created, the pressure of
air surrounding the wing is disturbed and unbalanced, causing
the moisture to form trails. The F-22 has been able to
decrease the likelihood of these contrails because of the
horizontal stabilizers located on the aft part of the
aircraft. These stabilizers help evenly distribute the
lift of the aircraft so that contrails are avoidable.
The
F-22 was painted with a medium gray. This gray matches the
sky closely enough to fool the naked human eye enough to not
stick out like a sore thumb.
This
is a somewhat dangerous, yet old and effective way of avoiding
radar detection. This method is used to fly below radar
cover, basically, flying so low to the ground, that all the
trees and obstacles (hills, buildings, etc.) scramble the radar
waves (remember that radar bounces off of
everything). This
method is beginning to age. With new detection methods,
the radar is able to pick out the plane from the ground
clutter. Following
from F22-Raptor
"Stealth
features of the F-22
Taking
a look at the F-22, quickly reveals the fundamental principles
of a stealthy design as discussed earlier.
Airframe
features
The F-22 has a low height triangle appearance from the front.
This physical cross sectional view ensures a small signature
from the front and low observability touches such as paint and
materials, as well as little "W" shapes where straight
lines might have appeared, all tend to break up the signature by
absorption or redirection.
The "W" shapes are found at numerous places on the
stealth aircraft. For instance, in the forefront of the cockpit
glass, there is a very apparent "W" shape. This
reduces the radar energy reflected during a head-on pass to the
radar emitter. The "W" shape is also found on landing
gear doors, engine inlets and outlets, as well as other
openings.
The leading and trailing edges of the wing and tail have
identical sweep angles (a design technique called platform
alignment). The fuselage and canopy have sloping sides. The
vertical tails are canted. The engine face is deeply hidden by a
serpentine inlet duct and weapons are carried internally.
Engine
nozzles
Reduction of radar cross section of nozzles Is also very
important, and is complicated by high material temperatures. The
approach taken at Lockheed is to use ceramic materials. The
ceramics may be either lightweight, parasitic sheets mounted on
conventional nozzle structures or heavier structural materials
forming saw-toothed edges.
|
Cockpit
The pilot's head, complete with helmet, is a major
source of radar return. This effect is amplified by the
returns of internal bulkheads and frame members. The
solution is to design the cockpit so that its external
shape conforms to good low radar cross section design
rules, and then plate the glass with a film similar to
that used for temperature control in commercial
buildings. Here, the requirements are more stringent: it
should pass at least 85% of the visible energy and
reflect essentially all of the radar energy. At the same
time, one would prefer not to have noticeable
instrument-panel reflection during night flying.
|
Antennas
On-board antennas and radar systems are a major potential source
of high radar visibility for two reasons. One is that it is
obviously difficult to hide something that is designed to
transmit with very high efficiency, so the so-called in-band
radar cross section is liable to be significant. The other is
that even if this problem is solved satisfactorily, the energy
emitted by these systems can normally be readily detected. The
work being done to reduce these signatures is classified.
|
Paint
scheme
In order to make the F-22 disappear for the human eye on
the ground, when in flight, special camouflage schemes
have been developed. This way the plane will blend with
the background sky as much as possible viewed from the
bottom and disappear in the ground texture when seen
from above."
|
Interactive
Stealth Tutorial
(Flash Needed)
Click
Here For More!
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