1.0
Stealth features of the F/A-22
Taking a look at the F/A-22, quickly reveals the fundamental
principles of a stealthy design as discussed earlier.
2.0 Continuous curves
The F/A-22 uses a combination of different ways to keep
radar waves from bouncing back to their origin. The most
sophisticated system is the use of so-called continuous
curvature.
Many of of the surface shapes of the F/A-22 are curves with
constantly changing radii. These scatter radar beams in
all directions instead of back to the radar source. There
are no right angles on the exterior of the design.
In order to calculate the curves and the effect
they have on radar reflections form any point in
3D space, requires a tremendous computing power.
The first plane using this technology
extensively is the B-2 stealth bomber, also known as the
flying wing.
Since computer- and software development has sky-rocketed
over the past 20 years, prediction models can now be calculated
quite precisely ,taking in account radar reflection versus
the shape of the plane, while supporting more naturally
aerodynamic shapes.
3.0 Planform alignment
The second way to keep radar waves from returning to the
sending antenna, the leading and trailing edges of the
wing and tail have identical sweep angles (a design technique
called planform 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.
4.0 Saw-toothed edges
The F/A-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.
5.0 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.
6.0 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.
7.0 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.
8.0 Paint scheme
In order to make the F/A-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.
9.0 Conclusion
The result of all these as well as a number of un-disclosed
or non mentioned measures is the F/A-22's BVR
capability, meaning that it can detect, engage and
kill an opponent fighter, while staying invisible itself.
