applying a variable tint to the cockpit canopy of a fighter
aircraft. In theory, such a coating could also be used over a
white-painted skin to vary its color.
But what about concealing an airraft from an enemy flying above
it! Defense contractors have told POPULAR SCIENCE that an even
more exotic skin is being tested on two stealth aircraft at the
high-security Groom Lake air base in Nevada. The skin is derived
from an electromagnetically conductive polyaniline-based radar-absorbent
composite material. It is optically transparent except when electrically
charged, much like the LCDs used in laptop computers.
What makes this new material attractive is that it can change
brightness and color instantaneously. Photo-sensitive receptors,
mounted on all sides of the plane, read the ambient light and
color of the sky and ground. An onboard computer adjusts thebrightness,
hue, and texture of the skin to match the sky above the plane
or the terrain below it.
The system is also claimed to make the aircraft even stealthier.
The electrically charged skin dissipates radar waves, reducing
Groom Lake, engineers have turned the entire skin of an aircraft
into a missile jammer.
A flickering skin could help aircraft hide from a new generation
of missiles that use visual and infrared sensors to build an image
of a target. Older heat-seeking missiles could be lured away from
aircraft by decoys; hot flares ejected during flight. But the
newer missiles use visual sensors to "see" the edges of an aircraft
and distinguish its shape from that of a decoy. A shimmering skin
confuses the missile's sensors by displacing or distorting the
Engineers have also taken steps to reduce the heat signatures
of military aircraft. In the1970s, infrared sensors had a much
greater range than visual imaging systems. Infrared accordingly
became the stealth designers' second priority, after radar.
Infrared sensors detect hot spots, such as engine exhaust or
the wing's leading edges, which are heated by air friction. At
closer ranges, sensors detect solar radiation glinting off curved
surfaces or scattering from the skin more attention to visual
stealth. Designers countered infrared
to visual stealth. Some basic physical problems still need to
be solved. For example, even a very efficient lighting system
requires a lot of energy to match the brightness of the sky, equivalent
to several times the power absorbed by the fighter's radar.
Experts in the field of electrochromic materials caution that
major technical hurdles have not vet been cleared in the unclassified
world, and not for lack of interest: The building industry would
love to see a practical, large area electrochromic film, because
it could greatly reduce the energy needed to heat and cool buildings.
Electrochromic materials must not only be able to change color,
but also to withstand sunlight and extreme weather, and continue
operating through many switching cycles. The problems are compounded
for a stealth aircraft, because the material must also be compatible
with existing radar and infrared technologies.
This may well be the reason why, for now, visual stealth measures
are confined to a few experimental aircraft and may stay that
way for some time.