Re: How does Stealth technology work

Thanks for this wonderful question!

Start by going back to the battle of Britain, 1939-1940.  The British had 
developed radar (very TOP SECRET) and so, even though well outnumbered, 
were able to direct their few fighters to exactly where the German aircraft 
were.  The Germans were not stupid and figured out that their aircraft were 
being detected at a distance beyond visual range (100 miles?) but never 
found a good way around the British radar in time, fortunately for us.  
However, the Germans did find that by flying very low their aircraft could 
avoid being detected and this is probably the first use of 'stealth' in an 
aircraft:  here, fly low and stay 'invisible' to probing radar;  the 
transmitted radar pulses would be above the aircraft's path and so the 
plane remained undetected.  That's why drug running aircraft fly at an 
altitude of perhaps 100 feet above the ocean.  Then when everyone figured 
out radar the race to build a 'radar-invisible' aircraft was on.  You might 
think that the older wood and fabric aircraft would be pretty much 
invisible, but the engine and especially the propellor make good radar 
reflectors.

This gives us the working definition of 'stealth':  being invisible to the 
other side's detection methods.  A very simple method in very wide use 
everywhere is just to camoflage the aircraft:  use a black airplane at 
night, a sky-blue one during the day, etc.  But I first think of 'stealth' 
as being invisible to radar.  What happens is that in radar the transmitted 
pulse hits a highly conductive surface (the metal skin of the aircraft) and 
this radio pulse is reflected back to the radar site.  The more conductive 
the surface, the better the reflection  But remember that to get reflection 
to the original radar site, the surface has to be 'normal' (perpendicular) 
to the radar site, just like a mirror.  OK, this suggests two ways to make 
a plane (or missile, or satellite) radar 'invisible':  reduce the 
electrical conductivity of the aircraft skin or/and make the aircraft have 
lots of wierd shapes so that the aircraft skin is never exactly 
perpendicular to the radar site, so anything that does get reflected does 
not bounce back to the originating radar.  Both of these are just what are 
done on the U.S. 'stealth' fighter, the F-117, and the 'stealth' bomber, 
the B-2:  the aircraft skins are of carbon-fiber epoxy (low conductivity) 
and the planes have lots of strange angles or curves.  I've seen the F-117 
from ~20 feet; there are almost no 'flat' surfaces or sharp angles.  You 
can imagine the work that went into trying to make these aircraft surfaces 
'non-radar-reflective' as they pass by a radar site.  One last point:  you 
can never achieve perfect stealth, you can just get close.  And remember 
that there are the other detection methods besides radar, such as tracking 
the heat of the aircraft engine.  That method's been in use since the 
1950's, e.g. the Sidewinder antiaircraft missile.

So we can see a good way to do an experiment/demonstration, and a laser 
beam is a perfect tool.  I'd try first off using one 'black' object and one 
shiny one and see the intensity of the reflected light (=radar here).  One 
catch is that you'll need to have the observer looking straight down the 
laser beam's path to simulate radar, and remember that YOU'LL NEED EYE 
PROTECTION FROM THE LASER AT ALL TIMES but especially when you use a shiny 
object.  And of course you can use a range of surfaces ranging from black 
to dull to shiny and note the intensity of the reflection.

A second demo would be just to use a mirror to show that even when the 
laser light is reflected, it can only go back to the transmitting site when 
the reflecting surface is normal to the beam.  Another trick would be to 
get a 'corner reflector' from Edmund Scientific and thus show that the 
right combination of angles can reflect the laser beam back to the source 
even though there's no surface 'normal' to the beam here.

Last, you'll be able to see that when you shine a laser beam on your 
simulated airplane the laser beam is reflected *somewhere* even though not 
directly to the transmitting laser site.  So if you wanted, you could set 
up an array of directional receivers and through some awful math detect and 
track the simulated aircraft you thought was invisible.  This demonstrates 
the importance of using a non-radar-reflective skin on the aircraft.