"Ralph Jones" wrote in message
...
On 26 Nov 2004 01:37:03 GMT, Nyal Williams
wrote:
[snip]

Boating stores sell radar reflectors made of cardboard
and covered with aluminum foil. They are in three
parts and can be disassembled. When put together they
make a sphere about 12-14 inches across and they provide
the 3D right triangles that are supposed to reflect
a signal back.

I inquired about their use in gliders (practically
no weight and could go in fuselage behind wing) and
someone told me they would not give a strong enough
signal for aircraft use owing to the speeds involved.
I have no idea about the validity of this statement.
Couldn't hurt to try it.

That is a corner reflector: three flat, mutually perpendicular
surfaces. It has the special geometric property that a signal striking
it from any direction will reflect from surface to surface and wind up
going back exactly the way it came. On radar, it looks much larger
than an irregular-shaped object the same size.

Apollo crews left at least one optical corner reflector on the moon,
and astronomers can bounce laser light off it to make precision
orbital measurements.

Signal strength is not the problem: a fiberglass ship with a one-foot
corner reflector inside it will look bigger than a metal sailplane.
The bad news: air traffic control radars are "moving target" systems,
which means they filter out returns that don't have any Doppler shift
to indicate a moving object. I don't know what the minimum detectable
speed is, but if you're under it, they just won't see you.

rj

I dunno how slow the moving target filter is.

I was working Holoman AFB approach inbound for ALM when they called out a
"large, slow moving target at 12 O'clock, five miles". I looked and saw
nothing in the severe clear. "How large?", I asked. "Really big, sir", came
the reply.

Now the Tularosa Basin is known for its UFO sightings. Maybe I'm going to
see one. I'm thinking a Klingon Bird of Prey with the cloaking device on
'cause I can see all the way to Mexico in the 12 O'clock direction.

Finally, I noticed a line of 18 wheelers northbound on Route 54. "Approach,
does your radar see trucks?" I asked. "Sometimes, sir", came the reply.
Oh, well. Maybe they should require trucks to have transponders.

Bill Daniels