U.K. near-midairs

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