In rec.aviation.soaring WingFlaps wrote:
On Apr 29, 5:51?am, Larry Dighera wrote:

I would guess the controller would need to adjust his scope from it's
usual setting to see primary targets, so a radio call may be
necessary. ?While a corner reflector would doubtless increase the
radar energy returned to the radar antenna and provide a brighter
primary target, I doubt that would be sufficient to cause the glider
so equipped to become visible on ATC's scopes without reconfiguring
them to display slow-moving primary targets.

How slow does a target need to be to be undisplayed -typically? I
would have thought that even a glider is fast (45 knots) compared to
usual clutter.

A cruising glider is likely to be faster than that. However, gliders
climbing in a thermal are making tight little circles, and I believe this
will look like a stationary target to the radar. Worse, a glider climbing
in wave really will *be* stationary, as the glider will try not to move by
matching airspeed to wind speed at altitude. I have heard stories of
unintelligent GPS units deciding the airplane was parked and shutting
themselves off in this situation.

--
Michael Ash
Rogue Amoeba Software