mm wrote:
"Eric Greenwell" wrote in message

Are airliners more likely to be coming at you from below or above? I
decided it was a toss-up, so I put my antenna on the bottom to improve
the return for ground radar (that's on an all carbon fiber glider - on
your fiberglass gliders, it might not make a significant difference).
This will aid ATC in keeping non-TCAS equipped aircraft away from me, I
hope.

Modern airliners climb out much more steeply than they descend, so you are
more likely to see an airliner coming at you from above. (unless you are
within class B/C airspace)

Actually thinking about this leads me to change my mind: unless an
airport is accumulating airliners, there are just as many leaving it as
arriving at it, so, on average, the glider will encounter just as many
above as below. Based on mm's observation, the glider will encounter
"down-going" airliners further from the airport than the "up-going".

Maybe a pilot should do a survey of other pilots in the area he will be
flying in before picking an antenna location (just joking). I suspect
antenna position is irrelevant for alerting TCAS equipped aircraft, as
they will very close (a few miles) when it is needed, so a strong signal
isn't needed. Metal airplanes put them on the bottom, and I haven't
heard of any concerns about putting them there.

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Eric Greenwell
Washington State
USA