David Dyer-Bennet wrote in :

I seem them hovering, or moving very slowly, quite frequently. No idea
what they're actually doing of course.


Are you aware of the height-velocity curve for helicopters? There
are altitude and speed combinations that you just want to avoid
if at all possible as in case of an engine failure, you don't have
the altitude and/or speed to effect a (relatively) safe landing.

http://en.wikipedia.org/wiki/Height-velocity_diagram

All the police helicopters I've ever seen fly fast low circles
around their point of interest. Probably around 500-1000 feet AGL.

News helis, OTOH, I've seen them hover fixed, but at thousands of
feet. But then, many have gyrostabilized long range telephoto cameras.

Brian
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