Maybe this wil help - I am looking at the feasibilty of a lower, slower version of that used by C-47s
http://en.wikipedia.org/wiki/Fulton_surface-to-air_recovery_system
I'm doing background research on a real application. At high altitudes (and/or when people are shooting at you) helicopters can't stop and hover, but could snag a survivor or critically injured litter patient at around 30 knots (15 meters per second) A similar device (Fulton Recovery system)...