"Soon they decided to try the bucket drop, a technique Dad had developed to deliver and retrieve items from missionaries who had no airstrip. He circled his plane overhead in tight circles while a long cord with the goods attached was reeled out behind the plane. Air friction on the basket at the end of the line would make the cord cut to the inside of the circle flown by the airplane, while the weight of the basket caused the cord to fall. When enough line was extended behind the plane, the end of the line would actually hang motionless in the air. Letting out more line at that point would make the line drop straight down where it could be made to hover just above the ground."
I have never before heard of this technique. Sounds like it would take a lot of experience to make it work. Very cool.
The documentary "Beyond the Gates of Splendor" http://www.imdb.com/title/tt0337868/ is quite good. You can stream it from Netflix. Although I'm not religious, I must admit it demonstrates the value of the Christian ideal of forgiveness. The movie has lots of old footage, including his father's inventive method of delivering supplies from his airplane to the natives via a tethered bucket
Yes, this story is amazing. He came to speak at my university with some of the members of the tribe, one of whom was in LOVE with flying. He couldn't speak English, read, etc. but he was apparently a pretty good pilot. By the way, this same guy was one of those in the group that killed his father. Amazing stuff.