Tying cargo nets, 4x4 Timbers, or anything to act as “Spoilers” is a necessity. Use a long line to keep the load (airplane) well beneath the helicopter is the preferred method. Adding a drag chute incorporating a swivel also helps stabilize the load.
SLOW is good.....if the load begins to fly....release it and head home for Tea.
I had the unpleasant task of retrieving the bodies of five CHinook Crewmembers who had an O-1Bird Dog airplane fly up under the nose of the Chinook then back and up into the Aft Rotor System.
They were going way too fast and the underslung airplane departed from a stable ride too quickly for the Crew to respond.