A 12 inch length is about right. This light, thin plastic will respond to the slightest change in wind direction and serve as your personal windsock. You don't have to turn around to see the club's windsock or take your eyes off your plane. Incidentally, if you don't have a blank or damaged tape to use, I recommend cutting up a rap or heavy metal music tape. As a glider guider, I try to be sensitive to the wind as one clue to finding thermals, so I am naturally surprised when I see a flier attempting a downwind take off.
Ground speed means nothing without air speed.
You really can' t fool Mother Nature. From HCRC Flier, Peter Ciosek, editor. I love defenseless animals, especially in a good gravy. During a cross country flight in my old Cub, I began looking for an airport where I could refuel. As my fuel condition worsened, I added gas stations with suitable landing areas to my search list.