The sail is a six-sided polygon. The top and bottom side are the same length. The top left and top right side are the same length, but about half the length of the bottom left and bottom right side. A heart-shaped or circular hole, about 3/4 the width of the bottom side is placed about 1/4 of the height of the sail from the bottom side. The heart shaped hole flies slightly better. The point of the heart should point at the bottom of the kite. The heart shaped hole can be slightly smaller than a circular hole.
The scotch sled has one, two or three spars which hold the sail open from top to bottom. The spars are parallel, running from the top left corner to the bottom left corner, and from the top right corner to the bottom right corner. Very large sleds add a third spar in the center. Very narrow sleds can have a diamond shape, with a single spar going from the top to the bottom.
The spars are best made from very light, flexible wood rods. Any other material will serve. Some sleds use inflatable pockets, with the scoops for the pockets being on the top edge of the sail. The tension of the sail must not pull the scoops closed.
The bridle string goes from the left and right corners of the sail to the main string. The bridle string is usually a loop, with the main string tied to it with a movable lark's head, so that the two sides of the bridle can be adjusted to be even.
The sail must be cut precisely so that the bridle's vertical positioning is good. Too high and the kite glides to the zenith directly overhead and collapses from lack of wind pressure. Too low, and the kite is unstable, turning in circles, and hitting the ground.
One of the most amusing quick-and-dirty kites is a scotch sled cut from a 33 gallon plastic garbage bag. The kite can be the same height as the bag. Use very sharp scissors to cut both sides at the same time, using the fold as the center of the kite. 3mm (1/8") wooden spars and a bridle about four times the height of the sail can be taped to the sail with good quality plastic office tape. The bridle attachments with tape are critical: tie the end of the bridle loop around a length of tape, and run the tape on the edge of the sail. If one simply tapes the string to the sail, the string will pull out from under the tape.
You might have to cut several sails to find the best vertical position for the bridle, and the desired size and shape of the hole. Garbage bags are cheap, so don't hestitate to experiment! Once you find one you like, measure it, and keep the measurement asyour kite recipe! Each flyer finds his own favorite recipe for stability and performance!
Lightweight, polyester (Dacron (TM)) kite string will perform best with the garbage-bag kite, but ordinary string works fine.
See also kite flying