Because of this they have a very low angle of attack. Consequently they don't pull very hard at all. The sail forms a billow, and this, combined with a keel in place of a bridle, allows deltas to fly without a tail. The sled is similar to the parafoil in that it relies on the wind to hold it open. It has several spines running the length of the kite, but no cross-spars.
Sleds often have vents cut in the sail, near the bottom of the kite, instead of using a tail.
They pull very hard and fly with a high angle of attack. Safety rules about kite flying. Never fly a kite in a thunderstorm or while it is raining. The kite, or the flying line, might be hit by lightning. Never fly a kite with wire, or anything that could conduct electricity through the flying line to you, and don't use a wet flying line.