The area of the sail is correlated to the weight of the pilot on the hang glider because the surface area of the sail needs to be able to lift ≤ (greater than or equal to) weight of the pilot.
The larger the surface area of the sail, the heavier the pilot can be and safely use the glider.
Explanation:
A hang glider must be able to support the weight of the pilot. The air pushing up under the sail (wing) of the glider helps support the weight. The more sail (wing) that you have, the more air pushing up, and the more weight it can hold.
