Because a heavier person flying the same size canopy has a higher wing loading, resulting in faster movement.
Wing loading is referring to the ratio of sq ft of fabric to weight of the jumper+ weight of the rig(parachute) being used. So I'm about 150 lb, plus 30 lb of gear = 180 lb. I jump a 210 canopy; a canopy with 210 sq ft of fabric. So, 180/210 = .85, so my wing load is .85:1.
Now my friend Brad, who also jumps a 210, weighs closer to 170, putting his wing load at .95:1.
Because of the higher wing load, he's going to fly faster than I do. Assuming that the winds are about 10 mph, both flying upwind, he's going to be going near 10 mph, whereas I will be closer to 8 to 9 mph. Because the wind has more effect when the wing loading is lower, like mine. Even on no wind days, at full flight, he's going to be going near 20 mph, where I will be at 17-18 mph.
Wing loading is referring to the ratio of sq ft of fabric to weight of the jumper+ weight of the rig(parachute) being used. So I'm about 150 lb, plus 30 lb of gear = 180 lb. I jump a 210 canopy; a canopy with 210 sq ft of fabric. So, 180/210 = .85, so my wing load is .85:1.
Now my friend Brad, who also jumps a 210, weighs closer to 170, putting his wing load at .95:1.
Because of the higher wing load, he's going to fly faster than I do. Assuming that the winds are about 10 mph, both flying upwind, he's going to be going near 10 mph, whereas I will be closer to 8 to 9 mph. Because the wind has more effect when the wing loading is lower, like mine. Even on no wind days, at full flight, he's going to be going near 20 mph, where I will be at 17-18 mph.
