The other day I saw a video of a person who was wingsuit flying and I wanted to know some of the physics behind it. First, we can look at how a skydiver who is dropping vertically. When he falls toward the earth, he accelerates and his velocity increases. However, he will eventually reach a point where he is no longer accelerating and reaches his terminal speed. This is due to the fact that at this point his drag force is equal to his force of gravity. Up until this point, his force of gravity was greater than his drag force causing him to accelerate. Since Fg = Fd, and Fd is equal to ½Cd⍴airAv2 where Cd is the drag coefficient ⍴air is the density of air A is the cross sectional area and v is velocity, we can solve for the terminal velocity.
½Cd⍴airAv2 = mg
v = √(2mg/(Cd½⍴airA))
When skydiving, as well as wingsuit flying, a person is able to manipulate their terminal speed by changing their cross sectional area. One can go faster by pointing their head straight down and their legs up so that their area is as small as it can be. If they lay perpendicular to the drag force, their area will be maximized and their terminal velocity will be slower. In the case of wingsuit flying however, the design of a wingsuit allows for the velocity in the direction of the force of gravity to be converted to horizontal velocity. Lift force also affects wingsuit flight which helps them fly horizontally. Glide ratio is determined based on the relationship between lift, drag, and weight, or force of gravity. Most wingsuits have a glide ratio of 2.5:1 which means that they are able to move horizontally 2.5 m for every 1 m dropped vertically. Overall, lift is the main force that affects the horizontal flight which normal skydivers cannot achieve.