Published: May 15, 2017
Terminal Velocity of a Skydiver
Ah, science! You probably learned about this stuff in high school, but you never learned it like this.
Remember 'terminal velocity' from physics? Your high-school self might have dropped a ball bearing into oil, taken some readings and scratched down an equation or two. You'd have learned (yawningly) that the terminal velocity of a falling body occurs when the force exerted on it by gravity is exactly balanced by the force exerted on it by resistance, such that the body experiences zero acceleration. Well--that's a ball in oil. This is skydiving.
What is the Terminal Velocity of a Skydiver?
The downward speed achievable by the human form in freefall is a function of several factors--including the body's mass, orientation, skin area and surface texture--but the usual math standardizes all that. For a human-shaped object, the equation spits out a terminal velocity of 60 meters per second--about the terminal velocity of the typical skydiver, which clocks in at of 55 meters per second.
It ain't that simple, though, as you might imagine.
Skydiving doesn't just revolve around tandem jumping. It doesn't even revolve around the type of skydiving--called Relative Work, or "RW"--that involves falling with your belly pointing toward the Earth, as the above equation assumes. Since different skydives result in different air resistance, they end up resulting in what can be very different terminal velocities. For instance: In a stable, belly-to-earth position, a jumper's terminal velocity hangs out at a zippy 120 mph. Change that body position to head-down--which looks exactly like it sounds--and you've just ramped up that terminal velocity to around 150-180 mph (which is fast enough to result in damage to both parachute and skydiver if that skydiver doesn't do him/herself a favor and slow the heck down by changing position and waiting before pulling). There are ways to minimize that drag even further by streamlining the body, which allows for speeds in the vicinity of, ya know, 300 mph.
Here are a couple examples of skydiving disciplines on the opposite ends of terminal velocity. These will do much to show-and-tell about how this can be the case.
Terminal Velocity in Speed Skydiving
Speed skydiving is a skydiving discipline that has supported competition divisions since the mid-2000s. It's a big enough deal that it has its own association--the International Speed Skydiving Association, naturally--which sets the goal to "achieve and maintain the highest possible terminal velocity." Speed skydiving has the distinction of being the fastest non-motorized sport on Earth.
The tricks of the speed skydiving trade have been developed to cheat nature as much as possible. Obviously, the skydiver cannot increase his or her mass enough to significantly increase his or her terminal velocity. Additionally, the skydiver can't change his or her shape much beyond the use of an aerodynamic helmet, and shoulders notoriously get in the way. In fact, the primary tool in a speed skydiver's kit is the reduction of friction--that "surface texture" point in paragraph number two. To that end, competitive speed skydivers often prefer to wear slick bodysuits and skillfully maintain a strictly streamlined head-down body position to minimize the coefficient of drag. They have to do all of that lickety-split after exit, too, in order to hit that maximum speed high enough up that the air is extra-thin. It's a challenging discipline, and well worth checking out!
Terminal Velocity in Wingsuit Flying
Wingsuit flying aims to translate as much of the downward speed of a skydive into forward speed. Terminal velocity drops precipitously so that the throttle forward can roll way the heck back.
To that end, wingsuit pilots (as indeed, pilots they very much are) integrate ram-air airfoils into their suits, which pressurize in much the same way as a parachute and fly using many of the same dynamics as an airplane. While some of these designs have three distinct ram-air wings (which connect the arms to the torso and the legs together) and some are mono-wing (which turns the whole suit into one large wing with a human kinda floating around in the middle somewhere), the overview of the design is the same: A wingsuit combines various materials in order to construct an airfoil around the frame of the human body, converting downward speed to forward.
As the discipline of wingsuit flying has advanced, the results have been nothing short of incredible. One recorded instance shows a vertical instantaneous velocity of a scant 25 mph--100 miles an hour less than the textbook 125 miles per hour we're all so familiar with. However, the speed at which the wingsuit pilot pierces forward through the sky zooms over 100 km/h in some instances, so this doesn't really qualify in anyone's book as slow...just not so downward.
Interested in feeling what 120 miles per hour of terminal velocity feels like? Hop down to the San Jose Skydiving Center, and we'll be happy to show you!
I highly recommend them.
» Ken K.