How I Got to 7000 Feet

Getting to 7000 feet with a device that I can carry on my back may seem unlikely, but a paraglider is a real aircraft capable of going up.

I start of by laying my paraglider out into a horseshoe configuration with the openings of the leading edge exposed. I then pull the wing toward me, inflating it as it rises. My paraglider is referred to as a ram-air canopy, which means that air is forced inside through openings in the leading edge by the forward motion. A standard parachute is also a ram-air canopy.

With a little headwind I am off. As I fly the shape of the resulting pressure maintains the airfoil. The airfoil is very similar to those on airplanes. It lifts me because the top surface is curved and the bottom surface is straight. Because the upper surface is curved, air must move farther in order pass over the wing than the air under the wing needs to travel. As a result, the air pressure is greater under the wing than above it. This creates the lift I need to fly.

I am suspended by four rows of Kevlar lines. I have two handles, referred to as the brakes or toggles that pull the trailing edge down, slowing the wing. If I pull one brake, I will turn. I can also turn by shifting my weight sideways, which banks the wing. If I pull both brakes, I will slow down. If I pull the brakes too far, I will stall the wing. A stall occurs when the wing flies too slowly or the front of the wing is tilted too high. Air no longer flows smoothly over the wing, but becomes turbulent, and the pressure differential is lost. Altitude is quickly lost, and the pilot must allow the wing to speed up to recover.

Having a wing above me and forward motion is not enough to take me up. I need some help from nature, in the form of a thermal. Thermals are nature’s way of releasing heat from the earth. The sun does little to heat the atmosphere directly; most of the heat transferred to the air comes from the ground. Air is constantly moving up and down when the air heated by the ground is hotter than surrounding air. (Pagen, 1992)

But, this depends on the weather conditions. The air must also be cooler as altitude increases. The amount that the air cools is called the lapse rate. On an overcast day, when the ground is as cool as the air above, there is little thermal activity. In the high desert, where the ground in hot and the air above is cool, the resulting lapse rate results in powerful thermals.

Thermals don’t always rise in steady columns. They can also be intermittent in the form of bubbles or plumes. In humid air they are marked by cumuli, the puffy clouds that form when moist air is carried aloft and condenses. Thermals also rotate due to a force called Coriolis Effect, which is the deflection caused by the rotation of the Earth. Water circling a drain is an example of Coriolis Effect. Furthermore, the air in the center of the thermal rises faster than at the edge. At the very edge, rising air meets sinking air. When all these forces act together, it makes for a wild ride to the top of the thermal.

Negotiating thermals with a paraglider is a tricky business. A paraglider may collapse if air is not continuously forced into the openings. If not corrected, the paraglider may spin. A spin occurs when one wing stops flying and the other wing flies in a circle due to the drag of the stalled side. If a collapse occurs, first maintain a straight course using the brake on the opposite side, then pump the brake on the collapsed side, and voila, the collapse is cleared.

A paraglider appears to be a simple flying device, but much goes into the design and manufacture of one. It is tricky to fly, and understanding their physics is essential to being safe.