FreeFly Paragliding - Wing Technology

Aerodynamics: Both paragliders and hang gliders are essentially wings, aerofoils. An aerofoil is a structure designed and produced to create lift when moving in air - note the tear-shape design in the diagram to the right - this is typical of all aircraft wings. Of course, it was Mother Nature's design originally! Because the upper surface is more curved than the lower surface the air passing over the top of the wing has to travel further to get to the trailing edge (back) than air travelling under the wing. This causes the air travelling over the top of the wing to speed up and according to a key law of physics (Bernoulli’s Theorem) this causes a reduction in air pressure above the wing - so the wing effectively gets sucked up into the area of lower pressure above, away from the area of higher pressure below. This is lift.

As the glider and pilot move through the air, they collide with air molecules. The frictional force caused by these collisions is known as drag, which slows the glider down. The amount of drag is proportional to the airspeed of the glider: The faster the glider moves the more drag it creates.

To launch, the paraglider or hang glider the pilot must run down a slope to simulate wind and get air moving over the surface of the wing and therefore generate lift, the force that counters gravity and keeps the glider aloft. Once aloft, gravity (the weight of the hang glider and pilot) pulls the glider back toward Earth and propels the glider forward, continually causing air to flow over the wing, facilitating a glide through the air.

Paraglider Wing Technology

The paraglider wing is known in aeronautical engineering as a ram-air airfoil, or parafoil. Such wings comprise two layers of fabric which are connected by internal supporting material in such a way as to form a row of cells. By leaving most of the cells open only at the leading edge, incoming air (ram-air pressure) keeps the wing inflated, thus maintaining its shape. When inflated, the wing's cross-section has the typical teardrop aerofoil shape (as outlined above). Pilots control the aircraft by weight-shifting and pulling control lines that change the profile of the wing.

The pilot is supported underneath the wing by a network of lines, which are gathered into two sets as left and right risers, which are then connected to the pilot's harness by two karabiners. The pilot is comfortably buckled into a harness which offers support in both the standing and sitting positions. A reserve parachute is also typically connected to a paragliding harness.

Paraglider wings typically have an area of 20-35 m2 with a span of 8–12 m, and weigh 3–7 kg. The glide ratio of paragliders ranges from 8:1 for recreational wings, to about 11:1 for modern competition models. For comparison, a typical skydiving parachute will achieve about 3:1 glide. A hang glider will achieve about 15:1 glide. Some sailplanes can achieve a glide ratio of up to 72:1.

The speed range of paragliders is typically 20–60 km/h (12-34 mph), from stall speed to maximum speed. Beginner wings will be in the lower part of this range, high-performance wings in the upper part of the range.

A key positive attribute of a paraglider is the ease of transport. The entire kit packs neatly into a backpack (weighing in the region of 8-18kg) that could be transported internationally as normal airline baggage and carried up to remote mountain launch sites.

Hang Glider Wing Technology

The hang glider is actually a triangle-shaped airfoil, a modified parachute (known as a flexible wing) made of nylon or Dacron fabric. The triangular shape is maintained by rigid aluminium or composite tubes and cables and is designed to allow air to flow over the surface to make the wing rise. Newer, high-performance hang-glider designs use a rigid wing with stiff aluminium or composite struts inside the fabric to give it shape, eliminating the need for supporting cables.

The pilot is suspended from the hang glider in a harness attached to the centre-of-mass of the glider, just behind the control bar, manoeuvring the hang glider by shifting his or her weight (changing the centre-of-mass) in the direction of the intended turn.

The pilot can also change the angle that the wing makes with the horizontal axis (angle of attack), which determines the airspeed and the glide ratio of the hang glider. If the pilot pulls back on the glider, tipping its nose down, the glider speeds up and vice versa.

With each generation of materials and with the improvements in aerodynamics, the performance of hang gliders has increased. Here are some performance figures as of 2006:

• Topless gliders (no kingpost): glide ratio ~17:1, speed range ~30 to >145 km/h

• Rigid wings: glide ratio ~20:1, speed range ~ 35 to > 130 km/h

Hang gliders are a little more work than paragliders to prepare for launch. The pilot must unpack the glider, assemble the control bar, unfold the crossbar, stretch the sail out, rig the various wires and insert the battens. As the kit is a lot bigger and heavier than a paraglider it is not easy to transport internationally or to carry up to launch sites where there is no access for vehicles. However, the faster speed and superior glide ratio of hang gliders are very attractive attributes.