Equipment: wing, gear, regulations

Inside the wing: what a paraglider is actually made of

A paraglider is a soft wing. Its shape is given to it by the oncoming airflow and by the air that inflates it from inside. All its virtues and all its limitations come from that.

The wing is sewn from two surfaces — the upper and the lower. Between them, sewn in vertically, are the ribs: fabric walls that divide the wing into cells and hold the profile. The profile is the shape of the wing in a section across the span. The line between the two furthest points of the profile is called the chord. Along the leading edge the ribs are cut away — that is how the cell openings are formed. The inflated central part of the wing is called the canopy.

Between the ribs, diagonal ribs are sewn in. They spread the load from one line across several ribs at once. That means fewer attachment points, fewer lines and less drag.

Not every cell has an opening of its own: some ribs are made closed. Air reaches such cells sideways, through cross-ports in the ribs. Pressure is equalised across the span, and in a collapse the air from the neighbouring cells helps the folded side to reopen.

• The wingtips (stabilos) are the outermost sections. They are what you fold in when you take big ears.
• Mini-ribs along the trailing edge stop the fabric from sagging, so the flow leaves the wing more cleanly.
• The label carries the model, size, serial number and weight range. Without it the wing will not pass an airworthiness check.

The geometry of a wing is described by its span and its area. From those you get the aspect ratio: the span squared divided by the area. Remember that term: later it will explain the difference between wing classes.

Profile and stiffeners: why modern wings are shaped the way they are

A profile has three dimensions that decide almost everything: the chord (the length from nose to tail), the thickness and the camber — how much more convex the upper surface is than the lower. A thick profile with plenty of camber holds on at low speed and forgives rough flying. A thin one flies faster but has less in reserve.

The key idea is the stagnation point. This is the place on the leading edge where the flow divides: some of the air goes over the wing, some under it. The pressure there is at its highest, and that is where you would like to put the opening. But the point does not stay put: on the speed system the angle of attack decreases and it moves up; with a little brake it moves down.

Designers used to choose a compromise. An opening lower down means good inflation at low speed, but the wing holds its pressure less well when accelerated. Higher up is the other way round. That is where the shark nose came from — the concave leading edge. The concave section narrows the range in which the stagnation point wanders: the opening keeps working both at low speed and on full speed system, and it can be made smaller.

Stiffeners hold the shape where the fabric cannot:

• Nylon rods in pockets along the leading edge. They keep the nose open and stop the edge crumpling at speed.
• Mylar — a film insert along the edge of the opening that sets the shape of the intake.
• Diagonals and tension straps inside the wing hold the ribs vertical under load.

The rods are the reason a wing is packed in a concertina: the ribs gather one against another and the stiffeners stay straight. A wing crushed into a ball breaks the rods, and a broken rod changes the shape of the nose — the wing inflates less well and takes a hit of turbulence less well at exactly that spot.

Lines, cascades and risers

Lines are braided from Dyneema, aramid (Kevlar, Technora) or polyester. The thin upper lines are often unsheathed — with no outer protective cover. They have less drag but are more sensitive to kinks and dirt.

The lines are gathered into cascades — tiers in which thin lines converge into thicker ones. Dozens of thin upper lines come together in twos and threes into the middle tier, and the middle tier into the thick lines of the lower one. The lower tier arrives at the risers: two webbing straps by which the wing is clipped to the harness. From front to back the lines are grouped into rows — A, B, C and sometimes D. The brake lines run separately, to the trailing edge.

Here is an exam trap. A paraglider has exactly two risers — left and right. A riser is the intermediate part between the harness and the lines. What does vary is the branching of each riser: it can be 2-, 3-, 4- or 5-row. Do not confuse the two: a “four-line wing” means two risers with four rows on each.

What is on the riser itself: maillons or soft links for the lines of each row; a split A row, from which a thin line runs to the wingtip — that is what you pull to take big ears; the speed-system pulleys and cords; a magnet for the brake handle and colour coding for the rows. If the A row is not split, big ears on that wing are taken differently — check the manual.

Line geometry is no small matter. Lines stretch and shrink unevenly: differently by row, by material and by hours flown. As soon as the lengths drift, the shape of the wing is spoilt and the angle of attack changes — the angle at which the wing meets the oncoming flow. That is why the regulations set tolerances. Deviation from the factory dimension — no more than 5 cm. The difference between parallel lines in the same row — no more than 0.5 cm. If the manufacturer gives different figures, the manufacturer’s apply.

Line rows: 2-, 3- and 4-line wings

The number of rows decides how the wing holds its shape, how it is controlled at speed and what happens in a collapse.

Line drag is a noticeable part of the total drag. So, all else being equal, a two-line wing glides further. The price is different mechanics.

Control at speed. On a three-line wing an accelerated wing is steered with the C row — by the handles on the risers. A two-line wing has no C row at all, so B-row handles are fitted instead: you change the angle of attack with almost no deformation of the profile.

Brakes and speed system do not mix. A two-line wing holds its shape by fabric tension, and a kind of hinge appears between rows A and B. A brake input at large speed-system travel loads that hinge — and you get a collapse instead of a turn. The rule: at speed you work the B row, brakes released.

The scale of a collapse. On a two-liner more material folds: losing the A row is closer to losing A and B at once on a four-line wing. The reopening is sharper and it costs more height. And one more thing: two-line wings feel “solid” in the air and pass on less of the small chop. Pilots take that for calm air and fly into places they are not yet ready for.

Materials: canopy cloth and lines

Cloth. The canopy is sewn from ripstop polyamide. Ripstop means that a grid of reinforced threads is woven into the fabric: it stops a tear from spreading. On top, the fabric is coated — with polyurethane or silicone. It is the coating that makes the cloth airtight and protects the threads from ultraviolet.

Cloths are distinguished by the weight of a square metre. As a guide: around 27 grams per square metre is light cloth for wings you hike into the mountains with; 38–40 grams is dense cloth for training wings and for pilots who fly a lot. The lighter the cloth, the lighter the rucksack — and the shorter the life.

Sheathing. A line can be sheathed — with an outer protective cover — or unsheathed, with the load-bearing fibres working bare. The sheath protects the core from abrasion, sunlight and dirt, but it adds no strength: only thickness, and therefore drag. That is why the upper tiers are often unsheathed and the lower ones sheathed: those are handled more often and dragged along the ground.