The arc of happiness
Bastienne Wentzel
We talk about arc in the design of a paraglider, but what does that actually mean?
The release of some recent high EN-B gliders re-sparked the discussion about 'high arc'. High arc gliders are more curved when looking head-on, instead of the earlier, flatter designs. But high arc is not a number in the specs of a glider. There is not even a definition that designers agree upon, let alone we would be able to calculate high arc. The arc of a canopy does however have an influence on the flying properties of the glider and it's related to the airfoil shape, span and aspect ratio as well. We talked to some designers to find out more.
Natural curves
Being flexible, a paraglider can not be a flat wing when we are suspended underneath. A paraglider canopy is not flat when it flies - it naturally arches. This is what we call the arc of a paraglider. Lots of design parameters depend on this and vice versa: arc is among others related to aspect ratio, span and area of the canopy.
Aspect ratio (AR) tells us how slim the wing is. It is the ratio between the span and the chord. To calculate it you need the flat area of the wing (see the sidebar).
But because a paraglider canopy is arched in flight, the area of the wing that interacts with the air and generates lift and drag is not the flat area. One can argue that the 'projected' AR and span are more realistic values to use when talking about glider properties. Often the projected area is taken as the area of the 'shadow' the wing casts on the ground. If you use the projected area and projected span to calculate aspect ratio you get the projected aspect ratio.
The projected AR is often used as an indication of the performance of the glider, explains Bruce Goldsmith of BGD. "Higher projected AR gives you more performance. It also gives you the projected span which tells you how much inertia there is in the glider." The latter has an influence on yaw and roll of the glider.
But these numbers need to be treated with care when using them to draw conclusions about the performance of gliders. There are lots of other ways to calculate projected AR and the value itself is 'pretty useless' according to Bruce Goldsmith of BGD. "Projected AR depends on the degree of taper (the shape of the wingtips) and the degree of arc. Therefore you can't make any decisions based on projected AR alone."
(...)
This feature was published in Cross Country magazine 258, July 2025.
Natural curves
Being flexible, a paraglider can not be a flat wing when we are suspended underneath. A paraglider canopy is not flat when it flies - it naturally arches. This is what we call the arc of a paraglider. Lots of design parameters depend on this and vice versa: arc is among others related to aspect ratio, span and area of the canopy.
Aspect ratio (AR) tells us how slim the wing is. It is the ratio between the span and the chord. To calculate it you need the flat area of the wing (see the sidebar).
But because a paraglider canopy is arched in flight, the area of the wing that interacts with the air and generates lift and drag is not the flat area. One can argue that the 'projected' AR and span are more realistic values to use when talking about glider properties. Often the projected area is taken as the area of the 'shadow' the wing casts on the ground. If you use the projected area and projected span to calculate aspect ratio you get the projected aspect ratio.
The projected AR is often used as an indication of the performance of the glider, explains Bruce Goldsmith of BGD. "Higher projected AR gives you more performance. It also gives you the projected span which tells you how much inertia there is in the glider." The latter has an influence on yaw and roll of the glider.
But these numbers need to be treated with care when using them to draw conclusions about the performance of gliders. There are lots of other ways to calculate projected AR and the value itself is 'pretty useless' according to Bruce Goldsmith of BGD. "Projected AR depends on the degree of taper (the shape of the wingtips) and the degree of arc. Therefore you can't make any decisions based on projected AR alone."
(...)
This feature was published in Cross Country magazine 258, July 2025.