An overview of how different design traits of wings make certain wings better tools for different jobs, such as racing down a mountain or using thermals to travel great distances.
Many thanks to Torsten Siegel from Gin Gliders, Luc Armant from Ozone Gliders, Kevin Hintze from Fluid Wings, Blake Pelton from Super Fly and Francois Bon from Level Wings for their input and help with this article. These are some of the greatest minds in the freeflight world, and it was an extreme privilege to have their input and feedback on this article.
Paragliding is a great way to stay up in the sky. No motor, with the ability to land right back where you started from, maybe even travel a few or a few hundred miles in a day. Grab rising air and stay up. Speed flying is more about getting down a mountain in an exciting way.
Is it possible to stay up in the air with something billed as a speed wing? What about a long sled ride on a so-called paraglider that involves some wingovers and kicking a bush or two on the way down? Like any problem, there are some specialized tools to solve them.
Let’s take a look at the differences in the anatomy of a wing that make them better for racing down the mountain or flying for hours above them. Looking at a dedicated speed wing or paraglider side by side on launch can reveal a lot of obvious differences. These are some of the most easily noticed differences that people can see while watching their friends kite or when they pull a new glider out of the bag. There are many differences that even a seasoned pilot cannot see right off the bat, and those are best left for the designers to know about.
Plan View: When viewed flat on the ground
Size is one major factor differentiating speed wings from paragliders, but it isn’t everything. Size can also be thought of as how much the wing is loaded (weight divided by surface area of wing). For the best chance to stay up, a big person would choose a big wing. To get down the mountain in a hurry, a big person would choose a smaller wing or a small person would choose a really small wing. The differences start to get fuzzy in the 15-18m2 range. The Ozone Litespeed and Gin Yak both come in a 15m2 but fly very differently.
A good start to differentiate paragliding from speed flying could be to assign a number to wing loading. But, if a pilot at the top end of the wing loading range ate a big breakfast and went over that wing loading range, it would be silly to say she is going speed flying. Wing loading, or lack thereof, is just one factor in how a pilot might choose to stay up for a while or race down the mountain. Interestingly enough, weight does not change glide ratio. Instead, glide ratio is determined largely by the shape of the wing. Different weights under the same wing (different wing loading) changes forward speed and sink rate proportionally. What shapes lend themselves to getting down a mountain in an exciting way or staying up and flying far?
Aspect ratio: Aspect Ratio (AR) is the ratio of the wingspan to surface area. Aspect Ratio for a rectangular wing is equal to wingspan (measurement from wingtip to wingtip) divided by chord (measurement from front to back). A non-rectangular wing such as a hang glider, jet fighter, or paraglider is truly described as the span squared divided by surface area, but the same concept of the same surface area being distributed over a large wingspan or small wingspan still applies.
Rectangles: AR=s/c Everything else: AR=s2/a
A high aspect ratio means that the wingspan is large and the chord is smaller, with the wingtips far away from the center. A low aspect ratio means that the wings generally look short and fat, with more of the wing surface area closer to the center. Wings can have the same exact surface area but greatly different aspect ratios. A 25m2 Advance Epsilon (Low B wing) has a flat AR of 5.15 and a span of 11.35m and a 25.6m2 Gin Boomerang 11 (One of the fastest XC Competition wings) has a flat AR of 7.9 and a span of 14.2m. To generalize the difference in performance, high aspect ratio wings glide well but do not maneuver very quickly, and low aspect ratio wings can maneuver quicker but do not glide as well. The XC pilots who fly for 8 hours at a time and set distance records typically launch a long, skinny wing. The Gin Boomerang and Ozone Enzo series are the extreme examples of these very high aspect ratio wings.
The way a wing tapers is also important and easily noticeable. Taper is how the wing has a larger chord (front to back measurement) in the middle and smaller chord towards the tips. More taper allows for more efficient glide, as wingtip vortices and therefore induced drag are minimized. Tapering a wing also reduces the amount of material way out at the tips. A high taper wing will stall at the tips first, helpful for letting a pilot know when to ease off the brakes before the stall grows towards the center. A lower taper wing will have more drag and be more ground hungry, but the flare can be much more authoritative. A wing looking to cover some distance will likely be more tapered than a wing designed to hug the ground.
Getting down the mountain in a hurry while diving near terrain lends itself to wanting a lower aspect ratio. Observing aspect ratio and wingloading alone can create some confusion when looking at an A-rated paraglider such as the Nova Susi (Flat AR 3.95) and the popular speedwing Ozone Rapi-Dos (Flat AR 3.86). If an 80kg beginner pilot is happy flying the XXS Nova Susi, would it stand to reason that their 50kg teenager would enjoy many of the same flight characteristics if they hooked into a ready made 15m2 Rapi-Dos? Probably not, as the airfoil profiles are very different, among many other traits.
Profile: Cross section when viewed from the side
The profile of the wing is one of the most important parts of how a glider performs. This is essentially the shape of the center cell when viewed from the side. Some gliders are very obviously thicker than others (tall leading edge). Increased thickness will require more air for inflation and more air to be pushed aside as the wing flies, meaning it is slower to inflate and slower to move forward. A thin wing needs less air to fill it and can slice through the surrounding air as it flies, so it can inflate and fly faster.
Thickness: Stall and slow flight performance is affected by thickness. A thick glider has friendly stall recovery characteristics, while a thin glider treats the pilot fairly mean upon stall recovery. A thicker profile is often found on more beginner-oriented wings, and a thinner profile is more prevalent on a wing where the pilot knows more about how to avoid stalls or purposefully induce them. Getting down the mountain in a hurry and efficiently gliding in ridge lift or from thermal to thermal can benefit from a thinner profile. Interestingly enough, wings made for skiing such as the Neo X Ride are made to fly very very fast but have a fairly thick profile. This helps for slow-speed flying while the pilot skis on the ground.
Camber: The most important part of how a wing flies is how it is curved from front to back. Differences from one glider to the next generally are not noticeable while kiting or laying out on launch. This curve is called camber. Differences in where the camber is, how much it is cambered, and how camber changes from the center out to the wingtips are critical in how a wing flies. Camber also changes as a pilot makes brake and speedbar inputs. When a wing works well, competitors will buy that wing just to take it apart and study the camber and how it changes from the center out towards the wingtips. Differences of a few millimeters in amount and location of camber can make a wing a winner or loser.
Cells and Openings
How air enters and pressurizes a wing is largely dictated by the number of cells and the openings. More cells creates a smoother wing surface, which allows for smoother air flow from the center to the tips along the top and bottom surface. This means less drag and better glide. More cells also means more ribbing. This increases weight and the amount of walls the air has to pass through during inflation and comes into play on launch. Somebody looking for a fast descent and launching at the top of a mountain in little to no wind would value a tool that can inflate quickly, with fewer cells aiding this. Somebody launching in some wind and kiting for a bit before leaving the ground could handle a slower inflation, or even desire it in high wind.
Opening size is largely dictated by the thickness of the wing and intended range of angles of attack. The latter is not something that can easily be seen. Some cells don’t have openings in the front. Where these cells are closed off relative to the wingtips is easily visible and can lend some clues to how a glider might perform. A closed off front is more aerodynamic; the air can easily split around a surface rather than flow into an opening. Closing off the front also prevents pressure from being lost out the front, as the air in the closed cell must flow sideways into an open cell to exit the glider. In the event of a deflation where a wingtip gets stuck in some lines, the ability to exhaust air through the front is critical to recovery. If the lines snag around a very closed off wingtip, the air within the closed off cells near the tip will be trapped like a balloon and the tip can remain stuck for a long time. A wing used by somebody who values efficiency and can diligently prevent deflation might have more cells closed off near the wingtips. A wing used by somebody who would rather sacrifice aerodynamic efficiency for quick recovery from deflations will have fewer cells closed off near the wingtips. Some wings have triangular or elliptical shaped openings, which are more to create a signature look than to affect performance.
Lines and Arc
Fundamentally, all freeflight methods are a pendulum. The center of gravity is suspended from something—be it a paraglider, hang glider, or speed wing. The lines that suspend the pilot under the wing are an important part of how a wing flies.
Line Length Proportion: Line length is very easily noticeable as soon as a new wing is pulled out of the bag, as well as diameter and number. Some wings of a similar size have relatively long or short linesets. Small wings tend to have shorter lines, and big wings tend to have longer lines. But the important thing is proportion. In general, to get the line tension and angle correct, a higher aspect ratio wing will have a longer lineset than a lower aspect ratio wing. A long lineset acts like a long rope-swing. Changes in direction take a longer time to happen, and the opposite is true with a relatively shorter lineset.
Arc: Something that is also noticeable is how much arc the wing has. On a basic level, this is how high off the ground the center of the wing is compared to the wingtips. A high-aspect ratio wing with already long lines is not particularly prone to turning, and an increased amount of arc helps to make a wing maneuver more readily, making a nice balance. On the other end of the spectrum, a low aspect ratio wing with short lines is very maneuverable, and less arc is incorporated to the design to prevent it from being too maneuverable. A tool made for diving in and out of canyons and close to terrain might work better if it incorporates features that lend themselves to turning and coming back to level quickly. Or, comparatively long lines might help hold a long lazy turn in the core of a thermal or ridge lift band.
Lines: The lines themselves are important as well. Drag caused by lines is a huge factor in speed and glide efficiency. The thinnest, least amount of lines possible helps to achieve staying high for a while as well as getting down the mountain in a hurry. However, thin (unsheathed) lines wear out and tangle more easily and require more diligence from the pilot. Fewer lines reduce drag but allow the wing to be more susceptible to larger deflations. More pilot care is required to prevent or recover from a large deflation. Almost all slow beginner wings have a high number of thick lines. Small speed wings and hot XC racing wings both have very skinny and comparatively few lines.
These are some of the obvious traits that an interested pilot might observe right off the bat while laying their glider out next to their friend’s. Most generally, a purpose built speedwing will be smaller and have a lower aspect ratio compared to a soaring wing. Stacking a few traits up that lend themselves to flying high and going far or getting down a mountain in a hurry will certainly steer the recipe in that direction, but does not at all make it something enjoyable to fly. Most of the real magic in what makes a wing fly the way it does is stuff that can’t be seen. Camber, trim, subtleties in arc, location of line attachments, and wash of the wing are just a few of the factors that can drastically separate one wing from another. It is even possible for a designer to make a wing look like it will perform one way, but by tuning the subtleties the right way, it can perform completely different. The balance that designers are capable of achieving is incredible. There’s a wing on the market that can solve every problem a pilot wants to solve.