In the last 10 years there have been significant developments in hang glider wings. That may come as a surprise to KITPLANES® readers. After all, the wings don’t look much different from one another, so the changes must be subtle, right?
Well, yes and no. In fact, many subtle changes have occurred as these wings have steadily progressed from a glide angle of 4:1 in the 1970s to the 15:1 glides that are common today. Even as they gained efficiency, the wings haven’t changed a lot in appearance.
But not all of the changes are so subtle. The ATOS VX I flew in late 2004 illustrates a radically different approach to wing design. The ATOS VX can achieve a glide angle of 20:1 and a sink rate of only 118 fpm. The latter number makes this wing competitive with many sailplanes, even though the pilot hangs in the airstream.
An Innovative Design
The design is produced by Aeronautic Innovation Rühle (AIR) and is the creation of Felix Rühle, who worked with composite materials for many years in his role with the German government’s Center for Research and Development in Aerospace Technology in Stuttgart. This experience helped Rühle obtain precise calculations and provable experimental arrangements for the ATOS project.
It also gave him the confidence to abandon familiar aluminum tubing for an airframe structure built of 90% carbon fiber. Earlier versions of the ATOS (the C, V and VS models) employed an aluminum tube for the keel (the central fore-to-aft structure at the wingroot). With the VX model, that component is now also carbon fiber, and the material is also used on the leading edge D-cells and in the wingribs.
Some of these changes come because this large wing, the biggest of the series, is built for large pilots, two-place operations or for use on lightweight trikes. Hang glider wings have long been vehicle-tested to load the wings in a dynamic situation thought to be more effective than upside-down static loading of wings, and the ATOS has survived testing to 2000 pounds. The German DHV (the German Hang Gliding and Paragliding Federation, a government-sanctioned private organization) performs testing of hang glider wings and awards certification—actually a Gütesiegal, which means Seal of Approval—to those wings that pass these challenging tests. A powerful vehicle with a tall structure built on top of it positions the wing in clean air (see photo). Inside the van, computers record the results of wing testing such as load limits and pitch stabilityat various angles of attack.
Like the wing D-cells and internal ribs, the ATOS tail is also built of carbon fiber with a fiberglass exterior finish that is then painted white. It weighs a mere 2 pounds. Most hang gliders use no tail and, indeed, the ATOS can be flown without one. But the fixed ATOS tail is set for a positive angle of attack. This has the advantage of producing some additional lift (unlike most horizontal tail surfaces), while increasing pitch damping. The result is a glider that has improved handling as well as a reduced stall speed.
The moderated pitch response makes the wing more pleasant to fly and expands the flying envelope of the glider. It permits pilots to fly in strong winds and turbulent conditions, and reduces the risk of a tuck (a nose-under condition that often causes structural failure; it can occur in tailed aircraft as well as flying wings).
Thanks to the unique tail, an incipient stall is easily recognized, as the control bar will begin to shake as the glider approaches stall speed. According to AIR, yaw stability is also improved, and it is more difficult to induce a spin on the glider. During a stall, the ATOS may drop one wing slightly, but it will recover gently on its own.
The VX’s canted-up wingtips are also designed for added stability. “Wings with higher aspect ratios tend to tighten in turns,” Rühle explained. “With the additional [outboard] dihedral, the glider flies more stably in turns.”
Every ATOS can be easily fitted to the latest point of development, a laudable quality for any product. So earlier ATOS models can add the tail if desired. The prototype of the ATOS VX was made in either solo or tandem (dual) configurations; however, the VX is now available only in the tandem form. Therefore, I thought it would be a good experience to fly the two-place with Rühle to see how it performed.
I have flown two other advanced wings like the ATOS, but always atop trike carriages. I was eager to fly this one as a pure hang glider, and what better way to learn the characteristics than to fly with the designer?
We were towed aloft at Malcolm Jones’ famous Wallaby Ranch near Orlando, Florida. The tow went easily even though two persons in the control bar made for a cramped space.
Most hang gliders turn by the pilot shifting his weight left or right, which in turn causes a sail shift that angles the wings slightly. It works well; hang gliders are highly maneuverable.
The ATOS VX has a control bar, but it isn’t structural and it doesn’t facilitate shifting of your weight. As you move the bar, cables activate a set of cascading spoilerons located far out on each wing. By cascading, I mean each wing has two sets of spoilers. As you move the bar gently, one set of spoilers raises and you turn that direction. If you move aggressively, the first spoiler lifts the second spoiler for faster results. It’s quite effective.
On our flight, we gained thousands of feet in several thermals. After landing, I went aloft solo in the big wing for an evening flight after the lift had died. Instead of trying to catch thermals, I banked and turned the wing with increasingly assertive movements. It behaved perfectly.
I was impressed with the flight qualities of the ATOS VX and marveled at its superbly clean construction. Produced by AIR in Germany, the aircraft is priced at €12,500. With the sinking dollar, this translates to about $16,400 (in January 2005). If I could, I’d buy one tomorrow to put on my soaring trike.
FOR MORE INFORMATION on the ATOS VX, contact AIR at Borsigstrasse 17, D-71277 Rutesheim, Germany; phone 011-49-7152-351-251; e-mail firstname.lastname@example.org; web www.a-i-r.de.
To review all “Light Stuff” columns that have appeared in KITPLANES®, visit www.ByDanJohnson.com, which links to the KITPLANES® web site with articles of interest.