The Xaos-21 is a 21-chamber cross-braced tri-cell canopy and one of Precision Aerodynamics' highest regarded ultra performance wings. We weren't exactly really sure at first what one rather analytical so-and-so meant when he firmly uttered "The mysterious paradox is that the Xaos-21 demonstrates the epitome of recalcitrance as it rebels against the authority of the laws of gravity, because it is only through the laws of gravity that this machine flies at its best," but we think he meant "It likes to be loaded."
We have been manufacturing different versions of cross braced tri-cells for several years, and the Xaos-21 includes a number of refinements we have made during our continuing research and development of ultra performing crossbraced canopies.
You don't have to be a NASA Pilot in the Space Program to appreciate the awesome flight of the Xaos-21, but after you fly it, you will think you are.**
Our developmental program for the Xaos began in the summer of 1999 and has continued for two years, culminating in the most advanced airfoil we have produced to date. The primary focus in our development of this 3rd generation cross braced tri-cell airfoil was to generate a true 3-D wing whose strong suit centered on high speed swoops with a tremendous reservoir of lift available to be unleashed during the landing phase of flight.Several changes would have to be implemented to the existing technology in order to achieve our final goal. Always present in a designer's mind is the challenge to increase lift and reduce drag at the same time in order to enhance speed and efficiency, while paying mindful attention not to sacrifice the details of pack volume and durability in the process. The development of a superior flight required a very detailed evaluation of each and every separate element in the canopy's construction, with careful consideration of the effects that any component may have on the performance of another.
Stabilizers Evolve into Stabilribs
We began by evaluating one area has been overlooked for many years by most all manufacturers, the stabilizers. What do stabilizers really do? What are they supposed to do? What do they stabilize? Why are they there? Take a look at any existing canopy in flight and ask yourself why the stabilizers aren't just called "tacked on flappers" or "flailing fabric slider-stop holders."
The general concept of what a stabilizer panel is supposed to do was lost back around the time that the slider was first utilized as a deployment-reefing device on ram-air canopies. The original concept for stabilizer panels was to minimize the effects of wing tip vortices of a canopy, effectively increasing the virtual aspect ratio for any given design.
That was all fine and good, and stabilizers on early ram-air canopies did just that, in theory. Then along came the slider, and while the slider did get us away from pilot chute controlled reefing and all of its associated malfunction modes, it was quickly discovered that the slider could cause considerable canopy damage if some protection were not installed between the slider and the canopy.
Voila, along came slider-stops. In the beginning, slider stops were made from all the old reefing rings that were now no longer necessary, and they were abundant, but they were not cheap. They still cost about a dollar each. As I recall, one enterprising canopy manufacturer began sewing half-dollars into the stabilizers to serve as slider stops, thereby cutting his cost in half. Except for the half-dollars, stabilizers remained pretty much unchanged for many years, and to this day the stabilizers still provide a convenient place for a canopy maker to install slider stops.
In many instances, however, the shape and attachment method of stabilizers has historically been a subset of the preferred placement of the slider stop (and subsequently the opening characteristics), and less associated with the canopies flight performance . Stabilizers on more than 99% of canopies flown today are installed as a separate piece of fabric holding the slider stop, and simply tacked onto the end-cell suspension line, left flailing in the breeze at full flight and creating significant amounts of drag.
With the Xaos-21, as well as other Ground Zero canopies, we have instituted a technology that we refer to as a "Stabilrib", integrating the stabilizer panel with the end rib as a solid piece, and attaching the outboard suspension lines to the bottom of the Stabilrib instead of the lower surface of the canopy. By designing and constructing the canopy this way, several things happen, and all of them are good.
First, the suspended load imposed on the end cell is evenly distributed throughout the chord of the wingtip, resulting in better airfoil performance during all flight modes. Diffusing the end cell loading throughout the chord also eliminates the inefficient point loading of traditionally built canopies, and puts the Stabilrib to work full time, producing more efficient flight at full glide, creating a positive control point during quick turns, and channeling airflow more efficiently across the lower surface generating a more powerful flare.
Drag Reduction, Higher Flight Speed, Dynamic Performance, and Line Durability...
A Win-Win-Win-Win Combination
Another area of concern in the development of the Xaos and other Ground Zero canopies was to find a material to use in suspension lines that would not only yield a lower coefficient of drag but also a material that could tolerate the friction of the slider for the duration without detrimental effects.
For years, parachute designers have utilized a myriad of synthetic fibers and geometric braids in search of the elusive perfect material for parachute suspension lines. Nylon had been used for many years in round canopies, and it worked well in those designs, but Nylon is not suitable for use in ram-air canopies because of its elongation (stretch) properties.
Dacron (polyester) became the fiber of choice early in the development of ram-air canopies. Polyester braid is stable, and although it does stretch considerably during deployment, it has a good memory and therefore retains its original dimension much better than Nylon. The only real downside to polyester braid is that it is relatively bulky when compared to some of the newer line materials like Spectra and Vectran.
Spectra became popular as a low bulk option for some ram-airs, and many tens of thousands of ram-air canopies have been rigged and jumped utilizing Spectra braid. Some of the early braids of Spectra, however, proved to be unsuitable for use in some parachutes because of the significant shrinkage of Spectra fiber as a result of the friction of the slider grommets. This shrinkage is most evident in a canopy's control lines and end cell outboard suspension lines. The resulting trim degradation is slow to onset, and many jumpers do not notice it as any specific change in performance on any particular jump, but rather degradation in performance over a period of time. We have seen some spectra-lined canopies in need of an entire replacement line set with fewer than 300 jumps.
Vectran fiber appeared to be a very real option for parachute suspension lines when it was first introduced in 1999. The braid geometry was stable, and the bulk was only a tad bit more than Spectra. The best part was that Vectran did not suffer from the friction-induced shrinkage that users of Spectra had experienced. As a matter of fact, the melting point of Vectran fiber is high, and Vectran braid is difficult to cut with a traditional hot knife, while the same braid of Spectra line can be nearly be cut with a hot knife when waived over the line like a magic wand. Early indications in controlled testing indicated that Vectran would be a strong replacement for the popular (but unstable) Spectra braid.
Unfortunately, the results of controlled testing for durability of Vectran line were not manifested in Vectran's widespread and common use. On more than one occasion, a Vectran control line would snap at the most inopportune time (on the landing flare) and with high performance canopies, this is absolutely not acceptable. Users of canopies with Vectran line must inspect their canopies before every jump, and monitor the wear of both the suspension lines and the control lines.
With the Xaos-21 and other Ground Zero canopies, Precision is utilizing a fiber known as HMA for suspension and control lines. HMA is an acronym for High Modulus Aramid fiber. Our experience during the past two years indicates that HMA line not only packs smaller, it also tolerates the slider's friction quite remarkably, while at the same time retains its linear stability as well as Vectran. Xaos-21 canopies (and other Ground Zero canopies) each contain three different sizes of HMA line including 352, 440, and 946-pound tensile strengths. The braided diameter is smaller than either Spectra or Vectran.
Continuous Suspension Lines
We have outfitted the Xaos-21 and other Precision Ground Zero canopies with continuous suspension lines. By eliminating the suspension line cascades we have done several very important things. We have eliminated a library of malfunctions associated with cascaded suspension lines, we are able to use a much smaller diameter suspension line (less drag), we have minimized the front riser pressure while enhancing riser flight control on both front and rear risers.
Some people who have closely inspected the Xaos-21 have noticed and commented on the addition of lower surface lateral reinforcement bands. It is interesting to note that the general impression is that these bands are intended for opening integrity, and while that may certainly be true, the real reason for spanwise lower surface reinforcement bands is flight stability, especially during radical flight maneuvers. The spanwise lower surface reinforcement bands allow the airfoil to retain its proper 3-D shape during all phases of radical canopy flight.
The Refined Leading Edge
One of the least noticeable, but most significant changes in the Xaos-21, is the refinement of the canopy's leading edge. We spent months on this small but important element of the Xaos airfoil. Take a close look at the shape of the Xaos leading edge as compared to other cross-braced canopies available. While it is not so apparent in full flight because of typical speed distortion, the refined leading edge of the Xaos-21 airfoil explodes dynamically into play throughout the entire landing phase of flight, while it works in concert with each of the previously mentioned enhancements (Stabilrib technology, HMA fiber braided suspension lines, continuous line geometry, and lateral lower surface reinforcement bands) to deliver an ultra-performance canopy flyer's dream... an ultra performance canopy flight that defies gravity.
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