-There are about as many registered Aussie pilots as U.S. pilots.
-The prime flying season in Australia is November through April (the Auss'ie summer), although some spots are „on¾ throughout the year.
-The Hang Gliding Federation of Australia („HGFA¾) requires visiting pilo'ts to obtain a Visiting Pilot Membership (good for four months) at a cost of $4-$5 Australian.
-You can use your 2 Meter radio (illegally), however the Aussie pilots use CBs. [26.925-27.405 and 476.425-477.400 Mhz -Ed.]
-The Aussies are very hospitable and there are plenty of adventurous things todo when conditions are not flyable.
Prior to making our trip to Australia, we contacted the HGFA who sent us a recent copy of their official publication, Skysailor, as well as a print-out with names and phone numbers of paragliding instructors and club contacts in Australia. We began writing/faxing/phoning and e-mailing pilots and we're happyto see how responsive they were.
The majority of the paragliding sites in Australia are along the south eastern coast, in Victoria, New South Wales and Queensland. Our original plan was to fly into Sydney, soar the coastal ridges at Stanwell Park (30 miles south of Sydney) for a week and then head up to the Great Barrier Reef for some beachtime. Unfortunately, the sea breezes weren¼t cooperating at Stanwell and we had to go to plan B.
The High Adventure Air Park is in Johns River NSW, about four hours north of Sydney. The owner/operator boasted of „launches in every direction¾ and offered us accommodation on their beautiful property, which consisted of rolling hills between the local mountain and coastal sites. The Air Park is very well run and the sites looked great. The only problem was that a front was coming in, the wind was howling and the locals didn¼t expect the conditions to change for several days.
Reports were that Manilla, a paragliding „mecca¾ with inland thermals (located between Sydney and Brisbane), would also be too gusty for several days. We were starting to get discouraged, tired of paradriving and parawaiting and desperate to get airborne, as our itinerary called for us to fly north to Cairns (grea diving, but not much flying) at the end of the week.
We remembered that an Aussie we met while paragliding in Maui told us about aplace called Rainbow Beach, which is about three hours north of Brisbane. As it turned out, we had the name of a pilot who lives in Noosa (an hour and a half south of Rainbow Beach) from our pre-vacation research. We called Jean'Luc, an instructor-in-training, to see how the weather was along the Sunshine Coast and to learn a little about the sites in the area.
Jean'Luc felt certain that the weather conditions were changing and he promised us we would fly if we stayed in Noosa. Fortunately for us, we put our faith in Jean'Luc and cancelled our plans to head to the Reef. We settled into an apartment in Noosa, which is a lovely beach town. There are several coastal sites in Noosa, including Sunshine Beach, Sunrise Beach, Alexandria Bay and several more sites on the beach route to Rainbow. (Tewah and Pyramid are beautiful sites, but are onlyaccessible from the beach, so you need a 4x4).
Jean'Luc took us under his wing (pardon the parapun) and spent the enti re week with us. Our previous flying experience had consisted of lots of inland sled rides and no coastal soaring or flying inheavy winds/thermals. Jean'Luc worked with us on our ground handling skills, as the sea breezes on soarable days werebetween 15-18+ mph. He gave us thorough site intros and lots of practical tips about interpreting the clouds, listening to the trees, reading the waves on the water and following the eagles as they soared above us on the coastal dunes.
The sites on the Sunshine Coast were magnificent. Some of the ridges had stretches of 10-15 miles of breathtaking dunes, with wide unspoiled beaches below. We got to see whales and dolphins in the ocean below us. We felt like we owned the sky, as there were only a few pilots flying each day. For us,this was a paragliding paradise!
We learned that the keys to travelling with your wing are patience and flexibility. Plan your vacations so that you can easily move on if the conditions aren¼t favorable. If it¼s „on,¾ stay put and have fun. Get to knowthe area and the local pilots so that when you return, you won¼t be a tourist-- you¼ll be family!
Let me know if you¼re thinking about making a paragliding trip to Australia. I¼d be happy to give you a list of sites and contacts.
Paragliding Design
Deane Landreth and Tom Moock
Many readers of Ridge Dancer have access to the internet, and some are aware of the mailing lists of interest to hang- and paragliding enthusiasts. The hang gliding list is the most comprehensive, covering both hang gliding and paragliding topics.Lesser known is the North Western Paragliding list (nwpglide), devoted exclusively to paragliding letters. Although most postings on this list pertain to last weekends¼ spectacular flights (or spectacular accidents), letters devoted to more general threads (topics) do comeup. This one is about Paraglider Design.
It started when Deane Landreth placed an ad for paraglider design software. I responded that, although I was not a buyer for thesoftware, I was interested in the general topic of PG design. Were there any books on PG design? Unfortunately, it is very much a proprietary engineering discipline at present, and there are no booksthat I know of. Later, Hannes Papesh from Nova chimed in, saying „ask yourdesign question.¾ So I did, see below. But the answers came fromDeane Landreth. What follows are questions and answers on paraglider design considerations. Remember that there are no generally available bookson the subject, so there can be no dumb questions.
Paraglider Design Questions
Although these are general questions, I specifically mention Nova gliders, as well as gliders I have owned: the entry level WillsWing 125 (similar to the Prodesign Challenger), and the intermediateSwing Mythos. These are used as examples only; the principles should apply to all gliders.
Wing Design and Collapses
While inducing assymmetric collapses, the A-risers on the WW125 took gorilla strength to pull down and hold, and required extremeweight shift and opposite brake to-the-beener to fly straight. TheMythos A¼s could be pulled down easily and required little weightshift and no brake to fly straight. In real conditions, the WW125 never had a major collapse, even at Marshalls (CA) and Pine Mt (OR) in summer, and Owens Valley in fall. I got a 50% and a full frontal in the Mythos on the 2nd day of ownership, in San Diego in winter. The Mythos flew so smooth (in trashy air) that I didn¼t realize I was flying with 1/2 a wing. Yet, it seems to me that if I got a 50% collapse on the WW125, I would be in a spin before I could say åOh Sh-¼. Which is åbetter¼, and what design factors affect this?
Cell Design
My Mythos has many more (and smaller) cells than the WW125, and there seems to be a trend toward more cells in the high performance wings. Presumably this produces a more precise airfoil. The Nova Phocus has few big fat cells, yet its specs are up with the best of the intermediate wings. Comments? I also note that the Omega Advance has very small opennings in the leading edge. Does this make the wing more prone to collapse?
Cell Design and Line Cascadess
Both my wings have one set of lines for each cell. Yet theNova Xyon has one set of lines for every OTHER cell, to reduce line drag. The Airwave Alto also has 1/2 the lines. If one can get awaywith this (and the Xyon seems to be an excellent peformer), then why doesn¼t everyone do it? Is there a stability factor here? I also note that my Mythos has quite narrow (dyneema, technora) lines, but the WW125 has fat lines. I accept that thin lines produce less drag, but the Prodesign Profeel (another top performer) has the same fat lines as my WW125. Comments?
3 vs 4 Risers, and Speed Systems
My WW125 has ABC, my Mythos has ABCD. My naive assumption was that the 4-riser system would allow a more precise airfoil when the speed system is engaged. My WW125 pulled down AB¼s, but the Mythos pulls AB¼s and 50% (via pully) C¼s. I felt fine about this explanation, until I saw the Profeel, which has only 3 risers. Any ideas?
Best Glide, Minimum Sink
Although the glider manual doesn¼t discuss this, my assumptionabout the WW125 was that its best glide (in still air) was at trim, and minimum sink was around 50% brake. Most people I talk to about other gliders concur. But the Mythos manual places best glide at 50% speed bar, and minimum sink at 20% brake, and a recent posting to this list noted that the Nova Xyon has its best glide at 100% speed bar. What are the manufacturers looking for in setting best glide, trim speed, etc.? It struck me that setting the trim speed lower than best glide would be quite reasonable for a very fast glider. Other Spin Control My friend Jeff Greenbaum noted that the Flight Design A5 turns AWAY from a small collapse. This is certainly not true of my WW125, and is counterintuitive. Yet the Mythos, in my hands, has a slight tendancy to fly away from small tucks as well; it is subtle, but reproducible. It occurred to me that manufacturers may design the wing tips with a bit of extra drag, to reduce collapse-induced spins. Is this true?
Deane Landreth Replies: I answer these questions from my own perspective. I do this because I received a number of responses, asking what the [heck] I thought I was doing, advertising paraglider plans for sale in this forum. I work on my own account as a paraglider designer, and I amalso a part owner of a manufacturing operation CLOUDBASE NZ Ltd. This company markets under the name Pacific Wings in the US.
In my reply I tried to use a minimum of aerodynamic jargon. It is not a complete discussion of issues of paraglider design, as this would certainly fill a book or two.
The art of paraglider design is all about compromise. No single factor can be taken in isolation to any other, and it is this characteristic that makes it endlessly fascinating. By answering one question, inevitably you must consider a whole host of related factors as well. But I will try to be specific.
Tom¼s first question was comparing a high initial stability, with a severe turn on collapse (WW125), to a lower initial stability, with a lower rate of turn (Mythos). These two factors are not directly related: you can have both high stability AND low rate of turn in a collapse. I¼ll describe these factors separately.
Inital stability
A gliders¼ initial stability (how often it collapses) is not directly associated with its recovery characteristics. One can trace the inital stabilty to four factors: trim angle , wing loading, foil shape, and aspect ratio.
Trim Angle
The paraglider will collapse (or „luff¾) when the angle of attack goes negative and the airflow pushes the wing down. To lessen the likelihood of collapse, you need to keep the trim angle of attack high enough. Too high an angle of attack results in a wing that is stable but slow; this was common before designers put more effort into airfoil selection.
Wing Loading
Increasing the wing loading increases the air speed for anygiven angle of attack. For a heavier-loaded glider, a gust impinging downwards on the wing needs to be of a larger magnitude to bring the angle of attack to a negative value, and collapse the wing. Higher wing loading also means a higher minimum sink, but if you compensate by raising the aspect ratio, the effect is neutral. A higher wing loading also creates a faster wing, which creates a higher inflationpressure and a stiffer wing.
Airfoil Shape
To avoid collapse, you need an airfoil with a low-negative or a positive PITCHING MOMENT. The easiest way to explain pitching moment is to look at what happens to a foil at zero angle of attack, and producing no lift . A foil with a negative pitching moment (an unstable foil) will continue to want to pitch forward, worsening the situation. A foil with a positve pitching moment (a stable foil) will want to pitch up, improving the situation. When a paraglider encounters a downward gust, an unstable foil will pitch foward faster than the pendular stabilty can recover, and the wing will collapse. The stable foil will sit far more comfortably at low angles of attack, giving more time for pendular stability to recover the wing to normal flight.
A stable foil is characterised by having the high point well forward on the chord, with no under camber, and with the low point behind the upper-surface high point. A lot of air foils used in paragliders are at least slightly unstable (negative pitching moment); This is because stable foils are generally less efficient lift producers. An inflated beam (a circular one, anyway) increases its stiffness as the diameter increases, by a factor to the power of four; that is, double the diameter and the stiffness is 16 times higher. As stiff thick airfoil is a big bonus on encountering turbulence, up to the point when it actually collapses. Beyond that point, it can become a liability, as we will see in the next section.
Aspect ratio
As the aspect ratio goes up, the stiffness of the wing drops quickly. I prefer to say that a wing doesn't actually collapse, but merely adapts its shape to the local airflow; too bad if the air flow happens to be going in different directions on either side of your wing. The larger the span or aspect, the more problems you have in keeping the entire wing flying in the same direction
Stability After a Collapse
After a wing has collapsed, a whole other set of variables come into play to determine how it recovers. To achive a slow rate of turn once the wing is collapsed, you can do several things with the design:
1 Minimize drag of the deflated side
Larger openings allow the wing to deflate, presenting less drag area. Smaller openings mean less reinflation is nessasary, and it progresses more quickly. But the extra drag of the deflated side means the glider turns more quickly. Remember the Trilair ? It had almost no openings at all, and it would spin like a top with half the wing down; but it would instantly reinflate if you brought the angleof attack back to a positive value by coming down hard on the brake.
2 Line length
By using longer lines, the glider does not bank over to as bigan angle with half of it collapsed and so it turns less quickly.
3 Twist
How the lift is distributed across the span is important. More lift at the tips means the glider feels more stable initially, but turns more quickly after a collapse. Glide performance, spin recovery and flare characteristics are reduced with too high an angle of attack at the the tips.
4 Droop tips
A pronounced droop in the tips causes the lift force at the inflated tip to pull the glider away from the collapsed side, and reduces the turn speed in a collapse. A wing called the ATMOS 90 took this to the extreme, and would turn quite stongly away from the collapsed side . I found this unnerving to fly, as it is, as Tom Moock said, counterintuitive . It also took a while to reinflate: by turning away from the collapse, the angle of attack was lowered on the collapsed side, and it took a mighy heave on the brakes to get the attack angle positive again. These droop tips are also not good for performance, as they add drag without increasing lift
5 Trim Speed
The trim speed has a big effect on handling after a collapse. High angle of attack (low trim speed) means the glider turns less quickly off heading. This is easy to discover if you have a gliderwith a trim system: haul down the risers and note the difference in recovery times at various trim settings (do this at an SIV course!) The trim speed is also very important for handling, however, and once you have chosen a trim speed you need too employ other methods to control the rate of turn. For paraglider design, the key is employ all methods in some form to achieve the right balance of characteristics. I lean towards letting the glider turn a little more quickly than a lot of current designs, because it gives the pilot more control over the reinflation characteristics. With half a wing down you are doubling the wing loading on the inflated side and so the stall speed increases to squareroot( 2) x the normal stall speed. Rigging the glider for a slow rate of turn decreases the overall airspeed and brings it closer to the stall point in a collapse. If the pilot applies counter brakes, as is common for some one who is used to a faster turning wing, they can stall theinflated side and spin in the opposite direction. Turbulence excaberates the problem, and can cause a stall even if the pilot applies no brake. This is not a hypothetical situation; I have seen it happen at many SIV courses and in real flying situations. The slow turning wing is a product of the certificationprocess, which favors no pilot input. I prefer a wing with a wider range of airspeed control in a collapse, and this necessarily means a faster turning wing. The final solution on this one is achiveing theright compromise.
Performance considerations
You want to produce the maximum amount of lift while minimizing drag. Lots of cells produce a more slippery profile . Lots of lines produce lots of drag. Every line you add must be compensated for by a correspondingly cleaner sail shape.
Stick a tuft of wool in the dip between two cells, and you will see the turbulence formed by the indentation. This means nothing but drag. If you add more dips (cells), you add more of these little turbulence producers, although they do get smaller. If you also add more lines to hold the cells in place, you have achieved nothing but more drag.
The Phocus is a good example of a wing that looks „rough¾ to the eye, but not necessarily having higher drag due to the fewer number of indentaions . It is also quite a high aspect wing with few lines, which also accounts for its good performance.
I haven¼t been able to develop a simulation of cell spacing / indentation size vs turbulence drag that draws any analytical conclusions yet, but I have arrived at some conclusions by experimentation. The key is to minimize the number and size of the dips in the wing without adding lines. The route followed by NOVA, with few lines and diagonal ribs, is proving to be the best method of doing this, I believe. Count on most manufacturers following suit for their performance wings.
There are a few down sides to this approach. The diagonal ribs make for a more complicated shape to design and manufacture. Cost go up, margins come down, but this is not a problem if people are prepared to pay the extra price. It also makes for a heavy wing which can affect reinflation times.
One other factor (I haven¼t seen this myself, but others have noted it) is an increased tendancy for the wing to lodge itself in the lines when it all gets really messy. This is due to the wider gaps between lines, resulting in an unrecoverable spin.
Trying to reduce line drag by reducing line diameter produces diminishing returns. If, for example, you use two 1mm lines, you get more drag than using one 2 mm line. In aerodynamic terms the drag coefficient rises as the Reynolds number decreases (consult a fluid dynamics text for information on this sort of stuff).
The other problem with reducing line size is that if you halve the diameter, the strength will be four times less. (This is not quite true with sheathed lines, where all the load is taken by the core.) There have been more than a few occasions where pilots were left toponder the pay offs of increased glide at speed punctuated by rapid descents as their wing unzips above them.
The number one route to performance is high aspect ratio. A high aspect wing produces less induced drag due to the tip vortices being smaller in relation to the overall span . It is more efficientat producing lift.
However a high aspect wing also requires more lines to support it. Back in the early days, one designer was saying that aspect ratios over three wouldn¼t produce better performance due to the extraline drag. This is obviously not the case, as the higher aspect wings have obviously resulted in better performance. I did do a computer simulation on this topic, which showed that for a given cell spacing, increasing the aspect ratio beyond a certain point would not result in increased performance. For the wing smoothness I was then achieving, this was at an AR of about 7.5. Unless someone comes up with a really ingenious solution , aspect ratios much over 6 won¼t be making it big in the market; they are too demanding to fly. In fact, for the average level of pilot skill aspect 5.3 or below is about the limit.
There are many other considerations in Paraglider Design, but it would be better covered by a book.