Technical Tips and Articles    

                                              

 

This page contains tips and articles that can help solving many everyday problems paraglider pilots faces. You also find here answers to some of your burning questions of a technical character and advice to follow when buying your equipment. They are based on my long flying experience and a deep knowledge of the technical side of paragliding. Most of them have been published in Australian and overseas magazines. I'm doing my best to keep them up to date, but as the sport and technology is developing constantly, it is an uphill battle. Any e-mail alerting me to a redundant erroneous or obsolete content will be highly appreciated. Any material presented here is to be treated as my opinion only and I recommend to use your own judgment before following any of the tips or advices.

                                         Jiri Stipek

 

Useful technical solutions

                                     

Modification of  the T-bar type of harness

There were quite a few fatal accidents and close calls associated with the combination of T-bar style of leg straps and instrument panel. While the T-bar is one of the safest designs if used alone, the combination with instrument panel it can be deadly. A typical sequence of events leading to a fatal accident:
Pilot gets in the harness. Before closing the T-bar he clips the instrument panel on. The panel obscures his view on the buckle creating the "out of sight, out of mind" situation. At the same time the panel puts a bit of tension on the main karabiners causing a false feel of a closed T-bar. The pilot takes off - period.
After this type of fatal accident in Australia a few years ago I designed a modification virtually 100% preventing this possibility. It is simple, costs nothing, it can be done virtually by anybody and it doesn't have any side effects. I've been using this setup for a number of years and I wouldn't get back to the unmodified harness for all the money in the world. Here is how to do it:
Remove the female clip for the cockpit from one side of the harness and stitch it in the middle of the T-bar facing the direction where it was originally.
              
Do not worry about the sophisticated part on my harness involving insulation tape, it has nothing to do with this modification. I used it to stop the central buckle catching on the zipper of my flying suit ;-). Your setup is ready for a trial. Put the harness on and clip the unmodified side of the cockpit as usual. Now, run the other strap thru the main karabiner and attach it to the clip you stitched to the T-bar. Check if the cockpit doesn't pull the karabiners together relieving tension from the T-bar. If you can't adjust it long enough, you may have to change this piece of webbing for a new one.
That's all. From now on, you can't clip your cockpit on the harness before at least one of the sides of T-bar (enough to prevent you from falling from the harness) is properly closed. In fact, if you omit to close one side, you can hardly fail to notice it while clipping the cockpit in. You have just made sure you won't become the victim of one of the most frequent causes of PG fatalities.

Risers joining strap

Unless you are a masochist, you don't disconnect your harness from the glider after every flight (I will never understand, why some people do so.). The time, labor, courtesy to other pilots and safety advantages are obvious and there is no need to go to details. The only problem I encountered was, time to time I found myself flying with one or both risers twisted. Reason: throwing the harness thru the risers at some stage of handling the aircraft. Twisted risers are not necessarily life threatening - but they don't add to a peace of mind either.It took me about 5 years (yes, that is how slow I am ;-)) to find this solution - and never had this problem since: A small Velcro strap I wrap around the risers immediately after every landing. I remove it again only just before I get into harness getting ready for the next flight. To have it always ready, I put it around my left shoulder strap. After landing, I reach there, take it off and put it around the risers. A foolproof routine, takes about 5 seconds...

 

 Speed bar 'keep up' olives

I know only a few things more annoying than a speed bar banging into your calves while walking around in your harness. A variety of Velcro patches to hold it up proved to me rather short lived solution, as they attract dirt and wear off quickly. The best method I found so far (not my invention, I saw it somewhere and promptly copied) is a little spring-loaded olive (used on clothing and bags) on each of the lines. I pull them down the lines after every landing and they hold the bar off the way. They slide up easily during the first use of the speed system in the air. Comfy!

 

Airspeed sensor installation

Some flight computers need an airspeed sensor for a proper function. In a paragliding application it is a serious problem. Proximity of the pilot affects the accuracy considerably. The 'professional' solution, speed probe hanging down, is highly impractical and also accentuates the pendulum effect. No good at all. After many experiments I ended up with a solution equally practical and accurate: I fitted the probe in the 'C' lines, just above the Mailons. Have it there for a few years now - never looked back. One has to be aware of some limitations of this solution: the sensor is not able to adjust to the direction of the airflow so in extreme cases - acro - it may give a false reading. For a normal CX flying however, it works with a very satisfactory accuracy. Aligning the sensor as precisely as possible with the glide direction is very important for accuracy. Calibration in the computer menu is always needed for the best results.

 

Radio installation

After experimenting with variety of ways to mount my radio, I ended up with having it at the rear riser. I was thinking about it since the day one - but the bulk and weight of the old 5W unit put me off it. Only the recent introduction of small, light, efficient radios allowed me to go back to the original idea. After using it for about 2 years now, I couldn't be happier. The advantages are numerous. The antenna is vertical and it is not obstructed giving the beast possible performance. The control panel is in a plain view and all operations can be done while holding the brakes. If you are nor really fussy, you can even get away without a headset. The mike is close close to your mouth and it is no affected by wind noise. Warning: make sure the radio doesn't interfere with a free movement of the risers. Also, a heavy radio on the rear riser can affect the recovery characteristic. Ideally, the radio should be attached below the point the risers are joined.

 

 Bundling your glider

Often, when you need to bundle your glider just to get if quickly of the way, you may find yourself short of something to tie the looped lines with. Leaving them lose is a sure recepy for having them tangled. The solution is strikingly simple: put the wingtip thru the loop...

 

Getting electrocuted?

It is always better to leave a paddock thru the gate. If you find a padlock on it - well, you have no choice. Besides of trying to your best not to damage the fence you also don't want to get zapped by the electric fence. It hurts! Your problem can be solved by about 30 cm of wire (doesn't even have to be insulated) with crocodile clips. I never leave home without it! Before climbing the fence, I clip one end on some non-active metal part of the fence and the second (the sequence is vitally important) on the live wire. When safely on the other side, I unclip the 'live' end - again, the sequence has to be right - and then the other. Simple and painless, doesn't harm the electric fence either..

  Brunnel Hooks on your speed system keep separating?

A simple help: a few twists on the speed system lines before you join the hooks - just enough to produce a small torque. The hooks will became much harder to disconnect again without your help. But the ultimate solution: replace the useless gizmo with a small karabiner...

  Press Studs on your brakes get hard to separate?

I tried just about all the lubricants you can think of and none of them worked properly - until I came across graphite powder. I'm not searching any further, this stuff works magic! Just one application and you will not recognize your old press studs. It typically lasts a whole season. The powder is available from auto parts outlets like Autobarn or hardware shops.

 

Can we trust the numbers?

In the dark ages of paragliding some 12-15 years back) manufacturers were holding a serious competition who presents the most impressive performance data in their glossy booklets. Speed was the most popular parameter to stretch closely followed by glide and sink rate. According to these some paragliders were closing fast on the 60km/h barrier then already! The race was fierce and every argument possible was used to support the crazy claims. One of the renowned companies followed the speed data for their prodigious baby with measured by GPS statement. Quite entertaining! One of the reasons anybody was able to claim anything was the fact, the performance data are very difficult to obtain or check. There are too many factors in play and even the most honest manufacturer can slip by miles from the real figures. It gets worse: there are no fixed standards to be followed while obtaining this data and even while using the same instruments the figures obtained by different testers can vary substantially. It can be due to a different environment or some other parts like harness or pilot’s clothing. I don’t want to go into details here; if you want to get a better idea how complex this issue is, look it up in the Paragliding Forum . Prepare yourself for a long reading and a few surprises.The situation has stabilized greatly over the years and most of the figures manufacturers are presenting us with now are at least quite realistic. Still, I would advise using a great caution while using them for comparing gliders in the same category. The differences between the performances of gliders by the top manufacturers are so small, it is virtually impossible to measure them reliably. Even if the claimed difference exists, using it as main point for choosing your glider is rather pathetic. Some manufacturers are better at creating number-hypes about their gliders than others. If they tell you their glider has 0.3 better glide than anything else in that particular category, it sounds impressive. It can be actually true – but let’s put it in a perspective.

Fig. 1 is showing different glide path with different glide ratio – the angles are true. For simplicity I used glide 10 (realistic for the contemporary comp gliders) to illustrate my point.  The 0.3 extra gliding ratio has some noticeable effect in the region of 4 or less but it becomes insignificant in the 8-10 area. On a 1km glide it gives the “better” glider 30m (just over 2 spans of you glider) longer path – a difference that can be negated by anything - like less effective takeoff, less aerodynamic harness or even body position. If the extra gliding ratio is really there, it is certainly a sign somebody has done a good job in this best glide area – but nothing more. The advantage in the real world is rather academic. Besides of being truly miniscule the “guaranteed” benefit in the form of a longer flight path is only in the best glide configuration (usually trim) used in absolutely still air. How often do we fly in conditions like this? We are totally in the dark what will happen when the wing is being flown with a speedbar or some brakes – and that is what is happening in the real world. A lot of surprises can be hiding here. Only the whole polar curve can answer our questions. But, you can guess: if a single piece of performance data is hard to obtain, getting enough information for constructing a reasonably accurate polar is virtually impossible. The generic curves presented on the Para 2000 website are probably as accurate as they can be – and that means “not too much”. It is easy to prove how ridiculous the attempts of achieving one or two decimal points accuracy are. I had a closer look at the data published on Para 2000 for two recent gliders (according to the manufacturer each of them the best performer in its category) and found these discrepancies: the first glider has in the “best glide” box numbers 9.2-9.5. Fair enough. But: only 2 lines up there is speed and sink rate at the best glide: 39km/h and 1.1 sink. If you calculate the glide from these figures the result is whopping 9.8! In the case of the other glider it works the other way round: the claimed best glide is 8.9-9.2 while the one calculated from the speed data is meager 8.5!
If you want to see a more practical example, look at fig. 2. You can see 2 tracklogs there from one of the major competition last year. One is by a 6 years old glider where the manufacturer claimed a modest 8.5 glide, while the other is by the latest (and, according to the manufacturer, the best performer in the 2-3 category) machine with glide about 9.3! Sorry, I can’t tell you which one is which because the gliders flew virtually abreast for the most of the task. The winner could hardly claim his better gliding ratio had a major part in the final result.



Now, to make sure you understand me correctly: I’m not saying the new glider is not better. I’m saying it is extremely hard to turn the higher efficiency figures alone in a practical advantage. Trying to do it on the base of higher numbers at the first or even second decimal place is a joke.
Considering the above facts one may finally appreciate this disclaimer on the website of one of the major manufacturers:
“The performance data presented here are for general information only and by no means should it serve for making comparisons with products by other manufacturers. The methods for obtaining this data vary and there are no fixed standards. Any comparisons based on this data can be misleading.“
How refreshing!

The secret of those dream flights

There is hardly a month in the year you wouldn't hear about at least one flight that makes you turning green with envy. Pilots flying hundreds of kilometers, staying in the air for hours reaching stratospheric altitudes and crossing stretches never crossed before. Also the sheer amount of airtime over a period of time achieved by some pilots can be awe-inspiring. It all makes you wondering: why them and not me? A truly great flight is almost always result of the rare combination of skilled pilot superior equipment and excellent weather conditions - not necessarily in that order. If there is some deficiency in any of these areas, it has to be balanced by some extra strength in the one or both others. There are situations, where magic air carries a poorly equipped pilot of average skills to exceptional distances - or you see a genius pilot with average equipment going places in average conditions. These flights are the exceptions of the rule and I don't know many cases of world records achieved on this type of compromise. In short: everything has to click.
How can we help it? The skills and equipment ingredients are fairly straightforward: work on your skills and borrow steal or buy (if you have no other choice) the right equipment for yourself. It is as simple as that. The 'Perfect Conditions' ingredient is the hardest part. We are talking weather here - and it involves (besides of a sound knowledge of meteorology) a serious amount of luck, black magic and a crystal ball. In the end it is mainly a game of numbers. The more often you try, the greater are your chances. It is extremely unlikely pilot would achieve anything really exceptional unless he (she) makes paragliding his (hers) lifestyle. Full time job, a family (not to mention the combination of these two) is a serious hindrance consuming too much of one's valuable time that could be used for flying. For most people carrying those burdens is trying to catch up with the sky gods a futile and frustrating exercise. In most cases it ends by contracting AIDS (Aviation Induced Divorce Syndrome). The inability to be at the right place at the right time often enough presents a compounded problem: it statistically reduces your chances and it also deprives you of the opportunity to acquire the coveted superior skills. Set realistic goals that fit your situation. If you work from 8 to 5 and live somewhere in the inner suburbs, it is not likely you will ever make one of those epic flights the PG bums living close to the prime sites are doing just about weekly. If it does happen, count your blessings and mark that day by a red ink in your calendar.
Your problem is not so much a lack of time in the absolute value. The keyword is 'Flexibility' - the ability to hop in the car and go flying when the conditions look right and do your work when you can't fly. If you live close to a good flying site, the total time you spent on paragliding may not be too long and it may be fairly close to your airtime. There even may be enough time left to do some serious work (to earn enough money to feed your paragliding addiction) as long as it can be done at night or something. That's why the bulk of the active pilots are known to work in the IT industry or fill in the box 'occupation' something as obscure as a 'company director'. But not all of us are in this enviable situation. In most cases the best you can do is to reduce your driving/flying ratio.
A system introducing some efficiency in your time (and money) management is more important than the efficiency of your glider. Here are some tips I can offer from my long and frustrating experience: Use only one source of weather forecast and use it every time. Change it only if you find it EXTREMELY unreliable over a long period of time. There are many sources available and NONE of them is 100% right. Gets worse: they often vary significantly in their predictions. If you regularly browse thru them, you always find what you subconsciously want to see: either a good reason to go flying - or not to go - depends if you are pessimist or optimist by nature. Eventually, you end up either doing an enormous amount of driving and, yes, hooray, you will also log some airtime - but you will have to extend your hydroponics grass plantation to cover the cost - or you simply will never go anywhere and will sell your gear by the end of the first year. The idea is to stick with one (it almost doesn't matter which one) source of forecast and go flying whenever (your circumstances allowing) it promises good conditions. You will be surprised to see that even the worst source of forecast is about 80% right! Another rule is: Work with the forecast, don't wait for the observations to be right. This is especially important at the coast, where the flying conditions rarely last more than 2 or 3 hours at a particular site. Unless you live 15 or so minutes from the site, waiting for the weather stations to show the right stuff, then drive there in a hope you will have a great time is a waste of time and money. With all likelihood you will arrive just to watch everybody landing because the show is over. Your best punt is to TRUST THE FORECAST (I know it sounds insane) and get on your way well before the conditions start to appear ideal. You may spend some time parawaiting - but most likely you'll be rewarded eventually. Making a 100 or more km trip and go home with no flight under your belt is infuriating. Make sure it won't happen too often. On the other hand, learn to live with the fact it just has to happen sometimes. If the flying site is more than some 200 km away, try to avoid one-day trips. They seldom pay off. You really want some margin in the case the first day turns bad. With the current prices of petrol a cheap overnight stay usually compensates for the cost of an extra trip, not to mention the stress of long driving. Ideally, try to get yourself a retrieve driver, but I'm really stretching my imagination here. Most of us have to cope without this luxury.
Polishing your groundhandling skills is another vital part on your way to great flights. There is nothing more frustrating than being at the right place at the right time (finally!) and not being able to peel of the ground. I've seen this situation too many times - and believe or not, I don't laugh watching it. It is not funny. But, it is almost always the pilot's fault and he (she) is the only one to blame for the frustration and waste of time. If you live under the impression you finish your course and then you just go and fly, you are for a big disappointment. Paragliding, especially the first 20 or so years, is mostly about learning trying falling etc. Flying comes just as the icing on the cake. Don't miss a single bit because of your inferior groundhandling skills. Practice as often as you can. The beauty of it is, it can be done in much wider range of places and conditions, so there is no excuse. If you apply the above tips, you may be surprised how fast your airtime will start accumulating and in some time you will also find a few flight in your logbook to brag about. The main thing is to persist and not to give up. One doesn't have to fly hundred hours a year or break world records to have a real pleasure from our wonderful sport!

Are the pictures in our textbooks right?

 

We all know these pictures from our license course or some paragliding textbook. We take for granted they are correct – after all, they’ve been around for some 30 years. I admit, I never gave them a real thought. They were drawn by the top brains in the paragliding industry, so, why not just accept them as they are?

A certain gentleman from Scotland suddenly popped up on the Xtreme Big Air forum, stating, they are all wrong! What part? Well, in his opinion, the wing should be pitched down – not up as all these drawings show. An idea almost blasphemous. Denis Pagen can’t be wrong! Or can he? A heated discussion on the Internet ensued and it is still going on. “Can wing maintain a steady glide with a positive pitch?” No light at the end of the tunnel.

The best way to find out it is to go and see. And, if you look at a paraglider in a steady flight, you will believe the drawings are right. The wings are showing a distinct “nose up” position. So, no wonder we don’t see anything strange on these drawings. They only depict it the way we can see it.

But let’s analyze it a bit closer. Can wing maintain a steady glide while being tilted upwards? To simplify things, let’s replace the cambered wing with a flat sheet of paper. If we let it fly, the only factor determining the direction of its flight will be its pitch. This “wing” will always move in the direction of its lowest point. It will always fly with a negative pitch! In a simplified view, it is a case of 'action and reaction'. Wile the plate (wing) is being moved down by gravity, it 'spills' the air over its highest edge. It is necessary to understand, the top surface has its role in this process as well (becomes significant in a cambered wing). Reaction to this air movement moves the wing in the opposite direction.

Illustration from ABC of paragliding by H. Aupetit

That puts some smoke screen over our observation of a paraglider and it is time for another experiment. I made an improvised spirit level and fitted it to the bottom surface of my canopy. After I took off and established a steady glide I looked up and even took a few photos. Surprise surprise! The bottom surface was distinctly tilted nose down. This experiment confirmed my suspicion: the way we see paragliders pointing up while watching them from the side is an optical illusion! A strong one and very convincing too. I had to repeat this experiment a few times with different gliders to convince myself I really can’t trust my eyes. But I’m sure about it now: despite of what I seem to see, paragliders (at least the ones I tried) in a steady glide have the bottom surface tilted down. The drawings in the textbooks are based on an optical illusion!
Now, let’s get back to the great dispute: 'can wing maintain a steady glide while having a positive pitch at all?' Why all the participants in that endless discussion can’t find a conclusive solution to such a trivial problem? The answer is strikingly simple. The QUESTION IS WRONG – and nobody can find a correct answer to a wrongly formulated question.
First, we look at the definition of pitch: “Pitch is the angle between Chordline and horizon.” So far so good. Now, what is “chordline”? Chordline is the “line drawn between the most distant points of the wing profile.” Ops… something not quite right here. Does the bottom surface of our wing represent the chordline? Catch No. 1: it does not (in most case anyway). So, we can’t use the bottom surface neither for visual nor exact (spirit level) measuring of pitch angle.
Catch No 2 is even worse: chordline is a meaningless reference too – it is purely engineering (or geometric, if you want) term, but it has no relevance to the aerodynamics of the wing whatsoever! We started to use it in the dark ages of aeronautical engineering and somehow forgot to fix the mistake. As a result, we can now see certain wing profiles that still produce lift at negative angles of attack – something what screams “WRONG” at the first glance. The reason for this oddity has nothing to do with physics (or rather pseudophysics). We simply used that convenient but aerodynamically meaningless chordline as a reference for angle of attack. If we want to start to see some sense in our numbers, we have to use the “absolute” angle of attack term. In this case we relate the angle to the direction of relative wind that produces zero lift.  Finally, to our relief, we see “zero lift” at a “zero AoA (absolute)”. Uf…!

In the picture above is the (guestimated ;-)) 'relative wind producing zero lift' tilted less down than chordline. But, depending on the wing profile, it can be vice-versa as well. If you move glide path angle in our picture between chordline and the direction of relative wind producing zero lift, AoA will be negative - but the wing will still produce lift!
Now, let’s get back to our pitch. In the light of the above, pitch, the way it is defined (or the way we can see it) has nothing to do with the aerodynamics of a wing. So, the question if it should be negative or positive is entirely meaningless. The only case where it makes sense is a flat or symmetrically cambered wing. In such a wing chordline coincides with the direction of the relative wind producing zero lift. And, yes, for a gliding flight pitch has to be negative in this case. It simply determines the direction of flight.
In all other cases it all depends on the wing profile. With the “right” profile glider can fly happily with a positive “pitch” as pitch is conventionally defined.

 

Where is the difference?

Where is the difference?  A question I can often hear from beginner pilots after they manage to keep their pace with some of the hottest gliders around. This situation is not uncommon.  During a simple ridge soaring inside a small bowl there is little more at play than sink rate. A beginner's canopy being flown at the bottom of the weight range can come very close to a performance glider being flown fully loaded. The trim speed will most likely be almost the same as well.  While thermaling over a small area the situation will be very similar. Pilot's skills will show here more, than the performance of his glider. Now, really: Where is the difference between the DHV (German categorigasation generally recognised as a norm worldwide) categories?
Don't  worry. It is there - for everyone to see when it comes to crossing gaps - especially in headwind. As soon as the pilots set for a glide, some interesting facts will surface. The easiest way to show the truth is to look at the polar curve of each particular category of a paraglider. If you can't read these, you'd better do something about it. It is simple, anyway.
Curve A is a generic curve of a modern beginner class paraglider, typically rated DHV1.
Identifying features:  About 30 cells, aspect ratio around 5.0, thick material, thick lines - smart pilot. The whole thing has 'stability' and 'durability' written all over it. As there is no such a thing as free lunch, it will show some deficiency in the performance department. But as we have seen above, for a beginner or an occasional pilot it doesn't have to be any great disadvantage. The stability of their gliders can pay well off.    
Behavior: Docile. This thing doesn't bite unless you seriously abuse it. Virtually no active control needed. Have a nap. If you try to do something wild, do not be surprised if it refuses to do it.
The polar will reveal most of the secrets. The min. sink of some 1.3m/s is at a speed very much in line with the other categories - 28kph. On the left there is a nice, not very steep arch leading to a stall point. The speed span between these two is 8kph. A great safety feature! To the right we have the best glide of 1/7.5 at 35kph. Not bad at all for a glider as stable as we have. This point is usually the trim configuration as well.
We were doing OK up to here. Now we are getting to the moment of the truth: We step on the speed bar. A steep arch to the right of the right of the best glide doesn't look too flashy. It ends at a Vmax of about 46kph and an alarming speed rate of 2.5m/s. The glide would be 1/5 here. A quick glance at the polar of a competition glider ('C') reveals, its pilot is barely tickling the speed bar at that speed, his sink rate is still only 1.2m/s and his glide is almost unchanged! The most noticeable difference would be in a headwind of 46kph. Our ugly duckling will get sadly stuck, going nowhere. The pilot of the comp widow maker still can get  groundspeed of some 16kph!
Polar 'B' is a signature curve of a Performance Class canopy, almost always rated DHV2-3. (For simplicity sake I've omitted the Sports Class, which is the favourite of intermediate pilots. This, obviously, falls somewhere in the middle between beginner's and performance. These are rated DHV1-2 or DHV2) 
Identifying features of the Performance Class:  About 50 cells, aspect over 5.5, thin profile, thin lines - a fairly impressive looking machine. Its pilot should sport the 'Advanced' sticker on his helmet if he should be called 'smart' as well.  Going thru a SIV course before flying one of these should be a matter of common sense.
Behaviour: In a ridge soaring situation no special skills are necessary. A bit of caution while trying to do something more radical is needed. This wing may be responsive beyond your expectation - this is one of the most frequent ways of getting hurt by these.  Inland - a good degree of active flying is needed. This type of wing may not collapse too easily IF TREATED RIGHT. When they do, they expect some help with recovery if it should be reasonably swift. Will punish severely any pilot, who doesn't give them what they need. A 'cascade' type of accidents is common as a result of overcorrecting a super-responsive glider in critical situations.   
The polar is more interesting. The back of it is similar to the one of the previous. Anybody capable of stalling this wing accidentally deserves what he gets. There is a wide, hard to overlook margin. Min. sink is again around the speed of 30kph but it is only about 1.1m/s. That's nice! From here the polars gets much flatter through the best glide (often trim), which may be at a speed  marginally higher than in the beginners class. But the glide is very impressive indeed: 1/8.5! Then it continues, bending only slightly, to the Vmax point. At a tad over 50kph it will still sink only 2m/s. This is about all the performance a serious CX, non-comp pilot may ever need.    
Polar 'C' is that of a serious, latest generation competition wing. Safety rating: open class, no DHV certification. 
Identifying features:  Seventy or more cells, aspect ratio of about 6.5 and a dental floss for lines. If you realize what you are looking at, you should get goose bumps right away. A VERY recently re-packed reserve is an essential part of the package. The pilot's face should be known to you from some glossy magazines. He is likely to be sponsored by a major manufacturer. Alternatively, he might be an escapee from a nearby mental institution.    
Behavior: This glider eats average pilots for lunch. Even in the coastal condition this widow maker can show to the uninitiated what it has in stock. Just a fast release of the speed bar can lead to a steep climb ending by stall. Inland - definitely - 'For  Sky Gods only'. It will collapse easily even under the best management and refuse to recover without a substantial expert help. The rewards: high speed, enormous glide ratio and ultra-high agility.    
The polar should put you off at the first glance of it. The back part of it is especially nasty. A sheer drop from the Min. sink (under 1m/s!) to a stall takes only 4kph. Any odd puff from behind while having brakes a bit deeper - and you are in a serious trouble. This is the product of a high aspect ratio, needed for the mind-boggling best glide of 1/9.5+. The gentle arch leading to Vmax of 60kph+ is achieved by a highly unstable profile and almost invisible, unshielded lines. Notice, that even close to its maximum speed this marvel of technology still has a gliding ratio matching the best glide of a beginner's paraglider! Very inviting - but unless you are a true professional - give it a wide berth!

 

How wing flies

The mechanics of flight is not as simple as you might think after finishing your license course. In fact, it is so complex that a lot in this area is still to be discovered. As there is no need for a recreational pilot to have a deep knowledge of physics, we have a few of popular explanations that give a nice simplified picture of the interaction between wing and the air. You probably know the one using the difference between airspeed at the flat bottom of a wing and over the top, cambered surface. Makes sense, but as most of these simplified explanations, it has its catches. For instance: how do you explain inverted flight? What about a paper aeroplane – Look mum, no camber! – and, boy, doesn't it fly!? You are stuck.
In fact, the whole ability of a wing to provide lift has more to do with angle of attack than the shape of the wing. Even a brick will fly if subject to airflow strong enough striking at the right angle. The soundest and probably easiest to comprehend explanation of the function of a wing is the one based on the “action and reaction (Newton's)” principle. It has very few weak spots and a very sound and accurate mathematic backing. Oddly enough, this story is the best to start with helicopters. It is being traded among pilots that these things are simply so ugly, the earth repels them - and that's how they fly. There can be something about it – but if you ever found yourself under a hovering helicopter, you might realize the downdraft could have something to do with their ability to fly as well. The huge stream of air is hard to ignore – especially if you are flying a paraglider at that time. It is easy to imagine the rotor of a helicopter as a big fan accelerating air down. To do so, the rotor has to apply a force to the air – that induces a reaction force of exactly the same size, lifting the chopper up.
What has a fan to do with a wing? Well, the blade of a helicopter rotor IS a wing! Only, it moves in a circular motion eliminating the need for the whole machine to move thru the air. Otherwise the principle is exactly the same. As any other wing the blade can even stall – surprise, surprise – if the chopper flies too FAST! In that case the retreating blade (the one moving backwards) loses its airspeed, the angle of attack increases over certain point and the blade stalls!
Wing of a fixed wing aircraft does exactly the same what the rotor blade does: while moving thru the air, it deflects it downwards. The accelerating force induces reaction we call lift. Why this is not so obvious in a fixed wing? Unlike in a hovering helicopter, this wing deflects a parcel of air and moves forward to deflect another one at a different spot so the belt of sinking air doesn’t reach very deep. You would be surprised: the downwash from a fast flying chopper is not any worse than from an aircraft of a similar size traveling at the same speed. As soon as chopper starts hovering, one parcel of the deflected air has to displace the one below and so on – the result being the typical fast dropping column of air under the rotor. Our wing is nothing but a pump pushing air down (action) and receiving lift (reaction) in return! Obviously, it needs energy to do the job, but that’s another story.

How fast?

How fast should I fly? That's a burning question pilot starts to ask when he wants to get as far as possible as fast as possible. This issue is simple and complicated at the same time. The simplicity is in the fact, all the answers are in the polar curve. The complications come with the fact they are, in its raw form, valid only for a still air. To make some use of polar curve in a real life, we need a whole set of data about the air we are flying in: its both horizontal and vertical speed, direction of the airflow and its relation to our path. To obtain all this information we need a lot of hardware: vario-altimeter, GPS and an airspeed sensor. Processing the data fast enough to make them useful in real time is task for a serious computer. There are instruments on the market incorporating all the above. They are not cheap and require a lot of attention from the pilot during his flight. Before investing in one of these, an average recreational pilot should spend some time studying the polar curve of his machine and get some understanding of the principles involved. It can improve his flying dramatically. Polar curve is a graph showing the relation between airspeed speed and sink rate of a particular glider. It is of a roughly parabolic shape. The flatter and longer the curve is, the more efficient is the wing we are dealing with. The polar curve of a paraglider stands out from other flying machines like a sore thumb. It is short and looks like a camel's back. Yes, paraglider is a bit of a dog. A good reason for us to try to get the most of the little performance this contraption can offer.

Fig. 1 is is a typical polar of DHV 1 or low DHV 1-2 paraglider. Tangential line 'G' reveals the best glide point of the curve and the best glide angle. The gliding ratio in this case is 1:7. A line from '0' to any particular point of the curve reveals the glide angle for that point. Easy!
But, wait! All this is true in relation to the block of air we are flying in - or to the ground if the air is perfectly still. What about wind, lift and sink? If these conditions exist, we have to move the polar to get the ground-related data. It involves a bit of work. Print the picture above first on a normal paper. Then once more, on a transparency. Replace the polar (only on the transparency), if needed, by polar of your own glider. Now, let's say, you want to know how to get the best distance in 10k/h headwind and 2m/s sink. Move the transparent sheet so that the 'lift' line crosses -10k/h and the 'speed' line crosses -2m/s on the paper. Draw a tangential line line from the '0' on the paper to the polar on the transparency. Bingo! You have to fly at airspeed of 46 k/h. Your gliding ratio will be rather disappointing 1:2.5. Not too inspiring, but true... Play with this setup to simulate different situations. One surprise will follow another, I'm sure. Remember: read the ground-related data from the paper, the air-related ones from the transparency. Another point to realize is, the 'lift' and 'sink' numbers are not what your vario tells you (unless you have it set on 'net') and you have to compensate for the sink of the glider at any particular point of the polar. Have fun!

Interference Eliminator Code (CTCSS) – any good for us?

Radio communication in the PG and HG community is mostly conducted on the UHF CB – a public band with very few rules and regulations or even licenses (a dedicated commercial channel has been purchased by HGFA only recently and it will take time to start using it). With the availability of cheap UHF transceivers and lack of discipline among users this band is becoming less and less suitable for any serious use. If you scan all the 40 channels in the vicinity (up to about 100 km radius if you are in the air) of any major city, you hardly find one without a heavy traffic. As we'll see later, unless the interfering station is pretty close, it won’t really cut our communication off. But just the constant flood of garbage from the speaker makes it difficult to pick up those few sentences intended for us, and has adverse effects on our much needed concentration. One imbecile getting kicks from transmitting his call tone every 10 seconds can render the sound of your vario completely useless. No good at all.
There seems to be a light at the end of the tunnel: most of the new UHF transceivers are now equipped with Interference Eliminator Code (CTCSS). It is not a 100% substitute for a paid commercial frequency, but for our purposes it comes close enough. Let’s see, what it does.
In the CTCSS each of the 40 UHF channels is effectively divided into 38 Tone Squelch coded subchannels, giving about 1,500 choices. The "subchannels" on a particular channel vary only by a different low frequency tone (60-260 Hz) continuously transmitted on the squelch level. The receiving station is looking for a prticular frequency in this range while receiving on that channel. If the frequency is different or the tone missing completely, the receiving station interprets the signal as interference and supresses the audio autput.
To communicate, all parties have to be on the same channel and subchannel. Anybody using 'open' UHF channel can listen to the CTCSS coded channel, but can't interfere. The CTCSS can be switched off and the unit can be used as any other UHF radio. Unfortunately, CTCSS it is not really 100% reliable. Besides of the fact everybody on the particular open channel can hear what’s happening on all subchannels, a strong interference signal can also “capture” the receiving station, blocking the desired sender – similar way as if we are using an open channel. The difference is, if we have CTCSS, we won’t hear the interfering station and have a silence instead. A blessing in most cases. There is another advantage: as soon as the receiver is “locked” in the CTCSS coded signal, the uncoded one won’t block it even if the interference signal is stronger. So, it looks like this type of radios is an elegant solution for most of our situations.
The biggest problem is reaching an agreement everybody should use Tone Squelch coding. Another point to consider is the effect on another users of the UHF CB channels. With the use of CTCSS the whole character of the CB changes. With the use of open channels it was possible (in theory anyway) to rely on the courtesy of other users if you needed to free a particular channel urgently. Not any more. The user of an open channel can plead for a “breaker” as long as he wishes. If the party blocking his channel is using CTCSS - bad luck. The offending party simply can’t hear anything and it is blissfully unaware it is causing some distress. This is what we have to be aware off and realize, the use of UHF radio for emergency is a bit less suitable than before. True: there are 3 (No. 5, 35 and 11) channels in UHF CB assigned only for emergency use and the new transceivers have these 3 channels uncoded. So, you can transmit no worries – the question is, if anybody listens on the other end.
The conclusion is: the CTCSS feature is available, convenient, cheap and legal. People will use it if we like it or not. With the speed the technology is progressing, in a year or two a transceiver without CTCSS will be about of the same value as a turntable – if you still remember what it was. We won’t save the world if we stay out of it being worried we may block somebody else’s communication. If we don’t, other people will. For better understanding of what’s going on, see the attached diagram. It works on the assumption all stations are over a flat surface using the same transmitting power. In a situation like this the strength of the signal is purely an inverse function of distance. Our stations will be A and B. The rest will be an open channel interference stations. Without CTCSS both A and B stations will have to listen to all what all the other stations have to say. Both A and B can have their communication blocked by either station F or D. All other stations will have to listen to stations A and B, but only F and D can have their communication (with any other station) actually blocked by our broadcast. With the CTCSS our A and B will have exactly the same effect on all the other stations. However, A and B won’t hear any of them and stations F and D will block our communication only if they are transmitting already at the moment one of our station initiates its transmission.
I’d like to encourage clubs into adopting the policy of using CTCSS. It will become a necessity sooner or later and the longer it takes to make a decisive switch, the longer we’ll have communication problems. If a club once decides to take the plunge, it will put some pressure on its members. Some of them will have to replace they (obsolete anyway) radios with new ones. However, a suitable radio can now be obtained for about $100 – not a great deal, taking in account the cost of our sport on the whole. The larger clubs should probably purchase a couple of units for the use by visiting pilots and keep them until these radios become common enough. I can see it as one of the best investments in the safety of our sport we can make. While using the code, we have to realize we do can block or make unpleasant somebody’s communication without knowing it. It should be mandatory to check the local traffic first, especially in the rural areas. If we know the local farmers are using a particular channel, let’s get on a different one before we even start. It may be a good idea to check the channel for other users periodically by using the “monitor” button. Close to big cities – I don’t think much courtesy is needed. It’s the law of the jungle there and the stronger one wins. Most of the users occupying the airwaves there don’t use UHF for any serious purpose. It is easy for them to swap the channels if we should become nuisance for them. It is not so easy for us; first, being a large group, second due to the fact we are in the air busy with other things than fiddling with the radio.

Comfy enough?

In our sport we concentrate heavily on the safety of our equipment – for a good reason. Anything going wrong with it can hurt. Comfort seems to be a secondary issue and however we find flying in comfort more pleasant; we may not pay enough attention to small details. Sometimes, it may turn against us in a nasty way – if we like it or not, comfort and safety are closely connected. Example - how many times you lost direction, almost running into somebody while trying to adjust your harness? Never? Well, either you are a prodigy or you are fooling yourself.
Once in the air, you want to have everything at the right place, accessible and comfy. You don’t want anything restricting your movements and visibility or having to perform contortionist exercise to get to your radio or drink. Some people are getting more annoyed by discomfort than other. I, unfortunately, belong to the group of people who have to have everything a 100% and wouldn’t stop until they have it. A zipper on my flight suit scratching my neck can spoil my day to the point I rather land if I can’t fix it. Some of these nuisances can be detected during a pre-flight check. Some you can find out only when you are airborne and it is too late to do anything with it for the duration of the flight. In that case it is important to take a mental note of it and make a firm resolution: “I will rectify that bloody problem before my next flight.” I admit I sometimes don’t keep that promise given to myself – just to regret it bitterly later. Often the excuses can be: “It is not going to happen again.” For instance, the cable to my headset kept getting caught between my body and the flightdeck every time I got in a landing position in my harness. Not a major problem – until you find out you can’t lift your head to look upwards. Every time it happened, I was convincing myself it was an odd chance not likely to be repeated. And indeed, whenever I tried to achieve it under simulated conditions with the harness suspended from a beam, the cable ran free every single time. Obviously, I forgot a small detail – the relative wind. Anyway, I allowed this nuisance to spoil my whole season before the cable finally broke. Replacing it with one 10cm shorter took me 15 minutes… Problem with any cables getting under tension in some situations should be solved ASAP for the sake of the cables and the gadgets they connect as well. Something is going to snap eventually causing problems during the flight and incur some expenses later.
Besides of the above mentioned cables the most common sources of discomfort and distraction are – besides of ill fitting underpants (very serious):
Poorly fitted or designed instrument panel. If you have to fiddle with it each time you want to look at your instruments, it is time to do something about it.
Radio at a place you can’t see or operate it comfortably. Especially if you have to reach somewhere to press PTT, the radio can bring more trouble than benefits.
Camera - a cool pilot is not complete without one. Just getting it from your pocket in flight is often source of a major distress, not to mention taking pictures and then trying to put the camera back. If you want to use camera, make sure you are well organized. A helmet-mounted camera with a remote control of a sort is one of the best solutions. Beware of the safety issues concerning the helmet though.
Ill fitting helmet. Helmet should fit snugly without moving around on your head or, on the other hand, causing headaches by being too small.
Zipper scratching your neck. I find this one especially distractive. A neck warmer is not only good for your health, but it will also deal with this nuisance.
Ill fitting gloves. If too big, they make operating fiddly bits difficult. Too small ones will cause numbness of your fingers after a short while.
Speedbar you can’t get to without using our hands. If you have one of these, get yourself a proper one.
Mobile phone. Take it with you, by all means, and have it somewhere you can reach it without getting off the harness. But: have it switched off to eliminate the temptation answering an incoming call during flight. No call is likely to be worth the trouble.
Harness you have adjust after takeoff. In general, ANYTHING you have to adjust after takeoff. Also, if the harness has the habit of catching cables or lanyards of your instruments, camera etc on its buckles needs your urgent attention. I’m sure, you can add a few items to the list yourself. Do not underestimate these “trivial” details. They can become big issues in some situations and it is not worth the risk trying to cope with them. Get comfy – get safe!

Drag Rocket!

For simplicity sake, the weight of the canopy has been omitted throughout the article.The load produced by the weight of the wing acts in a different way than the main (pilot induced) load and can cause changes in AoA. As the weight of the canopy represents only 5% of the weight of the whole system, these changes are negligible in the situations covered by this article. They will have to be taken in account if an extreme drag is applied (deploying reserve).

An interesting article has been published in the Cross Country magazine recently. It was dealing with problems of drag caused by PG pilot and his harness. This part caught the most attention and it is still being discussed in some forums at the Internet: drag at the pilot’s end is not necessarily a bad thing. It can actually cause an increase of airspeed! No, it wasn’t an April issue. Follow the logics behind it as presented: We all know, when you want to make a glider fly faster, you simply increase its negative pitch – point its nose down – and gravity will do the rest. So, if you increase drag at the pilot’s end, you effectively apply a torque to the system and it will rotate. The system will tilt forward until a new equilibrium between the pilot’s drag and his pendulum is reached. The pitch of the wing will become more negative and – BINGO. We’ll fly faster! Or, will we?
It is interesting how many principles from a fixed wing planes can’t be applied to an aircraft with a strong pendular stability such as a paraglider. To see why, we have to establish some less obvious (or less known) facts first: The first thing we have to realize, paraglider is not being loaded directly by the weight of the pilot. Our wing is being loaded by a force in the direction of the lines (direction best visible on the risers just above hang points). This force is a vector of pilot’s weight and his drag. It is always slanted forward against horizontal, as a result of the pilot’s drag.
Again, there were lengthy discussions on some forums, if the drag adds to the load or reduce it. To make it obvious, try to apply an extremely high drag – a large drogue chute, for instance. It is easy to imagine the pilot being suspended now between the chute and the wing, its weight divided between these two. A simple vector diagram confirms our suspicion: the force on the lines is ALWAYS lower than pilot’s weight.
Another fact, rather hard to absorb, is: the angle of attack (AoA) of a paraglider is given exclusively by the trim of the glider – by the length of the respective lines. It is vital to absorb this fact as it is the key for understanding to virtually anything in PG flight mechanics. Doesn’t matter if the PG is in a steady flight, being deployed or towed: the direction of the “lines” force relative to the canopy and thus AoA of the glider remains the same - As long as we don’t change the length of some of the lines (applying brakes or speed system), that is. The magnitude of the force may change, but not its direction relative to the canopy. Still, we have to understand, the ONLY factor determining the airspeed of a given wing, flying at a given AoA, is its load: the bigger load, (or, more accurately, the square root of load), the higher airspeed and vice versa. Now we are ready for the close: we add drag at the pilot’s end. The glider pitches forward. At the same time the glide path (L/D) becomes steeper. As result, AoA stays the same (we know it can’t change anyway). The added drag reduces the force on the lines thus the load of the wing. Now we have the same wing, flying at the same AoA, with a smaller load. The net result: it will be SLOWER. Period.
If you don’t wont to bother about all the stuff above, just follow my intuitive reaction on reading the “Drag Rocket” (as I call it) theory: “So, if hanging in a strong wind just above the launch, going nowhere, I should ask somebody: ‘please, pull me back a bit, I need to penetrate!’ And, I idiot, always ask people to push me forward…” By the way, pushing is not the best solution either. A forward force in the direction of glide path (at pilot’s level) also causes reduction of load and consequently reduction of airspeed – but the glider will be climbing in this case. If you ever tried, you know! A vector diagram would show you why. The right words in this situation are actually “Pull me down! ( help me to load the glider more)".
The gist of this whole article: if you found somewhere a piece of advice suggesting to stand up in you harness (to increase drag) if you are in the danger of being blown back, think twice. It may work (to a degree) in some special cases while flying a very heavy glider, probably made from a wet wool. In that case the load caused by the weight of the canopy may become significant enough to cause a miniscule increase of speed.

Myths and Physics

We’ve established already that in the world of aviation we rarely get what we see. In an environment like this, it is no surprise, a number of myths or misconceptions appears and often holds for many years. Some of them are harmless other can cause serious problems or even accidents in some situations. We have to admit there is still a lot to be discovered in aeronautics and there are parts nobody fully understands yet. On the other hand: it would be foolish to believe the mechanics of flight has some exemptions from the general laws of physics. For this reason there is no such a thing as a “compression zone” on the top of a hill. By using this term we are contradicting a lifetime work of an 18th century physicist, Daniel Bernouli. He discovered the pressure exerted by fluid is in reverse proportion to its speed. A hill causes a virtual narrowing of the cross section available for airflow, forcing it to move faster. As a net result the pressure on the top of a hill is lower!
Very much the same mistake are making people, trying to explain Ground Effect as a result of “air compressing between wing and the ground”. The exact opposite applies! A venturi effect would actually cause the wing being “sucked” towards the ground – if it ever comes close enough. Ground effect is caused by blocking off wingtip vortexes.
“A less loaded paraglider will stall easier than a more loaded one…” A proper interpretation is needed here. Your glider will stall at the same position of brakes, regardless of its load. The truth of the initial statement will appear only if we apply it to a turbulent air. The less loaded wing will be slower in both, horizontal and vertical direction. Sudden changes in airflow will more easily change its angle of attack and stall will be more likely to occur.
“If we overload a wing, it will stall.” Not true. Stall is a result of an excessive angle of attack. In a paraglider the angle of attack is given by the trim and can be increased by pulling on brakes. Again, angle of attack will remain the same regardless of load. If we apply more load the sink rate will increase. But the forward speed will immediately increase by the same rate and angle of attack will remain the same. We can get some problems in extreme cases, where the overloading approaches the limits of structural integrity. Nothing changes on the above principle, but the changes in the shape of the wing (stretching of lines etc.) can change angle of attack.
“The stall speed (or any other speed) of this wing is xxx kph.” A meaningless number. This statement is valid only if a load is specified for that particular instance. Wing can stall at any speed – in dynamic situations even at very high speed – if the critical angle of attack is reached. It is true: within the weight range the differences in speed are rather insignificant. But we have to realize a load is not always only the static force exerted by the total weight.
“Weight shifting in the direction of turn will make turning more efficient.” This belief survived about 2 decades and only the birth of Acro Paragliding helped to dismiss it. Acro pilots need to turn more efficiently and safely than CX pilots. They discovered soon, the accepted technique doesn’t work. If you look at the mechanics of it, you’ll easily understand why: In a turn, you want the outer wing to fly faster than the inner one. In order to make it fly faster, you need to put more load on it. Furthermore, you want to maintain the correct angle of attack. If you reduce the load at a given speed, angle of attack will get lower and the wing will eventually tuck. The inner wing, on the contrary, has to fly slower and you can guess: loading it more doesn’t exactly help the cause. We also want it to stall as late (at as low speed) as possible. A funny thing… the higher the loading, the higher the stall speed is. So, now: why, for god’s sake, should you transfer more weight to the inner wing? Possibly to bank the wing into the turn... Do you really think you can bank (to any significant degree) a wing with a strong pendular stability by weightshifting? If there is no any other force but gravity (straight flight), you will aways hang straigh down, wighshifting or not. Bank will come as result of the turn (certifugical force), it will not cause it.
Despite of the mechanics of it was clear to me from the day one, it took me almost 2 years to learn the new technique and find it perfectly natural. The reason it took so long: I believe we have some instincts inherited from riding a motorbike. Takes a while to get over it. At this stage I apply more weight in the direction of the turn only for a brief period needed to initiate the turn and associated bank. Why it is needed and why it works at all is a bit of a puzzle. I discussed this phenomenon with some highly involved people. Nobody was able to give me a full explanation. The whole thing seems to be several factors working together (or against each other). Changes in the shape of the wing seem to be one of them, but I wouldn’t try to elaborate on this problem myself. The final result depends on the proportion of each of the factors involved and it may not be the same with different wings and in different situations. Anyway – from the point of initiation of the turn I transfer my weight immediately to the outside wing while braking on the inside – and bingo: everything works exactly the way the theory says. A word of warning: Timing is an important part of the equosion and it may not work for you until you master it properly. However, when you once do it right, you'll recognize it right away. Once having it right you can get results you never dreamed about before. Applied during a spiral you go down more than 20m/s during the second turn. In a wingover you’ll find yourself above the canopy before you know it. Do NOT use this technique for any kind of radical maneuvers unless under supervision of an instructor and in a safe environment (above water). For improving the efficiency of your “normal” turns however, it is perfectly safe. Tuck of the outside wing will become a history and negative spin will be harder to induce. Do not push it too far though and discuss the matter with your favourite instructor before trying at home.
“The number of collapses and their severity is directly proportional to the strength of thermals.” Not true. Wing has no idea how fast the vertical movements of the air are. It will fly exactly the same way in a parcel of air rising 20m/s or falling at the same rate. It does take notice of the speed of the changes. Acceleration will cause a change of its loading (“F=m * a” - where “F”[N] represents the load, “m”[kg] the mass of the aircraft and “a”[m/s^] acceleration). If the change of vertical speed is fast the loading will change dramatically. Just an example: if you enter a 10 m/s thermal within one second, the wing loading will DOUBLE during this period of time. Due to the pendulum effect the results in a paraglider are especially unpleasant. However, as soon as the wing adopts the new ground related vertical speed, its load and resulting airspeed (both vertical and horizontal) will become the same as in a still air. The problem is not in the absolute speed of the air movements. It is in the horizontal distribution of them and related speed of the changes applied to the glider. Especially if one part of your wing finds itself in an air moving vertically only a fraction of m/s faster than another, the change of angle of attack will cause a serious tuck or collapse. Flying in broken thermals of speed of 1m/s or so would become a frightening experience, while entering a 10m/s boomer can be a pure pleasure if the transition is slow. In the next issue we will have a closer look at the units and terms we are using to measure and calculate some of the aspects of our flying.

Flying and optical illusions 

Most of our experience at perceiving the world around us comes from living as earthlings. So, we know that “down” is towards the earth, “up” is towards the sky “forwards” “backwards” and “sidewise” is always towards the horizon. As soon as we leave the earth surface and apply a bit of dynamics, all this can change dramatically and all our previous experience becomes a burden. If you keep relying on visual references like horizon or the ground in dynamic situations, you’ll come to grief sooner or later. It is hard to overcome our natural instincts and it may take a long time of conscious effort before pilot stops judging angle of attack (for instance) from the position of the wing to the horizon. Towing is the best example, how deceiving this reference can be.
Two interesting, and never-ending, threads popped up on the famous Xtreme Big Air discussion group. Both of them became so complicated, because some of the participants refused to accept the above. One Scottish gentleman has developed a completely new theory of a paragliding flight based on his observation that wing appears to fly in front of the pilot. As lines can transfer only “pull”, not a “push”, his conclusion was simple: Wing is producing a force (a component of lift) that pulls the pilot thru the air. He claimed, he’s discovered a 30 years old mistake in the theory of flight - causing a ferocious verbal battle between his followers and opponents. He fell in a simple optical illusion trap - using horizon for a reference. He watched the situation from the human perspective. Paraglider is different from a human - it can’t see. Our wing senses only two aspects of the surrounding world: the pull on the lines (it is NOT vertical) and the relative airflow (glide path) that is NOT horizontal. Any other concepts, like the horizon, are entirely foreign to it and wing behaves only in relation to the two references above.
So, if we look at our vector diagram from the perspective of the wing (using the glide path as a main reference), we see the PILOT is IN FRONT of the wing. A component of gravitation force applied to the pilot pulls the wing forward generating the required speed. For a better understanding see caption 1.

Effect of the weight of the wing and drag on the lines were omitted as negligible for our purpose. Pilot’s drag is responsible for the slight visible declination of the lines from the vertical. A reaction for this drag is the pendulum effect (not drawn) as the pilot is continuously trying to swing directly under the wing - so, he is being pulled by it after all! Well, in a sense, yes. Depends on the frame of reference we are using - either conclusion is correct. But the "prime mover" is always gravity.
Another mayhem on the forum was triggered by somebody’s query: “Can wing stall while shooting forward of the pilot?” A seemingly stupid question: We all know, wing will stall while well behind the pilot. Or does it? The first thing to take in account is, it is not always the movement of the wing that causes the apparent change of mutual position of the wing and pilot. It is more often the swinging motion of the pilot (the surrounding air has to be used as a reference to get the right picture) in relation to an almost steady wing that creates this impression. We are getting sucked into perceiving this as movements of the wing as we use the pilot’s position as a fixed observation point. The second aspect: go back to the beginning of this article and forget the horizon. And you have the answer. Yes, you can stall your wing while it is “shooting in front of you” if you apply enough brakes - exactly the same way as if the wing is above or behind you.

 

 

           
  Capt. 2                                                       Capt. 3

Look at caption 2. Everything fits in the picture, as you know it. Wing stalling behind the pilot – but only before you look at caption 3 and realize caption 2 is only an inverted crop from caption 3…  The story of this picture (I talked to the pilot after taking it): This pilot decided to abort a tumble (felt like he didn’t have enough speed) and stalled the wing by applying brakes while the lines were approx. 45 dg up. But, there was plenty of speed after all and the wing-pilot system kept rotating another 45 dg, almost causing the pilot falling in the canopy. He missed it by inches… So, beware: In the air things are rarely exactly as you can see them!

Marinated Electronics

We all like flying. Unfortunately, sometimes things do not go exactly as planed and we end up with a totally different activity: bush walking or swimming, for instance. Landing in the water, Needles to say, is a health hazard. But even such an innocent event like tripping on a beach landing and rolling in an ankle-deep puddle can be very painful - for your pocket. An average hang glider or paraglider pilot carries at least $1,000 worth of electronic equipment on him nowadays. These things do not need much salt to be rendered worthless; as little as a few drops of a sea water and that is it. I've seen enough of these. My swimming pool served as a regular first aid for canopies of those pilots who didn't quite make it on the east coast. Unfortunately, often by the time they arrive, it is far too late for their high tech gadgets. Knowing what to do after flooding your toys by that solution of sodium chloride can save you a fortune - but not always. The little factor called luck is always needed here as well. The actions described below are acts of desperation, but they are worthy of trying. Once the item has been in salt water, there is very little left for you to spoil...
The most important part just after the flooding is the speed by which you remove the batteries. Do not waste time by switching the gadget off. Not only it is useless (salt water is highly conductive and will bridge the contacts regardless), but you may even destroy the switch! And worse: if the instrument case is almost watertight and there is a couple of minutes delay, the electrolytic process will fill it with an explosive mixture of hydrogen and oxygen. Your action will produce the last important ingredient for every good blast: A spark.
The first objective is to REMOVE the batteries. In fact, you often have only a few seconds to perform this task and still have some chance of success. All the following effort will help only if you were fast enough on this primary task! The batteries safely out, take the unfortunate gadget and drop it unceremoniously in a bucket of fresh water. Leave it there for some 15 minutes, stirring occasionally. Even if it doesn't help, at least you'll attract a crowd of spectators and you can charge some moderate fee for the show. Then you can relax a bit. Drive to the nearest petrol station and buy a couple of litres of distilled water, by which you replace the existing brine. From now on the treatment will vary for each different kind of equipment. Devices with some mechanical and optical components (cameras) shall be left in the water, the container filled to the top, made airtight and delivered ASAP to a specialized service facility. Look for people specialized in drowned equipment - they advertise in SCUBA diving magazines. A regular service technician might send you, well, somewhere else. If the camera was a modern SLR (the past tense here is fully justified), don't bother. Give it to your 3-year-old. If you get a smile in return, smile too. You've made a bargain! With radio gear, varios and similar you have a good chance even without professional help. Leave the items the distilled water for about 2 hours and stir a few times. After that, put them briefly in methylated spirits, blow off with a low pressure compressed air and place them in an oven (not microwave!) heated to 50 dg C for about 4 hours. After cooling down, spray all switches, contacts, potentiometers and metal parts by a water displacing lubricating agent, like CRC2/26. Keep this stuff well away from RF parts (especially varicaps) pressure sensors and soft push buttons. It can cause some problems there.
Now you are ready for the moment of the truth. In most cases everything will work like a chime! Often only a speaker, with a paper diaphragm, suffers and has to be replaced. A very cheap experience indeed! If it doesn't work at all, see professionals.
The rechargeable sealed battery packs need special attention too. Take the word "sealed" with reservation. The casing will positively let the salt water in, SEALING it perfectly inside - hence the name. Such a pack will become a serious fire hazard and it will fail shortly, often with spectacular sound and light effects. To give you some idea what it can do, I can show you (for a small fee) one of my old radios. To eliminate this time-bomb factor, DISCHARGE THE PACK THOROUGHLY ASAP through an automotive globe or a similar load. Never shorten it! Until it is completely flat, wear glasses and gloves as it can explode at any moment. Then break it open, wash and dry thoroughly in similar fashion as described above and glue it back together. If you do not want to bother with the above, GET RID OF IT! Beware; none of the drowned items is as healthy as it looks now: DO NOT FULLY TRUST THEM AGAIN! The most effective, but highly unethical solution is to sell them quickly to an unsuspecting enthusiastic. If you want to keep them, replace all insulated wires inside (usually, there are not many of them) within about a month. The salt water seeped under the insulation and there is no way of getting it out. After powering the gadget again, it will start eating the core at a surprising speed. The terminals or soldered ends will usually fall off within a few weeks... After the wires exchange you can expect ALMOST the original reliability.
Finally, for god's sake, do not fall for some much faster and simpler treatments, unless you want to make sure nobody will be able to fix your gear ever again! One of the recipes circulating here is, to wash the items in VINEGAR, which NEUTRALIZES!!! the see water! Mere spraying them with some moisture-displacing agent is at least harmless, but equally useless. And the last advice: if you are being offered a second hand electronic device, look for the telltale greenish-blue deposits of copper chloride around the positive terminals. If these are present, politely decline the offer, even if it looks like a deal of the century!

Water & paragliders

Water and paragliders - DO NOT MIX. Sounds obvious. Nobody will put his $4,000+ toy in the drink by purpose. Just the associated health hazard should put you off well enough. But your glider can get wet by some different means as well. Rain for instance. Or, flying at the coast in close to 100% relative humidity and with a high lapse rate. After a descent from mere 100m of altitude, in the warmer air the moisture will condensate on the colder material rendering it DRIPPING wet. Salt water is the worst enemy - even when paragliders are made from materials resilient to the chemistry of seawater. Sharp salt crystals grinding the microscopic fibbers of the lines is the last thing you need. It will keep absorbing moisture as well. So, if it gets in the bay, SOAK the whole glider thoroughly in fresh water and let it dry SLOWLY. Are you out of the woods? Far from that. The fabric and the cores of the lines will cope well. The main problem is the protective shielding of your lines. Invariably, it will shrink - sometimes substantially so. As all the lines will shrink at the same rate, not a big issue - yet. It will show only after a few flights. The coating will need relatively small load to get back to normal. In the case of A and B lines this load will be probably reached after the first spiral or a tow. The rest will remain shortened. Result: a higher angle of attack with all the consequences. Treatment: stretch the rest of the lines by applying about a quarter of the breaking load to all lines, one by one. The result is not guarantied though. Check the length of each line against the manufacturer's specifications. If there are differences of more than few millimeters, changing of the whole set is the answer. My sympathy... not cheap, but better safe than sorry!

Barometric Vario-altimeters – how they work and what they do

Generally known as “varios” these instruments went a long way during the last 15 or so years. From simple mechanical pressure gauges to the modern flight computers they became essential parts of the paragliding equipment. Varios use changes of air pressure with altitude to monitor height and the rate of lift or sink. This data is conveyed to the pilot via LCD or fed to a computer for further processing. Bear in mind, the air pressure changes quite dramatically with weather conditions and a frequent calibration is essential for accuracy. To get some idea: at sea level 1 Hp corresponds roughly 8 m of height. This ratio increases rapidly with altitude.
The heart of an electronic vario is a pressure sensor. It is usually a capacitor where the plates bend with air pressure, changing its capacity. This capacitor is a part of an oscillator where the changes of capacity control the output frequency – and that is what we measure. A sophisticated, usually software-driven circuitry process’ this signal and gives us the information usually in both digital and analog form, often accompanied by an acoustic signal as well. The peaks are stored in memory for a later basic flight evaluation. Most of the entry-level instruments now also include thermometer and watch/timer.
Used together with GPS (not connected to it) it tells to a typical recreational pilot just about all what he needs to know about his flight. The more sophisticated instruments are using the gathered data for further processing. This enables us to get information like wind speed and direction, speed to fly, height over the next waypoint etc. While choosing a vario to suit our purposes we have to asses how effective this features are and how much we really need them. Remember: you have to pay for them. To start with: due to a low speed and efficiency of paragliders the value of some of the more sophisticated functions is rather questionable. Even with the most elaborated instruments the pilot has to apply a lot of skills to filter off “noise” from useful information. Some of the best pilots in the world are still flying with very basic equipment achieving excellent results. However, as the technology is improving and getting more accessible, flying by the seat of one’s pants is getting increasingly rare.
Another point to stress: the “medium range” of instruments (in the Digifly range represented by the Archimede Plus) has some limitations. For the advanced functions information about the horizontal movements of the air is needed. While there is no input from GPS (external or integrated) this information has to be entered by pilot before the flight. Any changes of these conditions render all the related calculations inaccurate at the best. Any expensive vario offering glide ratio based functions without GPS is a poor value for money. Go for an instrument like the Archimede Plus only if you can justify paying something extra for a barograph - the most useful of extra features.
Then we are left with either the basic type (Archimede) or, if needed, the impressive flight computer (Cartesio Plus). The latter have an impressive price tags attached as well. Most manufacturers make instruments where GPS is integrated in the vario now. The compactness of such an instrument (Leonardo) is its advantage. The Cartesio style (external GPS), on the other hand, offers more data at glance without having to scroll between them (two displays) and saves you some money on the purchase price if you have a GPS already. It also offers an important backup for the basic functions if one of the instruments fails or runs out of battery power.
To get a full use of the computer, another piece of hardware is needed: an Airspeed Sensor. Computer uses the airspeed data to determine the point of polar curve the wing is flying at any given moment. Needles to say, the correct polar curve has to be known to the computer as well. In a PG application the position of the sensor presents a huge problem. Taking in account the Venturi effect around pilot’s body and pendulum movements of the pilot, the ideal place would be somewhere in the lines near the wing. This brings out serious safety issues and I strongly advise against this solution. I mounted it just above the Mailons eventually, but it still leaves me with the pendular movements problem. This has to be taken in account every time I evaluate the info received. A lot of practice is needed for this one. Any software solution to this problem proved to be ineffective in practice so far.
So, what an instrument like the Leonardo or Cartesio Plus can do for you? Besides of what virtually any other vario tells you (altitude, sink/lift, temperature etc.) Leonardo has a lot of other bells and whistles. One of the most important features is a detailed 3D recording of your flight including vario data and airspeed. The tracklog is an excellent tool to analyze your flight and identify any mistakes – after the flight, that is. Software like CompeGPS can project your flight into 2 or 3D map and let you re-play it with an incredible reality. In flight Graviter gives you visual and acoustic information about the proximity and validation of waypoint (adjustable FAI cylinders). That’s just for a starter. The other functions include:
Auto Start recording – anybody who ever lost a comp because he forgot to switch recording on knows where the value of this feature is. Leonardo starts recording automatically when it detects certain ground speed and change of altitude at the same time.
Wind speed and direction – an invaluable information for safety and evaluating your chances to reach your goal.
This is further refined by the Speed To Fly function. A set of arrows advises you to fly either faster or slower for achieving the best ground-related glide ratio. To evaluate your chances of arriving at a preset height above the next waypoint the actual (custom averaged) gliding ratio is being constantly displayed, together with the gliding ratio needed for that task. It can be replaced by a display of the height you will arrive above the next waypoint if flying with the current gliding ratio. Extremely useful in long glides.
McCready Function should help with reaching the next waypoint at the shortest possible time. I found it virtually useless (for paragliders anyway) though, as it requires a lot of guestimated input at each occasion. This function has more use for sailplanes or hanggliders.
The Total Energy Compensation function helps you to ignore false lift generated by washing off excessive speed. A bit of an overshot for a paraglider – but, yes – it works.
Netto Vario is an option for monitoring vertical movements of the air instead of movements of the glider. Some pilots find it more useful than normal vario. Again, it needs the correct polar curve for the machine you are flying.
Stall point warning – no of much use in the PG application. The best you can do with it is to switch it off to prevent driving you mad due to false low airspeed reading during swings back.
Air speed display – flying a paraglider you know your speed from the position of the brakes anyway. This function has its use only while checking if your wing characteristic hasn’t changed after taking it for a swim or a tree landing. There is also a special recorder setting for recording polar curves.
The list can go on – if you are a serious XC or comp pilot, it may be worth considering an instrument like this. The latest hit is a pocket computer using CompeGPS software linked to GPS. It puts you on the map in real time and gives you all the above functions as well. It shows your path as you fly, marks the thermals helping you to find them if you fall out and much more. Very little left for imagination. A scary stuff… Only autopilot can beat this. I wouldn’t be surprised if somebody is working on it already!

Mysteries of UHF radios unraveled

I followed with interest the discussions concerning UHF 2 way radios on Topica. As there are lots of myths surrounding these gadgets, I decided to shed some light on the subject. UHF CB stands for Ultra High Frequency Citizen Band radio. This band (around 470 MHz) is assigned by the Department of Transport and Communication to non-licensed radio operators and can be used by anybody who can put his hands on an appropriate transceiver. There are simple rules to follow, which, however, are hard to impose. One of them is 90% of the transmitting has to be a human voice. It is also prohibited to re-transmit any broadcast or recording except by approved repeaters on duplex (more below). The ban of foul language and swearing has been lifted a few years ago - so, help yourself. A plain courtesy dictates not to block channels deliberately and allow other users to communicate. After all, there are 40 channels in that band. The only ones subject to some restrictions are Ch. 5 and 11, reserved for emergencies only. Ch 22 and 23 are reserved for telemetric data transfer. Channel 40 is being dominated (but not licensed to) by truckies. Do not let your children listen to this one.
Skyhigh club is using Ch. 16 but be aware: This channel is as public as any other in the CB system. More privacy can be achieved by using CTCSS (tone squelch) interference elimination. Skyhigh is using tone squelch 97.7 Hz to achieve this objective now. This frequency can be listed under different subchannel numbers depending on the manufacturer. The most used: Icom and Motorola - subchannel 11; Feidaxin - subchannel 12.
The maximum transmitting power is restricted by law to 5 W. A serious power in fact, as it allows reaching distances of some 200 km in ideal conditions - or even more using special antennas. The range is a tricky subject, as UHF signal is in the habit of traveling in a straight line, bending only slightly by the earth magnetic field. The result is, two radios, held at the head level can communicate even in a perfectly flat terrain, only over some 10 km. Then the signal gets blocked by the earth's curvature. This problem can be, off course, fixed by gaining elevation over the terrain. Even a small elevation can increase the distance dramatically. Gets worse with any solid obstacles in the way - hills, buildings or vegetation. These block the signal very effectively and any conceivable increase in transmitting power is futile.
Special cases are conductive objects of 1/4 wavelength long. These act as simple quarter wave antennas, absorbing and weakening the signal even if they are not directly in its path. Gum leaves fit the bill almost perfectly.
Knowing the above is a part of the answer on the "Should I have 300mW or the full 5W radio?" $5,000,0000 question. True, in ideal conditions - at the distances we normally communicate - there is no difference worth to mention and the smallest hill will block 5W as reliably as 300mW. As 1W radio has about 60% of the range of a 5W one, the expensive 5W units are hard to justify. However, if the extra power shouldn't cost you much, go for it. The more power, the better - no doubts.
Antennas are another story. Do not try to improve you signal by simply lengthening the antenna. You'll be tampering with a finely tuned device, making things only worse. The simplest antenna is a piece of straight wire exactly 1/4 of wavelength long. It transmits - or receives - signals from all directions except of sharp-angle cones in the directions of the tip and the base of the antenna. For our purposes it works fine. The performance can be improved by an antenna with a gain. There is, in fact, no gain whatsoever. These antennas only direct signal in certain directions, reducing emission in the others. Typically, they widen the angle of the above-mentioned "Cones of Silence", strengthening the signal around the rod. This is making the antenna more sensitive to its position as well. With any rod-type antenna the area in the direction of the antenna tip or base has virtually no coverage. The worst result is achieved by pointing the tip or the base of the antenna to the other station. The position of antenna is important for other reason as well. Our radio signal is polarized. It means two communicating antennas work the best if they are parallel. Any deviation of this positioning will significantly reduce their effectiveness. The worst results (about 20% effectiveness) will be achieved if the communicating antennas will be poised 90 dg one to another. As the UHF CB signal is, by agreement, vertically polarized, try to keep your antenna as close to the vertical position as possible.
Earlier on, I mentioned repeaters. We seem to stubbornly ignore these devices, despite of their ability to let us talk over the hills. Repeaters on CB are privately owned, but a part of the license agreement is, they have to be available for a public use. They can be found on channels 1-8 and work this way: If you switch you radio on "duplex" and use, let say, Ch. 4, your radio will transmit on Ch. 4 + 30, i.e. 34. The repeater will receive it and re-transmit it on Ch. 4. Another transceiver switched on either "duplex" or "simplex" Ch. 4 (or 34) can receive that signal. If the repeater is on a top of a hill - and that is where they mostly are - the coverage can be enormous. To find out if a particular area is covered by a repeater is simple. Switch you radio on "duplex". Select channel 1 and press the PTT button momentarily. If you, immediately afterwards, receive a burst of static-like noise, it is the repeater. If not, try the next channels up to 8. Beware: the louder the response is, the weaker is the repeater signal. A good, strong signal induces a barely audible response! Repeaters also introduce themselves in certain intervals by Morse-coded signals, for instance "M 3" means Melbourne, Ch. 3. By the way: this particular one situated somewhere near the Police Academy is virtually useless as it is being continually misused by all kind of lunatics. But the ones in country areas - where we need them the most - do not suffer from this problem that often.
Still - a word about courtesy. In situations where our channel 16 is busy - like the club's fly-ins, use this channel only for information of either of general interest or short messages to a particular person. If the conversation is likely to be more than a few sentences long, it should look like this: "A to B, A to B. Go to Channel 12 (or whichever), confirm." After receiving the confirmation go on that channel and discuss your dinner arrangement for as long as you wish. Needles to say, your channel selector has to be accessible while in flight. This feature prevents you disturbing other users and also stops you from transmittig message that may not be received.
While using CTCSS it is a good idea to check if the channel is not busy by pressing the "monitor" button before transmitting. Some radios can be programmed to block transmitting if the channel is not free.
Another spot of annoyance are handheld radios without a proper headset or a wrongly positioned microphone. Nothing can beat VOX (voice activated microphone) on the scale of annoyance. Never use it! Do not be surprised, when you get told off. Rig your radio properly and TEST IT before using it at a flying site. A proper headset with a finger-mounted PTT is the way to go. Hand-held speakerphones not only compromise safety but they also produce a lot of wind noise.
A blocked PTT button can spoil a whole day to a whole bunch of pilots. It can happen to anybody, any time. But the problem shouldn't last long. If you can't hear anything for 5 minutes or so, it is time to check your "Transmit" LED. If it is on, switch the radio off immediately and leave it that way until you fix the problem. It is highly recommended to use only radios with TOT feature. These will stop transmitting after a preset short period of time. The most educating example of the consequences of ignoring this advice would that tandem pilot in Bright a few years ago. He accidentally transmitted his one hour presentation intended for the ears of his female passenger only. The whole flying fraternity was glued to Ch. 22!
Also, while in the air and communicating only over a few kilometers distance, switch your radio on "Low Power". Note, this will affect only your transmitting range. Reception will not be affected. This will make you less obnoxious to not participating distant stations but also SUBSTANTIALLY save your batteries. You are also less likely to attract attention of some imbecile who is taking pleasure in blocking other people's communication. The world is full of these.
Orthodox radio geeks are using their own language. We are not obliged to follow but it comes handy to know at least the basic:
Affirmative - Yes
Negative - No
Roger - Received, understand
Say again - Repeat
A copy B, A copy B - A, please, answer B
Go ahead, B - Answer to the above
Radio check - Is my radio working?
You are working - answer to the above
Breaker - Sorry to interrupt you conversation, I have something important to say
Go ahead, breaker - answer to the above (more common is "Get f%&cked", but one can always try)
Over - end of my transmitting, but I'm still listening
Over and Out - end of my transmitting, switching off.
And the most important ones - NEVER use these without a sufficient reason and NEVER interrupt these transmittings:
Mayday Mayday Mayday - My life is in danger. Details will follow.
SOS - obsolete and rarely used nowadays is the equivivalent of the above. Used in the past for its easy to remeber Morse Code shape.
Pan Pan Pan - Somebody's life is in danger. Details will follow.
Securite Securite Securite - Important message concerning safety in general will follow.
I hope you found this article useful and we'll see some improvement in our radio communication. We need it.

Does size matter?

We'll be talking about flying, so the answer won't be as clear as you might expect, girls. Take all the following with a grain of salt as in this field very few things are as black & white as they might appear in other areas. Also, please, fill in the usual "(she)"; after every "he" for yourself as I'm tired of it. Why aren't all languages as accurate as Czech?
One of the crucial questions while buying a new wing is: "What size?" Pilot often finds himself in a situation, when he has to choose between being either on the top or at the bottom of the weight range. NOW WHAT!? There are a few aspects we have to consider. Stability: The more loaded wing will collapse less easily - on the other hand - when it does, things will be happening more quickly and the height loss will be more substantial. Pretty well balanced situation - toss a coin and then adjust your flying to the situation :-).
Gliding Ratio (efficiency): In the general mechanics of flight the answer is clear. It will stay the same. But paraglider, the nightmare of every aeronautic engineer, has its own peculiarity; While the drag and lift of the wing itself will change at the same rate with the size of it, we have to consider the drag of the pilot as well. As it stays the same, the total drag of a larger wing will be relatively smaller then the one of the smaller wing. Net result: A large wing will have a better glide than its smaller counterpart! That is, if we ignore Reynold's Numbers and aero-elasticity. Effects of these two are largely unpredictable. A tough decision.
Speed: Again, in the general mechanics of flight, the smaller wing will be faster. But the two factors mentioned above (especially significant in paragliders) can play strange games with us. If speed is your objective, the smaller one should be the right pick. Still, don't worry too much: The difference will be somewhere between 1-2 k/h.
Sink rate: Very much as the above, just the other way round. The outcome is even more predictable than it is with speed: Virtually always the lower wing loading will result in a better sink rate - just a tad, but as we'll see later, it can show in some situations.
Agility: The more loaded wing will, invariably, be more agile. If you want to do large wingovers, SATs, loops - your aim should be ABOVE the recommended weight range. Conclusion: The choice of size is largely a personal matter and it depends on what you want to use that thing (paraglider, we are talking about) for. For a recreational pilot flying often on the coast and not too concerned about speed, a better sink rate can bring almost unfair advantage during ridge soaring. Due to the character of a ridge lift, you will be on the top of the stack all the time, regardless how good or bad pilot you are. It can also make the fundamental difference between bombing out or not in light conditions. In strong winds - if the small variation of speed should make the difference between you penetrating or not - you should not be flying in that conditions anyway.
Competition pilots, almost always, go for a high wing loading. In thermal conditions the marginal advantage of a better sink rate can be wiped out by one tuck or a single wrong turn. You are either able to core that thermal, or you are not. Again, in light conditions the better sink rate does can show. Now; assuming two pilots flying differently loaded wings reached the top of the thermal at the same time and set on a glide: The more loaded wing will be faster. Furthermore, in a headwind, that wing will have a better ground-related gliding ratio - and in a comp - you can't beat that. Play a bit with the polar curve, shifting it back and forth along the best glide line to see what I mean.
Sumarizing: Unless your have special reasons for some extremes in either direction, the choice should be somewhere in the middle. If this choice is not available - I, personally, go for the higher loading. I like the dynamics. But, that's me. Your needs might be different. It is important to realize; you fly in different conditions and a variety of tasks. Whatever you choose, you sometimes will get in a situation when you regret you don't have the other size. So, don't get too stressed about the choice. If really desperate, toss a coin!

Choosing a paraglider

I'm aware, anything I say can be used against me, but I'll try to be as objective as possible. By all means, all the following is only my opinion. It might be worth considering: I've been flying paragliders for more than 15 years, purchasing (for myself) in total eight of these contraptions on the way. I also used to sell them (and now do it again - some people never learn) so I know well the dilemmas pilots are facing.
Size: I wrote quite an exhaustive chapter about it above.
Manufacturer: If anything was this easy. Buy GRADIENT! Just joking... The reasons why I'm buying ( selling and flying as well) this brand, are very much in line with the philosophy and principles you can apply on a lot of other brands too. There are dozens of manufactures around the world. In Australia we live under the impression there are about five. The chosen few found by some means their way to the local market. Their popularity here doesn't always reflect the same in Europe or other countries. By all means all the locally established brands are at least good enough to deserve their share of our market and any of them is worth considering when you have to make that hole in your budget. If you live in Australia buying a glider which is being marketed in here is a wise idea. Buying anything else can cause enormous problems if anything goes wrong. Even if it doesn't, the re-sale value of that glider will be close to zero (do not have any illusions about the re-sale of ANY paraglider anyway), but in this case you will probably have to pay somebody to dispose it off. My personal policy is to fly paragliders to destruction. No headaches with reselling. If you renew them as fast as I do, at the end of their useful life good canopies will be still fairly competitive to the latest models.
Buying an unknown brand has also a distinct physical danger. We are putting our lives in the hands of the manufacturer here. Do not have any illusions. A large proportion of them consists of converted tent makers who know close to nothing about flying. They are only copying the products of the "real" people. Some of them do it well and can be very competitive price-wise. The design and certification factor in the price of a paraglider is significant. Things do can get dangerous when these people start mucking around with the design or materials. As you never know - keep your hands off! Note: This advice is for an average pilot. There are some people around with enough knowledge, information and connections who can go against this advice, saving some money and still be safe. Do not try at home if you are not one of them. Summarized: You are looking for a manufacturer represented in Australia, with a good reputation overseas who's gliders show some success in international comps (adds the credibility and also it's the image-building factor behind your re-sale value) and whose products are reasonably priced. The presentation and service (cost of repairs, namely the cost of a set of lines, is worth investigating before you buy) is an important aspect as well.
Warranty can be quite tricky. Product without warranty should be dismissed right away. One year or three years (the two most common terms today) obviously can make a difference. How big, depends on the conditions applied to the multi-years warranty. In some cases you realize that to get something out from those extra years you shouldn't fly your machine at all. Most paragliders today are made from the same materials and using similar production technologies. Why one should be expected to last 3 times longer then another?
Avoid miracles. An enormous amount of "bull" is oozing from some of those glossy pamphlets. Just about every manufacturer is the best in the world and has just released the latest model speed (the most popular area) of which is about 10k/h higher then anybody else's. A flight with a Speed Sensor can become a real eyes-opener. Also the glide at the max speed can be something of a surprise as the general policy is not to publish polar curves. A very touchy subject... At the current state of information technology and competition the field is almost even. If somebody finds a way to improve the existing design just a tad, others copy by the speed of a lightning before the novelty even hits the market. Some of the "revolutionary design miracles" are products of wishful thinking not based on any science known to mankind. Note that the basic shape, layout and structure of a paraglider didn't change significantly in the last ten years. All those batons, inflatable spars, aerodynamic lines, deviations from the elliptical ground plan etc. Disappeared as quickly as they popped up. If you find a miracle, WAIT AND SEE. The real ones are not frequent.
The design features giving some manufactures that little edge you are looking for are rarely visible by a naked eye. A skilful application of existing principles and meticulous attention to details is what makes the difference between the winners and losers today. Steer away from gliders displaying some highly conspicuous design features. If they work so well, why nobody else copies them? These are mostly marketing tools and you pay for the privilege of being sucked in.
Certification and stability: The stability of your would-be glider is important. Unfortunately, it doesn't stand alone, and you have to balance it with performance. This can lead to some nail-biting situations because both of these aspects have large grey areas. There are some reasonably exact ways how to asses the performance of a glider. But stability is an untidy mess of various standards, opinions, numbers, with pure random occurrences topping the list. There is not an Australian benchmark for paragliders. We merely accept the opinion of testing authorities of other countries - and we even do not insist on these. But, if you do not have rocks in your head, look for a glider, which has been tested by some organization with a good international reputation (ACPUL SHV DHV...).
The most stringent is DHV (compulsory only in Germany). These people test paragliders with all the famous German rigidity, sense for order and accuracy. Unfortunately, what you are getting is called in statistics "an accurate product of inaccurate numbers". If you are going to fly in a glasshouse, sit stiffly in your - DHV certified - harness then you will get what they did. In a real world a DHV 1 glider can send you plummeting from the sky in a series of cascade collapses which any pilot of a hot twitchy comp bastard never even dremt of (been there, seen that). You were supposed to sit still and avoid any turbulence while falling you dummy!
I'm not trying to discount the DHV (or any other tests). Just trying to show these numbers are not a bible. They are only an indication what you can reasonably expect from the glider if something goes wrong. Furthermore, they will not tell you at all HOW EASILY things can go wrong. The more flexible SHV and AFNOR tests will do very much the same job for you, as the testing situations are virtually not duplicable anyway. The gliders are differently categorized in each system and the categories are loosely corresponding to the DHV rating. For instance: SHV "Standard" corresponds to DHV 1 to DHV 1-2. SHV "Performance" to DHV 2-3, SHV "Competition" to DHV Open Class. The more experienced pilot you are the higher (worse) rating you can afford to go for.
It has almost become a rule lately: "I'm an intermediate pilot now, I want a DHV 2 glider." It looks like we automatically associate safety rating with performance. This is true only within certain limits and DHV 2 rated glider doesn't necessarily have to a better performer then DHV 1 by another manufacturer or of a younger generation - although it's reasonable to assume so. Our simplified approach can often lead to purchase of a glider only because it has a WORSE safety rating. Be especially careful where the difference is only 1/2 a point. Some amazing performers are in the DHV 1-2 class now and if you are really safety conscious recreational pilot, you may never find the need for anything more. There are pilots consistently winning major comps with DHV 2 or even lower rated gliders. Often the extra stability in rough air can overweight the slight performance disadvantage. 
Test flights: I have some amazing stories about these. I might cause a serious stir of the hornet nest but my sincere advice is: "unless you are a very experienced pilot, do not use a test-flight as a major decision point." If you base you decision mainly on test flights, you are likely to end up with a dog of a glider which you happened to test-fly in a perfect condition. You can also as easily miss out on real gem just because you didn't set that chest strap right. The worst scenario is, if you manage to crash the demo. Even assuming you walk away from the crash, it would be my educated guess your quotient of desire to buy the machine might have been severely depleted. If there is any damage to it (imaginary or real), the dealer will try to "persuade" you to buy the wreckage. The legal side of that practice is worth investigating, but more often or not - you'll become a happy owner. 
As for myself - I bought all of my 8 gliders without testing them - and never regretted one. Do not have me wrong, I did my homework at each of the cases VERY thoroughly. I got all the references I possibly could from the best pilots I could find. Talked to the manufacturer, looked at the official test results, waited for about 6 months after the glider hit the market to see if some hidden flaw wouldn't surface (do not underestimate this one, these cases are quite frequent). Then I bought that thing - and took my time learning how to fly it. It took me many hours to squeeze the best (if I ever got that far) out of each of my new toy. If there was anything I had a problem with it always was me using an inappropriate technique for the particular model and a simple change of my approach have solved it all.
I have a deep admiration for anybody, who tells me everything (or anything at all) about a new glider after a 5 minutes sleddy. I can't do it. Do your homework, have your test flight if you like - every hour under somebody else's canopy is good for your back pocket - but put most of the weight on reliable, professional, and independent references. I know cases where even the most experienced competition pilots, like Craig Collings or Ron McKenzie bought their gliders without test-flying them. They just followed the simple recipe above. How do I know? They bought them from me. If I can judge from the results they both achieved in the recent comps, they have to be quite happy with them!
Let's close this chapter with one of the many test flight stories... Some years back a friend of mine was trying to sell his almost new DHV 1 glider by a reputable manufacturer to a new pilot. The asking price was ridiculous but the customer wanted a TEST FLIGHT. Well, we made a trip to 3 Sisters and set everything up. I took off first - and immediately wished I wouldn't have. I wanted to go home. The inside of a cloth dryer seemed to be a serene paradise in comparison with the air I was flying in. Having no radio, I couldn't warn my friends and they didn't get the message from the way I flew either - they thought I was enjoying myself! I managed to land somehow, scared of my wits and not having anything to say as where or when I actually wanted to meet the ground. The new pilot launched in the meantime. I was getting airsick only from watching him and used all the prayers I knew from my early childhood. The guy landed in about 15 minutes, fresh as a daisy, about 20 meters away from me. "No, I do not want it. I almost missed the paddock with this one. The one I flew at school had much better handling!" Many happy test flights! 

Two Ways Radios – Which one?

Every pilot should regard a 2 ways radio as an essential part of his equipment nowadays. The question is not if you should have a radio – the question is “Which one?” As for the frequency band, it is simple – at least as long as you are going to use it only in Australia. The UHF CB has been adopted here as the first option and you can’t go wrong. As for features and brands – a different story. Only some 3 years ago there wasn’t much of a choice either. Icom or Uniden – had to be 5 watts if you wanted some decent quality. Anything else was just a toy and better to avoid.
Lately – it seems like every man and his dog in China is making UHF radios of a very acceptable quality packed with features – for about 2 bowls of rice a piece. If you are willing to spend around $100, you can expect a very good product already. The problem is, not everything you buy will suit our purposes. We are a fussy bunch of customers with specific needs. If the product doesn’t do exactly what we need, all kind of dramas will follow. Let’s have a look at the features one by one to make sure your next radio