How fast is it? How we test paraglider speeds
Measuring the performance characteristics of a paraglider, including paraglider speed, has always been notoriously difficult. But new tools are allowing pilots and manufacturers to do just that. Cross Country’s Hugh Miller reports on speed tests he’s been carrying out for the last year
Flymaster’s True AirSpeed (TAS) probe
When Flymaster’s new True Air Speed (TAS) probe was released a couple of years ago we started to measure the trim and top speeds of the paragliders we review. However, we’ve been very surprised by the results. In short, paragliders really aren’t as fast as most pilots – and manufacturers – believe they are.
First, a bit of science. It’s obviously important for powered aircraft pilots to know their exact speed. However, despite any effects of wind, planes go faster at altitude than at sea level due to the lower air pressure – that’s why passenger jets cruise at such high altitudes.
Their instruments rely on pitot tubes to measure what’s known as their ‘Indicated Air Speed’ – which gives the same speed reading regardless of whether the plane is flying at sea level or 30,000ft. When a pitot tube freezes up, it can have disastrous consequences, as the pilots lose any indication of their stall speed. This is what is thought to have contributed to the Rio-to-Paris Air France flight 447 crash in 2012.
Explaining the instrument
In paragliding and hang gliding, we’ve long relied on propeller-based air speed indicators and GPS figures, to give us our speeds. But neither of these are accurate. In fact, the effects of altitude alone will mean that in still air, a paraglider flying at a top speed of 51km/h at just above sea level would be flying at 58km/h at 3,000m. You just go that much faster in thinner air and propeller-based air speed indicators don’t compensate for this.
Obviously you don’t want to be re-working out the stall speed of your Boeing 747 at different altitudes, hence the importance of indicated air speed, measured by pitot tubes. A GPS speed figure doesn’t make this compensation for differences in temperature, density and pressure – and of course doesn’t factor in wind speed and direction, either. GPS is great for accurate ground speed, but useless for air speed.
The boffin test … Our speed probe in Oxford University’s wind tunnel
Anyhow, we were so surprised by the low readings our Flymaster TAS probe gave us that we sent it to Oxford University to be checked against their calibrated hot-wire anemometer. Hot-wire anemometers have been used for many years in the study of fluid dynamics. They are extremely sensitive and are almost universally employed for the detailed study of turbulent flows.
Adrian Thomas, a former British Paragliding Champion and regular contributor to Cross Country, ran the tests in Oxford University’s wind tunnel – where normally he tests the aerodynamics of small insects.
“A pitot tube like Flymaster’s gives you a reading that reflects the forces acting on the pitot tube, and those vary in exactly the same way as the forces acting on the wing”, Adrian explained.
“The Flymaster TAS probe gives a nicely linear result”, he told us. “It slightly over reads – the real air speeds are consistently a fraction lower than the given figures across the 20-60 km/h range.”
“All pitot tubes need regular calibration, and it’s something sailplane pilots put a lot of effort into. NASA have also developed a calibration system between GPS figures and pitot tube figures, and it would be easy technology for instrument manufacturers to bring into paragliding”, he explained. Current methods used for aircraft pitot tube calibration include trailing cones, tower fly-bys, and pacer aeroplanes, which are all obviously time and cost intensive. The NASA method could actually be incorporated into paragliding instruments in the future.
Following the wind tunnel tests Adrian gave us a recalibration formula to calculate precise indicated air speeds which match GPS speeds at sea level. Going forwards, we will be using these results to inform our glider reviews, recalibrating our Flymaster TAS probes at six-monthly intervals.
To be absolutely sure that we can have faith in what our calibrated TAS probe tells us, I spent a day cycling up and down the seafront with the TAS probe and three GPSs. The TAS was wobbling a little on the shorter string dangling from my handlebar, but its reading was steadily consistent with the GPS ground speed.
It is worth noting that most manufacturers obviously don’t go through this whole rigmarole – they just compare their new prototype paragliders against their previous models, and measure what’s known as the ‘delta’ – the difference between trim speed and top speed. For CCC class, they report the speed system travel associated with that delta. So, for example, the Boomerang 10 has 15cm speed system travel, and a delta of 18km/h.
Does it matter?
Does top speed really matter? In competition, of course it does. Some test pilots claim the latest CCC wings are capable of 67km/h. In our view, this is an impossible Indicated Air Speed figure. We’ve tested the Ozone R11, widely regarded as the fastest paraglider ever made, and recorded a maximum of 65km/h. The R11 we tested featured standard risers, not extended risers which allow even further travel. CCC wings don’t feature trimmers like the R11 and have necessarily been restricted.
“I hardly ever see ground speeds consistently in the 60s, and I use full bar a lot”, said Adrian, who flies a Boomerang 10 and is also involved with glider development at GIN.
“On the other hand, I go as fast as anyone else so what does it matter?” he asks. “There is a little maturity appearing in the comp scene. Pilots have realised that trimming their wings fast means they lose out on climb and particularly on the gains you get going straight in lifty air at trim. At the most recent Superfinal, the wings that were checked were all within millimetres of manufacturers’ defined trim settings.”
We measured the top speed of some of the hottest three-liners: the UP Trango XC3, Ozone’s M6 and the GIN GTO2. Using the Flymaster TAS probe, we measured a top speed of 50-51km/h for all three wings, flown at 3kg below the top of the weight range. The new 777 King is a little quicker. This is indicated air speed, and should be the same at sea level as at cloudbase.
Try telling an EN-D pilot that though, and they’ll likely be a little shocked. They may also say they have recorded a GPS speed of 55-56 km/h when flying in the still evening air in the Alps. Both of us, however, are telling the same story.
Problems with measuring speed
However, obtaining accurate results using a TAS probe still isn’t easy. Thermik magazine editor Norbert Aprissnig told us: “We too have looked at providing accurate speed figures for our reviews but it has been a learning exercise in just how difficult it is to get accurate figures.”
He added: “Although modern TAS probes allow for automatic compensation for temperature and altitude, we still have to make sure the wings are in stable flight before taking measurements. Air movements cause fluctuations and we as test pilots end up filtering the data as best we can.”
Also worth noting is the instrument’s wind-speed indication. Most instrument systems, including XCSoar and the Oudie, provide information on wind direction and strength, but as you’ll know if you’ve ever used them much, the figures fluctuate enormously. You have to be flying consistent circles for the instrument to generate an approximate calculation. However, a pitot tube system like the Flymaster TAS is the only way to obtain accurate wind information as it will run a precise comparison between your aircraft speed with your GPS speed.
Finally, just to confuse things a little, Flymaster’s TAS probe stands for ‘True Air Speed’. From an aviation perspective, this is misleading, as ‘true air speed’ is different from the ‘indicated air speed’ that we’re interested in – the bald, pressure-based truth of an aircraft’s speed irrelevant of altitude.
What does it all mean?
Perhaps unsurprisingly the figures reveal that as a sport we have regularly over-estimated the speed of our wings. Just as one example, some pilots claim their paragliders have a trim speed of 40km/h. Meanwhile, Moyes states a trim speed of 35-37km/h for their Litespeed RX competition hang glider. Spot the difference.
Let’s face it, pilots are loathe to be told their ‘60km/h’ wing only really hits 51km/h, and manufacturers understandably don’t want to publicise potentially slower figures. No one wants to be slower than the next pilot, or their manufacturing rival. But our testing has shown that most ‘mid-B’s can get to around 44-45km/h accelerated, while ‘hot’ EN-B wings and many C class wings have a top speed of 46-48km/h. Only EN-Ds and a handful of the very fastest C’s make it beyond 50km/h.
Of course, top speed in still air means nothing if the leading edge is too fragile for the speed to be usable in real life conditions. So let’s not get into a bidding war for the fastest wings on the block. In our reviews we will continue to focus on a wing’s usable speed range, accelerating through turbulent air to test its rigidity and cohesion, as this will always be a better indicator of a good, fast wing than any number.
This article was first published in Cross Country 172 (August 2016). Hugh Miller is a review pilot for Cross Country Magazine and UK XC League Champion 2016. If you enjoyed this sample article, perhaps you’d consider subscribing and supporting the world’s only international free flying magazine?
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Paraglider capabilities: altitude, range and flight time
Today, paragliding in tandem with an experienced instructor is perhaps one of the few quick ways to realize an old dream – to climb to the clouds and see the whole world in the palm of your hand. To do this, you do not need to buy expensive equipment or undergo special long-term training. Professional instructors will organize the entire flight and will accompany you. You will only have to admire the picturesque views of nature from a bird’s-eye view.
Earlier we have already talked in detail about paragliding, as well as about who invented the paraglider, and how it flies. Today we will tell you what this ultralight aircraft is capable of, namely, how high it can take off, and how long the flight will last.
How the paraglider works
To begin with, a few words about the paraglider device. This aircraft consists of a soft wing, a sling, and a suspension system in which the passenger sits, lies or is in a reclining position. Externally, the paraglider looks like a “wing” type parachute. But if a parachute is designed to jump out of an airplane and slowly descend to the ground, then a paraglider was invented to fly. It is equipped with lighter and stiffer materials, which provides a soft aerodynamic shape, which, in turn, allows you to soar in the sky, “glide” through the air.
And, if the weather conditions are good (there are updrafts), then the pilot can spend hours under the clouds, and make fascinating trips along routes of varying complexity. The classic paraglider is not equipped with a motor, so it gains altitude with the help of wind or updrafts. There is no other way. In order to plan, that is, to move forward and control the aircraft, the pilot needs to effectively spend the gained altitude, overcoming air resistance and gravity. The higher the altitude, the longer the flight lasts, which means it will be possible to overcome a greater distance and see the incredible beauty and power of nature. Paragliding in tandem with an experienced instructor takes place in the mountains, with a suitable climate and weather conditions. Another popular way to lift a paraglider into the sky is to start from a winch. It is used for flights over plains or coasts, that is, in places where there are no high mountains. The winch allows you to gain a starting altitude from 300 to 600 meters, after that the pilot can soar in the sky for a long time.
The capabilities of the paraglider are really impressive. Despite its lightness and compactness, it is able to fly high and for a long time. The maximum soaring time, according to experienced pilots, is about 10 hours. But in this case we are talking about the record of a professional athlete-pilot. For tourists, instructors organize shorter flights, but at the same time in fantastically beautiful places. For example, a summer sightseeing tour over the Caucasian Ridge in Georgia with the company “SkyAtlantida” lasts 25-30 minutes. You will spend so much time in the air with an instructor, and you will see incredible landscapes. You will start from a height of 2100-2750 meters, and fly a distance of 6 kilometers on a paraglider, landing at the resort of Guduari. However, there are longer flights. For example, a route, 40-50 minutes long. During this time, the instructor pilot will make a sightseeing flight through the Cross Pass, the Guduari resort, the Aragvi Canyon. More than 12 kilometers of the way. A breathtaking adventure!
Meanwhile, flights are carried out not only in summer. You can climb into the sky in winter! To do this, SkyAtlantida has four flight programs:
- Short flight, 10-20 minutes;
- sightseeing flight, 20-35 minutes;
- VIP canyon flight, 8-15 minutes;
- aerobatics, 35-50 minutes.
The flight time in each program is calculated from weather conditions, including. It is worth noting that the price of each tour necessarily includes:
- free transfer in Gudoari;
- warm clothes, special shoes, necessary flight equipment;
- HD quality video.
The paraglider is considered one of the slowest aircraft. The minimum horizontal speed is up to 25 kilometers per hour. However, where to hurry when the clouds are just around the corner?
Today, even children from the age of five can take part in a paragliding flight in tandem with an experienced instructor! Paragliding is a type of transport that is also accessible to people with disabilities. Special passengers in the company of professional instructors can, just like everyone else, take off and soar along with the clouds. SkyAtlantida instructors have extensive experience and knowledge, regularly undergo training, thereby confirming the high rank of professionals.
Altitude and flight distance
Of course, the altitude of the flight, and hence the distance that the paraglider will overcome, depends on many factors. This is not an airplane that will strictly perform the entire journey according to the specified parameters. But even the work of the “iron bird” depends on the weather. And the worse it is, the more likely that the flight will be postponed to another time.
Same with a paraglider. In clear sunny weather, the flight will last longer. The pilot will be able to catch thermal updrafts, which are formed due to uneven warming of the earth. Warm air rises up in “bubbles”. These are thermal updrafts, they depend on solar activity. By processing the so-called thermals, the pilot will be able to climb higher and higher.
The world of paragliding has its own records. Among the major achievements is the world altitude record in 2021. In July, athlete Antoine Girard was able to climb a paraglider to a height of 8,407 meters! Only planes are higher. For example, passenger airliners fly at an altitude of 10000-12000 meters. And small light-engine small aircraft do not rise into the sky above two thousand meters at all.
SkyAtlantida instructor pilots fly at an average altitude of 2100-2750 meters. This is enough to fully enjoy all the magnificent landscapes of the Caucasus Mountain Range in Georgia, and to see all the details of the local nature. However, the program of one of the winter route tours is designed to start from a height of more than three thousand meters. This is a sightseeing flight that lasts 20-35 minutes, and is also available to children aged five and over.
We have already said that the higher the flight, the further the paraglider will fly. The longest route on a non-motorized aircraft was more than 500 kilometers, and it lasted more than 10 hours. But, as a rule, the average figures of record holders are 250-300 kilometers. For tourists, of course, sightseeing tours are conducted along routes with a much smaller distance. And this is due not only to the time in flight, but also to special training. Not every athlete will sit for several hours in a suspended device. Therefore, for those who want to fly a paraglider in tandem with an instructor, routes have been developed that are optimal in time and distance.
A paraglider is considered an ultralight aircraft. Its weight is only 5-10 kilograms. It easily fits into a backpack, and is ready to take off on the spot in five minutes. The most compact, mobile aircraft actually has great capabilities!
How can paragliders fly?
You’ve probably been wondering what makes these pieces of fabric fly or why all of the gliders typically have the same shape or even how this flexible structure manages to stay aloft above the pilot’s head. Our focus on flight mechanics in this chapter will attempt to provide answers to all of these questions at the very least it will give you the basic understanding you’ll need to pilot this peculiar aircraft: a paraglider.
The paraglider’s aerodynamic profile
Let’s start by looking at the basic shape of our paragliders. We will demonstrate the importance of the wing’s profile the goal is to optimize its penetration through the air and reduce drag as much as possible.
We’re going to see what happens to the air have it flows over these three profiles: looking at the first profile, a simple plate, the molecules of air contained in the air stream are
completely blocked in the middle, the air that flows beyond the plate is turbulent which significantly increases drag. The airflow over this profile is similar to what happens when rowing a boat the oar needs enough force to displace water and have it displaces the water small swirls form behind it.
The second profile penetrates the air a lot better. As we can see here the result is much
smoother airflow, the molecules of airflow smoothly over the front of the profile. However, too much drag is still created by this profile.
The third profile has been improved so that the airflow is smooth from start to finish our profile will travel through the air with little resistance, thanks to its cambered shape.
It will also reduce drag by replacing the air in its wake. This is an ideal aerodynamic profile.
How a paraglider creates lift
If you were to cut the paraglide in half you’ll find this cambered shape along the entire wingspan, from the leading to the trailing edge. This is how manufacturers optimize the
wings penetration and movement through the air, but this doesn’t explain what makes a paraglider fly.
Let’s move on to a phenomenon that you’ve probably already heard of: lift.
Let’s take another simplified cross-section of our wing and observe what happens as air flows over its profile in flight: the angle created by the paraglider swing and the relative
wind is called the angle of attack. As the molecules of the air come into contact with the wing they are separated into two streams by the leading edge the first stream flows along the upper surface of the wing, the other along its lower surface even though. The upper surface is longer than the lower surface. Experiments have shown that both air streams reach the trailing edge at the same time: there’s only one way for the molecules taking the longer route along the upper surface to arrive at the same time, they have to accelerate.
Thanks to a principle formulated by Swiss mathematician and physician, Bernoulli, in 1738, we know that half the speed of a fluid increases its pressure decreases. In other words, the faster-moving air over the upper surface of the profile creates a low-pressure zone on top of the wing which is the source of lift. On the other side of the wing, air molecules push against the lower surface, creating a high-pressure zone. This is also a source of lift. About 3/4 of the lift results from the low pressure above the wing and 1/4 from the high pressure under it. Most of the lift occurs near the profiles leading edge.
This simplified explanation of what causes lift should help you understand why our wings fly.
Aerodynamic forces in a paraglider
Lift is thus created by the flow of air over the profile, but how is this phenomenon is sustained when there isn’t any wind? what is the paraglider’s motor?
In order to answer these questions will turn to the science of mechanics. This science deals with the action of forces on bodies. The forces we’re interested in are those that act upon the pilot and paraglider.
Let’s start with a simplified model of the low and high-pressure zones lift. This force acts upon a point known as the center of pressure. This point is merely an average of the lift forces acting upon the paraglider. When travelling through the air a paraglider encounters resistance and creates turbulence in its wake the force that opposes its forward movement is known as drag. Since these are the two main forces that act upon the profile we can add them: their sum gives us the resultant.
The altitude is the “fuel” of a paraglider
How do we obtain the relative airflow necessary to create lifts when there isn’t any wind? By simply transferring his weight to the wing, the pilot pulls it towards the ground forcing it to move forward through the air. This movement we call airspeed and this creates the relative airflow required to reduce lift.
Altitude, therefore, is the paragliders energy reserve and by using our weight to draw on his reserve we’re able to fly.
The angle of attack in a paraglider
As mentioned before the angle of attack is the angle at which the relative wind meets the profile this angle should not be confused with the angle to the horizon, learners attitude.
As it’s possible to have a relatively high angle of attack with the wing at any attitude, in normal flight the paraglider remains at a constant angle of attack and at a constant airspeed. The pilot can influence the angle of attack and thus the speed by using the brakes or speed system. The angle of attack and airspeed are very much related: if you change the
angle of attack the airspeed too will change until a new equilibrium is achieved. The angle of attack can be increased by applying the brakes, evenly this causes a corresponding decrease in airspeed. The greater the angle of attack, the more lift is produced, however,
more drag is also produced. If too much brake is applied then the smooth airflow over the profile cannot be maintained and the airflow breaks away from the top surface: This is known as a stall.
Being aware of the stall is very important when learning to fly since inadvertent stalls are very dangerous and should be avoided, always keep your hands high and make sure you feel good airspeed on your face whilst trying to avoid the stall.
Only when making the landing flare should you use deep brake inputs.
The angle of attack can be decreased using the accelerator system, as the angle
decreases drag is reduced and the speed increases. The glider continues to accelerate until a new equilibrium is found, the wing then stabilizes at this new speed and sync rate.
At low angles of attack, paragliders are more prone to collapse. This is why you should not use the speed system when close to the ground or flying in turbulent air.
Lift to Drag ratio in a paraglider
Let’s turn to the concepts of lift-to-drag and glide ratios. The lift-to-drag ratio is the angle at which the paraglider glides. These concepts will help you understand why a student barely manages to lift off from a slope. There are simply ratios that measure the glide capability of your wing, these ratios are obtained by dividing the horizontal distance covered by the vertical distance lost. In an example, 750 meters divided by 100 meters gives us a ratio of seven and a half.
As you may have guessed, the greater the horizontal distance is the greater this ratio will be and the longer your glide. This is called your lift-to-drag ratio, it’s a technical specification of your wing. The lift-to-drag ratio doesn’t change unless the wing is damaged.
We’ll see later on in the flight chapter that the wind or micrometeorology can influence the trajectory the distance covered will vary and in this case, would refer to its glide ratio.
Let’s go back to the example with our student: he can’t lift off because his lift-to-drag ratio is too close to the angle of the slope. The launches will need a hill whose slope is steeper than the lift-to-drag ratio of our wings.
Modern paragliders have a lift to drag ratio between six and ten to one. For reference, you can compare this with a lift to drag ratio of 15 to one for hang gliders and almost sixty to
one for sale planes.
Speed to fly in paragliding
Paragliders have a large speed range and knowing when to use these different speeds is very important. You have control of the speed with the brakes and the speed bar. This
is known as speed to fly.
Knowing to fly at the right speed depending on conditions or the site is the basis of safe and efficient piloting. Understanding different flying speeds will make you a better pilot, the correct speed and just the right timing makes it possible for the student to make a smooth landing.
As a general rule when in lift slow down and when in lift or headwind speed up. This increases your efficiency and prolongs your glide performance. Flying at trim-speed your glider will achieve its best glide angle in calm air. The pilot’s arms are high with no pressure on the brake handles. At this speed, the profile isn’t warped in any way and therefore create the least amount of drag flying like this will allow you to cover the maximum distance. Most modern paragliders have a trim speed of around 36 or 37 km/h. When learning the main reason for flying at such a speed is to accelerate before landing and build up energy that will eventually be converted into a flare. This makes a soft landing possible flying at trim speed also reduces the likelihood of problems caused by the wind gradient, such as inadvertent stalls or sudden altitude
last near the ground.
Applied the brakes approximately 30 to 40 centimetres to reach the minimum sink rate. The pilot’s arms are about level with his shoulders or just below and there is a positive pressure through the brake handles. Applying pressure to the brake handles will also improve your sensitivity to the wings movements and increases the internal pressure and
angle of attack of the wing which reduces the likelihood of collapses. Flying at min sink increases the angle of attack and significantly increases drag which reduces the ability to glide and consequently reduces the distance that can be covered. However flying like this gives you the slowest vertical speed, in other words, you sink at the slowest rate. You can
take advantage of this when flying in lifting air.
Note also that other than the landing flare it is never necessary to fly slower than the minimum sink rate.
This post is a transcription of the video “Learn to Fly” (Kitchen Productions)