Welcome to some serious paragliding theory. Here we will be taking a look at the various theoretical aspects associated with paragliding. Each section is divided into questions and answers for easy reference. Lot's of good info for the more technical flyer. Used with many thanks from:Gary
Taylor |
| Question: Wing features: What is the camber and chord of a paraglider? |
Camber - Curve in the airfoil section (can be at the top or bottom of the airfoil). Chord - The measured distance between the leading edge and trailing edge of a wing. |
| Question: What is meant by the term "aspect ratio"? |
Aspect ratio - The relationship between the span of the wing and its chord. High aspect ratio = a wing with a big span and a narrow chord. |
| Question: What is the effect of reducing the camber in a paraglider's wing design? |
The speed of the glider will be increased. |
| Question: How does a wider wing span influence a paragliders response and handling? |
A reduction in directional stability during handling as apposed to a lower span wing. Therefore greater pilot input is required during handling a wider span wing. The wing is more "twitchy" and prone to more cell closures or collapses. The wider the wing span the more responsive the wing is to conditions and pilot input. |
| Question: What amount of brakes would you use to obtain best L/D (lift/drag), and why? |
This will be entirely dependent on the conditions. Certain conditions require the application of more breaks to enhance your glide ratio which is effectively the same as the L/D (lift/drag) ratio, as apposed to less brakes under other conditions. Flying into stronger winds would require less application of the brakes (possibly 5% to 25% brakes) as opposed to flying into lighter penetrating winds where more brake application would be necessary (possibly 25 % - 50%). |
| Question: What possible causes can there be for a paraglider to have an inherent left turn? |
An inherent left turn on a paraglider is the result of the right side of the wing flying faster than the left side, i.e. more drag on the left side or the angle of attack is lower on the right side. Possible causes could be: - Manufacturing error ie unequal amount of cells e.g. more cells on the right side or inversely less cells on the left side of centre wing. - Line fault ie stretched lines or shorter lines e.g. shorter D-Lines and/or brake lines on left or longer D-Lines on right or A-lines on left. |
| Question: How does weight shift turn a paraglider, and is it more efficient than using brakes/flaps? |
Your centre of gravity is immediately altered with weight-shift causing a decrease in drag on the opposite side of your weight shift. That side then flies faster e.g. lean to the left decreases drag on the right of the wing therefore the right side of the wing flies faster, therefore enabling a left turn. By using weight shift your turning will be more efficient because the glider's speed is not effected and no induced drag is provided from the weight shift turn. Conditions will determine whether weight shift is more effective than applying brakes, as it may be necessary to reduce ground speed to core a thermal, i.e. to increase drag and reduce air-speed. |
| Question: What conditions can be expected near dust devils? |
There will be visible ground disturbance at the base area of the dust devil, e.g. dust, leaves and other debris. Strong thermic development above the base area of the dust devil. |
| Question: What is a berg/föhn wind? |
It is an unstable, warm air mass, which moves from inland areas towards the coast. Berg/föhn winds can be regarded as non-buoyant air, and therefore not conducive to good flying conditions. |
| Question: What conditions can be expected whilst flying in a berg wind? |
Dense air and minimal thermal development. Strong winds (pre-frontal) with lots of turbulence with a high degree of humidity in the air. |
| Question: What are 3 primary causes of turbulence? |
Mechanical turbulence - Obstruction of the path of the wind by solid objects, e.g. trees. Thermal turbulence - Convection currents or thermals. Shearing turbulence - e.g. wind shear. |
| Question: Which major factors work to produce the greatest ridge lift components? |
The angle of the slope - the steeper the better. The height of the slope - the higher the better. The length of the face - the longer the better. (a ridge is much better than a hill since the air can go around the hill instead of over it) The strength of the wind - the stronger the better, up to about 32 km/hr. The angle the wind hits the hill - a perpendicular wind is best; the lift drops quickly as the wind begins to cross. |
| Question: What conditions can be expected in unstable air? State your reasons. |
Cumulus clouds - cloud types are always indicators of stability. Cumulus or tumbled clouds are caused by vertical currents and always imply instability. Clear air - a clear night followed by a clear morning will bring unstable conditions, for the clear night allows a thick layer of cold air to form which is unstable with respect to the air warmed at ground level in the morning. Erratic winds/gusty winds and dust devils - away from turbulence inducing structures indicate unstable air. |
| Question: Would you expect wind gradient to be stronger in stable or unstable air? |
Unstable air (conditions). |
| Question: What is meant by "lapse rate"? |
It is the rate of temperature loss with height gain of rising air. |
| Question: Define a temperature inversion. |
A layer of warm air on top of a layer of cold air is a temperature inversion. This inversion gradually lifts as the air beneath the inversion layer is heated and begins to lift and mix with the warmer air above. |
| Question: What conditions accompany a temperature inversion? |
The area beneath an inversion layer is often stable and not good for soaring pilots. The air beneath an inversion is pleasantly warm. The light will be hazy. Thermals will not be able to penetrate the inversion layer, causing little vertical movement of air (this will change as the air beneath the inversion begins to warm). |
| Question: Define convergence? |
Convergence is when a moving airflow meets an opposing one and the air is forced upwards. |
| Question: Where would you expect convergence to occur? |
Along the coast when a sea breeze meets a light prevailing wind from the land. When the air flowing along two valleys that merge into a V meet, convergence of the two air flows occur. In gullies along ridges. Between two close mountains and channels convergence of air occurs. |
| Question: What is a wind shear? |
It is when two layers of air lying next to each other move with different velocities. A shearing action takes place between them. Also when different air masses, e.g. cold air moving down a slope and warm air moving above it and up the slope meet one another, a shearing effect between the two air masses takes place. |
| Question: What is cloud suck, and how is it formed? |
Cloud suck is the vigorous climbing of air beneath a thermal cloud. It is formed by thermal air feeding the base of a cumulus cloud. This means an upward movement of air. With this upward movement of air the cloud size is increased drawing more air at a faster rate i.e. a high lapse rate near the base of the cloud. |
| Question: What are the dangers of flying in the vicinity of or below a thunderstorm? |
Turbulence - All the updrafts and downdrafts in a thunderstorm create considerable turbulence due to shear around the vicinity of and below a thunderstorm. Cloud suck - Tremendous updrafts in a thunderstorm that can reach an incredible speed. Hail, Rain and Snow - Precipitation often occurs very suddenly and a sudden collapse of an updraft can allow rain or hail to fall in a gush. Lightning - The processes in a thunderstorm cause a separation of changes that induce large voltage potential differences from place to place. |
| Question: Describe the changing weather characteristics and cloud features as a cold front approaches and passes a given point. |
It will become darker as thick clouds arrive, and soon rain will fall. It may be heavy and last from a few minutes to two hours. This is the sign that the cold front has arrived. Some cold fronts may produce a line of thunderstorms called a squall line which can be as long as 800km. After the front has passed the change in the weather is sometimes quite surprising. The heavy rain stops, and the barometer indicates that pressure is rising and the clouds move away towards the North East as fresh clear air flows in from the West or SW (southern hemisphere). The sun or stars come out, the humidity is low and the weather feels very refreshing. |
| Question: What factors contribute to cause cloud formation? |
All clouds are a result of lifting air which is caused in three ways: Frontal movement, rising terrain and heating (thermals). |
Question:
Describe the following types of cloud, and state under what circumstances
they will form:
|
Cumulus - Puffy, heap-like clouds formed at low altitudes. They occur when localized heating causes a warm mass of air to rise to condensation level. Nimbo-cumulus - Same as above except rain is falling from the cloud. Banner clouds - Forms on a mountain crest where rotor air blowing up-slope on the downwind side of the mountain as well as drifting snow combine to create a cloud that streams out downwind from the crest. This cloud usually foretells high winds at cloud level. Lenticular clouds - They form when the air undergoes up and down undulations (waves) caused by the air blowing over hills or mountains. They are orientated perpendicular to the wind. |
| Question: Describe a thermal from formation to dissipation. |
The sun heats the earth's surface. If heating is slow the warm air may rise in a light continuous plume. In a faster heating process a bubble may form that remains on the ground for a period of time before it releases in a sudden rush. The thermal will rise until it cools to the point that any moisture it curtains is condensed and a cloud forms. This is the familiar cauliflower or cotton puff cloud. Thermals can exist without producing clouds if the air is dry (blue thermals). |
| Question: What factors determine moderate thermal development, release, rate of ascent, and decay? |
Development - The surface areas that produce thermals best are parking lots, ploughed fields, dried grass areas or bare rocks (to mention but a few). Release - A general surface wind serves to release thermally as it swirls around ground obstructions. Rate of ascent - On clear, hot days it is common to get a layer very close to the ground that is superheated. This layer is called the superadiabatic layer. This layer has a lapse rate greater than the cooling rate of thermals. As a result the difference between the thermal temperature and that of the surrounding air is continually getting greater as the thermal rises through this layer. Thus the thermal accelerates upwards. This aspect influences the rate of ascent of a thermal. (Temperature difference between thermal cooling rate and lapse rate increases - thermal rate of ascent increases). Decay - When a thermal reaches an inversion layer its climb is stopped. When the thermal reaches dew point level and forms a cumulus cloud mixing occurs. When a thermal enters neutrally stable air it mixes with the surrounding air and gets weaker. All these factors lead to thermal decay. |
| Question: Describe a wave formation. |
Waves are produced just like ripples in water down-stream from a sunken log. Waves rebound from a mountain and continue moving up and down for a considerable distance downwind from the mountain that forms them. |
| Question: What is a cloud street, and how is it formed? |
Cloud streets - A cloud street can be a solid line or lines of clouds in moist conditions or sparse dots of clouds in drier air. A long line of cumulus clouds usually forms in parallel rows. Streets are formed when a steady wind causes a long line of lift rows with sink rows in between. The clouds will form above the lift rows in a line behind each other. |
Question:
Describe the following winds:
|
Sea Breeze - During the day air warms over land and rises it is replaced with cold air from the sea and in turn replaces the cold air over the sea. This cycle continues as long as the sun shines. Land Breeze - As evening falls, the land cools and the water becomes the warmer body since water has a huge heat capacity. As a result the situation reverses with a breeze blowing from the land to the sea known as a land breeze. Anabatic Breeze (Valley - Up-slope Breeze) - During the day the sun's heating tends to warm the air at the surface so it flows upward along a slope. In the valleys or low areas the air is usually sinking to replace the air flowing toward the slope and upward. Catabatic Breeze (Mountain - Down-slope breeze) - Evening down-slope breeze due to cooling at the surface. Also known as Mountain winds, gravity winds or catabatic flow. At night the reverse is true. As the surface cools, the air it contacts becomes cooler also and slides down the slope since it is denser and heavier. |
| Question: Under what circumstances can you safely turn downwind and fly behind a ridge? |
Only go over a mountain when you are more than its height above it. If you use this rule you avoid possible sink, rotor and turbulence. Furthermore, when attempting to fly over such a mountain be sure to fly downwind as far as you can. |
| Question: Describe the correct take-off technique from a cliff. |
A cliff launch in calm conditions requires enough running room before the cliff to inflate, flight check and abort take off if necessary before reaching the cliff. In windy conditions rather avoid cliff launching as there is a problem with the presence of rotors and gustiness behind the lip of the cliff, which often makes it impossible to inflate the glider. The correct technique could be either an alpine start or a reverse inflation depending on the conditions or the slope/cliff. The correct technique should allow the pilot sufficient space before the cliff to do a canopy check and abort if necessary. In general, the standard procedure is to use assistance and get the wing situated in the smooth air flow as much as possible. This requires moving to the edge of the cliff where the air flow just begins to break up. The presence of rotors may require a quick release away from the cliff. |
| Question: Describe the execution of a good top landing. State the precautions to be taken. |
Before attempting a top landing ensure that there is plenty of unobstructed clearance above the top of the hill and a wide open area on top in which to land. A smooth rounded hill is the best candidate for top landing. Check wind streamers and don't fly too far behind the ridge as rotor and turbulence exist there. The pilot uses his altitude to drift back over the lip of the hill, and turns into the wind to land. He should not turn downwind to drift back but start from the side with the least crab angle. That way you will only have to produce a 90° turn to head into the wind and thus avoid the dangerous downwind landing if you hit unexpected sink. |
| Question: What do you check for when preparing to make an out landing in an unfamiliar landing area? |
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| Question: Describe the two correct approach patterns from a position high over the landing field. |
Figure Eight Landing Approach - Enter the pattern with ample altitude, remain over the end of the field by performing greater than 180° turns in calm winds. Also remain within a 60° angle to the sides of the field. Begin the final approach when at a 30° angle from the chosen landing point. Tee landing approach - In this approach the pilot enters the pattern on the upwind side of the field and performs a series of figure eights that drift him back to the far end of the field at which point he performs his final approach. This method is most used in higher winds to overcome the potential problem of not being able to maintain a position over the end of the field. A further method which may be used (specifically in lighter conditions) is losing height above your landing area i.e. upwind through figure eights. At pattern height (30m) you enter the downwind leg, turn 90° to the base leg, then another 90° to head into the wind on the final landing approach. |
| Question:
Explain the procedures for a forced landing in water. Explain the procedures for a forced landing in trees. |
First undo your chest buckle before you hit the water. This should be done at least 46m. Remember that's only 20-30 seconds before you hit the water. Next, head into the wind so the canopy falls behind you. Just as you hit take a deep breath and release the leg straps or climb out of them (depending on the harness). Once you are free of the harness swim upwind away from the canopy to avoid entanglement. Try to avoid surf for it will greatly complicate your escape from the canopy. Try to aim for the middle of the crown. The greatest danger is falling out of the tree once you hit. Cross your legs at the ankles to prevent broken legs and organs. Break to as soft a landing as possible then quickly cover your face as you continue into the tree. Don't unbuckle your harness until you are sure you can climb down or reach the ground safely. |
| Question: Which way must you turn if you enter a thermal which is already being worked by another paraglider? |
Always turn in the same direction as the pilot who is already in the thermal. |
| Question: You are established in a thermal, and another paraglider below is climbing towards you, what action must you take? |
The glider with the slower climb rate shall give way to gliders climbing towards them. |
| Question: During a cross country flight, what two things should you be studying on the ground at regular intervals? |
Possible landing areas (with alternatives). Wind direction on the ground. |