Kite Physics 101

What is "FLYING?"

CLICK HERE. Why click? Due to the low-quality education from organized kiting, few kite flyers on Planet Earth know what "FLYING" a kite is!

How does a dual-line kite turn?   

The same way snow skiers, water skiers, surfers, bicyclists, and runners turn: you turn in the direction of the lean. No lean, no turn. Lean right, turn right. Lean left, turn left. The more the lean, the tighter the turn. To stop the turn, do away with the lean.

Aircraft -- including dual-line stunt kites -- turn exactly the same way. The only difference is that with airplanes, leaning is called "banking."

Be aware that some stunt kites turn like parachutes -- a crude method of turning -- rather than like aircraft: CLICK HERE.  And that most stunt kites -- including the most-popular deltas and parafoils -- are missing the bridle lines needed to turn like aircraft: CLICK HERE.

The WindDance 1 shown below -- flying STRAIGHT, turning RIGHT, turning LEFT -- happens to be flying at point K on its flight envelope. The flyer, standing at location F and facing the kite at point K, is controlling the wing banking angle with respect to the flying lines by using two control handles.

• Flying STRAIGHT: flyer is holding both control handles even. Pull in both flying lines is even. The wing is not banked with respect to the flying lines, causing the kite to fly straight.

• Turning RIGHT: flyer is pulling back on the right control handle while holding the left handle forward. Pull in the right line is high, pull in the left line is lower and possibly zero. This sharply banks the wing to the right with respect to the flying lines, which causes the kite to turn to the right.

• Turning LEFT: flyer is pulling back on the left control handle while holding the right handle forward. Pull in the left line is high, pull in the right line is lower and possibly zero. This sharply banks the wing to the left with respect to the flying lines, which causes the kite to turn to the left.



For a gentle turn, bank the wing slightly. For a sharp turn or tight spin, bank the wing as far as it will go -- so far that all the pull is in one line.

It's like driving a car: Center the steering wheel and the car goes straight. Turn the steering wheel and the car turns and keeps turning. Keep the steering wheel turned and the car drives in circles. Re-center the steering wheel and the car goes straight again but in a different direction.

As you control a WindDance, it feels somewhat like steering and turning a car because a WindDance has a similar increasing-resistance steering-and-turning feel. This important feel -- the pull rises when you turn -- provides the positive feedback needed for fast learning and superb control, gives a WindDance part of its exciting feel, and delivers good exercise.

By regulating the banking angle of the wing using the two control handles, you can fly and maneuver a dual-line kite at will all over a large flight envelope. Point K -- where the kite happens to be at any given instant -- can be anywhere on the flight envelope, and as you fly can travel everywhere on the flight envelope. When you take advantage of the entire flight envelope, the kite flies at a wide range of speed, and you experience a wide range of pull. Tremendous fun, especially if you're flying a WindDance!

The flight envelope

The "ideal" flight envelope

The flight envelope is the quarter-sphere surface on which a kite flies at the end of its lines. Except for different "edge" locations, this shape is the same for all kites.

The flight envelope also describes the airspeed & pull of a kite. Airspeed & pull characteristics vary widely from kite to kite. For kites that deform very little under the forces of flight, the kite's straight-flight airspeed & pull are close to the "ideal" flight-envelope values.

Straight-flight speed & pull behavior is described by iso-power lines, power-gradient lines, the kite's Airspeed Ratio & Pull Ratio table, the kite's peak powerzone airspeed with respect to wind speed, and the wind speed. All this is explained below.

The Airspeed Ratio & Pull Ratio table, which is for an "ideal" kite, describes the maximum speed & pull variation that can occur as the kite flies from the edge to the powerzone. The more a real kite deforms as it flies, the less that speed & pull variation. With some real kites, speed barely changes as the kite flies from the edge to the powerzone.

Maneuvering-flight speed & pull behavior is determined by the kite's turning characteristics (whether speed & pull typically rise or fall when you turn) and by the way you turn (pull-turning causes speed & pull to rise or fall depending on the kite, push-turning generally causes speed & pull to fall).

The upwind edge of the flight envelope -- the edge -- is the semicircle LUR extending from the left-side edge L to the upper edge U to the right-side edge R. While anywhere on the edge, the kite hovers with zero groundspeed and its airspeed equals wind speed. The edge is always downwind from the flyer F, and can range from slightly downwind to far downwind depending on the "wind window." All points on the edge illustrated below, including L and U and R, are located 80° from the wind direction FP (<PFL = <PFU = <PFR = 80°).
 


The wind window -- defined by the sport as <LFR = 2 x (<PFL) = 2 x (<PFU) = 2 x (<PFR) -- is a measure of the angular size of the flight envelope. The wind window can range from almost 180° wide (edge almost directly above and to the sides of the flyer, the widest window possible) to less than 60° wide (upper and side edges far downwind from the flyer, a narrow window).

The angular size of the wind window -- and the location of the edge -- depend on the aerodynamic characteristics of the kite and flying lines, and on the wind condition:

• WIDE wind window: Kite has high aerodynamic efficiency. Kite is tuned for high performance. Short, thin flying lines. Medium to strong winds. Smooth winds.

• NARROW wind window: Kite has low aerodynamic efficiency. Kite is tuned for low performance. Long, thick flying lines. Light winds. Turbulent winds.

The blue semicircles are iso-airspeed/iso-pull lines -- or iso-power lines -- on which kite airspeed and pull are the same no matter what direction the kite is flying. It makes no difference if the kite is flying along a line, or crossing a line. Iso-power lines represent different power levels. As shown in the table, airspeed and pull increase as the kite flies from the edge to point P, and decrease as the kite flies from point P to the edge. The section of the flight envelope in the vicinity of point P, say from point P to the 20° iso-power line, is the powerzone where kite airspeed and pull are highest.

As you fly, your kite's location K continuously moves on the flight envelope (except when it hovers motionless at the edge), and passes through and along many iso-power lines. Suppose you fly along the 50° iso-power line (<PFK = 50°), or cross it in several different places from many different directions. Whenever your kite is on that line, its airspeed and pull are the same every time.

Example: Suppose you are flying a WindDance in 10 mph wind. When K is at P the WindDance's airspeed is about 4 times the wind speed or about 40 mph, and for this example assume the WindDance's pull to be 50 lb when K is at P. What is the kite's airspeed and pull whenever the WindDance is on the 50° iso-power line? From the table, the airspeed at <PFK = 50° is 64% of the airspeed when the kite at P or 26 mph, and the pull at <PFK = 50° is 41% of the pull when the kite is at P or 21 lb. When you fly from <PFK = 0°, the center of the powerzone, to <PFK = 50°, airspeed drops from 40 mph to 26 mph and pull drops from 50 lb to 21 lb. You feel and hear this as you fly. (But you don't see it exactly -- you see "groundspeed," which is always greater than or less than "airspeed." This mystery is explained on the Kite Physics 102 page.)

For a "non-ideal" kite flying in "non-ideal" wind, the above table and example numbers are different. This topic is discussed below, and on the Kite Physics 102 page.

The red quartercircles are airspeed-gradient/pull-gradient lines -- or power-gradient lines -- along which kite airspeed and pull change the fastest as you fly along any such line. Power-gradient lines represent the shortest route from one iso-power line to the next. All power-gradient lines are identical: lines at the side of the flight envelope and lines at the top of the envelope have the very same effects on kite airspeed and pull. When you fly along any power-gradient line from point P toward the edge, as from a self-launch at P to an edge hover at U, airspeed and pull decrease the fastest. When you fly along any power-gradient line from the edge toward point P, such as along the quartercircle UP to get up speed for a loud and high bounce-'n'-fly trick, airspeed and pull increase the fastest.

The above description of the flight envelope is for an "ideal" kite flying in "ideal" wind. "Ideal" wind is smooth and steady and is the same all over the flight envelope down to ground level -- sometimes the wind is near-ideal, totally ideal except for the thin layer close to the ground, the boundary layer, where the wind is slowed by the ground. An "ideal" kite is very light in weight compared to its pull, does not distort as it flies from the edge to the powerzone, and does not distort as the wind speed increases -- lightweight kites that deform only negligibly are near-ideal away from the edge.

When flying a near-ideal kite in near-ideal wind, except for the thin wind boundary layer near the ground and a different edge location (different wind window), the real flight envelope looks just like the "ideal" one and the kite's airspeed & pull are slightly less dynamic than the "ideal" airspeed & pull changes as the kite flies from the edge to the powerzone.

In smooth and steady winds, the "ideal" flight envelope describes a WindDance's airspeed & pull not exactly but reasonably well.

The REAL flight envelope

Effects of non-ideal WIND

Sometimes the wind is far from ideal. Rapidly-shifting winds can rotate the flight envelope around the pivot-point F like a nervous weathervane as the line FP keeps itself lined up with the wind direction. Pull may violently spike upward as the side-edge suddenly becomes the new powerzone! While at the side-edge, wind may suddenly hit the top of your kite, a harsh indication that point K is now far upwind of the edge of the new flight envelope where it can't possibly fly! Changing wind speed and changing turbulence may move the edge upwind and downwind, widening and narrowing the wind window as you fly. The wind may be stronger up high -- the usual case, especially if there are obstacles upwind that impede the flow of the wind near the ground -- which shifts the lower ends of the edge and the iso-power lines downwind along semicircle LPR plus stretches the tops of those lines upward and upwind along the envelope, having the effect of stretching the powerzone upward. Or the wind may be faster at the ground than up high -- as when flying on the crown of a smooth hill -- which shifts the lower ends of the edge and the iso-power lines upwind along semicircle LPR plus moves the tops of those lines downward and downwind along the envelope, having the effect of flattening the powerzone. In extreme turbulence, wind speed and direction fluctuate very wildly in real time and from point to point on the flight envelope. Think of extremely-turbulent wind as being a horizontal blizzard of gobs of air of billions of different sizes from tiny to huge, many of them spinning like a vortex, with the gob sizes, speeds, spins, and directions changing wildly and randomly. Imagine a real-time flight-envelope holograph complete with brightly-lit edge, iso-power, and power-gradient lines, all of them rapidly shifting on the quarter-spherical surface, the flight envelope rapidly pivoting side-to-side around point F. That's what a real flight envelope looks like when flying in unsteady, shifting, turbulent winds!

Near-ideal wind, which has a steady flight envelope, is great fun to fly in. But gnarly wind, with its ultra-dynamic flight envelope, is a huge thrill to fly in!

Effects of non-ideal KITES

Although non-ideal winds are fun, non-ideal kites are not. For kites that deform excessively under the forces of flight, airspeeds are less dynamic -- edge-to-powerzone acceleration is less, and responsiveness to the wind is less, both of which grow worse with kite proximity to the powerzone and with increasing wind speed. For some non-ideal kites, airspeed in the powerzone can be less than airspeed at the edge!

Non-ideal kites that deform a lot feel "dead" in gnarly winds. Near-ideal kites such as WindDances feel exciting and alive in those winds!

Safety 

The flight envelope intersects the ground along semicircle LPR. That's where you launch, land, relaunch, do ground tricks, crash, and bounce your kite. The sport has no special name for that important and heavily-used portion of the flight envelope, perhaps because it can be a dangerous place, perhaps because of the accidental kite damage and injuries to bystanders and other flyers that have occurred there. Imagine a delta kite crashing straight down into hard ground at 50 mph. Imagine being hit by a half-pound delta kite flying at 50 mph. It can be worse than being hit by a blunt arrow. We call the semicircle LPR the impact zone, a term which has danger and fun connotations. Just for fun, to get people to listen up for their own personal safety, sometimes we call it the "Arc of Death."

Within the sector FLPRF, flying lines can swoop close the ground as the kite flies. Safety-educated flyers know that tightly-stretched flying lines can cut like a knife, but most bystanders do not. The sport has no special name for this area, perhaps because it can be a dangerous place, perhaps because of the injuries and property damage that have occurred there. We call this entire sector -- which includes the impact zone -- the danger zone.

Popular flying areas become crowded with dual-line flyers. Some flyers roam as they fly -- their moving flight envelopes envelop bystanders, and intrude into the flight envelopes of other flyers. New flyers arrive, set up very close to other flyers, and begin flying -- sometimes from within other flight envelopes, and sometimes their new impact zones arc through other flyers. Inexperienced flyers typically walk backwards as they fly, sometimes hundreds of feet without looking where they are going, directly into impact zones. People, sometimes with small children, casually walk through flying areas and stop and watch, sometimes directly beneath kites and lines that are flying fast.

What can happen when flight envelopes touch or overlap? What can happen when people walk into and stand on impact zones or within danger zones, or when a flyer moves and begins flying over bystanders?

• L/R danger-zone overlaps: If the intruding flight envelope's impact zone does not reach flyer at F, possible kite damage and severed flying lines to both parties. If the intruding impact zone does reach or pass point F, possible injuries to flyer at F (hit by other kite, lacerated by other flying lines), as well as possible kite damage and severed flying lines to both parties.

• F/P danger-zone overlaps: Possible injuries to downwind flyer (hit by upwind kite, lacerated by upwind flying lines), possible kite damage to upwind party, possible severed flying lines to both parties, .

• Bystanders positioned in the impact zone or within the danger zone: Possible injuries to bystanders (hit by kite, lacerated by flying lines).

Dual-line stunt kite flying is fun. If all flyers become educated in the few simple and sensible safety basics -- all manufacturers, wholesalers, and retailers could easily educate their customers at near-zero cost per kite -- and if flyers look out for their own safety, look out for the safety of others, and graciously educate others about safety as the need arises, it can become a safer sport, too.

Speed & pull

The speed & pull described below occur when you fly "passively," that is, when you gently steer your WindDance all over its flight envelope and let the wind do its thing. (When you fly passively, you're just the pilot standing there twiddling the controls.)

When you fly "actively," that is, when you accelerate strongly by pulling hard on both lines or when you turn fast & powerfully by pulling hard on one line (all that pulling action, "pumping air," is high-quality exercise), the speed & pull is substantially higher than described below. When you fly actively, you convert the many kilocalories of energy from your previous meal into spectacular high-speed aerobatics. You're the pilot and the engine and you body tells you so as a pleasant burn, and perhaps as weight loss if you WindDance often enough.

Pull is determined by:

• Wind speed and wind quality, the strongest two influences on pull.
• Location of kite on its flight envelope, the second-strongest influence.
• WindDance size.
• Kite's state of performance tuning: bridle setting, air resistance of tails, and flying-line length and thickness.

For a given WindDance model and state-of-tune, pull is caused entirely by kite airspeed: pull increases in proportion to the square of kite airspeed. When kite airspeed rises 41% (say from 10 mph to 14 mph), pull doubles. When kite airspeed doubles, pull quadruples. When kite airspeed triples, pull is 9X stronger. When kite airspeed quadruples, pull is 16X stronger. And so on.

Kite airspeed is determined by a COMBINATION of wind speed and location of kite on its flight envelope.

Kite airspeed increases in proportion to wind speed: When wind speed doubles, kite airspeed doubles. When wind speed triples, kite airspeed triples. And so on.

Here is how kite airspeed and pull vary when the wind is steady, that is, how location of the kite on its flight envelope affects kite airspeed and pull. Suppose you fly from anywhere on the edge (minimum kite airspeed and pull) to the powerzone (maximum kite airspeed and pull): kite airspeed increases from wind speed to 4X wind speed, and pull increases 16X.

Here is how kite airspeed and pull vary when the wind is gusting, that is, how change in wind speed and location of kite on flight envelope COMBINE to affect kite airspeed and pull. As you fly from the edge to the powerzone, suppose the wind speed doubles due to a gust: from the edge to the powerzone, kite airspeed increases 8X and pull increases 64X. This is why you have to be careful in gusty winds.

The kite-airspeed and pull behavior described above, although theoretical, is fairly close to what actually happens with WindDances in reasonable winds.

The kite's state-of-tune affects pull: Bridle setting can be adjusted to make pull stronger or weaker. Tails reduce kite airspeed and pull. Increasing flying-line length and/or thickness decreases kite airspeed and pull.

Wind quality also affects pull: Gusts momentarily increase airspeed and pull. Turbulence and dead spots reduce airspeed and pull. Smooth and steady wind generates the highest speed and pull of all.

How to reduce pull

• Choose to NOT fly in excessively strong and gusty winds.
• Fly only along the edge of the flight envelope.
• Fly a smaller WindDance instead.
• Add a pair of big tails. The more effective they are as "airbrakes," the greater the reduction of speed & pull. Reduce bridle setting if necessary.

Strong-wind flying

Strong winds are generally unsteady. Pull can be very choppy. In wind averaging 20 mph, wind speed can randomly spike down to 10 mph (pull briefly equals 25% of 20-mph pull) and up to 30 mph (pull briefly equals 225% of 20-mph pull). Gust-induced jolts can be nasty, and totally unpredictable. Once, while test-flying a WindDance 3 prototype in strong wind, a gust instantly snapped both 200 lb-test flying lines!

The safest way is to ease into strong-wind flying by starting with really-big tails and reducing tail size when it seems safe, and by being fully prepared to let go of the flying handles if a rogue gust hits. That means taking the precaution of flying very far upwind of other flyers and anything else that a released kite and lines and handles could possibly drift into. Better yet, wait for calmer winds.

Wind quality

Wind is rarely steady. Its strength & direction in the vicinity of the kite constantly vary as you fly:

• Changing wind speed changes your kite's airspeed and pull. You can feel the changing pull far more sensitively than you can see the changing speed.

• Wind direction near your kite can rapidly shift side-to-side and up-and-down. In addition to affecting airspeed and pull, this can alter the kite's flying direction and knock it out of the sky!

Blustery wind can be demanding, forcing you to quickly respond to your kite. A gust may suddenly yank you hard -- requiring you to give to prevent the pull from rising too high. Wind may suddenly blast against the top or one side of your WindDance and making the lines go slack -- requiring you to take up the slack to regain control. In extreme turbulence, wind speed and direction can fluctuate so wildly you can't fly straight and you may experience jolts of strong pull in only one flying line at a time while trying to.

Farther aloft, where real aircraft fly, occasional turbulence is far more intense and serious. Turbulence collapses paraglider wings. Turbulence slams jet airliners downward so fast that cabin tops hit passengers who are not buckled up. In comparison, the turbulence you experience while dual-line flying is nothing.

Ever notice on some days how the wind seems weak and your kite won't fly well, even though the wind is the same strength as before as measured by your meter? The culprit is low-quality wind: Turbulent wind, wind that's chopped up into tiny swirling pieces. And wind filled with zillions of dead spots, "swiss-cheese" wind (although meters have difficulty sensing the small holes, kites sure can and your skin can feel the dead spots also).

Turbulent wind and swiss-cheese wind reduce speed & pull. Smooth and steady laminar-flow wind generates the highest speed & pull of all. Sometimes a very smooth & steady 5-mph wind can generate more speed and pull than low-quality 10-mph wind!

How to measure and judge the wind

The best wind speed meter is also the least-expensive one: the "Dwyer Wind Meter," the one that looks like a thermometer. It responds really fast to peaks and dips in the wind. It's good at indicating turbulent wind, too -- the little ball bounces up and down like crazy as it follows the spasms!

You also need a "windwand" to tell wind direction. If the yarn tell-tale rapidly pivots like a nervous weathervane, the wind direction is shifting rapidly (and the wind speed is probably changing rapidly, too).

Good wind, wind that generates the most speed and power, is smooth-and-steady wind that's free of any turbulence. The wind-meter's little ball and the windwand's yarn stay rock-steady. Trees bend, possibly way over in strong wind, but they do not wave or sway at all. If you are flying near a lake, the waves and ripples have a uniform texture and the surface has an even color and brightness. Listen carefully as it rushes past your ears: it sounds smooth.

Bad wind, wind that generates the least speed and power, is unsteady turbulent wind. The wind-meter's little ball bounces up and down -- bouncing-up-and-down slowly means the wind is unsteady, bouncing-up-and-down very rapidly (vibrating) means the wind is turbulent. The windwand's yarn weathervanes wildly and rapidly, side-to-side mostly but sometimes up-and-down too! Trees and branches wave and sway like crazy. If you are flying near a lake, the surface has an uneven texture, color, and brightness -- light and dark areas move around, appear and disappear, the darker the color the stronger the wind. The wind even sounds rough when you listen to it.

The most boring kind of wind? Steady turbulent wind. The meter's little ball and the yarn stay pretty much in the same positions but they vibrate, indicating the constant turbulence that kills off flight performance. Low speed and pull. Kite feels dead.

The most exciting kind of wind? Unsteady smooth wind. The meter's little ball and the yarn change position -- sometimes rapidly -- but the ball and yarn don't vibrate which means the wind is smooth. It's lively, powerful wind! Hot speed and strong pull with smooth jolts of speed and pull whenever the wind pulses! Your WindDance feels alive!

If your Dwyer meter says 5 mph and the ball is steady, call it 5 mph wind.

If the ball moves up and down between 2 mph and 8 mph -- averaging 5 mph -- call it 2 mph wind because that's how the kite feels.

How speed & pull affect performance

The kite airspeed and pull characteristics in the above Speed & pull section are for a theoretical idealized kite, a kite that does not deform at all while flying.

Real kites aren't like that.

While flying, suppose you feel a pull of 50 lb. Well, the kite feels it too: bridle lines pull 50 lb on the wing from one direction, net aerodynamic forces pull 50 lb on the wing from the opposite direction, causing stress and strain within the wing's structure. The stronger the pull, the more the wing distorts from its original low-pull shape. This happens with diamond, delta, parafoil, and hybrid dual-line kites.

That wing distortion reduces the kite's aerodynamic efficiency (L/D, lift to drag ratio), which slows the kite down. That's why wing distortion causes kite airspeed and pull to increase less than the theoretical ideal as wind speed increases and as the kite flies from the edge to the powerzone. Speed & pull cause performance to deteriorate.

Dual-line kites are subjected to relative forces that real aircraft cannot possibly take. For example, the 5.5 oz WindDance 1 can withstand 100 lb of pull with little distortion. That is equivalent to a real airplane being subjected to a 300-g gust or turn! Aircraft distort by disintegrating in the 10-g to 20-g range. So when you look at the big picture, all dual-line kites do quite well.

For kites that deform a lot, large parafoils and large and/or lightweight deltas for example, the distortion is substantial and the speed loss is huge. For example, our first from-scratch experimental delta (1989), the worst kite we have ever flown, distorted so much and lost so much aerodynamic efficiency as it flew from the edge toward the powerzone it came to a halt before it could even reach the powerzone!

For kites that deform very little, such as well-engineered parafoils and deltas, the speed loss is small.

Typically for delta and parafoil kites, the larger the kite the slower it flies. Why? Larger kites usually distort more, which causes them to lose more aerodynamic efficiency and speed. That's one reason why most flyers think smaller kites are faster and bigger kites are slower.

Exactly how much is the speed loss caused by L/D loss? See the fundamental performance equations of dual-line kite FLYING on our Kite Physics 102 page.

Real-kite examples:

For a delta kite, the inherently-low structural efficiency common to all delta kites causes several kinds of wing-shape distortion to occur when the kite is subjected to pull and airspeed. A delta kite's many different "in-flight shapes," which range from its "light-wind edge shape" to its "strong-wind powerzone shape," are very different from its "showroom shape." The changes in shape of the frame, sail, and dihedral can be large and easily seen by flyers and bystanders. And often heard, too, such as when a quiet kite begins to flutter a little at first and then more and more severely as the wind increases. As the shape of the wing changes due to pull and airspeed changes, the bridle setting needed for best performance changes. To maintain the best flight performance, the bridle must be re-adjusted as the kite flies across the flight envelope, and it must be re-adjusted as the wind changes. Automatic in-flight bridle adjustment, however, is not yet available. Therefore a delta kite's bridle setting is not correct for best performance most of the time, even when flying in steady wind. Most deltas come equipped with a large bridle-adjustment range for the purpose of accommodating winds of different strengths. But what can you do when the wind changes rapidly and substantially while you are flying? Distortion-caused speed loss, as well as lack of a bridle that constantly self-adjusts to the necessary optimum settings as the kite's airspeed and pull change, are why delta kites in general do not accelerate well as they fly from the edge to the powerzone, why they do not respond well to the wind, why they do not fly well in unsteady winds, and why they have relatively narrow wind ranges. The less a delta kite deforms when subjected to pull and airspeed, the better its flight performance. That is the aeronautical and structural engineering challenge.

For conventional parafoils, similar problems occur. The engineering challenge is the same as with deltas.

For WindDance parafoils, wing-shape distortion is low when the kite is subjected to pull and airspeed. There is no visible difference between the "light-wind edge shape" and the "strong-wind powerzone shape." Once the High-Performance bridle setting has been tuned in, and is maintained by occasional re-tuning as the kite undergoes wear-and-tear, the bridle setting does not have to be changed for different winds. The bridle setting that's best for very light winds is also best for strong-wind power flying, for all wind strengths in between, and for all kite locations on the flight envelope. Low distortion under bridle and aerodynamic loading is also one reason why WindDances accelerate so well as they fly from the edge to the powerzone, why they respond so well to the wind, why they fly so well in unsteady winds, and why they have such a wide wind range. All this was accomplished through careful aeronautical and structural engineering.

Apparent speed vs. actual speed 

How do kite size and line length affect perception of "speed?"

If a large aircraft and a small aircraft fly past you one at a time at the same speed and altitude, the small aircraft seems "faster," an illusion.

If either aircraft flies by at an altitude of 500 ft and then at 1000 ft, the same speed each time, the lower-altitude speed seems "twice as fast," another illusion.

The same illusions occur with dual-line kites:

A smaller kite seems "faster" than a larger kite that flies at the same speed -- to the flyer and to bystanders.

From the flyer's standpoint, a kite on 50 ft lines seems "twice as fast" as when on 100 ft lines -- but bystanders see no speed difference.

To the flyer, a two-foot-long kite flying at 50 mph on 100 ft lines has the same size and speed as a one-foot-long kite flying at 25 mph on 50 ft lines -- but to bystanders, one kite is obviously twice as fast as the other.

Note: Switching from 100 ft to 50 ft lines does increase the kite's actual speed due to the reduced aerodynamic drag of the lines, but only slightly.

How can you use the kite size and line length speed illusions? To make a kite seem "faster" to the flyer by flying it on short lines. To make a kite seem "slower" to the flyer by flying it on longer lines. To sell "fast" kites: tiny kites on very short lines.

Airspeed vs. groundspeed

Kite "airspeed," the speed the kite experiences, is the speed you feel in the form of pull and is the speed you hear.

Kite "groundspeed" is the kite's speed that you see.

All of the time, those two speeds are different. Sometimes very different. The speed you feel and hear never match the speed you see!

Sometimes groundspeed is higher than airspeed. That happens when your kite is flying from the edge to the powerzone.

Sometimes groundspeed is less than airspeed. That happens when your kite is flying from the edge to the powerzone. For example, while your kite hovers stationary at the edge, its groundspeed is zero and its airspeed equals the wind's speed.

While WindDancing side-by-side with a friend, the two WindDances can have identical airspeed & pull at some particular instant but very different groundspeeds: one WindDance can be seen flying twice as fast as the other!

These mysteries of speed, as well other interesting things about speed & pull, are explained on the Kite Physics 102 page.

WindDance dual-line parafoil stunt kites/sport kites are developed, sold, and backed by Seattle AirGear.
WindDance, WindDancing, Seattle AirGear, and AirGear are trademarks of Seattle AirGear.
Copyright © 1995-2017 Seattle AirGear.
This page last revised Jan-9-2000