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Suit Yourself™ International Magazine #22: Go Fly A Kite

  

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Suit Yourself™ International Magazine #22: Go Fly A Kite 

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This week we take a break from our series and talk about flying kites and where to do it on Islesboro Island. This is the 22nd in our articles series and I hope this information is helpful.

All previous articles in the series can be found in our library and in the magazine archives.  Upon request, reprint permission and an addendum of substantiating resources are available for all magazine articles. When requesting reprint permission or addenda, please include the issue date and full issue title. All magazine articles are copyright © Debra Spencer, Suit Yourself ™ International. All rights reserved. ISSN 2474-820X. 

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Ideal public locations on Islesboro Island for flying kites include:
Maddy Dodge Soccer Field, on Hewes Point Road.
The Flag Green, at the Islesboro Ferry Landing.
The Islesboro Town Beach, located at the southern end of the island.
Sprag's Beach, located at the northern end of the island.

 

 

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 GO FLY A KITE!   

 

How to fly a kite, where to fly one on Islesboro Island, and why a kite flies at all.

Animated Geese In Flying Formation; Japanese Ukiyo Woodblock Print Gif.  

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Flying kites are beautiful things.  In San Francisco, contests of kites in the forms of flying dragons, sea monsters, streamers, and birds, can be seen as undulating, souring rainbows, bouncing over the tops of city houses, streets, and buildings, almost as if they actually lived amongst the clouds. The kite, milvus lineatus, is a large carnivorous bird that gave its name in English to the aerial toy from China introduced to Europe sometime before Giambattista della Porta wrote Magia Naturalis in 1589, the earliest literary notice of kites. The Chinese characters 'chih yuan' mean 'paper kite' where 'kite' is indeed the bird. Chinese kites were often fashioned to look like birds or dragons. 

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Les Cerf-Volants.

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Wikipedia states that kites were invented in China (https://en.wikipedia.org/wiki/Kite), and by 549 AD paper kites were certainly being flown, as it was recorded that in that year a paper kite was used as a message for a rescue mission.  Dr.  J. B. Calvert disagrees about the origins (http://mysite.du.edu/~jcalvert/tech/kites.htm). Calvert states that although kites were common in Southeast Asia , they were unknown in the West. The origin of kites, which is apparently not Chinese, is ancient and unknown. They had uses in religious rites, and the Chinese are said to have used them to carry fish-hooks away from boats to help fool the fish. Apparently, they were also used with humans attached to them, as a divination method; a prisoner or vagrant was tied to a mat that served as the kite, and flown as high as possible to find out whether or not a sea voyage would be successful. If they got the man in the air, the voyage would be prosperous. There are no records of whether or not the prisoner or vagrant survived the process.

 

Les Cerf-Volants S.O.S.

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Kites are also much more than toys or divination 'methods';  flying a kite is a very practical skill to have. Kites have been used to deliver food bundles and propaganda leaflets inside besieged towns, and as signals. Some kites had aeolian chimes that sounded as they flew. Kites have proved useful in many serious science experiments. Alexander Wilson used kites in 1749 to carry a thermometer into the sky for measuring air temperatures up to 3000 ft altitude. Benjamin Franklin flew a kite in 1752, using a conducting string, and in the strong electrical fields near a thunderstorm, to demonstrate that atmospheric electricity and static electricity had the same properties, and were, in fact, the same. On May 10, 1752, Thomas-François Dalibard of France conducted a similar experiment using a 40 feet (12 m) iron rod instead of a kite, and extracted electrical sparks from a cloud. Lucky him. In 1893, Lawrence Hargrave invented the box kite, a form of kite with greater stability and lift, and suggested the biplane. By 1899, the Wright Brothers were using kites to test their design theories. Indeed, kites are the precursors of today's drones that will soon be delivering your groceries and household shopping supplies. 

 

The Kites Of Charles Deffain, who was a commercial traveler in wooden toys and kites at M. Georges Tranchant, located in Montreuil-sous-Bois, near Paris. Charles Deffain joined the Turchet company in 1910.
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You can fly a kite on virtually any day; with light winds, you can try and fly your kite at a higher altitude, while with heavier winds, you might want to fly your kite lower. Should the weather start to drizzle, reel in the kite!  It's not safe to fly the kite once the weather starts to drizzle, and you should not fly a kite when there is rain or lightening. Look up what happened to Benjamin Franklin and don't let that happen to you. Forces are real; they are not imaginary, and flying a kite is a beautiful way to actually FEEL and INTERACT with the aerodynamic forces of Mother Nature.  She surrounds you!
 

 

You can fly a kite on virtually any day. Harry Whittier Frees photograph: Kitty spider kite prank

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LAUNCHING AND FLYING A KITE

A kite is launched by running with the string, and paying the string out as the kite rises. At altitude, the stronger wind takes over to keep the kite aloft, so you as kite-flyer can stop running.

Most kites have three parts: the frame body and its' covering, the harness, and a tether control line.  There are many different kite shapes and they all fly a little differently, with different abilities and tradeoffs, such as stability versus maneuverability.  

 

Most Kites Have Three Parts; old kite illustration "how to put in the sticks".

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Most kites are shaped and angled so that the air moving over the top moves faster than the air moving over the bottom. Kite frames are usually made from solid materials like wood or plastic. To overcome the weight of the kite, the frame is covered with a paper, plastic, or cloth "skin" which interacts with the air to generate the lift necessary to overcome the kite's weight.  
 

 

Fabrication cerf volant, 1902.

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There's s a design balance between being light enough to fly well, yet strong enough to withstand winds at a higher altitudes than where you're standing when you fly the kite. 
 

 

Comment fair un cerf-volant en forme de losange.

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The forces acting on the kite are essentially its' weight, the pressure of the air on the kite, and the tension in the string controlling the kite. The attitude of the kite must be maintained so that the force of the air is upward, which can be done by attaching the string correctly, or by hanging a weight from the end of the kite that should be down. 
 

 

Hanging a weight from the end of the kite that should be down: Fier Drake, 1634 kite woodcut.

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It's challenging to determine the forces acting on kites! The Wright Brothers learned a lot from doing this. They had no small challenge developing their successful 1903 aircraft and as early as 1899, were using small maneuverable kites and flying their gliders as unmanned kites at Kitty Hawk, North Carolina.  NASA has a KiteModeler for creating different models of kites and for learning what these models do. It helps solve the equations of the forces and torques on the kite, the sag in the control line, and gives an approximation of the actual flight characteristics of your kite's design. You can even test how your kite design would fly on Mars, or how high your kite design will fly off the top of a mountain. NASA's Interactive Kite Modeler https://www.grc.nasa.gov/WWW/K-12/airplane/kiteprog.html

 

It's challenging to determine the forces acting on kites and the Wright Brothers learned a lot with them. Harry Whittier Frees photograph: Kitty Aviator

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The kite's motion through the air is the result of the four aerodynamic forces of weight, lift, drag, and thrust being applied to the kite,  and the kite responds to these forces according to Newton's laws of motion. 
 

For a recap of Newton's Laws, see 
NASA's section 'Laws Of Motion' at 
https://www.grc.nasa.gov/WWW/K-12/UEET/StudentSite/dynamicsofflight.html#forces 
and NASA's Newton's Laws of Motion at 
https://www.grc.nasa.gov/WWW/K-12/airplane/newton.html 

 

The kite's motion through the air is the result of the four aerodynamic forces; the toss up (old illustration).

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SUCCESSFULLY LAUNCHING THE KITE

To launch a kite, you have to create a lift force greater than the weight of the kite; the important factor for generating lift is the relative velocity between the air and the kite, the velocity of the air going by the kite.

 

To launch a kite you have to create a lift force greater than the weight of the kite.The Lift changes with the square of the velocity. Harry Whittier Frees photograph:  3 kitten balloonists.

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While wind is obviously a big part of kite flying, it doesn't matter whether the air blows over the kite, or the kite is pulled through the air. To keep the kite aloft, lift must overcome weight, and thrust must overcome drag. 

The size of the lift force is affected by many factors, including the size and shape of the kite's wing, the angle at which the wing meets the oncoming air, the speed at which the wing moves through the air, and even the density of the air. But the important factor for generating lift in the first place is the relative velocity between the air and the kite. 

 

The size of the lift force is affected by many factors. Harry Whittier Frees photograph: Flying Kitty Witch.

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Air density varies based on your altitude (where you're located on planet earth); the higher your elevation, the lower the air density. So lift will vary with altitude.

If you face the kite and have the wind at your back, you already have some relative velocity provided by the wind. On windy days, this velocity, plus a small tug on the line, is usually enough velocity to lift the kite into the air. 

On less windy days, you may have to move backwards or run into the wind to get the kite flying. 
 

 

On less windy days you might have to run into the wind to get the kite flying. Harry Whittier Frees photograph: Kitties skating.

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As the kite rises during its' launch, you can usually just stand still and the kite will fly just fine, because the velocity of the wind normally increases as the altitude increases.  The change in velocity from the surface of the earth to some altitude is caused by the boundary layer of the earth's atmosphere. Inside the boundary layer, the velocity is low and may be unsteady. But with enough altitude, the velocity (and the lift force) become fairly constant.

Once the kite has launched, the kite will cruise at an altitude, and in an attitude, where all the forces and the torques are balanced. If the forces are changed, the kite moves until the forces are again in balance.

 

 

Once the kite is launched it will cruise at an altitude where the forces are in equilibrium. Harry Whittier Frees photograph:  Full moon balloon kitties afloat in their balloon.

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You can slightly increase the velocity of the kite by pulling on the control line. This increased velocity increases the lift, which causes the kite to climb. If the wind velocity is even slightly higher at the new altitude, the kite will remain at that altitude. 

Letting out the line will initially cause the kite to drop slightly,  due to the increased weight of the line and decreased tension in the line (slight decrease in velocity). Pulling or tugging on the line can move the kite back up to a higher altitude.

The air velocity is the relative speed between the kite and the air.  The lift changes with the square of the velocity. When you  pull on the control line, the velocity becomes the wind speed plus the speed of your pull.  When the kite is held fixed by the control line, the relative air velocity is the wind speed. If the line breaks, or if you let out the line, or if you let the line go slack, the velocity will be something less than the wind speed. 

When the kite is cruising in flight, notice that the control line produces a gentle curve from your hand to the kite, as the line sags under its own weight. Because the weight of the control line is evenly distributed along the length, the line hangs under its own weight.   More technical information on the control line, see NASA's Control Line Equations, here:
https://www.grc.nasa.gov/WWW/K-12/airplane/kitesag.html
You can use the equations for sag on a control line to determine the altitude of the kite.

To determine the maximum altitude of a kite:
https://www.grc.nasa.gov/WWW/K-12/airplane/kitehigh.html

This information is also very useful for rescuing your cat stuck in a tall tree, and for figuring out what size ladder you are going to need to get the cat down and out of the tree.


 

This information is also very useful for rescuing your cat! Kitty and friends climb the wall to 'execute' a rescue. Harry Whittier Frees photograph: Over The Wall Rescue.

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The aerodynamic lift of your kite depends directly on the surface area of the kite, and the surface area depends on the particular design of your kite. For those of you interested in how to compute the area of the geometric shape of your kite, and determine the lift and drag that it generates, I love NASA's simple and straightforward AREA article, here: https://www.grc.nasa.gov/WWW/K-12/airplane/area.html

So, to launch a kite into the air, the force of lift must be greater than the force of weight.  To keep the kite flying steadily, the four aerodynamic forces of weight, lift, drag, and thrust must be in balance.  Lift must be equal to weight, and thrust must be equal to drag.
 

 

To launch the kite into the air, the force of lift must be greater than the force of weight. Harry Whittier Frees photograph:  Taking The Plunge.

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WHY DO KITES FLY? 

Like birds, bees, leaves, and airplanes, kites are heavier than air. So how can these things 'fly'? Aerodynamics is the study of air interacting with things, and things interacting with air.   Understanding how to fly a kite, and why heavy things can 'fly', requires a little knowledge of aerodynamics.  It helps to remember what happens when you sit down on something that can't support your weight, and to imagine air as if it were water, a freely flowing fluid liquid. 

What's a 'fluid'?  
A fluid is some continuous, amorphous, constantly changing substance, that is this way because its' molecules all move around freely past one another. Fluids have the tendency to assume the shape of the container they're in. In physics, a fluid is a substance under some applied shear stress that makes it continually deform / change shape / 'flow'. Now you know where the term 'traffic flow' comes from.

 

 

What's a 'fluid'?  Harry Whittier Frees photograph: Fishing.

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What's 'shear stress'? 
 Picture a milk carton; it's a rectangle sitting up on its' short edge, and now hold that end in place; now sit down on the milk carton (use your imagination not your real rear end!); this means you're applying a force to the top. Oomph! You flatten it, don't you?  This result is called 'the resulting shear stress' that 'deforms' the rectangle milk carton into a parallelogram. The 'area' involved would be the top of the parallelogram, where you sat down. The short hand for this whole idea of 'resulting shear stress' is abbreviated in writing by using the Greek letter τ to represent it, called TAO, and pronounced 'dow'. And 'the resulting shear stress' is the area ('A') where you sat down, divided by the force ('F') of your weight when you sat down. Your force acts perpendicular to the milk carton's surface.  Force is a 'vector quantity'; it has both magnitude (your weight) and direction (where and how you sit down). 
τ = F/A. 
τ = the shear stress;
F = the force applied;
A = the cross-section of area of material, with that area parallel to the applied force vector.

 

What's shear stress? Harry Whittier Frees photograph: Rolling Dough.

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What's 'Aerodynamics'?
The word 'aerodynamic comes from Greek words aer (air) + dynamics, and it means the study of the motion of air. Aerodynamics studies the way air moves around things, and quantifies what's needed for things in air to move around, up and down, faster or slower. Aerodynamics uses four concepts, the forces of  weight, lift, drag, and thrust. Varying the amount of each of these forces changes how the object moves through the air, and how the air moves around the object.

 

What's aerodynamics? Harry Whittier Frees photograph: Swinging kitties.

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Weight & Lift
For anything to fly requires that there is something pushing it in the opposite direction from gravity, and the weight of the object controls how strong that push has to be. Lift is the push opposing the weight; it's the mechanical force generated by a solid moving through a fluid.  For something to fly, there has to be more lift than weight. 

 

Weight & lift; Harry Whittier Frees photograph: Helping Themselves To Get The Jam.

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Many things create 'lift' by using curves on wings, to change the distribution of air pressure on each side of the curved wing, causing a differential that makes the 'lift'. Kites 'lift' comes from a curved shape. Boat sails are like curved wings used to make the sailboat move. Airplane's wings are curved on top, and flatter on the bottom; this curved shape makes the air flow faster over the top than under the bottom, so the air flow and air pressure over the top is different from the flow and pressure over the bottom, and with more pressure on the bottom and less pressure on the wing top, the wing, and the attached airplane, lift up, up, and hopefully, away.  For a more technical explanation, see NASA's Dynamics Of Flight at   https://www.grc.nasa.gov/WWW/K-12/UEET/StudentSite/dynamicsofflight.html#forces .

 

Many things create 'lift' by using curves on wings. Harry Whittier Frees photograph: Catching fireflies and butterflies.

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Lift occurs when a moving flow of gas is turned by a solid object. The flow is turned in one direction, and the lift is generated in the opposite direction, according to Newton's Third Law of action and reaction. For a recap of Newton's Laws, see 
NASA's section 'Laws Of Motion' at 
https://www.grc.nasa.gov/WWW/K-12/UEET/StudentSite/dynamicsofflight.html#forces 
and NASA's Newton's Laws of Motion at 
https://www.grc.nasa.gov/WWW/K-12/airplane/newton.html 

 

The lift is generated in the opposite direction. Harry Whittier Frees photograph: Seesaw Kitties.

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Because air is a gas and the molecules are free to move about, any solid surface can deflect a flow. For a curved surface such as an aircraft wing, both the upper and lower surfaces contribute to the flow turning. Neglecting the upper surface's part in turning the flow leads to an incorrect theory of lift. 

Lift is a mechanical force; it is generated by the interaction and contact of a solid body with a fluid (liquid or gas).  For lift to be generated, the solid body must be in contact with the fluid: no fluid, no lift. Without air, there is no lift generated by wings. Lift is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid: no motion, no lift. It makes no difference whether the object moves through a static fluid, or the fluid moves past a static solid object. Lift acts perpendicular to the motion. Drag acts in the direction opposed to the motion.

 

Lift acts perpendicular to the motion. Drag acts in the direction opposed to the motion.
Harry Whittier Frees photograph: Fishing by the seat of his pants.

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There are, incidentally, many erroneous, misleading, and just plain incorrect explanations on lift found in encyclopedias, various web sites, and even some textbooks; I suggest NASA as a reference, especially
What Is Lift?  https://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
and
https://www.grc.nasa.gov/WWW/K-12/airplane/wrong3.html 

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Drag & Thrust
The more air that hits a surface, the more the air will slow down the movement of that object. It makes it hard for an object to move.  This effect is called 'drag'.  For a more technical definition, please see NASA's article on Aerodynamic Forces at
https://www.grc.nasa.gov/WWW/K-12/airplane/presar.html

Clearly, changing an object's shape alters the amount of drag. Flat surfaces usually drag more, or 'have more drag', than round surfaces, and wide surfaces will usually drag more, or 'have more drag', than narrow surfaces.

Thrust is the push that moves something forward. Thrust is used to overcome the drag.  For anything to continue moving, thrust must be greater than drag; it must have more thrust applied to it than drag holding it back. 

 

For anything to continue moving, it must have more thrust applied to it than drag holding it back. Harry Whittier Frees photograph: Oops

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Paper airplanes, for example, are 'gliders'; they get all their 'thrust' from their initial toss from your arm, and that energy can only go so far; they fly only until drag wins, slowing down the paper airplane and causing it to 'land'. The drag is caused by the difference in air pressure between the front and back of the paper airplane glider, and the friction of the air moving over the surface of the paper airplane glider.  

 

Pliage du cerf-volant en origami. 

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Air, Flow, & Pressure
Air molecules mostly move around freely and this random motion of air molecules is what causes air pressure. When 'air' meets object, it has to 'get around' the object, just like you do when driving in traffic, and you decide to change lanes. But 'air' at low speeds acts like water, not like your solid car.  Air can't just 'drive around' an object; air has to change itself in two ways to flow around an object. But like your car, all the air has to move on, to flow past the 'block' .

If you have seen the Harry Potter movie "The Prisoner Of Azkaban", the Magic Bus scenes are visual examples similar to what happens. Air reacts to a block in its' path by narrowing its' flow, and this squeezes the air, compressing it. When air is squeezed, two things happen: first it speeds up, and second, as it speeds up, the pressure, the force of the air pressing against the side of the objects it passes, goes down. Once the air is past the objet, its' pressure goes back up to where it was before it 'met' the object, and it expands again.

Whenever air moves through an area that has narrowed or widened due to a block or some other cause, the air has to speed up, or slow down, to maintain a constant amount of air moving through the area.  It has to rearrange its' 'shape' , from moving randomly and freely, to moving in a 'stream' of directed motion. And all the air, all of the 'Magic Bus',  has to move on, to flow on, past the 'block'. 

When air rearranges its' 'shape', it changes its' pressure, and thus the effect it has on things it surrounds.  Air creates more pressure when its' molecules are moving randomly and freely than when moving in a directed 'stream'; thus, we say air moving in a stream flow has lower air pressure.

 

Air Flow & Pressure; Harry Whittier Frees photograph: Accordion dance lessons.

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When two solid objects interact in a mechanical process, forces are transmitted, or applied, at the point of contact. But when a solid object interacts with a fluid, the effects are more difficult to describe because the fluid can change its shape. For a solid body immersed in a fluid, the "point of contact" is every point on the surface of that solid body. The fluid can flow around that solid body, and maintain physical contact at all points. The transmission, or application, of mechanical forces between a solid body and a fluid occurs at every point on the surface of the body. And the transmission occurs through the fluid pressure.

This knowledge is the result of brilliant observations by Daniel Bernoulli, an 18th century Swiss mathematician; we thank-you, Monsieur Bernoulli!

 

Comment fabrique ton cerf-volant.

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NOW GO FLY A KITE! 

To repeat, ideal public locations on Islesboro Island for flying kites include:
Maddy Dodge Soccer Field, on Hewes Point Road.
The Flag Green, at the Islesboro Ferry Landing.
The Islesboro Town Beach, located at the southern end of the island.
Sprag's Beach, located at the northern end of the island.

 

 

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HAVE FUN!  ENJOY!

Animated Kites; Japanese Ukiyo Woodblock Print Gif.  

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I sign our magazine articles "See Into The Invisible". Thanks for reading.

Best Wishes, 
Debra Spencer

All Content is © Debra Spencer, Suit Yourself™ International. Technical Library FAQ Index ISSN 2474-820X. All Rights Reserved. Please do not reproduce in part or in whole without express written consent. Thank you.
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All Content is ©2019 Debra Spencer, Appanage™at www.suityourself.international Suit Yourself ™ International, 120 Pendleton Point, Islesboro Island, Maine, 04848, USA 44n31 68w91 Technical Library FAQ Index ISSN 2474-820X. All Rights Reserved. Please do not reproduce in part or in whole without express written consent. Thank you.

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All Content is ©2019 Debra Spencer, Appanage™at www.suityourself.international Suit Yourself ™ International, 120 Pendleton Point, Islesboro Island, Maine, 04848, USA 44n31 68w91 Technical Library FAQ Index ISSN 2474-820X. All Rights Reserved. Please do not reproduce in part or in whole without express written consent. Thank you.
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