Kites: lifting a line, signalling, fishing

A kite is a surface held at an angle to the wind by its bridle: the air it deflects downwards pushes it up and back, and the line holds it. The pull rises with the square of the wind speed: twice the wind, four times the pull.

• Pressure of the wind, ½ × air density × speed²: 19 Pa at 20 km/h, 43 Pa at 30 km/h, 76 Pa at 40 km/h.
• A kite of 1 m² pulls roughly 1.5 kg at 20 km/h and 6 kg at 40 km/h.
• Most kites fly in winds of about 6–28 km/h (Beaufort 2 to 4); the tailless Eddy flies in a light breeze and is steady (Kitecraft).

The flight guide has the lift equation and the table.

• Eddy (tailless diamond): two sticks of equal length, the cross-stick one fifth of the way down and bowed back. The simplest steady kite, for light and moderate wind; the line-carrying kite is one.
• Box kite: two open cells of cloth on a frame of up to sixteen sticks. Steady in gusts and a strong puller: Lawrence Hargrave linked four and was lifted 4.8 m on 12 November 1894 (National Museum of Australia).
• A train of kites on one line lifts more than any one of them: the way to raise a heavier aerial or signal.
• Kites with tails — the bow kite and most shaped kites — need the tail's drag low down to keep the head up.

From Kitecraft (1914):

• Sticks: soft, tough, straight-grained and seasoned: spruce is best; pine, basswood or cedar will do; split bamboo for curved frames. For a 5 ft (1.5 m) kite, 10 × 19 mm.
• Balance each stick on a knife blade and whittle the heavy end until centre and balance agree.
• Lash, do not nail: wind diagonally round both sticks in both directions, then round between the sticks to draw it tight, and glue it.
• String the frame with hard-twisted cotton cord, which does not stretch, through notches in the stick ends; measure both sides until they are equal.
• Leave the cover loose: on a 3 ft kite, cut it 2.5–4 cm outside the string and turn in only 1.3 cm. A tight cover makes the kite dart and dive.

The bridle spreads the line's pull over the frame and fixes the kite's angle to the wind (Kitecraft).

• Eddy: tie the bridle at the crossing and at the tail of the spine, long enough that, stretched out sideways, it just reaches a bow tip; the towing point is there.
• Towing point higher (towards the head): the kite flies higher and more overhead. Lower: it flies lower and pulls harder.
• Adjust in steps of 1–2 cm and fly again.

• Rate the line for four times the pull at the wind you fly in: a gust of twice the wind pulls four times as hard.
• Wear gloves and let line run over them; never wrap line round a hand, which a sudden gust can cut to the bone.
• Wind it on a winder, not in loose loops, and anchor it to something that will not move before handing over.
• Pay out and take in steadily: a jerk in a gust is what breaks lines.

• Never near power lines. If a kite snags one, let go of the line and move away: kite line conducts electricity, above all when wet (PSE&G).
• Never with thunder about: a kite line is a tall lightning conductor.
• Clear of roads and airfields. Large kites are aircraft to the law: in the US, one over 5 lb may not fly above 500 ft, within 5 miles of an airport, within 500 ft of cloud, or in visibility under 3 miles (14 CFR 101.13).

How the first line crossed the Niagara gorge in 1848 (Nebraska State Historical Society):

1. Fly from the upwind bank, so the wind carries the kite over the gap.
2. When it is well past the far bank, pay out line fast: with no pull the kite loses lift and settles there.
3. The far party takes the line and makes it fast.
4. Tie a stronger cord to the near end and haul it across gently; then a rope; then a cable. Each must be light enough for the one before to pull.

The same method raises a line to the top of a cliff, or over a tree for an aerial.