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The Box Kite: Two Cells of Cloth That Hold Themselves Steady

Unknown author · Public domain

أنشأه

Spartan

27. سبتمبر 2026

The Box Kite: Two Cells of Cloth That Hold Themselves Steady

Flat kites need a tail to stay steady and fly only in a narrow range of wind. Lawrence Hargrave, an English-born engineer working in Sydney on the problem of flight, built kites of two open boxes of cloth on a light frame in 1893. The horizontal faces lift, the vertical faces keep the kite facing the wind like a weathervane, and it flies steady without a tail. On 12 November 1894, at Stanwell Park beach, he lifted himself off the ground under a train of four box kites. He published his work freely and took out no patents, believing discoveries should be shared. The box-kite cell shaped the early biplanes. This rung works out a box kite's lift and the wind it needs, and builds one.

مبتدئ

About 4 hours

التعليمات

Lift, weight and the wind it needs

جارٍ تحميل دفتر Jupyter…

Where lift was first measured

Cayley measured the lift of inclined surfaces on a whirling arm. The embedded blueprint repeats it; a kite is the same surface held on a line.

Build a Hargrave box kite

Cut four 900 mm pine dowels as longerons and eight 400 mm dowels as cross-spars. Sew two bands of ripstop nylon, each 1600 mm round and 300 mm wide, with a pocket at each corner for a longeron: these are the two cells, set 300 mm apart on the longerons. Slide the longerons into the corner pockets so the bands form two square tubes. Fit two pairs of cross-spars inside each cell, diagonally, notched at the ends to grip the longerons and tension the cloth. Tie a bridle to one longeron at the front of the front cell and the front of the rear cell, and tie the flying line to it about a third of the way back from the front. Fly it in open ground well away from power lines and roads.

المواد لهذه الخطوة:

طقم أوتاد صنوبر1 قطعة

نايلون ريبستوب1 قطعة

خيط مطبخ قطني1 قطعة

خيط صيد (أحادي الشعيرة)1 قطعة

الأدوات المطلوبة:

ماكينة خياطة

مسطرة

شريط قياس

مسدس شمع لاصق

Measure the line pull against the wind

Tie a spring scale into the line near the ground anchor and read the pull at steady flight. At the same time measure the wind speed at head height with a handheld anemometer. Repeat on several days. Plot line pull against wind speed squared: roughly a straight line, as lift goes with $v^2$. Fit it and work out your kite's $C_L$ from the notebook's formula, using the area of its horizontal faces.

الأدوات المطلوبة:

مقياس رياح محمول

مقياس قوة (ميزان زنبركي)

ساعة إيقاف

A box kite that will not fly well

Box kite problems.

Flow

History and honest limits

**Lawrence Hargrave** (1850–1915) developed the box kite in Sydney in 1893 and lifted himself under four of them at Stanwell Park on 12 November 1894. He shared his results openly and did not patent them. Early aircraft makers, including those building the first European biplanes, took up the box-kite cell. **Honest limits.** The lift coefficient in the notebook is an illustrative value; your measurements give your kite's. Man-lifting kites are dangerous and are not something to try.