Line-carrying kite
A 1.5 m Eddy kite of spruce and cloth, with a bridle set by rule: steady in light wind, strong enough to carry a line across a river or a gorge.
Home: In the air, Level 2 · Forge, level 1 of 6 in its track. Serves 1 step.
Every build on this site has hazards that injure or kill — quicklime, carbon monoxide, molten metal, collapsing ground. Read the safety notice before starting, and read this build's own failure modes below.
What it is and why this shape
The Eddy kite — two sticks, the cross-stick bowed back — flies steadily in a light breeze without a tail (Kitecraft), which is what carrying a line needs: a kite that climbs and holds station while the line runs out over the gap. Its proportions and bridle are set by rule, so it flies first time.
Line-carrying Eddy kite, front and side
Fig 1
TimberLoose fill / grain
Carrying a line across a gorge
Fig 2
Earth / subsoilLoose fill / grainWater
Keyed parts
| 1 | Spine | 1.5 m, straight, balanced at its centre. |
| 2 | Bow | 1.5 m, lashed across the spine 0.3 m from the top and bent back 12.5 cm by a bow string. |
| 3 | Frame string | Round the four tips through notches; both sides measured equal. |
| 4 | Cover | Cut loose and turned over the frame string. |
| 5 | Bridle | Two legs, tied at the crossing and at the tail of the spine. |
| 6 | Towing point | Where the bridle, stretched sideways, reaches a bow tip: about 0.74 m out from the crossing. |
Specifications
| Spine and bow | 1.5 m each, 10 × 19 mm spruce | Kitecraft's size for a 5 ft kite. |
| Bow position | 0.3 m from the top | One fifth of the spine. |
| Bow depth | 12.5 cm | Bent back about 1/12 of its length. |
| Sail | about 1.1 m² | Cloth, cut loose. |
| Pull | about 1.7 kg at 20 km/h, 3.8 kg at 30 km/h | Lift coefficient about 0.8 assumed; measure yours. |
| Line | 300 m, rated 20 kg or more | Four times the pull at 30 km/h, with margin; enough for a 240 m gap. |
| Wind | about 6–28 km/h | Beaufort 2 to 4. |
Bill of materials
| Material | Quantity | Notes and substitutes |
|---|---|---|
| Spars | 2 × 1.5 m, 10 × 19 mm | Straight-grained, seasoned spruce; or pine, cedar or split bamboo. |
| Cover | about 1.6 × 1.6 m | Light cotton cloth (cambric) cut on the straight grain, or strong paper. |
| Frame and bridle cord | about 10 m | Hard-twisted cotton, which does not stretch. |
| Flying line | 300 m | Breaking load at least 20 kg. |
| Winder | 1 | A stick with two cross-pieces, or a reel. |
| Glue or shellac | a little | Over every lashing. |
| Gloves | 1 pair | For the flyer. |
Tools: Knife · Saw · Needle and thread · Measuring cord · Spring balance
Construction
Choose and balance the sticks
Two straight-grained, seasoned sticks, 1.5 m long and 10 × 19 mm. Find each one's centre by measuring, then balance it on a knife blade; whittle the heavy end until the balance point and the centre agree (Kitecraft). Cut a notch or a saw-cut in each end for the frame string.
Lash the cross
Mark the spine 0.3 m from the top (one fifth). Lay the bow across it there, centred, and lash: wind diagonally round both sticks in both directions, then round between them to draw the lashing tight. Glue or shellac it.
String the frame
Tie hard-twisted cotton cord at the top of the spine, run it through the notches at both bow tips and the tail, and back to the top. Measure the two upper sides until they are equal, bind the tips so the cord cannot slip, then do the same for the two lower sides: the spine may have sprung.
Bow it back
Tie a bow string across the back from tip to tip, and shorten it until the middle of the bow stands 12.5 cm behind the line between its tips. The bend gives the kite its keel, which is what lets it fly without a tail.
Cover it loose
Lay the cover flat, the frame on it. Cut 4–6 cm outside the frame string and turn in only 2 cm over the string, then glue or sew: the rest is slack that lets the cover bag evenly in the wind. A tight cover makes the kite dart and dive (Kitecraft). Cloth must be cut on the straight grain, or it stretches unevenly.
Tie the bridle
Tie one end of the bridle cord at the crossing and the other at the tail of the spine, on the front. Make it long enough that, stretched out sideways, it just reaches a bow tip — about 2.15 m — and tie a small loop there: the towing point, about 0.74 m in front of the crossing when flying. Tie the flying line to the loop.
Test-fly and trim
In a steady 10–20 km/h wind, launch from a helper's hands with 20–30 m of line out. Loops or dives: move the towing point 1–2 cm towards the tail. Sags or will not climb: move it towards the head. Once it holds a steady angle, measure the pull with a spring balance in the line.
Carry a line across
Fly from the upwind bank until the kite is well past the far one; pay out line fast so it settles there. The far party makes it fast; tie a stronger cord to your end and let them haul it across, then a rope. Keep the flying line clear of anyone's hands and anything that can snag it.
Tolerances that matter
| Dimension | Target | Why it matters |
|---|---|---|
| Left and right frame strings | equal within 5 mm | Unequal sides make the kite pull to one side and refuse to climb. |
| Bow crossing | one fifth down the spine | Kitecraft's proportion for the tailless kite. |
| Line strength | at least 4 × the measured pull | A gust of twice the wind pulls four times as hard. |
How this fails
A tight cover: the kite darts and dives. Loosen it.
Unequal sides: it pulls away to one side.
Towing point wrong: too far forward it will not climb; too far back it loops.
Near power lines or with thunder about: do not fly. If it snags a line, let go.
Line round a hand: a gust can cut to the bone. Gloves, and a winder.
How you know it worked
VerificationThe kite climbs and holds a steady angle in a 15–20 km/h wind, its pull has been measured and is under a quarter of the line's breaking load, and it has been flown with nothing in its fall zone.
Scaling and variants
A bigger kite pulls in proportion to its area: double the spine and bow and it pulls about four times as hard, so the line must be four times as strong. A train of kites on one line lifts more without a bigger kite. For stronger wind, build a box kite (Kitecraft).