How to Read the Beaufort Scale for Kite Flying

Most forecasts give you a wind speed and leave the hard part to you. Eighteen miles an hour: is that a lovely afternoon or a broken spar? The Beaufort scale answers that question in a way a bare number never quite does, because it was built around what wind does — to smoke, trees, flags and water — rather than what an instrument says about it.

Learn a handful of forces and you can stand in a field, look around, and know which kite to rig before you unzip the bag.

What the Beaufort Scale Actually Tells You

Francis Beaufort, a Royal Navy officer, devised the scale in the early nineteenth century so that ships' logs could record wind consistently. It runs from 0 (calm) to 12 (hurricane), and each number carries a set of observable effects plus a matching speed range.

Two things about those speeds are worth holding onto. They are averages, not peaks, so a Force 4 afternoon will have gusts well above its nominal top end. And the reference measurement is taken 10 metres above open ground. Your local park, with its trees, hedges and houses, is not open ground.

A Field Guide to Forces 0 to 8

These are the ranges you will actually meet on a British flying field, with the signs to look for.

• 0 Calm (under 1 mph): smoke rises straight up. Nothing flies unless you keep moving.
• 1 Light air (1–3 mph): smoke drifts, you can just feel it on one cheek. Only the lightest single-liners.
• 2 Light breeze (4–7 mph): leaves rustle, flags barely stir. The bottom of the usable range for most kites.
• 3 Gentle breeze (8–12 mph): leaves and small twigs in constant motion, light flags extended. Excellent kite weather.
• 4 Moderate breeze (13–18 mph): dust and loose paper lift, small branches move. The widest choice of kites.
• 5 Fresh breeze (19–24 mph): small trees in leaf begin to sway, whitecaps appear on inland water. Time to shrink your sail.
• 6 Strong breeze (25–31 mph): large branches move, overhead wires whistle, umbrellas become a struggle. Serious flying only.
• 7 Near gale (32–38 mph): whole trees in motion, walking into it is hard work.
• 8 Gale and above (39 mph+): twigs snap off trees. Not kite weather, whatever the kite.

Matching Your Kite to the Number

The force a kite feels rises with the square of the wind speed. Move from Force 3 at roughly 10 mph to Force 5 at roughly 22 mph and the wind has more than doubled, which means four or five times the load on the sail, spars and line. A kite that is comfortable at Force 3 is not "a bit lively" at Force 5. It is overloaded.

So the practical rule is simple: one step up the Beaufort scale, roughly one third to one half less sail area. If you fly a 2.5 metre delta at Force 3, reach for something around 1.5 metres at Force 5. The reverse works just as well: if your kite is barely clawing into the sky at Force 2, don't fiddle with the bridle, just rig something bigger.

Rough mappings

• 0–1: ultralight single-liners, zero-wind gliders you launch by running, or nothing at all.
• 2–3: the golden band. Beginner deltas, most single-line kites, light-wind stunt kites. Best conditions for teaching a child.
• 4: standard dual-line stunt kites, large single-line display kites, small power kites. This is the busiest part of the shelf.
• 5: smaller, stronger stunt kites and traction kites for confident fliers. Children's kites get dragged, stretched and eventually shredded.
• 6: small, well-built stunt kites only, and only if you know the site and its gusts. Land-based traction kites become genuinely dangerous for most people.
• 7 and up: pack up. Lines and sailcloth are not the main concern. People are.

Lines matter as much as the kite. A thin line that behaved perfectly at Force 3 will ping without warning at Force 5, and the same goes for tired bridles and stretched seams. If you are stepping up a force, step up the line too, and check it for nicks before you launch rather than after.

Reading the Wind Where You Actually Stand

Beaufort numbers are measured 10 metres up in open country. Your flying site almost certainly is not that. Trees, walls, buildings and hedges slow the wind and stir it into turbulence, so the air five metres above a car park can bear no resemblance to what the forecast described.

Treat the scale as a starting point, then trust your eyes and skin:

• Smoke, flags and long grass tell you direction and strength in seconds.
• Treetops tell you what is happening higher up, where your kite is heading.
• Ripples on a pond or a puddle are a decent proxy for the surface wind.

Sites also change through the day. On the coast, the sea breeze typically builds as the land warms, so a Force 2 morning can be a Force 4 afternoon. Inland, a ridge or hilltop can be a full force stronger than the valley a mile away, while a field tucked behind a wood is calmer but lumpy and full of holes.

Choosing a Location by Beaufort

In light winds, go high and go open. A hilltop, a large playing field with nothing upwind, or a wide beach will find every scrap of Force 2 that exists. Sheltered gardens and tree-lined parks are the worst places to be in a light breeze, because the trees are stealing the wind you are trying to fly in.

In stronger winds, do the opposite and look for shelter. An inland field with a treeline upwind takes the edge off a Force 5 and turns it into something pleasant. Exposed clifftops and long open beaches hand you the full force of the wind with nowhere to hide — fine for the experienced, miserable for everyone else.

Wherever you go, keep well clear of overhead power lines, roads, railways, airports and crowds. Never fly in or near a thunderstorm: lines conduct, and a kite can carry a charge from a storm that still looks miles away.

Before You Launch

Sixty seconds of checking saves a lot of walking back down the field.

1. Check the forecast average and the gust figure. A wide gap between the two means the field will be livelier than the average suggests.
2. At the site, read the trees, flags and smoke, and settle on a force number.
3. Match kite and line to that number, not to the number you were hoping for.
4. Watch the wind for a full ten minutes before you rig. Lulls and gusts show up in that window and nowhere else.
5. Pick your launch spot with clear, empty space downwind. That is where the kite ends up if anything goes wrong.
6. Set a limit in advance. If it is blowing harder than you enjoy, the honest answer is to come back tomorrow.

The Beaufort scale rewards a little attention. Once you can glance at a swaying tree and think "that's a five", you spend far less time wrestling an overloaded kite and far more time flying the right one in the right place. That is most of what good kite flying amounts to.

Photo: RiccoStange / Pixabay