Anti-Hail Net Impact Energy & Cable Tension Calculator

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 7 inputs are read from the form on every keystroke: Hailstone Diameter, Ice Density, Drag Coefficient, Air Density, Stones per Square Metre, Net Deflection on Impact and Span Between Supports.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Impact Energy per Stone together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Terminal Velocity, Stone Mass, Peak Arresting Force, Cable Tension and Storm Energy Density — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

The tool loads with this case already solved — the Impact Energy per Stone shown above is its answer. Change one value and the difference from this baseline is the sensitivity of the result to that variable.

How to use it

1. Work through the input groups in order — Hailstone and Canopy. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Impact Energy per Stone in the dark results panel — that is the headline figure, expressed in J.
4. Check the supporting rows underneath (Terminal Velocity, Stone Mass, Peak Arresting Force, Cable Tension and Storm Energy Density) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Impact Energy per Stone before a trial is booked, so machine time and material in Agrotextiles & Environmental Shielding are committed against a calculated figure rather than an estimate.
• Costing and quotation — Impact Energy per Stone is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Hailstone Diameter) shows how much of the gap in Impact Energy per Stone each variable explains.
• Teaching and study — the accepted ranges bracket normal Agrotextiles & Environmental Shielding practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Assumptions and limits

• Terminal velocity assumes a smooth sphere at steady state in still air; real hail is lobed, tumbling and often falling through a downdraught that adds to the speed, so the energy here is a floor rather than a worst case. The arresting force uses a linear energy-to-deflection conversion, which ignores how a net stiffens as it stretches — the true peak is higher and arrives faster. Cable tension is the reaction from a single stone; a storm loads the whole canopy at once and the structure must be checked against the accumulated load, not this figure. Structural design of canopy supports is engineering work requiring a qualified sign-off.
• Every input is bounded to the range normal practice occupies (Hailstone Diameter 5 to 120 mm, Ice Density 600 to 920 kg/m³ and Drag Coefficient 0.2 to 1.2, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Questions people ask