Type into any box and the rest of its row follows. Every row is a quantity the design sheets actually ask for, and nothing else is here. The factors are exact where the definition is exact — an inch is 25.4 mm by definition, not by measurement — and the table at the bottom lists them all so you can check the arithmetic rather than trust it.
An inch is 25.4 mm by definition, so this row is exact. Spans and chords are in millimetres everywhere on this site; propellers are the one thing still sold in inches, which is why Sheet 08 takes them that way and converts internally.
The avoirdupois ounce is 28.349523125 g exactly — the troy ounce used for precious metals is different and has no business here. All-up weight is in grams on every sheet.
Wing area is in square decimetres, which is a strange unit until you notice it makes a model's wing a two-digit number. A square foot is 9.29 dm².
Metric on the wire, always: every figure that travels between sheets is in km/h regardless of what you typed. A knot is 1.852 km/h exactly because the nautical mile was redefined to make it so.
The first of the two everybody gets wrong. One ounce per square foot is 3.0515 g/dm², so the 12 oz/ft² a forum calls a docile trainer is 36.6 g/dm². Getting this backwards by a factor of three is the commonest arithmetic error in the hobby.
Grams of thrust is a force, not a mass. It means the force that mass would weigh under standard gravity, which is 9.80665 m/s² exactly by definition. Every motor is advertised in grams and every equation wants newtons; Sheet 08 and Sheet 13 both use newtons internally.
The second one everybody gets wrong. One kg·cm is 13.887 oz·in, and servos are catalogued in both depending on where they were made. Sheet 11 adds the thing the catalogue does not say: that figure is stall torque, at a stated voltage, and you should not size to it.
Horsepower here is the mechanical one of 550 ft·lbf/s. The metric horsepower is 1.4% smaller and is what European engine figures usually mean, which is a difference nobody notices until they compare two motors.
The Atmosphere tool asks for station pressure, which is what a barometer at the field reads. A forecast quotes sea-level QNH instead, and at 500 m the two differ by about 60 hPa — enough to spoil a density calculation entirely.
Not a scaling, because two of the three have an offset. Absolute zero is −273.15 °C, and the atmosphere block works in kelvin throughout because Sutherland's law for viscosity and the gas law both need an absolute temperature.
Sea-level standard is 1.225 kg/m³, which is worth memorising because half the equations on this site are a fraction of it. A gram per cubic decimetre is the same number, which is occasionally convenient.
Capacity is not energy. Milliamp-hours are charge; they only become watt-hours once you say at what voltage, which is why the last box is not a unit. The 11.1 V here is three cells at their nominal 3.7 V — the mean voltage under load is lower and is what actually determines the energy you get, and Sheet 09 is where that difference lives.
| Quantity | Relation | Exact? | Where the sheets use it |
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Horsepower is the mechanical horsepower of 550 ft·lbf/s, not the metric one, which is 1.4% smaller. Inches of mercury are quoted at 0 °C. Everything else above is exact by definition of the unit.