How these are worked out — the atmosphere model, its sources and what it assumes — documented under Sheet 01, where it is first used.
Where people go wrong
The errors this method actually invites, and what it does about each. Every one of them is already a warning somewhere — in a note that appears when your own figures trip it, in the scope statement, or in the equations behind the page. Collected here so you can read them before you need them.
Using the standard atmosphere where you actually fly. It is 15 °C at sea level, and the places these sheets are published for are routinely thirty degrees hotter. At 45 °C and dry the air has lost 9.4% of its density — which is 5.1% on the stall speed and 16.1% off the Reynolds number.
Expecting humid air to be heavier. It is lighter. Water vapour is less dense than the nitrogen it displaces, so a muggy day costs you density on top of whatever the heat has already taken.
Reading density altitude as a height. It is the altitude in the standard atmosphere where the air is as thin as the air you are in. The aeroplane behaves as if it were up there; it is not up there.
Leaving the temperature blank and assuming it asked. Blank falls back to the standard lapse rate silently, and gives you a perfectly reasonable answer for a day you are not having.
| Altitude | Temp | Pressure | Density | Speed of sound | Kinematic viscosity |
|---|