What this sheet works out
Constraint diagram
How these are worked out — the equations behind this sheet, their sources, and what each one assumes.
What each requirement demands at the design point
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.
Reading the design point as the best aeroplane. It is the smallest wing the brief allows, which is a convention rather than a law. A larger wing usually flies on less power, and the sheet reports where the envelope is lowest so you can see the trade you are declining.
Dismissing the practice floor because it is not derived. It is compiled from build practice and it catches what a cruise-and-climb calculation cannot see — control authority and headroom. It is the boundary most worth overruling, and the one to overrule deliberately rather than by accident.
Trusting the climb and launch boundaries. A single cruise propeller efficiency is applied at every speed, so those two boundaries sit lower than the truth. That is the optimistic direction, and it is the one that costs you a motor.
Sizing the wing from a mass the wing changes. The method assumes the mass is known while the mass depends on the wing being sized. Run Sheet 05 with the answer and come back; two passes usually settle it.