Originally Posted by Machinbird
If you define Nz as your g measurement, then when your aircraft is pitched up in level flight near stall speed, your z axis is inclined to the vertical, perhaps 15 degrees.
The applicable regulation defines Nzw as the acceleration measured normal to the flight path, i.e. vertical in level flight, whatever the pitch attitude. In certification flight test the airplane is decelerated 1 kt/second with idle thrust, i.e. on a slightly descending flight path at slightly less than 1 g. As the airplane approaches the stall speed, the Drag-to-Lift ratio increases so the flight path steepens slightly, curving downwards. For most swept-wing airplanes the minimum speed occurs after passing the point of maximum lift, because the airplane is still losing airspeed due to high drag while the flight path steepens further downwards.