How do flue pipes differ from reed pipes in an organ?

In a pipe organ, flue pipes and reed pipes differ primarily in how they generate sound.12

Flue Pipes

Flue pipes operate on the same principle as a recorder or tin whistle. Pressurized air enters the foot of the pipe and is directed through a narrow slit called the flue. This airstream strikes a sharp edge known as the upper lip, which sets the air column within the pipe into vibration. The pitch is determined by the pipe's speaking length, and the tone quality is influenced by factors such as the pipe's scale (diameter relative to length), shape, and wind pressure.3

Reed Pipes

Reed pipes produce sound through a vibrating brass reed actuated by forced air. In a typical beating reed pipe, air pressure forces a brass tongue against a cylindrical opening called a shallot, causing it to vibrate rapidly. These pulsations are then stabilized and amplified by a resonator, which is often flared. The pitch is determined by the effective length of the reed tongue, while the resonator's shape and size significantly influence the resulting timbre.14