Most sources describe this as a large-scale open stop of 8' or 4' pitch, whose loud tone is a hybrid between a Principal and an Open Flute. While Audsley and Irwin both describe it as being of metal, a number of wooden examples are known. Skinner uses the name Principal Flute for an 8' Harmonic Flute, which he describes as having a scale of 47 (at 8' C), perforated 5/12 of the way up from the languid.

Solo Prinzipal-Flöte

Principal Flute 8' (wood), Great; Congregational Church, Great Barrington, Massachusetts, USA; Roosevelt 1883. Principalflute 32' Pedal; Tonhalle, Zuerich, Switzerland; Kleuker & Steinmeyer 1988.

Prinzipalfloete 2', Pedal; Stadtkirche St. Peter und Paul, Weimar, Germany; Walcker 1908. Principalflöte 4', Schwellwerk; Sejong Cultural Center, Seoul, Korea; Schuke 1978.

Principal Flute 8', Great; Woolsey Hall, Yale University, New Haven, Connecticut, USA; Skinner 1928. (metal; harmonic) Principal Flute 8', Great; Kellogg Auditorium, Battle Creek, Michigan, USA; Aeolian-Skinner 1933. (wood & metal)