It was clear very soon, just after the first heavy-than-air “steps”, that the numerous stall accidents due to too low flying speed made obvious the necessity of some sort of speed indicator. The Frenchman Albert Etévé provided it in 1911. Etévé’s indicateur de vitesse was an utterly smart gadget. As we seen here, the principle is simplicity itself: it measures the wind pressure against a surface linked to a graduated spring. This anemometer was usually placed in the interplane strut, near the pilot’s field of view. Certainly not the most precise of instruments, but sure cheap and user-friendly. Due to those qualities the Etévé was employed well into the 1930’s on light aircrafts -This one belongs to a de Havilland DH.82 Tiger Moth.
Gimme the basics.