A Comparison of Propeller and Centrifugal Fans for Circulating the Air in a Wind Tunnel
This is a 1928 NACA technical note comparing propeller and centrifugal fans for circulating air in a wind tunnel, issued by the National Advisory Committee for Aeronautics for aerodynamics engineers and researchers. The pictures include a plan diagram of a closed-return tunnel with honeycomb, guide vanes and fan, a dense drafting sheet of labelled airfoil or apparatus geometry, and a photograph of the six-inch tunnel with propeller fan drive beside recorded pressure traces. A designer might borrow the clean line-drawn schematic layout and the technical plate framing.
