Power Venturi Tube, Single Throat, AN5805-1, Type A-3A
This is a nice specimen of the Single Throat Power Venturi Tube used across US military aircraft of the US Army Air Corps/Force and US Navy before, during, and post WWII. The US Army Air Corps fighter P-39 Airacobra is an example of an aircraft which used this venturi. The US Navy's TBM Avenger Torpedo Bomber also used this venturi, see illustration from its Erection and Maintenance manual dated 1945.
Power venturi tubes provide a source of vacuum for the operation of air-driven instruments such as directional gyros, gyro horizons, and turn and bank indicators. The venturi is a tube shaped like a double "V" and has a small opening, called a throat, at the junction of the "Vs". It is typically installed externally on the side or beneath of the aircraft fuselage, with the small "V" pointed toward the front of the airplane. A volume of air enters the mouth of the tube, flows past the throat, continues through the broadening tube and passes out at the tail end. As the air passes the throat, it expands in the wide part of the tube, creating a partial vacuum. The vacuum draws air from the throat, which in turn sets up a vacuum in the pipe line leading from the instruments. See spec sheets in the photo gallery.
The Double Throat design, not pictured here, operates in the same manner but has greater air volume capacity for larger aircraft with more air-driven instruments such as a heavy bomber or transport.
This specimen is aluminum and appears to be camouflage painted with the upper and lower surfaces in contrasting black/gray color.