Was wondering if that was the siren under the nose so did some looking up....
Found this on Wikipedia:
"The aircraft is easily recognizable by its inverted gull wings and fixed spatted undercarriage. Upon the leading edges of its faired main gear legs were mounted ram-air sirens, officially called "Lärmgerät" (noise device), which became a propaganda symbol of German air power and of the so-called Blitzkrieg victories of 1939–1942, as well as providing Stuka pilots with audible feedback as to speed. The Stuka's design included several innovations, including automatic pull-up dive brakes under both wings to ensure that the aircraft recovered from its attack dive even if the pilot blacked out from the high g-forces, or suffered from target fixation.
The B-1 was also fitted with "Lärmgeräte", essentially sirens driven by propellers with a diameter of 0.7 m (2.3 ft)[ The devices caused a loss of 20–25 km/h (12–15 mph) through drag, and over time the sirens were no longer installed on many units, although they remained in use to various extent. As an alternative, some bombs were fitted with whistles on the fin to produce the noise after release."