The slight variation in pitch is due to the Doppler effect. The increasing air speed causes the plane’s propellers to spin faster, increasing the pitch of the engine.
Going into a dive bomb was a difficult task. Stuka pilots would have to ensure:
- Landing flaps at cruise position
- Elevator at cruise position
- Rudder trip at cruise position
- Contact altimeter ON
- Contact altimeter set to release altitude
- Supercharger set at automatic
- Throttle fully closed
- Cooler flaps closed
- Dive brakes open
As soon as the dive brakes were activated, the Stuka’s nose would automatically turn down and the plane would begin its descent. The maximum dive-speed was 600 km/h (373 mph).
In Star Wars, TIE fighters have a similar sound, which probably isn’t an accident:
Sound designer Ben Burtt created the distinctive TIE fighter sound effect by combining an elephant call with a car driving on wet pavement. In the book The Sounds of Star Wars, the engine roar is likened to German Junker Ju 87 “Stuka” bombers, who used sirens to frighten civilians on raids. This could have been a possible inspiration for the sound. Combat scenes between TIE fighters and the Millennium Falcon and Rebel Alliance X-wing fighters in Star Wars were meant to be reminiscent of World War II dogfight footage; editors used World War II air combat clips as placeholders while Industrial Light & Magic completed the movie’s special effects.