2 sound recordings of Spartan Executive aircraft, considered the Lear Jet of the 1930s, popular with US Oil Corporations and owned by the very wealthy.
First recording is of 2 Executives taking off.
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Spectrogram of Spartan Executive take off
Second recording of 2 aircraft in a display. The two aircraft are discernible by the note of the engine/propeller, obviously a radial.
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Spectrogram of 2 Spartan Executive in display
One of the aircraft is based (as far as I know) at Little Gransden. In the display is the leading aircraft.