03/31/2024. Remarks by Johan Visschedijk: "In an attempt to improve the high-altitude qualities of the Airacobra, this P-39D was equipped with a mock-up of a new external turbo supercharger. The pipe to the rear was to simulate a feed pipe to deliver compressed air to the engine. However, the drag by this configuration caused a speed drop of 40 mph (64 kmh), and this option was abandoned."