. A wind tunnel, however, was the main focus of Maxim's experimental work, and he built it in heroic dimensions. It was 12 feet long, with a test section 3 feet square. Twin coaxial fans mounted upstream and driven by a steam engine blew air into the test section at 50 miles per hour. The tunnel and whirling arm proved to Maxim that cambered airfoils provided the most lift with the least drag. He obtained a lift-to-drag ratio of 14 for a cambered airfoil at 4 degree angle of attack-a spectacular performance for the late 1800s. He was also the first to detect the effects of aerodynamic interference, where the total drag of a structure exceeded the sum of the drags of the individual components. He cautioned, therefore, that "the various members constituting the frame of a flying machine should not be placed in close proximity to each other.
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No half measures with Sir Hiram!
(Also note the reference to the discovery of interference drag- very important, even in those days, in considering things like biplane performance)