Sikorsky S-40

The Sikorsky S-40 was an American amphibious flying boat built by Sikorsky in the early 1930s for Pan American Airways.
Design and development.
Sikorsky designed the S-40 in response to a request from Juan Trippe, president of Pan American Airways, for a larger passenger carrying airplane. The S-40 could carry 38 passengers, a significant increase over the S-38's capacity of eight passengers. Wind tunnel testing of the S-40 started in October 1928, and models of the hull were tested in April 1929. The aircraft featured a pantry with an electric refrigerator and stove as well as beautifully appointed smoking lounge with book-ended mahogany wood paneling. Six life rafts were carried on board.
Despite its significant size and capacity increase over the preceding S-38, the S-40 design was a conservative iteration of the smaller aircraft; the numerous flying wires and strut braces that were used as an exterior support framework caused significant drag and prompted Charles Lindbergh, retained as a consultant for Pan American, to tell Sikorsky "it would be like flying a forest through the air." Only three were built as Sikorsky began designing the more advanced and streamlined S-42 to replace the S-40 shortly after the latter entered revenue service, based partly on input from Lindbergh. All three S-40s were built by the Vought-Sikorsky Aircraft Division of the United Aircraft in Stratford, Connecticut.
The first test flight occurred on August 6, 1931. The first aircraft was christened "American Clipper" by Lou Henry Hoover, wife of President Herbert Hoover, on October 12, 1931 at NAS Anacostia; after its christening, "American Clipper" flew around Washington, D.C.
In 1935 the three aircraft were refitted and re-designated as the Sikorsky S-40A. Upgrades for the S-40A included replacing the original Pratt & Whitney R-1860 Hornet B engines with smaller supercharged R-1690 Hornet T2D1 engines, eliminating the landing gear, and increasing the maximum weight slightly. Another source states the landing gear was removed soon after the type certificate was issued.
Operational history.
Passenger carrying service was initiated on November 19, 1931, with a S-40 piloted by Charles Lindbergh and Basil Rowe, flying from Miami, Florida to the Panama Canal Zone with stops at Cienfuegos, Cuba; Kingston, Jamaica, and Barranquilla, Colombia. Igor Sikorsky, the aircraft's designer, was on board as a passenger; during that trip, Sikorsky and Lindbergh began working on concepts that were used in the succeeding S-42.
The S-40 was Pan American's first large flying boat. "American Clipper" served as the flagship of Pan Am's clipper fleet and this aircraft model was the first to earn the popular designation of "Clipper" or "Pan Am Clipper". The three S-40s served without incident during their civilian lives, flying a total of over 10 million miles.
They were retired around 1940 and turned over to the US Navy during World War II, who used them as trainers for four-engined flight instruction. Under Navy service, the aircraft were designated Sikorsky RS-4. All three of the S-40s were eventually scrapped, starting in 1943.