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Percival Spencer’s 1941 Air Car design formed the template for two generations of amphibious lightplanes.

For ordinary Americans living through the Great Depression, the notion of privately owning a seaplane—even a small one used for sport—was pretty  extreme. Attempts to introduce such aircraft to the civil market during the 1930s had met either with very limited success or, in most cases, complete failure. Percival H. Spencer, a self-taught pilot and self-made aircraft designer, learned this the hard way. The two-place SL-12C amphibian he built in partnership with Sikorsky engineer Victor A. Larsen, when initially tested in mid-1939, revealed structural and design problems of such magnitude that it was dismantled after only 10 hours of flight. Concluding that the SL-12C was a lost cause, Spencer parted company with Larsen in 1940 to pursue what he believed was a more practical approach.

Spencer had considerable experience to draw from. In 1911, at the age of 13,“Spence” had made his very first flight from the Connecticut River near Hartford in a homemade hang glider towed behind his father’s motorboat. Three years later, two weeks after his 17th birthday, he soloed during his first powered flight in a Curtiss F flying boat that he and his father had salvaged and rebuilt.

From 1930 to 1934, Spencer served as chief test pilot for Ireland Aircraft (which became Amphibions Inc. in 1931), a manufacturer of single-engine amphibians for private and commercial customers. In the mid-1930s, he worked for Sikorsky Aviation, where he oversaw construction of S-43 amphibians and met Victor Larsen. In 1937 Juan Trippe of Pan American Airways hired him as an executive pilot to fly Fairchild F91 amphibians.

Spencer started construction of his ideal light amphibian, the S-12 Air Car, sometime during early 1941. Exactly why he elected to call it the Air Car rather than Air Boat or Air Amphibian is not clear, and while “S-12” suggests it was his 12th aircraft design, historical records identify only two others besides the SL-12C: a three-place, single-float biplane he built in 1918 or 1919, and a wheeled one-place monoplane known as the S-10 in 1925.

Although Spencer never mentioned it, he must have scrutinized the relative merits of other amphibian designs before deciding on the Air Car’s final form. Since he wanted to keep it simple and practical, the Air Car emerged with almost nothing in common with the SL-12C other than being a pusher. Instead Spencer chose a configuration roughly similar to that of Grover Loening’s Flying Yacht of 1921. Like Loening, he used the main float to provide a base for a nacelle-like fuselage that formed the passenger cabin and a mounting for the wings, extending the float afterbody far enough back to support the tail group. But Spencer went a step further in raising the nacelle high enough to house the aft-facing engine and provide propeller clearance over the main float. The nacelle’s height offered the added advantage of placing the wings above most of the water spray. One of his most noteworthy innovations was incorporating a door into the left side of the windscreen to permit easy ingress from a dock.

For the main float and fuselage nacelle, Spencer fabricated a metal framework that he skinned in marine plywood. The wings were simple, constant-chord structures, consisting of built-up wooden ribs and spars covered in fabric. A pair of conventional V-struts served to brace the wings and the metal stabilizing floats. A hand-operated landing gear simply rotated aft for water operations. To power his Air Car, Spencer chose a reliable 110-hp Franklin 4A 4-cylinder, air-cooled engine that drove a two-bladed, fixed-pitch wooden prop.

Spencer worked fast, making the Air Car’s first flight on August 8, 1941, under civil registration NX29098. But he was forced to put the project on hold soon afterward when he took a job as a production test pilot with Republic Aviation of Farmingdale, N.Y., initially flying P-43s and later P-47s.

When he resumed work on the Air Car in mid-1943, Spencer began incorporating improvements. To enhance streamlining and appearance, he fabricated an all-new forward fuselage nacelle using wood-molding equipment. He also reinforced the unsupported tail assembly by extending slender booms from the trailing edges of the wings to the tips of the horizontal stabilizers. He improved directional stability and strength by increasing fin area and adding a dorsal fillet. The Air Car exhibited a distinctive side profile that would become familiar to enthusiasts in years to come. Tests confirmed the plane’s excellent handling qualities in the air and on water.

Since he lacked the means to get his airplane into production, Spencer arranged to demonstrate the Air Car’s capabilities to Republic Aviation officials that fall. Like most large American aircraft manufacturers at that time, Republic was laying plans to produce lightplanes for an anticipated postwar civil aviation boom. The company was sufficiently impressed to purchase production rights, retaining Spencer as the project’s design consultant and test pilot. Republic’s engineers transformed Spencer’s Air Car into a beautifully streamlined, all-metal airframe.

On November 30, 1944, with Spencer at the controls, the Republic RC-1 made its first flight from Farmingdale. At first they considered calling it the “Thunderbolt Amphibian,” but then in early 1945, after receiving permission from the U.S. Navy, they decided on the name Seabee. Although the lightplane boom never materialized, Republic went on to build 1,060 Seabees (RC-3 production versions) between 1946 and 1948. To this day, it is the most-produced single-engine civil amphibian of any type.

But the Air Car story doesn’t end there. Homebuilt aircraft were increasingly popular in the postwar years under the aegis of the Experimental Aircraft Association. In 1968 Spencer partnered with retired U.S. Air Force Colonel Dale L. Anderson to create an improved version of the Air Car for homebuilders. Slightly larger than the 1941 S-12, Spencer and Anderson’s S-12C made its first flight in May 1970. While it retained the original’s layout and simplicity, the S-12C featured a 50-percent increase in power, tricycle landing gear and extensive use of molded fiberglass components. The definitive S-12E homebuilt version, powered by a 285-hp Continental IO-520 engine, appeared a few years later. By the time Spencer and Anderson sold their design rights to Robert Kearns in 1991, more than 300 sets of Air Car plans had been sold, and are still available today from the same source.

When Percival Spencer stopped flying in 1988 at age 91, he may or may not have been the oldest pilot in the United States, but he did hold the lowest pilot certificate number on the FAA’s airman registry. He died in January 1995.


Originally published in the November 2012 issue of Aviation History. To subscribe, click here.