Seaplanes (aircraft that use some form of pontoon rather than wheels) have played a major role in the development of aircraft. Waterborne craft were developed by many nations in the early years of flight because harbors were readily available and accessible as compared to airfields. Flying boats pioneered most international airline operations through the 1930s. The U.S. Navy relied heavily on them from 1911 through the Second World War and beyond. During the Vietnam war, for example, Martin P5M flying boats were used extensively for coastal and shipping patrols.
On 19 January 1951, Convair received an order from the U.S. Navy's Bureau of Aeronautics to develop two XF2Y-1 aircraft to be equipped with twin hydroskis (the twin hydroskis were "planing" skis and derived lift the same as a person using water skis. They were not skis that provided lift in the same manner as hydrofoils.). They were to be prototypes of a definitive water-based, single-seat, afterburning supersonic interceptor/fighter. This action resulted in an experimental test program that began in December 1952 and continued through 1957. A total of five aircraft, dubbed Seadart, were built. Only three ever flew. The last two were completed except for engine installation.
The first XF2Y-1 aircraft, Bu. No. 137634, is part of the Air & Space Museum's collection. The remaining four were YF2Y-1 aircraft, Bu. No. 135762 through 765, built and numbered consecutively. The Seadart aerodynamic design is best illustrated by the No. 3 aircraft (763). Unfortunately, these aircraft were designed, built, and flown before the supersonic "area rule" was first incorporated in aircraft designs. The area rule revealed that streamlining the aircraft fuselage into an hourglass shape, to compensate for the wing area, reduced aerodynamic drag-the unseen forces that slow aircraft down and increase thrust requirements. Compounding the issue, high-thrust engines were not available at that time.
On 14 December 1952, E. D. "Sam" Shannon, Convair's Chief of Engineering Flight Test, took the XF2Y-1 Seadart out into San Diego Bay for its first taxi tests. The aircraft "taxied" up the seaplane ramp after its first test run. Small wheels at the aft end of the skis plus a small tail wheel provided this land taxi capability. The airplane entered the water the same way. Taxi down the ramp was made with the ski oleos in the beach position for attitude purposes. Upon attaining flotation, the main wheels on the ski afterbodies were rotated 90 degrees by electrical switch and hydraulic action to place the tapered afterbody of the ski in the proper hydrodynamic position. Takeoff was accomplished by a combination of ski extension, retraction, afterburner thrust, and a rapid rotation at take off speed. Two Westinghouse J46 engines producing 4,000 lb. of thrust (augmented to 6,000 lb. with afterburner operating) powered the Seadart during most of its testing. The characteristic sharp rotation and liftoff was necessary to achieve positive separation from the water allowing rapid acceleration. The skis could be retracted immediately as with any retractable landing gear.
On 9 April 1953, Shannon made the first flight of the XF2Y-1. The dark blue paint with yellow markings provided aircraft attitude reference in instrumentation photos of taxi tests including take off and landing. Two afterburning Westinghouse J34 engines were soon replaced by Westinghouse's more powerful J46. The second Seadart exceeded Mach 1.0 on 3 August 1954.
The taxi tests revealed serious vibration and pounding that drastically increased with rougher water. In mid-1954, the first Seadart was refitted with a single ski in an effort to reduce vibration during water operations. The final flight of the twin-ski version was made on 28 April 1955.
Normal landing and takeoff procedures for both the twin-ski and single-ski configuration were to maintain a heading parallel to the major wave or swell condition and into the wind as much as possible. Usually, this involved a crosswind component of 30 to 60 degrees. Landing or takeoff directly into any sizeable wave pattern or swells was unacceptable and not attempted. A smoke float deployed during operations indicated wind conditions. Except for being underpowered, the open-sea handling characteristics were considered excellent by the test pilots. This was despite the 120-knot takeoff speed and 125-knot landing speed.
The large single-ski and oleo configuration finally derived for the XF2Y-1 aircraft was a very sound and satisfactory design for use on a delta wing, water-based, supersonic aircraft. The Seadart test program also proved the feasibility of designing and developing supersonic water-based aircraft for support of Navy Fleet Operations. Because of the lack of an approved operational requirement and the lack of funds for such an aircraft, the U.S. Navy did not continue Seadart development.
Wingspan: 33' 8"
Length: 51' 1.5"
Height: 17' 0"
Weight: Gross 22,000 Lbs.
Reference and Further Reading:
Long, Billy J. "Seadart" in American Aviation Historical Society, 1st Quarter 1979 (Vol. 24, Number 1), pp. 2-12.
Long, B. J. Sea Dart, Naval Fighters (number 23), 1992.
Angelucci, Enzo, and Peter Bowers,The American Fighter, Orion, 1987.
Swanborough, Gordon, and Peter M. Bowers, United States Navy Aircraft Since 1911, Smithsonian, 1989.
Wegg, John, General Dynamics Aircraft and their Predecessors, Naval Institute Press, 1990.
Wagner, Ray, American Combat Planes, Third Enlarged Edition, Doubleday, 1982.
XF2Y-1 SeaDart curatorial file, NASM, Aeronautics Division.
DAD, 11-11-01