The dark blue paint with yellow markings provided aircraft attitude reference in instrumentation photos of taxi tests including take off and landing.

The Navy sponsored a competition that was won by a Convair design featuring unique retractable hydro-skis on which the aircraft could operate from the water. These skis produced enough hydrodynamic lift to raise the aircraft up and out of the water during takeoff, and they could be retracted into the fuselage during flight. The goal of the contest was to develop a high-performance supersonic naval fighter aircraft which could operate in forward areas without the need for land bases. At that time, the Navy assumed that it would be impossible to operate high-performance supersonic jet aircraft from the decks of aircraft carriers. For this reason, the Navy actually stuck with lower-performance straight-winged carrier-based jet aircraft such as the F9F Panther and the F2H Banshee long after land-based air forces had switched over to higher-performance swept-winged fighter aircraft.

Convair entered the seaplane fighter contest on October 1, 1948. Initially, Convair's proposal was for a delta-winged design with a blended hull which rested on the water and rose up onto a retractable step for takeoff and landing. Convair also tested a large number of seaplane designs equipped with hydro-ski configurations.
Unfortunately, the Sea Dart became mired in a number of problems before its true potential could be realized. The greatest technical challenge remaining was severe vibration experienced by the hydro-skis. Convair used the XF2Y-1 to test a new approach using a single ski that corrected much of the problem. Additional ski designs were also tested on this aircraft and the second YF2Y-1, the final test model to fly, but none was entirely satisfactory.

The unusual plane was powered by two Westinghouse turbojet engines with inlets mounted above the wings to minimize ingestion of water spray. A total of five test aircraft were built including one XF2Y-1 prototype and four YF2Y-1 pre-production aircraft. A further twelve F2Y-1 production models were also ordered. The XF2Y-1 prototype equipped with Westinghouse J34-WE-32 turbojets made its first test flight on 9 April 1953, but was found to be underpowered. Later aircraft were upgraded with the more powerful J46-WE-2 afterburning turbojets that required modification to the aft fuselage to accept the afterburners.

It was in this form that the initial YF2Y-1 became the first (and so far only) seaplane to reach supersonic speeds on 3 August 1954. Flown by Convair test pilot Charles Richbourg, the Sea Dart was only able to exceed the speed of sound while in a shallow dive and not while in level flight. This limitation was probably surmountable if the fuselage had been shaped to conform to the area rule, a modification that was planned for an improved model called the F2Y-2.
Although operating from the oceans would allow such an aircraft to operate from forward areas, there was another reason for wanting to build such an aircraft: the Navy wasn't certain that a supersonic aircraft could be operated from a carrier of any reasonable size.

Convair's proposal won the competition on 19 January 1951. The contract specified two prototypes of a single-seat delta-wing fighter, to be designated the "XF2Y-1 Sea Dart", that took off and landed on water using two retractable "hydro-skis". The engines were mounted on the back of the aircraft, with the intakes well up above the wings to prevent water ingestion during takeoff and landing.

The Sea Dart had a vee-shaped hull, and its internal spaces were organized as multiple watertight compartments to keep it afloat if battle damaged. It had twin dive brakes on the lower rear fuselage that could be also be used as water brakes or rudders. Flight controls were hydraulic. The Sea Dart could not take off or land on a runway, but each of the hydro-skis had a small wheel at the end, and a third small wheel was mounted near the rear of the aircraft to allow it taxi onto or off of a seaplane ramp. The cockpit canopy pivoted up as a single unit, and featured a rather antique-looking windscreen with twin oval glass panels in a metal frame. Apparently pilot visibility was not very good.

The Sea Dart was originally planned to be powered by twin Westinghouse XJ46-WE-02 engines. The XJ46 engine, an afterburning derivative of the Westinghouse J34 axial-flow turbojet, was expected to give the aircraft a top speed well in excess of Mach 1. The aircraft was to be armed with four 20 millimeter cannon and a pack of 70 millimeter (2.75 inch) folding-fin air rockets (FFARs), though in fact no Sea Dart would ever be armed. The Navy was so enthusiastic about the Sea Dart that even before it flew, the service ordered a total of four "YF2Y-1" service evaluation aircraft and 16 "F2Y-1" production aircraft.

* As the first Sea Dart prototype was finished before the XJ46 engines were available, it was fitted with twin Westinghouse J34-WE-32 engines with 3,400 lb maximum takeoff thrust each. Taxi trials began in San Diego Bay in mid-December 1953, with test pilot Sam Shannon at the controls, leading to first official flight on 9 April 1953.

The Sea Dart was, to nobody's surprise, badly underpowered with its J34 engines and remained solidly subsonic. The hydro-skis turned out to give an extremely rough ride on takeoff and landing, though a redesign effort helped reduce this problem.
The XJ46 engines were installed in the prototype later that year, but they failed to meet their designed thrust levels. The detestable Vought F7U Cutlass carrier would use production J46 engines, and the lack of engine power and poor fuel economy would be high on the list of pilot complaints against the "Gutless", as it was known.

At this point, the Navy began to rethink the program. The second prototype was cancelled, with development moving on to the first service evaluation YF2Y-1, fitted with J46 engines, although the Navy was seriously looking for a better powerplant. The YF2Y-1 was similar in appearance to the XF2Y-1 but had a longer, redesigned exhaust, and the little beaching wheels were removed from the hydro-skis and the fuselage, meaning it had to be fitted with external beaching gear to be brought up on shore.
The YF2Y-1 began test flights in 1954, and on 3 August 1954, Convair test pilot Charles E. Richbourg took the machine through Mach 1 in a shallow dive. The Sea Dart is believed to be the only seaplane to ever achieve Mach 1. However, as it had been designed before the new "area ruling" scheme was introduced, its supersonic handling characteristics were poor.

The YF2Y-1 was lost in a crash during a low-level demonstration on 4 November 1954, killing Richbourg. It seems that the aircraft had gotten pushed past its safety margin during a low-altitude, high-speed flypast, and the plane disintegrated in midair as a result of pilot-induced pitch oscillations. Bits and pieces of flaming debris fell into the bay. All SeaDart operations were temporarily suspended after the crash. This accident essentially killed the program as well. The Navy was no longer particularly frightened of operating supersonic aircraft off of carriers, and despite improvements in the hydro-ski design, the Sea Dart still suffered from serious vibration on takeoff and landing.

The Navy had begun cutting back the program in December 1953, before the delivery of the YF2Y-1, cancelling ten of the production aircraft. The other six were killed off in March 1954, well before the fatal accident. Following the accident, the program was further scaled back to a test exercise, and plans to produce an "F2Y-2" with area ruling and a single Pratt & Whitney J75 turbojet with 15,000 lb thrust were abandoned.

The XF2Y-1 was then refitted with twin J46 turbojets and a single-ski configuration in hopes that would solve the takeoff and landing problems. The fit was strictly experimental. The ski was not fully retractable and the wells for the old twin skis were not faired over. The new single ski had a pair of retractable beaching wheels at the end, allowing the aircraft to beach itself.

The modified XF2Y-1 first flew in late December 1954, and after some initial problems the single-ski scheme proved remarkably successful, allowing safe takeoffs and landings even in fairly rough seas.

The second YF2Y-1 performed its first flight in March 1955. It was powered by twin J46 turbojets and had a modified twin-ski system, with pivoting beaching wheels at the end of each ski. The twin-ski system didn't work much better than before, and the aircraft was put into storage at the end of April 1955, never to fly again.

The original XF2Y-1 was used for further tests of various ski systems until the fall of 1957, when it was finally withdrawn. Two more YF2Y-1s were built but never flown, and all four aircraft are now in museums. One YF2Y-1 serves as a "gate guard" on a pylon in front of the the San Diego Aerospace Museum at Balboa Park, and certainly provides a distinctive and unusual display.

Sea Dart Details:
The hull of the SeaDart had multiple watertight compartments in the lower fuselage to prevent sinking in the event of a puncture. The lower fuselage of the SeaDart had the V-shaped profile of a boat, as would be expected for a water-based aircraft. Both the elevons and the rudder were hydraulically-powered. The aircraft was fitted with a set of dive brakes on the lower rear fuselage which also doubled as water brakes and as a water rudder while taxiing on the surface. When sitting at rest in the water, the SeaDart floated with the trailing edge of the wing and the elevons being flush with the water, and the leading edge of the delta wing at the juncture of the fuselage being about 18 inches above the water.

The one-piece cockpit canopy structure was hinged from behind the cockpit. When open, there was no windscreen in front of the pilot. The canopy was provided with two small windows on either side, separated from each other by a center post which obstructed the directly forward view. By all accounts, the view from the cockpit was rather poor, and would certainly have to had been substantially improved had the SeaDart ever entered service as a combat aircraft.

The aircraft took off and landed on a pair of retractable hydro-skis that extended outward on oleo legs from recesses cut into the lower hull, one ski on each side of the hull. During takeoff, the skis were initially fully retracted into their wells. Then as power was applied and the leading edge of the ski broke the water at 9-11 mph, the skis were extended to an intermediate position until 45-55 mph was reached. The skis were then extended to their fully-extended position, and the aircraft accelerated to a takeoff speed of about 145 mph.
When the aircraft was sitting on dry land out of the water, it tilted backwards on its extended skis, its tail resting on the ground. Each of the twin retractable hydro-skis had a small fixed wheel at its aft end, and there was a small fixed swiveling tailwheel mounted underneath the rear fuselage. This provided for a limited amount of ground maneuverability, which made it possible for the aircraft to enter or leave the water via a long ramp under its own power. However, the aircraft could not take off or land on conventional runways.
Proposed armament for the production F2Y-1 aircraft was a set of four 20mm cannon and a battery of 2.75-inch folding-fin unguided rockets. These aircraft were to be powered by a pair of J-46 afterburning turbojets, each offering a thrust of 6000 pounds. Shortly thereafter, the contract was amended so that the the first four F2Y-1s would be built as YF2Y-1 service test aircraft.
In the late autumn of 1952, the completed aircraft was transferred from the experimental shop at Convair's Lindbergh Field facility to the Convair seaplane ramp area on San Diego Bay. On December 14, 1952, E. D. "Sam" Shannon began taxiing trials in San Diego Bay with the XF2Y-1 prototype. On January 14, 1953, he made an inadvertent first hop of 1000 feet during a high-speed taxiing run. The XF2Y-1 prototype made its official maiden flight on April 9, 1953.

In 1953, the XJ46 engines finally became available and was installed in the prototype. However, they failed to reach their projected thrust output. In search of more power, the Navy proposed that a single 12,000 lb.s.t Wright J67 or 15,000 lb.s.t. engine be fitted in an improved version of the SeaDart, the XF2Y-2.

These are a couple photos of the Sea dart model early stages

 

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Since the SeaDart had been designed before the advent of the area rule, the aircraft experienced high transonic drag and was unable to exceed the speed of sound in level flight. Flight tests indicated some wing spanwise airflow, and a single airflow fence was mounted on each upper wing surface near the tip. No other SeaDart was fitted with wing fences.In the meantime, the Navy had been gradually losing interest in the SeaDart project. By this time, the Navy had overcome its earlier reluctance and was already planning for the introduction of supersonic carrier-based fighters, and the need for a water-based supersonic fighter did not now seem to be as critical as before. In addition, the problems with the vibrating waterskis had continued to plague the SeaDart, and seemed to be insoluble. As a result, the Navy cancelled ten of the sixteen production F2Y-1 aircraft in December of 1953, even before the first of the YF2Y-1 service test aircraft had been delivered. The remaining six production F2Y-1s were cancelled in March of 1954. The fatal crash of the first YF2Y-1 aircraft later that year, with the surrounding bad publicity, did not help matters any, and the SeaDart program was relegated to test status only.

Also cancelled was the F2Y-2, which had been envisaged as the definitive production version of the SeaDart. It had a single waterski, an area-ruled fuselage, plus a single afterburning Pratt and Whitney J-75 turbojet of 15,000 pounds of thrust.

In spite of the project cancellation, tests continued with the sole XF2Y-1. During the summer of 1954, the XF2Y-1 was extensively reworked. The aft fuselage was brought up to YF2Y-1 configuration with afterburning Westinghouse J46 turbojets. The aircraft was fitted with a large, single hydro-ski in place of the original pair of skis. The single-ski installation was not fully retractable, since high-speed flight was never planned. The previous twin-ski fuselage wells were not filled in or covered over for the single-ski installation, and during flight, the single ski was held below the fuselage in an external position parallel to the aircraft's longitudinal axis. The rear part of the ski was extended downward for takeoff or landing. The rear part of the single ski had a pair of retractable wheels on either side for use in moving the aircraft into and out of the water, the aircraft resting nose-up on a small tailwheel. Like the dual-ski XF2Y-1, the aircraft could be launched or recovered from the water without the need for auxiliary beaching gear. The XF2Y-1 flew for the first time in this configuration on December 29, 1954, with Convair test pilot B. J. Long at the controls.

The first tests with the single sky encountered the divergent and uncontrollable hydrodynamic longitudinal pitch oscillations. These were corrected by adding a new ski oleo damping device what sensed stroke rate and varied the oleo hydraulic orifices and provided the needed damping qualities. Lateral directional control problems that had been encountered were corrected by doubling the lateral deflection of the elevons relative to the pilot control stick movements. The single ski could even safely handle crosswind takeoffs There is a rather odd postscript to the SeaDart story. In 1962, five years after the official termination of the SeaDart project, the Navy was ordered to redesignate all of its fighter aircraft in order to conform to the new tri-service unified aircraft designation scheme. For some obscure reason, the SeaDart was assigned the designation F-7. Why would the Navy bother to redesignate an aircraft which had never entered service? Perhaps some clerk in the Defense Department had some fond memories of this warplane, and decided to honor it posthumously with an official F-number.
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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.

F2Y Sea Dart Design
When stationary or moving slowly in the water, the Sea Dart floated with the trailing edge of the wings touching the water. The skis were not extended until the aircraft reached about 10 mph during its takeoff run.