Cold War, Experimental

The F2Y Sea Dart is the Only Supersonic Seaplane Ever Built

The F2Y Sea Dart was an ambitious project by Convair to produce a supersonic jet-powered seaplane for the US Navy. Floating above the water on skis, Convair partially achieved this goal, as the F2Y is the first, and last supersonic seaplane ever made.

The hull was made watertight, and it intakes were placed on top to reduce water ingestion. However the design proved fatal when an F2Y broke up above San Diego in front of the press, killing the pilot.



By the end of the Second World War, the jet engine was already shaping up to be the propulsion of choice for aircraft of the future. They offered much greater speeds and the ability to carry greater payloads.

The jet engine made it possible to break the speed of sound in level flight, and would spawn supersonic aircraft in the early Cold War.

Naturally, the US Navy were interested in taking advantage of this new avenue of design, but early jet engines had a number of quite significant drawbacks that made them less approachable for the navy.

F9F Panther in flight.
The Navy retained lower-performance jets like the F9F Panther as they could comfortably land on carriers.

They were much less responsive than piston engines and had slower acceleration, requiring longer runways and additional pilot skill for go-around landings.

For the Navy this was particularly problematic, because carrier aircraft needed good acceleration to take off from the short decks, and responsive engines in case of a bolter (failure to catch the arrestor hook and cables).

Aircraft optimised for supersonic flight only exacerbated this problem, as they have poor low-speed handling, requiring higher speed, and therefore longer distance landings. The variable geometry concept, such as the swing wing found on the F-14 Tomcat, was a later approach to this problem, but in the 1940s they had to use alternative methods.

F-8 Crusader.
Later Navy aircraft, such as the F-8 Crusader, had variable incidence wings that could tilt up to provide more lift at lower speeds for carrier landings.

One idea considered was actually removing the carrier deck altogether – what if they took off directly from the water? This was Convair’s proposal to the US Navy’s 1948 requirement for a supersonic, jet-powered interreceptor.

Named the F2Y “Sea Dart”, it was a revolutionary, but flawed design that eventually proved fatal.

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Convair used the F-102 Delta Dagger as the basis for the design, and planned to add skis, special air intakes for the engines, and make it watertight to withstand punctures in the fuselage. Armament was to come in the form of four 20 mm cannons and unguided rockets.

F2Y drawings.
Plans for the F2Y. This example has a single engine.

The Navy was very interested in Convair’s proposal and placed an order for two prototypes in January 1951, designated XF2Y-1. Then in August 1952, the Navy ordered 12 service test aircraft, even though no prototypes had even been flight tested yet. These examples were designated YF2Y-1.

The F2Y’s design would see it set a number of a firsts: the first supersonic seaplane, the first delta wing seaplane, and the first combat aircraft with retractable skis.

F2Y Sea Dart Design

The F2Y followed a similar general layout to the F-102 it was based on. It was a classic delta wing design, with a large triangular wing that was sectionally very thin, and a wedge-shaped vertical tail.

The pilot sat at the front of the aircraft behind a short nose, under a single-piece hinged canopy that offered poor visibility.

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Like the F-102 the F2Y was small in stature, with a wing span of 34 ft (11 meters) and a fuselage length of 51 ft (15.6 meters).

At the rear of the fuselage was two turbojet engines. They were supposed to be Westinghouse J46 afterburner-capable engines that produced a maximum of 6,100 lbf of thrust each, but due to supply issues the first prototype had to be fitted with Westinghouse J34s.

F2Y during taxi tests.
F2Y during taxi tests. Note the delta wing, and top-mounted air intakes.

These produced a little over half the thrust of the J46s, and resulted in the F2Y prototype being woefully underpowered and incapable of supersonic flight. Later examples were fitted with the J46, but still struggled to break the speed of sound.

This was partly due to its design lacking the area rule, which requires aircraft to have an equal frontal cross section area along their length to reduce drag as they approach and pass through the sound barrier.

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Aircraft that lack this design element encounter more resistance around the speed of sound, making it more difficult to pass through it.

Sea Dart rear.
Rear view of the F2Y. This example has J46 engines, indicated by the nozzles that extend past the vertical stabilser. Image by Bennetblake CC BY-SA 4.0.

Air intakes for the engines were located on top of the fuselage mid-way along its length. Their top-mounted position was intended to reduce water spray ingestion.

Watertight compartments lined the lower-section of the fuselage so the aircraft would be capable of floating even with a perforated outer skin. When stationary, the F2Y sat directly on the water with its nose pointed slightly up, so the leading edge of the wing was around 18 inches above the surface.

Underneath were a pair of retractable skis. During take off, the skis were remained retracted until around 10 mph, by which point the aircraft would be lifted onto a plane and the front of the skis were exposed.

F2Y skis.
A good view of the F2Y’s skis when deployed, shown here in flight.

At this speed the skis were partially extended until around 50 mph, when they would would move to their maximum position. The aircraft would reach a speed of around 145 mph before lifting into the air.

At the rear of the skis, and on the tail under the fuselage, were small wheels. These allowed the F2Y to move from water to land via solid slipways under its own power.

The first prototype was later fitted with a single ski, which actually provided better performance than the twin skis.

When taxiing, the F2Y Sea Dart was steered via its dive brakes that served as a rudder in the water.

F2Y taxiing onto land.
XF2Y-1 showing off its ability to power itself from water to dry land.

A Fatal Failure

The first prototype, the XF2Y-1, began tests in late 1952. Its first flight was actually an unplanned one, with the XF2Y-1 accidentally flying for 1,000 ft during a high-speed taxi run on January 14, 1953 – an early indicator of things to come.

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Its first planned flight occurred on April 9, 1953, where the XF2Y-1 was found to be extremely underpowered and had sluggish handling. Of course, much of this was because of the underpowered J34 engines.

The second XF2Y-1 prototype was cancelled later that year, so the second F2Y built was actually the YF2Y-1 service test aircraft.

F2Y in flight.
XF2Y-1 in flight. This is the first prototype with J34 engines, indicated by the shorter engine nozzles.

Convair test pilot Charles E. Richbourg flew this F2Y for the first time in 1954. The YF2Y-2 now had the more powerful J46 engines, but it lacked the ski and tail wheels, so specialist equipment was needed if it was to be brought onto land.

It was quicker than the prototype, but it still couldn’t break the sound barrier in level flight, likely due to excessive drag resulting from a lack of the area rule. On one occasion though, Richbourg managed to brake the sound barrier in a shallow dive.

On the water, the skis were a constant issue that persisted throughout the project. Despite being supported by shock absorbers, they transmitted severe vibrations into the aircraft when taxiing and taking off on water.

F2Y skis close up.
Close view of the F2Y’s skis. Note the boat shape of the fuselage bottom. Image by tataquax CC BY-SA 2.0

The vibrations were slightly reduced by improved dampers, but the problem never fully went away.

Then, on November 4, 1954, the F2Y project took a massive hit when Richbourg was killed when his YF2Y-1 disintegrated at low level above San Diego Bay, in front of press and Navy observers.

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The aircraft experienced pitch oscillations after seemingly being pushed past its limits, and broke apart.

This resulted to all F2Ys being grounded, and the Navy essentially lost all interest in the aircraft. In addition to this crash, the problem of landing supersonic aircraft on carriers had now been overcome, so there was no longer any need for aircraft like the F2Y.

Smoke from Sea Dart crash.
Smoke eminates from the wreckage of Richbourg’s aircraft after it disintegrated in flight, killing him.

Had it even entered service, the F2Y would have been maintenance intensive due to constant and intense exposure to salt water.

All existing orders for the F2Y were cancelled. Five were built in total. The proposed F2Y-2, a version of the F2Y with a single Pratt and Whitney J-75 turbojet that produced 15,000 of thrust was also cancelled.

Still, testing and research still continued with the first prototype. It had been fitted with J46 engines, and trialled a single ski. This ski was not fully retractable, but it proved to be much better than the two-ski alternative.

In fact, it was capable of working in waves up to 10 feet in height, and in strong crosswinds with one wingtip touching the water.

Sea Dart outside the San Diego Air & Space Museum.
F2Y Sea Dart outside the San Diego Air & Space Museum. Image by tataquax CC BY-SA 2.0.

Testing continued until 1957, just a year before the Mach 2.2-capable F-4 Phantom carrier-based interceptor/fighter first flew.

Two of the five F2Ys built never flew. The F2Ys were placed into storage and the type was officially retired in 1962.

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Today, all four F2Y Sea Darts still survive, and can be seen in museums in the US.