THE 456th FIGHTER INTERCEPTOR SQUADRON

THE PROTECTORS OF  S. A. C.

 

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Convair XF2Y-1 Sea Dart

 

Convair XF2Y-1 Sea Dart

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The Sea Dart test program began in December 1952 and ended in late 1957 with the three test aircraft performing over 300 test operations. All tests were conducted from the Convair San Diego Bay seaplane ramp. Four Convair engineering test pilots were involved, plus several Navy test pilots from the Naval Air Test Center, Patuxent River, Maryland.

Five Sea Dart aircraft were built. Only three were flown, with four aircraft still in existence today. The second aircraft crashed on 4 November 1954, and the last two aircraft were completed as airframes only, without the engines ever being installed.

       

Type: XF2Y-1
Function: fighter
Year: 1953 Crew: 1 Engines: 2 * Westinghouse J34-WE-32
Wing Span: 10.26m Length: 16.03m Height: 6.32m Wing Area: 52.30m2
Empty Weight: 5793kg Max. Weight: 7497kg
Max. Speed: 1328km/h Ceiling: 15300m Max. Range:
Armament: 21500lb (never fitted)
 

The first prototype flew on April 9, 1953. On August 3, 1954 the YF2Y-1 reached speed of sound.

 

 

The History Of The Convair XF2Y (F-7) Sea Dart

by Joe Baugher

 

The Convair XF2Y SeaDart water-based fighter was the result of a design contest initiated by the US Navy in 1948 for a supersonic interceptor seaplane. 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.

On January 19, 1951, Convair was awarded a contract for two prototypes of a water based fighter with a delta wing plan form, a single delta-shaped tail, and a watertight hull. The aircraft was to take off and land on a pair of hydro-skis that retracted into wells in the side of the lower fuselage. The two prototypes were assigned the designation XF2Y-1 and were issued the BuAer serial numbers 137634 and 137635. The name SeaDart was assigned.

The SeaDart aircraft was to be powered by a pair of 6100 lbs.thrust afterburning Westinghouse XJ46-WE-02 engines. The engines were to be fed by a pair of lateral intakes mounted high up on the sides of the fuselage well above the wings and behind the cockpit, this location being chosen in order to prevent water spray from entering the air intakes during takeoff and landing. 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 transparencies 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 tail-wheel 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.

The Navy had such confidence with the design that they ordered 12 production F2Y-1 aircraft on August 28, 1952, even before the first prototype had flown. Serials were 135762/135773, which curiously were in a batch earlier than those of the two XF2Y-1s ordered more than a year earlier. 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 (BuNo 135762/135765) would be built as YF2Y-1 service test aircraft.

Later, eight more F2Y-1 production aircraft were ordered. Their serials were 138530/138534, plus three others which I don't know. This brought the total SeaDart order to 22 aircraft.

Pending the availability of the J46s, the first prototype XF2Y-1 (BuNo 137634) was fitted with two side-by-side non-afterburning Westinghouse J34-WE-32 engines of 3400 lbs. thrust each. 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.

The first flight tests revealed (as expected) that the aircraft was severely underpowered for its weight. In addition, the water-skis vibrated continuously during takeoff and landing, so much so that the aircraft was extremely difficult to control. In order to cure the vibration problem, the skis were redesigned and the oleo legs were improved. This seemed to help somewhat. However, the absence of an area-ruled fuselage (plus the lack of adequate engine power) meant that that the XF2Y-1 could not exceed the speed of sound in level flight.

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 lbs. thrust Wright J67 or 15,000 lbs. thrust engine be fitted in an improved version of the SeaDart, the XF2Y-2.

On October 14, 1953, the remaining XF2Y-1 (BuNo 137635) was cancelled.

The first YF2Y-1 (BuNo 135762) service test aircraft joined the test program in early 1954. Since the second XF2Y-1 (BuNo 137635) had been cancelled, YF2Y-1 BuNo 135762 was the second SeaDart aircraft actually to be built. It was powered by a pair of afterburning Westinghouse J46 turbojets. In overall appearance, the YF2Y-1 was similar to the XF2Y-1 except for the J46 engines. However, the aft fuselage at the engine exhaust area was significantly different, with the engine nacelles and nozzles extending further aft. The YF2Y-1 differed from the XF2Y-1 in not having wheels on the rear of its twin skis, so auxiliary beaching gear was required during entry to or exit from the water.

 Convair test pilot Charles E. Richbourg made the initial flight tests of the number two SeaDart. On August 3, 1954, Richbourg took BuNo 135762 through the sound barrier while in a shallow dive. This made the SeaDart the first (and to date the only) seaplane to go supersonic. 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 span wise airflow, and a single airflow fence was mounted on each upper wing surface near the tip. No other SeaDart was fitted with wing fences.

Unfortunately, Richbourg was killed on November 4 of that year while demonstrating BuNo 135762 over San Diego Bay to Navy officers and press representatives. It seems that the aircraft had gotten pushed past its safety margin during a low-altitude, high-speed fly-past, and the plane disintegrated in midair as a result of pilot-induced pitch oscillations. Bits and pieces of flaming debris fell into the bay. I still remember the rather vivid photos of this accident that appeared in Life magazine. All SeaDart operations were temporarily suspended after the crash.

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 water-skis 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 water-ski, 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 tail-wheel. 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 and landings with a wingtip dragging in the water. The aircraft could even operate in waves of up to 6 to 10 feet in height, far in excess of the requirement. The last single-ski test with the XF2Y-1 took place January 16, 1956, when an open-sea landing and takeoff was carried out. After the completion of the tests, the XF2Y-1 was placed in storage.

 The number three SeaDart, YF2Y-1 BuNo 135763 joined the test program in March of 1955. It was the nearest of the three aircraft to a full production model, and carried no special test instrumentation. It flew for the first time on March 4, 1955. It was powered by a pair of Westinghouse J46 afterburning engines, the same as those retrofitted to the XF2Y-1 when the single-ski was installed. The aircraft featured a revised twin-ski format, with beaching wheels once again as an integral part of the skis. The bottom plan form of the ski after-bodies were the same as the best design finally derived on the number two aircraft, which did not have wheels. The after-bodies were tapered and pointed, with a retractable wheel mounted flat on the top surface of each ski after-body, with a slight overhang on the inside of the bottom planning surface. The after-bodies rotated 90 degrees just aft of the ski main oleo struts. When the aircraft was sitting out of the water on the ramp with the wheels extended, the bottom after-bodies faced outward and appeared as spurs. Upon water entry, the ski after-bodies were retracted inward at the bottom to a 90-degree position, with the wheels safely tucked out of the way on top of the skis. Vibration was still unacceptable with the two-ski example, and after open-sea trials, testing with the second YF2Y-1 formally ended on April 28, 1955. The aircraft was placed in storage and never tested again.

In late 1956, the XF2Y-1 was taken out of storage and the entire large single-ski oleo system was removed and replaced with a small rigidly-mounted hydrofoil ski. Actual flight with such a configuration was not possible, since the rigid mounting and placement of the ski would not permit the ~20 degree nose-up attitude that was required for takeoff. The first test was carried out on March 21, 1957. Violent pounding caused every taxiing run to be aborted at speeds between 50 and 60 knots. Another rigid ski configuration was tested in the autumn of 1957. It too caused too much vibration, and further tests were abandoned. The XF2Y-1 was placed in storage after these tests were completed, never to be flown again.

The other two YF2Y-1 prototypes (135764 and 135765) were completed but never flown.

The four surviving SeaDarts are all preserved in museums. The XF2Y-1 prototype (BuNo 137634) was reportedly at one time with the Maryland Aviation Historical Society at Strawberry Point (I'm not sure where this is, even though I am from Maryland. It might be at the site of the old Glenn L. Martin plant near Baltimore). However, it is now in storage at the Paul Garber Restoration Facility of the Smithsonian Institution in Suitland, Maryland, waiting eventual restoration. It is in terrible shape, with lots of rust, a smashed canopy, and the wings having been cut off by a blowtorch. The 3 surviving YF2Y-1s are with the San Diego Aerospace Museum at Balboa Park (135763), the Wings of Freedom Air and Space Museum at NAS Willow Grove, Pennsylvania (135764) and the Sun n' Fun site at the Lakeland, Florida airport (135765) respectively.

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 re-designate 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 re-designate 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.

 

Serials of Convair X/YF2Y-1 SeaDart:

137634/137635 	Convair XF2Y-1 SeaDart 
			137635 was cancelled 
135762/135773 	Convair F2Y-1 SeaDart
			135762/135765 delivered as YF2Y-1.  
			remainder all cancelled.  
138530/138534 	Convair F2Y-1 SeaDart 
			cancelled contract.  

Specification for the Convair YF2Y-1 SeaDart:

Engines: Two Westinghouse J46-WE-2 turbojets, rated at 6000 lbs. thrust each with afterburning. Maximum speed: 695 mph at 8000 feet, 825 mph at 36,000 feet.

Initial climb rate 17,100 feet per minute.

Range 513 miles.

Service ceiling 54,800 feet. (these are estimated performance figures, which I don't think were ever achieved in test).

Stalling speed 132 mph.

Wingspan 33 feet 8 inches, length 52 feet 7 inches (YF2Y-1 no. 3 51 feet 1 1/2 inches), height 16 feet 2 inches (skis retracted) 20 feet 9 inches (skis extended), wing area 568 square feet.

Total internal fuel capacity: 1000 US gallons.

Weights: 12,625 pounds empty, 16,500 pounds gross, 21,500 pounds maximum takeoff.

Armament: The SeaDart was never equipped with any armament.

Sources:

  1. The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.
     
  2. United States Navy Aircraft Since 1911, Gordon Swanborough and Peter M. Bowers, Smithsonian, 1989.
     
  3. General Dynamics Aircraft and their Predecessors, John Wegg, Naval Institute Press, 1990.
     
  4. Ray Wagner, American Combat Planes, Third Enlarged Edition, Doubleday, 1982.
     
  5. Convair XF2Y-1 and YF2Y-1 Sea Dart, B. J. Long, Naval Fighters, 1992.
     
  6. E-mail from Steven L. Simpson

Courtesy of Joe Baugher
 

 

 

Convair XF2Y (F-7) Sea Dart

 

The Sea Dart grew out of a 1948 request for proposals by the US Navy for a supersonic interceptor seaplane. 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 afterburning engines with 2,720 kilograms (6,000 pounds) thrust each, which were 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 1,540 kilograms (3,400 pounds) 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. 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 power plant.

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. 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 strong vibration on takeoff and landing.

The Navy had begun cutting back the program in December 1953, before the delivery of the YF2Y-1, canceling 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 6,800 kilograms (15,000 pounds) 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.

 
 SPECIFICATIONS FOR THE CONVAIR YF2Y-1 SEA DART:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                10.26 meters        33 feet 8 inches
   length                  16 meters           52 feet 7 inches
   height, skis extended   6.33 meters         20 feet 9 inches

   empty weight            5,725 kilograms     12,625 pounds
   loaded weight           9,750 kilograms     21,500 pounds

   max speed at altitude   1,325 KPH           825 MPH / 720 KT
   service ceiling         16,700 meters       54,800 feet
   range                   820 kilometers      510 MI / 445 NMI
   _____________________   _________________   _______________________

   Performance values are estimates.
 

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.

COURTESY OF VECTORSITE.NET    

 

 

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 hydro-skis (the twin hydro-skis were "planning" 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.).

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 after-bodies were rotated 90 degrees by electrical switch and hydraulic action to place the tapered after-body 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.

Click on Picture to enlarge

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.

Click on Picture to enlarge

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.

COURTESY OF THE SMITHSONIAN NATIONAL AIR AND SPACE MUSEUM

 

 

The concept of seaplane fighters was neither new nor novel – several examples had been put to desultory effect during WW2 and even combining floats with jets (like the British SR.A.1) still failed to overcome the shortcomings of the type. The problem lay in a combination of weight and drag – ruthless enemies where fighters are concerned as both weighed mightily against maneuverability and speed. Drag usually factored large because of either the fixed floats (configured in either a single centerline with smaller wing floats or twin floats) or the effects of a flying boat hull (see the previous FF account of the P6M SeaMariner).

By the early 1950s though, there was thought that retractable skis, called hydroskis, would solve the drag problem and more powerful, afterburning engines allay, if not overcome the weight issue. The advent of jet engines removed the issue of propeller location/clearance that had plagued previous hydroski designs – unlike a float plane, a hydroski plane rests on its hull until sufficient speed is built up to raise it on the skis. Of note, the use of hydroskis was not scalable. In other words, as aircraft size and weight grew hydroskis were not an option; therefore they remained viable only with small airframes.

In 1950, Convair had embarked on a design study that yielded a series of swept wing, shallow, blended hull, jet-powered seaplanes, one of which was a fighter design (the Skate). While Convair was working on developing a good hydronamic shape, the NACA (predecessor to NASA) was working in the opposite direction – take a good aircraft and adapt it to seaborne operations through the use of hydroskis. .

Parallel to Convair’s studies, BuAer (predecessor to NAVAIR) was investigating the feasibility of long-range strike and fighter aircraft that could be sea-based, complimenting the carrier-based aircraft by expanding the basing options and building on several decades of experience in operating sea-based patrol aircraft. This dovetailed with Convair’s ongoing development efforts through a formal Operational Requirements issuance (OR) on 30 Nov 1949 (OR CA 05501A). The OR called for an advanced seaplane fighter capable of operating from forward bases in all weather conditions. Convair would continue refining the Skate, but also investigate the use of hydroskis. As research results showed increasing promise in the use of hydroskis, the Navy revised its performance requirements upward.


Development

Over in another part of Convair, a radical aircraft was taking shape for the Air Force. Based on the XF-92A, the YF-102 was taking shape – a delta wing, afterburner fighter designed for the interceptor mission. Using the lessons learned from the XF-92 and YF-102 development, the Y2-2 began to emerge as a twin-engine, delta wing fighter that would rely on a 2-hydroski arrangement. On 19 Jan 1951, BuAer issued a Letter of Intent for Contract (51-527) for two Y2-2 airframes for R&D purposes necessary for a seaplane-class of fighters. Westinghouse J-46-WE-2 engines (2) would provide the thrust. The pressurized cockpit used two panes of class that formed a sharp-V, similar to the YF-102. For the prototypes only, there would be no additional canopy – production model aircraft would have a more conventional arrangement.

Designated the XF2Y-1 Sea Dart (BuNo 137634), the first prototype was launched into San Diego Bay on 16 Dec 1952. Problems developed with the twin-ski arrangement and a phenomenon called “ski-pounding.” At about 50 KIAS, a thundering vibration set in that was aggravated with greater wave heights. As the skis flexed, the buffeting was resonated throughout the airframe, reaching the point where the pilot was unable to read the instruments. Several minor mods were made and the second prototype was configured with a single ski in an attempt to counter the pounding. It would only be after many high speed taxi runs and several months before the Sea Dart would take to the air on 9 April 1953.

Once in the air, the Sea Dart experienced the same problems so many other jets of that period encountered – engines that underperformed and top speeds that fell well short of the design mark. In the case of the Sea Dart, optimistic engineers had predicted Mach 1.5 in level flight (the OR specified M1.25) – yet it only reached Mach .99. Engine inlet problems with airflow induced by the location of the ducts atop the fuselage aggravated the already poor performing J46’s and unknown to Convair’s engineers at the time; the Sea Dart was suffering from the same aerodynamic issues that would plague the YF-102. Eventually, Convair solved the problem for the YF-102 by implementing an area-rule fuselage and that, along with a more powerful single engine, was planned for a follow-on production model.


CONOPS

Armed with 4 x 20mm cannon and 44 x 2.75 in folding fin rockets in retractable pods in the forward fuselage, guided by an AN/APQ-50 radar tied into the Aero 13E weapons system, the Sea Dart would provide forward air defense from amphibious ships, submarines, or coastal bases. In fact, the Marines conducted a 1954 study on the uses of the Sea Dart as part of what it was calling the “seadrome” (think – “Sea Base”). In essence, this base would be rapidly deployed to support amphibious operations, providing immediate air cover. The seadrome would consist of all the equipment needed for daily operations and required by the Sea Dart – maintenance, fueling, re-armament, etc. The Sea Dart itself was designed with at sea maintenance in mind. Everything was placed to facilitate access from above either directly or through access points.

Unfortunately, the seadrome required development of entirely new support and logistic equipment for a limited mission – and the Sea Dart would in turn utilize but only a small part of that. Tied as it was to close/inshore locals, the seadrome would be more vulnerable to attack than a carrier farther out to sea and with the advent of the super carrier as epitomized by the Forrestal, those capabilities would be significantly strengthened. Then there remained the issue of the Sea Dart’s ability to operate under poor sea states owing to the still unresolved ski-pounding issue.


Twilight

With the end of the Korean War came mounting concerns over whether the capabilities offered by the Sea Dart offset it’s growing costs, support requirements and questions over resolving the ski-pounding and top end speed were justified. The Sea Dart had exceeded Mach 1, but in a shallow dive. Prototype 2 was destroyed in a high speed pass, killing the pilot, C.E. Richbourg. The cause of the break-up was again, a phenomenon common to the early trans-/supersonic aircraft, pitch divergent oscillations. Pitch divergence was encountered at transonic speeds in low level flight and the hydraulically-boosted flight controls of the day were inadequate to cope with the induced oscillations, causing a rapid build-up of aerodynamic pressures on the airframe leading to in-flight breakup. The Sea Dart would not fly any more high speed profiles. As post-war funding levels for conventional forces started to be scaled back, the Navy determined that the costs did not offset perceived benefits and by the end of 1954, the program was terminated after 5 prototypes had been built.

Today there are four remaining examples with the original XF2Y-1 being held by the Smithsonian for future restoration and others in San Diego, Willow Grove,PA and Lakeland, FLA.


General characteristics

Crew: 1
Length: 52 ft 7 in (16 m)
Wingspan: 33 ft 8 in (10.3 m)
Height: 16 ft 2 in (4.9 m)
Wing area: 568 ft² (53 m²)
Empty weight: 12,625 lb (5,730 kg)
Loaded weight: 16,500 lb (7,480 kg)
Max takeoff weight: 21,500 lb (9,750 kg)
Powerplant: 2× Westinghouse J46-WE-2 turbojets, 12,000 lbf (53 kN) each
Performance (estimated)
Maximum speed: 695 mph (604 knots, 1,120 km/h)
Range: 513 mi (446 nm, 826 km)
Service ceiling: 54,800 ft (16,700 m)
Rate of climb: 17,100 ft/min (86.7 m/s)
Wing loading: 29.0 lb/ft² (142 kg/m²)
Thrust/weight: 1.45
Armament (planned)
Guns: 4× 20 mm (0.787 in) cannon
Rockets: Unguided rockets

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The Convair XF2Y SeaDart water-based fighter was the result of a design contest initiated by the US Navy in 1948 for a supersonic interceptor seaplane. 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.

On January 19, 1951, Convair was awarded a contract for two prototypes of a water based fighter with a delta wing planform, a single delta-shaped tail, and a watertight hull. The aircraft was to take off and land on a pair of hydro-skis that retracted into wells in the side of the lower fuselage. The two prototypes were assigned the designation XF2Y-1 and were issued the BuAer serial numbers 137634 and 137635. The name SeaDart was assigned.

The SeaDart aircraft was to be powered by a pair of 6100 lb.s.t. afterburning Westinghouse XJ46-WE-02 engines. The engines were to be fed by a pair of lateral intakes mounted high up on the sides of the fuselage well above the wings and behind the cockpit, this location being chosen in order to prevent water spray from entering the air intakes during takeoff and landing. 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 transparencies 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.

The Navy had such confidence with the design that they ordered 12 production F2Y-1 aircraft on August 28, 1952, even before the first prototype had flown. Serials were 135762/135773, which curiously were in a batch earlier than those of the two XF2Y-1s ordered more than a year earlier. 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 (BuNo 135762/135765) would be built as YF2Y-1 service test aircraft.

Later, eight more F2Y-1 production aircraft were ordered. Their serials were 138530/138534, plus three others which I don't know. This brought the total SeaDart order to 22 aircraft.

Pending the availability of the J46s, the first prototype XF2Y-1 (BuNo 137634) was fitted with two side-by-side non-afterburning Westinghouse J34-WE-32 engines of 3400 lb.s.t. each. 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.

The first flight tests revealed (as expected) that the aircraft was severely underpowered for its weight. In addition, the waterskis vibrated continuously during takeoff and landing, so much so that the aircraft was extremely difficult to control. In order to cure the vibration problem, the skis were redesigned and the oleo legs were improved. This seemed to help somewhat. However, the absence of an area-ruled fuselage (plus the lack of adequate engine power) meant that that the XF2Y-1 could not exceed the speed of sound in level flight.

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.

On October 14, 1953, the remaining XF2Y-1 (BuNo 137635) was cancelled.

The first YF2Y-1 (BuNo 135762) service test aircraft joined the test program in early 1954. Since the second XF2Y-1 (BuNo 137635) had been cancelled, YF2Y-1 BuNo 135762 was the second SeaDart aircraft actually to be built. It was powered by a pair of afterburning Westinghouse J46 turbojets. In overall appearance, the YF2Y-1 was similar to the XF2Y-1 except for the J46 engines. However, the aft fuselage at the engine exhaust area was significantly different, with the engine nacelles and nozzles extending further aft. The YF2Y-1 differed from the XF2Y-1 in not having wheels on the rear of its twin skis, so auxiliary beaching gear was required during entry to or exit from the water.

Convair test pilot Charles E. Richbourg made the initial flight tests of the number two SeaDart. On August 3, 1954, Richbourg took BuNo 135762 through the sound barrier while in a shallow dive. This made the SeaDart the first (and to date the only) seaplane to go supersonic. 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.

Unfortunately, Richbourg was killed on November 4 of that year while demonstrating BuNo 135762 over San Diego Bay to Navy officers and press representatives. 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. I still remember the rather vivid photos of this accident that appeared in Life magazine. All SeaDart operations were temporarily suspended after the crash.

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 and landings with a wingtip dragging in the water. The aircraft could even operate in waves of up to 6 to 10 feet in height, far in excess of the requirement. The last single-ski test with the XF2Y-1 took place January 16, 1956, when an open-sea landing and takeoff was carried out. After the completion of the tests, the XF2Y-1 was placed in storage.

The number three SeaDart, YF2Y-1 BuNo 135763 joined the test program in March of 1955. It was the nearest of the three aircraft to a full production model, and carried no special test instrumentation. It flew for the first time on March 4, 1955. It was powered by a pair of Westinghouse J46 afterburning engines, the same as those retrofitted to the XF2Y-1 when the single-ski was installed. The aircraft featured a revised twin-ski format, with beaching wheels once again as an integral part of the skis. The bottom planform of the ski afterbodies were the same as the best design finally derived on the number two aircraft, which did not have wheels. The afterbodies were tapered and pointed, with a retractable wheel mounted flat on the top surface of each ski afterbody, with a slight overhang on the inside of the bottom planing surface. The afterbodies rotated 90 degrees just aft of the ski main oleo struts. When the aircraft was sitting out of the water on the ramp with the wheels extended, the bottom afterbodies faced outward and appeared as spurs. Upon water entry, the ski afterbodies were retracted inward at the bottom to a 90-degree position, with the wheels safely tucked out of the way on top of the skis. Vibration was still unacceptable with the two-ski example, and after open-sea trials, testing with the second YF2Y-1 formally ended on April 28, 1955. The aircraft was placed in storage and never tested again.

In late 1956, the XF2Y-1 was taken out of storage and the entire large single-ski oleo system was removed and replaced with a small rigidly-mounted hydrofoil ski. Actual flight with such a configuration was not possible, since the rigid mounting and placement of the ski would not permit the ~20 degree nose-up attitude that was required for takeoff. The first test was carried out on March 21, 1957. Violent pounding caused every taxiing run to be aborted at speeds between 50 and 60 knots. Another rigid ski configuration was tested in the autumn of 1957. It too caused too much vibration, and further tests were abandoned. The XF2Y-1 was placed in storage after these tests were completed, never to be flown again.

The other two YF2Y-1 prototypes (135764 and 135765) were completed but never flown.

The four surviving SeaDarts are all preserved in museums.
 

 

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