Convair YF2Y-1 Sea Dart by Mach 2

1/72 scale
No Kit Number
Decals: One version – United States Navy
Comments: Limited run kit requiring clean-up of high degree of flash; basic cockpit; delicate engraved panel lines will need reinforcement

History

The Convair XF2Y-1 Sea Dart was the subject of an experimental flight test program that began in December 1952. Its purpose was to test the feasibility of a jet powered, delta wing, supersonic seaplane fighter prototype that was developed with the support of the U.S. Navy. The Sea Dart’s testing program ran for five years, concluding in late 1957. Convair had experimented with delta wing aircraft beginning with its XF-92 prototype in 1948, a design that, while itself was unsuccessful, led to the F-102 Delta Dagger and F-106 Delta Dart fighters, which formed the front line of the Air Defense Command’s strength for over 20 years.

The Sea Plane Strike Force
The Sea Dart was part of the Navy’s mobile base concept for fielding a sea plane strike force that was to allow the Navy greater flexibility in projecting force in different hot spots around the world, at a time when the U.S. Air Force, the primary service charged with the delivery of nuclear weapons in the early years of the Cold War, had begun claiming a larger share of defense appropriations. The idea was for the Sea Dart, together with the Martin P6M Sea Master, a jet-powered nuclear bomber that was also designed as a sea plane, to operate from virtually any waterway or ocean in the world. Since two-thirds of the Earth’s surface is water, this concept would have eliminated the need to operate from prepared concrete runways and facilitated the timely projection of American airpower virtually anywhere in the world, without the limiting factor of runways that hampered the Air Force in the years following World War II.

The Water-Skiing Seaplane
The Sea Dart’s design required elevation of the nose of the plane during taxiing and the run-up to take-off speed, high enough to prevent excess ingestion of sea water through its intakes. This entailed a unique twin ski design that evolved during the course of the testing program, but derived their lift in the same way as water skis — they were not hydrofoils in the true sense of the word. Initially the Sea Dart featured fully retractable twin skis that extended from beneath the fuselage (the front struts were mounted directly below the pilot), but these caused such intense vibration and pounding that conditions for the pilot were unacceptable, including loss of vision due to the amount of vibration in the cockpit as the plane neared take-off speed.

This close-up of the kit’s single sprue highlights the amount of flash the modeler must contend with.

It should be noted that the canopy and windshield design of the Sea Dart were similar to the “V” windshield of the North American X-15. Visibility from this windshield was acceptable for a research aircraft, but would have been insufficient for a front-line fighter, and would have required a redesign had the Sea Dart ever entered production. Pilot’s reported that the windshield was too small, poorly placed, did not allow insufficient light in the cockpit see the instruments properly, and hampered forward visibility somewhat.

The initial fix for the excess vibration of the skis was to taper their outboard edges at the aft end. But because a good portion of the vibration was caused by the flexing of the skis between their forward and aft mounts at both taxiing and landing speeds, the best configuration for reduced vibration for this delta winged, water-based plane was a large single ski that could be extended along the aircraft’s centerline, but which could not fully retract. At 125 knots, the Sea Dart’s nose rotated sharply upwards to between 17 and 19 degrees for lift-off from the water’s surface. For landing both the single and twin skis had to be fully extended. Initially the XF2Y-1 had small wheels fitted to the aft end of its skis, allowing it to taxi down the Convair sea plane ramp abutting San Diego Bay under its own power for flight tests. Later versions deleted the wheels, giving rise to the need for a special beaching dolly. In the water, the combined use of asymmetric power (setting each of the two jet engines at different power levels), employing the speed brake as water rudders, and lateral control (banking) was very effective at executing turns at speeds of 15 to 20 knots.

The Sea Dart was powered by two Westinghouse J-34 turbojets (the J-46 engine was planned for this airframe but was not ready in time; eventually J-46’s were installed on the YF2Y-1 version) and had a maximum speed of 825 mph (Mach 1. ). The XF2Y-1 featured extensive test instrumentation for both aerodynamic and hydrodynamic evaluation of its performance, facilitating data analysis after each test flight. Water ingestion by the engines was not a severe problem if proper pilot techniques were employed. But, normal operations in a salt water environment did cause problems. Engine compressors could stall, afterburner thrust would decay and tail pipe temperatures could reach excessive levels with repeated flights, due to salt water particles drying on the engine compressor blades and disrupting the air flow over the blades, just as ice or snow could do when it accumulated on the leading edge of a wing. This problem was remedied by spraying fresh water into the intakes while the engines were at idling speed ashore prior to each flight — this practice restored engine efficiency and thrust, so much so that a 20-gallon fresh water tank was mounted within the fuselage behind the cockpit, and with appropriate tubing and a small electrical pump, fresh water was routinely sprayed into each inlet duct via a switch that was rigged up in the cockpit.

Fatal Crash: November 1954
On November 4, 1954, the U.S. Navy and Convair scheduled a flight demonstration of the Navy’s “Mobile Base Concept” aircraft, and facilitated national press coverage. Flights of the XFY-1 “Pogo” vertical take-off and landing (VTOL) aircraft, the R3Y Tradewind turboprop flying boat, and the XF2Y-1 Sea Dart were featured. The Pogo and Tradewind flights went off without incident. Then the Sea Dart took off with test pilot Charles Richbourg at the controls. Richbourg made a spectacular take-off run from the San Diego Bay, retracting the twin skis immediately after lift-off. Within moments, Richbourg was out over the city of El Cajon, east of San Diego, and radioed that he was turning back for his east-west fly-by run.

The Sea Dart was moving a at estimated 575 mph when Richbourg flew over San Diego Civic Center and fired the afterburners. This sudden application of increased power caused a nose-down pitching motion, which Richbourg instantly tried to correct by pulling back on the stick. The Sea Dart, like many early supersonic aircraft designs, had a “full power” hydraulic system allowing pilots to control the aircraft in spite of extreme and otherwise unacceptably high control forces on the aircraft. This full power system required more force on the stick than usual to move it out of its default center trim position — referred to as “break out” force.

Here, the spartan cockpit tub reveals the opportunity for detailing the Sea Dart’s interior with which modelers are presented.

At a higher altitude, where the air was thinner, this might not have been a problem. But moving at relatively high speed at lower altitude, where the air is thicker and provides more friction on the airframe, can be trickier. In this instance, the physics involved created something called divergent longitudinal pitch oscillation – in short, two very strong opposing physical forces trying to move the nose of the aircraft up and down at the same time, as it approached transonic speeds — and this triggered structural failure which broke the Sea Dart apart during the second nose-down pitch. As the Sea Dart broke apart, the forward section of the fuselage separated from the rest of the airframe behind the cockpit with one ski still attached. At nearly the same time, the fuel tank exploded, producing a fireball. The nose section crashed inverted into San Diego Bay, killing Richbourg on impact. Sea Dart operations were temporarily suspended until the Navy’s accident board could complete its investigation.

The Navy found that divergent pitch oscillation, partly induced by the full power flight control system, and partly pilot induced, caused the fatal crash. It was a type of accident that occasionally occurred in all early supersonic aircraft, even years later with more advanced airframes — the investigation ruled out as potential contributing factors the fact that the Sea Dart was a seaplane, or that there was any design flaw in the plane itself. Flight test operations resumed on December 29, 1954 and continued through most of 1957. In that time, a number of open sea take-off and landing tests were conducted, with both the original double ski (YF2F-1) and later single ski (XF2Y-1) configuration, including jet assisted take-off (JATO) tests and water loop maneuvers. Throughout the Sea Dart’s test program, vibration and severe pounding during take-offs and landings continued to be a problem to the point that the pilot could not see the instruments in the cockpit, and this tended to be worse in bays and semi-protected waterways where wave patterns were more consistent, than on the open sea, where the surface tends to be more irregular. This problem was less severe with the single ski configuration of the XF2Y-1, but was never completely resolved (although the JATO tests were done to reduce the time and distance required for lift-off, when all vibration would cease instantly).

The Sea Dart never went into production, in part reportedly due to the Navy’s declining interest in the project as it solved the challenge of producing a supersonic fighter capable of operating from carrier decks with the introduction into fleet service of the Douglas F4D Skyray in April 1956. It is worth noting that there is no record during the flight test program of preparations for the necessary modifications, such as altering the canopy design to improve the pilot’s visibility, or providing for weaponry, that would have made the Sea Dart an effective fighter. Also, the expense and logistical challenge of maintaining a seaborne maintenance and supply capability to support Sea Dart operations may have been too daunting. Finally, another factor may have been that the Martin SeaMaster the seaplane strategic bomber for which the Sea Dart would have provided fighter escort, was itself a complex and costly development project that was ultimately cancelled in favor of the Polaris submarine program. Although the flight test program did not culminate in a fleet of Sea Darts, it was an impressive technical accomplishment that demonstrated the feasibility of a waterborne jet fighter.

The Kit

Mach 2’s SeaDart is injection molded in bone white and consists of 30 parts, 29 in color on a single sprue and one clear plastic part for the canopy, which strongly resembles that of the X-15. On this clear part, all but the portion representing the transparent section of the “V” windscreen is frosted, which will facilitate painting. At a glance, it is clearly a short-run kit, as there is a small amount of flash on many of the parts, most notably on the cockpit tub, delta wings, and skis, and while there are engraved panel lines throughout the exterior of the airframe, most of them will require some clean-up and reinforcement, so a scribing tool or equivalent instrument will be helpful. Portions of the plastic are discolored to the point that they look dirty, but more likely indicate some imperfection in the plastic used in the molds. NOTE: The first step of building any kit should be to wash it with mild detergent in warm water as a matter of routine — but with this kit particularly.

A great deal of attention was paid to the detail and accuracy of the fuselage halves, right down to the distinctive bow spray rails, and they definitely pass the naked eye test in capturing the Sea Dart’s lines. However, there is a conspicuous absence of locator pins, so a bit of extra care will be in order when cementing the fuselage together to ensure proper alignment. The wings look accurate, including the small wing fences on their undersides that helped provide lateral stability in the water. There are separate parts for the oleo struts and twin skis that enabled the Sea Dart to take off from and land in the water (the struts in particular are reasonably detailed, and the basic shape of the skis appears accurate), as well as for the large intakes that run about two-thirds of the length of the fuselage. As for the cockpit, the pilot’s seat is decent, not especially detailed and will also require some cleanup. A control yoke and instrument panel hood are provided, but there is no actual instrument panel, nor is there a decal to represent the panel face. In the cockpit tub, there is a small amount of engraved detail for the left side panel instrumentation, but that’s it. There is no sidewall detail of any kind. As this kit is 1/72 scale and most of the cockpit interior will not be visible on the finished kit, these details, or lack thereof, will not be a big deal for most modelers.

The Sea Dart getting up to speed for a take-off run in San Diego Bay, 1954.

The instructions are very basic, providing a single exploded drawing of the kit parts, but do not bother exploding the four cockpit components (tub, hood, seat, and control yoke) — these are depicted fully assembled for some reason. A rudimentary paint guide is provided, and does not reference any manufacturer’s paint numbers. As an example, modelers are advised to paint the cockpit interior black, the seat green, and all exterior surfaces sea blue gloss. However, this information all appears to be accurate, particularly given B.J. Long’s account in the Naval Fighters book on the Sea Dart about the difficulty test pilots had seeing the instruments in the cockpit. The small sheet for the kit decals contains markings that are crisply done with a nice glossy sheen, and should not present any difficulties. There is no indication as to who the decal manufacturer is, but they look quite similar to Propagteam in quality.

Conclusion

If you have the patience to tackle short-run kits, this is an interesting and very likely rewarding subject of an innovative and technically advanced Cold War experimental fighter design, that never went into production but remains an impressive piece of aviation engineering. Highly recommended.

Reference

• Naval Fighters Number 23: Convair XF2Y-1 and YF2Y-1 Sea Dart by B.J. Long, Copyright 1992 Steve Ginter
• Footage: http://www.youtube.com/watch?v=SOrj2cSDO-M