Subject: Convair F-7 SeaDart

From: [email-masked] (joseph.f.baugher)
Date: 21 Aug 94 01:04:23 GMT

The Convair XF2Y Sea Dart water-based fighter was the result of a 
design contest initiated by the Navy in 1948 for a supersonic interceptor 
seaplane.  Initially, the plan was for a delta-winded design with 
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 retractable hydro-skis.  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.  
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.  In 
order to prevent water spray from entering the air intakes during 
takeoff and landing, the intakes were situated well above the wings 
and behind the cockpit.  The hull of the SeaDart had multiple 
watertight compartments in the lower fuselage to prevent sinking in 
the event of a puncture.  Both the elevons and the rudder were 
hydraulically-powered.  The aircraft was fitted with a set of dive 
brakes which also doubled as water brakes and as a water rudder while 
on the surface.  The lower fuselage of the SeaDart had the V-shaped 
profile of a boat, as would be expected for a water-based aircraft.  
The aircraft took off and landed on a pair of retractable hydro-skis 
that extended outward from recesses in the lower hull, one ski on each 
side of the hull.  For takeoff, the skis were fully retracted, 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 out of the water, it 
tilted backwards on its skis, its tail resting on the ground.  The 
twin retractable hydro-skis had small wheels at the aft end and a 
small swivel tailwheel mounted underneath the rear fuselage, which 
allowed a limited amount of ground maneuverability.  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 were curiously
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 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 was fitted 
with two side-by-side afterburning Westinghouse J-34-WE-32 engines of 
3400 lb. st. each.  On December 14, 1952, E. D. "Sam" Shannon 
began taxiing trials with the XF2Y-1 prototype (BuNo 137634).  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 tests revealed (as 
expected) that the aircraft was severely underpowered for its weight.  
In addition, the waterskis vibrated continuously during takeoff and 
landing.  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 engine finally became available and was installed in 
the prototype, but it failed to reach its 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.  On August 3, 1954, Convair's test pilot Charles 
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.  (Question: did the Martin P6M Seamaster 
ever go supersonic?).  Unfortunately, Richbourg was killed on November 
4 of that year while demonstrating BuNo 135762 in an airshow over San 
Diego Bay.  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.  

In the meantime, the Navy had been gradually losing interest in the 
SeaDart project.  The Navy 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.  

The last two YF2Y-1s (#135764 and #135765) were delivered to the Navy, 
but were never actually flown.  

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 reworked.  The aft 
fuselage was brought up to YF2Y-1 configuration and the aircraft was 
fitted with a large, single hydro-ski in place of the original pair of 
skis.  The XF2Y-1 flew for the first time in this configuration on 
December 29, 1954.  After some refinements, the single ski arrangement 
was found to work out fairly well, finally curing the vibration 
problems that had plagued the twin-ski SeaDarts.  The single ski 
could even safely allow 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.  

Testing with the single ski continued up to January 16, 1956.  Later 
in 1956, the XF2Y-1 was fitted with a hydrofoil ski (as opposed to the 
earlier planing skis), but it was found that such a configuration 
would not permit the ~20 degree nose-up attitude that was required for 
takeoff.  

The third SeaDart (YF2Y-1 BuNo 135763) flew on March 4, 1955.  It 
featured a revised twin-ski format, but vibration was still 
unacceptable, and after open-sea trials, testing with the second 
YF2Y-1 formally ended on April 28, 1955.  

Evaluation of the surviving SeaDart aircraft continued until 1957, 
when the program was finally terminated.  Despite satisfactory results 
with the single ski, no further work was undertaken because of the 
lack of any Navy requirement for such an aircraft.  

The four surviving SeaDarts are all preserved in museums.  The XF2Y-1 
prototype (BuNo 137634) is reportedly with the Maryland Aviation 
Historical Society at Strawberry Point (I'm not sure where this is, 
even though I am from Maryland).  The 3 surviving YF2Y-1s are with the 
San Diego Aerospace Museum at Balboa Park (135763), NAS Willow Grove, 
Pennsylvania (135764) and Lakeland, Florida (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 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 was 
no longer in 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.  

137634/137635 	Convair XF2Y-1 SeaDart (137635 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: 

Two Westinghouse J46-WE-2 turbojets, rated at 6000 lb.s.t.  each.  
Maximum speed: 695 mph at 8000feet, 825 mph at 36,000 ft.  Climb rate: 
35,000 feet in 1.7 minutes.  Range 513 miles.  Service ceiling 54,800 
feet.  Climb to 25,000 feet in 1.7 minutes.  (these are estimated 
performance figures, which I don't think were ever achieved in test) 
Stalling speed 132 mph.  Initial climb rate 17,100 feet per minute.  
Dimensions: 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: 630 US gallons.  Weights: 12,625 pounds empty, 
16,500 pounds gross, 21,500 pounds maximum takeoff.  The SeaDart was 
never equipped with any armament.  

Sources:

  The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.

  United States Navy Aircraft Since 1911, Gordon Swanborough and
  Peter M. Bowers, Smithsonian, 1989.

  General Dynamics Aircraft and their Predecessors, John Wegg,
  Naval Institute Press, 1990.

  Ray Wagner, American Combat Planes, Third Enlarged Edition,
  Doubleday, 1982.

Joe Baugher			**************************************
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