RogerBW's Blog

Convair F2Y Sea Dart 04 July 2014

The Sea Dart (try not to associate that in your mind with Lawn Dart) was to be a supersonic flying-boat fighter.

It was clear in the late 1940s that supersonic interceptor aircraft were going to be needed at sea. However, there was distinct dubiety about operating them from aircraft carrier decks: those early supersonic aircraft needed very long takeoff runs and high landing speeds, and tended to be unstable and hard to control when close to landing. None of these things works well with carrier operations, and this is why the US Navy ended up buying a lot of subsonic fighter aircraft.

However, a possible solution was offered by a flying-boat design: no need to worry about a long takeoff run if you have the entire ocean to do it on. Convair came up with the Sea Dart; one prototype and four "service test" aircraft were constructed.

The Sea Dart was a delta-wing fighter with a watertight hull. Two retractable "hydro-skis" (just one, on the prototype) were attached via shock-absorbing oleo mounts. Two turbojet engines were fed from intakes over the wing, to minimise spray ingestion. These were meant to be Westinghouse XJ46s, but they weren't ready in time, so J34s were installed in the prototype, developing about half the planned power. (This was the same pair of engines that Vought used in the F7U Cutlass, around the same time.)

At rest, the skis would be retracted. At the start of a takeoff run, the pilot would extend the skis; as speed increased the aircraft would rise on the skis (and on the rear of its fuselage and, at low speeds, the trailing edge of its delta wing) into the nose-up attitude required by the wing. Once it had taken off, the pilot would retract the skis again, giving an aerodynamically clean shape.

As it turned out, the prototype's single ski worked better than the dual skis of the service test aircraft. Vibration through the skis was a huge problem, and hitting two different bits of water at slightly different angles made it much worse.

Performance also wasn't what it might have been. Even once the J46 became available for the service test aircraft, it was underpowered, and they never became supersonic in level flight, though one of the service test articles was able to exceed Mach 1 in a shallow dive (the only seaplane ever to have flown faster than sound).

However, the problems of operating supersonic aircraft from carrier decks were largely solved (mostly by the F-8 Crusader) and with unimpressive performance and continuing vibration problems the project was cancelled; the final two service test aircraft never even flew.

Footage of the Sea Dart in flight

  1. Posted by John Dallman at 10:26am on 04 July 2014

    It's notable that most of the problems with early jet-powered aircraft were solved by better jet engines. The J57 in the F-8 Crusader was the first really good US jet engine, as evidenced by the range of aircraft that used it successfully.

  2. Posted by Owen Smith at 12:01pm on 04 July 2014

    The phrase "supersonic flying boat" is one of those things that just says "don't" in my mind. Still, it gave me a giggle at work.

  3. Posted by RogerBW at 02:12pm on 04 July 2014

    It seems to me that the need for this aircraft was dictated in part by the poorness of the engines (slow throttle response that can't get you out of trouble when a landing goes wobbly, low thrust so you need a long takeoff run), so it wouldn't have had a niche even if someone had come up with it as a new idea once the J57 was available.

    Yes, having a boat hull does rather compromise your aerodynamics for other things once you're trying to go up above 200mph or so.

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