Giant Amphibian

Japan has one godzilla of a seaplane

ShinMaywa’s US-1A, cleansed of the corrosive sea after every mission, continues an ancestral line of flying boats. (Tim Wright)
Air & Space Magazine

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For Kawanishi, the postwar years were difficult ones. While Japan was under U.S. occupation, the company was forbidden to build aircraft. Its workers transferred their skills in aluminum and metal working to making pots and pans, and later the company expanded into building and maintaining trucks. Before long, the massive hangars where the Emily had been assembled were rebuilt and filled with hundreds of trucks in various stages of construction or repair. Kawanishi changed its name to ShinMaywa to escape some of the notoriety that stemmed from its World War II operations.

At the outbreak of the Korean War, ShinMaywa was invited back into the aircraft business as a maintenance depot for U.S. military transports. The company had retained its expertise in flying boat construction and seized the opportunity to continue working with the technologies it had developed during World War II. Among its areas of interest was short-takeoff-and-landing (STOL) technology for marine aircraft.

With the help of the U.S. Navy, ShinMaywa acquired a Grumman UF-1 Albatross, an amphibious search-and-rescue aircraft with a 2,850-mile range that served not only the Navy but the U.S. Air Force and Coast Guard as well. The Albatross could accommodate a crew of six and was powered by two 1,425-horsepower Wright R-1820 engines. To create a STOL aircraft, ShinMaywa added two 600-hp Pratt & Whitney R-1340 engines, stretched the nose, and refitted the aircraft with a high T-tail. The modified Albatross was named the UF-XS and became a research platform for investigating STOL technologies.

The limiting factor in open-ocean operations is the impact stress created by waves slamming against the hull during takeoff and landing; reducing takeoff and landing speeds reduces the stress on the aircraft. ShinMaywa experimented with an array of high-lift devices to enable the UF-XS to take off and land at slower speeds. The tailplane and outer sections of the wings had leading edge slats. Flaps on the inner sections of the wings’ trailing edges could be deflected as much as 80 degrees, and on the outer sections, as much as 60 degrees. Engineers augmented these movable surfaces with an experimental system for controlling the boundary layer.

The boundary layer is a thin layer of air molecules near the surface of an aircraft (or any object moving through the air) that, because of the air’s viscosity, moves at a different velocity from the air farther from the surface. In fact there are a number of “layers” in the boundary layer, all flowing at slightly different velocities.

As an aircraft approaches the low speeds associated with landing, the boundary layer flowing over the wing becomes increasingly turbulent and the wing loses lift. To retain smooth flow, and therefore lift, as long as possible at slower speeds, ShinMaywa devised a system to blow air over the flaps and the elevator to keep the airflow smooth, enabling the aircraft to maintain lift and control at low speed. The air was produced by a 1,250-hp General Electric T58 turboshaft engine mounted in the aircraft cabin.

The UF-XS research showed that aircraft with such a system for boundary layer control (BLC)—as well as improved hull designs—could operate in much rougher seas than had been possible before. ShinMaywa incorporated the high-lift devices developed for the research program into the design of the anti-submarine PS-1 and the US-1/US-1A rescue aircraft.

The company built 23 PS-1 anti-submarine aircraft and 18 US-1/US-1A search-and-rescue aircraft. Although their BLC systems are unique, the amphibians inherited their configurations in part from their noted ancestor, the Kawanishi H8K-2 Emily. Their four General Electric T64 turboprop engines, license-built by Ishikawajima and each rated at 3,493-hp, are suspended from a wing set high on the fuselage. Seaplane designers place the engines as high off the water as possible to keep the air intakes from ingesting water. Also, saltwater is abrasive and corrodes propellers as well as the numerous rotating blades inside turbine engines. Besides mounting the engines high, ShinMaywa designers added a spray-suppressing chine around the forward hull.

All PS-1 and US-1 aircraft have been retired, but seven US-1As remain in service, and the type is still in production. As US-1A number 19 neared completion at the Kobe factory last year, the next generation of rescue amphibian was emerging right beside it.

The US-1A “Kai” is based on the 1960s technology of its predecessors and therefore has the same capabilities for STOL and rough-sea takeoffs and landings. But the Kai (Japanese for “modification”) also incorporates a pressurized hull that will allow the aircraft to fly at 30,000 feet instead of its current 10,000. At higher altitudes, the Kai will have greater range and will avoid the weather that limited US-1A operations. The Kai will also include modern satellite navigation and communication systems. The flight deck features a head-up display and night vision technology and resembles the glass cockpits of contemporary airliners. The first airframe was completed last month, and a rollout is scheduled for March 2003.


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