The Shin Meiwa PS-1 / US-1 & Harbin SH-5 Flying Boats

v1.1.1 / 01 apr 03 / greg goebel / public domain

* While the large flying boat is generally a thing of the past, there are a few survivors. Among them are the Japanese Shin Meiwa "PS-1" and "US-1", and the Chinese Harbin "SH-4". These big, elegant, four-turboprop aircraft remain in service in limited numbers. This document provides a short history of the PS-1, US-1, and SH-5.

[1] UX-FS

[1] UX-FS

* The Japanese Kawanishi aircraft company had designed a number of flying boats into World War II, most significantly the superlative H8K ("Emily"), one of the best flying boats of the conflict.

While Japan's defense industries were suppressed by the American occupation authorities after the country's defeat, they slowly began to re-emerge as the US turned to Japan as an East Asian ally in the Cold War against the Soviet Union. The Kawanishi company was resurrected in 1949 as "Shin Meiwa", in the relatively humble role of a service company that overhauled American, and later Japanese, military and civil aircraft.

However, the company had not forgotten its roots, and in 1959 Shin Meiwa rebuilt a Grumman UF-1 Albatross provided by the US Navy to experiment with new flying boat concepts. The modified Albatross, designated the "UX-FS", performed its initial flight on 25 December 1962.

The UX-FS was fitted with four engines, two of them its normal Wright R-1820 radials with 1,425 horsepower each, plus two additional Pratt & Whitney R-1340 radials with 600 horsepower each. The aircraft's hull was extensively modified, and the Albatross's conventional tail was replaced by a tee tail.

The UF-XS was also fitted with a General Electric (GE) T58 turboshaft engine with 1,250 horsepower, mounted above and behind the cockpit. This engine simply blew air over the flaps and tail to provide a "boundary layer control (BLC)" system for improved short take-off & landing (STOL) performance. The UF-XS was flown in trials into 1964, and validated many concepts in improved flying boat design.



* In January 1966, the Japanese Defense Agency awarded Shin Meiwa a contract for further development of the company's flying boat concepts. The contract specified development of two full-scale prototypes, with the project designation "PX-S" and company designation "SS-2". The PX-S was intended primarily for antisubmarine warfare (ASW). Dr. Shizuo Kikuhara was in charge of the design team.

The first PX-S prototype took to the air from Kobe harbor on 5 October 1967, with the second following on 14 June 1968. Evaluation by the Japan Maritime Self-Defense Force (JMSDF) began late in 1968. The results of the evaluation were positive, and two preproduction "PS-1" aircraft were ordered in March 1969, with initial delivery in late 1971.

* The PS-1 was powered by four General Electric T64-IHI-10 turboprop engines with 3,060 horsepower each, built under license by Ishikawajima, mounted on a high-set wing. Each engine drove a three-blade reversible-pitch Hamilton Standard propeller.

As with the UF-XS test aircraft, a GE T58 turboshaft engine, also built by Ishikawajima, was mounted in the upper center of the fuselage to drive a BLC system for improved STOL performance. The T58 could also be used as an auxiliary power unit (APU). STOL capability was further enhanced by leading-edge slats on the outboard sections of the wings and the horizontal tailplane, as well as overwing spoilers and large flaps. Take-off speed was about 90 KPH (55 MPH).

The aircraft was fitted with an interesting system in which water was pumped alongside the fuselage to suppress sea spray. Spray was also deflected by strakes mounted alongside the nose of the aircraft. These measures helped to ensure that the engines were not inundated with sea water on landings and takeoffs. A sea anchor was carried in the bow.

The aircraft's boat hull was unusually slender, making it very stable in rough seas, and it could land and take off in swell heights of up to 4.3 meters (14 feet). Most flying boats can operate only on calm seas or protected waters, but the PS-1 was capable of landings and takeoffs under severe ocean conditions. The seaworthiness of the PS-1 was far beyond that of any World War II flying boat.

The PS-1 featured a tall tee tail like that of the UF-XS. A fixed stabilizer floats was fitted to each wingtip, and the aircraft had built-in retractable tricycle beaching gear, though it could only actually land on water. The nose gear retracted into the hull, while the main gear pivoted up into the sides of the fuselage.

Sensor systems included search radar with the antenna in a prominent nose radome; a "magnetic anomaly detection (MAD)" system with a retractable tail "stinger; a "Jezebel" passive sonar system with 20 sonobuoys; a "Julie" active sonar system with explosive charges; and a searchlight mounted under the right wing.

Four 150 kilogram (330 pound) depth charges could be carried internally. Pods between the engines on each wing could carry two homing torpedoes each, for a total of four, while a pod on each wingtip could accommodate three 127 millimeter (5 inch) rockets, for a total of six. There was no defensive armament.

The PS-1 carried a crew of nine, including pilot and copilot; flight engineer; radio operator; radar operator; MAD operator; two sonar operators; and a tactical coordinator. The raised flight deck provided excellent visibility, and bunks were included for long-range patrols.

* The JMSDF ordered a total of 21 PS-1s, with the last delivered in the spring of 1978. However, as often happens with Japanese defense programs, the protracted development and small production run of the PS-1 led to very high unit costs. The program was politically controversial, all the more so because PS-1s suffered a series of accidents, though they were not related to design or construction faults.

Although the idea of using a flying boat for ASW operations had its attractions, in that the aircraft could set down on the water and drop a dunking sonar to hunt for submarines, in practice land-based aircraft could do a perfectly adequate job of ASW at much lower cost. Procurement of the PS-1 was halted in 1980 in favor of the Lockheed P-3C Orion, and the PS-1 was completely out of service by 1989.



* Retirement of the PS-1 did not take Japan completely out of the flying boat business. Early in PS-1 production, the JMSDF asked Shin Meiwa to develop an amphibian version of the PS-1 for "search and rescue (SAR)" operations to replace the service's Grumman UF-1 Albatross flying boats.

The new SAR flying boat was given the military designation of "US-1" and the company designation of "SS-2A". As the aircraft was very similar to the PS-1, there was no prototype. Initial flight of the first US-1 was on 15 October 1974, with introduction to service in 1975.

The US-1 looks much like the PS-1, but lacks armament and all sensor systems except ocean search radar. It has additional fuel capacity, and is fitted with true landing gear to allow it to take off and land on airstrips. The main gear resembles that of the PS-1, but is scaled up, featuring two wheels on each gear assembly, and retracts into prominent fairings on the fuselage under the wings. The track is narrow, but the aircraft still handles well on crosswind landings.

Additional "bubble" windows are provided for observers, and along with rescue hatches with folding ramps, a large sliding door is built into the right side of the aircraft to allow launch and recovery of an inflatable rescue dinghy. A hoist is fitted above the sliding door; a loudspeaker system allows the flight crew to give instructions to survivors; and a dye-marker launcher with a capacity of ten markers can be used to mark patches of sea during rescue operations.

The US-1 has a crew of nine, including pilot; copilot; flight engineer; navigator; radio operator; radar operator; and two observers. Up to five medics or rescue divers can be carried as well. The aircraft can accommodate 12 stretchers and three sitting passengers, or 36 sitting passengers. In principle, the SAR gear could also be removed to allow conversion of the US-1 into a troop transport with seating for 100.

   _____________________   _________________   _______________________
   spec                    metric              english

   _____________________   _________________   _______________________

   wingspan                33.15 meters        108 feet 9 inches
   length                  33.46 meters        109 feet 9 inches
   height                  9.82 meters         32 feet 3 inches

   empty weight            25,500 kilograms    56,220 pounds
   loaded weight           45,000 kilograms    99,200 pounds

   max speed at altitude   495 KPH             310 MPH / 270 KT
   service ceiling         8,200 meters        27,000 feet
   range                   4,200 kilometers    2,610 MI / 2,270 NMI
   _____________________   _________________   _______________________

An initial batch of 12 US-1s was built. The seventh and following aircraft were fitted with uprated T64-IHI-10J turboshaft engines offering 3,490 horsepower each. These aircraft were designated "US-1A". Earlier production aircraft were upgraded to the same standard.

The US-1 has proven extremely useful and capable, and was heavily employed in maritime SAR activities after the shoot-down of Korean Air Lines flight 007 by the Soviets in 1983. Two more US-1As were built in the early 1990s, and the type remains in service, though the exact numbers still flying is uncertain.

* Shin Meiwa proposed a commercial transport version of the US-1 with seating for 69 passengers, but it was just too expensive and didn't happen. The first prototype of the PS-1 and a US-1 were also used in trials by the JMSDF and National Fire Agency as a "water bomber" to fight forest fires. While the big flying boat is obviously too expensive for purchase of new aircraft for the fire-fighting role, it is possible that retired aircraft may be employed in this role.



* While the Japanese were developing the PS-1, the Chinese began work on a comparable aircraft. In early 1970, after several years of consideration of various preliminary designs, the Harbin Aircraft Manufacturing Corporation (HAMC) and the Chinese Seaplane Design Institute began formal work on a four-turboprop flying boat that could be used for maritime warfare, SAR, and cargo transport roles. The aircraft was to be designated the "Maritime Bomber 5 (Shuishang Hongzhaji 5 / SH-5)", though sources mention an alternate "PS-5" designation.

A static test airframe was completed in 1971, but due to the upheaval of the Chinese "Cultural Revolution", did not begin tests until August 1974. In the meantime, a flying prototype had been rolled out in December 1973, beginning taxi trials in May 1975 and performing its first flight on 3 April 1976.

The slow pace of the program continued, a single production batch of six aircraft being completed in 1984 and 1985, with four of them handed over to the People's Liberation Army Naval Air Force in 1986. They have been retained in service, and may have received some combat electronic system updates.

* The SH-5 has a very general resemblance to the PS-1 / US-1, with a long, relatively slender, fuselage and hull, a high wing with four turboprops, and a fixed float near each wingtip. However, in detail it shows clear influence of Soviet Beriev flying boat designs, with a twin-fin tail and very similar nose layout.

The SH-5 is powered by four Dongan WJ5A turboprop engines with 3,150 horsepower each, driving four-bladed propellers. The aircraft is a pure seaplane, though it does have built-in beaching gear roughly similar to that of the PS-1. There are spray-suppression strakes on each side of the nose, and a small sea rudder at the rear of the hull.

The SH-5 is armed with a dorsal turret mounting twin cannon, and there are two stores pylons on each wing, one placed between the hull and the inboard engine, the second placed between the inboard and outboard engines. These four stores pylons can each be fitted with a C-101 antishipping missile, or each of the outer stores pylons can be fitted with three homing torpedoes.

Six tonnes (13,200 pounds) of other stores, such as depth charges, mines, bombs, sonobuoys, or rescue gear can be stored in a rear compartment in the fuselage. A Doppler search radar is fitted in a thimble radome in the nose, and a fixed MAD boom is fitted to the tail. If configured as a cargolifter, the SH-5 can carry 10 tonnes (22,000 pounds) of cargo.

The SH-5 carries a flight crew of eight, including a pilot; co-pilot; navigator; flight engineer; radio operator; and three systems specialists. The number of specialists may vary depending on the mission.

The fuselage is unpressurized. There are three freight compartments behind the cockpit area, followed by a cabin for the mission crew, a compartment for communications gear, and finally the stores compartment. There is a corridor connecting all three compartments, with watertight doors into the compartments. There is one crew door on the left side of the aircraft and two on the right.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                36 meters           118 feet 1 inch
   length                  38.9 meters         127 feet 8 inches
   height                  9.8 meters          32 feet 2 inches

   empty weight            26,500 kilograms    58,400 pounds
   max loaded weight       45,000 kilograms    99,200 pounds

   max speed at altitude   555 KPH             345 MPH / 300 KT
   service ceiling         10,250 meters       33,650 feet
   range                   4,750 kilometers    2,950 MI / 2,565 NMI
   _____________________   _________________   _______________________

One of the aircraft not delivered to the Navy was apparently evaluated as a "water bomber" for fighting forest fires, but no additional SH-5s have been built.



* Sources include:

* Revision history:

   v1.0   / 01 may 01 / gvg / Originally discussed PS-1 / US-1 only.
   v1.1.0 / 01 jan 02 / gvg / Added comments on SH-5.
   v1.1.1 / 01 apr 02 / gvg / Very minor typo fixes.