The first Japanese indigenously designed military helicopter is poised for its first flight.

Paul Lewis/TOKYO

JAPAN'S FIRST INDIGENOUSLY developed helicopter, the Kawasaki OH-X scout, is scheduled to have its maiden flight within a few days. The new military machine has been designed specifically for Japan's mountainous island environment and introduces major technological advances for the country's aerospace industry.

The programme's roots can be traced back to 1991 and the Japan Defence Agency's (JDA) search for a Kawasaki/McDonnell Douglas (MDC) OH-6J/D helicopter replacement. Development began the following year, with initial funding for the JDA's Technical Research & Development Institute (TRDI) to begin preliminary design work.

The OH-X programme was veiled in stealth-like secrecy over the first two years of its development. This can be explained partially by Japan's low-key approach to defence spending, because of its militaristic past. Others have suggested that the JDA was keen to pursue quietly its own development, without being politically railroaded into a similar venture to that of the FS-X, which was based on a foreign design.

Tadahiko Udagawa, deputy director of the JDA's aircraft division, claims that US and European helicopters had been considered, but rejected as unsuitable. "In view of Japan's mountainous regions, we wanted a very small, lightweight helicopter, with range and manoeuvrability. We searched for a model to import, but found the best solution was to build our own," he explains.

Another major consideration, however, is the Japanese aerospace industry's overwhelming reliance on defence contracts for continued work. "As a policy in Japan, we want to foster a domestic aircraft industry in order to keep up with research-and-development technology," acknowledges Udagawa.

In line with Japan's "conveyor-belt" approach to awarding work, Kawasaki Heavy Industries (KHI) was named OH-X prime contractor in September 1992. As part of its 60% stake, the company was given responsibility for the helicopter's forward fuselage, dynamic components, final assembly and initial flight testing.

With Mitsubishi Heavy Industries (MHI) and Fuji Heavy Industries (FHI) committed to licence-production of the Sikorsky S-70 and Bell AH-1S, respectively, each took a 20% share. MHI was contracted to supply the centre fuselage and landing gear, and FHI the empennage, stub wings, engine cowling and canopy.


From the outset, the Japan Ground Self-Defence Force (JGSDF) wanted an armed machine, capable of co-ordinating and directing other anti-tank helicopters, such as the AH-1S. It would be required to operate at the forward edge of the battlefield, with a heavy dependence on agility and high performance for its survival. A self-defence capability was also stipulated, for aerial protection from other helicopters or fixed-wing aircraft.

Maj Syuichi Sasaki, of the JGSDF's material R&D division, explains: "As Japan is surrounded by sea-we expect any offensive action to come from the sea or air. The JGSDF will try to counter-attack and to do this efficiently, we have to have helicopters for the purpose of reconnaissance and command-and-control."

When KHI finally took the wraps off the OH-X engineering mock-up in September 1994, it revealed an attack-helicopter type of configuration quite distinct from that of the OH-6. Featuring a narrow, 1m-wide fuselage, tandem-seat cockpit, mini stub-wings and non-retractable tailwheel-type undercarriage, it has all the design hallmarks of a light anti-tank machine, such as the marginally larger Agusta A129 Mangusta.

The tandem-seat layout was adopted to provide for better all-round crew vision, with the added advantage of a narrow fuselage being harder to detect. "Eyesight was a priority, and it may have also reduced the helicopter's radar cross-section, but we don't yet have any accurate data to prove that," says Udagawa.

The OH-X's drive system includes some notable technological firsts for Japanese aerospace, including a composite hingeless hub and four-blade main rotor. The KHI-designed rigid hub, which has already been tested by the TRDI on a modified OH-6D, should assist enhanced manoeuvrability at low level. About 40% of the OH-X's structure is made of composite material, including its ballistic-tolerant carbon-graphite blades.

A ducted tail rotor is another new feature for a Japanese machine, while its eight asymmetrically spaced blades are claimed to be a world first. The JGSDF opted for a fenestron-style tail assembly to provide added protection from trees, etc, while the helicopter is in confined areas. The machine's unevenly arranged tail-rotor blades are intended to reduce noise and vibration resonance.

It is unclear whether an MDC-type no-tail-rotor (NOTAR) system was ever seriously considered in place of a ducted tail for the OH-X. According to a senior KHI official, a NOTAR solution was looked at, but after a rough comparison, "-was found to be less efficient in terms of energy". The JDA contradicts this, however, claiming that a lack of Japanese NOTAR R&D ruled it out from the start as a possible alternative. "We didn't consider NOTAR an option," recalls Major Sasaki. "We had to make a choice between a conventional tail or a ducted tail."

The OH-X is powered by two side-by-side-mounted 660kW (885shp) XTS1-10 turboshaft engines. The home-grown powerplant has been developed by prime contractor MHI, with help from Ishikawajima-Harima Heavy Industries and KHI. The latter is responsible for the full-authority digital engine-control, combustor, transmission and inlet-particle separator.

Relatively little information has been released by MHI or the JDA about the XTS1-10 or its selection for the OH-X. The engine is a derivative of MHI's MG5 turboshaft, first used to power the experimental RP-1 helicopter, as well as its planned new ten-seat MH2000 civil machine now under development.


Western engines, including the LHTEC T800 and Turbom,ca TM 333, were offered, but rejected, as were offers of technological collaboration to develop a new turboshaft powerplant. "The engine was the only one that was small and light enough with the right shaft horsepower. The technology had already been researched by the TRDI and so we began developing it in parallel with the OH-X," explains Udagawa.

The twin XTS1-10 turboshafts will give the 3.5t helicopter a maximum level design speed of 140kt (260km/h). The OH-X will have an operational radius of 200km (110nm), which can be extended by a further 1h with the addition of two external auxiliary fuel tanks.

The OH-X's avionics and sensor suite also appears to be almost entirely locally sourced. Both the pilot and rear-seat co-pilot/observer positions are fitted with twin Yokogawa Electric liquid-crystal multi-function displays, linked to a MIL-STD 1553B databus.

Other cockpit features include a Shimadzu head-up display, an automatic flight-control system, with stability augmentation and holding functions, and hands-on-collective-and-stick-configured controls.

KHI's Precision Machinery division has developed a gyro-stabilised sight system for the OH-X. Housed in a roof-mounted turret, the optical sight can be rotated 110û in azimuth and 40û in elevation. Its sensors include an NEC colour television and laser rangefinder and Fujitsu forward-looking infra-red imager.

There are no plans so far to fit the OH-X with either a laser designator or real-time data-transfer system. "Visual data cannot be transmitted. Instead, the pilot is in charge of disseminating information and providing command and control for other helicopters," says Sasaki.

The OH-X's two stub wings will be used primarily to carry short-range air-to-air missiles (AAMs) and additional fuel. A total of four Toshiba Type-91 infra-red AAMs can be accommodated in two twin launchers, mounted on outer hardpoints. The helicopter's inner hardpoints have been plumbed to take two 160litre auxiliary fuel tanks.

KHI rolled out the first OH-X prototype in March at its Gifu plant and is preparing for a maiden flight some time in August. The helicopter will undergo an initial flight-test programme, to validate its airworthiness and basic functionality. It will then be handed over to the TRDI in May 1997 for more comprehensive flight testing and evaluation.

Two static airframes have already been delivered to the TRDI's test centre at Gifu. Load tests were begun in February, followed in May by the start of dynamic tie-down tests of the OH-X's engine and rotor system. Individual helicopter components have been undergoing separate fatigue tests since December 1995.

A further three flight-test prototypes will follow, having their first flights before the end of the first quarter of 1997, with delivery to the TRDI shortly thereafter. The TRDI and JGSDF plan a combined flight-test programme, totalling about 1,000h, by April 2000.

Sasaki explains: "The first and second test helicopters will concentrate on flight performance and basic design features. The third and fourth prototypes will be fully equipped and will focus on the helicopter's practical features and how we can really use it operationally."

Completion of the flight-test programme will followed by delivery of the first production-series OH-X in fiscal year 2000. To meet this target, the JDA hopes to begin production in 1997. As part of its next fiscal-year budget request, the agency is asking for funds to order an initial four machines (Flight International, 19-25 June, P18).

A Government green light to begin the work hinges largely on the initial results of the OH-X flight-test programme. The JDA's budget request will be submitted to the finance ministry in August and is subject to cabinet and parliamentary review before passing into law at the end of March 1997.

Japan's five-year mid-term defence build-up plan for the period 1996-2000 is understood to call tentatively for a total of 15 helicopters to be built. The JGSDF's ultimate requirement is to replace all of the 185 OH-6Ds now in service. It is unclear, however, given spending constraints and cuts in the size of the JGSDF, whether the present scout helicopter will be replaced by the OH-X one-for-one.


The OH-X will be used for different missions by both the army-aviation and divisional-aviation branches of the JGSDF. The helicopter will provide command and control for AH-1S-equipped anti-tank units attached to each of Japan's five army groups. The remaining machines are to be allocated to 13 divisional squadrons and they will be employed in the observation and reconnaissance role.

Given Japan's '89 billion ($816 million) outlay to date on the programme, and the relatively small domestic market, keeping unit costs down is likely to prove problematic. While other manufacturers can fall back on foreign sales to help cover costs and boost production, Japan's post-war constitution bars the export of any weapons.

Japanese industry is therefore left with the choice of either trying to spin off OH-X systems in new applications, such as using the MG5 to power the MH2000 civil helicopter, or possibly developing further the existing tandem-seat military design.

Beyond replacing its OH-6D machines, the JGSDF's long-term attention is focused on finding an attack-helicopter successor to the AH-1S. No formal AH-X requirement has yet been drawn up, but it will almost certainly be near the top of the JDA's equipment wishlist for the next (2001-5) five-year plan, suggest local defence and industry sources (Flight International, 31 July-6 August).

For now, the JDA refuses to confirm officially the existence of the AH-X, claiming instead that it is just industry speculation. The OH-X design, however, does allow a margin for further growth, such as uprated engines.

"Technically, there is some room for development and, when there is a need or order for a function, then we will start developing it," says Udagawa, "but, at the moment, all the requirements are met by the OH-X."

Source: Flight International