The title of this article in print is "Tripling Thrust"
Maximum thrust exceeds 33,000 lb.
Compressor and turbine stage counts match the F119’s
Inlet diameter will be about 1 m
The airframe for Japan’s proposed indigenous fighter is for now only a concept, but the engine is turning into actual hardware. Government defense engineers are this month beginning testing the core of the advanced turbofan for the proposed 2030s fighter.
Lockheed Martin, meanwhile, has responded to Tokyo’s request for information on alternatives for its Future Fighter. The company says it has offered no specific type, though the F-35 Lightning, already on order for the Japanese Air Self-Defense Force, must be a prospective candidate, probably in modified form.
The indigenous fighter would be much bigger than the F-35, with a twin engine installation. The turbofan is the XF9-1, says the defense ministry’s Acquisition, Technology and Logistics Agency (ATLA), naming the engine for the first time. Maximum thrust with afterburning, previously stated as 15 metric tons (33,000 lb.), is now said to be above that level, but the exact figure has not been disclosed. Maximum dry thrust will be more than 11 metric tons.
Considering how few countries have the technology to build advanced and powerful aeroengines, this is a notably ambitious program. Japan has previously developed no combat aircraft engine bigger than the XF5-1 demonstrator, which generates less than a third of the XF9-1’s thrust.
Japan’s aerospace propulsion specialist, IHI Corp., is the main contractor for the engine program and the XF5-1. IHI built the core and performed functional testing on it before delivery to ATLA on June 28. “Testing at the ATLA will begin in July to verify its performance,” says the agency. A full demonstrator engine is to be completed by the end of June 2018, it adds, confirming and refining a schedule published in 2015.
The agency’s predecessor, the Technical Research and Development Institute, said in 2010 that it wanted to pursue this program as part of a technology-acquisition effort for a possible indigenous combat aircraft, what is now an option for the Future Fighter program that would replace the Mitsubishi Heavy Industries (MHI) F-2 in the 2030s. The airframe design has been studied extensively but will not be built unless and until the government goes ahead with full-scale development of the fighter.
The XF9-1 demonstrator is due to be complete by the end of June 2018. Credit: Japanese Defense Ministry
IHI says it was contracted in 2010 to study components for the engine and in 2013 to build the core, which comprises the high-pressure compressor, combustor and high-pressure turbine. The core was preceded by a compressor and combustor, each tested independently. The complete demonstrator XF9-1 will be built under a 2015 contract.
It will have a diameter at the inlet of about 1 m (39 in.), compared with the 1.2-m maximum diameter of the General Electric F110. A drawing of the XF9-1 suggests that the case downstream of the inlet is only a little wider than the inlet, if at all, though accessories will add to width and depth, as usual. The length of the XF9-1 will be about 4.8 m. The core is about 1.5 m long. The quoted thrust levels are for the static, sea level condition.
If published material is taken at face value, the design has lost a previously intended feature, three rows of fixed and variable inlet guide vanes that would have acted together as a radar blocker, impeding radio-frequency energy on its way to and from the compressor. A 2011 illustration showed that feature, but more recent pictures, including the latest, depict a conventional single row of inlet guide vanes. The usual type of radar blocker, which Japan has worked on, is not part of the engine but rather is installed in the inlet duct upstream from it.
Other key features from the early design of the engine remain: a three-stage low-pressure compressor, six stages in the high-pressure compressor and single-stage high- and low-pressure turbines. Those features, and the counter-rotation of the low- and high-pressure spools, match the configuration of the Pratt & Whitney F119 of the Lockheed Martin F-22.
A 3D vectoring exhaust nozzle, directing thrust up or down as well as to one side or the other, is planned.
Average temperature at the turbine inlet will be 1,800C (3,300F), ATLA says, repeating an earlier figure. At least early in development, in the 1980s, the Pratt & Whitney F119 had a temperature at the combustor exit, just upstream from the high-pressure turbine, of about 1,600C. The same company’s F135 engine, fitted to the Lockheed Martin F-35, operates at about 2,000C.
Japan is due to decide between the indigenous fighter and the alternatives in fiscal 2018. Since the government will presumably first want to see the results of testing of the complete demonstrator engine, a decision late in the fiscal year is likely.
Lockheed Martin has proposed an improved version of the F-35, says the Nikkei, a reliable newspaper. But the company says it has not gone as far as suggesting any particular model. It submitted a draft response to a ministry request for information at the end of June “which did not provide any specific offering of aircraft type,” a spokesman for Lockheed Martin says. “The Japanese ministry of defense continues to define their requirements for the F-2 replacement and discussions between U.S. and Japanese government offices are ongoing.”
Nonetheless, an upgraded F-35 is an obvious possibility for Future Fighter. The manufacturer would be keen for Japan to pay for improvements that would support extended production, while commonality with Japan’s F-35As would cut the country’s operating costs. Most importantly, starting with the current design should greatly reduce the expense of development.
Indeed, the Nikkei says that adapting an existing design is the cheapest of three options for the Future Fighter, the others being developing an aircraft independently and doing so with another country. It cites no sources and notably fails to mention an even cheaper possibility that the government has been considering: importation of an unmodified fighter type.
MHI is assembling most of the 42 F-35As that Japan is buying. It could be expected to undertake any necessary development, fabrication and assembly of the airframe for an updated, specifically Japanese version, which would presumably be called the F-35J.
The Lightning in its current form is rather distant from the ideal of Japanese defense ministry engineers for a 2030s fighter. Their concept for an all-new aircraft includes internal carriage of six long-range air-to-air missiles, such as MBDA Meteors, and two of short range. Looking for great range and endurance, they have produced concept designs for a fighter larger than the Lockheed Martin F-22 Raptor and much larger than the F-35.
Britain is integrating the Meteor on the F-35, but the U.S. fighter will carry no more than four such weapons internally, and then with no room for short-range air-to-air missiles. Lockheed Martin could conceivably improve the F-35’s range and endurance with external tanks, perhaps conformal and at some cost to stealth. It could also fit the lightest Lightning version, the F-35A, with the bigger and more voluminous wing of the F-35C, the variant designed for catapult launch and arrested recovery at sea.
Japanese avionics would also be possible for an F-35J. Israel will at least load its own software on its version, the F-35I.
In June 2016, the Japanese defense ministry sought information from aircraft manufacturers about three possibilities for the fighter program: creating a new type, modifying an existing one or importing.
The possibility of international joint development has since emerged as a variation on the first option. Britain and Japan agreed in March to look at the possibility of jointly creating a fighter for the 2030s; BAE Systems would be the obvious partner for MHI, while Rolls-Royce would work with IHI. Sweden’s ambassador to Tokyo says Japan should consider Saab, too.
The F-2 was a modification of an existing type, the Lockheed Martin F-16. The U.S. company supported the development effort.