By Graham Warwick at Farnborough
US industry leans toward solutions that can switch from manned to unmanned
A new word is entering the aerospace lexicon as the US Air Force analyses its long-range strike options - unmannable: an aircraft that could begin its life manned, then evolve over time to unmanned operation; or one that could switch between missions, flying unmanned when the persistence required or threat faced is beyond a manned aircraft.
Designing the aircraft to be unmannable - or optionally piloted, as it is sometimes described - could defuse the brewing debate over whether the USA's next bomber should be manned or unmanned. The concept of phasing in unmanned capability could also help achieve both the USAF's aggressive initial operational capability (IOC) target of 2018 and its stated goal of having 40% of its long-range strike (LRS) capability unmanned.
"A lot of the long-range strike missions are well within existing technology to be unmanned," says George Muellner, president of advanced systems for Boeing Integrated Defense Systems. Meeting a 2018 IOC means using existing technology, but industry does not see any technological advantage in delaying service entry to 2020, as has been suggested, although a target date 2025 or even 2035 could allow new supersonic or even hypersonic options to be considered.
Industry has been supplying data for a US Air Force analysis of alternatives (AoA) to be completed in March next year. This is looking at a range of options for new or upgraded weapons or platforms, including subsonic and supersonic, manned and unmanned. The outline requirements are for greater than 4,500kg (10,000lb) payload over a 3,700km (2,000nm) radius with next-generation stealth, but "we are waiting for the AoA to define the end game", says Muellner.
Companies are already positioning themselves based on their experience. Boeing believes the ability to convert range into persistence, so the aircraft can remain over the target area for extended periods, favours subsonic over supersonic designs. "You do not gain survivability until you get very fast," says Muellner. "The materials used for signature reduction get stressed above Mach 2, and you have to get much faster if you are going to rely only on speed to survive. A fast aircraft with range and persistence is much further out [than 2018]."
Lockheed Martin believes a subsonic design would be vulnerable, and favours a supersonic unmanned aircraft system (UAS). "We are looking at speed for the future," says Frank Capuccio, executive vice-president and general manager advanced development programmes. A subsonic "son of B-2" could provide persistence with moderate development risk, but might not be enough, he says, whereas a Mach 2.5 UAS with long endurance and next-generation low observability would be the most survivable. "LRS is well positioned for supersonic," he says, adding that Lockheed's concept combines aspects of the Mach 3 SR-71 and its quiet supersonic business jet design.
Supersonic capability
An FB-22 strike version of Lockheed's F-22 stealth fighter would be low risk for a 2018 IOC, and would offer a supersonic dash capability, but would have only medium range. "We like it from an industry perspective as it has the lowest NRE [non-recurring expense], but the issue is range," says Capuccio. Launching a long-range, high-speed strike weapon from the F-22 is another option being studied by Lockheed, which is developing the RATTLRS Mach 4 missile demonstrator for the US Navy.
Northrop Grumman may favour subsonic over supersonic, based on its B-2 experience, but is looking at both options. "The next-generation bomber could be unmanned for survivability and persistence. If we talk subsonic, then our X-47 UCAS [unmanned combat air system] could be scaled up to bomber size," says Gene Fraser, vice-president unmanned systems. "But supersonic unmanned is a serious option - sustained and dash - and we know supersonic stealth from the YF-23."
All the companies agree an unmanned bomber is feasible, even as early as 2018. "There are two classes of vehicle where the man could be removed: the bomber, because of the long time on station; and the supersonic UAS, which could then be very streamlined," says Capuccio. But technology may not be the issue. "Are we ready at a national level for an unmanned bomber?" asks Fraser. "An ICBM [intercontinental ballistic missile] is by definition, and a bomber can be recalled or retargeted."
Making the aircraft unmannable could "take away the angst of unmanned", says Fraser. There could be design penalties to pay, such as the fuselage size to accommodate the cockpit, or the conflict between the need for over-the-nose visibility when manned and sensor field-of-view when unmanned. But designing the aircraft to be manned initially and unmanned later could be a low-risk approach, believes Capuccio. "Spiral 1 could be manned, then you could slowly phase the man out."
Source: Flight International
