Judging solely from what Boeing's Phantom Works development organization has in the pipeline, the company has lots to look forward to. Now it just has to prove it can turn some of these technology demonstrators into cash flow.

Doing so will be no easy task given increasingly tight military budgets, although flying the hypersonic X-51 at Mach 6, or the Phantom Eye unmanned aircraft for 10 days, is no trivial assignment either. What is clear is that answers to some of the technical questions will start emerging in the coming months, whereas validating the business case for some of these endeavors may be years off.

The self-funded Phantom Eye unmanned aircraft effort may provide the earliest test case. Boeing is trying to win a position in a heavily contested market against rivals that already have government funding (such as Northrop Grumman's Global Hawk), in the high-altitude endurance marketplace. Nevertheless, Boeing sees a window as the U.S. Air Force looks to save money by putting the Global Hawk Block 30 fleet into storage and canceling the Blue Devil 2 blimp program. The financial constraints “we see as a benefit,” says James Dodd, vice president of Advanced Boeing Military Aircraft at the Phantom Works. “Phantom Eye's cost per flight hour is a lot less than particularly Global Hawk,” he asserts.

But the company still needs to validate that Phantom Eye can deliver on its promises. Boeing hopes to return the liquid hydrogen-fueled Phantom Eye unmanned aircraft demonstrator to flight this year after it suffered damage on landing following its June 1 first flight.

Investigations into what happened are almost complete, but the problem appears linked to the design of the landing gear, rather than a material issue, says Boeing program manager Andrew Mallow. Most of the damage to the Phantom Eye's wing and nose section appears relatively easy to fix, while some strengthening of parts of the structure may be needed for a more robust nose landing gear.

Once the assessment is finalized, a new program plan will be set, Mallow says, noting that he'd like to see the air vehicle fly again this year. Boeing has brought in some F/A-18 landing gear experts to help with the redesign. The skid main landing gear proved itself in the first flight, although minor changes may be made.

The overall program impact is relatively minor, Mallow suggests, noting that Boeing was considering an aircraft modification in any case after first flight to make some electrical changes and an oil pump change.

Phantom Eye flew for 28 min. at Edwards AFB and reached about 4,000 ft. The near-term testing plan would be to reach around 10,000 ft. and then increase altitude to 65,000 ft. in 10,000-ft. increments. The vehicle is designed to stay aloft four days, but that may never be tested mainly because of the logistics of personnel management for such an effort. An operational version would be designed to stay airborne up to 10 days depending on the payload size. Carrying around 2,500 lb. of payload would permit endurance of around seven days. The vehicle would have a 250-ft. wingspan. The company is also talking to potential international customers.

Boeing's long-running quest to demonstrate a viable hypersonic vehicle is also back on track after a year-long investigation into the premature end to the second flight of the X-51A scramjet-powered demonstrator in June 2011. The third missile-like vehicle is being prepared at Boeing's Palmdale, Calif., facility and will be transferred to nearby Edwards AFB for the flight, which will take place over the Pacific test range after launch from a B-52H carrier aircraft. “The vehicle is nearly ready for shipping,” says Boeing X-51A program manager Joe Vogel.

Boeing, along with scramjet maker Pratt & Whitney, and the Air Force Research Laboratory (AFRL), “is waiting on approvals” to start preparations for the test which will take place by year-end, he adds. The vehicle includes a series of hardware and software changes to counter issues that are thought to have interrupted the last flight after 9.5 sec. of powered flight at around Mach 5.

The X-51A is designed to demonstrate technologies for sustained air-breathing hypersonic flight up to Mach 6.5, and provide the springboard for propulsion systems for a new generation of high-speed missiles, strike and reconnaissance aircraft and eventually access to space. For each test, the X-51A is dropped from the B-52H at around 50,000 ft. and accelerated by a modified Atacms missile booster to Mach 4.5 where the scramjet is designed to take over.

The first flight on May 25, 2010, reached Mach 4.88, against a target speed of Mach 6. Although failing to hit Mach 5, the test was considered a success as 143 sec. of the vehicle's 210 sec. of total powered flight time was under scramjet power, making the flight 11 times longer than any previous air-breathing flight with a scramjet. The second flight, on June 13, 2011, ended more abruptly when the X-51A's engine failed to transition from the ethylene that starts the scramjet to the JP7 fuel that is used for sustained flight.

During the botched switch to the hydrocarbon fuel the vehicle experienced an inlet un-start, effectively blocking flow through the engine and shutting it down. An “un-start” occurs when the leading shock at the engine inlet moves too far out in front of the inlet face. At the time AFRL said the hypersonic vehicle attempted to restart and oriented itself to optimize engine start conditions, but was unsuccessful.

Despite the truncated flight, Vogel says “it is a purely science and technology demonstration program. I consider it successful, we flew it all the way down to the sea,” he adds, referring to the deliberate termination of the flight in the ocean.

For the third flight, “we've made it more robust and added software modifications to better refine how the vehicle operates,” Vogel says. It also incorporates better sealing between the interfaces in the engine flow path which are thought to have suffered “burn-through,” allowing hot gases to fatally penetrate the vehicle's interior on the first flight two years ago. In addition, the development team has conducted several laboratory tests of the fuel-air combinations “to make sure we understand the mixing,” he adds.

Although there are currently no funds allocated for the testing of the fourth and final X-51A, studies also continue into options for a semi-tactical demonstration of what the vehicle could accomplish beyond simply accelerating. The options—which likely depend on achieving a 240-sec. flight-test time on the engine, and Mach 5 or 6 during flight three—include demonstrating maximum range, or conducting a waypoint navigation demonstration.

Flight trials also are being prepared for the latest iteration of the X-48 blended-wing body (BWB) remotely piloted research aircraft. Phantom Works plans to start a six-month flight- test program in July at NASA's Dryden Flight Research Center.

The X-48C is a rebuilt twin-engined derivative of the three-engine X-48B tested between 2007 and 2011 in 92 flights. In this new configuration, the engines are mounted further forward from the trailing edge and shielded between vertical tails which are moved inboard and replace wingtip-mounted tails. The low-noise design is “a configuration of the BWB that represents a vehicle we are actually studying,” says Boeing X-48B/C project manager Mike Kisska.

The sub-scale aircraft is being studied as a potential future military and commercial airlifter/tanker, as well as for possible strike and reconnaissance roles. The design, which is also under evaluation by Boeing as part of NASA's Environmentally Responsible Aviation (ERA) program, has shown the potential for up to 50% lower fuel burn and 40 dB less noise than a similarly sized tube-and-wing aircraft.

Initial testing of the first-generation X-48B explored the low-speed stability and control characteristics of its unusual design over 92 flights. Boeing was particularly keen to demonstrate that the BWB design was viable and safe, and not prone to stalls at high angles of attack. An advanced flight- control system was tested to its limits during the early phases with the X-48B and showed it was possible to maintain control at both high angles of attack and high sideslip angles.

The upcoming testing with the new configuration “gives us the opportunity for back-to-back testing,” says Kisska, who adds that Boeing “is looking to start flying toward the middle or late next month [July].” The test effort will run to December and include around 25 flights.

Boeing originally hoped to develop purpose-designed miniature turbofans to power the X-48C but was forced to adopt turbojets developed by Advanced Microturbo (AMT) of Geldrop, Netherlands, when this proved problematic. The AMT turbojets replace the X-48B's original trio of JetCat P200s, and are enclosed in the larger nacelle ducts representative of the higher-bypass engines which were to have powered the X-48C.

The company has therefore shelved plans to validate the noise characteristics of the low-noise configuration and Kisska confirms that the use of the low- bypass AMTs rules out any acoustic evaluation. Longer term, Boeing hopes to use the X-48C as a stepping stone to tests of a scaled BWB demonstrator vehicle “large enough for a pilot to fly.”

The advanced technology unit is trying to secure other flight-test work, with its eyes on a NASA downselect in the Reusable Booster System program. The agency is expected to name one company to build a pathfinder demonstrator to validate the boost technology around 2015.

Boeing also recently submitted a proposal for NASA's solar-electric propulsion demonstration program and, next year, expects to compete for the next phase of the cryogenic propellant storage and transfer program NASA is running, notes Steve Johnston, director for advanced space exploration at Phantom Works.