How cool is this? A high-altitude spyplane that can stay airborne for four days, driven by a liquid hydrogen power system, was unveiled last Monday at the Boeing Phantom Works in St. Louis, Missouri. Darryl Davis, the president of this advanced technology development shop, is here at the Farnborough show to describe rapid progress with the Phantom Eye program. A scale model is in the Boeing Pavilion here this week.
Davis will likely also report here the first engine runs and taxi trials of the Phantom Ray, an unmanned combat air vehicle (UCAV) technology demonstrator that Boeing has salvaged from the Pentagon’s J-UCAS (joint unmanned combat air system) program.
The Phantom Eye is designed to fly at 65,000 feet on the power of two 2.3-liter truck engines, modified to run on LH2 fuel. The dumpy-looking fuselage design is driven by the need to accommodate two eight-foot diameter tanks in line, each holding 1,000 pounds of liquid hydrogen. Between these two storage tanks is placed a large accumulator tank into which the LH2 flows in a gaseous state after boil-off. From there it is fed to the two turbo-charged engines, mounted on a high wing with a 150-foot span. They drive eight-foot diameter, four-bladed propellers.
Payloads of up to 450 pounds can be carried in the Phantom Eye’s nose and on external mountings. The empty weight is 7,500 pounds.
“This air vehicle could be a platform for a variety of missions, ranging from military intelligence, surveillance and reconnaissance [ISR] through communications relay to border patrol,” said Davis. “For a small country, it could be an alternative to expensive satellites.” He explained that the version that is scheduled to fly early next year is only a 60-percent scale demonstrator. The ultimate goal of the Phantom Works is to produce a UAV that can fly a 2,000-pound payload for up to seven days or a 1,000-pound payload for 10 days.
“We aim to beat the Condor!” he added. Enthusiasts for high-altitude long-endurance (HALE) vehicles will remember the Condor, a 200-foot wingspan all-composite UAV that Boeing designed in the 1980s. It claimed a world record 67,028-foot altitude for a piston-engine-powered machine in February 1989, and stayed airborne for 58 hours 11 minutes the following November.
Davis is tapping some of that old expertise with the Phantom Eye. And he has an experienced partner: Aurora Flight Sciences has built the wing, which like the composite structure for the fuselage is cured at room temperature without recourse to an autoclave.
Like the Condor, the Phantom Eye will take off from a dolly and land on a skid to save the weight of an undercarriage. HALE aficionados may recall that the U-2 spyplane was designed with a similar arrangement–until Kelly Johnson of the Lockheed Skunk Works was persuaded otherwise by the U.S. Air Force.
The very name of the Phantom Works suggests an outfit that embraces similar blue-sky aeronautical thinking. Indeed, the Boeing division is engaged in
a wide variety of leading-edge projects (see box above right). Davis and his colleagues are presumably also hard at work in the classified domain.
The Phantom Ray seems to occupy a space in the defense sector that is partly a classified “black” program and partly unclassified. Davis confirmed to AIN last month that this low-observable UCAV design is the same X-45C vehicle that Boeing nearly completed for the J-UCAS program, which was mysteriously cancelled in early 2006.
Funding from the U.S. Navy subsequently allowed Northrop Grumman to proceed with its J-UCAS contender–the carrier-capable X-47B. Since then, Lockheed Martin has emerged as a black-world provider of at least one stealthy UAV to the U.S. Air Force, in the shape of the RQ-170, also known as the Desert Prowler. The RQ-170 is yet to be fully revealed, but was deployed in secret to Afghanistan last year.
Meanwhile, Boeing–the company that pioneered the development of UCAVs for the U.S. Air Force in the original X-45A program–was seemingly left out in the cold. Davis said that the Phantom Ray is being completed and test-flown entirely with Boeing’s own money. “At some point, the [U.S. military] services are going to require it,” he added.
The Phantom Ray was unveiled last May and is due to fly next December. It is 36 feet long with a wingspan of 50 feet, and is powered by a General Electric F404-GE-102D engine. A full-scale model of this UCAV is on display here at Farnborough. It has a strike radius of 1,200 nm with a payload of 4,500 pounds, such as two internally carried JDAM bombs.
According to Davis, the Phantom Ray could serve as a testbed for demonstrating autonomous aerial boom-and-receptacle refueling. Potential missions could include ISR, suppression of enemy air defenses and electronic attack.
The Phantom Works is developing an “open-mission management system” that could work with either the Phantom Eye or the Phantom Ray, or both. Boeing first started this work as a part of J-UCAS, where it was known as the common operating system. It has an open, service-oriented architecture; uses a high-order language; has nonproprietary interfaces; and is NATO STANAG-compliant, according to Davis.
This Boeing system is PC- and Linux-based, and is designed so that a single operator can control multiple, different types of UAVs. It has already been tested by flying three Scan Eagles. “We believe that the DOD [U.S. Department of Defense] will one day have a competition for UAV control stations,” Davis said.
Despite recent cutbacks in U.S. government budgets for science and technology research, the Phantom Works is apparently still advancing along multiple paths.
“Within Boeing, we’re not throttling back on research. It’s the future,” declared
Liquid Hydrogen as a Propulsion Fuel
It is just over 50 years since a NASA scientist, John L. Sloop, published his seminal work with the title, Liquid Hydrogen as a Propulsion Fuel. Writing at the dawn of the space age, Sloop’s book mostly covered the history and prospects of LH2 as a rocket fuel. But he also described a top-secret program called Suntan, in which the Lockheed Skunk Works together with Pratt & Whitney tried to develop a supersonic, hydrogen-powered jet successor to the high-flying U-2 spyplane. After two years, even the redoubtable Kelly Johnson and his team had to give up. Elsewhere, aeronautical engineers in Germany and Russia have periodically been funded to explore the feasibility of liquid hydrogen.
The work has foundered mostly because of volume problems: for equal combustion energy, LH2 requires more than four times the tank capacity of kerosene (although it weighs 70 percent less). Technical issues have included how to develop efficient evaporators, pumps and engine controls. Then there are the logistics problems of storing and transporting LH2. Against all that, liquid hydrogen is three times more efficient than jet fuel.
Now the hunt for alternatives to fossil fuels has been renewed. And according to Phantom Works boss Darryl Davis, Boeing has developed “a breakthrough liquid-hydrogen propulsion system.” The process of raising the fuel to near-room temperature has been re-thought. “We don’t require a compressor or fuel pump,” explained Bill Norby, manager of the team that is integrating the engines to the Phantom Eye. “We use the tanks, a set of cryogenic valves, a couple of heat exchangers, and relief valves,” he added. Norby also noted that because all the fuel is stored in the two big fuselage tanks, the wing design was much simpler.
The two 150-hp, four-cylinder engines have already been tested at 65,000 feet in an altitude chamber for nearly 100 hours.