Sky-high Hydrogen Flyer
By Bill Moore
The air is thin and very, very cold at 65,000 feet. Only a handful of specialized military aircraft like the U2 and now-retired SR-71 "Blackbird" have regularly operated along the ragged edges of the stratosphere.
Now Monrovia, California-based AeroVironment hopes to someday deploy its Global Observer Unmanned Aerial Vehicle (UAV) in a host of high-flying, wide-ranging missions, both commercial, military and government funded. In the age of heightened national security concerns, as well as environmental ones, aerial platforms that fill the niche between conventional reconnaissance aircraft and satellites could be valuable assets in monitoring the health of the planet politically and ecologically.
EV World -- which acknowledges AeroVironment as one its "Platnium Sponsors" -- talked with Ted Wierzbanowski (pronounced "where's-bah-now-sky") , who oversees the company's growing UAV programs for the US Army and Navy, about the Global Observer project and the challenge of remaining aloft at such high altitudes for so long a period of time.
We first asked him to briefly recount the company's long history of record-breaking aircraft development starting with Dr. MacCready's -- the company chairman -- efforts to capture the Kremer Prizes for man-powered flight in the 1970's, which made the good doctor one of my personal heroes.
Out of those prize-winning triumphs came the predecessor of the Global Observer, a long-endurance UAV powered by early 1980's solar-electric technology, which simply couldn't deliver sufficient energy at the time to meet the objectives of the program. That aircraft was rolled into storage and the company moved on to electric cars, developing the Sunraycer and Santanna, the latter a prototype that eventually became the GM EV1, itself now a piece of automotive history and lore.
According to Wierzbanowski, photovoltaic cell and battery storage technology had progressed enough in the 1990's, that the company was able to convince NASA to fund a 10-year program dedicated to exploring remote sensing using the old solar plane that had been stored away for nearly a decade. With longer wingspan and more powerful solar cells and batteries, the Pathfinder was born, eventually soaring to altitudes of 70,000 feet. Pathfinder paved the way for Helios which flew unmanned on solar power alone to 97,000 feet last year before being destroyed in an accident off the coast of Hawaii.
But large UAVs are only a small part of AeroVironment's repertoire of self-guided, electric-powered reconnaissance aircraft.
"What folks probably don't realize is that we have a family of very small electric-powered aircraft that are being used by the military today that normally fly below 400-500 feet above the ground with electrical, optical infrared cameras on them. They are used by the frontline soldiers. They hand launch these. They're able to get video back to see what's over the next hill or behind the building; and they are finding them quite valuable in a lot of the areas of the world we're in right now".
AeroVironment now has two distinct, but interrelated business focuses: energy and flight. A small percentage of its business comes from building rapid chargers for commercial applications such as industrial forklifts. UAVs now constitute the largest segment of its business.
It's world-class expertise in energy efficiency and thinking "out-of-the-box" led to the development of the electric car, its solar and electric-powered aircraft and even a prototype electric generator nicknamed "M&M" that makes power from ocean waves.
"We have a lot of synergy between those two businesses", Wierzbanowski explained, adding that the company, which began experimenting with UAVs more than 20 years ago, made a strategic decision early on that it would focus its research on electrically-powered UAV's that operated below 500 feet and over 50,000 feet. None of its aircraft utilize fossil fuels.
The lessons learned on Pathfinder and Helios in terms of both super-light UAV engineering and remote sensing, in turn, is paving the way for the future development of the Global Observer that will be propelled by eight, highly-efficient electric motors powered by a liquid hydrogen fuel cell.
NASA's interest in this class of UAV's stems from its charter to not only explore the outer reaches of space, a mission they are best known for, but also to study the workings of the biosphere, itself. A slow, high-flying, non-polluting vehicle like the Pathfinder is an ideal platform for collecting samples for analysis of the lower reaches of the atmosphere up to 100,000 feet.
While the actual Global Observer has yet to be built, the prototype pictured above has flown two, hour-long, proof-of-concept flights to demonstrate the feasibility of powering a UAV using liquid hydrogen.
Unlike previous solar class UAVs that were flying wings with massive amounts of photovoltaic cells embedded along the top of the wing, the prototype Global Observer assumes a more conventional plane form with rudder and elevators mounted at the end of a slender boom-like tail. Wierzbanowkski explained that this is because of the differences in power sources. A slow-flying solar-only UAV has its mass largely distributed along the entire span of the wing.
"However, there are limitations to solar-powered airplanes", he noted. While they can generate more than enough electric power from sunlight to propel the aircraft, power the instrument payload, and recharge batteries for night-time operation, they are restricted to operating only in lower latitudes at or below 20 degrees latitude. The further north above 20 degrees one flies, the less sunlight that's available overhead to power the vehicle, and in the winter, the problem only compounds with shorter hours of daylight.
This limitation moved AeroVironment to look at the hydrogen fuel option, which in turn, meant a change in the plane form from a span-loaded design to a point-loaded design with a more conventional wing, fuselage and tail assembly. The Global Observer will house a large, 300-pound insulated storage tank capable of holding 1000 pounds of liquid hydrogen; it will be mounted in the center of the payload pod. The hydrogen is converted to electric energy by an onboard fuel cell which powers the eight 1kW-plus, ironless-core motors and the instrument payload, which can weigh up to 1000 pounds and draw up to 6kWhr of power.
"The liquid hydrogen is what's key to this (week-long) endurance", Wierzbanowski told me, noting that the prototype has a smaller tank and fuel cell than what's planned for the production vehicle. He also explained that the company is looking at both fuel cell and internal combustion engine options. In the latter case, hydrogen would power the IC engine, which would power a generator. It's not as elegant a solution as a fuel cell, but its likely to cost less and have as long, if not longer, operating life.
The company selected the target ceiling of 65,000 feet because it is at this level that atmospheric winds blow at the lowest speeds. Above and below this regime, wind speeds increase, making it harder to the vehicle to station-keep and maneuver.
Wiezrbanowski said that he and the company are confident that they can remain airborne for longer than a week, In fact, 7 days is the minimum duration they are planning. The operator also can drop the operational altitude down to 60,000 feet and extend its mission limit another two days.
Long before the events of 9/11 and the pressure to secure the nation's borders, infrastructure and citizenry against the threat of terrorism, AeroVironment was looking at commercial applications for its HALE (high-altitude, long-endurance) UAV program, which Wierzbanowski also refers to as a "stratospheric satellite" or "twelve mile-high" tower.
"One of the initial applications that we've been looking at was the use of the airplane for broadband Internet connection…where you would park an airplane like this over an urban or rural area and there would be access to a fiber optic system". As envisioned, a high-speed fiber optic hub would beam its data streams up to the Global Observer, which would relay them down to commercial customers over a very wide area, obviating the need for laying cable.
Along a similar line, the vehicle could be deployed as a communications relay replacing cell phone towers. AeroVironment demonstrated this capability several years ago with an advanced Pathfinder aircraft in cooperation with the Japanese, which included third generation cellular telephone that included video, as well as broadband Internet.
"We actually used the airplane as a high definition tv rebroadcast antenna", he said, pointing out that in Tokyo it requires 50,000 watts of power to broadcast a high quality HD signal. Using Pathfinder at 65,000 feet reduced the wattage required to just one watt without loss of signal quality.
Because a Global Observer aircraft can be redeployed, unlike fixed antenna, it can also respond to emergency situations where restoring communications is often critical to saving life and property. Because of its high operating altitude and slow speed, the aircraft would loiter above the eye of a hurricane and slowly follow its progress, relating data in real-time to forecasters. Forest fires can be more precisely monitored with fire fighters directed to hotspots and warned to dangerous wildfires sneaking up behind them.
"This is a paradigm shift", he said comparing it to the advent of Sputnik, the first man-made satellite that surprised the World in the late ‘50's and started the Space Race. "Folks were trying to figure out what you were going to do with a satellite, and folks are starting to look at this in the same way… There are a lot of applications and I think we've just started to scratch the surface".
Autonomous Control and Redundancy
The Global Observer will have largely autonomous operational capability with communications instructions relayed directly either from the ground or relayed via satellite when the vehicle is over the horizon.
"Because of these long missions, you wouldn't want to have somebody flying this thing".
Wierzbanowski told EV World that the Global Observer has numerous redundant systems built into it, including enough power to fly the mission on reduced power or with multiple engine failures.
To date, the prototype has flow twice at low altitudes for about an hour on each mission.
"What we were really trying to do in those flights with the airplane was… gather some more aerodynamic information and aero-elastic information on the airplane. But also people have asked, can you really fly an airplane on liquid hydrogen… can you do it safely? So, one of the main focuses was to prove and show that liquid hydrogen is a viable fuel for airplanes"…
Beyond the actual flights, AeroVironment spent a lot of time developing fueling and de-fueling procedures in the event of an aborted take-off, creating checklists and getting as comfortable with the day-to-day operation of a hydrogen aircraft, as possible.
The Global Observer prototype isn't the first aircraft to fly on hydrogen, Wierzbanowski recounted. The US flew a B57 bomber with one engine using hydrogen in the 1950's and the Russians flew an experimental jetliner in the 1980s on hydrogen.
Big Brother Concerns?
I asked Wierzbanowski if he had any concerns about their technology being used to facilitate a "Big Brother" society where privacy is threatened by silent spy aircraft loitering high above the our cities.
He responded that he wasn't worried, that the benefits will far outweigh any potential abuses.
"Think about instant infrastructure in a third world country," he said, "where one of these airplanes in a matter of days we could launch an aircraft over an area and you could get instant cellphone, instant Internet, instant disaster response.
"We think there will be good things for mankind out of this, just like satellites".
He also thinks that this will be a big business for AeroVironment.
"We're looking at different ways of operating that business, whether it's selling airplanes, whether it's leasing airplanes, whether it's actually operating them… That's why we're doing this. We're spending our own resources on developing this capability. In addition to the work we did with NASA, we've invested quite a bit of money in this because we thinks that's the case".
Our interview with Mr. Wierzbanowski is some 38 minutes in length and write-up constitutes a summation of the main points of our discussion. We suggest you listen to the entire interview by playing the MP3 file associated with this article.