As unmanned surveillance airships approach deployment in Afghanistan, attention is widening from their ability to stare at targets for days to weeks and rekindling decades-old interest in the ability of such vehicles to haul heavy loads over long distances.
But the blooming of opportunity for airships has come late in the day, and with the U.S.facing steep spending cuts it will be a race against time to prove that airships can be operated effectively and with significant savings in manpower costs over conventional unmanned aircraft. And while commercial interest in cargo airships has reawakened, the military has yet to embrace the idea.
Recent events have highlighted the lingering perils of operating airships. In August, World Surveillance Group's unmanned Argus One was damaged by strong gusts while being moved into its hangar at Yuma Proving Ground, Ariz., where it was being prepared for flight tests. Argus One is small expendable airship with a segmented envelope designed to make it easier to handle in winds.
A month earlier, the first flight byof the U.S. Army's HALE-D high-altitude long-endurance demonstrator ended early when a helium leak prevented the solar-powered surveillance airship from reaching its targeted 60,000-ft. altitude and the 240-ft.-long aircraft made a forced landing in Pennsylvania. The HALE-D is designed to stay aloft for 15 days.
The U.S. Air Force, meanwhile, has opted to transport its 370-ft.-long Blue Devil 2 surveillance airship to theater by sealift because self-deployment proved too tricky owing to unpredictable weather and the cumbersome process of gaining clearance to overfly foreign countries en route to Afghanistan. There are only a handful of ships capable of carrying the massive airship, and a hangar must be designed for its safe transit on the ship. This could delay deployment, slated for February, and will push up the program's cost to $152 million from $86 million.
The Pentagon has several irons in the fire when it comes to airships. In addition to the Air Force's Blue Devil 2, which is a traditional non-rigid airship, there is the Army's Long Endurance Multi-Intelligence Vehicle (LEMV), which is a hybrid airship using a combination of buoyant, aerodynamic and propulsive lift. The $517 million LEMV program calls for deployment of the multi-sensor surveillance aircraft to Afghanistan by year-end. There is also the much smaller Pelican program, aimed at demonstrating an advanced hybrid cargo airship.
Funded by the Office of the Secretary of Defense to the tune of around $50 million over five years, Pelican is a much scaled-down follow-on to the's (Darpa) Walrus program to demonstrate technology for a heavy-lift hybrid airship capable of carrying more than 500 tons over 12,000 nm. Darpa planned to build a 30-ton-payload demonstrator, but Walrus was canceled by a skeptical Congress.
Walrus contractors Aeros and Lockheed Martin Skunk Works continued work on the technology. Lockheed in March signing a commercial contract with Canada's Aviation Capital Enterprises (ACE) to build the SkyTug hybrid cargo airship. CEO Kirk Purdy says ACE is on track for delivery of its first 20-ton-payload vehicle in 2012, for flight test, followed by a second in late 2013 for certification and demonstration trials. The target market is the oil and gas sector and heavy-lift transport missions in inaccessible regions.
's partner on the LEMV program, U.K. airship developer Hybrid Air Vehicles (HAV) in August signed a similar deal with Canada's Discovery Air Innovations to develop a 50-ton-capacity cargo version of the surveillance hybrid. Aviation services company Discovery Air has signed to take up to 45 of the air vehicles, with the first slated to be delivered by early 2015.
Aeros, meanwhile, has continued to refine the rigid-structure and buoyancy-control technologies it proposed for Walrus through a series of small Darpa- and company-funded demonstrations. The Pelican program is bringing this work together in a flight vehicle to demonstrate the ability to takeoff and land vertically and hover at maximum payload without offboard ballast. Controlling buoyancy by compressing the helium lifting gas is key to this capability.
While a conventional airship like Blue Devil 2 is lighter than air throughout its envelope, adjusting buoyancy by using ballast or venting helium, a hybrid airship like LEMV is heavier than air throughout, with buoyancy providing 60-80% of the required lift and the rest coming from aerodynamics and vectored thrust. Aeros's advanced hybrid can transition between heavier-than-air (HTA) and lighter-than-air (LTA) flight by compressing and decompressing the onboard helium to control buoyancy.
For takeoff and landing, a conventional airship needs support from a ground crew to capture and release the LTA craft. An HTA hybrid is easier to handle on the ground, but at higher weights needs an airstrip to takeoff and land because of the requirement for forward speed to generate aerodynamic lift. To stay on the ground as cargo is unloaded, both types must take on ballast that has to be offloaded as cargo is added.
By compressing and storing the lifting gas in lightweight tanks, allowing more-dense air to fill the envelope, an advanced hybrid can stay heavier than air throughout unloading and loading without exchanging ballast. The vehicle can also hover by precisely controlling buoyancy, says Philip Hunt, vice president of Washington operations for Aeros. Key to this is the ability to compress the helium fast enough to use buoyancy as an altitude-control mechanism.
Another key aspect of the Aeros design is its rigid structure. Blue Devil 2 and LEMV both have non-rigid structures, relying on pressure differential to maintain the shape of the envelope—which in the case of a hybrid airship is critical to generating aerodynamic lift. In both types, a loss of pressure can lead to loss of structural integrity, most critically at the mounting points for engines, payload and flight controls.
The Pelican has a lightweight lattice-girder structure and rigid skin giving it an aerodynamic shape, covered in impermeable fabric to contain the helium. Engines and aerodynamic lifting and control surfaces are attached to this structure. Instead of a gondola hung from the envelope, a production version would have the payload bay inside the vehicle.
When the helium is compressed and stored in tanks, outside air flows in through valves to fill diaphragms inside the rounded “cheeks” of the airship. “We compress the helium and take on offboard air to increase the weight of the vehicle to compensate for the weight of the payload being unloaded,” Hunt says. “To take off, we allow helium back into the outer shell to displace air in the envelope.”
At larger sizes, where stresses in the envelopes of non-rigid airships require heavier fabrics, a rigid structure can be lighter and less expensive, says Hunt. He points out that the most modern airship flying, the 250-ft.-long Zeppelin NT, is semi-rigid, with a pressure-stabilized envelope enclosing a truss structure with hardpoints to which engines, empennage and gondola are attached.
Aeros separately proved the principles of both its lightweight structure and buoyancy control system in flight under Darpa contracts, but Hunt acknowledges these were not robust demos of the technologies. The Pelican program is focused on building a flight vehicle that pulls the two together and shows that buoyancy can be controlled well enough for an advanced hybrid airship to be viable.
“We want to demonstrate vertical-takeoff-and-landing in ambient conditions and show we can generate weight fast enough to have sufficient control authority to land and take off,” he says, adding “The system looks fully responsive.” The Pelican program began in fiscal 2008 and is funded through 2013. The rigid structure of the demonstrator is already taking shape in Aeros's hangar at Tustin, Calif., with a first flight planned for 2012.
A builder of small airships, Aeros would like to follow the demonstrator with a 60-ton-payload prototype. The demonstrator will lift just 2,000 lb., but Zachary Lemnios, assistant secretary of defense for research and engineering, whose organization is funding Pelican, says “We have a concept for a 1-million-lb. lifter.” This would use hydrogen as the lifting gas as it is slightly lighter and much cheaper than helium, but the safety questions with hydrogen remain to be answered.
While the commercial deals struck by HAV and Lockheed indicate there is a market for heavy-lift cargo airships, the Pentagon's near-term focus is on the airship's advantages as a persistent, “unblinking” platform for intelligence, surveillance and reconnaissance. The LEMV is designed to stay aloft at 22,000 ft. for 21 days carrying a 2,750-lb. multi-sensor payload. Like the Blue Devil 2, the LEMV will be optionally manned—flying with a pilot on board for testing and deployment and unmanned for surveillance missions.
Blue Devil 2, which is being integrated by prime contractor MAV 6 and based on an Polar airship built by TCOM, is intended to stay aloft for five days carrying a 2,500-lb. payload. The Air Force hopes to fly Darpa's-developed Autonomous Real-Time Ground Ubiquitous Surveillance Imaging System (Argus-IS), a giga-pixel wide-area electro-optical sensor capable of providing up to 65 separate “Predator-class” video feeds.
If Argus-IS is unavailable, the Air Force would use a system already developed to provide an electro-optical capability. The service also is planning to install infrared full-motion sensors and additionally has opted to put two separate Axsys Technologies gimbaled cameras on the airship capable of providing high-definition video feeds. The Pennant Race signals-intelligence collector, an upgraded version of a system that now flies on the Reaper UAV, will also be on the airship, according to Air Force sources.