SAN DIEGO—Google co-founder Sergey Brin’s LTA Research is preparing to begin outdoor flight tests of its Pathfinder 1 large rigid airship after getting the 120-m-long (393-ft.) technology demonstrator airborne inside Hangar 2 at Moffett Field in Mountain View, California.
LTA plans initial flights of the electric-powered airship at Moffett Field and in the San Francisco Bay Area before relocating the Pathfinder 1 to the former Goodyear Airdock airship hangar in Akron, Ohio, which the company has acquired as its future manufacturing location.
The 2019 decision to relocate operations from Hangar 2 at Moffett Field to the Airdock in Akron means the Pathfinder 1 has to be upgraded from battery-electric to hybrid-electric propulsion to extend its range, LTA CEO Alan Weston told the American Institute of Aeronautics and Astronautics’ Aviation forum here on June 13.
As initially flown, the piloted Pathfinder 1 has two battery packs powering 14 electric propulsion units, four along each side of the envelope and four in a cruciform arrangement on the tail. Using electric engines from the Pipistrel Alpha Electro light aircraft, the pusher-propeller units can vector thrust 180 deg. for vertical takeoff and flight control.
LTA is working with VerdeGo Aero and Pathfinder development partner Zeppelin to develop the hybrid-electric power system. The airship will be equipped with two VerdeGo 150-kW generator sets based on diesel-cycle aeroengines and fitted with five tanks for Jet A fuel. Along with the 24 batteries, the system will provide redundancy in power, Weston said.
Cutting the time required to manufacture large rigid airships is one of LTA’s objectives. The Pathfinder’s structure uses deep self-supporting mainframes made from 288 carbon-fiber tubes connected by 96 welded-titanium hub joints.
All 13 circular mainframes were assembled on the same universal jig, each taking a day, he said. The frames were then mounted in roller cradles that allowed them to rotate, enabling 30 people working at ground level to connect the frames together using more tubes and joints.
Helium lift gas is contained in 13 cells made from ripstop nylon coated with urethane. A light detection and ranging (LIDAR) system senses the helium volume in the gas cells for balance and performance. Skins made from laminated Tedlar were attached during the final rotation of the structure in the cradles.
The Pathfinder 1 is the first passenger-carrying, electric-powered airship, Weston said. The gondola and landing gear are from the Zeppelin NT. The two-pilot crew have joysticks for fly-by-wire flight control of the airship using the vectoring propulsion units and rudders on the cruciform tails.
The airship was designed for a cruise speed of 70 kt., with a safety factor of 1.5, but LTA has reduced this to 60 kt. to increase the safety margin. There are no certification regulations for rigid airships, he says, so the company is working with the FAA and airship community to develop guidelines.
LTA is developing a hydrogen fuel cell propulsion system for the Pathfinder 1. The company is taking delivery of fuel cells from Sweden’s PowerCell and plans to fly this year first with gaseous hydrogen storage and later with a liquid hydrogen tank, Weston said.
The company is also looking at a hydrogen-fueled turbogenerator. LTA has also looked at using hydrogen as a lift gas and at putting a hydrogen bag inside a helium bag as a potential route to certification. “Using hydrogen as an energy source will be the first step,” Weston said.
LTA plans to build a bigger rigid airship, up to 180 m long, as its next vehicle and has already demonstrated it can assemble a bigger mainframe using its universal jig. This would be large enough to carry a flying hospital for disaster relief and other humanitarian missions.
