Apus Aircraft Design Stores Hydrogen in Wing Spar Tanks

The Apus i-2 uses hydrogen to power fuel cells, which deliver electricity to two electric motors. Wing spars double as hydrogen fuel tanks. (Photo: Matt Thurber/AIN)

On display last week at Aero Friedrichshafen was a mockup of Apus Group’s zero-emission hydrogen-powered twin-motor i-2 airplane, equipped to highlight the fuel cell and power controller installation in the forward fuselage.

The designer of the i-2 opted for an efficient “structurally integrated hydrogen storage system” using tubular wing spars as tanks. Each wing will have four spars, extending for about the first two-thirds of each wing’s span. According to Apus CEO Phillip Scheffel, the round carbon fiber spars can handle pressure up to 300 bars, and the aerodynamic load is only about 30 percent of the load imposed by the pressurized hydrogen. Each spar weighs 80 to 85 kg.

When full, the eight spar tanks can hold 23 kg of hydrogen. Together, the i-2’s two 135 kW electric motors burn five kilograms per hour, giving the airplane a range of 500 nm and cruise speed of 160 knots. Each propulsion system includes its own PowerCell fuel cell, power controller, and motor operating as identical power lanes. “These lanes are separated in normal operational mode and may become interconnected by a switchable crossfeed to balance the load,” Apus said.

Each motor nacelle will also carry a 40-kW booster battery to supplement the fuel cell during power-intensive operations such as takeoff.

The airplane will accommodate four occupants—one pilot and three passengers—and when fully fueled has a payload of 400 kg. Mtow is 2,200 kg. At an assumed hydrogen price of €5/kg, Apus estimates that operating costs will be 80 percent of those of a conventional Cirrus SR22 piston single.

Avionics will be a Garmin G1000 suite. Flight controls are conventional cables for ailerons and rods for elevators, actuated by two side yokes on the outboard sides of the cockpit. Landing gear is retractable and will be electro-hydraulically actuated.

Apus is now testing the power train and hydrogen tanks and plans to roll out the first i-2 early next year. First flight should take place at the end of 2023, Scheffel said.

Along with the i-2 program, Apus is also developing a larger multi-mission model, the i-5, that features the same tubular spar hydrogen storage system as the i-2. This airplane will have four 150 kW Rolls-Royce motors mounted on the leading edge of the wing.

With mtow of 4,800 kg, the i-5’s payload will be 1,770 kg. In passenger configuration, it can carry up to 14 people. Cruise speed is the same 160 knots as the i-2 and range will be 800 nm. Operating cost is projected as 40 percent less than a Cessna 208B Grand Caravan turboprop single.

Source: by Matt Thurber – ainonline.com

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