By Dan Gettinger, VFS Managing Editor Vertiflite, Sept/Oct 2022
Munich-based startup SilentWings is pioneering a novel concept for a vertical takeoff and landing (VTOL) drone that combines a hydrogen fuel cell and a unique tail-tilting design. The objective, said CEO Dr. Stefan Mändl in an interview with Vertiflite, is to produce an aircraft that relies entirely on electric power while avoiding some of the pitfalls of lithium batteries.
Founded at the end 2018 by Mändl and supported by TQ Systems, a global electronics firm also headquartered near Munich, Germany, SilentWings is currently finalizing the development of the SilentOne, its flagship hydrogen-electric VTOL uncrewed aircraft system (UAS). It aims to develop a production-ready serial drone in 2023 and launch sales of the aircraft the following year. TQ Systems continues to provide technical expertise and financial support to the company.
The SilentOne features a short fuselage and mid-mounted, tapered wings, as well as a twin-boom tail with a horizontal stabilizer. The aircraft has a 35-kg (77-lb) maximum takeoff weight (MTOW) and a 10-kg (22-lb) payload capacity. Though the SilentOne’s performance may vary depending on the mission package, it can fly as far as 700 km (435 miles) and has an endurance up to six hours.
The demonstrator to date has flown exclusively under battery-electric power while off-the-shelf fuel cell systems are being evaluated. In parallel, the aerodynamic configuration has been significantly refined.
Power is provided in the form of two wing-mounted propellers and one propeller in the tractor configuration. During cruise, the SilentOne relies on hydrogen fuel cells to provide power to the electric engines and electronics, a technology which the company says contributes to the aircraft’s capacity for long-range operations.
Although integrating the fuel cells can prove challenging, SilentWings prefers hydrogen for its high power and low weight when compared to lithium batteries. However, like all VTOL hydrogen aircraft, the SilentOne does rely on conventional lithium batteries for high-power VTOL phase.
Another novel aspect of the SilentWings design is its method for transitioning between vertical take-off and landing and horizontal flight. Like a standard tailsitter aircraft, the SilentOne does not tilt the wings or propellers after take-off. Rather, the aircraft sits on the ground with its twin-boom tail in a position perpendicular to the fuselage. After take-off, the tailplane is actuated to 90 degrees of the fuselage for forward flight.
SilentWings submitted a patent for this design in 2018 and says it yields several significant advantages to the aircraft by improving the efficiency of cruise flight and by contributing to the low weight of the aircraft, creating opportunities for additional payload.
In developing the SilentOne, the company has prioritized a low vertical integration approach, preferring to rely on third-party suppliers for elements such as the safety parachute and flight controller. In terms of the payload, the aircraft is relatively agnostic. “We see ourselves as specialists in the flying platform,” said Mändl. “The customer can mount any camera they want to as long as the maximum payload is not exceeded.”
The company sees a large market potential in providing long-range inspection services for large infrastructure such as oil and gas pipelines, transmission lines, and railroad networks. Many such missions are currently conducted by crewed helicopters; SilentWings expects it can achieve significant cost advantages for customers with its drone.
“We can reduce the operational cost and automate these kinds of inspections, creating the opportunity for customers to do predictive maintenance,” said Mändl. Other potential applications include surveillance, precision farming, medical transportation and fire monitoring.
SilentWings has displayed its drone at several recent air shows, including EUROPEAN ROTORS in November (see “Inaugural EUROPEAN ROTORS Reunites Vertical Flight Community,” Vertiflite, Jan/Feb 2022) and AERO Friedrichshafen in April, where the company registered significant interest in the fuel cell technology. It is exploring several pilot projects with potential customers and is currently undertaking another fundraising round.
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