Hydrogen promises green aviation

Uploaded 10 Nov @ 10:27am

Even now, more than 80 years after the event, many will be aware of the disastrous result of humankind’s early efforts to combine hydrogen and flight. The result was the incineration of the German passenger airship LZ 129 Hindenburg and the death of 35 of the 97 souls on board. The subsequent decline in passenger confidence effectively killed the fledgling industry.

Today, however, aerospace engineers are re-examining the virtues of this lightest of all elements. Their interest, this time, is not its buoyancy properties but its potential as a propellant.
Despite current uncertainty among the world’s airlines due to COVID-19 restrictions, commercial flight will remain vital, post-pandemic. Before lockdown, aviation was on track to account for about 1 billion tons of CO2 this year - more than 10% of humanity’s total carbon emissions. That figure could double by 2050 once unrestricted travel resumes.

Limited progress in developing batteries able to sustain long flights has seen hydrogen become the best prospect as a green alternative. One obvious benefit is that it is far lighter than batteries or kerosene. More significantly, though, when burned to provide thrust or used in a fuel cell to generate electricity, hydrogen produces only heat and water.
Aviation is a highly competitive field. While some manufacturers are still examining the pros and cons of hydrogen propulsion, others have already progressed from the drawing board to the skies.

A World-first from UK Government-funded manufacturer
While the name ZeroAvia may not be as well-known as Boeing, Lockheed and Airbus, that could be about to change. As the catchy company name implies, ZeroAvia’s prime objective is emission-free flight. To that end, it has received Government funding for a venture aptly named Project HyFlyer – its goal to complete a flight of 300 miles under hydrogen power.
The startup has returned value for money, clocking up a world-first with the successful test flight of its newly-developed, hydrogen-powered passenger plane.

The aircraft in question, a modified single-prop, 6-seater, Piper M-Class, which took to the skies over Bedfordshire on June 23 of this year, was more than just a proof of concept.
While hydrogen-fuel cells have powered prototypes in the past, this was the first flight of a licensed, commercially available aircraft. Indications are that hydrogen could reduce fuel and maintenance cost by as much as 75% and, in turn, reduce the cost per flight by up to half. Development of the company’s zero-emission powertrain will continue with the objective of achieving progressively longer, commercially viable flights.

The initial success of this project has established ZeroAvia as a leading innovator among those attempting to decarbonise commercial flight. If everything goes according to plan, the company will be ready with a range of 10 to 20 seat models by 2023 and could be rolling out hydrogen-powered aircraft with a capacity of between 50 and 100 seats as early as 2030.
While ZeroAvia may have been first to market, others in the industry are hot on its heels with a variety of projects large and small.

An aerial taxi
One of the smaller craft combines the characteristic structure of a helicopter with that of a drone. Under development by US manufacturer Alaka’i Technologies and known as Skai, its VTOL capability positions it as a commuter vehicle with a range of around 4 hours or 400 miles.

When licensed, Skai will offer seating for five passengers and derive its lift from six rotors each driven by a hydrogen fuel cell. In keeping with the popular vision of a flying taxi, Skai owes its distinctly futuristic lines to Designworks, the same studio that serves the BMW Group.

Singapore-based manufacturer HES Energy Systems has joined the ranks of those who see hydrogen as the saviour of aviation. Development of a fuel cell passenger craft named Element One began in 2018, its goal to produce a working prototype no later than 2025.

While Element One seats only four passengers, its range poses less of an issue. Although restricted to just over 300 miles when fuelled by compressed hydrogen, this increases tenfold when switching to liquid hydrogen. Refuelling involves swapping nacelles and reduces the time required to just 10 minutes.

NASA is on board
Given its extensive experience with fuel cells, it is not surprising that NASA is looking to apply this technology to inner space. As part of its continuing project to develop CHEETA (Cryogenic High-Efficiency Electrical Technology for Aircraft), the organisation is funding researchers at the University of Illinois’ Department of Aerospace Engineering to the tune of $6 million.

The department’s brief is to produce a liquid hydrogen fuel cell propulsion system. The extremely low temperature needed to maintain the liquid state will also generate a superconductive state which, in turn, will improve motor performance and energy transmission, thereby maximising efficiency.

Although once a proponent of battery-powered flight, Airbus has been disappointed by slow progress in the development of batteries that are sufficiently light while delivering enough power. The airframe manufacturer is now backing hydrogen propulsion systems for its future products. Currently, the company is examining three concepts.

Two of these rely on conventional twinjet and turboprop designs while the third pro-poses a blending of the wings with the fuse-lage to maximise fuel storage [see page 30].
Just two things stand between us and pollution-free air travel. The first is the lack of adequate ground facilities for refuelling and servicing of these new aircraft. If the transition is to succeed, the time to start developing them is now.

The second could prove more problematical. Emission-free aircraft can only be fully-effective if green technology is employed to produce hydrogen. ZeroAvia envisions a system in which wind and solar farms drive large-scale electrolysers to extract hydrogen from water. Hopefully, other manufacturers harbour similar visions.

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