Passenger aircraft have traditionally been designed with efficiency and safety in mind, although climate neutrality is increasingly being taken into account. So the question arises: Will we ever be able to fly from Paris to New York in less than an hour without exacerbating global warming?
This is what the European project STRATOFLY proposes: a Mach 8 aircraft, that is, a hypersonic aircraft that reaches a speed of at least 9,500 kilometers per hour, or approximately eight times the speed of sound. The STRATOFLY project, carried out between 2018 and 2021, in turn built on three previous European research projects on the same topic. “It won’t be easy,” says Nicole Viola, STRATOFLY coordinator and professor at the Turin Polytechnic (Italy). “We may not be ready for Mach 8 yet, but I’m sure I’ll get to see a hypersonic aircraft in life.”
STRATOFLY designed a prototype in the form of a computer model of a hypersonic hydrogen-powered aircraft. The project focused on innovative ways to power an aircraft capable of carrying three hundred passengers.
Meanwhile, political interest in the EU for supersonic passenger air transport has diminished, mainly due to environmental issues, to which must be added the noise and polluting emissions that cause climate change. Recent EU legislative initiatives, including a new law to cut aviation emissions, have highlighted political skepticism in Europe, as they limit incentives for commercial supersonic flights.
Even so, in the fields of civil aviation and research, ambitious ideas continue to emerge to develop faster and cleaner aircraft. Although it could take many decades for these technologies to become operational, scientists believe it’s important to dream big.
Not so fast
The STRATOFLY design posed many technological difficulties. However, one of the biggest hurdles was not really creating an aircraft that can fly fast, but designing one that can also fly slowly. “The problem is not the hypersonic phase,” explains Viola.
The hypersonic plane that Viola and her colleagues dreamed of must not only fly at high speeds, but also take off and land at much slower speeds. This complicates the design phase. An engine capable of hypersonic speeds, for example, is not the best option for lower speeds. A hypersonic engine also requires a large intake to “suck in” air, which is mixed with hydrogen. “The higher the speed, the greater the air intake”, says Viola. But at lower speeds, the engine needs to draw in less air, forcing scientists to find a middle ground in design.
The ninety-four meter aircraft has a large air intake in the nose, with sliding doors to regulate the air intake. From takeoff to reaching a speed of 5,000 kilometers per hour, six smaller engines do all the work. Above that speed, a huge engine that spans the length of the tail propels the plane forward. Beyond purely design issues, STRATOFLY has demonstrated the advantages of using liquid hydrogen instead of hydrocarbons as aviation fuel.
Return to the future
The STRATOFLY proposal is merely a concept designed to demonstrate what a hypersonic aircraft would look like. It allows researchers to test and ponder new technologies that could take decades to successfully materialize.
Today, however, the aviation industry could return to supersonic planes like the famous Concorde, which was around for over thirty years before it was retired in 2003. It was used by Air France and British Airways, and owes its notoriety especially for its Paris-New York and London-New York routes, with a one-way trip time of between three and three and a half hours.
US company Boom Aerospace has already signed supersonic design contracts with United Airlines and American Airlines. Hypersonic flight is already attracting attention beyond civil aviation. The space industry is targeting this technology to build ships that can take off like an airplane; a development that could reduce the need for expensive rocket launches. “Hypersonics is somewhere between aviation and space,” says Viola. “So, ultimately, we’ll see how one of the two camps adopts this technology.”
clear the environment
Regardless of whether these high-speed flights are possible, making aviation fuels cleaner is a growing priority for the EU. Today, aviation accounts for approximately 2.5% of global CO₂ emissions.
Hydrogen could be the solution, according to Professor Bobby Sethi of Cranfield University in the UK. “We have been researching aviation hydrogen for a long time,” explains Sethi. “However, the costs dampened enthusiasm for a long time, although its adoption is a matter of time, not conditional.” He has coordinated the European ENABLEH2 project, which concluded in November of last year after four years of studying the potential of hydrogen in aviation.
Hydrogen offers many advantages, according to Sethi. It is one of the most abundant elements on Earth and, if it is generated with renewable energy, it does not emit CO₂. In addition, ENABLEH2’s research has shown that hydrogen combustion systems will emit less NOx, another greenhouse gas, than kerosene.
On the other hand, hydrogen-powered aircraft can travel longer distances than electric aircraft, which may be used for short- and medium-range flights.
transition pathways
But the costs must not be neglected. Hydrogen behaves differently from conventional aviation fuel, which means redesigning planes and some airports, a transition that could take 20 to 30 years, Sethi says.
“We could technically redesign an existing aircraft, like the Airbus A380, to run on hydrogen,” he says. “But hydrogen tanks would have to be installed on the aircraft. We cannot store the fuel in the wings as it is done today, so this model is not very competitive with normal or sustainable aviation fuels”.
For this reason, most predictions envision an interim period in which the industry could use alternative sustainable aviation fuels (SAFs), which are typically made from biomass or waste and produce less CO₂ over time. of the life cycle than conventional ones.
According to Sethi, it would be better to “focus on sequestering the carbon generated by aviation emissions in the interim period and invest aggressively in hydrogen to reduce the transition time.” Whichever path is taken, the key for Sethi is a long-term and sustainable future for the industry. “Aviation has enormous social and economic benefits,” he points out. “It has drastically reduced transportation time around the world and has boosted economic growth thanks to, for example, tourism. We cannot let it be destroyed.”
The research described in this article has been supported by EU funds. Article originally published in Horizon, the European Union Magazine for Research and Innovation.
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