The unveiling of a newly refurbished hangar at Cranfield Aerospace Solutions marks a new step in its progress to net zero flight. Ed Hill was at the opening ceremony to find out more.
The development of greener forms of flying is a challenging task. Replacing combustion power that has been part of its evolution from the outset means a complete transformation in engine design, fuel types, and aircraft configurations; made even more difficult with net zero targets that impose stringent timescales.
Any organisation taking on this challenge must think hard about what is achievable, practical, and importantly profitable. This approach seems to encapsulate Cranfield Aerospace Solutions’ (CAeS) philosophy when it comes to what it calls Project Fresson.
The project, partly funded by the Aerospace Technology Institute, aims to replace the existing piston/turboprop powered engines used on the Britten-Norman Islander sub-regional STOL nine-seater aircraft, with hydrogen fuel cell electrical power.
At the newly refurbished hangar on the Cranfield University site, where much of the development work on Project Fresson is being carried out, Paul Hutton, CEO of CAeS, outlined how the task was progressing.
“We decided to take the research and development capabilities that we normally use on behalf of large OEMs and develop our own product,” he begins. “We wanted to develop an environmentally friendly solution, so our first consideration was what type of aircraft would be a credible option to start with?”
There were many reasons why the Islander fits the bill. Firstly, it’s a well-proven light utility aircraft (with its origins dating back to the sixties) used for multiple uses around the world. In fact, the twin-engined workhorse has accumulated more than 20 million flight hours providing vital services to remote communities. Secondly, it’s in the 9-19 passenger size platform where Cranfield believed there were already credible technical solutions to provide net zero power, and thirdly, currently around 85% of the flights that it makes (for example, hopping from one island community to another) are under 60 minutes.
“The first step on this process will be very challenging, whatever technology you choose,” Hutton says. “We rejected an eVTOL option because you don’t have the benefits that wings give you in getting into the air. We considered the best alternative was a sub-regional aircraft because that would attract interest and investment from the market, and lastly it is a segment with fewer competitors.”
Cranfield also believe that as a relatively overlooked market, many of the existing aircraft servicing it are older and in need of replacement.
Initially Cranfield considered an electric, battery powered version to replace the engines on the Islander, but as the calculations were made, it became clear that this would not be operationally viable.
“We considered batteries to give us 60 minutes of flight with 45 minutes reserve, in fact with that option we wouldn’t even be able to make the reserve,” explains Hutton.
Other options such as a hybrid power source with a battery and engine range extender were also proposed but with the added weight this would also substantially reduce the aircraft’s range and would still produce some CO2 emissions.
“There are advocates in the net zero aviation space, who say a particular technology is the only answer, but we are most concerned about what will practically work on an aircraft that is sustainable.
“We chose the Islander because it demonstrated it was likely to have a realistic commercial application, which means it is more attractive to buyers and we can attract the investment required. That is also why we chose hydrogen fuel cell technology with hydrogen gas as the fuel, because it is the best pragmatic solution.”
In the Islander’s case, Cranfield believe the gas – as opposed to liquid hydrogen fuel – offers more benefits, not just for the aircraft but for the convenience of the infrastructure needed to support it.
Firstly, liquid hydrogen must be cooled adding more complexity and weight to the storage and fuel system on board. Secondly, at present the production and storage of liquid hydrogen is not widely available, particularly in the remote areas of the world that the Islander is likely to operate.
“There are benefits with liquid hydrogen because it uses less volume but what would be the availability at smaller airfields?,” Hutton notes. “Gaseous hydrogen can be transported in bottles on the back of a truck. Furthermore, you only need small amounts because it is very energy dense. For example, the total gas hydrogen fuel load for an Islander would be around 36kg, which is more practical for the typical island-hopping role the aircraft has when it takes off and lands several times a day.
“The other factor is that islands are often able to produce large amounts of sustainable electricity, so it would be easy to install a mobile electrolyser plant to produce the hydrogen needed for the aircraft and that hydrogen could also be used for heavy goods vehicles, plant etc. used by the community and produced at night when the island is not using electricity for its own power.”
Cranfield also has plans to develop larger aircraft in the future using hydrogen as the main fuel. These include an aircraft up to 100 seats. So how will the technology it is developing for the Islander help with larger aircraft in the future?
“Zero emission technologies will not be introduced in larger aircraft for some time. However, the technical problems needed to be overcome can be achieved on much smaller aircraft like the Islander and applied to larger aircraft, so the intellectual property’s value is not just about the product that we create it’s about the problems that we solve too.”
Cranfield’s partner, Reaction Engines has already been brought in to help solve the issue of heat management using a hydrogen fuel cell.
“The heat we need to lose from the fuel cell nacelle on the Islander is similar to that when using a conventional engine but in a conventional engine most of that is dissipated out of the exhaust,” Hutton explains. “There is no exhaust in a hydrogen fuel cell so how do you remove that heat from the aircraft and not create drag by using an option like a radiator?”
The solution is Reaction Engines’ revolutionary heat exchanger technology. A design has been chosen for the Islander that has low drag but meets all the performance and durability requirements.
“Thanks to their thermal management expertise we have identified a problem, solved the problem and are now integrating that into the platform as a solution. Ultimately this development it is all part of creating our own hydrogen fuel cell aircraft design guide, which will be invaluable.”
And for the Britten-Norman Islander the new power source will also help to secure the aircraft’s longevity.
“Operators love the aircraft because of its versatility and of course they have successfully flown it with combustion engines for many decades. However, as the piston powered aircraft currently uses AVGAS (Aviation Gasoline) which is getting costlier and harder to source as fewer refineries produce it, there is ultimately a need to find a net zero option.”
This has led to the aircraft OEM offering the Britten-Norman’s Green Futures scheme which means operators who order the latest Islander will be able to upgrade it to the hydrogen powered version in the future. This offer is all part of plans for a new merged company that is being created that will leverage Cranfield’s R&D expertise with Britten-Norman’s aircraft manufacturing capability.
Project Fresson aims to have a demonstrator aircraft completed by the end of 2024 with certification for a passenger-carrying version finalised in 2026. So, CAeS is developing early hydrogen powered solutions with a distinct, no-nonsense attitude and hoping to help the UK industry make the most of this sea change in aviation.
“We have a great aerospace industry in the UK, but it is mainly focused on the existing supply chain. Longer term we have the chance to create a new net zero market for sub-regional and regional aircraft. If we don’t invest now that opportunity will be gone, Hutton concludes.”