Hydrogen refuelling in aviation isn’t just a logistical hurdle, it’s an engineering puzzle layered with fluid dynamics, cryogenics and data systems. What began as a continuation of earlier research into refuelling procedures quickly evolved into something far more unexpected. Starting with a focus on real-time monitoring between aircraft and ground systems, our intern Julian Winterdal followed the thread left by his predecessors and explored an alternative: subcooled liquid hydrogen. Borrowed from the heavy-duty transport world, this approach could potentially sidestep complexity altogether and transform how aircraft are refuelled. In this interview, we spoke with Julian about his research, his pivot and the potential impact of sLH₂ on the future of sustainable aviation.

How did you narrow down from the broader topic of the DutcH₂ Aviation Hub to your specific research focus?
I was initially tasked to continue research on Jelmer’s findings, which concerned the process of refuelling of liquid hydrogen for aviation, which is a very relevant topic within the DutcH₂ Aviation Hub. At the time, the next step for me was to dive deeper into his research. This next step was to specifically look into designing a data exchange system that monitors and communicates the pressure and temperature between the aircraft and the refuelling unit. Such a data system complicates the design significantly, especially when you compare it to current refuelling systems for Jet A, which are very simple in comparison. That’s how the process went for me initially to come up with the topic of the research.
 

How does your approach relate to the work done by Maurice and Jelmer? What did you take away from their research?
Maurice initially researched the operations and logistics that were required on the airport itself for the introduction of hydrogen into aviation. Jelmer then continued on this research, by narrowing down the research done by Maurice. As explained before, Jelmer really dove into the aspect of refuelling technology specifically. He laid out the procedure and an initial concept for a general liquid hydrogen refuelling system to be used in aviation. 

Jelmers research did not consider the data communication system, which was then a logical next research topic for the next intern. This was eventually the starting point for my research. I used the knowledge obtained by his research to start my literature research.
 

Where and why did you choose to take a different direction and what insights, challenges or new opportunities did that lead to?
After several weeks of reading scientific literature on the subject, I found that very recently a more efficient refuelling method has been demonstrated in the heavy duty industry. The refuelling station was designed and manufactured by Linde and Daimler Truck. They called it the Subcooled Liquid Hydrogen (sLH₂) Refuelling Station. 

Their technology is based on initially increasing the pressure of the liquid, to a point where evaporation losses during refuelling are eliminated. Since evaporation losses are eliminated, the flow inside the system can now be evaluated as a single-phase flow, which greatly simplifies the process. This then eliminates the need for this data communication system. My first question was then immediately if this could be a feasible method for refuelling in aviation as well. After several convincing discussions with my supervisors Loes and Stephen, we finally agreed that the best way forward for my research was to focus on analyzing the feasibility of this method of refuelling for aviation.
 

In what way does your research contribute to accelerating the transition to sustainable aviation?
Refuelling of liquid hydrogen has been a challenge for decades, where usually complex sensor and communication systems are required, accompanied with low mass flow rates and substantial losses in the refuelling process. This makes refuelling liquid hydrogen a pain point in the entire supply chain, specifically when you consider large aircraft. My research brings attention to a new method, where these problems are minimized. 

Because ideally, the refuelling procedure has to be as similar to current jet A refuelling practices as possible. sLH₂ refuelling seems to be a promising solution for this, ensuring minimal extra training requirements for refuelling operators. At the same time, using subcooled liquid hydrogen refuelling, similar turnaround times and minimum losses in the process can be achieved.
 

How could your work be translated into a concrete product or service within this ecosystem?
The model could form the basis for an actual subcooled liquid hydrogen refuelling station, to be manufactured and used in the future to refuel liquid hydrogen aircraft. However, to design and develop an actual prototype would require for example a lot more research, gathering of experimental data, design, data verification, validation and certification. However, for now, the possibilities and advantages are highlighted by my research, and will hopefully spark a lot of interest among researchers and designers at universities and companies to start designing and manufacturing an actual sLH₂ refuelling system for aircraft refuelling.
 

Looking back at the start of your internship, what would you approach differently now?
I look back on the internship as a great learning experience, where I even got involved in several other projects that were running in the company at the moment. There are almost no things that I regret or would have done differently. The only thing that could have been interesting, was to seek more engagement with actual researchers in this field. It could have definitely added to the experience and the results, had there been an opportunity to arrange for example some interviews with experts in the field, to get an insight into their view on the concept. Their insights could have been very helpful into directing the research and helping with modelling the system.
 

What do you see as the next steps for the topic you’ve been working on?
There is still a lot to do before hydrogen powered aircraft can truly take off at any airport in the world. The next critical steps for fully enabling this, are green hydrogen production, efficient hydrogen transportation methods, liquefaction plants, airport infrastructure requirements, loss-free storage methods, efficient refuelling technologies, compact and light hydrogen fuel systems and of course, efficient conversion into propulsion inside the aircraft. Work into any of these topics can be seen as critical steps into enabling liquid hydrogen aircraft in the future.
 

In your view, what would be a valuable angle for a future intern or researcher to explore?
There are many aspects of the model that can be improved. One instance would be to provide more detailed models to provide more accurate physics. The downside is that two-phase flow is intrinsically complex, and most often requires costly CFD calculations. 

One example where the model could be improved easily, is by implementing more in-depth calculations of the heat flux for the airport storage tank, fuel hose and the aircraft tank. This could provide better predictions of boil-off and evaporation in the refuelling system. Multiple models for conductive, radiative and convective heat transfer need to be produced for this. 

Another aspect could be a more detailed design for the pump, to accurately predict cavitation and performance of the pump, in terms of pressure increase, temperature increase, and mass flow rate. A detailed model for evaporation in the pipe, using several detailed models for each corresponding evaporation zone, is another aspect in the model that can be improved.

What’s the next step for you?
The next step for me is to finish my Master’s degree in Aerospace Engineering at the Delft University of Technology. I will start my thesis project on liquid hydrogen fuel systems in aircraft, to hopefully be able to further contribute towards making hydrogen aircraft a reality in the near future. 

And what are the next steps regarding your research at Unified?
As I said, there are many aspects of this project that are still to be improved and require additional research. Unified International is looking for a new intern to continue this research project in liquid hydrogen refuelling. At Unified International, we believe in guiding interns to develop the talents of tomorrow and help shape the future of the workforce. 

Looking for an internship at Unified?

If you are looking to do an internship project on finding solutions to one of the most challenging problems for realising sustainable, emission-free aviation, please send an email to loes@unifiedinternational.net. 

As aviation strives toward net-zero emissions, hydrogen, eSAF, and electric flight are emerging as key solutions. But innovation alone isn’t enough scalable infrastructure is essential. The industry faces a classic Catch-22: aircraft development, infrastructure investment, and supply chain readiness all depend on each other, delaying progress.

Hydrogen-powered aircraft require robust refueling networks. eSAF production must scale to meet demand. Electric aviation needs grid capacity and charging infrastructure. Without coordination across these areas, the transition will stall.

Unified International (UI) is helping break this cycle by aligning stakeholders behind scalable infrastructure strategies. In the Netherlands, UI supports the DutcH₂ Aviation Hub at Rotterdam The Hague Airport, where it is helping RHIA bring together stakeholders across infrastructure, energy, aircraft, operations, research and government, while connecting with other international airport hubs.

UI also initiated the next-generation hydrogen propulsion system by Conscious Aerospace for regional aircraft, with a pathway to broader adoption in larger systems.

“The biggest challenge isn’t whether hydrogen, eSAF or electric aviation work—we know they do. The key is ensuring all stakeholders act now to build the infrastructure needed to scale these solutions,” says Stephen Hands, Senior Associate at UI.

Overcoming the Catch-22

The shift to zero-emission flight is only just beginning. For airlines, pressure is mounting, yet aircraft availability and cost uncertainty remain major barriers. SAF and eSAF are more expensive than fossil fuel, hydrogen aircraft are still in development, and electric aviation, while promising, is constrained by battery and infrastructure limitations.

Hydrogen propulsion is increasingly seen as the long-term solution for short- and medium-haul flights, offering scalability beyond regional markets. But manufacturers still face challenges in commercial readiness, and refueling networks lag behind. Battery improvements are expanding electric flight potential, but adoption depends on coordinated infrastructure rollouts.

This situation mirrors Airbus’ delay of its Zeroe program, a perfect example of the Catch-22: decisions are postponed until the rest of the ecosystem is in place.

Airports, too, face growing infrastructure demands. They must balance investment in SAF blending, hydrogen refueling, and electric charging, each requiring time, funding, and space. Hydrogen storage adds complexity with cryogenic systems and new procedures.

Fuel and energy suppliers hesitate to invest in eSAF and hydrogen infrastructure without clear offtake agreements. Large-scale production of eSAF and green hydrogen demands high upfront investment, further delayed by policy uncertainty.

Early-stage investments must be de-risked through enabling stronger airline commitments and supportive government incentives. Progress must accelerate, and not wait for each piece to fall into place. With aligned investment, policy and infrastructure, aviation can unlock a sustainable future.

Accelerating the Transition

SAF mandates are driving progress, and investment in hydrogen and electric aviation is growing. However, to achieve commercial scale, infrastructure must advance in parallel. Airbus has underlined the need for refueling systems to be in place before new aircraft enter service. Addressing the Catch-22 is vital: infrastructure must come first, not follow.

Collaboration is key. The industry needs strong government support, clearer policy signals, and close cooperation between airports, suppliers, and airlines. Strategic investments in grid upgrades, hydrogen infrastructure, and eSAF production can create the foundation for zero-emission flight at scale.

UI works with industry leaders to transform vision into action—by aligning policy, infrastructure, and supply chain efforts to create real momentum.

Four Solutions to Unlock Progress

“Now is the time to align investment, policy, and infrastructure timelines across the ecosystem,” says Hands. “Through partnerships, regulation, and structured industry adoption, we can accelerate this transition.”

To bridge the gap between innovation and adoption, four priority areas must be addressed:

• Public-private partnerships (PPPs)
  Subsidies, tax incentives and guaranteed demand programs can reduce risk and encourage early investment from suppliers through to airlines.
• Infrastructure-first development
  Hydrogen supply lines, SAF production, and charging stations must be built ahead of fleet deployment to ensure readiness.
• Clear and consistent regulation
  Governments must set ambitious, achievable goals for SAF and hydrogen use—providing confidence for long-term investments.
• Energy infrastructure upgrades at airports
  From grid reinforcement to hydrogen refueling and energy storage, airports must act now to prepare for zero-emission flight.

“Any journey starts with the smallest step. The regional market is the ideal starting point for the transition to zero-emission flight. By scaling gradually and working together, we can focus on clear issues and solutions,” adds Hands.

Unified International’s Role in the Transition

Unified International works closely with airports and aircraft manufacturers to develop phased, infrastructure-first strategies that anticipate future needs and help overcome the industry’s gridlock.

By aligning infrastructure development with supply chain and regulatory milestones, UI helps address the Catch-22 and unlock momentum. Its role within the DutcH₂ Aviation Hub at Rotterdam The Hague Airport exemplifies how stakeholder collaboration can deliver tangible change, locally and globally.

UI is committed to ensuring that sustainable aviation infrastructure evolves ahead of demand, turning ambition into action.

“We’re not just talking about the future of aviation, we’re actively helping to build it,” concludes Hands. “I hope we can connect with more like-minded companies and people and explore how we can help them in their journey towards sustainable aviation.”

Is Europe prepared for the new era of shifting world orders? Global power shifts are forcing Europe to rethink its defence industry. With the U.S. adjusting its geopolitical priorities and security threats rising, Europe must strengthen its own industrial base and technological capabilities fast. The war in Ukraine has underscored the urgency of reducing reliance on external players and accelerating regional defence production.

“As the world order evolves, Europe must adopt a proactive approach. Strengthening our defence industry and technological capabilities is essential for greater self-reliance, rather than depending heavy on American support. This shift is crucial for our safe future, it is no longer a matter of choice, but of necessity”, says Michel van Ierland, Managing Partner at Unified International.

As Europe strengthens its industrial base, it is in the US’s strategic interest to support this effort and reinforce transatlantic ties. We are committed to a new balance where Europe takes a decisive step forward.

Europe’s defence industry, while strong, remains fragmented. To increase production, it must invest in advanced technology, expand production capacity and foster cross-border industrial cooperation. A more integrated approach is essential. Countries should work together, fostering innovation, efficiency and resilience to strengthen Europe for the challenges ahead.

The need for acceleration and strategic cooperation

The urgency to strengthen Europe’s defence capabilities is increasing and the sector is undergoing an unprecedented shift.

“The challenge today is not a lack of technology but the speed at which we can scale it up. Innovation is valuable, but without instant industrialisation, we remain vulnerable. As Michel puts it, ‘Where there used to be time but no money, now the opposite is true: there is money, but no time”. Rapid execution is the real challenge. This demands a shift from traditional methods of procurement and project execution to an approach where innovation and speed go hand in hand”.

However, the current diversity and fragmentation of EU defence systems, coupled with complex decision-making, delay a rapid and effective response. Standardisation across European defence industries is critical to ensuring interoperability and efficiency in joint operations. Without combined technological frameworks, Europe’s defence effectiveness remains compromised. The European agencies can play an important role here.

Adopting high-tech industry principles, flexible production, rapid iterations and pragmatic decisions, can drive this shift. The need for speed also creates opportunities.

In addition to a stronger Europe, the transatlantic cooperation remains essential. European capabilities are valuable to American defence industries, just as U.S. technologies are critical to European defence efforts. A balanced, reciprocal partnership is key further strengthening Europe’s independence without severing ties.

A clear (new) national and EU strategy will help companies meet rising defence demands, while new players can help transform industrialisation.

Technology and industrial capacity as key factors

New technologies are reshaping modern warfare. In Ukraine, high-tech innovations such as drones and autonomous systems have proven to be powerful and cost-efficient. Europe must invest in these technologies but also in the capacity to innovate and produce them quickly and also on a large scale.

Despite strong innovation in drone technology, the Netherlands lacks the large production capacity needed to rapidly deploy these solutions at scale. While the country excels in research and development, the challenge lies in transitioning from innovation to high-rate industrial production. Addressing this requires renewed investment in manufacturing, ammunition production and flexible, low-manpower production lines.

Michel emphasises this point, stating, “The Netherlands has strong knowledge and expertise but limited large-scale established production facilities for some defence sectors. This presents a key opportunity to strengthen our industry and enhance our role in the global defence sector”.



Beyond drones, the Netherlands has positioned itself for obvious reasons as a leader in AI, cybersecurity, quantum technology, hypersonic weapons, satellite communication and advanced radar and detection systems. However, the key challenge remains implementation, ensuring that innovations are tested and scaled more rapidly within the operational defence environments so that Europe evolves from a developer to a producer of advanced defence technologies.

Independence and geopolitical resilience

Many defence technologies depend on scarce raw materials and external supply chains. Globalisation has brought Europe economic benefits but also strategic vulnerabilities. To increase geopolitical resilience, new alliances must be formed and supply chains must be diversified.

The geopolitical developments make clear that Europe has no time to lose. By prioritising speed, agility and collaboration, Europe can build a strong and independent defence industry capable of meeting future challenges. This means investing not only in domestic industry but also in strategic partnerships to secure access to critical materials and technologies.

Unified International: Bridging Industry and Defence

Unified international plays a key role in strengthening cooperation between governments and industry within the defence sector. Our expertise helps companies navigate the complex defence market, secure procurement opportunities and execute program management meeting the defence operational and technical needs. From bid management and strategic roadmaps to business case development, we ensure companies position their innovations for success into the field. With extensive knowledge of procurement strategies, we guide organisations in working with OEMs and integrating seamlessly into the defence supply chain.

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Find out how we can support your business and achieve your strategic goals.

 – Unified International’s role in driving strategic partnerships for security and sustainability 

The protection of critical infrastructure (digital and physical) is more urgent than ever due to increasing cyber threats and geopolitical tensions. The Netherlands and the EU are investing in regulations and technology to enhance resilience, such as the ‘Cyber Resilience Act’ and the ‘Law on Promoting Digital Resilience for Businesses’. Collaboration between the government and the private sector remains crucial, as critical infrastructure is often in private hands.  

Advanced monitoring, via manned and unmanned platforms as well as satellites, followed by AI-enabled analysis are essential for detecting and countering threats at an early stage. Additionally, Europe must strategically reduce its dependence on foreign technologies and invest in autonomous solutions. 

Unified International plays a connecting role in this by understanding both public and private interests and supporting them in developing a joint approach. By facilitating innovation and collaboration, Unified International helps strengthen resilient critical infrastructure that can withstand future threats.

We spoke with Michel van Ierland, Managing Partner at Unified International about this topic and Unified International’s role in it in a short interview. 

How can defence and the private sector collaborate more effectively to tackle cyber and physical threats to critical infrastructure?
The responsibility for securing critical infrastructure lies with both the government and private entities, as many assets, such as those in the North Sea, are privately owned. This requires a joint approach, with clear definitions of roles and responsibilities. A shared common operating picture is crucial, which can only be achieved through structured information exchange. This must be widely available to authorized users so that anomalies can be quickly detected and addressed. Currently, various software solutions are available, but the use remains fragmented and need better integration. Monitoring is done using drones, satellites and sensors, but to effectively recognise and respond to threats, a layered and coordinated use of these technologies is necessary. 

What are the biggest current threats to our infrastructure, both digital (cyberattacks) and physical (such as sabotage of pipelines or energy networks)?
Critical infrastructure is at risk of disruptions that could have a major impact on energy supply, data traffic and economic stability. Cyberattacks, such as ransomware and state-sponsored threats, are increasing in both frequency and complexity. At the same time, physical threats, such as sabotage of energy networks and undersea cables, pose a real danger. Another challenge is that critical infrastructure is often located in hard-to-reach areas, making damage recovery time-consuming. The Netherlands is also dependent on foreign technology and energy sources, which increases vulnerability in times of geopolitical tension. 

Which technological innovations (such as AI, drones, satellite monitoring) help protect infrastructure on land, at sea and in the air?
New technologies, such as AI-driven monitoring and -analysis, advanced satellite surveillance and drones, are playing an increasingly important role in protecting critical infrastructure. These systems help detect anomalies and abnormal patterns in both cyber and physical threats. However, it is essential that t Europe reduce their reliance on foreign technologies to ensure the autonomy and security of these systems.

What are the biggest obstacles to collaboration between businesses and government/defence in protecting critical infrastructure and where are the main bottlenecks?
One of the biggest challenges is the effective sharing of information between businesses and the government. There is often reluctance to share sensitive data, even though a shared threat assessment is crucial for a swift and coordinated response. Additionally, there is a need to invest in digital resilience and redundancy to ensure that infrastructure can withstand disruptions. This highlights a third problem: often responsibilities are fragmented between commercial and multiple government entities: who is responsible for the investments it takes? Finally, long-term vision and structural collaboration are essential in this regard.

What role can Unified International play as a connector between defence and the private sector and how does Unified International help both parties collaborate effectively?
Unified International can act as a bridge between public and private entities by providing insight into each other’s needs and responsibilities, bringing together the right technologies and operational capabilities. It supports impactful, relevant security solutions while ensuring a sustainable investment model that does not disrupt business operations.  Unified International facilitates long-term collaboration and reliable agreements with the government, helping stakeholders invest in security while addressing practical challenges. 

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Find out how we can support your business and achieve your strategic goals. 

* The Cyber Resilience Act is an EU regulation ensuring cybersecurity for digital products through lifecycle security measures and transparency. Source: (EU Digital Strategy) 
 
* The Law on Promoting Digital Resilience for Businesses is a Dutch law helping companies strengthen cybersecurity via government guidance.  

Navigating long, complex procurement processes while the government faces hurdles in turning new defence strategies fast into action. Close collaboration between the industry and government is crucial to enhance its capabilities and achieve strategic autonomy. How can industry and government work together to address these challenges? Unified International plays a key role for Industry in bridging this gap. 

We spoke with Albert Timmers, Senior Associate ‘Defence’ at Unified International, to explore these challenges and gain insights into the company’s approach to addressing them. With a career as a navy officer and as a reservist, Albert is familiar with high-performance, 24/7 organisations like the Defence organisations. His experience positions him perfectly at the intersection of industry and government, making the defence sector a natural fit for his expertise. 

Now, in his current role, Albert continues to contribute to the defence mission, protecting what is dear to us. “For me, this means ensuring that those whom we, as a society, send into harm’s way are as well-prepared as possible, equipped with the best materials available”, he explains. 

Can you describe the current challenges in the defence sector? What are the biggest obstacles? 

There are two perspectives to answer this question: industrial and governmental.  

On the government side, the new Defense note 2024 (published in September) indicates many initiatives to be fulfilled. However, implementing the Defence Industry Strategy effectively remains challenging.  It requires a lot of coordination, budget and manpower to translate the new policy into operational capabilities on land, in the air and at sea.  

From the industry’s perspective, it is clear that outsider companies, whether civil or foreign, face significant challenges when transitioning into the Dutch defence sector. The Dutch defence landscape and material processes, has specific requirements, networks, language, and procedures that can be difficult to understand. Furthermore, we see that it is challenging for companies to secure financing for investments. We have experienced firsthand that, while agreements have been made with banks at the strategic level, it remains difficult for the industry to obtain working capital in the day-to-day operation, even with an already signed defence contract in hand.

How does Unified International support the navy, air force, industry and army in overcoming these challenges? 

At Unified International, we are the connecting link and interface between industry and government.  We are on a daily basis actively involved in the network of industry, defence organisations, and policy ministries. We see and hear a lot, connecting the dots to create win-win situations, meeting operational needs and meanwhile creating sustainable business. As a result of this it is our ambition to fulfill a defence capability, and the industry sells its products. For us, this goes far beyond just a transactional relationship. We believe it is important to generate energy collaboratively and involve as many Dutch parties as possible. Unified International plays a key role in bridging this gap.

What unique expertise does Unified International bring to the table?

We combine competencies in several key areas, including military operations, technical knowhow,project and program management and legal expertise. This, coupled with an entrepreneurial spirit and a ‘can-do’ attitude, sets us apart. Our former colleagues at the Ministry of Defence also value our support, understanding that our involvement aligns ultimately with their interests as well.

How does Unified foster collaboration between the Dutch industry and the Ministry of Defence, and why are these partnerships crucial for achieving success in defence projects? 

We strive to create a connection between industry and the defence organisation by bringing together people and knowledge. It is crucial that our military operational units receive the equipment they need to succeed. Through our network, we connect with companies that can supply this equipment and we support companies in making the right developments with future military use in mind, including international co-production and scale-up opportunities. By fostering EG cross-sectoral collaboration, we aim to enhance innovation and effectiveness in defence-related projects.

What opportunities do you see for collaboration and innovation between civil and defence sectors?

Investing in defence is not just about ‘buying’ military- or dual-use products; it’s also about ensuring that we are prepared and remain flexible to address any future challenges. In other words: creating a future-proof capability. This means fostering an ecosystem of industry and government together in which civilian innovations can be seamlessly integrated into defence systems, meanwhile, autonomy and adaptive capabilities are key. Government support plays a crucial role in this process by creating favourable financing conditions, offering clear guidance on development priorities, and providing guarantees on future contracts.

What factors do you consider when evaluating the feasibility and potential success of industry products?  

First and foremost, we evaluate the alignment with military operational needs, assessing whether the product meets the specific operational requirements of military personnel in the field and its potential to be integrated into existing systems. 

Secondly, we consider the product’s flexibility, particularly its ability to adapt from civilian use to military applications (dual use). This adaptability often requires minor adjustments but demands strong commitment and collaboration from the industry. 

Finally, we emphasise a solid supply chain and local support. We evaluate the product’s support infrastructure, including the proximity of maintenance and operational support. Ensuring critical enablers are available close to key locations, such as military bases, is crucial for strategic autonomy and long-term success. 

Can you provide examples of defence initiatives Unified is currently (or has been) involved in? 

Unified International has supported Fokker Services Group for the last two years in becoming part of the recently signed acquisition contract for the C390 Tactical Transport aircraft at Embraer. Fokker Services Group will be responsible for the conversion of the aircraft into a deployable NATO weapon system and will provide maintenance during the ‘entry-into-service’. This arrangement allows the RNLAF to meet its need to have this critical enabler close by (at the same airbase, Woensdrecht) and contributes to the desired deployability and strategic autonomy of the RNLAF in the long run.  

About us
Unified International Defence is a recognised consultancy firm that supports companies and the government within the Dutch defence domain. In defence advisory projects, our focus is on strategic positioning, procurement, and materiel projects. We are also strong in project and program management. Unified International leverages strong relationships at all levels within the defence domain and relevant ministries on a daily basis. We are entrepreneurial, proactive, and have a can-do attitude.