Hydrogen-Powered Ultralight Training Aircraft — A Systems Engineering Approach
Sebastian Piotr Kuk
Profil Orcid 
Publié en ligne: 30 juin 2025
Pages: 1 - 17
Reçu: 07 avr. 2025
Accepté: 09 mai 2025
DOI: https://doi.org/10.2478/tar-2025-0006
Mots clés
© 2025 Sebastian Piotr Kuk, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
Aviation as a sector is responsible for ever-increasing emissions harmful to the environment, including oxides and dioxides of carbon, nitrogen, and sulfur, as well as water vapor. With the current industry approach of incremental improvements in inter-turbine temperatures and bypass ratios, progress in turbine engine specific fuel consumption has begun to stagnate. To decisively close the pollution gap between reality and sustainability, the aviation industry must make a strategic shift akin to the automotive sector’s earlier transition – toward electrification of propulsion and, in particular, the adoption of hydrogen as a fuel.
The application of hydrogen in aviation is not new. As early as the 1970s, significant resources were devoted to evaluating the viability of hydrogen as a primary fuel for passenger aircraft [1][2]. Yet, no commercial hydrogen-powered aircraft have emerged. This is surprising, given hydrogen’s success in other transportation sectors, including electric cars and forklifts, and prompts the question: why not aviation?
There are several potential explanations, but one stands out – hydrogen in aviation has traditionally been regarded as a research pursuit, not as a commercially viable product. Technical barriers are both well-known and well-documented. Hydrogen storage presents difficulties in both gaseous [3] and liquid [4] forms, and the magnitude of infrastructure investment required has deterred serious commercial attempts. In the absence of robust regulatory frameworks for aircraft and airport operations involving hydrogen [5], most projects have remained confined to research settings.
This paper adopts a systems engineering approach [6] and utilizes the Minimum Viable Product (MVP) development methodology to identify the most promising aircraft architecture for initial commercial deployment. The goal is to provide actionable guidance to manufacturers and researchers on where to focus efforts and how to initiate commercialization pathways.
The study begins by outlining key barriers to hydrogen aviation and proposing mitigation strategies. It then identifies the MVP as a training aircraft in the Light or Ultralight category, powered by a Proton Exchange Membrane (PEM) fuel-cell electric propulsion system, with hydrogen stored onboard as high-pressure gas. This configuration circumvents many integration and infrastructure challenges and offers a realistic opportunity to deliver a competitive, economically viable aircraft.
Finally, the paper proposes a conceptual framework demonstrating that with current technology, a hydrogen-powered airplane is not only feasible but could represent a worthwhile investment. It concludes with suggestions for future research topics necessary for further development of hydrogen aviation.
In 2018, global aviation broke the important barrier of emitting over
Most technological progress in successive generations of turbofans have focused on two main areas: increasing bypass ratios and raising inter-turbine temperatures. However, as the chart in Fig. 1 shows, fuel consumption improvements have begun to plateau, suggesting that further significant reductions in fuel consumption using only this approach are unlikely. Aviation may not be the most carbonogenic industry in the world – but it is arguably one of the hardest to de-carbonize [9].
Relative specific fuel consumption for aircraft engines, plotted against certification year [8].
As global air traffic – measured in passenger-kilometers – has grown steadily since World War II, so too have emissions. Since 2008 total CO2 emissions have increased yearly by about 4%, [10][11] compared to a 5% annual increase in air traffic (passenger-kilometers). This distinction is important: if no technological or operational advancements had been made since 2008, emissions would have risen in direct proportion to traffic growth – by 5% per year. Instead, thanks to improvements in aircraft technology, enhanced operational practices, and the adoption of Sustainable Aviation Fuels (SAFs) [12], the annual increase in emissions has been reduced to 4%. While this represents a roughly 20% reduction in emissions per passenger-kilometer – a notable achievement – it still falls short of what is required to meet the sector’s long-term sustainability goals.
This paper explores one potential solution to this challenge: the broad implementation of hydrogen as an alternative energy source in aviation.
Hydrogen has the highest energy density by weight of all chemical fuels. As such, it was one of the primary energy sources considered in the aerospace industry, where weight matters above all else. Few modes of transportation are as sensitive to onboard weight as aviation – with the notable exception of space vehicles, which tellingly already rely heavily on hydrogen.
Hydrogen, like all fuels, is only an energy storage medium, and to access this energy it must undergo a chemical reaction, typically with oxygen. There are two main ways to do this – either burning it in a combustion engine or using fuel cells to generate electricity. Each method poses distinct engineering challenges due to hydrogen’s unique physical and chemical properties, and thus both approaches merit separate consideration.
When hydrogen is used in turbine engines, especially for aviation, the overall operational principles remain the same – air is sourced from outside the airplane, put through a compressor, mixed with fuel and burned in a combustion chamber. The resulting high-energy gases drive a power turbine, used to power a propeller or a fan. There are some differences, however, that prevent the same engines from being used for both kerosene-based fuels and hydrogen:
Hydrogen burns at a higher temperature than kerosene-based fuels – ergo it requires the redesigning of most of the main flowpath hardware and cooling systems to withstand higher working temperatures.
Hydrogen has a higher flame speed than kerosene-based fuels – this has implications for fuel system elements, especially valves and nozzles, and means an additional increase in working temperature for the flowpath hardware, as the flame is literally closer to the surface of the parts and coatings. This also means that hydrogen is flammable and prone to explosions in lower concentration than most other gases.
One additional note is that hydrogen combustion produces a different mix of exhaust gases than kerosene-based fuels. While it obviously eliminates emissions of carbon dioxides, its higher combustion temperatures can increase the formation of nitrogen oxides. Furthermore, combustion of hydrogen generates large quantities of water vapor, which can act as a greenhouse gas. Nonetheless, the most basic goal of eliminating carbon emissions is met completely.
In general, electric propulsion offers significantly higher efficiency than combustion engines. When deciding to use hydrogen for an airplane, it is logical to at least try applying an electric motor before switching to a combustion engine, as the same issues with hydrogen storage and infrastructure must be resolved for both approaches.
Hydrogen-electric architecture for aviation has been the subject of great interest since the early 2000s, especially after successful adoption within the automotive industry. With much research already done, a general overview of the proposed system architecture and its typical characteristics can be outlined.
Among various fuel cell types, Proton Exchange Membrane (PEM) fuel cells are currently the most suitable for aviation applications. This is due to their favorable balance of weight, efficiency, and operational temperature (up to approximately 120°C), making them the lightest and most power-dense option currently available.
In its most basic configuration, a hydrogen-electric propulsion system takes the schematic form shown in Fig. 2.
Conventional vs. hydrogen-electric airplane propulsion systems.
Hydrogen must be stored onboard, either as a liquid or gas, and then delivered to fuel cells stack, together with air from outside. The electricity so generated powers an electric motor, which in turn powers a propeller or a fan, and excessive heat and water are dumped back into the atmosphere.
This simplified schematic, however, does not include many other aspects of fuel cell operation, such as the following:
Fuel cells must be periodically cleaned to remove pollution from air or hydrogen and excessive humidity – this requires a precise FC stack management system. Temperature and pressure of incoming air and hydrogen should be controlled if efficiency is to be maximized, most typically via an additional compressor. Fuel cells have a lag of about 1–2 seconds in responding to the power management system. This is too slow for any rapid airplane power adjustments, e.g. in emergency situations. Most often an additional battery is implemented in the system between fuel cell and electric motor to cover short-term peaks in power demands. Fuel cell stack efficiency degrades over time of operation, albeit at a rate not much different from the degradation process of combustion engines.
There are well-researched and documented examples of recently developed UAVs [13][14], moto-gliders [15] and light airplanes [16][17] using hydrogen-supplied PEM fuel-cells in-flight. Although no commercially available aircraft exist to date, these developments demonstrate that the concept is technically viable. Compared to other strategies for reducing aviation emissions, hydrogen propulsion offers a more direct and comprehensive path towards carbon neutrality in air transport. However, the deeper the concept of hydrogen propulsion is analyzed (either with a combustion engine or electrical motor), the more consistently the same issues are cited as critical “showstoppers” for this technology: hydrogen storage problems, problematic airplane integration, limited hydrogen production and distribution infrastructure, and residual emissions of water vapor.
The following sections will review these challenges in detail and propose mitigation strategies for each. The primary objectives of this analysis are to identify the most viable pathway for commercializing hydrogen propulsion in aviation and to present a conceptual design for an aircraft optimized for this technology.
While hydrogen architecture in aviation offers a number of advantages, it also faces serious obstacles – the most important of these being hydrogen storage, airplane integration, and operational challenges.
Because of its molecular characteristics, hydrogen is highly problematic to store. At atmospheric pressure (1 atm), hydrogen remains a gas of very low density – 0.0899 kg/m3 vs ex. 0.717 kg/m3 for Liquified Natural Gas (LNG). Cooling it all the way down to 20K temperature turns it into a liquid, but the density problem persists – liquid hydrogen is still at least 10 times less dense than kerosene (71 kg/m3 vs 800 kg/m3). Solid-state hydrogen is possible under the immense pressure of 400 GPa and further cooling down to only 14 K, but even then its density increases to only 86 kg/m3, making it one of the least dense solids.
This density problem means that despite hydrogen’s high energy density by weight, when recalculated into volume the numbers look drastically different:
Energy density comparison of different fuels.
| Hydrogen (Gas at 1 bar) | 120 | 0.1 |
| Hydrogen (Gas at 300 bar) | 120 | 3.03 |
| Hydrogen (Gas at 600 bar) | 120 | 6.06 |
| Hydrogen (Liquid) | 120 | 8.49 |
| Jet-A Fuel | 45 | 34 |
| Gasoline | 44 | 31.5 |
| Diesel | 46 | 35 |
| Ethanol | 28.8 | 20 |
These figures clearly illustrate the core issue: although hydrogen delivers more energy per kilogram, it delivers far less energy per liter compared to conventional fuels. Consequently, in major design studies such as those conducted by Lockheed Martin [1] and Airbus [2], hydrogen was stored exclusively in liquid form within cryogenic tanks. However, this approach also comes with significant trade-offs:
Compressed gas storage requires high-pressure tanks, which are heavier and may offset the weight advantage of hydrogen. Cryogenic liquid storage necessitates specialized insulated tanks and continuous energy input to maintain temperatures near 20 K. Additional energy is also needed to vaporize the hydrogen before it enters the combustion chamber or fuel cell stack.
It is worth noting that conventional storage of electrical energy in batteries is even less efficient than gaseous hydrogen (requiring approximately twice the volume and four times the weight to store the same amount of energy [18]).
Another quite peculiar property of hydrogen is how small its molecules are. Consisting of only one proton and one electron, hydrogen atoms are very penetrative. Even with the best available sealing technologies, it remains very difficult to keep them in any container for a long time – another consideration for safety of on-board hydrogen storage.
Outside of storing hydrogen as liquid and gas, there are multiple alternative ways of storing it by bonding it to a metal surface (adsorption) or into metal itself (absorption). Such methods, called metallic-hydrogen storage, have been studied, but so far every indication is that they offer lower energy density than high-pressure gas or liquid storage. As such, their use for aviation purposes is excluded from further consideration within this paper.
In summary, based on the previously cited research and also more recent analyses [19][20][21][22][23] comparing electrical energy storage options for aviation – as well as those specifically focused on problems of hydrogen storage (both as gas [24][25] and as liquid [26][27]), the following conclusions can be drawn:
Compared to currently used kerosene-based fuels, hydrogen systems have a lower energy density and energy volumetric density. However, when compared to batteries, their capacity for storage is higher, therefore there should be a preferred choice for powering electric airplanes (at least from a purely technical standpoint). When using hydrogen in aviation, two storage methods are available – high pressure gas tanks or cryogenic liquid tanks. Cryogenic liquid storage is more weight- and volume-efficient but requires a number of supporting systems to maintain cryogenic temperatures. These cooling systems do not scale well into small applications, but perform comparatively better in larger airplanes. Consequently, it is generally accepted that gas storage should be used for light and ultralight aviation applications, whereas liquid storage is applicable to medium to large aircraft.
Determining the appropriate storage method depends on numerous factors, including the efficiency of system components, energy and power density requirements, aircraft mission profiles (such as range and flight duration), and even non-technical considerations. These may include the availability of airport infrastructure (as gaseous hydrogen requires greater storage volume) or environmental conditions (since maintaining cryogenic temperatures in hot climates is more energy-intensive). For these reasons, the choice between gaseous and liquid hydrogen storage should be made within the specific context of the aircraft’s intended mission and operating environment.
Integrating hydrogen propulsion into an aircraft introduces a range of technical challenges. Some are an inherent feature of the hydrogen propulsion system itself, while others arise from its interfaces with and integration into the airplane structure.
As previously mentioned, hydrogen propulsion system components can contribute considerable weight relative to other aircraft elements or even the airframe itself. Additionally, some of these components have rigid geometric constraints and cannot be shaped freely.
Pressurized tanks, in particular, come with severe limitations to their shape. Generally, in order to maximize the fuel to tank weight ratio, tank shape should be as close as possible to spherical, which minimizes the surface area (and hence tank weight). This is true for both gas and cryogenic liquid tanks, although for different reasons. For gas tanks, the structural integrity of the tank favors a minimized tank surface, as it allows more material to resist internal pressure through tensile forces rather than bending. For cryogenic liquid tanks, in turn, the surface must be minimized in order to limit heat exchange with the much warmer ambient environment, hence reducing the energy needed to keep the tank in a cryogenic state.
In practice, cylindrical tanks are the most common, since a spherical shape is difficult to manufacture and hard to integrate with other elements. Cylindrical tanks, especially with low L/D ratio, are usually placed inside the fuselage, since putting them outside would significantly increase the drag of the aircraft. However, filling the fuselage with large hydrogen tanks comes at a price, too, as available space for passengers and cargo is limited, making this solution less economically viable. This is a major disadvantage of hydrogen solutions with respect to kerosene-based fuel, which is often stored in variable-geometry tanks integrated into otherwise unused cavities in the wings and fuselage.
For hydrogen combustion solutions, integration challenges largely end after the fuel leaves the tank, as it is transported via fuel lines to the engine, both of which are fairly similar to currently utilized solutions. For hydrogen-electric propulsion, however, the next element in the system is a fuel cell stack with all the necessary supporting infrastructure. The shape of the stack is rectangular, which is helpful in terms of integration with other elements, but its size is strictly defined by current/voltage requirements and cannot be changed without altering those. Air must be provided for it, and excessive heat and water vapor removed, which limits its placement within the aircraft infrastructure. Finally, high-power electric cables must connect it with the electric motor, so nearby placement is preferred, as it reduces overall weight of propulsion system and energy loss due to cable resistance. A similar observation applies to hydrogen tanks, although to lesser extent, as the fuel lines are usually lighter and allow for more flexible routing than high-voltage electric cables.
Finally, the electric motor itself is cylindrical, but its weight and volume are much less than these of a combustion engine of comparable power. It also generates much less heat and vibrations, does not require external air intake or exhaust systems for removing combustion products. In this aspect, hydrogen-electric propulsion offers a major advantage over conventional airplane propulsion, where engine placement and integration are of primary importance during design process.
The next feature to address are hydrogen leaks. As mentioned above, due to its molecular properties, hydrogen is prone to leaking from tanks and valves. This can result in either unwanted circulation of hydrogen within the propulsion system when it is supposed to be shut down, or even accumulation in undesired spaces, posing a risk of fire or suffocation to crew or passengers.
Uncontrolled hydrogen circulation in a propulsion system primarily entails fuel loss, which is never desired. However, the risk of self-ignition in combustion engines or spontaneous current generation in fuel cells are not likely, since both require a supply of air from outside to maintain the reaction. Hydrogen accumulation within the aircraft, in turn, is equally unlikely precisely because of the aforementioned molecular properties – when leaks from a fuel system do occur, hydrogen tends to escape quickly to the outside environment instead of accumulating inside.
As for the risk to humans onboard, hydrogen is not directly toxic, and excluding the risk of open flame or explosion – both of which are not likely for concentrations below 4% – the only serious risk is asphyxiation, which would require a hydrogen concentration in the air high enough to decrease the oxygen concentration below breathable levels. In this regard, hydrogen is no different than any other non-toxic gas.
As previously discussed, the only significant source of heat in hydrogen-electric propulsion systems – aside, of course, from hydrogen combustion engines – is the fuel cell stack. However, PEM fuel cell stacks have been in use for a long time, including in a wide range of space and automotive industry applications, and current cooling systems are tackling the problem effectively.
A hydrogen combustion engine is assumed to have heat rejection close enough to currently utilized turbofans and as such does not require a separate analysis here.
Finally, special attention must be given to cryogenic liquid hydrogen tanks. These tanks must be thermally insulated and kept away from major heat sources in order to minimize hydrogen boil-off and reduce the energy needed to maintain cryogenic conditions.
When hydrogen is stored as a gas, only tanks that can withstand the highest possible pressure should be considered. As noted above, hydrogen loses a lot of its advantages when stored at low volumetric density. However, this increases the risk for crew and passengers, as well as for ground crew and operators, since any damage that compromises tank integrity can have serious consequences. This balance must be carefully considered when designing the system and all possible precautions against overpressurizing the tank (limiting heat rejection to it, redundant safety valves, structural supports and protections) should be applied where possible.
For cryogenic liquid tanks, the risk of overpressurizing is lower and easier to manage with controlled boil-off and low gas pressure in the system. Nonetheless, it should not be neglected, as high temperature gradients within the system are more likely to generate defects and damage over time.
The high cost of world-wide implementation of hydrogen airport infrastructure remaines the most often-cited roadblock to the hydrogenization of air transport. Even assuming a slow and gradual implementation, the minimum steps are very extensive:
Establishing regulatory and policy frameworks that facilitate the actual implementation of hydrogen as an aviation fuel [28]. This includes the certification of propulsion systems, engines and airplanes, handling and maintenance requirements, as well as the airport infrastructure itself (relevant ISO regulation 15594 was withdrawn in 2004 [29]). Lastly, it includes policies and incentives on the part of governments and major international organizations to lower the entry barriers for early technology adopters. Scaling up the production of hydrogen from renewable sources to meet future demand. A lesson can be drawn here from the limited uptake of Sustainable Aviation Fuels (SAF), where insufficient output led to reduced interest in the technology and flatlined its advancement. Based on currently available numbers for hydrogen production, the following conclusions can be drawn:
According to IATA estimates [30], global consumption of kerosene in 2024 was roughly 100 billion US gallons, so about Assuming kerosene energy density of 43 MJ/kg, total energy consumed was Hydrogen combustion systems have similar total efficiency to currently utilized turbofans. Hydrogen-electric propulsion systems have a much higher efficiency, but this gain may be reduced by overall challenges of handling and distributing hydrogen worldwide, especially in cryogenic state. For the purposes of this simplified estimation, all efficiency impacts will be neglected. Assuming a hydrogen energy density of 120 kg/MJ, replacing all kerosene-based aviation propulsion with hydrogen propulsion would entail total worldwide demand of about Current worldwide production of hydrogen is about Additionally, “green” hydrogen is currently more expensive than conventionally produced hydrogen, and this price premium is expected to persist for much of the scale-up phase. Developing a distribution network from hydrogen production facilities to at least most major airports worldwide Installing hydrogen storage and refueling infrastructure at airports.
Even if smaller aircraft and regional airports continue to rely on fossil fuels for an extended transitional period, the scale of this undertaking is vast. Although detailed cost assessments are still limited, it is reasonable to estimate that full implementation will require billions of dollars in investment and several decades to complete.
While eliminating carbon oxide and dioxide emissions is an undeniable advantage of hydrogen propulsion, it is important to acknowledge than using hydrogen either in a combustion or electric propulsion system results in significant emissions of water vapor. For instance, when 1 kg of hydrogen is burned, 9 kg of water are produced. Based on the previous global consumption estimate, this would translate to roughly
The issue of increased contrail formation resulting from hydrogen use is intentionally omitted from this discussion, as it currently lacks sufficient research and conclusive findings regarding its environmental impact.
So far, this paper has identified three main barriers hindering the widespread implementation of hydrogen aviation – hydrogen storage problems, insufficient hydrogen infrastructure, and problematic airplane integration. In this section, a Minimum Viable Product (MVP) approach will be used to determine the most suitable platform that would serve as the first step to commercial hydrogen aviation.
The first step to make hydrogen aviation a reality is to define a product which will be the easiest to bring to market. A concept deriving from Lean Startup methodology, a Minimum Viable Product (MVP) is the simplest possible version of a product, designed to test a product idea and gather feedback from first clients. It focuses on delivering just enough to satisfy early customers and allow for validation of product assumptions. MVPs enable quick prototyping and stress-testing of product concepts to iterate and improve based on real-world user experience.
History shows that transformative innovations are best introduced gradually, allowing users to familiarize themselves and adopt them step by step. This incremental exposure reduces resistance and fosters acceptance. Consequently, the initial rollout of hydrogen in aviation should not aim to replace large commercial aircraft but should instead follow a cautious, phased approach, taking the smallest possible steps, similar to that adopted for SAF. If the first implementation is too ambitious, it is unlikely to gain traction. It is imperative to remember that this is a major modification of existing technology, and every major stakeholder is likely to oppose it:
Existing airplane production companies will fight to remain on the market. Regulators will not prepare new regulations unless there is great external pressure for them to do so. The general public – in this case, airlines customers – will not support an innovation they find unfamiliar or view as less safe.
Cost is another critical consideration. Developing a hydrogen-powered airliner will require hundreds of millions of dollars, while a smaller airplane much less expensive.
Taken together, these factors – the cost of introduction, the amount of regulations to be re-written, and competition from already established aviation market giants – entail that the MVP for hydrogen aviation should be a Light or Ultralight category General Aviation (GA) airplane.
The second major issue to be addressed in this paper is determining the most suitable hydrogen storage method and propulsion type. Based on considerations in the previous chapter and the first requirement defined above, it can be assumed that for a Light or Ultralight category airplane storing hydrogen as a gas in pressurized tanks is the most feasible solution. As for the propulsion type – combustion or electric – this can also be decided purely based on the size of the airplane. Light or Ultralight airplanes generally do not need much power in comparison to airliners and tend to use propellers instead of turbine engines. Given these two characteristics, electric propulsion with a propeller is the most suitable option for powering the MVP hydrogen aircraft.
The cost of implementing hydrogen infrastructure at airports on a wide scale will be significant, to say the least. A major limitation is that airplanes – in opposition to cars – travel to a wide array of destinations over their lifetimes. With cars, it is relatively straightforward to install hydrogen refueling stations within a limited geographic area, allowing all vehicles in that area to access fuel reliably. In contrast, aircraft operate across vast and often international networks: equipping just two airports with hydrogen infrastructure is a significant investment, yet it would enable just one route to be serviced by hydrogen-powered aircraft. Given that commercial aircraft from leading manufacturers are sold and operated globally, it is unlikely that the aviation industry would seriously consider hydrogen airliners without a minimum of 50 major international hubs being equipped for hydrogen refueling.
However, an alternative strategy – particularly relevant for a Minimum Viable Product strategy – could involve adapting just a single one airport with hydrogen infrastructure and limiting airplanes to start and land on this one airport. This mirrors the operational model of most flight training schools, where aircraft take off and land at the same airport. This strategy offers multiple benefits:
It drastically reduces initial infrastructure costs, making the first steps toward hydrogen aviation financially viable, without requiring billions of dollars at hand. It aligns with existing flight training models, which predominantly use two-seat Light or Ultralight category aircraft. These aircraft have low fuel requirements, minimizing hydrogen demand and easing supply and storage logistics. It eliminates the need for international coordination and broad regulatory change in the early stages of development.
By focusing on the training segment of general aviation, this infrastructure model provides a practical and scalable starting point for hydrogen aviation, allowing the technology and its supporting systems to mature before broader deployment.
As with any integration of complex engineering systems, optimal results are achieved when an aircraft and its propulsion system are designed together from the outset of the design process. This approach enables a more streamlined and efficient design, allowing potential integration challenges to be identified and addressed early in the development process.
A common limitation among previous hydrogen-powered aircraft projects – such as the Martin B-57B, Tupolev Tu-155, and ENFICA-FC – was that they were based on adapting already existing designs. This invariably results in highly sub-optimal integration of the propulsion system into the airplane infrastructure, negating a large share of the advantages that hydrogen propulsion can offer. The sole exception – the HY4 project – was purely a research platform and did not have any commercial mission defined.
An aircraft designed from the outset with the explicit intention of incorporating hydrogen propulsion is far more likely to fully realize the advantages of this technology and effectively mitigate its inherent limitations.
In a world of ever-increasing environmental awareness, the need to reduce aviation-related emissions is beyond dispute. Among the long-term alternatives to conventional combustion engines, hydrogen propulsion, involving either combustion engines or fuel cells and electric motors, is a particularly promising solution.
This paper has reviewed the principal challenges hindering the development of this technology – hydrogen storage problems, insufficient hydrogen infrastructure, and problematic airplane integration being the three most significant ones. While it appears that these challenges are considerable, they are not insurmountable – although overcoming them will require substantial investment of both time and financial resources.
As a first step of implementation, a Minimum Viable Product is proposed for hydrogen aviation. This MVP may be defined as follows:
This definition allows for all the challenges discussed within this paper to be addressed and offers the best chances of successful early commercialization of hydrogen aviation. In addition, this airplane should meet all the requirements usually stated for training airplanes, which mostly result from the fact that such airplanes are operated by inexperienced students. It ought to have a quite low stall speed, gentle stall characteristics and a high stall angle of attack, be stable and controllable across whole range of allowable flight speeds, and reliably recover from dynamic disturbances. Regarding its performance, the airplane’ range and endurance should be maximized, as both of these allow for more extensive pilot training.
Further research is needed to explore the broader implications of using hydrogen in aviation, with key focus areas including:
the long-term climate impact of increased water vapor emissions, detailed regulatory requirements for the safe usage of hydrogen in airplanes and at airports, the most efficient methods for the production, delivery and long-term storage of sustainable hydrogen, increasing the energy density of hydrogen storage systems and the power density of hydrogen combustion engines, fuel cells and electric motors the life cycle, utilization, monitoring and failure modes of hydrogen airplanes and propulsion systems.