Amsterdam’s NLR completed the first flight of its drone powered by liquid hydrogen in Dutch airspace. The flight tested hydrogen technology and safety procedures.
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Amsterdam-based NLR – Netherlands Aerospace Centre announced the first test flights of its HYDRA II drone powered by liquid hydrogen. The flights were carried out at NLR’s site in Marknesse, a village in the Dutch province of Flevoland.
This marks the first time an aircraft has flown in Dutch airspace using liquid hydrogen as a fuel source. The drone remained airborne for several minutes, confirming the use of liquid hydrogen as a fuel carrier and its safe handling during flight.
The HYDRA II drone’s electric motors ran on power from a fuel cell, with a battery adding extra thrust when required.
NLR stated that drones serve as a platform to test new energy systems in aviation. Hydrogen is considered one of the potential alternatives to kerosene in the effort to reduce emissions from aircraft. Its use requires modifications to aircraft and ground infrastructure.
Joost Vreeken, NLR programme leader for ‘Unmanned & Autonomous’, says, “For drones, the use of hydrogen comes into its own when flying long distances. A VTOL (Vertical Take-off and Landing) initially takes off vertically, using batteries, as that phase requires a relatively high power output. Once airborne, it transitions to horizontal flight, similar to a conventional aircraft, and that’s where hydrogen comes in.”
“With the current configuration, we specifically focused on demonstrating the functionality of the technology during a short hover flight.”
NLR advances hydrogen aviation research
NLR flew the HYDRA II drone powered by liquid hydrogen, following earlier tests in 2019 with the HYDRA I, which used gaseous hydrogen.
In the HYDRA II, hydrogen is stored in a vacuum-insulated aluminium tank developed in collaboration with a partner. The tank is placed under the drone and is not actively cooled. Heated hydrogen gradually escapes from the tank and is directed into a fuel cell, where it is converted into electricity to power the drone.
Tineke van der Veen, CEO of NLR, says, “If hydrogen is produced sustainably, it can contribute to reducing the impact of fossil fuels on the climate, as water (vapour) is the only emission from the vehicle, in this case, the drone. We see that many organisations, both domestic and internationally, are working hard to make commercial applications a success.”
“In parallel with this drone project, we are also working closely with Dutch companies such as Cryoworld and zepp.solutions to integrate liquid hydrogen into our electrically powered Pipistrel Velis Electro.”
Joost Vreeken further adds, “For NLR, the milestone achieved with the HYDRA II is of great importance because it not only shows that we have mastered the technology but also that we can safely manage the complex logistical processes involved. This includes the flight plan with safety procedures, technical aspects related to the Working Conditions Act, and the logistical chain from delivery to storage and ‘refuelling’ of the drone.”
Besides the Netherlands, others have also shown that flying on liquid hydrogen is possible. In 2023, German company H2fly conducted a test flight with support from Slovenian aircraft maker Pipistrel.
Hydrogen use and safety in aviation
Hydrogen (H2) is a very simple and common element. At normal temperatures, it is a gas that has no colour, smell, or harmful effects. When it gets extremely cold, below -252.77 °C, it turns into a liquid. This is close to absolute zero (0 kelvin).
The HYDRA II drone does not get energy from hydrogen itself, but uses it to carry energy. Inside a fuel cell, hydrogen mixes with oxygen from the air. This creates water and produces electricity, which powers the drone, along with some heat.
NLR mentions in a statement that in aviation, weight (or mass) is very important. Hydrogen has a lot of energy for its weight, which is an advantage. But because it is light, its energy in a given volume (per litre) is low at normal pressure. Cooling hydrogen to about -253 °C increases the energy per volume, but it still provides only about four times lower energy compared to diesel or kerosene.
All energy carriers, including hydrogen, have risks. Hydrogen itself is not more dangerous than other fuels if it is handled and stored correctly. However, it can catch fire more easily and requires less energy to ignite than fuels like petrol or natural gas.
To manage these risks, the HYDRA II drone has been given experimental certification, allowing NLR pilots to fly it without a Special Airworthiness Certificate (S-BvL). Additionally, during test flights, the airspace above NLR can be closed to other aircraft to ensure safety.
Advancing aerospace research and collaboration
NLR is an applied research organisation that has operated for over 100 years, focusing on making aerospace safer, more sustainable, and more efficient.
The organisation provides technical expertise and solutions through its research facilities, including field labs, simulators, and wind tunnels.
NLR works independently with the national and international industry and government. It supports safety and sustainability in society while strengthening the position of Dutch industry. The organisation connects science, industry, and government, translating research into practical applications.
In aerospace, NLR serves as a strategic partner to the Dutch government and Defence and collaborates with both small and large companies. Through these partnerships, NLR contributes to the development and implementation of aerospace technologies.
