At the AIAA Aviation Forum 2024 in Las Vegas, a selected panel of experts from across the aerospace sector came together to address one of the most pressing challenges facing the industry today: the impact of in-flight icing on disruptive aircraft designs, such as fully-electric aircraft, UAVs, and eVTOLs. The panel was led by the director of the NTNU UAV Icing Lab, Dr. Richard Hann, and featured leading voices in the field, including Dr. Andy Broeren (NASA Glenn), Dave Leopold (Archer Aviation), Galdemir Botura (Collins Aerospace), Paul Pellicano (FAA), and Rohit Goyal (Boeing).

The panel discussed that as the aerospace industry accelerates towards advanced air mobility (AAM) and new aircraft configurations, the traditional understanding of in-flight icing and its mitigation is being pushed to its limits. The discussion highlighted that with these novel aircraft designs, the industry is venturing into uncharted territory—what the panel referred to as “unknown unknowns.” These unknowns encompass a range of new challenges that are emerging as the industry strives to meet the demands of next-generation aviation. One of the most critical takeaways from the panel was the pressing need for research to address these emerging challenges. The complexity of these new aircraft designs, combined with the lack of historical data, has created a knowledge gap that the industry must urgently fill. The panelists emphasized the necessity of targeted research and collaboration to better understand the icing phenomenon as it relates to these innovative platforms.

Another key point of discussion was the uncertainty surrounding the certification roadmap for these advanced aircraft. The current certification requirements, designed for traditional aircraft, may not adequately address the unique vulnerabilities of eVTOLs, UAVs, and other new configurations. The panel called for more specific requirements and the development of icing envelopes tailored to these designs, stressing that regulatory bodies need to support this research to ensure safety without stifling innovation. Innovation is undoubtedly at the heart of the solutions being proposed to tackle these challenges. However, the panelists also acknowledged that while there are many promising ideas, they often lack the maturity needed for practical application.

In conclusion, the panel at AIAA Aviation Forum 2024 underscored the importance of a collaborative approach to address the “unknown unknowns” in in-flight icing for advanced aircraft. As the industry moves forward, continued dialogue between industry leaders, researchers, and regulatory bodies will be crucial to develop the necessary technologies and frameworks to ensure the safe and reliable operation of these next-generation aircraft. The forum served not only as a platform for knowledge exchange but also as a call to action for the entire aerospace community to work together in overcoming these emerging challenges.

Last week, the AIAA Aviation Forum 2024 took place in Las Vegas, with over 2,900 attendees from more than 41 countries. The UAV Icing Lab participated and presented the latest developments in the field of UAV icing. The following papers with involvement from the lab were presented at the conference:

• Hann, R., Müller, N.C., Wallisch, J. (2024). UAV Icing: Impact Testing of Ice Fragments on a Propeller. AIAA 2024-4352. AIAA Aviation Forum and Ascend. doi.org/10.2514/6.2024-4352
• Müller, N.C., Hann, R. (2024). UAV Icing: Validation of an Ice Protection System Design for a Propeller. AIAA 2024-3568. AIAA Aviation Forum and Ascend. doi.org/10.2514/6.2024-3568
• Løw-Hansen, B., Hann, R., Johansen, T.A, Deiler C. (2024). Time-Domain System Identification and Validation of Small Fixed-Wing UAV Dynamics. AIAA 2024-4653. AIAA Aviation Forum and Ascend. doi.org/10.2514/6.2024-4653
• Linder, M., Hann, R. (2024). UAV Icing: Comparison of Simulated 3D and 2D Ice Accretion on Wings. AIAA 2024-4451. AIAA Aviation Forum and Ascend. doi.org/10.2514/6.2024-4451
• Laurendeau, E., Blanchet, M., Zayni, M.K., Hann, R., Radenac, E., Mussa I, Pueyo A. (2024). Summary From the 2nd AIAA Ice Prediction Workshop. AIAA 2024-3604. AIAA Aviation Forum and Ascend. doi.org/10.2514/6.2024-3604

We are thrilled to announce that the Norwegian Research Council (RCN) will be supporting our 2nd International UAV Icing Workshop with a grant of 100,000 NOK. The workshop will be held in Trondheim 03-04 December and organised by the UAV Icing Lab. This funding will allow us to keep the event free for all attendees, ensuring broad participation and knowledge sharing. With RCN’s support, we are excited to enhance the workshop experience, offering more sessions and networking opportunities for professionals in the UAV industry. We thank the RCN for their support in advancing UAV technology and safety!

The NTNU UAV Icing Lab has obtained funding for a new research project in collaboration with UBIQ Aerospace. Together, they have received 9.1MNOK (0.8MEUR) in funding from the Norwegian Research Council for an innovation project with the title Zero Ice Shield: D•ICE Ice Protection for Aviation’s Green Evolution.

The project’s motivation is the development of new mobility solutions for aviation, transitioning towards green technologies like electric, hybrid, or zero-emission aircraft. These emerging green aircraft concepts, while still under development, will play a pivotal role in reducing emissions within the aviation sector and achieving climate goals. However, as these aircraft concepts are becoming more and more technically mature and commercially viable, they need to address an ongoing threat to aviation safety: in-flight icing.

Today’s ice protection systems are designed primarily for conventional large passenger transport aircraft (airliners) with large, power-intensive engines. Traditional ice protection systems do not align with the stringent size, weight, and power constraints required for novel zero-emission aircraft concepts. The mismatch highlights a pressing need for innovation in ice protection technologies – an innovation that will be addressed with the current research project.

Together, UBIQ Aerospace and the NTNU UAV Icing Lab, will adapt and develop UBIQ’s existing D•ICE electrothermal ice protection system and ice detection to be suitable for zero-emission large passenger aircraft. The project will furthermore focus on certification requirements for such technologies and conduct experimental testing in icing wind tunnels and flight.

In a recent presentation at the AIAA SciTech Forum and Exposition in Orlando, master student Markus Frey had the pleasure of representing the NTNU UAV Icing Lab. In this session, we explored innovative research set to revolutionize the safety and reliability of Unmanned Aerial Vehicles (UAVs) operating in challenging weather conditions. The focus was an Electro-Thermal Ice Protection System (ETIPS) designed specifically for UAV propellers, integrating both experimental and numerical investigations.

Propeller Sensitivity to Ice Accretion:

Propellers, with their high rotation rates and small size, are particularly sensitive to ice accretion. The consequences include a substantial reduction in thrust generation, increased torque, and potential dangers associated with ice shedding. Traditional ice protection systems, well established in manned aviation, present unique challenges when adapted for UAVs due to energy limitations and strict mass constraints. Our research is focused on ETIPS, specifically designed for UAV propellers. These systems operate on the principle of resistive heating, keeping the critical surface spots above the freezing temperature.

Balancing Act – Ice-Free Propellers and Structural Integrity:

One often-overlooked aspect in anti-icing investigations is the thermal impact on propeller structures, particularly those made from composite materials. While composites offer advantages in terms of weight, stiffness, and strength, they are sensitive to high structural temperatures. The delicate balance between electro-thermal heating to keep propellers ice-free and preserving the structural integrity of composite materials presents a major challenge.

Experimental and Numerical Investigations:

Our study builds on previous research and introduces protected propellers for experimental analyses, aiming to provide a more comprehensive examination of the internal temperature distribution. The goal is not only to keep the propeller surface ice-free but also to maintain low internal temperatures, ensuring the longevity of composite materials. Numerical conjugated heat transfer simulations, utilizing ANSYS FENSAP-ICE, play a crucial role in predicting temperature distributions within the propeller. These simulations, validated against literature and the experimental data, provide insights into the ETIPS performance under realistic in-flight conditions.

Two Optimization Strategies:

In optimizing our Ice Protection System, two key strategies emerge from our study. The first involves integrating additional ETIPS modules along the propeller’s surface, strategically placed between the glass fiber layers. This aims to maintain more of the upper surface above freezing temperatures, preventing runback ice accumulation. The second strategy explores the impact of material composition, specifically introducing a thin copper layer into the propeller structure. This alteration enhances heat conductivity, reducing heat resistance, and improving both ice prevention and heat dissipation. These strategies, guided by numerical simulations aligned with experimental conditions, offer promising results for enhancing the effectiveness of ETIPS and ensuring safer UAV operations in challenging weather conditions.

Conclusion:

In summary, our research on ETIPS for UAV propellers introduces innovative strategies. By incorporating additional ETIPS modules and exploring material enhancements like a thin copper layer, we aim to improve ice prevention and heat distribution. These findings contribute to the ongoing effort to enhance the operational safety of unmanned aerial vehicles in challenging climate conditions. Our research takes us a step closer to improve ice protection systems, ensuring that UAVs work reliably.

Reference: Frey, M., Müller, N.C., Wallisch, J., Hann, R. (2023). UAV Icing: Validation of a numerical model to calculasite the Temperature of an Ice Protection System for a Propeller of a UAV. AIAA SCITECH Forum. AIAA 2024-0871.doi.org/10.2514/6.2024-0871

Text: Markus Frey

Last week, our team from the UAV Icing Lab had the privilege of attending the NTNU Clean Aviation evening with Rolls-Royce, Avinor, and Widerøe. This event not only provided us with a deeper understanding of the latest trends in aviation technology but also opened our eyes to the significant potential for synergy between our work on UAV icing solutions and the emerging field of zero-emission aircraft.

The Challenge of Power Budget in Zero-Emission Aircraft
One of the most striking revelations from the event was the tight power budget that fully-electric or hydrogen-powered aircraft operate within, especially when compared to traditional aviation. These innovative aircraft designs are at the forefront of clean aviation, aiming to reduce emissions and revolutionize air travel. However, their success hinges on efficiently managing power consumption, a challenge where our expertise in UAV icing solutions can play a crucial role.

UAV Icing Solutions: Optimized for Efficiency
Our work at the UAV Icing Lab has always been geared towards optimizing solutions for size, weight, and power. These considerations are paramount in UAV design, where every gram and watt counts. By adapting these icing solutions, initially developed for UAVs, to clean aviation aircraft, we can significantly reduce the power consumption required for ice protection systems. This reduction is not just a technical improvement; it’s a critical step in making zero-emission aircraft feasible and viable.

The Road Ahead
Inspired by the discussions and insights gained at the NTNU Clean Aviation evening, the UAV Icing Lab is now more committed than ever to contributing actively to the clean aviation sector. We are excited to announce that we will be focusing on developing new research projects aimed at adapting our UAV icing innovations for use in zero-emission aircraft. This direction not only aligns with our expertise but also contributes to a more sustainable and environmentally friendly aviation industry.

The NTNU UAV Icing Lab, together with Mejzlik Propellers, and UBIQ Aerospace have developed a system to protect the propellers of UAVs when flying in icing conditions. In clouds in cold conditions, the propeller can collect ice and reduce the aerodynamic efficiency of the propeller. The developed electro-thermal ice protection system prevents ice accretion and retains propeller performance in icing conditions. Our research opens new possibilities for safe and reliable UAV operations in challenging weather environments. 

Ice accretion will decrease the propeller’s performance by disturbing the airflow around the propeller blade. This will lead to a significant loss of thrust and strong vibrations.  Propellers are very sensitive to icing and ice up very fast – within 100s the propeller can lose more than 80% of its efficiency. In addition, vibrations exceeding 10G can damage the drive train. These effects are a large hazard to the UAV and can lead to the loss of propulsion and subsequent loss of aircraft.

We used state-of-the-art CFD techniques to engineer an advanced propeller ice protection system tailored for in-flight use during icing conditions. The system incorporates carbon fiber heaters within the propeller blade, deterring ice formation and facilitating the shedding of any formed ice. 

The developed ice protection system was able to prevent ice accretion at a temperature of -5°C, and at lower temperatures, it was able to reduce the impact of atmospheric icing on the propeller significantly.   

This collaborative effort with UBIQ Aerospace, the UAV Icing Lab and Mejzlik Propellers represents the first step in developing a mature ice protection system for UAVs. This will enable UAV operations in cold-climate regions. 

Reference: Müller, N.C., Løw-Hansen, B., Borup, K.T., Hann, R. (2023). UAV icing: Development of an ice protection system for the propeller of a small UAV. Cold Regions Science and Technology, 213, 103938. doi.org/ 10.1016/j.coldregions.2023.103938

Text: Nicolas C. Müller

As the year 2023 comes to a close, it’s time to look back at a year filled with significant achievements and advancements in the field of Unmanned Aerial Vehicle (UAV) icing research. It has been an important year for the UAV icing research field and the NTNU UAV Icing Lab has contributed some of the key achievements.

Highlights from 2023

1. SAE Icing Conference: This year’s SAE Icing Conference in Vienna was a landmark event for UAV icing research. It featured a record number of papers dedicated to UAV icing. Our lab proudly contributed six of these papers on a wide range of topics such as icing on wings, propellers, ice protection systems, path-planning, and ice detection.
2. 2nd AIAA Ice Prediction Workshop: The 2nd edition of this workshop was another highlight of the year. Our lab contributed a UAV icing case with low Reynolds numbers that was featured in this important workshop. The results showcased that many ice prediction codes have substantial gaps for simulations of UAV icing cases.
3. Collaboration with UBIQ Aerospace: Perhaps one of our most impactful collaborations of 2023 was with UBIQ Aerospace. Together, we developed an ice protection system for UAV propellers. This system was tested under moderate icing conditions and impressively maintained 70% efficiency over a 10-minute period. This success marks a significant step forward in our quest to make UAVs safer and more efficient in icy conditions.

Outlook for 2024: Expanding Horizons

As we move into 2024, the UAV Icing Lab is poised for another year of innovation and discovery.

1. 2nd UAV Icing Workshop: Building on the success of our previous workshops, we are excited to host the 2nd UAV Icing Workshop. This will be a platform for sharing new research, fostering collaborations, and discussing the future directions of UAV icing research. More information will follow soon.
2. AIAA Aviation Conference in Las Vegas: We are geared up for the AIAA Aviation Conference in Las Vegas, where we aim to submit six papers. Our ongoing research promises new insights and advancements in UAV icing, and we look forward to sharing these with the global community.
3. Continued Collaborations and Wind Tunnel Tests: Our journey doesn’t stop here. We will continue our collaborations with industry partners and conduct more icing wind tunnel tests. These efforts are vital for developing more effective icing mitigation strategies and technologies for UAVs.

The NTNU UAV Icing Lab wishes you happy holidays and a good start to an exciting 2024!

**NEW PUBLICATION** Atmospheric in-flight icing is a significant threat for all aircraft, in particular for unmanned aerial vehicles (UAVs). Hence, most UAVs require a mitigation plan in order to fly safely in icing conditions, at least in the more severe icing conditions. One way of protecting the aircraft against the negative influences of icing is the use of ice protection systems (IPS). Most research on IPS for UAV wings has been with electrothermal IPS, i.e., systems that heat the protected area electrically above the freezing temperature. 

What is known and what isn’t 

Previous studies (How much energy is required to prevent ice on UAVs? and Efficient ice protection systems – Timing is everything) found that the operation of the electrothermal IPS in de-icing mode required less energy than the operation as anti-icing system. De-icing systems allow some ice to accumulate before the ice is removed, while anti-icing systems prevent ice to accumulate on the protected surfaces at any time. Additionally, previous studies showed that the usage of a parting strip increases the energy efficiency of the IPS. The parting strip is a continuously heated element that is located at the leading edge of the wing and divides the ice shape into two parts. As can be seen in the figure above, this allows the aerodynamic forces to push the ice from the wing once the primary and secondary zones have melted a sufficient layer of ice. 

Several studies exist that aimed to optimize the energy used on thermal de-icing IPS. However, only few studies also considered the aerodynamic influence of intercycle ice. Intercycle ice is the ice that is allowed to accrete before the de-icing is started. The studies that also considered the intercycle ice shapes typically only investigated the ice thickness of the intercycle ice. To our knowledge, no study exists that quantifies the energy required for an IPS and the energy required to generate enough thrust for the UAV to continue its flight in icing conditions. This gap is intended to be filled with the new publication. 

Energy efficiency – new results 

For this study, the required IPS energy was determined experimentally from icing wind tunnel tests. The intercycle ice shapes and the drag increase they cause were simulated using the icing CFD code ANSYS FENSAP-ICE. An exemplary result is shown below for the flight of a UAV in icing conditions at −2 °C with different intercycle times and allows for multiple findings. First, the required energy to compensate for intercycle drag is smaller than the energy required for an IPS. As a result, parting strip de-icing remains more energy-efficient than conventional de-icing and anti-icing, even when considering the intercycle drag. Second, the added intercycle drag can cause shorter intercycle times to be more energy-efficient than longer intercycle times. Third, flying without an IPS can be the most energy-efficient setting when only looking at the energy required to fly through a specified cloud. 

So should UAVs fly without IPS? 

While the results of the study indicate that no IPS might be the most energy-efficient method of flying in icing conditions, this does not mean that it is the best option for a UAV to not have an IPS at all. First, the study only compares the energy required for the flight through a specified cloud. If the UAV was not equipped with an IPS, it would continue to fly with the reduced aerodynamics caused by the ice accretion even after exiting icing conditions. Thus, when comparing an entire flight, flying with an IPS is likely to be more energy-efficient than flying without an IPS. Second, the quality of an IPS does not only depend on its energy efficiency. Ice accretions on the wing also reduce the stall angle and increase the risk of accidents in flight situations with larger angles of attack, e.g., during the approach. Furthermore, ice accretions are likely to reduce the maneuverability and stability of the aircraft. Hence, the perfect usage of an IPS is likely dictated by the amount of ice that can be on the wing of an aircraft without risking the aircraft to become unstable. 

The new publication presents valuable information on the energy efficiency of IPS for the wings of UAVs. This knowledge helps to develop better IPS and to implement IPS settings that optimize the energy need. The results show that longer intercycle times are in general more energy-efficient but the influence of intercycle ice on the aircraft’s stability was neglected in this study. Hence, for a further optimization of the IPS, investigating the influence of intercycle ice shapes on the stability and maneuverability of aircraft is required. 

Reference: Wallisch, J. and Hann, R., “UAV Icing: Intercycle Ice Effects on Aerodynamic Performance,” SAE Technical Paper 2023-01-1400, 2023, https://doi.org/10.4271/2023-01-1400. 

Text: Joachim Wallisch

Title image: Microsoft Bing Image Creater