Preliminary Design of Hybrid Aircraft Thermal Management System (Tms) Experimental Test Campaign in Cira Icing Wind Tunnel (IWT)
This paper outlines the preliminary design and ongoing upgrades of CIRA's Icing Wind Tunnel to enable full-scale experimental validation of hybrid aircraft Thermal Management Systems with power levels up to 0.5 MW under realistic flight conditions within the EU-funded AMBER project.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
The sky above is becoming a crowded place for a new kind of traveler. For decades, the aviation industry has relied on burning fuel to push massive metal tubes through the air, a process that releases carbon dioxide and other gases into the atmosphere. To meet global climate goals, engineers are now designing aircraft that run on electricity or a mix of electricity and fuel. These hybrid and electric planes promise a cleaner future, but they bring a hidden problem that has nothing to do with the air they fly through. The batteries, electric motors, and fuel cells that power these new machines generate an immense amount of heat. Just as a laptop slows down when it gets too hot, these powerful components can fail or lose efficiency if they cannot shed that heat quickly. The challenge is to build a cooling system that works perfectly whether the plane is sitting on the runway in summer heat or climbing through freezing air at high altitude. If the system is too small, the engine overheats; if it is too big, the extra weight and air resistance ruin the plane's range.
Researchers at the Italian Aerospace Research Centre, known as CIRA, are tackling this puzzle by building a new kind of laboratory test. They are upgrading their Icing Wind Tunnel, a massive facility originally designed to study how ice forms on airplane wings, to instead test the thermal management systems of these future electric aircraft. The team, led by Marco Invigorito and colleagues, realized that computer models alone were not enough. While simulations can predict how a cooling system might behave, they often miss the complex reality of how air flows around a real plane. To solve this, they first ran detailed computer simulations of a heat exchanger—a device that moves heat from a hot liquid to the cold air outside. They modeled a flight path for a regional aircraft, tracking the system's performance from the ground up to an altitude of 5,500 meters. The results of these simulations revealed a surprising and dangerous flaw in the way these systems are currently designed.
When the researchers looked at the data, they found that a cooling system sized to work safely on the ground would be dangerously overpowered once the plane took off. As the aircraft climbed higher, the air outside became colder and thinner. In their simulation, a system designed to handle 300 kilowatts of heat on the ground suddenly found itself capable of rejecting more than 900 kilowatts of heat at high altitude. This massive increase in cooling power, while seemingly a good thing, created a new problem. The fuel cells inside the plane operate best within a narrow temperature window. If the cooling system becomes too efficient at high altitude, it could drop the temperature of the fuel cell liquid to 50.8 degrees Celsius, far below the safe operating range. This "hypothermia" for the fuel cell could cause it to lose efficiency or stop working entirely. To prevent this, engineers would have to add complex valves and controls to throttle back the cooling, which adds weight and creates more points of failure. Alternatively, if they sized the heat exchanger only for the high-altitude conditions, it would be far too large and heavy for takeoff, creating unnecessary drag and wasting fuel.
To understand exactly how to solve this, the team is transforming their wind tunnel into a testing ground for full-scale cooling systems. The facility, which can simulate flight speeds up to Mach 0.7 and temperatures as low as minus 40 degrees Celsius, is being fitted with a new thermal generation system. This system can pump a heated liquid through a test article at rates of up to 1,200 liters per minute, mimicking the heat output of a real electric motor or battery. Unlike standard test benches that use fans to blow air over a radiator, this wind tunnel uses the natural pressure of the moving air to push air through the cooling system, just as a real plane does. This allows researchers to measure not just how well the system cools, but also the aerodynamic drag it creates and how ice might form on its surfaces during flight.
The upgraded tunnel will allow the team to run tests that match the specific flight profiles of regional aircraft, moving from ground conditions to high-altitude climbs while monitoring every degree of temperature and every drop of pressure. They plan to test how the system behaves when the plane is flying straight, but also when it is turning or slipping sideways, conditions that computer models struggle to predict accurately. By combining these physical tests with their earlier simulations, the researchers aim to create a reliable method for sizing these cooling systems. The goal is to find a design that is light enough for takeoff, powerful enough for high-altitude flight, and simple enough to be safe. This work is part of the larger AMBER project, funded by the European Union, which seeks to validate the technologies needed for a zero-emission aviation future. The findings will help ensure that the next generation of aircraft can carry their passengers safely and efficiently, without the risk of overheating or freezing in the sky.
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