Unravelling the links between heatwaves and aircraft performance

Engineers and pilots are well aware of the challenges posed to aircraft by the scorching heat waves hitting various countries these days. Let's delve into a simplified explanation for those less familiar with these phenomena, to explain why warm weather can deteriorate an aircraft's performance to the point that it must be grounded.?

One key factor impacting aircraft performance is air density. As we all know, the lift force is crucial for an aircraft to take flight. However, the lift force also depends on the fluid density, in this case the air that the wings move through. When temperatures rise, air density decreases, reducing the available lift force. The result? Higher take-off speeds, extended runway requirements, and flatter climbing angles. Each one of these factors can pose safety concerns.

Every time pilots take off, they meticulously analyze pressure, temperature, humidity and calculate their aircraft performance to ensure they have the necessary lift force to clear obstacles. Extreme summer temperatures can bring you to the point where your flight is delayed or cancelled for safety reasons.

Another critical aspect to consider is engine thrust. Engines have maximum turbine temperatures, and take-off demands higher thrust, which leads to increased internal temperatures. In hot weather, the external air temperature and lower air density put additional strain on the engine. To prevent overheating, pilots input external temperatures into flight computers to determine the achievable maximum engine thrust. It could not be enough for a safe take-off (where you should always consider the possibility of an engine failure too). ?

Just a curiosity: Airlines often use take-off power below 100% for noise reduction, extended engine life, and fuel savings. The aircraft computer defines the safe take-off power considering several factors such as weather, altitude, aeroplane weight and runway length.

The aircraft structure can suffer too. Metals expand with high temperatures, and modern aircraft, often made with composite materials, have temperature limitations, which pilots check during pre-flight inspections to ensure safe operation. Most aircraft are painted in light colours to help mitigate the temperature-induced stresses on the aircraft's structure.

Cold temperatures can also be problematic during flight. There is a minimum operational temperature, and if it gets too cold at high altitudes, fuel may freeze in the pipes, requiring descent or speed adjustments.

Looking ahead, aircraft design evolution also focuses on aerodynamics, light-weighting and new propulsion systems. Cutting-edge technologies like topology optimization, additive manufacturing, and composite materials are crucial in improving performance.

These advancements will not only improve planes' performances, allowing them to fly on hot days, but also drive fuel efficiency, environmental sustainability, and reduced operating costs.

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