Can it be too hot for airplanes to fly? Yes!
Airplanes rely on air density to create lift, which is the force that gets them off the ground. As temperature increases, air density decreases, affecting lift generation and thus, the performance of the aircraft. This issue impacts all aspects of flight, but it primarily a concern during take-off.
For example, dozens of flights were cancelled in Phoenix, Arizona in 2017, when temperatures exceeded 120 degrees Fahrenheit (49 degrees Celsius). The extreme heat created conditions that were not suitable for certain types of aircraft to safely take off.
Why Increasing Temperature Lowers Air Density
The relationship between temperature and air density is based on the principles of gas behavior described in the ideal gas law. The ideal gas law states that the pressure of a gas is directly proportional to its temperature and volume, and inversely proportional to the number of gas molecules.
When the temperature of air increases, the kinetic energy of the air molecules also increases, causing them to move more rapidly. This increased motion makes the gas molecules spread out or expand, occupying a larger volume. When the molecules are spread out, there are fewer of them in a given volume. In other words, there is a decrease in air density.
So, in the context of an airplane, as the air temperature increases, the density of the air (the number of molecules in a given volume) decreases. This decrease in air density reduce the aircraft’s performance. There are fewer air molecules interacting with the wings to generate lift and with the engines to provide thrust. This is why hot weather poses a challenge for aircraft, particularly during take-off when maximum lift is required.
Too Hot to Fly Because of Lift
Lift is the force that opposes the weight of an airplane and holds the airplane in the air. The flow of air over the wings of an airplane produces lift. Lift is a crucial factor in the take-off, in-flight stability, and landing of an aircraft.
The formula for lift (L) is:
L = (1/2) d v2 A CL
Where:
- d is the air density
- v is the velocity of the airplane
- A is the wing area
- CL is the lift coefficient, which is a number that encapsulates the lift characteristics of the airplane wing under specific conditions
As this formula suggests, lift is directly proportional to air density. Higher air density means more lift, and lower air density means less lift. When the temperature rises, air density decreases because the air molecules move faster and occupy a larger volume. This situation can lead to a reduction in lift, making it more challenging for an airplane to take off. Furthermore, a decrease in air density also causes the airplane to consume more fuel and reduce engine performance.
Too Hot to Fly Isn’t Just About Lift
The maximum operational temperature of an aircraft depends on several factors, not just its ability to take off.
Here are some factors that contribute to an aircraft’s maximum operational temperature:
1. Engine Performance: Engines are designed to operate within a certain temperature range. Exceeding this range leads to decreased performance, increased wear, or, in extreme cases, engine failure.
2. Material Limitations: The aircraft’s structural and non-structural materials have temperature limits. At high temperatures, certain materials lose their strength, expand, or contract, leading to structural issues.
3. Avionics Systems: The electronics and systems that control the aircraft (avionics) also have operational temperature limits. High temperatures can cause these systems to fail or malfunction.
4. Cabin Comfort: High temperatures make it uncomfortable or even dangerous for passengers and crew inside the cabin, particularly if the air conditioning system can’t sufficiently cool the interior.
While takeoff performance is a significant concern at high temperatures due to the issues with lift and air density, it is by no means the only factor that determines an aircraft’s maximum operational temperature. An aircraft is a complex system, and many of its components and subsystems are affected by temperature in various ways. Thus, ensuring its safe and efficient operation requires considering all these factors.
What Temperature Is too Hot to Fly a Plane?
There isn’t a universally applicable maximum temperature for all airplanes because different aircraft models have different operational limits depending on their design, materials, and engine performance. However, for many modern commercial jet aircraft, the maximum operational temperature is typically around 50 degrees Celsius (122 degrees Fahrenheit).
For instance, the Bombardier CRJ aircraft series has a maximum operational temperature of 47.8 degrees Celsius (118 degrees Fahrenheit). On the other hand, the Boeing 737, a common commercial jet, has a maximum certified temperature limit of 52.8 degrees Celsius (127 degrees Fahrenheit).
Heat Also Affects Helicopters
High temperatures also affect helicopter. Helicopters generate lift through the rotation of their main rotor blades, and the principles of air density apply in much the same way as they do for airplanes.
As the temperature rises and air density decreases, the rotor blades of a helicopter find less air to “bite” into, which reduces lift and makes it harder for the helicopter to climb. This is especially significant in activities like medical evacuations or firefighting, where helicopters often need to operate at maximum capacity in already challenging conditions.
What to Do When It’s too Hot to Fly
Airplane manufacturers and airlines have several ways of coping with high temperatures.
- Performance Data Adjustments: Aircraft manufacturers provide performance data for a range of temperatures. Pilots use this information for calculating the necessary speed for take-off and landing. During high temperatures, pilots may increase the speed to generate enough lift for safe operations. But, higher speed translates into a longer runway requirement so it is not an option at all airports.
- Weight Restrictions: To counteract the decreased lift, airlines enforce weight restrictions, which often involves reducing the load of cargo or limiting the number of passengers.
- Operational Timing: Another solution is operating flights during cooler times of the day, typically in the early morning or late evening, when temperatures are lower, and the air is denser.
Other Challenging Scenarios: High Altitudes
Hot weather is not the only scenario that decreases air density and creates flight difficulties. High-altitude airports, such as those in mountainous regions or the “Altiports” in the French Alps, pose unique challenges for aircraft operation. The higher the altitude, the thinner the air, which results in less lift.
These high-altitude airports require special considerations, including more powerful engines or specific design features to increase lift. Pilots also need additional training to safely operate in these environments.
Looking to the Future
As global temperatures continue to rise due to climate change, the aviation industry faces significant challenges. However, aircraft manufacturers and operators have a range of potential solutions that they can use to adapt to these conditions.
Improving Engine Efficiency
Engine efficiency plays a critical role in aircraft performance. If the engine can deliver more power without a proportional increase in fuel consumption, it helps counteract the performance issues associated with higher temperatures. Manufacturers are continually researching and developing more efficient engines, with many turning to advanced materials and innovative designs to achieve these gains.
Optimizing Aircraft Design
Aircraft design plays a key role in its performance. Enhancing the wing design for better lift generation, utilizing lightweight yet strong materials to reduce the aircraft’s weight, or optimizing the overall aerodynamics of the aircraft helps it perform better under high temperature conditions.
Developing Heat-Resistant Materials and Technologies
As temperatures rise, so does the importance of heat-resistant materials and technologies. By developing and incorporating materials that can withstand high temperatures without losing performance or structural integrity, aircraft can become more resistant to heat.
Adjusting Operational Procedures
Operational adjustments can also help deal with higher temperatures. Examples include changing the scheduling of flights to avoid the hottest parts of the day or implementing stricter weight limitations during hot weather. Additionally, more comprehensive and accurate weather forecasting helps operators plan more effectively for temperature fluctuations.
Expanding Runway Lengths
Higher temperatures and reduced air density require longer takeoff distances. Therefore, one possible solution involves expanding runway lengths at airports, particularly those in regions expected to be heavily affected by rising temperatures.
Investing in New Technologies
Looking to the future, manufacturers are investing in alternative propulsion technologies that could be less affected by temperature changes. Electric and hydrogen propulsion systems are among the technologies currently being researched and could provide more temperature-tolerant alternatives to traditional jet engines.
References
- Anderson, J. (2008). Introduction to Flight (6th ed.). McGraw-Hill. ISBN 978-0071263184.
- Auerbach, D. (2000). “Why Aircraft Fly”. Eur. J. Phys. 21 (4): 289–296. doi:10.1088/0143-0807/21/4/302
- Babinsky, H. (2003). “How do wings work?”. Phys. Educ. 38 (6): 497. doi:10.1088/0031-9120/38/6/001
- Jeans, J. (1967). An Introduction to the Kinetic Theory of Gasses. Cambridge University Press. ISBN 978-0521092326.