The Operating Environment and Aircraft Performance

 

One of the most prevalent conditions that affects aircraft performance is the effect of temperature on air density. Air density directly affects the amount of lift an aircraft can produce. Essentially the hotter the day the less dense the air will be, this requires careful planning and action to mitigate the risk of producing less lift.

Air like water is a fluid, and just like water the colder air becomes the denser it will become like ice (FAA, 2016). Conversely if temperatures rise water will become less dense in a vapor form, air behaves very similar. The Pilot’s Handbook of Aeronautical knowledge addresses the effect of temperature on air density and how a decrease in air density can even cause a propeller to become less efficient (FAA, 2016). Air density is a variable in the lift equation, known as rho (NASA, n.d.). The lower this value is, the less lift is produced if the other variables like wing area or velocity are kept constant.

To compensate for less lift produced during a takeoff roll either the velocity must be increased, or the coefficient of lift must be increased by changing the angle of attack. If the velocity is to be increased during takeoff either more power must be applied, or more runway must be used to allow the aircraft to accelerate to a greater velocity.  

                                                   The heat is on, how air temperature affects airplanes (Credit AOPA)

Turbine style engines are often limited to a certain temperature that cannot be exceeded. When temperatures are higher than average, there is often less power produced before the engine becomes temperature limited. Increasing the angle of attack with a greater degree of flaps during the takeoff roll is another method to increase the amount of lift performed.

Ultimately the biggest safety mitigation strategy that can be applied on very hot days is determining whether it is safe to take off, before entering the aircraft. Consult the applicable performance sections of the operator’s manual for the aircraft and have a plan for hot temperature days.

References

Administration, F. A. (2016). Pilot’s Handbook of Aeronautical Knowledge: FAA-H-8083-25B (ASA FAA Handbook Series) (2016th ed.). Aviation Supplies & Academics, Inc.

The Lift Equation. (n.d.). www.Grc.Nasa.Gov. Retrieved September 13, 2021, from https://www.grc.nasa.gov/www/k-12/airplane/lifteq.html

Weather - The heat is on. (2017, August 1). [Photograph]. https://www.aopa.org/news-and-media/all-news/2017/august/flight-training-magazine/the-heat-is-on