Since day one of flight training, we have all heard pilots say that aircraft perform better when it's colder outside.
You may have heard the term density that has to do with this factor but may have not have seen it actually broken down and explained before. So here's why:
Temperature and Density
When air is entering an aircraft engine to be mixed with fuel, it goes through the 4 phase process of "intake, compress, combust and exhaust" in order to generate power. This is the same for both jet and piston engines.
But how much air can actually enter the air inlet in order to enter the 4 step process?
Well, the slightly better question is how many air molecules.
jet engine design
As explained by BoldMethod.com, "cold air molecules move slower and collide with less energy than hot molecules, causing cold air to become denser. As temperature drops, more air molecules enter an engine, and as temperature rises, fewer air molecules enter an engine."
The more air molecules that can enter an engine, the more power/performance that can be generated, therefore cooler temperatures are more preferred.
Density Altitude & Performance
Since we're discussing the density of air in relation to temperature, density altitude goes hand in hand with the topic. Density altitude is altitude relative to standard atmospheric conditions at which the air density would be equal to the indicated air density at the place of observation.
Or for better terms, simply put it is the density of the air given as a height above mean sea level (MSL).
The higher you are above sea level, the less dense the air becomes, posing the same problem: fewer air molecules entering the engine, therefore, less fuel is mixed with it and lesser power is generated.
So if you're flying somewhere with a high field elevation such as Jackson Hole, Wyoming for example, and you're taking off in the afternoon where temperatures are at their hottest, you may want to double-check performance numbers. High altitude and high temperature is the worst combination for your aircraft.
This can even potentially stop you from being able to take off, where your only option is to wait out the temperature until the sun goes down and air cools off again.
So, if you've been flying and curious why your plane seems more sluggish than a few months ago, now you know! Airplanes like the cold!
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