Aircraft performance is a science. How an aircraft flies depends heavily on two factors - pressure and temperature. Atmospheric pressure applies a weight, and therefore a force on aircraft in flight (PHAK, 11-2). The atmosphere becomes less dense with increased altitude. Without acknowledging the environmental effect of air pressure on an aircraft, pilots would not have an accurate reading on their altitude or be able to determine the aircraft's capabilities.
The average atmosphere weighs 14.7 pounds per square inch (PSI) (PHAK, 11-2). This matters because as the atmospheric density decreases, there is less air for the engine to operate with, the propeller becomes less efficient thus creating less thrust, and lift is decreased due to less force on the airfoils (PHAK, 11-2).
Pilots rely on an instrument called an altimeter to get an accurate reading on pressure altitude, which affects aircraft performance and also when assigning aircraft to altitudes above 18,000 feet (PHAK, 11-3). The aircraft’s altimeter takes measurements in mercury and millibars. The standard surface pressure at sea level is 29.92 inches of mercury, and the altimeter automatically shows the altitude when operating in the standard atmosphere (PHAK 11-3). When the atmosphere has additional pressure forces, the pilots adjust their altimeter to account for the pressure changes and provide an accurate altitude. As the density of the air increases, so will the performance of the aircraft. Temperature also affects the density of the atmosphere. As the air temperature increases, density decreases. As air temperature decreases, density increases (PHAK, 4-4). Pilots need to know the atmospheric pressure and pressure to determine the aircraft's capabilities.
References
Federal Aviation Administration (FAA). (2016). Pilot’s Handbook of Aeronautical Knowledge (PHAK). Retrieved https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/
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Emily,
ReplyDeleteThe science of how an aircraft flies is quite fascinating. There are hundreds on little things to account for. I wonder if the wright brothers knew that the atmosphere became less dense as we increase in altitude. I’m sure they didn’t have the fancy gadgets or the knowledge of environmental effects like we have today. Altimeters are used very frequently by pilots but also a large chunk of the population use them as well. I use one on my watch (how neat is that) to track things like mountain biking, snowboarding, and hiking. The wright brothers would be amazed if they knew where technology was today.