Environmental Factors: The Effect on Aviation. Blog 2.3.

    Aircraft performance is determined by many factors, the environment being a huge one, but more specifically lets look at atmospheric pressure. Atmospheric pressure is the pressure air exerts on an object within the atmosphere(PHAK,2016). It is fluid like and changes depending on location, altitude, and it gives us vital flight information such as airspeed, vertical speed, and manifold pressure(PHAK, 2016). The one characteristic of atmospheric pressure that has the biggest effect is its density. Lets take a closer look at how density effects airplane performance.

    Density directly effects an airplanes power, thrust, and lift(PHAK,2016). These are all essential for an aircraft to take flight. The density of air is determined by temperature and altitude, air becomes less dense as you increase altitude and temperature. This causes the engine to lose power, thrust and lift to decrease, because there is less air entering the engine, less air for the propeller to use for thrust, and less air for the wings to use as lift. It is the inverse for more dense air. Air density is a complex environmental factor that needs to be taken into consideration for every flight but there are some ways to reduce its effects.

    Since air density is such a huge variable in aircraft performance there have many efforts to reduce its effects. Some efforts include, wing design, propellers that can change pitch, and powerplant upgrades like turbochargers for reciprocating engines and variable stator vanes in jet engines. For wing design, the shape of the airfoil is the primary factor in the amount lift it can generate given varying densities so to minimize the effect of density the use of flaps and slats can be used to change the shape of the airfoil to maximize lift(PHAK,2016). Since a propeller is an airfoil it has the same principles as the wing but to maximize thrust the pitch would need to be changed. This is done by variable pitch propellers which rotate along their longest axis, pilots can adjust this in flight to get the most performance out of the propeller for changing atmospheric pressure(UVPP,2015). Lastly, the powerplant has also been improved to minimize the effect or air density. Turbochargers provided a more consistent pressure and density of air to the engine by using a turbine wheel spun by exhaust gases to drive an intake impeller. The intake impeller compresses the air going into the engines intake and this is regulated by a waste gate to keep a consistent pressure(Jones, 2016). Jet engines use a similar concept to the variable pitch propeller to control the amount of air entering the engine. 

    The Pilot's Handbook of Aeronautical Knowledge is an excellent source of information on this subject. Atmospheric pressure is explained in Chapter 4 and again in Chapter 11 because it is that important to aircraft performance.  But aircraft performance is the culmination of it's design as covered in Chapter 3 and the aerodynamics of flight covered in Chapter 5. There is not one answer to the issue of air density but by studying each of the aspects that play into an aircraft's performance we can formulate different ways to lessen and overcome the negative effects. 

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  References

C. Hall Jones. (2016). Turbochargers. Retrieved from https://www.aopa.org/training-and-safety/students/solo/special/turbochargers

Pilot’s Handbook of Aeronautical Knowledge(PHAK). (2016). Federal Aviation Administration. https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/

Understanding variable pitch propellersc(UVPP). (2015). Hartzell Propeller, Retrieved from https://hartzellprop.com/understanding-variable-pitch-propellers/