Principles of Aerodynamics

This course will give you the basics of how an airplane flies and how it is controlled.  The slides that you should review are found here:  Basic Aerodynamics .  (The slide set contains 48 slides - Ignore any additional slides or presentations that appear after the last slide in the set).

Some of the slides get a bit technical but don’t worry - you will not be expected to know things in great detail.  The important thing is to understand the concepts - we will build on these concept as you progress through your training and through practical experience  Review the list below as you might also want to do some additional research on your own - or get into a discussion with fellow pilots to get some input from their points of view.

Some things you should know are:

  • The basic parts of an aircraft (note that the slides refer to the complete tail assembly  as the ‘empennage’)

  • What the primary control surfaces are and what they do

  • What the function of ‘trim’ is

  • What flaps and slats do (both their positive and negative effects)

  • The four forces that act on an aircraft in flight

  • A basic concept of what is meant by (aerodynamically) “stalling an aircraft” - where the angle of attack of the wing is increased to a certain point beyond which lift begins to decrease.  This is called the ‘critical angle of attack’ and the aircraft will always stall at this angle regardless of airspeed.

  • A wing produces lift as a result of Newton’s third law - by diverting air down (the “action”) resulting in pushing the wing, and subsequently the entire aircraft, up (the “reaction”).  The amount of lift depends on the mass of air that is pushed down so things that change the density of air change the mass per unit volume of air and therefore CHANGE THE AMOUNT OF LIFT THAT IS GENERATED.   Things that make air less dense are:

    • High temperature

    • High elevation (think KDEN - or KLXV !!!) - along with high field elevation high temperatures are the two principle factors that increase takeoff distance and decrease the rate of climb.  You can calculate both the percent increase in takeoff distance and the percent decrease in climb rate using your Koch Chart (Interactive Koch Chart}

    • High humidity (water vapor is less dense than dry air) - mostly causes a reduction in engine power - one rule of thumb is add 10% to the calculated Koch Chart takeoff distance and expect some further decrease in climb performance. 

  • Aircraft performance is a function of INDICATED air speed (IAS)·

    • For a given indicated air speed the true airspeed increases with decreasing air density (so, TAS increases with altitude, higher temperature and higher humidity for a given IAS)

    • IAS is NOT affected by relative winds (tailwind, headwind, crosswind)

    • Because of the way indicated airspeed is determined - the difference between the dynamic pressure developed when air stops in the pitot tube and the static pressure of air at the aircraft's current location - the influence of temperature and humidity is minimal to negligible. 

  • A general understanding of what happens aerodynamically when an aircraft turns (slide 21 in the slide set linked above):

    • The vertical component of the (now angled) total lift of the wing has to remain equal to the aircraft’s weight in order to prevent the aircraft from losing altitude so -

    • The total lift has to increase, which requires an increase in angle of attack of the wing which will result in the aircraft slowing or the need for additional power if the airspeed is to remain constant

    • The load factor (‘G-force’) on an aircraft maintaining constant speed and altitude during a turn is the same regardless of the actual speed of the aircraft - the load factor only varies with the bank angle of the aircraft (a 30° bank creates a load factor of 1.15 G, a 60° bank increases the load factor to 2 G).

  • Fundamental principles of weight and balance - review the materials in these two sites