Lesson 2: PRINCIPLES OF AERODYNAMICS

 

Basic structure of an airplane

Lesson 2:  PRINCIPLES OF AERODYNAMICS 



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lift,aerodynamics,airfoil,fluid mechanics,fluid dynamics,airplane,aeroplane,aerospace,bernoulli,weight,thrust,drag,bernoulli's principle,angle of attack,ground effect,static stability,aviation

 

Aerodynamics 

 As we learned before, the word “aerodynamics” is derived from two Greek words.  To some, speaking about aerodynamics is still Greek. Aerodynamics is most certainly a  language of its own so we must have a working knowledge of terms associated with  aerodynamics. 

Aerodynamics: CHARACERISTICS OF AIR.

Aerodynamics: CHARACERISTICS OF AIR.


See in this video, 
how birds apply the principle of aerodynamics


The air that passes over an airfoil will have a direct  affect on the ability of the airfoil to produce lift. As a result, an aircraft’s capacity to carry  fuel, cargo, passengers, and munitions is affected. Also, variables in the makeup of air  can affect the distance required for takeoff and landing. 

Density.

Although related to pressure, density measures the mass of air per  cubic foot and is directly related to lift production by an airfoil. 

Increased Density = Increased Lift 

Pressure.

The pressure exerted by the atmosphere at a given point. Its  measurement can be expressed in several ways. However, when used in aerodynamics  the force per unit area is in inches or millimeters of mercury (Hg). Also known as  barometric pressure. Barometric pressure and density are directly related. 

Increased Pressure = Increased Density 

Temperature.

Defined as the measure of molecular motion or the degree of  heat of a substance. It is measured on an arbitrary scale from absolute zero, where the  molecules theoretically stop moving. It is also the degree of hotness or coldness. In  surface observations, it refers primarily to the free air or ambient temperature close to  the surface of the earth. Of importance to our discussion, is that increased molecular  motion (associated with increased ambient temperature) means each air molecule  occupies more space. Therefore, fewer molecules can occupy a given volume, and we  see that temperature is inversely related to density. 

-  Increased Temperature = Decreased Density 

Humidity. 

Defined as the amount of water vapor present in the air. Water vapor  molecules are actually lighter than air molecules and will thus displace air molecules.  This reduces the air density and means humidity and density are inversely related. 

-  Increased Humidity = Decreased Density

RELATIVE MOTION.


relative motion of an aircraft


The motion that exists when one object changes its  position in respect to the position of another object, even though one or the other may  remain stationary with respect to a third object. Relative motion is important in many  applications; for example, a generator produces electricity by creating relative motion  between a magnetic field and a conductive material. With aircraft, we must create  relative motion between an airfoil and a body of air in order to create lift. From an  aerodynamic standpoint a minimum amount of relative motion (i.e. airspeed) is required  to create and sustain enough lift to hold the aircraft aloft. From a navigational  perspective, the aircrafts motion relative to the earth (ground speed) takes on  importance as we then concern ourselves with traveling from point A to point B. 

INDICATED AIRSPEED (IAS).


indicated airspeed (ias).


IAS is the airspeed shown on an airspeed  indicator. It is a measurement derived by taking the difference between STATIC  pressure and IMPACT pressure. Static pressure is the air pressure exerted on an  object, such as the static pressure port on an aircraft, when the air is not moving. Thus,  the static ports on an aircraft are located in an area out of the direct airstream. Impact  pressure is the pressure exerted by the air that impacts a pressure sensor (Pitot tube)  on the aircraft as a result of forward movement. The Pitot tube is then of course located  where it will be in the direct airstream. 

TRUE AIRSPEED (TAS).

At sea level, indicated airspeed gives us an accurate  measure of relative motion between the aircraft and the airstream (TRUE AIRSPEED).  However, as altitude increases and the air becomes thinner, the IAS becomes less  accurate. For example, at sea level a TAS of 440 MPH will equal an IAS of about 440.  At 20,000 feet, a TAS of 440 MPH will have an IAS of about 360. TAS adjusts IAS for a  given temperature and pressure. An air data computer receives inputs on actual  temperature and pressure readings outside the aircraft and makes the appropriate  calculations to correct the given IAS to a TAS. Thus, TAS is a measure of the velocity  of the relative motion of an aircraft. 

AIRFOIL.

By design, an airfoil, figure 1-2, is built to obtain a reaction upon itself  from the air through which it passes. In most cases, it is designed to produce lift. There  are other functions for airfoils as well, such as propellers, which are airfoils that produce  thrust. In addition to wings and empennages, even some aircraft fuselages are  considered airfoils. They produce limited lift on some heavy aircraft and a significant  amount of lift for fighters. Finally, flight control surfaces are airfoils that produce a  reaction, which allows the aircraft to be moved about an axis of rotation. This provides  controllability and maneuvering of the aircraft. 

RELATIVE WIND.

Relative wind is simply the air moving past an airfoil. Its  velocity and direction are directly equal to and opposite of the aircraft’s flight path.




Figure 1-2, Airfoils 

 

 

FLIGHT PATH.

flight path.


The path the center of gravity would follow in flight. Can be  changed by forces acting upon the aircraft (such as a crosswind), in addition to  directional changes resulting from flight control inputs. The center of gravity is located  at the intersection of the pitch, roll, and yaw axes for a given aircraft.