NIFE Aerodynamics 2-1-1

Question 1

Define Vector

Answer 1

A quantity that represents a magnitude and a direction

Question 2

Define air Density

Answer 2

Air Density is the total mass of air particles per unit volume

Question 3

Define Moment

Answer 3

A rotational force around a point or axis

Question 4

State the requirements for equilibrium flight

Answer 4

Equilibrium flight exists when the sum of all forces and the sum of all moments around the center of gravity are equal to zero.

Can be in Equilibrium in an ascent as long as there is no acceleration.

Question 5

State the requirements for trimmed flight

Answer 5

Trimmed Flight exists when the sum of all moments around the center of gravity is equal to zero.

Can be in trimmed flight on turns.

Question 6

Describe the relationship between temperature and altitude (average lapse rate)

Answer 6

Air temperature decreases linearly with an increase in altitude at a rate of 2 degrees C (3.57 F) per 1000 ft until 36,000 ft.

Question 7

Describe relationship between humidity and air density

Answer 7

As humidity increases, air density decreases as water molecules, which are less dense than air molecules and do not change the number of particles per unit volume of air, displace an equal number of air molecules.

Question 8

State the General Gas Law

Answer 8

Sets the relationship between the three properties of air: pressure (P), density (p), and temperature (T). R is a constant for any given gas.

P = pRT

Question 9

Define steady airflow

Answer 9

Exists when static pressure, density, temp, and velocity remain constant at any time.

Question 10

Explain the Continuity equation

Answer 10

A1V1=A2V2 (subsonic only)
The cross-sectional area of the tube multiplied by the air velocity at any point is equal to the value of any other point in the stream tube. (i.e. if the cross-sectional Area decreases on one side, the Velocity must increase on the same side so both sides remain equal)

Question 11

Explain Bernoulli’s Equation

Answer 11

Total energy of a fluid can be separated into potential energy and kinetic energy. Describes variation of pressure exerted by a moving mass of fluid. Applies to frictionless, incompressible airflow in a closed system.

Pt = Ps + 1/2(density)(V^2)
Pt = Total Pressure
Ps = Static Pressure
V = velocity

Question 12

State the different types of airspeeds

Answer 12

Indicated Airspeed (IAS) 
- Actual instrument indication of the dynamic pressure the plane is exposed to during flight. Calibrated for Knots Indicated Air Speed (KIAS)

Calibrated Airspeed (CAS)
- IAS corrected for instrument error

Equivalent Airspeed (EAS)
- CAS corrected for compressibility. The EAS is the true airspeed at sea level on a standard day that produces the same dynamic pressure as the actual flight condition. 

True Airspeed (TAS)
- The actually velocity at which an airplane moves through an air mass. Found by correcting EAS for the difference between the local air density (p) and the density of the air at sea level on a standard day (p0). At altitudes above sea level (lower density), TAS is higher than IAS. 

Ground Speed
- Plane’s actual speed over ground. GS = TAS + or - Wind

EX:
Sea level, normal desnity, 150 KIAS
At 10,000 feet, decrease in density = air particle are further apart, 150 KIAS is actually closer to 175 because of how the pitot static system works.
If there is a 10mph HW, then the GS would be 165. 10mph tailwind = 185.

Question 13

Indicated Airspeed (IAS)

Answer 13

The actual instrument indication of the dynamic pressure the airplane is exposed to during flight. Factors may create variances between IAS and actual flight speed. Shown in knots of indicated airspeed (KIAS)

Question 14

Calibrated airspeed (CAS)

Answer 14

Indicated airspeed that has been corrected for instrument error.

Question 15

Equivalent Airspeed (EAS)

Answer 15

Calibrated airspeed that has been corrected for compressibility error.

Question 16

True Airspeed (TAS)

Answer 16

Equivalent Air Speed corrected for density. The actual speed a plane moves through an air mass.

Question 17

Ground Speed

Answer 17

Airplane’s actual speed over ground. TAS corrected for wind

Question 18

Define Mean Camber Line (MCL)

Answer 18

The locus of points halfway between the upper and lower surfaces

Question 19

Define Chord

Answer 19

Chord is the precise measurement between the leading and trailing edges measured along the chord line

Question 20

Define Camber and Camber Types

Answer 20

The maximum distance between the mean camber line and the chordline, measured perpendicular to the chordline.

A positively cambered airfoil produces lift at zero AOA

Symmetric camber airfoil produces no lift at zero AOA

A negative cambered airfoil produces negative lift at AOA

Question 21

Define Wingspan (b)

Answer 21

The length of a wing, measured from wingtip to wingtip.

Question 22

Define Wing Area (S)

Answer 22

The apparent surface area of a wing from wingtip to wingtip. The area within the outline of a wing in the plane of its chord, including the area within the feuselage, hull, or nacelles

Question 23

Define Chordwise airflow

Answer 23

Airflow perpendicular to leading edge of an airfoil. Produces lift as it accelerates over the wing.

Question 24

Define Spanwise Airflow

Answer 24

Airflow parallel to the leading edge. Moves from root to tip and does not accelerate over the wing and therefore does not produce lift

Question 25

Define Pitch Attitude

Answer 25

Pitch attitude (θ) is the angle between an airplane’s longitudinal axis and the horizon.

Question 26

Define Flight Path

Answer 26

The path described by an airplane’s center of gravity as it moves through an air mass. Equal in magnitude and in the opposite direction of relative wind.

Question 27

Define Relative Wind

Answer 27

Relative wind is the airflow the airplane experiences as it moves through the air. It is equal in magnitude and opposite of flight path.

Question 28

Define Angle of Attack (AOA)

Answer 28

The angle between the chord line and the relative wind

Question 29

Define Angle of Incidence

Answer 29

The angle between the airplane’s longitudinal axis and the chordline of the wing.

e.g. how the wing is attached to the plane.

Question 30

DESCRIBE the airplane three-axis reference system

Answer 30

The longitudinal axis passes from the nose to the tail of the airplane. Lateral passes from wingtip to wingtip. Vertical passes through CoG

Question 31

Define center of gravity

Answer 31

The point at which all weight is considered to be concentrated and about which all forces and moments are measured. Can change as fuel is burned, ordnance is lost, cargo is shifted, etc.

Question 32

Define the Aerodynamic Center

Answer 32

The aerodynamic center is the point along the chordline around which all changes in the aerodynamic force take place. Approx 1/4 the length of the chord from the leading edge or at the thickest part

Question 33

State the two forces considered aerodynamic forces

Answer 33

Lift and drag

Question 34

Describe the pressure distribution around and airfoil

Answer 34

As air particles hit the leading edge of the airfoil they are forced to go around it. With a positive AOA, air particles that flow above the airfoil sense a bigger reduction in the cross sectional area compared to those that flow below. According to the continuity equation, as the area decreases, the velocity in the streamtube must increase. With Bernoulli’s eqn, as velocity increases, dynamic pressure will increase. With constant total pressure, static pressure will decrease. The difference in static pressure between the upper and lower surfaces will produce lift.

Question 35

Describe how factors in the lift equation affect lift production, given density, velocity, surface area, and coefficient of lift

Answer 35

L = (0.5)(p)(V^2)(S)(Cl)
p = density
V = Velocity
S = Wing Area
Cl = Coefficient of lift (can only control AOA and shape of airfoil)

Question 36

LIST the factors affecting coefficient of lift that the pilot can directly control

Answer 36

AOA and shape/camber of airfoil through flaps

Question 37

Define CLmax

Answer 37

The maximum value for the coefficient of lift as AOA increases.

Question 38

Describe the relationship between coefficient of lift and AOA

Answer 38

As AOA increases, the coefficient of lift increases up to a maximum value (Clmax). The AOA at which CLmax is reached is called CLmax AOA.

Question 39

Describe how flaps affect the coefficient of lift and Clmax

Answer 39

Flaps change the camber of the airfoil by changing the chordline, adding more positive camber to the airfoil.

CL is higher for a given AOA but the stalling AOA (CLmax AOA) decreases.