Aerodynamics Refresher

Question 1

Describe the relationship of different airspeed measurements

Answer 1

Indicated Airspeed (IAS) 
Calibrated Airspeed (CAS): IAS adjusted for instrument errors
Equivalent Airspeed (EAS): CAS adjusted for compressibility
True Airspeed (TAS): EAS adjusted for density altitude
Ground Speed (GS): TAS adjusted for winds

Question 2

Discuss the basic laws of aerodynamics

Answer 2

Lift is the component of airflow force that is perpendicular to the oncoming flow, it contrasts with the drag force, which is the component of the surface force parallel to the oncoming flow.

Question 3

Understand the relationship of the three axes of and stability as it relates to those axes

Answer 3

Longitudinal stability vs. pitch
Lateral stability vs. roll
Directional stability vs. yaw

Question 4

Chord line

Answer 4

Straight line from the leading edge to trailing edge

Question 5

Angle of Attack (AoA)

Answer 5

angle between relative wind and the chord

Question 6

Center of Gravity (cg)

Answer 6

Point on the chord where all effective weight is realized

Question 7

Center of pressure (cp)

Answer 7

Point on the chord where resultant aerodynamic forces act

-moves with AoA

Question 8

Aerodynamic Forces (AF)

Answer 8

happens through the cp and is the vector sum of lift and drag

Question 9

Aerodynamic Center (AC)

Answer 9

Point around which the pitching moment is measured (moment from lift is constant as AoA varies)

• also the central point of the lateral axis
• ROT: The AC is an average of the center point (cp) and center of gravity (cg)

Question 10

Describe the relationship between lift, drag, and thrust

Answer 10

Least drag and least thrust required to maintain straight and level flight

Question 11

Describe why an airfoil stalls

Answer 11

Stall is the point where an increase in AoA no longer produces an increase in CL - or where the critical angle of attack is exceeded
An aircraft stalls when their AoA is increased beyond the Critical Angle of Attack of and lift begins to decrease

Question 12

Describe the relationship between pitch, AoA, and FPA/FPV

Answer 12

AoA- The angle between the oncoming air or relative wind and a reference line on the airplane or wing
Pitch- Pitch angle, or attitude, is the angle between the longitudinal axis and the horizon
FPV/FPA
-Aero eng: angle between flight path vector (where the airplane is going) and the local atmosphere
-Flight crew: angle between the FPV and horizon
Because of the relationship of pitch, AoA, and FPA/FPV an airplane may reach a very high AoA with zero FPA/FPV

Question 13

Understand how the P-Factor is generated in a turbo-prop aircraft

Answer 13

At low airspeed, aircraft AoA increases and the propeller blade AoA changes
Airflow meets the propeller disc at the aircraft AoA, not “head-on”
the horizontal blade moving down will have a greater AoA producing more thrust than the horizontal blade moving up

Question 14

Define Lift / Drag maximum

Answer 14

Least drag and least thrust required to maintain straight and level flight