Aerodynamics

Question 1

Definition of Lift:

Answer 1

The upward force that opposes weight and supports an airplane in flight

Question 2

Angle of Sweepback of a wing

Answer 2

Angle between the lateral axis and a line represented by 25% root chord and 25% wing tip chord

Question 3

Stagnation Point

Answer 3

Point on the leading edge of an airfoil where the airflow splits to either follow the upper or lower surface of a wing

Question 4

Coefficient of Lift (Cl)

Answer 4

Wings ability to produce lift as a product of Angle-of-Attack (AOA) and the shape of the camber line

Question 5

Definition of Drag

Answer 5

Component of the total aerodynamic force, which resists the motion of body moving forward through the air

• Parasite and Induced

Question 6

V(smin) vs V(s1g)

Answer 6

V(smin): stall speed for conventional aircraft. Will stall with a load factor slightly below 1g

V(s1g): stall speed for fly-by-wire aircraft. V(smin) = 0.94 x V(s1g)

Question 7

Free Stream Airflow

Answer 7

Airflow that is far enough away from an aircraft that the aircraft does not disturb it

Question 8

What is Mach number?

Answer 8

The relationship between the speed of the aircraft through an air mass (TAS) and the speed of sound for the same air mass (LSS)

same atmospheric conditions

M = TAS / LSS

Question 9

What is Critical Mach Number?

Answer 9

Speed at which airflow over any part of the aircraft or structure first reaches (but does not exceed) the speed of sound (Mach 1.0) and results in shockwaves forming on the structure

Speed of sound is not exceeded

Highest speed without reaching supersonic flow

Shock waves, buffet, and airflow separation take place above critical Mach number

Question 10

Speed Spectrum

Answer 10

Subsonic: < 0.75M

Transonic: 0.75M - 1.2M

Supersonic: 1.2M - 5.0M

Hypersonic: > 5.0M

Question 11

Stability of an aircraft

Answer 11

the characteristic of an airplane in flight that causes it to return to a condition of equilibrium (steady state flight) after being disturbed.

Question 12

Static Stability vs Dynamic Stability

Answer 12

Static stability: What the airplane will do right now

Dynamic Stability: What an airplane will do in time

Question 13

Center of Pressure

Answer 13

Point where all aerodynamic forces act on the chord line

Question 14

Wing Dihedral

Answer 14

The upper angle of a wing which increases its lateral static stability

Question 15

Angle of Attack

Answer 15

Angle between the chord line of a wing and the relative wind

Question 16

Critical Angle of Attack (Clmax)

Answer 16

For any given aerofoil a stall always occur at the same angle regardless of IAS, flight attitude and/or weight

Question 17

Advantages of sweptback wings

Answer 17

• less drag
• higher cruise speeds
• higher critical Mach number
• greater lateral stability
• less sensitive to turbulence
• delay the onset of compressibility effects (boundary layer and shock waves)

Question 18

Disadvantages of sweptback wings

Answer 18

• tendency at low speed to stall at the wing tip first (center of pressure moves forward contributing to nose up pitch, less stall warning, and reduced lateral control)
• Dutch roll tendency
• reduced coefficient of lift (more of effect in subsonic flight)

Question 19

“Coffin Corner”

Answer 19

At some point, the stall speed of the aircraft in Mach number could equal the MMO of the aircraft, and the pilot could neither slow down (without stalling) nor speed up (without exceeding the max operating speed of the aircraft)

*with an increase in altitude at a constant Mack number KTAS reduces