1 aerodynamics

Question 1

maximum glide range

Answer 1

A maximum lift-drag ratio, obtained by the aircraft being flown at its optimal angle of attack and corresponding minimum drag speed (VIMD), produces an aircraft’s maximum glide range.

Question 2

the effect of weight on the glide range

Answer 2

The glide range does not vary with weight, provided that the aircraft is flown at its optimal angle of attack and speed for that weight, because the glide range is proportional to the lift-drag ratio, which does not vary with weight.
Therefore, if a heavy aircraft were flown at the correct angle of attack and speed, it would glide the same distance as a lighter aircraft. However, the heavier aircraft would have a higher airspeed than the lighter aircraft, and therefore, although it would glide the same distance, it would take less time to do so.

Question 3

rate of climb/descent

Answer 3

the time an aircraft will take to either climb or descend from a given height. It is normally expressed in terms of feet per minute.

Question 4

effect of weight on rate of descent

Answer 4

The heavier the aircraft, the greater its rate of descent.

Question 5

an aerofoil

Answer 5

a body that gives a large lift force compared with its drag when set at a small angle to a moving airstream, e.g., aircraft wings, tailplanes, rudders, and propellers.

Question 6

an aerofoil chord line

Answer 6

a straight line from the leading edge to the trailing edge of an aerofoil

Question 7

mean chord line

Answer 7

the wing area divided by the wing span

Question 8

mean chamberline

Answer 8

line from the leading edge to the trailing edge of equidistance on the upper and lower surfaces of an aerofoil.

Question 9

angle of incidence

Answer 9

the angle between the aerofoil’s chord line and the aircraft’s longitudinal datum.

Question 10

angle of attack

Answer 10

the angle between the chord line of an aerofoil and the relative airflow

Question 11

dihedral

Answer 11

the upward inclination of a wing from the root to the tip

Question 12

anhedral

Answer 12

the downward inclination of a wing from the root to the tip.

Question 13

lift

Answer 13

the phenomenon generated by an aerofoil due to pressure differences above and below the aerofoil.

Question 14

the formula for lift

Answer 14

½ R V2 S CL
½R = half the value of the air density
V2 = airflow velocity squared
S = wing plan area
CL = coefficient of lift

Question 15

coefficient of lift (CL)

Answer 15

the lifting ability of a particular wing. It depends on both the shape of the wing section (fixed design feature) and the angle of attack.

Question 16

center of pressure

Answer 16

a single point acting on the wing chord line at a right angle to the relative airflow, through which the wing’s lifting force is produced. The position of the center of pressure is not a fixed point but depends on the distribution of pressure along the chord, which itself depends on the angle of attack.

Question 17

direct lift control

Answer 17

elevator/stabilizer

Question 18

high lift devices

Answer 18

1. Trailing edge flaps (Fowler flaps) increase lift at lower angles of deflection.
2. Leading edge flaps (Krueger flaps) and slats increase lift by creating a longer wing chord line, chamber, and area.
3. Slots (boundary layer control) prevent/delay the separation of the airflow boundary layer and therefore produce an increase in the coefficient of lift maximum.

Question 19

Drag

Answer 19

the resistance to motion of an object (aircraft) through the air

Question 20

two major types of drag

Answer 20

Parasite and induced drag = Total drag
Parasite = zero-lift = profile drag
1. Form or pressure drag
2. Skin-friction drag
3. Interference drag

Question 21

Parasite drag and speed relationship

Answer 21

Profile drag increases directly with speed because the faster an aircraft moves through the air, the more air molecules (density) its surfaces encounter, and it is these molecules that resist the motion of the aircraft through the air. This is known as profile drag and is greatest at high speeds.

Question 22

Induced drag and speed relationship

Answer 22

Induced drag is caused by creating lift with a high angle of attack that exposes more of the aircraft’s surface to the relative airflow and is associated with wing-tip vortices. A function of lift is speed, and therefore, induced drag is indirectly related to speed, or rather the lack of speed. Thus induced drag is greatest at lower speeds due to the high angles of attack required to maintain the necessary lift.

Minimum drag speed (VIMD) is the speed at which induced and profile drag values are equal. It is also the speed that has the lowest total drag penalty,

Question 23

high-drag devices

Answer 23

1. Trailing edge flaps (in high-drag/low-lift position)
2. Spoilers
   a. In flight detent, used as a speed brake
   b. On the ground, used as lift dumpers
3. Landing gear
4. Reverse thrust (ground use only)
5. Braking parachute

Question 24

wing-tip vortices

Answer 24

a rotating flow created when the high-pressure area on the bottom of an airfoil pushed around the tip to the low-pressure area on the top, which causes turbulence

Question 25

effects of wing-tip vortices

Answer 25

1. Create aircraft drag (induced drag because the vortices induce a downward velocity in the airflow over the wing, causing a change in the direction of the lift force so that it has an induced drag component; therefore, it creates a loss of energy). 2. Vortices create turbulence, which may affect the safety of other aircraft within approximately 1000 ft below or behind the aircraft. 3. Downwash affects the direction of the relative airflow over the tailplane, which affects the longitudinal stability of the aircraft.

Question 26

winglets

Answer 26

aerodynamic efficient surfaces located at the wing tips. They are designed to reduce induced drag. They dispense the spanwise airflow from the upper and lower surface often at different points, preventing the intermixing of these airflows

Question 27

center of gravity

Answer 27

the point through which the total weight of a body will act.

Question 28

center of gravity range

Answer 28

The center of gravity range relates to the furthest forward and aft center of gravity positions along the aircraft’s longitudinal axis, inside which the aircraft is permitted to fly.

Question 29

Mach number

Answer 29

true airspeed indication, given as a percentage relative to the local speed of sound

Question 30

critical Mach number (Mcrit)

Answer 30

the aircraft’s Mach speed at which the airflow over a wing becomes sonic. Subsonic aircraft experience a rapid rise in drag above the critical Mach number, and because the aircraft’s engines do not have the available power to maintain its speed and lift values under these conditions, the aircraft suffers a loss of lift.

Question 31

speed margins

Answer 31

the difference between the aircraft’s normal maximum permitted operating speed and its higher certified testing speed.

Question 32

Vno

Answer 32

normal operating maximum permitted speed

Question 33

Vne

Answer 33

higher, never exceeded operating speed

Question 34

Vdf

Answer 34

the maximum demonstrated flight diving speed, established during design certification flight trials.

Question 35

why an aircraft stalls

Answer 35

the streamlined/laminar airflow (or boundary layer) over the wing’s upper surface, which produces lift, breaks away from the surface when the critical angle of attack is exceeded, irrespective of airspeed, and becomes turbulent, causing a loss in lift

Question 36

superstall

Answer 36

a stall from which the aircraft is unable to recover.

Question 37

What systems protect against a stall

Answer 37

Stall warner’s and stick pushers.

Question 38

Dutch roll

Answer 38

an oscillatory instability associated with swept-wing jet aircraft. It is the combination of yawing and rolling (and sideslip motions

Question 39

primary/main flight controls

Answer 39

Elevator. Controls the motion around the lateral axis, known as pitch/pitching. Ailerons. Control the motion around the longitudinal axis, known as roll/rolling. Rudder. Controls the motion about the normal/vertical axis, known as yaw/yawing.

Question 40

adverse yaw

Answer 40

a yawing motion opposite to the turning/rolling motion of the aircraft. It is caused by the drag on the down-going aileron being greater than that on the up-going aileron. The imbalance of drag caused the aircraft to yaw around the normal/vertical axis. Since the yaw is adverse and is opposite to the turn, adverse yaw is detrimental to the aircraft's performance.

Question 41

spoilers

Answer 41

opening panels that extend from the upper surface of the wing and have the effect of spoiling/disturbing the airflow over the wing (drag), thereby reducing the lift.

Question 42

three purposes of spoilers

Answer 42

1. Roll control (usually in combination with the ailerons). Note that the primary purpose of spoilers is roll control. 2. Air speed brakes 3. Ground lift dumpers

Question 43

Krueger flaps

Answer 43

leading-edge wing flaps used to increase the wing chamber and therefore increase the coefficient of lift maximum.

Question 44

Fowler flaps

Answer 44

trailing-edge wing flaps (usually triple slotted) used to increase the wing area and chamber, which increases the coefficient of lift maximum for low flap settings, e.g., 1 to 25°. High flap settings increase drag predominately more than lift and therefore are used to lose speed and/or height, most commonly during an approach to land.

Question 45

Moment

Answer 45

an aircraft's tendency to rotate about its CG

Question 46

Ground effect

Answer 46

the interference of the surface of the earth/water with the airflow patterns about an aircraft in flight

Question 47

Lateral Stability

Answer 47

An aircraft's tendency to return to its lateral level position along the longitudinal axis on the release of aileron in a sideslip.

Question 48

Directional Stability

Answer 48

The tendency of the aircraft to regain it headings after it has been directionally disturbed (e.g. an induced yaw) from its straight path.

Question 49

Longitudinal Stability

Answer 49

The ability of the aircraft to return to a stable pitch position along the lateral axis after disturbance

Question 50

Straight-wing aircraft

Answer 50

Straight-wing aircraft experiences sonic disturbed airflow, resulting in a loss of lift at relatively low speeds,

Question 51

Swept-wing design

Answer 51

Swept-wing design delays the airflow over the wing from going supersonic and allows the aircraft to maximize the jet engine's potential for higher Mach cruise speed.