Aerodynamics

Question 1

Theories of lift production

Answer 1

Bernoulli’s principle (the law of continuity and coanda effect) and
Newtons third law (downwash deflects aft and down, equal and opposite reaction is an upward and forward motion or lift!)

Question 2

What is total drag

Answer 2

The sum of parasite drag and induced drag

Question 3

What is the relation between airspeed and induced drag

Answer 3

As airspeed increases, induced drag will decrease

Question 4

What is L/D max

Answer 4

The lowest point on the drag curve (Vg, 73kts)

Question 5

Parasite drag

Answer 5

Skin friction: viscosity of the air and the surface of the airfoil
Form: size, shape, and speed of and object and how these variables affect the airflow over an object
Interference: harsh angles break the smooth flow of air over an object, creating an area of low pressure and turbulence and thus drag

Question 6

Induced drag

Answer 6

The tilting backwards of the lift vector by the wingtip vortices
Exaggerated by heavy, clean, and slow configurations

Question 7

Ground effect

Answer 7

The disruption of the development of wingtip vortices by the ground, resulting in a reduction of induced drag and the tilting forward of the lift vector (felt as the ‘float’)

Felt w/in one wingspan of the ground
1 wingspan - 1% reduction of drag
1/4 of the wing - 25% reduction
1/10 of the wing - 50% reduction

Question 8

What are the two components of lift

Answer 8

Vertical and horizontal

Question 9

Dynamic vs static stability

Answer 9

Static: initial response to a disruption
Dynamic: the over time response to a disturbance (static must be positive for dynamic stability to be possible)

Positive, neutral, negative

Question 10

Three axis of stability

Answer 10

Pitch: longitudinal stability about the lateral axis
Roll: lateral stability about the longitudinal axis
Yaw: directional stability about the vertical axis

Question 11

Factors affecting longitudinal stability

Answer 11

Location of the CG with respect to the wings and the horizontal portion of the tail (tail down force)
Size of horizontal portion of the tail

Question 12

Factors affecting lateral stability

Answer 12

Keel effect (pendulum)
Dihedral (low wing has a greater vertical lift vector, bringing the wing back up and vice versa)
Sweptback wings

Question 13

Factors affecting directional stability

Answer 13

Size of the vertical fin in relation to the CG
Area of the aircraft aft of the CG (weather vane effect)

Question 14

Spiral instability

Answer 14

Strong directional
Weak lateral

Question 15

Dutch roll/free directional oscillations

Answer 15

Strong lateral
Weak directional

Question 16

Load factor

Answer 16

Aircrafts weight to lift ratio

Question 17

How to the 4 forces change in climbs, descents, and turns

Answer 17

Climbs:
Descents:
Turns:

Question 18

Aerodynamics of a stall

Answer 18

When the critical angle of attack has been exceeded (18-20 degrees generally) and the airflow breaks off of the surface of the airfoil rather than flowing smoothly resulting in a gradual decrease in lift until the stall is fully developed and the lift being generated is not sufficient to maintain altitude

Question 19

Aerodynamics of a spin

Answer 19

When an aircraft in a stalled state is uncoordinated, one wing will be deeper stalled than the other
The deeper stalled wing is generating more drag, which pulls the wing down and the wing that is less stalled is generating more lift, pulling the wing up
The more stalled wing drops, swinging the less stalled wing over and down thus entering a spin
I like to think of it as the entire aircraft behaving like a prop as the spin develops (down-swinging blade generates more lift than the up-swinging blade) keeping the spin going until broken

Question 20

How do you break out of a spin

Answer 20

Procedure laid out in the POH
DA40 recovery: Power idle, rudder opposite, elevator down, aileron neutral, flaps up, recover

Question 21

4 stages of a spin

Answer 21

Entry
Incipient
Developed/inertially coupled
Recovery

Question 22

Why do we do each of the checklist items for spin recovery

Answer 22

Power idle to drop the nose and break the stall
Rudder opposite to break the yaw
Elevator down to further break the stall
Aileron neutral to prevent aggravating the spin
Flaps up so they aren’t damaged

Question 23

Why does maneuvering speed change with weight

Question 24

What is the lift equation

Answer 24

L = CL x V^2 x A / 2

Question 25

Maneuverability vs controllability

Answer 25

Maneuverability: the quality of an aircraft that permits it to be maneuvered easily
Controllability: the capability of an aircraft to respond to the pilots control inputs

Question 26

Effects of a forward vs aft CG

Answer 26

Forward: stall speed increases, stability increases, maneuverability decreases, cruise speed decreases, cruise AOA increases
Aft: inverse of forward

Question 27

Left turning tendencies

Answer 27

P-factor
Gyroscopic
Torque
Corkscrew