Aerodynamics Flashcards
Theories of lift production
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!)
What is total drag
The sum of parasite drag and induced drag
What is the relation between airspeed and induced drag
As airspeed increases, induced drag will decrease
What is L/D max
The lowest point on the drag curve (Vg, 73kts)
Parasite drag
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
Induced drag
The tilting backwards of the lift vector by the wingtip vortices
Exaggerated by heavy, clean, and slow configurations
Ground effect
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
What are the two components of lift
Vertical and horizontal
Dynamic vs static stability
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
Three axis of stability
Pitch: longitudinal stability about the lateral axis
Roll: lateral stability about the longitudinal axis
Yaw: directional stability about the vertical axis
Factors affecting longitudinal stability
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
Factors affecting lateral stability
Keel effect (pendulum)
Dihedral (low wing has a greater vertical lift vector, bringing the wing back up and vice versa)
Sweptback wings
Factors affecting directional stability
Size of the vertical fin in relation to the CG
Area of the aircraft aft of the CG (weather vane effect)
Spiral instability
Strong directional
Weak lateral
Dutch roll/free directional oscillations
Strong lateral
Weak directional
Load factor
Aircrafts weight to lift ratio
How to the 4 forces change in climbs, descents, and turns
Climbs:
Descents:
Turns:
Aerodynamics of a stall
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
Aerodynamics of a spin
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
How do you break out of a spin
Procedure laid out in the POH
DA40 recovery: Power idle, rudder opposite, elevator down, aileron neutral, flaps up, recover
4 stages of a spin
Entry
Incipient
Developed/inertially coupled
Recovery
Why do we do each of the checklist items for spin recovery
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
Why does maneuvering speed change with weight
What is the lift equation
L = CL x V^2 x A / 2
Maneuverability vs controllability
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
Effects of a forward vs aft CG
Forward: stall speed increases, stability increases, maneuverability decreases, cruise speed decreases, cruise AOA increases
Aft: inverse of forward
Left turning tendencies
P-factor
Gyroscopic
Torque
Corkscrew
