Aerodynamics Flashcards
4-forces of flight
Lift, Weight, Thrust, Drag
How is lift created?
Bernoulli principle…
faster airflow = lower pressure
Newton’s 3rd law…
action - airfoil (wing) turns airflow down
re-action - airflow pushes wing up
Draw an airfoil and explain chord line, relative wind, and angle of attack.
Draw an airfoil with low AOA, higher AOA, and beyond critical AOA. Depict laminar and turbulent airflow.
Explain relationship between AOA and…
…lift.
…drag.
Explain how angle of attack is NOT the same as pitch angle.
Two types of drag
Parasite and induced drag
Explain the relationship between parasite drag and airspeed. Draw a graph to illustrate.
Explain the relationship between induced drag and airspeed. Draw a graph to illustrate.
Explain the relationship between total drag and airspeed. Draw a graph including L/D max.
U-shaped curve. L/D max is at the minimum.
Explain the relationship between the four forces of flight and when they are in equilibrium.
Types of parasite drag
Form
Skin
Interference
Illustrate induced drag.
Draw an airfoil including relative wind, downwash, vortices, average relative wind, lift vector components. Show relationship of induced drag with higher AOA, increased vortices and downwash, and in/out of ground effect. Make a connection of lowered speed > higher AoA > greater induced drag.
Using a model airplane, explain the relationship of airspeed and AOA during level flight.
What is a stall? What causes it? What are the indicators? Recovery?
What’s a spin? Causes? Indicators? Recovery?
Spin avoidance. Common scenarios?
Phases of a spin?
Aerodynamics (ground)
Slipstream
- pushes tail right
- yaw nose left
Torque
- equal opposite reaction
- props CW, airplane CCW
- rolls left > yaws left (drag)
Aerodynamics (Lift off)
P-Factor
at high AOA (CW rotating propeller)… right descending blade produces more thrust than the left ascending blade.
Airplane will rotate about its center of mass. Because thrust line is offset to the right, the airplane will yaw left.
Accelerated Slipstream
aka Induced Lift.
The prop wash / slipstream encounters the wing and produces/induces more lift.
Because the center of thrust / slipstream is offset to the right, then the induced lift is also offset right, that causes the airplane to roll left
Spiral Slipstream
The slipstream / prop wash (primarily from the left engine) tends to spiral around the fuselage and hit the left side of the vertical tail > pushes tail right > nose yaws left
Torque
Equal and opposite reaction
Props CW > Airplane CCW > left roll
Spiral Slipstream (airspeed effect)
How much lift from… Accel Slipstream / Induced Lift
Accounts for… 50-60% lift
Problems w/ losing an engine
1 control problem
2 performance problem
3 sideslip problem
Adverse Effects of an Engine Failure (draw this)
1 Control issue
pitch - down (loss of slipstream over tail & )
rolls - toward dead (loss of accelerated slipstream /induced lift)
yaws - toward dead (less thrust, more drag)
See “Circle of Doom”.
2 Performance Issue
loss 50% thrust, loss 80-90% performance
- thrust (50%),
- lift (loss induced lift),
weight (same),
+ drag (from prop & induced drag)
Depending on weight and DA, climb rate may be negative! Calculate SE performance
3 Sideslip issue
Assuming wings level flight…
+ more parasite drag with sideslip (bad for performance)
- less rudder effectiveness with sideslip (bad for control)
See SE Level Flight.
Why 80-90% decrease in performance when OEI?
Thrust - loss of 50%
Lift - less induced lift
Drag - increase prop drag and + induced drag
Weight - unchanged
Circle of Doom
Less lift > descent > higher AoA > more induced drag > decreases velocity > less lift
…decreases velocity > also, rudder less effective at control!
…higher AoA > more p-factor
SE Level Flight aka 3 Sideslip Problem (draw this)
3 Sideslip issue
Assuming wings level flight…
Force vectors from rudder and SE thrust creates a Sideslip condition
+ more parasite drag with sideslip (bad for performance)
- less rudder effectiveness with sideslip (bad for control)
Corrected by banking (~5°) into the operating engine and splitting the ball (inclinometer) towards the good engine.
Wings level flight vs bank into good engine (draw this)
(Effect on Vmc)
Critical Engine
Engine that most adversely affects performance and control when inop.
Typically the left on a convention light-twin with CW rotating engines.
Each engine is equally critical with counter rotating engines.
Torque - OEI Left vs Right
Airplane rolls toward dead engine.
Torque rolls airplane left.
Left inop - torque rolls airplane to dead ):
Right inop - torque rolls airplane to operating engine (:
Critical Engine (draw PAST)
Vmc Condition
25.149
- critical engine inop and…
- propeller windmilling
- operating engine full power with…
- DA at Sea Level
- bank 5° towards operating engine
- outside ground effect
- aft CG
- light weight
- clean configuration
Define Vmc
What are the dangers of operation below Vmc?
Vmc
- Minimum speed at which control can be maintained.
- determined by manufacturer IAW 23.2135(c)
- ensures directional control (airflow to rudder), but airplane will not necessarily be able to maintain altitude. (P/2)v^2=dynamic press
WARNING: attempting to operate < Vmc = loss of control (Vmc roll) due to loss of rudder effectiveness.
How does FLAPS affect Vmc and Performance?
Induced lift > roll moment towards good engine
Lower AoA > less p-factor
Flaps - help control, hurt performance
How does FLAPS affect Vmc and Performance?
Induced lift > roll moment towards good engine
Lower AoA > less p-factor
Flaps - help control, hurt performance
How does GEAR affect Vmc and Performance?
G-dn > more drag behind CG > stabilizing keel effect
G-dn - helps control, hurts performance
Ground Effect on Vmc and Performance
Helps with control when dead engine drops into ground effect (decreases induced drag)
Decreases induced drag and improves performance and control
CG effect Vmc and Performance
Aft CG - hurts control (shorter arm to rudder), helps performance
Fwd CG - helps control (greater moment arm to rudder), hurts performance.
- Load nose first
Weight on Vmc and Performance
More Wgt > more horizontal component of weight when banking to good engine > more effective rudder
More Wgt - helps control, hurts performance
Density Altitude on Vmc and Performance
higher DA > less asym thrust (less power, less prop efficiency) > helps control > lowers Vmc (Vmc decreases with altitude)
DA - helps control, hurts performance
DA on Vs and Vmc
Vs - unchanged with DA
Vmc - decreases with DA
Above “Critical DA” - stall indication occurs first
At “Critical DA” - stall and loss of directional control occurs at the same time > spin EXTREMELY DANGEROUS!
Below “Critical DA” - loss of directional control occurs first
3-axis of flight
Yaws about Vertical Axis
Rolls/Banks about Longitudinal Axis
Pitches about Lateral Axis
Yaw
movement about vertical axis
primarily controlled with rudder
Roll/bank
Movement about Longitudinal Axis
Primarily controlled with Ailerons
Pitch
Movement about Lateral Axis
Primarily controlled by Elevator or Stabilator
Lateral Axis
Through the Center of Gravity/Mass
Pitches with Elevator about the Lateral Axis
Longitudinal Axis
Through the Center of Gravity/Mass
Rolls/banks with Aileron about the Longitudinal Axis
Vertical Axis
Through the Center of Gravity/Mass
Yaws with Rudder about the Vertical Axis
Turn
Bank lift vector to turn
Horizontal component of lift turns an airplane
Turn Rate and Radius
Are effected by bank and speed
Greater bank - faster rate, smaller radius
Shallow bank - slower rate, larger radius
Greater speed - slower rate, larger radius
Slower Speed - faster rate, smaller radius
How to turn with the smallest radius
Slow down and Bank steeper
Caution ⚠️ stall/spin hazard
Slip vs Skid
Slip
- greater horizontal lift
- ball inside of turn
- useful to create drag (ex fwd slip)
- useful to counter Xwind or OEI Sideslip
Skid
- greater centrifugal effect
- ball outside of turn
Coordinated
- horizontal lift = centrifugal force
- ball centered
Adverse Yaw
Yaw to outside of turn / furtherance of turn due to the aileron creating lift and drag during roll in/out of bank.
Overbanking and lateral stability with bank
Overbanking
- steeper banks
- differential radius/airspeed/lift
Lateral stability
- shallower banks
- wings level tendency
- dihedral, sweep wings, and keel effect
At medium banks they cancel
Turns and Load factor
Load factor increases with bank angle and speed
Limit Load Factor
Normal category certification limits
+3.8 G
-1.52 G
Beyond these limits it’s possible to experience structural damage
Does stall speed change?
Vs increases with Load (Mass or Gs)
Vnew = Vold * ^1/2(new wgt/old wgt) or G
Published Vs & Vso are 1G/level/MGTOW
See POH section 5 for tables
Load Factor
G ratio = Lift force / Mass
60° bank = 2 G
Critical Engine and Vmc
