Lesson 2 Aerodynamics of Flight
Terms And Definitions
Airfoil
Leading edge
Trailing edge
Camber – curvature of the airfoil
Chord line – line from leading edge to trailing edge
Mean camber line
Terms And Definitions
Angle Of Attack (a)
Relative wind
Angle of attack
Angle of incidence
Terms And Definitions
Aspect ratio, ratio of wing span to wing chord
Taper ratio, decrease of chord or thickness
Voyager
High aspect ratio is like a glider (decrease in drag)
Short chord, long span
SR-71
Low aspect ratio like a fighter (increase in drag at same velocity)
Long chord, short span
The 4 Forces
Lift
3 ways lift is created
1. Deflection – Newton’s 3rd law
2. Downwash – Newton’s 3rd law
3. Bernoulli’s principle
Positive pressure below
Negative pressure above
Lift
Different angles of attack generate different lift patterns at different speeds.
The stall angle of attack is always the same for any given airfoil.
Pressure Distribution
Lift
Critical angle of attack stall angle of attack
All of your lift is not lost all at once
Stall can occur at any attitude at any airspeed
Must reduce the angle of attack and stay coordinated
Weight
The force exerted by gravity = 1G
In any arc (turns, pull-ups, pushovers) the g’s change
Remember lift opposes weight
Thrust
Forward acting force
More thrust than drag = acceleration
Developed by the prop in our planes
Remember thrust opposes drag
Drag
The rearward force acting opposite to the airplanes forward motion
2 types of drag:
1. Parasite
2. Induced
Parasite Drag
Caused by protuberances extending in the air stream
Form drag e.g. Landing gear
Interference drag e.g.wing joins fuselage (combined forces of skin friction and form drag 50 to 200% greater in combination)
Skin friction e.g. Rivet heads, frost
Induced Drag
Is direct result of creating lift
Caused by the energy it takes to generate the wing tip vortices
Lift Vs Drag Curve
Drag varies at the square of the airspeed
Ground Effect
Airflow patterns change around the wing
Causing a lower value of induced drag
This causes a lower angle of attack for the same amount of lift
Thrust required is also lower
Ground Effect
Reduction of wingtip vortices
Reduces induced drag
This occurs half the wingspan above the ground
Wing span on the B-19 is 32’9″
Stability And Control
What kind of stability would be affected here?
Yaw Stability about the vertical axis
What kind of stability would be affected here?
Roll Stability about the longitudinal axis
Where’s the Depends when you need em?
Longitudinal Axis
Runs down the center of the fuselage.
This axis deals with roll stability or lateral stability about the longitudinal axis.
Stability on this axis determines how well the plane will right itself when encountering gusts.
Longitudinal Stability – Power Effects
Direct effects include the vertical location of the thrust line with respect to the longitudinal axis.
If below, nose up.
If above nose down.
Longitudinal Stability – CG
CG forward of limits
Very stable
Slower cruise
Hard to flare
Longer takeoff roll
CG aft of limits
Unstable
Faster cruise
Shorter takeoff roll, may stall on climb out
May be unrecoverable in the stall
Tail down force
Lateral Axis
Runs down the wings.
This axis deals with pitch stability or longitudinal stability about the lateral axis.
This stability is important because it determines the pitch characteristics of the plane.
Lateral Stability
Indirect effects are the tail down force.
The tail is the single largest contributor to longitudinal stability.
This increases with an increase in airspeed or propeller slipstream causing the pitch to increase.
Lateral Stability – Dihedral
Gust causes wing to bank
Bank without turn sets up side slip
Side slip increases angle of attack on downward wing
More lift then returns wings to level
Vertical Axis
Runs vertically through the fuselage.
This axis deals with yaw stability or directional stability about the vertical axis.
Yaw angle or beta is the primary reference in lateral stability as well as directional stability considerations.
Vertical Stability
Size and placement of vertical stabilizer
Strakes
Keel effect
Static Stability
Is the initial tendency of an aircraft to move, once it has been displace from its equilibrium position.
Static Stability
Positive static stability.
Would be the initial tendency to return to the original position.
Static Stability
Negative static stability.
Would be the initial tendency to move away from the original position.
Static Stability
Neutral static stability.
Would be the initial tendency to stop at a random point neither moving farther away from or towards the original position.
Dynamic Stability
Is the movement over a period of time.
This is usually explained in terms of oscillatory movement.
Dynamic Stability
Positive dynamic.
Is when the oscillations are getting smaller over time.
Dynamic Stability
Negative dynamic.
Is when the oscillations are getting larger over time.
Dynamic Stability
Neutral dynamic.
Is when the oscillations are staying about the same size over time.
Desired Combination
Positive static, positive dynamic
C.O.L.
The center of lift related to cg determines a large part of stability.
If the cg is lined up with center of lift neutral stability will result.
If the cg is behind the center of lift, negative stability will result.
If the cg is in front of center of lift, positive stability will result.
Four Left Turning Forces
Torque
Gyroscopic precession
P factor
Slipstream
Torque
Opposite and equal reaction to motor
Low speed high power
Torque
Gyroscopic Precession
When deflecting a spinning disk (prop) the force is applied 90° in direction of rotation
Happens during pitch changes
Causes a left turn when the tail comes up in tailwheel aircraft on takeoff
Gyroscopic Precession
P Factor
Descending blade on right side gets bigger bite
Happens in a climb
Also happens in a descent
P-factor
Slip Stream
Airflow off the prop strikes left side of tail
Lower airspeeds
Slipstream
Glide
Occurs at max L/D ratio
78 knots at gross weight
Configuration, wind
Forces In A Turn
Vertical component of lift controlled by pitch
Horizontal component of lift controlled by bank
Centrifugal force
Weight
Resultant load and total lift
Forces in the Turn
Forces In A Turn
Turns increases load factor or g’s
Higher stall speed with increase in load factor
Load factor squares as the stall speed doubles
vLF x 57 = new stall speed 2gs 60 degrees bank stalls at 80.6 knots
Rate and Radius of Turn
Let’s take a closer look at this stall/bank angle thing
No flaps stall speed of 57
Upwind to crosswind turn bank angle of 40°
Climbing at Vx 65 knots
40° is roughly equal to 1.3gs
Poof! Stall spin die
Thank you, thank you very much
Load Factor Vs Bank Angle
Other Turning Considerations
Adverse yaw
Over banking tendency