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