Aerodynamics of Flight

What is "limit load"?

A force applied to an aircraft that causes a bending of the aircraft structure that does not return to the original shape.

What is a "secondary stall"?

A stall that may occur after recovering too abruptly from a previous primary stall. It may be demonstrated with quick back pressure just after a stall occurs.

What is a "Spin"?

A uncoordinated stall resulting in auto-rotation about the vertical axis and a shallow, rotating, downward path.

What factors affect air density?

Altitude - The higher the altitude, the less dense the air. Temperature - The warmer the air, the less dense the air. Humidity - More humid air, the less dense the air.

What is an "Airfoil"?

An body moved through a fluid produces an aerodynamic force. The component of this force perpendicular to the direction of motion is called lift.

What is "Ground Effect"?

An improved performance that is experienced when operating within the same distance as the aircraft's wingspan near the ground. The ground disrupts wingtip vortices reducing lift induced drag.

Why is Load factor important?

An overload can possibly cause structural damage and an increase load factor increases the stalling speed, leading to an accelerated stall while in a turn.

What is "Washout also called wing twist"?

Angle of incidence is greater at the wing roots and decreases across the span, becoming lowest at the wing tip.

How does a wing create lift?

As the air flow changes direction as it passes over the airfoil and follows a path that is curved downward. According to Newton's second law, this change in flow direction requires a downward force applied to the air by the airfoil. Then, according to Newton's third law, the air must exert an upward force on the airfoil. The overall result is that a reaction force which is this.

What is "Torque Effect"?

As the propeller rotates clockwise, the opposite reaction will causes a left rolling tendency. Based on Newton's third law states that "for every action, there is an equal and opposite reaction".

Why does more weight increase Maneuvering speed?

As weight is increases, pitch angle also increases when flying at the same speed. The more closer the aircraft is at the Critical Angle of Attack, so Maneuvering speed must increase.

When can a stall happen?

At any pitch attitude or bank angle or at any airspeed.

What are "Wingtip Vortices"?

Circular patterns of rotating air left behind a wing as it generates lift. They rotate from bottom to top of the wing. Created by Induced Drag.

What is the recovery procedure for a spin?

Close the throttle, Neutralize the ailerons, Apply full rudder opposite of the rotation.

What is "Density Altitude"?

Density Altitude is the altitude in the standard atmosphere corresponding to a particular density.

Why does extending the flaps or slats, lower the stall speed?

Extending flaps or slats increases the wing camber and extends the cord line. Which increases the lift of the wing and allows the aircraft to fly at a smaller angle of attack.

What are the problems of Ground Effect?

Floating beyond intentional touchdown point and might run out of runway. Capable of taking off well below the recommended speed (Vr).

Why is it suggested that airplanes should operate under Va in turbulent air?

Gusts will cause the airplane's wing to stall before exceeding the limit load.

What is "Spiraling Slipstream"?

Happens as air flows though the propeller and wraps around the fuselage and then hits the left side of your aircraft's tail, creating a yawing motion, and making the aircraft turn left.

What is an "accelerated stall"?

Happens when the load factor is increased past the maximum positive lift capability, which causes the wing to stall.

How does a wind effect takeoff performance?

Headwind Increase in aircraft performance. Shorten takeoff distance. Increase angle of climb. Tailwind will have the opposite effect.

How does a wind effect landing performance?

Headwind Increase in aircraft performance. Steepening the approach angle. Reducing the landing distance. Tailwind will have the opposite effect.

If the aircraft was overloaded, how would it perform during landing?

Higher landing speed, Longer landing roll, and Excessive weight on the nosewheel.

If the aircraft's center of gravity was located forward, how would it perform?

Higher stall speed. Slower cruise speed. More stable. Greater back elevator pressure required to keep nose up.

What is "compressibility"?

In transonic speed ranges, air around the airframe begins to compress which causes a change in the density of the air.

How does a high density altitude (low air density) effect performance?

Increased takeoff distance. Reduced rate of climb. Increased airspeed on approach and landing. Increased landing roll distance.

What is the centrifugal force encountered while in a turn?

Inertia, Its the "equal and opposite reaction" of the airplane to the change in direction and acts equal and opposite to Centripetal force.

What is the result of a downward deflection of a aileron?

It increases the camber of the airfoil causing an increase in both lift and drag.

What is "Parasite Drag"?

It is comprised of all the forces that work to slow an aircraft's movement. It is not associated with the production of lift. There are three types of parasite drag: form drag, interference drag, and skin friction.

What is "ultimate load"?

It is the load factor applied to the aircraft beyond the limit load and at which point the aircraft material experiences structural failure (breakage).

What is the "Aspect Ratio" of a wing?

It is the ratio of its span to its mean chord. It is often used to predict the aerodynamic efficiency of a wing because the lift-to-drag ratio increases with aspect ratio, improving fuel economy in aircraft.

What is the "Planform" of a wing?

It is the shape of the wing as viewed from directly above and deals with airflow in three dimensions. Aspect ratio, taper ratio, and sweepback are factors in planform design that are very important to the overall aerodynamic characteristic of a wing.

What happens to the center of pressure when the angle of attack of a symmetrical wing is increased?

It will have very limited movement.

What can a pilot do to keep a constant airspeed when there is a constant power?

Keep a constant angle of attack.

What can increase load factor?

Level turns, turbulence, and increase in speed.

By changing the angle of attack of a wing, what can the pilot control?

Lift, Airspeed, and drag.

If the aircraft was overloaded, how would it perform during cruise?

Lower max altitude, Shorter range, Reduced cruising speed, Reduced maneuverability, and Higher stalling speed and Va.

If the aircraft's center of gravity was located aft, how would it perform?

Lower stall speed. Higher cruise speed. Less stable.

How does weight effect Maneuvering speed?

Maneuvering speed increases with an increases in weight.

What is "Gyroscopic Precession"?

Mostly happens to tailwheel airplanes, it is the result of the rising of the tail on take off. As the tail comes up, a force is applied to the top of the propeller. And since the propeller is spinning clockwise, that force is felt 90 degrees to the right. That forward moving force, on the right side of the propeller, creates a yawing motion to the left.

What is "Pressure Altitude"?

Pressure Altitude is the altitude in the standard atmosphere corresponding to a particular pressure. It the altimeter is set for 29.92"Hg the Altitude indicated is pressure Altitude as in Flight Levels

What are "Stall Strips"?

Small obstructions located at the inner leading edge of a wing that prevent the smooth flow of air over the wing at high angles of attack.

Why do wings have Stall Strips?

So the stall strips, located at the wing root, stalls the root before the wing tips. This provides the aircraft with continued aileron control and some resistance to spinning.

Why do wings have Washout or wing twist?

So the wing root stalls before the wing tips, providing the aircraft with continued aileron control and some resistance to spinning.

When is normal stall V-speed (Vs) reliable?

Straight and level flight.

How does a wind effect cruise performance?

Tailwind Increase in aircraft performance. Increase ground speed. Reduce fuel requirements. Headwind will have the opposite effect.

What is "Skin Friction Drag"?

The aerodynamic resistance due to the contact of moving air with the surface of an aircraft. Every surface, no matter how apparently smooth, has a rough, ragged surface when viewed under a microscope.

What is "Lift Induced Drag"?

The aft component of lift. Near the tips of a lifting wing, spanwise airflow flows from a region of high pressure below the airfoil into a region of low pressure above the airfoil. This creates wingtip vortices. Wingtip vortices also create downwash, which increases the angle of attack of the relative wind downward. Since lift is perpendicular to relieve wind, this creates an aft component of lift which is lift induced drag. This results in drag. As AOA increases, the pressure gradient increases. This creates stronger wingtip vortices, which creates more lift induced drag.

What is the "Angle of Attack"?

The angle between the oncoming air or relative wind and a chord line on the airfoil.

What is the "Angle of Incidence"?

The angle of the longitudinal axis of the aircraft and the chord line of the airfoil.

What is the "Critical Angle of Attack"?

The angle which produces maximum lift coefficient. Passing this causes an stall.

What is the "Relative Wind"?

The direction of movement of the atmosphere relative to an airfoil. Equal and opposite of the flight path.

What does the angle of attack of a wing directly controls?

The distribution of pressures acting on the wing.

What is "Form Drag"?

The drag on a body moving through a fluid as a result of the shape of the body. It can be reduced by streamlining

What is "Interference Drag"?

The drag that is generated by the mixing of airflow streamlines between airframe components.

What is the Centripetal force encountered while in a turn?

The horizontal component of lift, this overcomes the inertia of the Centrifugal force.

What is "Va, Maneuvering speed"?

The max speed at which abrupt control movements can be applied or could be flown in turbulence without exceeding the design load factor limits. The aircraft should stall before the load becomes excessive.

What is "Adverse Yaw"?

The natural and undesirable tendency for an aircraft to yaw in the opposite direction of a roll. It is caused by higher drag on the outside wing, which is producing more lift.

What is the "dihedral angle" of a wing?

The positive angle of the wings to the lateral axis.

What is "Load factor"?

The ratio of the total load supported by the aircraft's wings (lift) to the actual weight of the aircraft and its contents. Expressed as "Gs". Lift/Weight

What is "longitudinal stability"?

The stability of an aircraft in the longitudinal, or pitching, plane under steady-flight conditions.

If the aircraft was overloaded, how would it perform during takeoff?

There would be a Higher takeoff speed, Longer takeoff run, and a Reduced rate and angle of climb during climb.

What is the "Trailing edge Stagnation Point"?

This is where the airflow from above and below the wing joins after being separated.

What is the "Leading edge Stagnation Point"?

This is where the airflow separates and goes above or below the wing. Local velocity of the air is zero.

What is a "crossed-control stall"?

This stall demonstrates the importance of coordinated flight. It involves moving the ailerons in one direction and rudder in the other. This stall is likely to occur when poor planning with turning from base leg to final approach at a slow airspeed and controls crossed will result in a stall or spin.

What are the four forces acting on an aircraft?

Thrust, Drag, Lift, and Weight. They are equal in straight-and-level, unaccelerated flight.

What are the four Left Turning Tendencies?

Torque Effect, P-Factor, Gyroscopic Precession, and Spiraling Slipstream.

What is a "Stall"?

When the AoA passes the critical angle of attack, airflow begins to separate from the upper surface of the airfoil. This airflow begins to become turbulent and create eddies. This results in the wing is no longer producing enough lift to support the aircraft's weight.

Why do the wings have a dihedral angle?

When the aircraft is banked, the lower wing has a higher angle of attack and creates more lift. This helps with lateral stability as the lower wing rolls the aircraft to wings level. This is called dihedral effect.

What is "P-Factor (Asymmetric Loading)"?

When the aircraft is flying at a high angle of attack, the downward moving propeller blade is taking a bigger 'bite' of air causing a turn to the left. Also called asymmetric blade effect.

What causes a spin?

When the aircraft is in an uncoordinated stall. The wing on the inside of the turn is stalled more then the outside wing. The outside wing creates more lift.

What is a "elevator trim stall"?

When the airplane is in a gliding approach similar to a final approach for landing and is trimed for a hands-off glide, when go-around power is applied, the nose will rise until the critical angle of attack is reached. The airspeed will slow quickly as the airplane reaches a pitch attitude that is dangerously too high and stalls.

What is "Bernoulli's Principle"?

When there is an increase in speed of a fluid, there will be an decrease in static pressure.

What is "Principle of Continuity"?

With a flowing fluid, when there is a decrease in area, there is an increase in velocity.

Is lift still being produced in a stall?

Yes. But not enough to support the aircraft's weight.