Aerodynamic Principles of Flight

Airfoil

Any surface, such as a wing, which provides aerodynamic force when it interacts with a moving stream of air.

Aspect ratio

Relation ship between the length and width of a wing. It is the span of the wing, wingtip to wingtip, divided by its average chord.

Drag

The backward, or retarding force that limits the speed of the airplane.

Gyroscopic Precession

When you apply a force to the edge of a spinning object (propeller in this case) parallel to the rotational axis, a resultant force is created in the direction of the applied force, but 90 degrees ahead in the direction of roatation.

Erect spin

most common spin characterized by slightly nose down rolling and yawing motion in the same direction

Fully developed spin

occurs after the incipient stage when the angular rotation rates, airspeed, and vertical speed are stabilized from turn to turn and the flight path is close to vertical

Upwash

the deflection of the oncoming airstream upward and over the wing

Downwash

the downward movement of air behind a wing in flight

overbanking tendency

when entering a turn, the outside wing travel faster than inside wing, it produces more lift than inside wing, causes overbanking tendency

List the basic guidelines for stall recovery

1. Decrease the angle of attack (lower nose) 2. Smoothly apply maximum power 3. Once the airplane recovers, adjust the power as necessary while maintaining coordinated flight.

List the basic guidelines for spin recovery

1. Throttle to idle 2. Neutralize the ailerons 3. Determine the direction of rotation 4. Apply full opposite rudder 5. Briskly apply elevator to neurtral or slightly forward of neutral 6. As rotation stops, neutralize rudders 7. Gradually apply aft elevator (or stablilator) to return to level flight.

Newton's First Law of Motion

A body at rest tends to stay at rest, and a body in motion tends to remain moving at the same speed and in the same direction.

V-g Diagram

A chart that relates velocity to load factor. It is valid only for a specific weight, configuration and altitude and shows the maximum amount of positive or negative lift the airplane is capable of generating at a given speed. Also shows the safe load factor limits and the load factor that the aircraft can sustain at various speeds.

Dutch roll

A combination of rolling and yawing oscillations that normally occurs when the dihedral effects of an aircraft are more powerful than the directional stability. Usually dynamically stable but objectionable in an airplane because of the oscillatory nature.

Wingtip Vortices

A spinning mass of air generated at a wing's tip created by outward-flowing high pressure air from underneath the wing meeting inward-flowing low air pressure on the wing's upper surface. The intensity of a wing vortex - also referred to as wake turbulence - is dependent on an airplane's weight, speed and configuration

Describe how Newton's laws of motion and Bernoulli's principle explain the generation of lift by an airfoil.

According to Bernoulli's principle, the increase in speed of air on the top fo an airfoil produces a drop in pressure and this lowered pressure is a component of total lift. In addition, the decrease in the speed of air on the bottom of an airfoil produces an increase in pressure, and this higher pressure is the other component of total lift. These pressure changes cause the airflow to curve downward, creating downwash behind the airfoil. Newton's third law of motion explains that the action of causing downwash results in a reaction of positive lift.

Radius of turn

Amount of horizontal distance and aircraft uses to complete a turn.

Limit load factor

Amount of stress that an airplane can withstand before structural damage or failure occurs.

Rate of turn

Amount of time it takes for an airplane to turn a specified number of degrees.

Ground effect

As an airplane nears the ground, the flow over the wing cannot be deflected as far downward as it can in flight away from the ground. The result is that the lift is increased and the induced drag is decreased.

Bernoulli's principle

As the speed of a fluid increases, its pressure decreases.

Spiral instability

Associated with airplanes that have strong directional stability in comparison with lateral stability.

Select the true statement regarding the four forces of flight: A. During accelerated flight, thrust and drag are equal. B. The four forces are in equilibrium during unaccelerated flight. C. In straight-and-level unaccelerated flight, all four forces are equal in magnitude.

B

Weight

Caused by the downward pull of gravity

Skin friction drag

Caused by the roughness of the airplane's surfaces

Stall

Caused by the separation of airflow from the wing's upper surface resulting in a rapid decrease in lift.

If angle of bank and altitude are held constant, what can be done to increase the rate of turn?

Decrease airspeed

Does the propwash resulting from high power settings increase or decrease the contribution of wing dihedral to the lateral stability of an airplane?

Decreases

True/False. As airspeed increases, the angle of attack at which an airfoil stalls also increases.

False

True/False: Maneuvering speed increases with a decrease in weight.

False

Newton's Third Law of Motion

For every action there is an equal and opposite reaction

In relation to the center of gravity, in which direction would the center of presure normally move as angle of attack is increased on a cambered wing?

Forward

Induced drag

Generated by the airflow circulation around the wing as it creates lift.

True/False

In straight-and-level, unaccelerated flight, lift equals weight and thrust equals drag.

Will the wing's angle of attack increase or decrease when trailing edge flaps are lowered?

Increased

Explain why induced drag increases as airspeed decreases.

Induced drag is caused by the downwash created by wingtip vorticies formed when teh wing is generating lift. As the air pressure differential between teh upp erand lower surfaces of teh wing becomes greater wth an increase in angle of attack, stronger vorticies form and indcued drag is increased. SInce the wing is usually at a low angle of attack at high speeds, and a high angle at low speeds, a relationship between induced drag and speed can be determined. Indcued drag is inversely proportional to the square of the speed.

Is it more desireable for the wing root or wingtips to stall first and why?

It is preferable for the wing root to stall first. If the wing tips stall first before the root, the disrupted airflow near the wingtip can reduce aileron effectiveness to such an extent that it may be impossible to control the airplane about its longitudinal axis.

What relative airspeed, power, and angle of attack conditions produce the most noticeable left-turning tendencies common to single-engine, propeller-driven aircraft?

Low airspeed, high power settings, and high angles of attack

Design Maneuvering Speed (Va)

Maximum speed at which you can use full, abrupt control movement without overstressing the airframe.

Stall strips

Metal strips attached to the leading edge of each wing near the fuselage; used to ensure positive control during the stall.

Accelerated stall

Occurs at a speed higher than the normal one-G stall speed; critical angle of attack NOT airspeed is the reason for stalls.

Accelerated stalls

Occurs at a speed higher than the normal one-G stall speed; critical angle of attack NOT airspeed is the reason for stalls.

What factors can affect the longitudinal stability of an airplane at high power settings and low airspeed?

On many training aircraft, an increase in thrust increases nose heaviness due to the placement of the thrustline above the center of gravity of the aircraft. This helps counteract the nose-up moment caused by the increased downwash resulting from an increase in power.

The reduction in induced drag due to ground effect is most noticeable when the airplane is within what distance from the earth's surface?

One wingspan.

List the three forms of parasite drag and provid examples of aircraft features that reduce parasite drag.

Parasite drag normally is divide dinto three types: form drag, interference drag, and skin friction drag. Streamlining decreses form drag, and design features, such as wheel fairings and retractable landing gear, can reduce both form and interference drag. Skin friction drag can be minimized by eliminating protruding rivet heads, and emplying a glossy, smooth finish to airplane surfaces.

Load factor

Ratio of the load supported by the airplane's wing to the actual weight of aircraft and its contents.

Angle of incidence

Refers to the angle between the wing chord line and a line paralell to the longitudinal axis of the airplane.

Planform

Refers to the shape of the airplane's wing when viewed from above or below.

Glide ratio

Represents the distance an airplane will travel forward, without power, in relation to altitude loss.

Form drag

Results from the turbulent wake caused by the separation of airflow from the surface of a structure.

Name two design elements that can be used to help offset left-turning tendencies.

Rudder trim tab, an offset vertical stabilizer, or a horizontally canted engine.

An aircraft with strong directional stability and weak lateral stability is prone to what type of undesirable side effect?

Spiral instability

Spiraling Slipstream

Spiraling air over aircraft pushing tail to the right.

Asymmetrical thrust

Tendency of aircraft to yaw due to thrust of operating engine propelling aircraft forward and drag of failed engine.

Critical angle of attack

The angle of attack at which an airfoil stalls (loses lift) regardless of the aircraft's airspeed, attitude, or weight.

Stability

The characteristic of an airplane in flight that causes it to return a condition of equilibrium, or steady flight, after it is disturbed.

Lift

The force created by the effect of airflow as it passes over and under the wing.

Vectors

The forces acting on an airplane

Thrust

The forward force that propels the airplane through th eair. It varies with the amount of engine power being used.

Leading edge

The front, usually rounded, edge of an airplane wing or airfoil.

Trailing edge

The rear edge of a wing.

Positive dynamic stability

The tendency of an oscillating airplane (with positive static stability) to return to its original position relative to time.

Identify the aerodynamic force that opposes the rearward component of weight in a climb.

Thrust

Wing area

Total surface area of the wings

True or Fase: Lift is proportional to the square of the airplane's speed.

True

True/False: When landing in gusty winds, airspeed should be increased above normal to help guard against a stall.

True

Why are high wing aircraft normally designed with less dihedral than low wing aircraft?

Upwash passing around the fuselage just ahead of the wing tens to roll a high wing aircraft toward the upright position, contributing to lateral stability. In a low wing airplane, the downwash aroudn the fuselage tends to be laterally destabilizing since it tens to increase the roll. The amount of dihedral is adjusted to compensate for the effects of fuselage upwash and downwash resultin in a greater requirement for dihedral in a low wing airplane than in a high wing configuration.

Newton's Second Law of Motion

When a body is acted upon by a constant force, its resulting acceleration is inversely proportional to the mass of the body and is directly proportional to the applied force. This law may be expressed by the formula: Force= mass x acceleration

What causes an airplane to turn?

When an airplane is banked, lift is comprised of two components. The airplane turns because the horizontal component of lift creates a force directed inward toward the center of rotation.

centripetal force

Works against the tendency of the aircraft to continue in a straight line, inertia tends to oppose centripetal force toward the outside of the turn.

P-Factor

Yawing moment caused by one propeller blade creating more thrust than it's opposing blade. At high AOA, the downgoing blade produces more thrust and the aircraft yaws to the left. at low AOA it's reversed.

Adverse yaw

Yawing tendency toward the outside of a turn.

All else being equal, will two aerodynamically identical aircraft with different weights be able to glude the same distance over the ground? If so, how can this be accomplished and why?

Yes. Variations in weight do not affect the glide ratio of an airplane, but the heavier aircraft will sink faster, and reach the ground sooner. To travel the same distance maintained by the heavier airplane. This higher airspeed, which corresponds to the best glide airspeed at that weight, increases ground speed and allows the heavier aircraft to cover the same horizontal distance even though its rate of descent is higher.

Identify three methods you can use to control lift during flight.

You can control lift by changing airspeed, changing angle of attack, or by employing high-lift devices such as trailing edge flaps.

Center of pressure

a point along the wing chord line where lift is considered to be concentrated.

Torque

a turning or twisting force

Power on stalls

are normally encountered during take-off, climb-out, and go-arounds

Power off stalls

are practiced to simulate conditions and configurations encountered during a normal landing approach

Best Glide Speed

at a given weight L/Dmax will correspond to a certain airspeed

Parasite drag

drag that does not contribute to lift generation; drag caused by landing gear struts, cooling intakes, antennas, rivet heads, etc.

Positive static stability

initial tendency to return to the position from which it was displaced

Coefficient of Lift (CL)

is determined by wind tunnel tests and is based on airfoil design and angle of attack

Crossed-control stall

is most likely to occur when a pilot tries to compensate for overshooting a runway during a turn from base to final on landing approach

Glide angle

is the angle between the actual glide path of your airplane and the horizon

Centrifugal force

not a true force, but an apparent force that results from the effect of inertia in the turn.

Interference drag

occurs when the airflow around one part of the airplane interacts with the airflow around an adjacent part.

Inverted spin

spinning upside down with yaw and roll occurring in opposite directions. Most likely to occur during aerobatic maneuvers.

Flat spin

the aircraft yaws about its vertical axis with a pitch attitude approximately Level with the Horizon. It is deadly.

maximum lift-to-drag ratio (L/Dmax)

the best glide angle, and the maximum gliding distance.

Spin recovery

the final stage of the spin that occurs when anti-spin forces overcome pro-spin forces.

Incipient spin

the portion of a spin from the time the airplane stalls and rotation starts until the spin is fully developed

Center of gravity

the theoretical point where the entire weight of the airplane is considered to be concentrated.