Aerodynamics

Question 1

What is the planform?

Answer 1

A planform is the shape of the wing as viewed from directly above.

Question 2

What factors go into the planform design?

Answer 2

1. Aspect Ratio
2. Taper Ratio
3. Sweepback

Question 3

What is Aspect Ratio?

Answer 3

The ratio of wing span to wing chord. Can be thought of as the length of the wing divided by the width of the wing.

Question 4

What occurs if the Aspect Ratio is increased?

Answer 4

An increase in aspect ratio decreases the drag, especially at high angles of attack. High aspect ratio results in smaller wingtips, which decreases induced drag.

Question 5

What is an important factor that needs to be remembered if you increase the aspect ratio?

Answer 5

With an increase in aspect ratio, there is an increase in the length of span, with a corresponding increase in the weight of the wing structure, which means the wing must be heavier to carry the same load. Part of the gain is lost because of the increased weight. A compromise is necessary to obtain the best results.

Question 6

Do most GA aircraft have relatively high or low aspect ratios?

Answer 6

Most GA aircraft have relatively high aspect ratios. This is because they are operated at high coefficients of lift because they are typically slower compared to other aircraft.

Question 7

What type of planes require low aspect ratios?

Answer 7

Airplanes that are developed to operate at very high speeds demand greater aerodynamic cleanness and greater strength and require lower aspect ratios.

Question 8

What does a low aspect ratio result in?

Answer 8

1. High wing loadings.
2. High stall speeds.
3. Coefficient of lift is generally lower, so the plane must be flying faster to compensate.

Question 9

What is taper ratio?

Answer 9

Taper is the decrease from wing root to wingtip in wing chord or wing thickness. Can be thought of as the ratio of the root chord to the tip chord.

Question 10

What does tapering cause?

Answer 10

Tapering causes a decrease in drag and an increase in lift. Smaller wingtips = less induced drag.

Question 11

What are the benefits of a rectangular wing?

Answer 11

1. Simpler to produce and repair.

2. The roots usually stall first, providing more warning of a stall with aileron effectiveness.

Question 12

What is sweepback?

Answer 12

The rearward slant of a wing, horizontal tail, or other airfoil surface.

Question 13

How is sweepback beneficial?

Answer 13

1. Helps planes flying at very high speeds.

2. Contributes to lateral stability in low-speed planes.

Question 14

What is controllability?

Answer 14

The capability of an aircraft to respond to the pilot’s control, especially with regard to flight path and attitude. It is the quality of the aircraft’s response to the pilot’s control application when maneuvering the aircraft, regardless of its stability characteristics.

Question 15

What is maneuverability?

Answer 15

The quality of an aircraft that permits it to be maneuvered easily and to withstand the stresses imposed by maneuvers. It is governed by the aircraft’s weight, inertia, size and location of flight controls, structural strength, and power plant. It is an aircraft design characteristic.

Question 16

What is stability?

Answer 16

Stability is the inherent quality of an aircraft to correct for conditions that may disturb its equilibrium and to return to or to continue on the original flight path. Primarily a design characteristic.

Question 17

What is static stability?

Answer 17

Refers to the initial tendency, or direction of movement, back to equilibrium. In aviation, this refers to the aircraft’s initial response when disturbed from a given pitch, yaw or bank.

Question 18

Describe the three different types of static stability.

Answer 18

1. Positive Static Stability: The initial tendency of the aircraft to return to the original state of equilibrium after being disturbed.
2. Neutral Static Stability: The initial tendency of the aircraft to remain in a new condition after its equilibrium has been disturbed.
3. Negative Static Stability: The initial tendency of the aircraft to continue away from the original state of equilibrium after being disturbed.

Question 19

What is dynamic stability?

Answer 19

Refers to the aircraft response over time when disturbed from a given pitch, yaw, or bank.

Question 20

Describe the three different types of dynamic stability.

Answer 20

1. Positive Dynamic Stability: Over time, the motion of the displaced object decreases in amplitude and, because it is positive, the object displaced returns toward the equilibrium state.
2. Neutral Dynamic Stability: Once displaced, the displaced object neither decreases nor increases in amplitude.
3. Negative Dynamic Stability: Over time, the motion of the displaced object increases and becomes more divergent.

Question 21

What is longitudinal stability?

Answer 21

Longitudinal stability is the stability about the aircraft’s lateral axis of rotation.

Question 22

What contributes to longitudinal stability?

Answer 22

The CG, CL, and tail. The CG and tail are downward forces, while the CL is an upward force. The CG and tail balance each other out, keeping the aircraft level.

Question 23

What is lateral stability?

Answer 23

Lateral stability is the stability about the aircraft’s longitudinal axis of rotation.

Question 24

What design factors contribute to lateral stability?

Answer 24

1. Dihedral
2. Sweepback
3. Keel Effect
4. Weight Distribution
5. Wing Location

Question 25

What is dihedral?

Answer 25

Dihedral is when the outer tips of the wings are higher than the wing roots. An upward angle of the wing.

Question 26

How does dihedral contribute to lateral stability?

Answer 26

When a gust causes a roll, a sideslip will occur. The wing slipping into the wind is subject to an increase in AOA and develops an increase in lift. The wing away from the wind is subject to a decrease in AOA and develops a decrease in lift. The changes in lift create a rolling moment that raises the windward wing.

Question 27

How does sweepback contribute to lateral stability?

Answer 27

10 degree of sweepback on a wing provides about 1 degree of effective dihedral. When a disturbance causes an aircraft to slip or drop a wing, the low wing presents its leading edge at an angle that is more perpendicular to the relative airflow. The low wing acquires more lift, rises, and the aircraft is restored to its original flight attitude.

Question 28

How does wing location effect lateral stability?

Answer 28

A high wing configuration can provide about 5 degrees of effective dihedral over a low wing configuration.

Question 29

Name the four turning tendencies.

Answer 29

1. Torque Effect 2. Gyroscopic Precession 3. Spiraling Slipstream 4. P-Factor

Question 30

Explain torque effect.

Answer 30

Involves Newton’s Third Law: For every action, there is an equal and opposite reaction. While the internal engine parts & propeller are revolving in one direction, an equal force is trying to rotate the aircraft in the opposite direction.

Question 31

What does torque effect cause when airborne?

Answer 31

The aircraft to rotate about the longitudinal axis to the left.

Question 32

What does torque effect cause when on the ground?

Answer 32

It wants to roll the airplane to the left, but can't since both wheels are on the ground. This causes the left main landing gear to have more weight applied to it, making the friction greater than the right landing gear. This causes the aircraft to yaw to the left.

Question 33

Explain spiraling slipstream.

Answer 33

The rotation of an aircraft propeller gives a corkscrew or spiraling rotation to the slipstream. The slipstream strikes the vertical fin on the left side, causing the aircraft to yaw towards the left.

Question 34

When is spiraling slipstream strong? Weak?

Answer 34

At high propeller speeds and low forward speeds, this spiraling rotation is very compact and exerts a strong sideward force on the aircraft’s vertical tail surface. As forward speed increases, the spiral elongates and becomes less effective.

Question 35

Explain gyroscopic precession.

Answer 35

Precession is the resultant action, or deflection, of a spinning rotor when a deflecting force is applied to its rim. When a force is applied, the resulting force takes effect 90 degrees ahead of and in the direction of rotation. The rotating propeller makes for a very good gyroscope. Any yawing around the vertical axis results in a pitching moment. Any pitching around the lateral axis results in a yawing moment.

Question 36

Explain P-Factor.

Answer 36

When an aircraft is flying with a high AOA, the “bite” of the downward moving blade is greater than the “bite” of the upward moving blade. This moves the center of thrust to the right of the propeller, causing a yawing moment to the left.

Question 37

Explain P-Factor more in depth in regards to velocity.

Answer 37

This asymmetric loading is caused by the resultant velocity. The right downward swinging blade, is passing through an area of greater resultant velocity than that affecting the left upward swinging blade. Since the propeller blade is an airfoil, increased velocity means increased lift.

Question 38

What is the general definition of load factor?

Answer 38

Load factor is the ratio of the total load acting on the airplane to the gross weight of the airplane.

Question 39

How is load factor measured?

Answer 39

Load factor is measured in the acceleration of gravity, or “Gs”. A LF of 3 means that the total load on the structure is 3x its gross weight, expressed as 3 G’s.

Question 40

Why is load factor important?

Answer 40

1. It is possible for a pilot to impose a dangerous overload on the aircraft structures. 2. An increased load factor increases the stalling speed and makes stalls possible at seemingly safe flight speeds.

Question 41

What are the category system, maneuvering load factor limits?

Answer 41

1. Normal : 3.8 to -1.52 2. Utility (mild acrobatics, including spins) : 4.4 to –1.76 3. Acrobatic : 6 to –3

Question 42

How are vortices created?

Answer 42

Whenever the wing is producing lift, pressure on the lower surface of the wing is greater than the upper surface. The high-pressure air wants to reach the low-pressure air. The path of least resistance are the wing tips. The high-pressure air under the wing tends to flow laterally outward on the wingtip and swirl up to the top of the wingtip and equalize with the low-pressure air. This causes a clockwise vortex on the left wing and a counterclockwise vortex on the right wing.

Question 43

What governs the strength of vortices?

Answer 43

The strength of the vortex is governed by the weight, speed, and shape of the wing. The AOA directly affects the strength. 1. As weight increases, AOA increases. 2. A wing in the clean configuration has a greater AOA than with flaps. 3. As airspeed decreases, AOA increases. As AOA increases, the pressure gradient steepens between the air below and above the wing, making the vortices stronger.

Question 44

What is the behavior of vortices?

Answer 44

Vortices tend to sink and travel with the wind. When larger aircraft vortices sink to the ground, they tend to move laterally (2-3 knots). A wind will decrease lateral movement of the upwind and increase movement of the downwind.

Question 45

How can you avoid wake turbulence when landing and taking off?

Answer 45

1. Landing: Stay above/land beyond the preceding aircraft’s touchdown point. 2. Takeoff: Lift-off before the preceding aircraft’s lift-off point.

Question 46

Name and give a general definition of the four forces of flight.

Answer 46

1. Lift : The upward force created by the effect of airflow as it passes over and under the wing. 2. Weight : Opposes lift, and is caused by the downward pull of gravity. 3. Thrust : The forward force which propels the airplane through the air. 4. Drag : Opposes thrust, and is the backward force, which limits the speed of the plane.

Question 47

Explain how lift is created using Newton's Third Law.

Answer 47

Newton's Third Law states, "For every action has an equal and opposite reaction". As an airfoil has air flowing over the top and bottom of it, the air gets deflected off the trailing edge in a downward motion called "backwash". The equal and opposite reaction is an upward motion, hence lift. Also as you increase the angle of attack, air is hitting the bottom of the airfoil at a more perpendicular angle, causing the airfoil to get deflected upwards. If you think of putting your hand outside a car window on the highway and subjecting it to an angle, your hand gets blown upwards.

Question 48

What is Bernoulli's Principle?

Answer 48

Daniel Bernoulli did an experiment using a Venturi tube. He measured the internal pressure and velocity of a fluid going through the Venturi. What he discovered was that as the fluid increased in velocity, the internal pressure of that fluid decreased.

Question 49

How does Bernoulli's Principle relate to lift?

Answer 49

The curvature or "camber" of the airfoil causes the airflow over the top surface to travel at a higher velocity than the lower surface. The air pressure on top of the airfoil is a lower pressure than the bottom since the airflow is at a higher velocity on the top than the bottom. High pressure always seeks out low pressure. The high pressure under the wing causes a force to push the wing up as it tries to get to the lower pressure on top of the wing. This is called a "pressure gradient", and produces lift.

Question 50

What is an airfoil?

Answer 50

An airfoil is a surface designed to create an aerodynamic force by the use of an airstream.

Question 51

What is a chord line?

Answer 51

The chord line of an airfoil is when you draw an imaginary line from the leading edge to the trailing edge of the airfoil.

Question 52

What is angle of attack and why is it important?

Answer 52

The angle of attack is the angular distance between the chord line of the airfoil and the relative wind. It is important because it directly affects the coefficient of lift, which affects the product of lift. It is also important when discussing stalls.

Question 53

What is the relative wind?

Answer 53

The relative wind is the oncoming direction of airflow in respect to the airfoil. Relative wind is always opposite and parallel to the flight path.

Question 54

What factors affect lift?

Answer 54

1. Density of the Air 2. Surface Area of the Airfoil 3. Coefficient of Lift 4. Velocity

Question 55

What is the lift equation?

Answer 55

L = (1/2)rho*V^2*S*CL

Question 56

Which factors affect the coefficient of lift?

Answer 56

The coefficient of lift is effected by the shape of the wing and the angle of attack.