Aerodynamics

Question 1

What are the four forces that act on an airplane?

Answer 1

Lift, Weight, Drag and Thrust.

Question 2

What flight condition will result in the sum of the opposing forces to be equal?

Answer 2

In steady-state, straight and level flight, unaccelerated flight. Can be climbing or descending as well.

Question 3

What is an airfoil?

Answer 3

A device designed to create lift.

Question 4

What is the angle of incidence?

Answer 4

The angle formed by the longitudinal axis of the airplane and the chord of the wing. It is fixed and cannot be changed.

Question 5

What is “Relative Wind”?

Answer 5

The direction of airflow with respect to the wing. When a wing moves forward and downward, the wind moves backward and upward. The flight path and relative wind are parallel but in opposite directions.

Question 6

What is the “angle of attack”?

Answer 6

The angle between the chord line and the direction of relative wind.

Question 7

What is “Bernouli’s Principle”?

Answer 7

As velocity of fluid increases, pressure decreases. Velocity of airflow above wing is higher than below the wing, therefore it is more pressure under the wing creating lift.

Question 8

What are several factors that will affect lift and drag?

Answer 8

Wing area, Shape of the Airfoil, Angle of Attack, Velocity of Air and Air Density.

Question 9

What is “torque effect”?

Answer 9

Based on Newtons 3rd Law, for every action there is an equal and opposite reaction. Propeller is rotating in one direction, causing airplane to roll in the opposite.

Question 10

How does torque effect affect the airplane on the ground and in the air?

Answer 10

On the ground it makes the plane turn to the left. In the air it makes the plane roll to the left.

Question 11

What are the four left turning tendencies?

Answer 11

Torque, Gyroscopic Pressecion, Spiral Slipstream and P-Factor.

Question 12

What is “load factor”?

Answer 12

The ratio of total load supported by the wings to the actual weight and it’s contents. High load factor means stalling at lower airspeeds.

Question 13

What causes an airplane to stall?

Answer 13

Excessive angle of attack. Airflow separates from the upper surface of airfoil, resulting in loss of lift.

Question 14

What causes “adverse yaw”?

Answer 14

When making a turn, the wing that is up and higher produces more lift than the other wing, resulting in more drag produced which causes a yawing motion in the opposite direction of the turn.

Question 15

What is ground effect?

Answer 15

A condition of improved performance when an airplane operates near the ground.

Question 16

What major problems can be caused from ground effect?

Answer 16

During Landing - Can cause you to float and land late.

During Takeoff - Can cause you to takeoff too soon without enough airspeed.

Question 17

What is the planform?

Answer 17

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

Question 18

What is Aspect Ratio?

Answer 18

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 19

What occurs if the Aspect Ratio is increased?

Answer 19

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 20

What is stability?

Answer 20

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 21

What is static stability?

Answer 21

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 22

Describe the three different types of static stability.

Answer 22

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 23

What is dynamic stability?

Answer 23

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

Question 24

Describe the three different types of dynamic stability.

Answer 24

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 25

What is longitudinal stability?

Answer 25

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

Question 26

What contributes to longitudinal stability?

Answer 26

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 27

What is lateral stability?

Answer 27

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

Question 28

What design factors contribute to lateral stability?

Answer 28

1. Dihedral 2. Sweepback 3. Weight Distribution 4. .Wing Location

Question 29

What is dihedral?

Answer 29

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

Question 30

How does dihedral contribute to lateral stability?

Answer 30

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 31

Explain spiraling slipstream.

Answer 31

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 32

When is spiraling slipstream strong? Weak?

Answer 32

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 33

Explain gyroscopic precession.

Answer 33

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 34

Explain P-Factor.

Answer 34

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 35

How is load factor measured?

Answer 35

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 36

Why is load factor important?

Answer 36

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 37

What are the category system, maneuvering load factor limits?

Answer 37

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

Question 38

How are vortices created?

Answer 38

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 39

What governs the strength of vortices?

Answer 39

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 40

What is the behavior of vortices?

Answer 40

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 41

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

Answer 41

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 42

What is the relative wind?

Answer 42

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 43

What factors affect lift?

Answer 43

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