Aerodynamics

Question 1

What are the four elements that cause or produce a twisting or rotating motion around at least one of the airplane’s three axes, resulting in left turning tendencies?

Answer 1

Torque
Spiraling Slipstream
Gyroscopic Precession
P Factor (Asymmetric Loading of the Propeller)

Question 2

What are the four forces of flight?

Answer 2

Lift, Weight, Thrust and Drag.

Question 3

What is the “angle of incidence?”

Answer 3

The angle of incidence is the angle formed by the chord line of the wing and a line parallel to the longitudinal axis of the airplane.

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Question 4

What is the “angle of attack?”

Answer 4

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

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Question 5

What is “relative wind?”

Answer 5

The direction of airflow with respect to the airfoil. With an aircraft, the relative wind is parallel to and opposite the flight path of the airplane.

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Question 6

What is “camber?”

Answer 6

“Camber” means “curvature.” The camber of an airfoil is the characteristic curve of its upper and lower surfaces. The upper camber is more pronounced, while the lower camber is comparatively flat.

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Question 7

What is an airfoil?

Answer 7

Any surface, such as a wing, propeller, rudder, or even trim tab, which provides aerodynamic force when it interacts with a moving stream of air.

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Question 8

What is an “aspect ratio?”

Answer 8

The aspect ratio is the span of the wing, divided by its average chord.

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Question 9

What is “asymmetric thrust,” or “P-factor?”

Answer 9

Asymmetric thrust, or P-factor, is the tendency for an aircraft to yaw to the left due to the descending propeller blade on the right producing more thrust than the ascending blade on the left.

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Question 10

What are the axes of an aircraft?

Answer 10

There are three axes, or imaginary lines, that pass through an aircraft’s center of gravity, and they are at 90* to each other.

• The axis from nose to tail is the longitudinal axis.
• The axis that passes from wingtip to wingtip is the lateral axis.
• The axis that passes vertically through the center of gravity is the vertical axis.

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Question 11

What is Bernoulli’s Principle?

Answer 11

Bernoulli’s Principle says that as the velocity of a fluid (such as air) increases, its pressure decreases.

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Question 12

What is the “center of gravity,” or “CG?”

Answer 12

The center of gravity (CG) is the point at which an airplane would balance if it were possible to suspend it at that point. It is usually expressed in inches from the reference datum.

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Question 13

What are “center of gravity limits?”

Answer 13

Center of gravity limits are the specified forward and aft points within which the CG must be located during flight. These limits are found in the airplane’s POH.

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Question 14

What is Centrifugal Force?

Answer 14

Centrifugal Force is the outward acting force that results from the effect of inertia during the turn.

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Question 15

What is Centripetal Force?

Answer 15

The horizontal component of lift creates a force directed inward toward the center of rotation during turning flight, and is known as centripetal force.

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Question 16

What is a chord line?

Answer 16

A chord line is an imaginary straight line drawn through an airfoil, from the leading edge to the trailing edge.

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Question 17

What is “Coefficient of Lift?”

Answer 17

The coefficient of lift (CL) is a way to measure lift as it relates to angle of attack. It is the ratio between lift pressure and dynamic pressure. CL is based on airfoil design and angle of attack, and is determined by wind tunnel tests. Every airfoil has an angle of attack where maximum lift occurs.

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Question 18

What is “Controllability?”

Answer 18

Controllability is the measure of the response of an aircraft relative to the pilot’s flight control inputs.

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Question 19

What is the “critical angle of attack?”

Answer 19

The critical angle of attack is the angle of attack at which a wing stalls, regardless of airspeed, flight attitude, or weight.

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Question 20

What is “Dihedral?”

Answer 20

Dihedral is the upward angle of the airplane’s wings with respect to the horizontal. It is usually just a few degrees, and it contributes to the lateral stability of the airplane.

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Question 21

What is Directional Stability?

Answer 21

Stability about the vertical axis is called directional stability. The primary contributor to directional stability is the vertical tail, which causes an airplane in flight to align with the relative wind, much like a weathervane.

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Question 22

What is “Drag?”

Answer 22

Drag is the force that acts opposite the direction of flight. It opposes the forward-acting component of thrust, and limits the forward speed of the airplane.

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Question 23

What is “Gyroscopic Precession?”

Answer 23

Gyroscopic Precession is the resultant action when you apply a force to a rotating body. It will react 90 degrees ahead of, and in direction of rotation, thus producing a left-turning tendency.

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Question 24

What are the two types of drag?

Answer 24

Drag is broadly classified a either parasite or induced.

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Question 25

What are the three types of parasite drag, and what is its relationship with airspeed?

Answer 25

As the airspeed doubles, parasite drag increases fourfold. There are three types of parasite drag:

• Form Drag: Anything protruding into the airflow that is not contributing to lift is causing form drag.
• Interference Drag occurs wherever one surface joins another, for example, where the horizontal stabilizer meets the vertical stabilizer, or the points where the wing strut is attached to the wing and the fuselage.
• Skin Friction Drag is caused by the roughness of the airplane’s surfaces.

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Question 26

What is “Induced Drag,” and how does it relate with airspeed?

Answer 26

Induced drag is known as the “byproduct of lift.” It is the component of lift that acts In a rearward direction. Induced drag increases as the airspeed decreases; it is inversely proportional to the square of the speed. If speed decreases by half, induced drag increases fourfold.
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