Airfoil Basics

Question 1

Define the Chord.

Answer 1

The chord, c , extends from the leading edge (LE) to the trailing edge (TE) of the airfoils.

Ref: Lecture 3 Notes

Question 2

Define the “thickness” of an airfoil.

Answer 2

The airfoil thickness is defined as the maximum difference between the upper surface and lower surface of the airfoil, generally expressed as a %of the chord distance.

Ref: Lecture 3 Notes

Question 3

Define the “Mean Chamber Line.”

Answer 3

The mean chamber line is the locus of points halfway between the upper surface and the lower surface as measured perpendicular to the mean chamber line.

Ref: Lecture 3 Notes

Question 4

Lift and moments on an airfoil are mainly due to ______.

Answer 4

The pressure distribution.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 324

Question 5

Below the stall, the pressure distribution around an airfoil is mainly due to the ______ theory.

Answer 5

Inviscid

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 324

Question 6

Define “chamber” with respect to airfoils.

Answer 6

The maximum distance between the mean camber line and the chord line measured perpendicular to the chord line.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 324

Question 7

Define “thickness” with respect to airfoils.

Answer 7

The distance between the upper and lower surfaces measured perpendicular to the chord line.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 324

Question 8

The higher cl_max, the ______ the stalling speed.

Answer 8

Lower

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 329

Question 9

Inviscid theory allows the prediction of what two properties of airfoil performance? What property calculation does it not allow?

Answer 9

1. Angle of attack at zero lift, and the lift slope.
2. cl_max

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 329

Question 10

True or False

The lift slope is not influenced by Re; however, cl_max is dependent upon Re.

Answer 10

True

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 329

Question 11

What is the Reynolds Number?

Answer 11

A dimensionless parameter that governs the strength of inertia forces relative to viscous forces in a flow.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 329

Question 12

True or False

The moment coefficient for an airfoil is independent of Re except at very large angles of attack.

Answer 12

True

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 330

Question 13

What two things contribute to the drag coefficient?

Answer 13

1. Skin friction drag
2. Pressure drag due to flow separation

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 330

Question 14

Pressure drag is commonly referred to as ____.

Answer 14

Form drag.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 330

Question 15

Profile drag is the sum of _____.

Answer 15

1. Skin friction drag
2. Pressure drag (aka form drag)

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 331

Question 16

Skin friction and flow separation are both ____ effects.

Answer 16

Viscous

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 331

Question 17

The profile drag coefficient (cd) is dependent upon what non-dimensional number? Why?

Answer 17

1. Reynolds Number (Re)
2. Because the profile drag coefficient is the sum of skin friction and form drag; both of which are viscous effects.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 331

Question 18

Define “Aerodynamic Center.”

Answer 18

The point on the airfoil about which the moment is independent of the angle of attack.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 331

Question 19

True or False
The circulation (Gamma) around a point vortex is equal to the strength of that vortex.

Answer 19

True

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 335

Question 20

How does nature enforce the Kutta conditions?

Answer 20

Through friction.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 342

Question 21

For a thin, symmetric airfoil, the lift coefficient is ______.

Answer 21

2pialpha

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 352

Question 22

For a thin, symmetric airfoil, the lift slope (a0) is ____.

Answer 22

2*pi

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 352

Question 23

For a thin, symmetric airfoil, the moment about the leading edge is _____.

Answer 23

-cl/4

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 354

Question 24

For a thing, symmetric airfoil, the moment about the quarter chord point is _____.

Answer 24

Zero.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 354

Question 25

Where is the center of pressure for a thin symmetric airfoil?

Answer 25

The quarter chord point.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 354

Question 26

For a thin, symmetric airfoil, the center of pressure and aerodynamic center are at the _____.

Answer 26

Quarter chord point.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 354

Question 27

For a thin, non-symmetric airfoil, the lift slope is ____.

Answer 27

2pi

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 359

Question 28

True or False

For a thin, cambered airfoil, the quarter chord is the center of pressure.

Answer 28

False

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 36

Question 29

For a thin, chambered airfoil, where is the aerodynamic center?

Answer 29

The quarter chord point.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 360

Question 30

The center of pressure for a cambered airfoil varies with _____.

Answer 30

Lift coefficient.

Ref: Anderson, Fundamentals of Aerodynamics, Pg. 361