Theory Videos

Question 1

What is the definition of the center of pressure?

Answer 1

The point about which no moment is produced by a distributed load.

Question 2

For a uniform load the center of pressure is located at the ____.

Answer 2

Centroid.

Question 3

In general, what three design choices can influence lift along the span?

Answer 3

1. Plan form shape/taper ratio
2. Twist
3. Airfoil chamber

Question 4

Downwash distribution is related to the lift distribution through the _____.

Answer 4

Bio-Savart Law

Question 5

What influences the strength of the downwash?

Answer 5

The trailing vorticies.

Question 6

For small angles of attack what is the formula for the induced angle of attack?

Answer 6

w/U_infinity

Question 7

Induced drag is a purely _____ effect.

Answer 7

Geometric

Question 8

If the downwash is zero then what are the values for the induced angle of attack and the effective angle of attack?

Answer 8

ai = 0
aeff = a_geometric

Question 9

For an elliptic lift distribution, is the induced angle of attack constant with chord?

Answer 9

yes

Question 10

Does lifting line theory tell you when the airfoil will stall?

Answer 10

No, only a viscous theory can provide something like that.

Question 11

For an elliptic case, how does the wing stall?

Answer 11

Everywhere all at once.

Question 12

What are the values for e and delta in an elliptic wing case?

Answer 12

e =1

delta =0

Question 13

Define the taper ratio

Answer 13

TR = CT / CR

Question 14

When using the co-location method, we only consider _____.

Answer 14

Symmetric lift distributions. (n = odd numbers for the Fournier coefficients)

Question 15

When using an elliptic lift distribution, you can usually assume what value for C_l_alpha? Can you assume the same value for C_L_alpha?

Answer 15

2*PI

NO!

Question 16

The lift curve for the slope of the wing is ____ 2pi.

Answer 16

Less than

Question 17

The amount that the lift slope for a wing is less than the lift slope for an airfoil depends on the ___.

Answer 17

Aspect ratio

Question 18

Does the geometric angle of attack vary with span?

Answer 18

No

Question 19

When using an alpha vs cl graph and you need to apply it to a wing, what should the value of alpha be? What is the exception?

Answer 19

The effective angle of attack

An elliptic wing

Question 20

For the 2D case, profile drag is the sum of what two drag components?

Answer 20

Friction and form drag.

Question 21

Profile drag is also called ____ drag when a 3-D case is considered instead of a 2D case.

Answer 21

parasite

Question 22

Total drag for a 3D airfoil is the sum of ____.

Answer 22

parasite and induced drag where parasite is the sum of the friction and form (pressure) drag

Question 23

Important!

For an elliptical lift distribution, the 2D lift coefficient is ____ along the wingspan.

Answer 23

Constant

Question 24

Define an aircraft’s range.

Answer 24

The distance an aircraft can travel per unit fuel or altitude.

Question 25

The max range occurs at _______ drag

Answer 25

minimum

Question 26

With respect to an aircraft's performance in flight; the max L/D gives you the ______

Answer 26

Max range

Question 27

Define "endurance," with respect to the performance of an aircraft.

Answer 27

The maximum amount of time that the aircraft can stay in the air.

Question 28

The speed for max endurance is _____ the speed for max range.

Answer 28

Less than

Question 29

True or False | For an elliptical lift distribution, the CL_max is the same as Cl_max.

Answer 29

True

Question 30

Give the formula for the chord distribution for a tapered wing.

Answer 30

c(y) = c_r*(1-2y/b)+ct*(2y/b)

Question 31

True or false | The geometric angle of attack is always constant.

Answer 31

True

Question 32

What is the general formula for the chord distribution as a function of span for a parabolic wing?

Answer 32

Ay^2 +b | Where you solve for the constants.

Question 33

With respect to potential theory; any flow fields that result in lift must contain a ______.

Answer 33

Vortex

Question 34

With respect to potential theory; no-slip is accounted for by a _____ in the superposition even though potential theory does not allow it.

Answer 34

Vortex.

Question 35

How does the chamber of an airfoil affect the pitching moment?

Answer 35

Negative chamber = shift up | Positive chamber = shift down

Question 36

On the cl(alpha) graph, how does affecting the chamber move the line?

Answer 36

Positive chamber = shift left | Negative chamber = shift right

Question 37

What is the location of the COP for a symmetric airfoil?

Answer 37

The quarter chord point

Question 38

How does adding flaps affect the cl vs alpha graph?

Answer 38

They shift the graph to the left.

Question 39

What does it mean to be in "trim?"

Answer 39

The forces and moments on the wing are zero.

Question 40

The lift and drag coefficients are functions of what three non-dimensional numbers.

Answer 40

Angle of attack Reynolds Number Mach Number

Question 41

What is the value of the pressure coefficient at a stagnation point?

Answer 41

1 (can be proved with Bernoulli's equation)

Question 42

What are the basic conservation laws?

Answer 42

Mass, momentum, and energy

Question 43

Under what circumstances would a non-internal control volume be needed?

Answer 43

If the CV is accelerating.