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Incompressible Flow > Theory Videos > Flashcards

Theory Videos Flashcards

1
Q

What is the definition of the center of pressure?

A

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

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2
Q

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

A

Centroid.

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3
Q

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

A
  1. Plan form shape/taper ratio
  2. Twist
  3. Airfoil chamber
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4
Q

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

A

Bio-Savart Law

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5
Q

What influences the strength of the downwash?

A

The trailing vorticies.

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6
Q

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

A

w/U_infinity

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7
Q

Induced drag is a purely _____ effect.

A

Geometric

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8
Q

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

A 
ai = 0
aeff = a_geometric
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9
Q

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

A

yes

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10
Q

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

A

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

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11
Q

For an elliptic case, how does the wing stall?

A

Everywhere all at once.

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12
Q

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

A

e =1

delta =0

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13
Q

Define the taper ratio

A

TR = CT / CR

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14
Q

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

A

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

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15
Q

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?

A

2*PI

NO!

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16
Q

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

A

Less than

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17
Q

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

A

Aspect ratio

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18
Q

Does the geometric angle of attack vary with span?

A

No

19
Q

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?

A

The effective angle of attack

An elliptic wing

20
Q

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

A

Friction and form drag.

21
Q

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

A

parasite

22
Q

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

A

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

23
Q

Important!

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

A

Constant

24
Q

Define an aircraft’s range.

A

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

25
Q

The max range occurs at _______ drag

A

minimum

26
Q

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

A

Max range

27
Q

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

A

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

28
Q

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

A

Less than

29
Q

True or False

For an elliptical lift distribution, the CL_max is the same as Cl_max.

A

True

30
Q

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

A

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

31
Q

True or false

The geometric angle of attack is always constant.

A

True

32
Q

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

A

Ay^2 +b

Where you solve for the constants.

33
Q

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

A

Vortex

34
Q

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

A

Vortex.

35
Q

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

A

Negative chamber = shift up

Positive chamber = shift down

36
Q

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

A

Positive chamber = shift left

Negative chamber = shift right

37
Q

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

A

The quarter chord point

38
Q

How does adding flaps affect the cl vs alpha graph?

A

They shift the graph to the left.

39
Q

What does it mean to be in “trim?”

A

The forces and moments on the wing are zero.

40
Q

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

A

Angle of attack
Reynolds Number
Mach Number

41
Q

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

A

1 (can be proved with Bernoulli’s equation)

42
Q

What are the basic conservation laws?

A

Mass, momentum, and energy

43
Q

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

A

If the CV is accelerating.

Incompressible Flow (6 decks)

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