Theory Videos Flashcards
What is the definition of the center of pressure?
The point about which no moment is produced by a distributed load.
For a uniform load the center of pressure is located at the ____.
Centroid.
In general, what three design choices can influence lift along the span?
- Plan form shape/taper ratio
- Twist
- Airfoil chamber
Downwash distribution is related to the lift distribution through the _____.
Bio-Savart Law
What influences the strength of the downwash?
The trailing vorticies.
For small angles of attack what is the formula for the induced angle of attack?
w/U_infinity
Induced drag is a purely _____ effect.
Geometric
If the downwash is zero then what are the values for the induced angle of attack and the effective angle of attack?
ai = 0 aeff = a_geometric
For an elliptic lift distribution, is the induced angle of attack constant with chord?
yes
Does lifting line theory tell you when the airfoil will stall?
No, only a viscous theory can provide something like that.
For an elliptic case, how does the wing stall?
Everywhere all at once.
What are the values for e and delta in an elliptic wing case?
e =1
delta =0
Define the taper ratio
TR = CT / CR
When using the co-location method, we only consider _____.
Symmetric lift distributions. (n = odd numbers for the Fournier coefficients)
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?
2*PI
NO!
The lift curve for the slope of the wing is ____ 2pi.
Less than
The amount that the lift slope for a wing is less than the lift slope for an airfoil depends on the ___.
Aspect ratio
Does the geometric angle of attack vary with span?
No
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?
The effective angle of attack
An elliptic wing
For the 2D case, profile drag is the sum of what two drag components?
Friction and form drag.
Profile drag is also called ____ drag when a 3-D case is considered instead of a 2D case.
parasite
Total drag for a 3D airfoil is the sum of ____.
parasite and induced drag where parasite is the sum of the friction and form (pressure) drag
Important!
For an elliptical lift distribution, the 2D lift coefficient is ____ along the wingspan.
Constant
Define an aircraft’s range.
The distance an aircraft can travel per unit fuel or altitude.
The max range occurs at _______ drag
minimum
With respect to an aircraft’s performance in flight; the max L/D gives you the ______
Max range
Define “endurance,” with respect to the performance of an aircraft.
The maximum amount of time that the aircraft can stay in the air.
The speed for max endurance is _____ the speed for max range.
Less than
True or False
For an elliptical lift distribution, the CL_max is the same as Cl_max.
True
Give the formula for the chord distribution for a tapered wing.
c(y) = c_r(1-2y/b)+ct(2y/b)
True or false
The geometric angle of attack is always constant.
True
What is the general formula for the chord distribution as a function of span for a parabolic wing?
Ay^2 +b
Where you solve for the constants.
With respect to potential theory; any flow fields that result in lift must contain a ______.
Vortex
With respect to potential theory; no-slip is accounted for by a _____ in the superposition even though potential theory does not allow it.
Vortex.
How does the chamber of an airfoil affect the pitching moment?
Negative chamber = shift up
Positive chamber = shift down
On the cl(alpha) graph, how does affecting the chamber move the line?
Positive chamber = shift left
Negative chamber = shift right
What is the location of the COP for a symmetric airfoil?
The quarter chord point
How does adding flaps affect the cl vs alpha graph?
They shift the graph to the left.
What does it mean to be in “trim?”
The forces and moments on the wing are zero.
The lift and drag coefficients are functions of what three non-dimensional numbers.
Angle of attack
Reynolds Number
Mach Number
What is the value of the pressure coefficient at a stagnation point?
1 (can be proved with Bernoulli’s equation)
What are the basic conservation laws?
Mass, momentum, and energy
Under what circumstances would a non-internal control volume be needed?
If the CV is accelerating.
