Lecture 10 - Power requirement for flight

Question 1

What is parasitic drag?

Answer 1

A combination of form drag and skin friction drag.

Question 2

What happens to drag as aircraft velocity increases?

Answer 2

Total drag starts high, decreases, then rises again (inverse parabolic shape)

Question 3

Thrust equation?

Answer 3

T=D=q_inf*S (C_Do + C_Di)

Question 4

Lift equation?

Answer 4

W=L=q_inf * S * C_L

Question 5

Velocity in level flight?

Answer 5

v = sqrt {2/rho*C_l (W/S)}

Question 6

minimum thrust velocity

Answer 6

v_min = sqrt {2/rho*S sqrt{1/pi * AR * C_Do}}

Question 7

Condition for max range / best glide ratio?

Answer 7

C_L/C_D –> MAX

Question 8

Condition for minimum power / minimum sink in glide mode?

Answer 8

C_L^3/C_D^2 –> MAX

Question 9

Power requirement for flight?

Answer 9

P = VD = VT

Question 10

There is a critical speed of
flight above which the elastic stiffness cannot hold the wing in a
stable position. What are the two instances of this?

Answer 10

1. When this occurs in such a way that inertial forces have a little
   effect, we call it a static aeroelastic instability or divergence.
2. When the inertial forces are important the resulting
   dynamic instability is called flutter

Question 11

aerodynamic centre definition

Answer 11

the point at which the pitching moment coefficient for the airfoil does not vary with
lift coefficient i.e. angle of attack

Question 12

Critical divergence speed?

Answer 12

V_div = sqrt {2*K_alpha / rho * ec^2 * alpha}