Ole

Question 1

What are the forces acting on an aircraft?

Answer 1

• Thrust
• weight
• Lift
• Drag

Question 2

The wing of aircraft will be tested in a water tunnel. To do so a 1/60 scaled down model of the wing is built. In order to create dynamically similar testing conditions,
the model must be tested at:

Answer 2

a free stream velocity 4 times higher than the prototype

Question 3

What airfoil angle of attack setting is required to produce zero net lift on a positively cambered airfoil?

Answer 3

Negative

Question 4

Consider an airplane which is cruising at a velocity of 720 km/h at an altitude of 10 km, where the ambient air density is 0.40 kg/m3. The weight and wing planform
areas of the airplane are 7000 kg and 35 m2, respectively. The drag coefficient at cruise is 0.010. The lift-to-drag ratio at cruise is:

Answer 4

> 23

Question 5

The complex potential of a flow is given by (e) w = a with a a constant. What do we know about the velocity?

Answer 5

U = 0

Question 6

An incompressible potential flow must satisfy?

Answer 6

del dot V=0

del cross V=0

Question 7

Draw an airfoil and a cylinder and indicate the regions where viscous forces play a role. Assume a flow from left to right

Answer 7

Boundary layer and wake.

Question 8

What does it mean if the flow around an airfoil satisfies the Kutta condition?

Answer 8

There is a stagnation point at the trailing edge

Question 9

Most of the drag force on an airfoil at low angle of attack is due to ——————- . For bluff bodies, most of the drag force is due to —————— .

Answer 9

1. skin friction

2. pressure drag

Question 10

Complete with laminar or turbulent:
To delay flow separation the boundary layer is preferably —————–. To reduce the drag on an airfoil at low angle of attack the boundary layer is preferably
—————— .

Answer 10

1. turbulent

2. laminar

Question 11

A necessary but not sufficient condition for having a separation point is:

Answer 11

partial (tau_wall)/partial(x) (@y=0) >0

Question 12

The downwash velocity created by a finite span wing with a fixed surface area

Answer 12

Decreases with increasing span.

Question 13

What is true about tip vortices?

• The strength of the tip vortices increases with increasing weight of the aircraft
• By guiding the flow around the tips of the wings, winglets increase the vorticity of the tip vortices
• Tip vortices yield a downward force on everything downstream of them
• More than one of the above statements are correct.

Answer 13

The strength of the tip vortices increases with increasing weight of the aircraft

Question 14

Consider a fully turbulent flow around a circular cylinder. What happens to the separation point if the Reynolds number increases?

Answer 14

Consider a fully turbulent flow around a circular cylinder. What happens to the separation point if the Reynolds number increases?

Question 15

The lift coefficient of a NACA4404 airfoil under steady conditions for alpha= 9 is

Answer 15

> 1

Question 16

Assume this airfoil experiences a sinusoidal variation in the angle of attack causing dynamic stall. Name two characteristic features of dynamic stall.

Answer 16

2 out of: lift overshoot, hysteresis, dynamic stall vortex, stall delay