1. A symmetric airfoil is operating with flow velocity of 350m/s. The lift produced by the airfoil is 21 N at 0.008 rad AOA. If chord is c m then, what will be the pressure difference across the airfoil?
a) 21/c Pa
b) 21c/2 N
c) 21 Pa
d) 21c N
Explanation: Given, symmetric airfoil
Flow velocity V=350m/s, Lift L=21N, AOA = 0.008rad
Chord = c m, Span of airfoil = 1 unit
Pressure difference = Lift/Area of airfoil
= 21/c*1 = 21/c Pa.
2. If an airfoil has lift of 200 N at 10° AOA, then what is induced drag produced by airfoil at that AOA?
a) 0 N
b) 100
c) 0
d) 100 N
Explanation: Given, Lift=200N, AOA = 10°
Here, airfoil is mentioned which is 2D shape.
For an airfoil Induced drag Di = 0N.
3. Find location of aerodynamic centre from leading edge if, chord is 10m and airfoil has flow velocity of 0.2 M.
a) 2.5 m
b) 0.2 m
c) 5 m
d) 10 m
Explanation: Given, velocity = 0.2M = 0.2*340 = 68m/s
Chord = 10m
Given velocity is less than the sonic speed.
Hence, location of aerodynamic center is = 25% of chord = 0.25*10 = 2.5m from leading edge.
4. Consider a NACA 2812 airfoil. It is operating with flow velocity of 900m/s with chord of 1m. What should be the maximum thickness of this airfoil?
a) 0.12m
b) 0.21m
c) 0.9m
d) 28.12m
Explanation: NACA-4 digit series is used to define certain airfoil characteristics.
Here, velocity = 900 m/s, chord = 1m
From NACA-4 digit,
Maximum thickness = last two digits in percent of chord=12% of chord = 0.12*1 = 0.12m.
5. An airfoil is subjected to the flow with temperature of 288.16K and flow is ideal. The velocity at the leading edge is ____
a) 0m/s
b) 250m/s
c) 288.16m/s
d) 16.882m/s
Explanation: Given, temperature T=288.16K
For idle flow, at leading edge flow is brought to rest isentropically.
Hence, velocity at leading edge = velocity of flow at the impact to leading edge = 0m/s.
6. Pitching moment co-efficient for an airfoil is given by _____
a) lift*area
b) drag*area
c) section pitching moment/dynamic pitching moment
d) lift/dynamic moment
Explanation: Lift*area will give moment. Drag*area will also provide moment but will be less. The ratio of sectional pitching moment and dynamic pitching moment is called pitching moment co-efficient.
7. Which of these is not part of an airfoil?
a) Leading edge
b) Chord
c) Camber
d) Fins
Explanation: Fins are extended surfaces which are used to improve heat transfer. Leading edge is foremost part of an airfoil. Camber is curve of an airfoil.
8. We are using the airfoil in the aircraft as _____
a) it is a streamline shape which provides better aerodynamics
b) it is a random shape can be changed to rectangular as well
c) it is easy to make than rectangular
d) it is not a streamline body
Explanation: Airfoil is a streamlined body which provides much smoother flow than non-streamlined body. Airfoil is designed in such a way that it can provide better aerodynamics than any other shape. Hence, in aircraft we use airfoils.
9. Pressure on the upper surface is _________
a) lower than lower surface
b) higher than lower surface
c) always 30.25 times lower surface
d) always same
Explanation: Pressure on the upper surface of an airfoil is lower than that of the lower surface. This will provide pressure difference which will generate lift force. Pressure will be the same if AOA is 0° in case of symmetric airfoil.
10. What do you mean by double cambered airfoil?
a) Airfoil with flat lower surface
b) Airfoil with flat upper and lower surface
c) Airfoil with curved upper and lower surface
d) Only upper surface is curved
Explanation: Traditionally, airfoils with only curved upper surface and flat bottom was termed as camber airfoil. However, if both surfaces are curved then, it is called a double cambered airfoil. In now days not most people use this terms but at some places it is still in use.