# Aerodynamics Questions and Answers – Modern Low Speed Airfoils – 1

This set of Aerodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Modern Low Speed Airfoils – 1”.

1. The standard NACA airfoils were based on ____
a) Computer modeling results
b) Numerical techniques and wind- tunnel testing
c) Experiment data
d) Theoretical data

Explanation: The earlier standard NACA airfoils were based exclusively on the experimental results from 1930s-40s. Later on, numerical techniques using the computer were used followed by wind-tunnel testing to develop modern airfoils.

2. Modern low-speed airfoils were developed using numerical methods using the computer directly. The given statement is_____
a) Partially true
b) False
c) True
d) Incomplete

Explanation: The modern low-speed airfoils were developed using numerical techniques on the computer which was followed by wind- tunnel testing to confirm the computer results. This gave the definite airfoil properties for the new airfoils.

3. The main motive behind redesigning standard airfoils to get the new airfoils was higher maximum lift coefficient and______
a) Lesser drag
b) Better shapes
c) Handling flow separation effects
d) Strength of material

Explanation: The use of computers led to the design of better airfoils since it made possible to get the definitive properties of the airfoils. This had many advantages like a higher coefficient of lift and shape to tackle the flow separation effects at high angles of attack.

4. Which of the following is a new NACA airfoil?
a) NACA 2212
b) NACA LS (1)-0407
c) NACA 0021
d) Both NACA LS (1)-0407 and NACA 2412

Explanation: The new airfoils are the low-speed airfoils (designated by LS). So NACA LS (1)-04XX are the new airfoils while the NACA XXXX are the standard airfoils.

5. A higher value of L/D ratio deteriorates climbing performance for the flight.
a) True
b) False

Explanation: The higher value of L/D ratio improves the climbing performance. It can be visualized as a higher lift with lower drag, which is essentially beneficial.

6. The NACA LS (1) – 04XX airfoils when compared to NACA airfoils with same thickness had higher L/D ratios. For a lift coefficient of 1.0, what was this increase approximately in percentage?
a) 80%
b) 20%
c) 50%
d) Less than 10%

Explanation: The lift coefficient of 1 is vital for the aviation sector. The new low-speed airfoils developed had higher L/D ratios. For a lift coefficient equal to 1, the increase was about 50%.

7. Which is not a feature of the first new NACA airfoil (GA(W)-1 or the Whitcomb airfoil) developed?
b) Higher symmetry
c) Higher maximum lift coefficient
d) Cusped trailing edge

Explanation: The larger leading edge radius gave a reduced peak in pressure coefficient at the leading edge. The trailing edge was cusped which increased camber, thus decreasing symmetry. These features reduced flow separation and gave a higher value of maximum lift coefficient.

8. The major breakthrough in high- speed airfoil industry was_____
a) GA (W)-1 airfoil
b) Supercritical airfoil
c) Standard NACA airfoils
d) Symmetrical airfoils

Explanation: The GA (W)-1 (also known as Whitcomb airfoil) airfoil was the first low-speed airfoil obtained under the new airfoils. It led to the development of supercritical airfoils which had an almost similar shape. The supercritical airfoils had lesser drag at high subsonic speeds, which was a major performance improvement.

9. Enlist the computer methods used which benefitted the airfoil performance along with wind- tunnel testing.
a) Panel method
c) Panel method and advanced viscous flow solutions
d) Hit – and – trial methods

Explanation: The numerical methods used were like source and vortex panel methods and numerical predictions of the viscous flow behavior, to analyze skin friction and flow separation effects. This was followed by experimental testing for verification of computer results.

10. The cl,max for the NACA LS (1) – 0417 is higher than that for the NACA 2412.
a) False
b) True

Explanation: The new low-speed airfoils had considerably higher maximum lift coefficients (around 30% higher) when compared to the standard NACA airfoils.

Sanfoundry Global Education & Learning Series – Aerodynamics.

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