The wing on a Piper Cherokee general aviation aircraft is rectangular, with a span of 9.75 m and a chord of 1.6 m. The aircraft is flying at cruising speed
a. If the flow were completely laminar (which is not the case in real life)
b. If the flow were completely turbulent (which is more realistic) Compare the two results.
(a)
The value of skin friction drags for laminar flow.
Answer to Problem 19.1P
The value of skin friction drag for laminar flow is
Explanation of Solution
Given:
The length of the wing is
The chord of the wing is
The cruising speed of the aircraft is
Formula used:
The expression for the area of wing is given as,
The expression for the Reynolds number is given as,
Here,
The expression for the coefficient of drag is given as,
The expression for the drag is given as,
Calculation:
The area of the wing can be calculated as,
It is known that the density of the air is
The Reynolds number can be calculated as,
The coefficient of the drag can be calculated as,
The drag can be calculated as,
Conclusion:
Therefore, the value of skin friction drag for laminar flow is
(b)
The value of skin friction drags for turbulent flow.
Answer to Problem 19.1P
The value of skin friction drag for turbulent flow is
Explanation of Solution
The length of the wing is
The chord of the wing is
The cruising speed of the aircraft is
Formula used:
The expression for the area of wing is given as,
The expression for the Reynolds number is given as,
Here,
The expression for the coefficient of drag is given as,
The expression for the drag is given as,
Calculation:
The area of the wing can be calculated as,
It is known that the density of the air is
The Reynolds number can be calculated as,
The coefficient of the drag can be calculated as,
The drag can be calculated as,
The value of skin friction drag for turbulent flow is
By comparing these two results, it is showing that the skin drag force in turbulent flow is 6.27 times greater than the skin drag force in laminar flow.
Conclusion:
Therefore, the value of skin friction drag for turbulent flow is
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