MAE 3241: Aerodynamics and Flight Mechanics Assigned: March 4, 2011
Homework #4 Due: March 18, 2011
Question 1: Consider an infinite wing with an NACA 1412 airfoil section and a chord length of 3 ft. The wing is at an angle of attack of 5º in an airflow with velocity 100 ft/s at standard sea-level conditions. Calculate the lift, drag, and moment about the quarter chord per unit span.
Question 2: The ratio of lift-to-drag, L/D, for a wing or airfoil is an important aerodynamic parameter, and may be considered as a direct measure of the aerodynamic efficiency of the wing. If a wing is pitched through a range of angle of attack, L/D first increases, then goes through a maximum, and then decreases. Consider an infinite wing with an NACA 2412 airfoil. Estimate the maximum value of L/D and indicate at which angle of attack the maximum L/D occurs. Assume that the Reynolds number is 9 million.
Question 3: Consider an airfoil in a free stream with a velocity of 50 m/s at standard sea-level conditions. At a point on the airfoil, the pressure is 9.5x104 N/m2. What is the pressure coefficient at this point?
Question 4: Consider a low-speed airplane flying at a velocity of 55 m/s. If the velocity at a point on the fuselage is 62 m/s, what is the pressure coefficient at this point?
Extra Credit (Question 3.19 from Fundamentals of Aerodynamics):
A typical World War I biplane fighter (such as the French SPAD shown below and in Figure 3.50) has a number of vertical inter-wing struts and diagonal bracing wires.
Assume for a given airplane that the total length for the vertical struts (summed together) is 25 ft, and that the struts are cylinders with a diameter of 2 inches. Assume also that the total length of the bracing wires is 80 ft, with a cylindrical diameter of 3/32 inches. Calculate the drag (in pounds) contributed by these struts and bracing wires when the airplane is flying at 120 MPH at standard sea-level. Compare this component of drag with the total zero-lift drag for the airplane, for which the total wing area is 230 ft2 and the zero-lift drag coefficient is 0.036.
1