The aim of this experiment is to examine the pressure distribution on an aerofoil and its variation with incidence.
An aerofoil is the two-dimensional cross section of a wing, tail or helicopter rotor blade. The lift and pitching moment on an aerofoil is determined by the pressure distribution on it. The pressure distribution changes with the angle of incidence. Understanding the behaviour of aerofoils requires some understanding of the variation of the pressure distribution with incidence.
This experiment uses a pressure tapped aerofoil mounted inside a low speed open return wind tunnel. The pressure tapings are connected to a multi-tube manometer, which is also used to measure the dynamic pressure.
Students should check and record all the connections on the multitube manometer. Procedure:
1. Level and adjust the multitube manometer in the vertical position with the indicator registering 90 , then incline it to approximately 40 to the horizontal. 2. Check and record all of the manometer connections.
3. Record the NACA aerofoil designation of the aerofoil.
4. Set the model at zero incidence and turn the wind tunnel on. Run the fan up to about ¾ of its full speed.
5. Record all of the manometer heights.
6. Adjust the angle of incidence to -4 and repeat the previous step. Adjust the motor control if necessary to maintain a constant dynamic pressure. 7. Repeat the previous step for 4 , 8 and 12
8. Determine the stall angle of the aerofoil and qualitatively observe the changes in pressure distribution near the stall angle.
The non-dimensional pressure coefficient is defined as:
Pi - pressure at tapping i
P - free stream pressure
ρ - air density
V - free stream velocity
S - wing area
c - aerodynamic mean chord
The quantity of 2
V is known as the dynamic pressure and for low speeds it is equal to the difference...