Lift analysis was done by setting the model (a wing, in our tests. NACA airfoil section 2412) at an angle and placing a weight on top of the balance arm, adjusting its distance from the fulcrum of the arm until it was balanced. By measuring this distance we were able to calculate the percentage of the weight (by the principle of leverage) the wing was able to lift at a given angle of attack. We then plotted angle vs. ratio of weight lifted, as shown below.
Wing mounted to arm and ready for testing.
After mounting the wing to the support arm, we balanced the assembly by adding weight to the opposite end of the lever on a bolt, fine tuning the adjustment by screwing a hex nut along the bolt. Once we did this, we turned the fan on and adjusted the angle of the model until the arm would not move, thus putting the model in stable flight with lift and weight at equilibrium. For further angle measurements, a transparent projector sheet with a protractor printed on it was taped up against the test section window, aligned along the wing's axis. From there, we set the wing at angles in increments of 2.5 degrees and tested the lift produced. The weight we used was 14 washers taped together; a crude weight, maybe, but one which did the job. The actual weight was not important, as the lift would be a percentage of it and not an actual weight. We printed a ruler and taped it to the top of the balance. This is what we used to determine the distance from the center of the arm that the weight was placed. We conducted several runs and averaged the results to produce our final data, which is shown in the data table and graph below.
These values are the fractions of the test weight and are intended to show how lift changes with angle of attack.
The data shows a near linear relationship between angle and lift with a very well defined stall around 17.5 degrees AoA. As the wing stalled, the lift began to decrease and ultimately became almost impossible to measure due to instability.
