Data Analysis

The above figure represents one experiment run using our airfoil in the wind tunnel. This particular test was run with all three weighted plates added to the torsional spring.

To keep our results standard over multiple experiments, we manually gave the airfoil a rotational disturbance every 60 seconds. If it was still oscillating, we brought it back to stationary after 30 seconds. The remaining time in between disturbances was left to allow us to increase the air speed of the wind tunnel. This process gave us 30 seconds of plunge acceleration data for each air speed used.

Chapter 2:

FFT

To examine the oscillation closer, we isolate one packet of data at one air speed. In this case, we choose to look at 59.5 miles per hour using three plates.

The FFT is an algorithmic implementation of the discrete Fourier transform that leverages the symmetry of the problem to run at speeds much faster than the classical discrete Fourier transform. The role of the FFT is to transform the data from the time domain to the frequency domain. We did this transform in order to see the frequency of our flutter, and thus the assumed frequency point in which the airfoil would be in a "critical" state, which the wing would break. Using Python's fast Fourier transform function, we can determine the frequency of our samples, as plotted above (right).

Shown above (left) is the acceleration data collected in the time domain. This FFT peaks the highest at 32.7 Hz and includes some lower frequencies at much smaller amplitudes.

Chapter 3:

Acceleration and Frequency Relationships

The entire experiment was performed with three different weight amounts on the torsional spring. The figures above illustrate the relationships between air speed and flutter plunge frequency and amplitude.

As air speed increased, the amplitude of flutter acceleration generally increased. Using two plates the amplitude increased slowest at the beginning, but showed a similar overall trend to using three plates. Using one plate, we saw a similar increase in amplitude to other weights up until approximately 70 mph, where the amplitude of one plate increased further.

The frequency of flutter did not change significantly across air speeds.