CIFER®-MATLAB Interfaces: Development and ... - Cal Poly

Figure 4.19: Lateral Velocity Perturbations, Flight Data
The second and final consistency check on the flight data was for w calculations for pitching
motion. Direct comparison of the two methods of calculation can be seen in Figure 4.20. Both
calculated responses appear to have the same trend. For a more exact comparison of the measured
data to the theoretical solution, Equation 4.8 can be rearranged to relate alpha, a z and q to 1/s as
shown in Equation 4.12.
U
oα
1
=
a + U q s
z
o
[4.12]
A series of frequency response arithmetic operations were used to generate the left side of
Equation 4.12, which was then compared to the plot of 1/s as shown in Figure 4.21. Overall the
data matches the 1/s value quite well. Discrepancies in the magnitude plots can be directly
correlated to spikes in the coherence. The most noticeable difference occurs in the phase plot;
there is a small phase offset from -90 o . The offset is fairly constant with frequency, which
suggests a hysteresis effect. The result is typical of airboom measurements such as were used in
the flight test, which tend to exhibit some amount of hysteresis.
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