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Helicopter Flight Simulation Motion Platform Requirements(62)

时间:2011-11-12 12:15来源:蓝天飞行翻译 作者:admin
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The pilot is assumed to close loops around vertical acceleration, vertical velocity, and vertical displacement.
In the model, the acceleration is derived solely from the motion feedback; however, it might be argued that acceleration could also be derived from the second time-derivative of the displacement. In the acceleration feedback path, two dynamical elements are shown. The first is a high-pass motion filter, which attenuates motion at all frequencies via K and at frequencies below ω . Both of these parameters are adjustable in a given simulation facility based on the task demands and the facility’s motion displacement capability. The second dynamic element is the motion-system servo hardware. Using the frequency-response testing techniques developed by Tischler and Cauffman (ref. 46), the simulator has vertical-axis drive dynamics (approximately) of
˙˙
h ()( 826 )
sim ()s = (B1)˙˙
h (s + 8)( s + 26 )
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The vehicle vertical velocity and displacement are derived from the visual system, which is represented by an 83-msec time delay. Hess and Malsbury point out in reference 61 that the vertical velocity sensing assumption affects the primary control loop, but that it is currently not known how to select the appropriate division of the vertical velocity estimation between the motion and visual cues, which is a motivation for Vertical Experiment III described in section 6.
The pilot gains shown in figure B2 are selected based on a set of adjustment rules proposed by Hess and Malsbury. For these tasks, only the high-pass filter was changed, and using the adjustment rules results in the change of three variables K˙˙h, Kh˙ , and Kh. The gain K˙˙h is determined so
that the lowest damping ratio of any oscillatory roots in the ˙˙hs() / ˙˙h ()s transfer function is at least 0.15. This
c
value of damping ratio is selected to represent a trade-off between stability and high-frequency phase-lag reduction (ref. 70). In reference 70, Hess points out that requiring an identical damping ratio of this loop for all configurations reduces the sensitivity of the modeling procedure to the particular value chosen.
Then, with the motion loop closed, K˙ is determined so
h
as not to violate the combination of a phase margin of 45° and a gain margin of 4 dB in the vertical velocity open-loop h˙ ()/ h˙ (). These values are selected by Hess to
ss
cue e
achieve adequate stability margins for the vertical-velocity loop. Again, Hess states that requiring all configurations to have the same level of relative stability (same phase and gain margin) reduces the sensitivity of the model to the particular values chosen.
Pilot
h
+

Finally, the gain Kh is chosen to have adequate frequency separation between the altitude and vertical-velocity loops while maintaining good altitude-loop crossover charac-teristics. A useful rule-of-thumb is to separate the altitude and vertical-velocity crossover frequencies by a factor of 4 (ref. 71).
 
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