United States Department of Transportation
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NTL Classification:NTL-AVIATION-AVIATION
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Abstract:A piloted, motion-based simulation of Sikorsky's Black Hawk helicopter was
used as a platform for the investigation of rotorcraft responses to vertical
turbulence. By using an innovative temporal and geometrical distribution
algorithm that preserved the statistical characteristics of the turbulence over
the rotor disc, stochastic velocity components were applied at each of twenty
blade-element stations. This model was implemented on NASA Ames' Vertical
Motion Simulator (VMS), and ten test pilots were used to establish that the
model created realistic cues.
The objectives of this research included the establishment of simulation-
technology basis for future investigations into real-time turbulence modeling.
This goal was achieved; our extensive additions to the rotor model added less
than a 10 percent computational overhead. Using a VAX9000 computer the entire
simulation required a cycle time of less than 12 msec.
Pilot opinion during this simulation was generally quite favorable. For
low speed flight the consensus was that SORBET (acronym for title) was better
than the conventional body-fixed model, which was used for comparison purposes,
and was determined to be too violent (like a washboard). For high speed flight
the pilots could not identify differences between these models. These opinions
were something of a surprise because only the vertical turbulence component on
the rotor system was implemented in SORBET. Because of the finite-element
distribution of the inputs, induced outputs were observed in all translational
and rotational axes. Extensive post-simulation spectral analyses of the SORBET
model suggest that proper rotorcraft turbulence modeling requires that vertical
atmospheric disturbances not be superimposed at the vehicle center of gravity
but, rather, be input into the rotor system, where the rotor-to-body transfer
function severely attenuates high frequency rotorcraft responses.
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