Two ground-based piloted simulation trials of
helicopter flight envelope tactile cueing have been
conducted. The objective of the trials was to develop
methods of helping the pilot to observe flight envelope
limits while conducting precise and demanding
evaluation tasks. In one trial, large-displacement
conventional inceptors were used; in the other, short
displacement sidesticks. The inceptors in both trials
were programmable and active.
Figure 1 shows the algorithm that was used to
estimate the inceptor position corresponding to a
vehicle limit. A polynomial neural network (PNN)
provided lead estimate of the limit variable, which
was then adjusted using a simple adaptation algorithm
before being compared with the preset limit to
determine the corresponding inceptor position. A
tactile force breakout which the pilot could override
(softstop) was then driven to the inceptor location
corresponding to the limit. The simulated limits were
time-varying in nature.
Figure 2 shows four time-histories of torque,
collective position, and collective force for the four
active sidestick test configurations. The movement of
the transient/do-not-exceed boundary can be seen as
the torque value transitioned above and below the
continuous limit of 80 percent. The pilots were
required to respect the limit using the instrument cues
and the tactile cues. For the configurations with
tactile cueing, the softstop movement associated with
the transient/do-not-exceed boundary can be seen.
The pilot's input tracked the softstop as it moved
downward in accordance with the cueing algorithm.
The collective force contributed by the softstop is
indicated. Typically, 2-3 times the friction force was
held when riding against the softstop. Maintaining
this force in order to achieve maximum performance
was associated with improved pilot acceptance and
task performance.
The following major points were noted. The
programmable nature of the active sidesticks enabled
implementation of all conventional inceptor functionality
including trim follow-up, beep trim, and trim
release, and yielded favorable pilot commentary
regarding posture, feel characteristics, and controllability.
With tactile cueing, conventional inceptors
and the sidesticks yielded nearly equivalent performance.
For both types of inceptors, tactile cueing
significantly reduced the time required to reach the
envelope limit, increased the dwell time at the limit,
reduced exceedances, and improved pilot opinion.
Tactile cueing enabled the pilots to easily track and
respect notional dynamic limits designed to account
for accumulated fatigue damage. Tactile cueing
enabled the pilots to easily track both torque and
rotor stall limits simultaneously while performing an
aggressive turning task with their attention focused
entirely outside the cockpit.
Point of Contact: M. Whalley
(650) 604-3505
mwhalley@mail.arc.nasa.gov
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