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behavior on the ground reasonably and safely. This
reproduction is especially challenging for helicopter flight
simulators, which is the subject of this work, for the pilot
is often inextricably dependent on external cues for pilotvehicle
stabilization. One of the important simulator cues
is platform motion; however, its required fidelity is not
known. Cockpit motion effects on pilot-vehicle
performance, on pilot workload, and on pilot motion
perception were examined in several experiments in order
to determine the required motion fidelity for helicopter
flight simulation. In each experiment, a largedisplacement
motion platform was used that, for some
configurations, allowed pilots to fly tasks with a one-toone
correspondence between the motion and visual cues.
In all evaluations, representative helicopter math models
were employed, and in two cases a specially developed
model from AH-64 Apache flight test data was used.
Platform motion characteristics were modified to give
motion cues varying from full motion, relative to the
visual scene, to no motion. Four of the six rigid-body
degrees of freedom were explored: roll rotation, yaw
rotation, lateral translation, and vertical translation. The
pitch rotation and longitudinal translation degrees of
freedom remain for future work; however, it was hypothesized
that their requirements mirror those of roll rotation
and lateral translation. Several key results were found from
the evaluations. First, lateral and vertical translational
motion platform cues had significant effects on simulation
fidelity. Their presence improved pilot-vehicle
performance, reduced pilot physical and mental workload,
and improved pilot opinion of how faithfully the simulations
represented flight. Second, yaw and roll rotational
motion platform cues were not as important as the lateral
and the vertical translational platform cues. In particular,
the yaw rotational motion platform cue did not appear at
all useful in improving performance or reducing workload.
Third, when the lateral translational motion platform cues
were combined with visual yaw rotational cues, pilots
believed they were physically rotating when the motion
platform was not rotating. Thus, an overall efficiency in
the use of motion cues can be obtained by combining
only the lateral translational platform cues with
satisfactory visual cues. Fourth, vertical and roll/lateral
specifications were revised and validated that provide
simulator users with a prediction of motion fidelity based
on the frequency-response characteristics of their motion
control laws. Fifth, vertical platform motion affected pilot
estimates of steady-state altitude during altitude repositionings.
This refutes the view that pilots estimate
altitude and altitude rate in simulation solely from visual
cues. Since these studies have shown that translational
motion platform cues had more important effects on
simulation fidelity than did rotational cues, an alternative
to today’s hexapod platform design is suggested which
emphasizes the translational cues. And sixth, the
combined results led to a general method for configuring
helicopter motion systems as well as for developing
simulator tasks that more likely represent actual flight.
The overall results can serve as a guide to future simulator
designers and to today’s operators.
3
1. Introduction
Background
Purpose of Flight Simulation
Flight simulation had its origins near to those of powered
flight itself (ref. 1). Since then, simulation has been used
principally for two distinct disciplines in aviation:
training and research and development. However, flight
training is its most frequent application, in which it is
used primarily to reduce cost and increase safety. Almost
all of the major airlines use flight simulation today
whenever they can receive a training credit for doing so.
This is because an hour in the simulator is less expensive
than an hour in the airplane. For example, a B-747 aircraft
costs about $12,500 per hour to operate versus about
$750 per hour for a 747 simulator (ref. 2).
These cost reductions are put to both training and
retraining uses. The Federal Aviation Administration
(FAA) will certify certain simulators such that, with only
simulator training, a new pilot may fly the actual aircraft
for the first time carrying passengers (ref. 3). Once a pilot
is qualified in a particular aircraft, mandatory periodic
proficiency checks are then conducted in the simulator.
Some of these latter checks may also include recovery
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Helicopter Flight Simulation Motion Platform Requirements(3)
