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Flight Science & Technology Research Group |
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Evaluation and Analysis of Helicopter Handling Qualities in the Degraded Visual Environment |
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OVERVIEW
Operations in reduced visibility or by night are made possible by using vision sensors like Night Vision Goggles (NVG) or Forward Looking Infrared Radar (FLIR). These sensors utilise artificial vision to improve the cues available to the pilot. Advanced displays that allow low workload Nap-of-the-Earth flight (NoE) are not yet available. Current sensor technologies cannot yet compensate for all the cueing deficiencies, and hence the DVE has a degrading effect on Handling Qualities. Insufficient work has been completed to date to analyse handling qualities in a degraded visual environment. The Aeronautical Design Standard for military helicopters ‘ADS33’ proposes an approach to deal with this problem. However, this approach needs to be tested,evaluated and improved if necessary
OBJECTIVES
To apply and evaluate the existing ADS33 specifications in DVE. Firstly, in a piloted simulation environment, and then in a real situation during flight tests. Relation
between Usable Cue Environment and Response Types
Figure 1
DEGRADED
VISUAL ENVIRONMENT (DVE)
The DVE is a facet of the Usable Cue Environment (UCE). The UCE ‘to date’ is primarily used in helicopter mission design to ascertain the required Response Types for hover and low speed near earth operations (Figure 1). UCE required response type process:
The
Degraded Visual Environment encompasses the upper (poor) end of
the UCE scale.
VISION
AIDS
Firstly; In order to create a ‘Good’ visual aid that would present all the necessary information to the pilot, it is of paramount importance to understand how pilots use visual cues to manoeuvre the aircraft. Here, A time-to-contact (temporal) method is preferred over a distance-to-contact (spatial) representation of the environment external of the aircraft. Figure 2
VISUAL
PERCEPTION IN FLIGHT CONTROL
Pilots
guide the aircraft by seeking out visual information from
optical flow on the surfaces over around around which they fly
via a process called ‘Optical Looming’ (Figure 3). This
information provides for a technique known as Tau-coupling
(Equations 1 and 2).
OPTICAL TAU
Is
referred to as ‘the Instantaneous time-to-contact or
encounter’
Figure 3 Equation 1
Ratio
of Distance to velocity = The Instantaneous Time to Reach the
viewpoint
(Tau
is a fundamental optical variable that has evolved in nature.)
TAU-COUPLING
General
Tau-theory applies to gap closure using any form of sensory
input. The pilot picks up information from the visual scene,
allowing them to co-ordinate and synchronise motions. This
synchronisation is achieved by keeping the Taus of the motion
gaps (say X and Y) coupled in constant ratio (Figure 4).
Figure 4 Equation 2 INTRINSIC MOTION GUIDES Activated in situations where there is a single dominant gap. Closure of a single motion gap is controlled by keeping the Tau of the motion gap coupled to an intrinsically generated Tau-guide. VISION AIDS DEVELOPMENT
3
STAGE APPROACH:
1.Quantify
visual information that Pilots use for performing Manoeuvres
from a Tau-based perspective.
2.Examine
how pilots cope when they are removed, up to the point where
safe flight is unattainable i.e. beyond UCE 3. Such degradation
will be reflected in the correlation of the Taus of the motion.
3.Design
synthetic world where Tau-coupling is restored and once again
coherent (in effect, synthetically improving the UCE).
Members:
Mr Gary Clark Research Student
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All pages © The University of Liverpool, 2003 | Last reviewed 05/02/2004 . Disclaimer. |