Investigation of outside visual cues required for low speed and hover

Hoh, Roger H.

doi:10.2514/6.1985-1808

Cited by 13 publications

(6 citation statements)

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“…One potential advantage of dynamic-scattering devices is the ability to vary the degree of fogginess of the lenses continuously between a minimum (transparent) and a maximum by raising or lowering the driving voltage. Some practical applications of that property, for example, include the development of a "cloud simulator" for pilot flight training applications (Witt, 1978) and an experimental investigation of visual cues used by pilots during helicopter hovering tasks (Hoh, 1985). The principal shortcoming of those liquid-crystal shutters, however, is their relatively long switching times, along the order of tens of milliseconds, which obviously preclude their use for most tachistoscopic experiments in visual perception.…”

Section: Resultsmentioning

confidence: 99%

A spectacle-mounted liquid-crystal tachistoscope

Milgram

1987

Behavior Research Methods, Instruments, & Computers

175

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A spectacle-mounted shuttering device, the Portable Liquid-crystal Apparatus for Tachistoscopy via visual Occlusion, based on light-scattering cholesteric liquid crystals, is introduced. Operating characteristics of the device are discussed with respect to the design objectives of comfort, switching speed, light transmission, light extinction, safety, and reliability. A number ofpractical research, clinical, and industrial applications of the spectacles as tachistoscope, stroboscope, and stereoscopic viewing apparatus are summarized.In its conventional form, a tachistoscope is basically an enclosed container, made of some lightproof material, into which an observer looks and in which, by means of special lamps, it is possible to illuminate specific objects within the container. By using a suitable optical system, one can present visual information in a precisely controlled manner to one or both eyes of an observer. To qualify as a tachistoscope in the literal sense, such a viewing apparatus must be capable of allowing very rapid presentation of visual information. (The word tachistoscope derives from a combination of the Greek words takhistos ["swiftest"] and skopeo ["look at"].) Often, instead of enclosed containers and special lamps, computer display screens or (computer-controlled) projection devices are used for tachistoscopic experiments (Green, 1978). In this paper, the design objectives, implementation, and applications of another type of tachistoscope, a spectaclemounted liquid-crystal shuttering device, are described.A photograph of a prototype of the electrooptic shuttering device, illustrating both its "open" and "closed" states, is given in Figure 1. The acronym given to the device is PLATO, for Portable Liquid-crystal Apparatus for Tachistoscopy via visual Occlusion. The emphasis on portability stems from the fact that, by wearing such a spectacle-mounted apparatus, the subject in an experiment is not restricted to remaining in front of an enclosed viewing container, or a fixed display device, or a projection screen; thus, a large range of experiments involving ambulatory subjects can be carried out. The reference to "visual occlusion" in the acronym as the means of implementing this tachistoscope derives from the fact that, rather than illuminating or projecting specific target images, as do other tachistoscopes, the PLATO device regu- lates image presentation instead by selectively blocking out the subject's view of the target, the illuminance of which remains independent of the state of the shutters.In the following sections, the background and the design objectives underlying the development of the PLATO device are presented, followed by a detailed description of its properties and, finally, a short discussion of some already demonstrated and further foreseen applications. BACKGROUND AND DESIGN OBJECTIVES

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Section: Resultsmentioning

confidence: 99%

A spectacle-mounted liquid-crystal tachistoscope

Milgram

1987

Behavior Research Methods, Instruments, & Computers

175

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“…5). Research has shown that, in the presence of sufficient microtexture cues; that is, fine-grained detail in the visual scene, a pilot can maintain satisfactory control over the aircraft with a FOV as small as approximately 40 deg laterally by 25 deg vertically [42]; such a region is also shown in Fig. 5.…”

Section: B Objective Functionmentioning

confidence: 97%

“…This metric could be estimated [43] from the control dwell fraction, which is the fraction of the duration of the piloting task in which the visual cues are sufficient to perform the task. Sufficient cues could be defined in terms of the modulation transfer function (MTF) [42], which is a measure of the loss of visibility caused by the brownout cloud [44][45][46], and linked to an equation like Eq. (11) with the MTF replacing the number of particles n P .…”

Section: B Objective Functionmentioning

confidence: 99%

Methodology for Rotorcraft Brownout Mitigation Through Flight Path Optimization

Tritschler

Celi

Leishman

2014

Journal of Guidance, Control, and Dynamics

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A methodology is presented for the selection of approach-to-landing maneuvers that may result in improved brownout characteristics. The methodology is based upon a brownout metric that assesses the relative brownout cloud volume densities in critical regions of the pilot's field of view. The metric becomes the objective function of a procedure in which a typical visual approach profile is parameterized and optimized to minimize brownout in a representative landing maneuver. The optimization is constrained to avoid maneuvers that would be conducive to the onset of vortex ring state or would result in flight within the "avoid" regions of a typical helicopter height-velocity diagram. The analysis uses a free-vortex wake model and simulates the dynamics of the dust particles immersed in the rotor downwash. The results show that the optimal approach trajectories affect the resulting flowfield, particularly the development of a ground vortex ahead of the rotor disk, which influences the rate of development, size, and volume density of the brownout cloud. The results are compared with prior experimental results, and potential operational interpretations of the outcomes are examined. Nomenclature A= rotor disk area, πR 2 , ft 2 BX = objective function, Eq. (12) bX; t = particle count in the "best" region of the pilot's field of view, Eq. (11) C T = rotor thrust coefficient, T∕ρAΩR 2 D = main rotor diameter, ft FX = additional design objective function gX = constraint equation, Eq.(2) H = Hessian matrix h = rotor hub height above ground, ft n ent = number of entrained particles n P = number of particles p app X = series of discrete points describing approach X p HV = series of discrete points describing the "avoid" region boundaries on a height-velocity diagram p VRS = series of discrete points describing flight regime boundaries where VRS may occur R = rotor radius, ft r = longitudinal range from landing point, ft r pd = longitudinal range from landing point at which the peak deceleration occurs, ft S = unit vector T = rotor thrust, lb V = forward velocity, ft∕s or kt V c = climb velocity, ft∕s v h = hover inflow velocity, ft∕s v 0 = initial (asymptotic) velocity, ft∕s or kt X = vector of design variables, γ v 0 r pd T X u = aircraft stability derivative, ∂X∕∂u γ = approach angle, deg ϵ = tolerance value for defining behavior constraints, Eqs. (15) and (16) θ = aircraft pitch angle, deg θ P , ϕ P , ρ P = particle location (azimuth, elevation, distance) in a spherical coordinate systemfluid density, slugs∕ft 3 χ = wake skew angle, deg Ω = rotational frequency, rad∕s Subscripts app = approximation max = maximum allowable value (upper bound) min = minimum allowable value (lower bound) Superscript = value for optimum configuration

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“…Research has shown visual texture to be a cue of vital importance in this process (Refs. [3][4][5]. For example, pilots utilize both "macrotexture" (large objects or, equivalently, low spatial frequency) and "microtexture" (fine-grained detail, or high spatial frequency) to provide information on the location, attitude, and motion of the aircraft.…”

Section: Introductionmentioning

confidence: 99%

Brownout Cloud Characterization Using the Modulation Transfer Function

Tritschler¹,

Celi²

2013

j am helicopter soc

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The paper describes how to extract the modulation transfer function (MTF) of a brownout cloud from video recordings of specific optical patterns. The MTF is a measure of the loss of contrast and resolution caused by the cloud and can be used as the basis for a quantitative metric of brownout severity. The application of two MTF calculation methods to actual flight test data is described. One requires the use of specially designed targets, such as a Siemens star, the other relies on simple dark/light visual edges. The results show that MTF extraction can be successfully performed with a standard consumer-level video equipment and appropriate postprocessing. Also, MTF extraction can be automated using suitable image-processing techniques. The results rigorously quantify the intuitively known facts that the visual degradation caused by brownout is a space-and time-dependent phenomenon and that high spatial frequency features, i.e., fine-grained detail, are obscured before low spatial frequency features, i.e., large objects.

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Investigation of outside visual cues required for low speed and hover

Cited by 13 publications

References 0 publications

A spectacle-mounted liquid-crystal tachistoscope

A spectacle-mounted liquid-crystal tachistoscope

Methodology for Rotorcraft Brownout Mitigation Through Flight Path Optimization

Brownout Cloud Characterization Using the Modulation Transfer Function

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