Dr. David L. Still Profile

Dr. David L. Still

at US Army Aeromedical Research Lab

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Publications (4)

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Proceedings Article | 17 April 2008 Paper

Hover training display: rationale and implementation

David Still, Leonard Temme

Proceedings Volume 6956, 695607 (2008) https://doi.org/10.1117/12.780135

KEYWORDS: Fourier transforms, Visualization, Stars, Control systems, Electromagnetic simulation, Nose, Device simulation, Video, Computer simulations, LCDs

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Hover is an essential component of rotary wing aviation but learning to hover is extremely difficult. From the viewpoint inside the cockpit, the beginning student neither sees nor understands what needs to be done to control the aircraft. This is because the out-the-window real world visual cues suffer from two primary shortcomings. First, the real world visual cues are ambiguous. For example, the relative motion of the ground moving under the nose may indicate forward flight, pitching upward, vertical ascent, or any combination of these. Second, human ability to judge aircraft pitch by itself is insufficient to stabilize the aircraft; such other clues as relative motion or parallax are needed to augment pitch judgments to set aircraft attitude adequately. We report a training display (TD) designed to assist training rotary wing hover. The TD is specifically constructed to communicate aircraft performance and attitude to the student pilot and to disambiguate the external world's features and motions cues into symbology that allows each cue independently to support sufficient levels of parameter resolution. Our preliminary observations, based on pilot data collected during the design, parameterization, and calibration of the TD indicate that it meets its goals in a fashion that enables beginning flight students to understand and interpret the motion cues of the real world out-the-window view.

Proceedings Article | 14 April 2008 Paper

The yaw, pitch, and roll of the head in a straight ahead orientation

Leonard Temme, David Still, Adrianus J. Houtsma

Proceedings Volume 6955, 69550K (2008) https://doi.org/10.1117/12.780133

KEYWORDS: Head, Visualization, Head-mounted displays, Calibration, Stereolithography, Eye, Light emitting diodes, Optical spheres, Light sources and illumination, Robotics

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Head mounted displays (HMD) are finding increasing use in a great many applications. These HMDs provide information ranging from a simple alphanumeric to complex graphical renderings of real or synthetic worlds. Some of these HMDs are opaque so that the user's vision is completely confined to what the HMD provides; others are see-through so that elements of the HMD may be superimposed simultaneously with the external world. Some see-through HMD applications incorporate graphical elements intended to be in some calibrated registration with elements of the external world such that the relation between the graphic and the world embodies the relevant information. For such displays to function as intended the head yaw, pitch, and roll are important. The present paper reports measures of head yaw, pitch, and roll when the head is in a straight ahead orientation. Volunteers oriented to either a visual or auditory target stimulus presented under a variety of conditions. For some conditions with the visual target, the visual field was restricted to less than 5 degrees (°); for other conditions vision was unrestricted. The auditory targets were presented in complete darkness. At the start of each trial, an acoustic warning signaled the volunteer to turn the head from an initial off-axis yaw and pitch to a target stimulus that defined the straight ahead yaw and pitch. Note that the stimulus left head roll completely undefined. Within- and between-subject head yaw, pitch, and roll statistics are reported and compared for the various stimuli.

Proceedings Article | 5 May 2006 Paper

Frequency response of helicopter pilot head azimuth, pitch, and tilt: approaching engineering specifications

Leonard Temme, David Still, Adrianus Houtsma

Proceedings Volume 6224, 622404 (2006) https://doi.org/10.1117/12.668016

KEYWORDS: Head, Visualization, Head-mounted displays, Optical tracking, Analytical research, Data storage, Visible radiation, Motion models, Data archive systems, Systems modeling

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Background: Since helmet mounted displays (HMDs) are slaved to a pilot's head, head motion is important for the design of HMDs and their symbology. This is particularly true since the lateral tilt of a pilot's head changes when the pilot shifts his/her gaze from the horizon visible outside the cockpit to the instruments inside the cockpit. This change in head tilt, which may contribute to episodes of spatial disorientation and possibly dangerous control input reversal errors, is commonly attributed to a neuro-muscular reflex driven by the apparent tilt of the visible horizon, the so-called optokinetic cervical reflex (OKCR). The present paper: (1) describes head motion in the frequency domain, and (2) elaborates a biomechanical explanation for the observed head tilt that is simpler than the neurological OKCR model. Methods: Fourier spectral decompositions were calculated from archived head pitch, tilt, and azimuth data recorded at 10 Hz from four pilots as they executed a slalom maneuver in an AH Mk 7 Linx helicopter. Pilots A through D performed the slalom 11, 12, 8, and 11 times, respectively, for a total of 42 flights. Results: The Fourier decomposition showed that the typical azimuth spectrum differs from that of pitch, and tilt. Discussion: These results provide: (1) spectral descriptions of head azimuth, pitch, and tilt to aid the design of HMD systems, and (2) further support for the biomechanical model of head tilt.

Proceedings Article | 19 May 2005 Paper

Correlations among the helicopter pilot's head azimuth, elevation, and tilt in visual flight and their implications for incorporating roll compensation in the HMD

Leonard Temme, David Still

Proceedings Volume 5800, (2005) https://doi.org/10.1117/12.602923

KEYWORDS: Head, Visualization, Head-mounted displays, Databases, Neck, Visual process modeling, Meteorology, Displays, Analytical research, Motion analysis

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The literature describes the opt-kinetic cervical reflex (OKCR) as potentially contributing to episodes of spatial disorientation and dangerous control input reversal errors. The OKCR is described as a reflex tilting of a pilot’s head that occurs when an aircraft banks and turns under visual meteorological conditions. The implication is that with the aircraft’s banking turn, the horizon appears to the pilot to bank in the opposite directions. This banking of the horizon relative to the pilot is thought to cause the pilot’s head to tilt in order to be perpendicular to the horizon. This OKCR head tilting phenomenon may be important for the design of the head mounted display systems since these systems may be referenced to either the tilting head or the aircraft. The choice is particularly important for the display of aircraft attitude information, which is most commonly referenced to the horizon. The present paper describes an alternative explanation for the observed head tilting behavior of the pilot in a banking turn. This explanation is based on the analysis of an archived database containing the head movement records of four military pilots as they executed a slalom flight maneuver in an AH Mk 7 Lynx helicopter. These data had been collected for purposes unrelated to the present discussion, and previous analyses addressing these original purposed have already been reported. In addition to the description of the new model based on the archived database, the present paper used some results previously published in the literature to compare the new explanation and the tradition OKCR explanation of the observed head tilting behavior of pilots. A clarification of the mechanisms responsible for the observed head tilt phenomena is important for the design of the head mountedinformational display systems.

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