1
HEAD ALIGNMENT OF THE
GENERAL AVIATION PILOT DURING FLIGHT
A thesis submitted in partial fulfillment
of the requirements for the degree of
Master of Science
By
KAZUHITO SHIMADA
M.D., University of Tsukuba, 1983
Ph.D., University of Tsukuba, 1987
1995
Wright State University
WRIGHT STATE UNIVERSITY
SCHOOL OF GRADUATE STUDIES
, 1995
I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY
SUPERVISION BY Kazuhito Shimada ENTITLED Head Alignment of General Aviation Pilot BE ACCEPTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF Master of Science.
Anthony J. Cacioppo, Ph.D.
Thesis Director
Stanley R. Mohler, M.D.
Department Chair
Committee on
Final Examination
Anthony J. Cacioppo, Ph.D.
Stanley R. Mohler, M.D.
Robin E. Dodge, M.D., M.S.
Satya P. Sangal, Ph.D.
Joseph F. Thomas, Jr., Ph.D.
Dean, School of Graduate Studies
1
ABSTRACT
Shimada, Kazuhito. M.D., Ph.D., M.S., Department of Community Health,
Wright State University, 1995. Head Alignment of the General Aviation Pilot During Flight.
The professional literature provides a lack of relevant research dealing with the dynamics of pilot head motion during flight. This study analyzed the head alignment of 10 civilian pilots during turns in flight using data collection from a head-mounted videocamera. Pilots were found to roll their head around the head x-axis in a direction opposite to the center of turn. The angle of aircraft roll and head roll had a linear relationship when pilots were flying solely with visual cues (V mode) or acting as second-in-command (P2 mode). Pilot head roll response plateaued when pilots were referring to both external visual cues and the attitude indicator (AI mode). Asymmetrical pilot head roll response was found in left and right turns when pilots were in V mode. The slope of the head roll angle vs. aircraft roll was the steepest in P2 mode and the shallowest in AI mode. Individual variation in pilot head roll response tended to relate to subject age and experience. Pilot head roll response had minimal phase difference to aircraft roll for roll-in, but had a lag for roll-out. Overshoot in pilot head roll was observed in roll-out. The magnitude and time course of head roll response in ground turns were similar to those in flight, except for the direction. The origin of pilot head response may have a relationship to the righting reflex. It is predicted that any combination of +Gz and pilot head roll response will produce a tangential force to the skull/C1/C2 joints.
TABLE OF CONTENTS
1
1
1.INTRODUCTION 1
2.BACKGROUND 3
3.RESEARCH OBJECTIVES 10
4.METHODS 11
4.1Subjects 11
4.2Aircraft 14
4.3Airspace and weather 14
4.4Head tilt recording 15
4.5Flight task 21
4.6Ground task 23
4.7Pilot briefing 23
4.8Experimental design 24
5.RESULTS 26
5.1Flight conditions 26
5.2Quality of recorded image 27
5.3Body leans 28
5.4Pilot head roll angle 29
5.5Comparison of three flight modes (AI, visual, and non-flying) 35
5.6Regression analysis 35
5.7ANOVA analysis 38
5.8t-test 40
5.9Comparison between the direction of aircraft roll (left or right) 42
5.10Comparison by subject age and flight time 46
5.11Time series analysis of pilot head roll response 52
5.12Head roll in turns on the ground 56
6.DISCUSSION AND CONCLUSIONS 62
6.1Existence of pilot head roll response 62
6.2Body leans 64
1
1
cont. 6. DISCUSSION AND CONCLUSIONS
6.3Head motion in other modes of transportation 65
6.4Response of non-flying pilot 70
6.5Response of visually flying pilot 71
6.6Response of partially visual, partially instrument pilot 72
6.7Individual variation in pilot head roll response 74
6.8Phase comparison of aircraft roll and head roll 74
6.9Response in ground turns 75
6.10Comparison with simulator study 76
6.11Implication for cockpit design 77
6.12Effect of peripheral vision 80
6.13Implication for pilot health stabilization 82
6.14Physiological background of pilot head roll and its implication for motion sickness 84
6.15Future study design 86
7.SUMMARY 89
8.APPENDICES 90
8.1Nomenclature for body axes 90
8.2Table 15. - Flight maneuver sequence for subject #8. 93
8.3Table 16.-In-flight raw data. 94
8.4 Consent form for subjects. 98
9.REFERENCES 100
1
1
LIST OF FIGURES
Figure 1.-Computer graphics attitude display. 4
Figure 2.-Variation in Attitude Indicator design. 4
Figure 3.-View of AI and the horizon. 5
Figure 4.-Head roll of F-16 pilot in 9 G turn. 9
Figure 5.-Research airplane. Cessna C172L Skyhawk, fixed-gear, 4-place. 12
Figure 6.-Instrument layout of the research airplane. 12
Figure 7.-Visual Flight Rule 1:500,000 sectional chart for the flight test air space. 13
Figure 8.-Videocamera mounted on a headset. 16
Figure 9.-Data acquisition system diagram. 16
Figure 10.-Dimension of videocamera setting in the research airplane. 17
Figure 11.-Calibration of videocamera angle. 18
Figure 12.-Cockpit picture in analysis. 18
Figure 13.-Head alignment of a pilot in 45° bank turn to the left. 19
Figure 14.-Head roll angle around head x-axis, in Attitude Indicator mode of flight. 30
Figure 15.-Head roll angle around head x-axis, in vidual flight mode. 30
Figure 16.-Head roll angle around head x-axis, in non flying flight mode. 30
Figure 17.-Pilot head roll around head x-axis during aircraft turn, in Attitude Indicator mode of flight. 32
Figure 18.-Pilot head roll around head x-axis during aircraft turn, in visual mode of flight. 33
Figure 19.-Pilot head roll around head x-axis during aircraft turn, in non-flying mode of flight. 34
Figure 20.-Regression coefficient (ordinate) for aircraft bank angle vs. head roll angle. 36
Figure 21.-Regression analysis for head roll angle vs. aircraft roll angle. 37
Figure 22.-Field of view for Cessna 172L. 43
Figure 23.-Scattergram of subject age vs. head roll angle, left aircraft roll. 47
Figure 24.-Scattergram of subject age vs. head roll angle, right aircraft roll. 48
Figure 25.-Scattergram of subject flight time vs. head roll angle, left aircraft roll. 49
Figure 26.-Scattergram of subject flight time vs. head roll angle, right aircraft roll. 50
Figure 27.-Head roll angle around head x-axis of each subjects. 51
Figure 28.-Time course of aircraft and head roll around their x-axis, Attitude Indicator flight mode. 53
Figure 29.-Time course of aircraft and head roll around their x-axis, visual flight mode 54
Figure 30.-Time course of aircraft and head roll around their x-axis, non-flying mode. 55
Figure 31.-Head roll in ground turn. 57
Figure 32.-Head roll during a 180° course reversal on the ground, time series. 58
Figure 33.-Head roll during a 180° course reversal on the ground. 59
Figure 34.-The relation between elapsed time and aircraft heading for Figure 32 and Figure 33. 60
Figure 35.-Head position of a passenger in 90° bank flight. 63
Figure 36.-Automobile driver’s head alignment during roll of vehicle around its x-axis (longitudinal axis). 66
Figure 37.-Head alignment of an automobile driver. 67
Figure 38.-Motorcycle rider and passenger’s head alignment in turn. 68
Figure 39.-Latest Head Up Display symbols. 79
Figure 40.-Cervical spine alignment on head roll. 81
Figure 41.-Nomenclature for axes. 92
LIST OF TABLES
Table 1.-Terms equivalent to ‘moving horizon’ and ‘moving aircraft’. 7
Table 2.-Profile of pilot subjects. 11
Table 3.-Ground simulator study result. 24
Table 4.-Head roll with body lean, subject #9. 28
Table 5.-Result of pilot head roll angle around head x-axis during aircraft turn. 31
Table 6.-ANOVA table for subject and flight mode. 39
Table 7.-Post-hoc test for head roll angle difference among flight modes. 39
Table 8.-A matrix of t-test for difference in head roll among flight modes at each aircraft roll (bank) angle. 41
Table 9.-Comparison of head roll angle between left and right aircraft roll, all flight modes. 44
Table 10.-Comparison of head roll angle between left and right aircraft roll, Attitude Indicator flight mode. 44
Table 11.-Comparison of head roll angle between left and right aircraft roll, visual flight mode. 45
Table 12.-Comparison of head roll angle between left and right aircraft roll, non-flying flight mode. 45
Table 13.-Regression coefficients from simulator and flight study. 76
Table 14. +Gz values for aircraft roll angles. 85
Table 15. - Flight maneuver sequence for subject #8. 93
Table 16.-In-flight raw data. 94
ACKNOWLEDGEMENTS
I would like to extend my sincerest thanks to the following people for their assistance in the undertaking of this study:
Stanley R. Mohler, M.D., Anthony J. Cacioppo, Ph.D., Satya P. Sangal, Ph.D., Robin E. Dodge, M.D., and Frederick R. Patterson, Ph.D.
I am grateful to Terry Taddeo, M.D. and Fumi Shimada for their help in manuscript preparation.
1
1
1.INTRODUCTION
Spatial disorientation is still a pilot killer. Spatial disorientation is associated with the experiencing of an orientational illusion for pilots [Gillingham 1985]. Loss of situational awareness has been a major concern in military aviation, where one encounters a wide aircraft aerodynamic envelope (acceleration and velocity) [Barnum 1968, Cheung 1995]. Requirements for close formation flying under poor weather conditions is another factor related to this phenomenon. Civilian aviation has not placed much emphasis on this pilot-system limitation [Kirkham 1978, Johnson 1989, AOPA 1993]. Is it a problem only for high-performance fighter pilots?
Recently spatial disorientation was identified as a link in the causal chain of factors related to a major US air carrier crash. A DC-9 jetliner had a collision with the ground because of an encounter with a microburst and the pilots’ subsequent loss of situational awareness due to somatogravic illusion [NTSB 1994]. The flight crew became disoriented during the transition from Visual Meteorological Conditions to Instrumental Meteorological Conditions.
What type of computer graphic display, head-up display, or head-mounted display might facilitate spatial orientation? What should be the contents of a training syllabus against disorientation? Is our understanding of its pathophysiology sufficient to permit the design of truly better instruments and training?
In aerospace medicine textbooks, there has been no quantitative description about natural body and head alignment of pilots other than in a straight and level flight. Only recently this was challenged by two ground simulator studies [Patterson 1995A, Smith 1995]. Some flight instructors teach students that keeping their head and body straight along the body z-axis (longitudinal axis, Figure 41) is the proper body alignment. But the simulator study found that pilots laterally deflect their heads during turning maneuvers.
Positional alignment of head and body during flight maneuvers is a significant limiting factor for the design of instruments and cockpit layout. The latest designs of Head-Up Displays or Head-Mounted Displays are more sensitive to this geometry because of their limited angle of view. In order to view some military head-up displays, the eyes must be kept within an 8 x 13 cm (3 x 5 inch) field. These limits are easily exceeded if pilots roll their head around their head x-axis (deflect the head laterally).
The physiological dynamics of pilot head motion during flight has yet to be investigated.
2.BACKGROUND
Actively controlled human flight began with hang gliders, under visual flight condition. The Wright Brothers from Dayton, Ohio began controlled, powered flight after their extensive experiments with gliders. The next breakthrough, was the invention of the aircraft’s attitude display.
Prior to the emergence of the apparatus, there was an interesting instrument arrangement used by Charles A. Lindbergh for his solo transatlantic flight in 1927. Since his forward view was blocked by a fuel tank, he used a periscope to provide a visual reference [Roscoe 1966]. Although he is said to have used forward slipping during approach to gain a better view of the runway, the periscope deprived him of peripheral vision, which is important for pilots [Kochhar 1978].
Based upon his design of a gyroscopic stabilizer for ships, Elmer Sperry, Jr. [Laboda 1995], in 1910, extended the technology by developing a gyroscope for use by pilots for determining aircraft attitude. The Sperry Artificial Horizon allowed Lt. James H. Doolittle to fly his NY-2 Navy trainer airplane ‘blind’ on 24 September 1929. This historic apparatus is on display at the US Air Force Museum, Dayton, Ohio.
Figure 1.-Computer graphics attitude display.
A display of a Fokker F-100 jetliner. It is the latest design in use, but stays with the concept of a stationary aircraft symbol with a moving horizon.
Figure 2.-Variation in Attitude Indicator design.
This AI in a 1966 Piper PA30B twin piston-engine airplane has a bank pointer that moves with the horizon bar, instead of with the miniature airplane. Many AI’s of this design are still in use today. This kind of design variation is also seen in VOR (Very High Frequency Omni Range) indicators.
Figure 3.-View of AI and the earth horizon.
The Attitude Indicator (arrow) and the earth horizon seen from cockpit of a CH2000 single engine airplane. The roll angle of the aircraft is 64° to the left. This picture is aligned to the page so that it looks natural to the reader, while actually it differs from the retinal image of the pilots in the cockpit because of the limited motion of the head in flight.
[ AOPA Pilot, 36(12),1993: 47 ]
There is a speculation that Lindbergh’s success with the periscope may have affected the design of the artificial horizon (now called the Attitude Indicator, Figure 1, Figure 2). All operational attitude indicators, except for those of Russian design, use ‘moving horizon’ symbolic design. The horizon bar (Figure 1) resembles that of a short portion of the earth horizon as if seen through a periscope (Figure 3).
Peripheral displays, such as the para-visual director, peripheral command indicator, HOVERING display, and the Malcolm horizon stimulate peripheral vision to provide aircraft attitude information [Stokes 1988]. They have proven to be relatively effective despite degraded visual acuity associated with peripheral vision. Visual acuity in Snellen’s fraction decreases from 1.0 in the visual center to 0.2 at 10° off center, 0.1 at 20°, and 0.07 at 30° [Westheimer 1992].
How can we present attitude information to maximize foveal vision? Although the options are many, modern Russian fighters use an attitude display whose miniature airplane, instead of a horizon bar, rolls.
In the past, no commercial competition was seen between the ‘moving horizon’ and ‘moving airplane’ display. This is probably due to the initial success of the Sperry artificial horizon and the comprehensive analogy of periscopic view (‘cut out’ earth horizon appears in an Attitude Indicator) [Poppen 1936, Roscoe 1966]. Other equivalent terms, which are often confusing, are summarized in Table 1. It is worth noting that an integrated display which changes from ‘moving aircraft’ to ‘moving horizon’ for roll-in has been devised [Fogel 1959, Roscoe 1975].
Table 1.-Terms equivalent to ‘moving horizon’ and ‘moving aircraft’.
moving horizonmoving airplane
inside-outoutside-in
fly-tofly-from
moving card or tapemoving pointer
earth referencedaircraft referenced
aircraft stabilizedspace stabilized
in aircraft coordinatesin earth coordinates
modified from [Johnson 1972]
A study by the Federal Aviation Administration Civil Aeromedical Institute with a Beechcraft T-34 [Hasbrook 1973] compared the two types of display and concluded that:
Data from many of these earlier studies suggest that the outside-in (moving- aircraft) indicator provides better pilot performance: but this in-flight study fails, in the main, to show any such well defined, overall advantage.
Despite pioneer efforts, it was not until 1930 that military pilots were taught that the instruments should be used as source for flight information and that they should not fly by the “seat of their pants” [Malcolm 1984]. This is not widely understood among today’s leisure pilots.
When one questions the dynamics associated in comparing a ‘moving horizon’ with ‘moving airplane’, the answer is ambiguous. Missing is the recognition of natural behavior of the pilots. What is the natural position of the head relative to the cockpit?
When asked if the head moves during flight, most pilots will answer ‘no’. Only a few pilots admit that they roll their head. Even demonstration team members of the US Navy [Patterson 1995A] and the US Air Force (Figure 4) were observed to roll their heads around the head z-axis (tilt their head) in a direction opposite to the center of the turn in visual flight. Pilots prefer to view a picture as if aligned to the earth horizon rather than to the cockpit (Figure 3). The only literature about head motion in flight, which surfaced, gave a general indication that subject pilots kept their head z-axis normal to the ground [Hasbrook 1973].
Recent simulator sutdies revived this old but unanswered question [Patterson 1995A, Smith 1995]. If pilots are rolling their heads, is a ‘moving horizon’ better adapted to prevent roll reversal (mistakenly initiate roll to the opposite direction)? What if the display moves with the head instead of being fixed to the cockpit? What is the natural motion of the head that should be assumed in a new display design? Which attributes of display design should be adopted?
Figure 4.-Head roll of F-16 pilot in 9 G turn.
This U.S. Air Force Thunderbirds demonstration team member is quickly rolling into 9 G turn. The roll (bank) angle of aircraft in this picture is 64° (BOH’). His head is rolled to the right around head x-axis (laterally deflected to the right) with an angle of 15° (90° - AOH) relative to the cockpit. Cockpit level is represented by line HH’. Because the body is leaned to the right with an angle of 3° (HOS), the angle of head roll relative to the body z-axis is 12° (15° - 3°). There is a slight yaw of the head to the left, which does not affect more than 1° for this head roll angle relationship to the cockpit. A transient maximum roll of the head of 24° relative to the cockpit was observed when roll of the aircraft was at 60° (just before this picture). After this picture, roll of aircraft was kept 82° to 85° to keep 9 G turn, which theoretically requires 83.6° of bank [ cos- 1 (1/9) ]. Head roll angle was kept approximately 6° to the right relative to the cockpit while 9 G 360° turn was continued.
[ International Video Corporation 1990 ]
3.RESEARCH OBJECTIVES
The purpose of this research is to determine how pilots (flying and non-flying) align their heads during actual flights in a general aviation aircraft.
It is hypothesized that general aviation pilots in visual flight rule (VFR) conditions align their heads with the horizon of the earth for visual orientation, which causes head rotations around the x-axis of the head. This study examines this hypothesis by recording and analyzing pilot head motion during actual VFR flight in a general aviation aircraft.
To supplement the flight test, head motion data were collected during the ground taxing phase of a flight.
4.METHODS
4.1Subjects