Abstract
Background:
Flying a helicopter requires greater coordination than flying a fixed-wing aircraft, because the pilot is required to apply force simultaneously to three controls: the cyclic, collective, and pedals. There has been one study of pilot applied forces during helicopter flight, but this investigation did not examine muscle activity patterns. The aim of this study was to examine the muscle activation patterns and control forces of helicopter pilots during routine maneuvers.
Methods:
Six pilots were tested in a UH-1 h Iroquois helicopter. The maneuvers involved hovering, winching, under-slung loads, a constant rate turn, and a high-speed valley turn. Variables recorded were pilot applied forces and electromyographic activity (EMG). Multivariate analysis of variance was used to test for differences between maneuvers.
Results:
Significant differences between the maximum forces recorded from each control across all maneuvers were recorded (p < 0.05). The greatest pilot applied forces were recorded from the pedals. No muscles were activated more than 25% of a maximum voluntary contraction for any maneuver. The greatest magnitude of EMG activity was recorded from vastus lateralis during high-speed valley turns. There were significant differences between the EMG activity of left triceps, right triceps, and right deltoid for some maneuvers (p <0.05).
Conclusion:
The control forces required to fly a helicopter during routine maneuvers are small. The levels of muscle activation associated with pilot applied forces are also low, but are similar to those reported during routine maneuvers in a fast-jet flight simulator.
Abstract
Background:
The helmet-mounted display (HMD) research program at the Flight Research Laboratory of the National Research Council of Canada examined the effects of HMD camera platform dynamics on pilot workload. Many currently fielded visually coupled HMD systems do not reproduce head movements in the roll axis which can lead to the presentation of visual information that is not consistent with vestibular and proprioceptive information.
Hypothesis:
Our hypothesis was that this sensory conflict can induce motion sickness and increase pilot workload.
Methods:
To examine this premise, three pilots flew a series of standardized maneuvers with or without roll compensation in the camera platform of a visually coupled HMD system.
Results:
Increases in motion sickness symptoms and pilot workload were noted during complex, high-workload maneuvers when no roll compensation was present in the camera platform. During the most demanding maneuvers, the lack of roll compensation in the camera platform made it difficult for the evaluation pilot to control the helicopter.
Conclusions:
Roll compensation in visually coupled HMD systems reduces pilot workload and motion sickness during critical flight periods where pilot workload may already be considerable.
Abstract
Background:
The push-pull effect (PPE) has been suspected of causing many aircraft accidents. The peffusion and then withdrawal of cerebral blood during the PPE may change the state of the cerebral blood vessel.
Hypothesis:
During head-down tilt (HDT) cerebral vasoconstriction occurs in response to the elevated perfusion pressure to maintain cerebral blood flow, and during subsequent head-up tilt (HUT) the increased resistance of the cerebral blood vessel recovers slowly.
Methods:
Ten healthy male non-pilots were exposed to the following protocol using a rotating-table to simulate the push-pull maneuver: HUT (+1 Gz) for 1 rain followed by transition to HDT (-1 Gz) 10 s followed by transition to HUT (+1 Gz) 1 rain. Cerebral blood flow velocity and pulsatility indices in the left middle cerebral artery were continually measured with a transcranial Doppler (TCD) instrument.
Results:
Mean blood flow velocity (Vm) increased significantly by 10% during the first 5 s of HDT, recovered to baseline during HDT 5–10 s, and remained unchanged during subsequent HUT. Systolic blood flow velocity (Vs) increased by 9% during HDT 5–10 s and 11% during HUT 0–5 s. Diastolic blood flow velocity (Vd) decreased by −9% during HDT 5–10 s, and −22% during HUT 0–5 s. Vs-Vd increased by 26% during HDT 5–10 s, and 41 %during HUT 0–5 s. Pusatile indices (PI) and resistance index (RI) increased by 26% and 15% during HDT 5–10 s, and by 40% and 27% during HUT 0–5 s, respectively. Vs, Vs-Vd, PI, and RI remained at the higher level, and Vd remained at the lower level to HDT 15–20 s.
Conclusions:
The results indicate that cerebral vasoconstriction occurred to prevent brain over-peffusion during HDT. During HUT, the elevated resistance of the cerebral vessel remained at the higher level for about 20 s, and may have worsened the cerebral peffusion from exposure to +Gz. This may be one of the mechanisms of PPE.
Abstract
Background:
Several aircraft each year are lost because of an unexplained collision with the ground. The attitude of most of these aircraft prior to impact was nose-low and with excessive bank, i.e., greater than 90° Prior to these accidents, each aircraft was noted as either changing heading or making an abrupt roll.
Hypothesis:
Could there be some underlying tendency for the pilot to make unnoticed stick inputs after completing a roll from one bank angle to another?
Methods:
Since ground-based flight simulators cannot create the true sensation of rolling an aircraft from one side to the other, the instrumented CALSPAN NT-33 aircraft was used for this study. Six pilots were given a series of three roll rates and two head positions while the aircraft automatically changed bank from 45° of bank in one direction to 45° of bank in the opposite direction. The subject's view of the external visual scene was restricted with a blue-amber vision restricting transparency combination. All attitude-indicating instruments were blanked, requiring the subjects to make stick inputs based on their vestibular (somatosensory) feedback.
Results:
Subjects experienced a consistent tendency to increase bank angle after given control of the aircraft immediately following the roll maneuver, while thinking they were maintaining a constant bank angle. In some cases, the pilots rolled the aircraft completely inverted.
Conclusion:
When pilots rely on their perception of bank, following a roll, they will inadvertently increase their bank in the direction of the previous roll.
Abstract
Methods:
Some 329 military high-performance pilots were anonymously surveyed to determine the occurrence rates for a symptom complex of acceleration-induced neurologic manifestations. The premise for this symptom complex is the theory that acceleration-induced neurologic effects are not always an all-or-none phenomenon with G-LOC as the operational endpoint.
Results:
A significant number of aircrew in selected types of aircraft reported symptoms such as euphoria, apathy, displacement, depersonalization, poor response to auditory stimuli, immediate memory, difficulties, sensory abnormalities, motor abnormalities, confusion, and dream-like state without loss of consciousness.
Conclusion:
These findings may signal a need for alterations in G-awareness training.
Abstract
Background:
Acceleration (or G) induced arm pain may develop in centrifuge runs and in flight with low arm position and assisted pressure breathing during G (PBG) in combination with an extended coverage anti-G suit. To decrease this arm pain, pressurized sleeves and gloves were developed.
Methods:
Eight subjects who earlier exhibited G-induced arm pain were tested on the centrifuge. The G-exposures consisted of a gradual onset run up to a maximum of +9 Gz, rapid onset runs to +3, +4, +5, +6, +7, +8, and +9 Gz and a simulated aerial combat maneuver (SACM) with peaks up to +9 Gz. On separate days, the subjects were tested without the sleeves and gloves, and with the sleeves and gloves pressurized to a maximum of 40, 60, or 80mmHg at +9 Gz. The subjects reported their left and right arm pain on a subjective rating scale.
Results:
G-induced arm pain, usually starting above +6 GGz, was often the reason for termination of the G-exposure without the pressurized sleeves and gloves. The pressurized sleeves and gloves significantly (p < 0.001 ) decreased arm pain, but no significant difference was found among the different pressures used. Heart rate was not different with and without the pressurized sleeves and gloves.
Conclusions:
The pressurized sleeves and gloves are an effective method to alleviate and sometimes eliminate G-induced arm pain.
Abstract
The mathematical models developed in this article predict the following human G-level tolerances: 1 ) rapid onset relaxed (ROR); 2) gradual onset relaxed (GOR); and, 3) straining-rapid onset. Included in the model are specific functions of: 1) anti-G suit; 2) positive pressure breathing (PBG); 3) baroreceptor reflex; 4) handgrip reflex; 5) anti-G straining maneuver (AGSM) increasing intrathoracic pressures (Pi); 6) leg elevation; and, 7) reclining seatback angles ≤ 55° These functions are based on sound physiologic principles. Also discussed in the development of this model, but not included in the models, were: 1) isometric muscle contraction reflex; 2) Qigong (Q-G) maneuver; and, 3) straining GOR tolerances. The straining GOR tolerance profile was calculated to be a measure of G-duration tolerance and not G-level tolerance. A maximum Pi of 125 mm Hg from the AGSM was used in these models that could be augmented with PBG to 185 mm Hg. G-level tolerance predictions using this model were validated with published data.
Abstract
Background:
When the human body is exposed to a high gravitational load, the blood supply to the brain is reduced and loss of consciousness may occur. Our goal is to identify the principal mechanical causes of reduced blood supply to the brain during high +Gz.
Methods:
We have developed a mathematical model to investigate the influence of Gz on the cerebral circulation. Blood flow is modeled using a one-dimensional flow approximation, in which the cross-sectional area of elastic vessels is determined as a non-linear function of the transmural (blood minus external) pressure. The intracranial vessels are subjected to cerebrospihal fluid pressure (Pcsf) which is determined from the condition that the cranial volume is conserved.
Results:
For a constant pressure difference of 100 mm Hg applied to the arterial and venous ends of the model, blood flow is diminished for +Gz. At approximately +5 Gz the blood flow predicted by the model is insufficient to maintain normal functioning of the brain. Pcsf is approximately equal to the blood pressure in the large intracranial veins for all values of Gz. Extracranial arteries and the intracranial vessels do not collapse, even when Gz is substantially higher than normal. However, the extracranial veins are collapsed even for moderate +Gz.
Conclusions:
Even if cardiac output is maintained at normal levels, cerebral perfusion will fall because of the increasing resistance of the cerebral flow circuit. This increase is largely due to the collapse of the extracranial veins, which begins at moderate Gz and becomes dominant at a Gz of approximately 4.5.
Abstract
Background:
The purpose of this study was to investigate nausea and vomiting during hyper-gravity flight at a slow rate of turn. During head-movements under these conditions, the semi-circular canals of the vestibular system function normally whereas the otoliths experience a G-excess effect, displacing further and moving faster than in a 1 G field.
Hypothesis:
Nausea and vomiting are greater during hyper-gravity flight compared with historical data collected in a 1 G field at a similar rate of turn.
Methods:
There were 27 subjects who were exposed to 1.8 G (hyper-G) during a slow rate turn on three NASA KC-135 flights. Subjects participated in one of three experimental periods, each period consisting of two 5.5-min hyper-G runs: 1) rest, with only incidental head movements; 2) active roll and pitch head movements; or 3) passive roll head movements. Subjective symptom data were collected pre-flight, following each experimental period and post-flight using a standardized nausea questionnaire. Electrogastrograms were obtained from eight subjects.
Results:
Seven subjects (26%) vomited during the flight. Nausea initially increased but was then stable throughout the flight. Nausea appeared highest during active head movements. In subjects who vomited, greater gastrointestinal distress and somatic distress were reported.
Conclusions:
The levels of nausea and vomiting observed during hyper-G cannot be explained by Coriolis cross coupling and are likely due to the G-excess effect on the otoliths. The nausea profiles observed in individuals who vomit during hyper-G appear similar to those previously observed during nausea produced by an optokinetic drum stimulus in a 1-G field.
Abstract
Background:
In order to evaluate the impact of in-flight stress on BP and sympathetic activity during a short fixed-wing flight, we have studied 18 healthy and normotensive commercial captain aviators, aged 37.5 ± 4.9 yr.
Methods:
The protocol consisted of a 120-rain flight period, divided into segments of pre-flight, take off, mid-cruise, approach and landing, and a 120-min control period. In both flight and control periods, all subjects underwent BP monitoring, heart rate recording and urine collection for cathecolamines.
Results:
Systolic and diastolic BP (SBP/DBP) were higher during the flight, as a whole, when compared with the control period (134 ± 11 vs. 121 ± 8 mmHg, p < 0.05 and 84 ± 8 vs. 76 ± 9 mmHg, p < 0.05, respectively). During the flight period, SBP increased in the pre-flight, take-off, approach and landing segments, whereas DBP increased in the take-off, mid-cruise, approach and landing segments. Heart rate did not change in any flight segment. Urinary cathecolamines increased during the flight period in comparison to control period 0.20 (0.10–1.8) mg ⋅ mg−1 creatinine vs. 0.10 (0.10–1.0) mg ⋅ mg −1 creatinine; p < 0.05).
Conclusion:
We conclude that inflight stress increases BP of the normotensive aviators by sympathetic activation during short-haul flights.
Abstract
Background:
The use of a three-dimensional (3-D) auditory display to significantly lower subject detection level while maintaining comprehension under sustained positive G-stress was explored in this study.
Methods:
Auditory threshold levels were measured for detecting a band limited pulsed signal in the presence of a broadband diotic masker at both +1 Gz (rest position) and under sustained +3 Gz. The pulsed signal was presented diotically and was spatialized at one of four static azimuth positions on the horizontal plane.
Results:
Results showed that auditory thresholds were not significantly affected by sustained +3 Gz stress. Compared with a diotic presentation, subjects reached an average of 6.8 dB lower auditory threshold at +1 Gz and under sustained +3 Gz when the pulsed signal was spatialized at a static position of 90° azimuth on the horizontal plane.
Conclusion:
The implication of these results and suggestions for further research are discussed.
Abstract
From 1988 to 1995, there were five reported cases of hemochromatosis among U.S. Army aviators. Three of the five are presented and discussed. The cases of hereditary hemochromatosis were discovered during unrelated work-ups or from investigation of a positive family history, and not by routine flying duty medical examinations. Recent studies show a prevalence of 5 per 1000 in the general population. This study shows the incidence among Army aviators is 0.296 per 1,000 aviator-years of observation. It is possible that there are cases presently undiagnosed in the Army aviation community. Without screening measures in place, the Army Aviation Branch has greater difficulty diagnosing and treating hereditary hemochromatosis. Heightened awareness and a high clinical index of suspicion are necessary to identify affected patients. Early detection and treatment is essential to prevent long-term end organ damage from iron deposition.
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