G Tolerance During Open- vs. Closed-Loop G-Time Control.

BACKGROUND: +Gz tolerance is traditionally determined in centrifuges with open-loop G control, i.e., the centrifuge is under operator control (open loop), and thus the test subject is unable to influence the Gz load. In modern centrifuges, however, the subject is commonly able to continuously control the Gz load (closed loop). It is a widespread opinion among fighter pilots that +Gz tolerance is higher under closed- than open-loop G control. The aims were to investigate whether +Gz tolerance is higher in closed- than open-loop G control, and whether it is possible to use closed-loop G control during precise determination of +Gz tolerance. METHODS: Relaxed +Gz tolerance was determined in eight men during rapid Gz-onset rate (ROR) under three conditions: 1) OL-VFB, open loop with visual feedback; 2) OL-NFB, open loop with no visual feedback; and 3) CL, closed loop. Straining +Gz tolerance was determined in 10 men during ROR in OL and CL conditions. RESULTS: Relaxed +Gz tolerance did not differ between CL (3.66 Gz), OL-VFB (3.70 Gz) and OL-NFB (3.64 Gz). Straining +Gz tolerance was similar in the CL (8.5 Gz) and OL (8.6 Gz) conditions. In the CL condition, the Gz load varied substantially and was on average lower than in the OL conditions, at any stipulated G-time profile. DISCUSSION: There is no systematic difference in relaxed or straining +Gz tolerance as determined in closed- vs. open-loop G-controlled systems. During closed-loop control, precision and reproducibility are too low to recommend it for accurate determination of relaxed G tolerance.Grönkvist M, Levin B, Eiken O. G tolerance during open- vs. closed-loop G-time control. Aerosp Med Hum Perform. 2018; 89(9):798-804.

Use of an adjustable hand plate in studying the perceived horizontal plane during simulated flight.

BACKGROUND: Quantitative data on spatial orientation would be valuable not only in assessing the fidelity of flight simulators, but also in evaluation of spatial orientation training. In this study a manual indicator was used for recording the subjective horizontal plane during simulated flight. METHODS: In a six-degrees-of-freedom hexapod hydraulic motion platform simulator, simulating an F-16 aircraft, seven fixed-wing student pilots were passively exposed to two flight sequences. The first consisted in a number of coordinated turns with visual contact with the landscape below. The visually presented roll tilt was up to a maximum 670. The second was a takeoff with a cabin pitch up of 100, whereupon external visual references were lost. The subjects continuously indicated, with the left hand on an adjustable plate, what they perceived as horizontal in roll and pitch. There were two test occasions separated by a 3-d course on spatial disorientation. RESULTS: Responses to changes in simulated roll were, in general, instantaneous. The indicated roll tilt was approximately 30% of the visually presented roll. There was a considerable interindividual variability. However, for the roll response there was a correlation between the two occasions. The amplitude of the response to the pitch up of the cabin was approximately 75%; the response decayed much more slowly than the stimulus. DISCUSSION: With a manual indicator for recording the subjective horizontal plane, individual characteristics in the response to visual tilt stimuli may be detected, suggesting a potential for evaluation of simulation algorithms or training programs.

Tactile cueing effects on performance in simulated aerial combat with high acceleration.

INTRODUCTION: Recent evidence indicates that vibrotactile displays can potentially reduce the risk of sensory and cognitive overload. Before these displays can be introduced in super agile aircraft, it must be ascertained that vibratory stimuli can be sensed and interpreted by pilots subjected to high G loads. METHODS: Each of 9 pilots intercepted 32 targets in the Swedish Dynamic Flight Simulator. Targets were indicated on simulated standard Gripen visual displays. In addition, in half of the trials target direction was also displayed on a 60-element tactile torso display. Performance measures and subjective ratings were recorded. RESULTS: Each pilot pulled G peaks above +8 Gz. With tactile cueing present, mean reaction time was reduced from 1458 ms (SE = 54) to 1245 ms (SE = 88). Mean total chase time for targets that popped up behind the pilot's aircraft was reduced from 13 s (SE = 0.45) to 12 s (SE = 0.41). Pilots rated the tactile display favorably over the visual displays at target pop-up on the easiness of detecting a threat presence and on the clarity of initial position of the threats. DISCUSSION: This study is the first to show that tactile display information is perceivable and useful in hypergravity (up to +9 Gz). The results show that the tactile display can capture attention at threat pop-up and improve threat awareness for threats in the back, even in the presence of high-end visual displays. It is expected that the added value of tactile displays may further increase after formal training and in situations of unexpected target pop-up.

Memory performance during G exposure as assessed by a word recognition task.

BACKGROUND: Pilots of modern fighter aircraft are exposed to substantial physiological and mental stressors. The objective of this study was to investigate how memory performance, in terms of encoding and/or retrieval processes, was affected by sustained +Gz exposure. METHOD: There were 18 healthy men ranging from experienced fighter pilots to novice riders who participated. A word continuous recognition task (CRT) was employed as a memory test. The task consisted of three consecutive phases: 1) encoding of familiar words at 1 G; 2) encoding and retrieval of words at 70% of the subject's relaxed G-tolerance level, equivalent to +3.7 +/- 0.54 Gz; and 3) encoding and retrieval of words at 1 G. In addition, each subject performed the CRT in a 1-G-only control condition. Physiological and psycho-physiological measures included continuous monitoring of ECG, arterial oxygen saturation, arterial BP at head level, and response time. RESULTS: Data analysis showed that the capability to recognize words encoded at 1 G did not differ between conditions, indicating that the retrieval process was insensitive to increased Gz load. However, the ability to recognize words previously encoded during G exposure was reduced by approximately 10% as compared with control. Since the analysis revealed that the words were perceived, this result suggests that the encoding process was impaired in hypergravity. CONCLUSION: The results indicate that memory encoding, but not retrieval, was affected negatively when exposed to substantial and sustained +Gz loads.