William W. Chung

Simulator Platform Motion Effects on Pilot-Induced Oscillation Prediction

Simulator motion platform characteristics were examined to determine if the amount of motion affects pilotinduced oscillation prediction. Five test pilots evaluated how susceptible 18 different setsof pitch dynamics were to pilot-induced oscillations with three different levels of simulation motion platform displacement: large, small, and none. The pitch dynamics were those of a previous in-e ight experiment, some of which elicited oscillations. These in-e ight resultsserved as truth data for the simulation. As such, the in-e ight experiment wasreplicated asmuch as possible. Objective and subjective data were collected and analyzed. With large motion, pilot-induced oscillation and handling qualities ratings matched the e ight data more closely than with small motion or no motion. Also, regardlessof the aircraft dynamics, large motion increased pilot cone dencein assigning handling qualitiesratings, reduced safety pilot trips, and lowered touchdown velocities. Whereas both large and small motion provided a pitch rate cue of high e delity, only large motion presented the pilot with a high e delity vertical acceleration cue.

Evaluation of a motion fidelity criterion with visual scene changes.

An experiment examined how visual scene and platform motion variations affected a pilots ability to perform altitude changes. Pilots controlled a helicopter model in the vertical axis and moved between two points 32-ft apart in a specified time. Four factors were varied: visual-scene spatial frequency, visual-scene background, motion-filter gain, and motion-filter natural frequency. Drawing alternating black and white stripes of varying widths between the two extreme altitude points varied visual-scene spatial frequency. The visual-scene background varied by either drawing the stripes to fill the entire field of view or by placing the stripes on a narrow pole with a natural sky and ground plane behind the pole. Both the motion-filter gain and natural frequency were varied in the motion platform command software. Five pilots evaluated all combinations of the visual and motion variations. The results showed that only the motion-filter natural frequency and visual-scene background affected pilot performance and their subjective ratings. No significant effects of spatial frequency or motion system gain were found for the values examined in this tracking task. A previous motion fidelity criterion was found to still be a reasonable predictor of motion fidelity.

EFFECTS OF VEHICLE BANDWIDTH AND VISUAL SPATIAL-FREQUENCY ON SIMULATION CUEING SYNCHRONIZATION REQUIREMENTS

Results of a recent flight simulation study suggested criteria for visual and motion cueing synchronization, but only for one vehicle bandwidth and one visual scene. The purpose of the study reported here was to determine if those synchronization criteria may be generalized. In particular, a complete factorial design was used to examine the flight simulation effects of the following five experimental factors: visual time delay, roll motion time delay, lateral motion time delay, vehicle bandwidth, and visual spatial frequency. Five experimental test pilots completed the full experimental matrix. The results show that the more limited set of synchronization criteria generalize for the variations examined. That is, regardless of the vehicle bandwidths or the visual cueing spatial frequencies examined, the same synchronization criteria are applicable for the visual, roll, and lateral cues. Thus, the results add further confidence to the recently suggested criteria, which suggested three guidelines. First, roll and lateral motion cues should be synchronized, but if they cannot be, the asynchronization should be no more than 40 msec. Second, the visual and roll motion cues should also be synchronized, but if they cannot be, the asynchronization should also be no more than 40 msec. Third, the synchronized roll and lateral motion cues can be allowed to lag, but should not lead, the visual cues. Nomenclature

A Study of Civil Tiltrotor Aircraft in NextGen Airspace

Tiltrotor aircraft have long been envisioned as being a potentially viable means of commercial aviation transport. Preliminary results from an ongoing study into the operational and technological considerations of Civil Tiltrotor (CTR) operation in the Next Generation airspace, circa the 2025 time-frame, are presented and discussed. In particular, a fleet of CTR aircraft has been conceptually designed. The performance characteristics of this CTR fleet was subsequently translated into BADA (Base of Aircraft DAta) models that could be used as input to emulate CTR aircraft operations in the ACES and AvTerminal airspace and terminal area simulation tools. A network of nine North-Eastern corridor airports is the focus of the airspace simulation effort; the results from this airport network will then be extrapolated to provide insights into systemic impact of CTRs on the National Airspace System (NAS). Future work will also be detailed as to attempts to model the systemic effects of noise and emissions from this fleet of new aircraft as well as assess their leveraged impact on public service missions, in time of need, such as major regional/national disaster relief efforts. The ideal outcome of this study is a set of results whereby Next Gen airspace CONOPs can be refined to reflect potential CTR capabilities and, conversely, CTR technology development efforts can be better informed as to key performance requirement thresholds needed to be met in order to successfully introduce these aircraft into civilian aviation operation.

Spatial frequency and platform motion effects on helicopter altitude control

An experiment examined how visual scene and platform motion variations affected a pilot’s ability to perform altitude changes. Pilots controlled a helicopter model in the vertical axis and moved between two points 32-ft apart in a specified time. Four factors were varied: visual scene spatial frequency, visual scene background, motion filter gain, and motion filter natural frequency. Drawing alternating black and white stripes of varying widths between the two extreme altitude points varied visual scene spatial frequency. Visual scene background varied by either drawing the stripes to fill the entire fieldof-view or by placing the stripes on a narrow pole with a natural sky and ground plane behind the pole. Both the motion filter gain and natural frequency were varied in the motion platfom command software. Five pilots evaluated all combinations of the visual and motion variations. The results showed that only the motion filter natural frequency and visual scene background affected pilot performance and their subjective ratings. No significant effects of spatial frequency or motion system gain were found for the values examined in this tracking task. A previous motion fidelity criterion was found to still be a reasonable predictor of motion fidelity.

Transfer of Training on the Vertical Motion Simulator

This paper describes a quasi-transfer-of-training study in the NASA Ames Vertical Motion Simulator (VMS). Sixty-one general aviation pilots trained on four challengingcommercial transport tasks under one of four different motion conditions: no motion, small hexapod, large hexapod, and VMS motion. Then, every pilot repeated the tasks in a check with VMS motion to determine if training with different motion conditions had an effect on task performance. New objective motion criter ia guided the selection of the motion parameters for the small and large hexapod conditions. Considering resu lts that were statistically significant, or marginally significant, the motion condition used in training affected 1) longitudinal and lateral touchdown position; 2) the number of secondary stall warnings in a stall recov ery; 3) pilot ratings of motion utility and maximum load factor obtained in an overbanked upset recovery; an d 4) pilot ratings of motion utility and pedal input reaction time in the engine-out-on-takeoff task. Sinc e the training motion conditions revealed statistical differences on objective measures in all the tasks pe rformed in the VMS motion check, with some in the direction not predicted, trainers should be cautious not to oversimplify the effects of platform motion. Evidence suggests that the new objective motion criteria may off er valid standardization benefits, as increases in the training motion fidelity, as predicted by the two conditions covered by the criteria, resulted in expected trends in pilot ratings and objective performance measures afte r transfer.

Civil Tiltrotor Aircraft Operations

The goal of the current study is to investigate the benefits and challenges of operating a notional fleet of civil tiltrotor aircraft (10-, 30-, 90-, and 120-passenger vehicles), in the commercial transport role, in the projected Next Generation airspace system. Considerable effort was expended in modeling and performing ACES airspace simulations of this civil tiltrotor (CTR) fleet. An extensive set of airport networks (assuming on- or near-airport property vertiports for CTR VTOL or STOL operations) were also modeled in the airspace simulations. In particular, the networks were mapped to three primary regions: the Northeast Corridor, an Atlanta regional network, and a Las Vegas regional network. Using JPDO demand/capacity projections for 2025 as a baseline, the potential impact of CTR fleet introduction to these regional networks was assessed. The NAS-wide average delay decreased from ~22 minutes for the conventional fixed-wing fleet baseline to 7-8 minutes with the combined introduction of the CTR fleet throughout all three primary regional networks. The study will next consider the operational implications of this notional CTR fleet in supporting major regional and/or National emergencies and disaster relief efforts. The CTR disaster relief analysis is being performed by means of specialized simulation tools. This work re-emphasizes the unique role of rotorcraft in supporting such life-saving missions.

An initial evaluation of the effects of motion platform and drive characteristics

Six motion cueing configurations were developed to investigate facility dependent effects on simulation fidelity. These configurations were tested on a large-amplitude motion-based flight simulator and, when possible, on a small amplitude hexapod flight simulator. On the large amplitude device, one configuration had no motion attenuation, and it served as the thruth-case motion reference. Five other configurations were developed to represent a continuum of motion fidelity from high to low. Results from this investigation indicate that only the one-to-one motion configuration consistently reflected the predicted handling qualities ratings based on an existing handling qualities specification. It was also noted that reductions in motion fidelity can falsely improve handling qualities ratings. Non-trivial differences were measured between the facilities, and those differences are currently being investigated.

Refinement of Objective Motion Cueing Criteria Based on Three Flight Tasks

This paper aims to refine objective motion cueing criteria developed in a previous experiment for the simulator motion system diagnostic test specified by the International Civil Aviation Organization. Fifteen airline transport pilots flew the same three tasks as in the previous experiment in the NASA Vertical Motion Simulator under six different motion configurations. The six different motion configurations covered the motion region between the motion fidelity uncertainty boundary found in the previous experiment and the mean motion response of a statistical sample of eight representative hexapod motion simulators. The motion condition significantly affected 1) roll deviations in the approach to a stall and maximum pitch rate in a stall recovery, and 2) heading deviation and pedal reaction time after an engine failure in the takeoff task. Significant differences in pilot-vehicle performance were used to develop new objective motion cueing criteria boundaries for the main motion responses. In addition, perception thresholds of false motion cues were used to develop motion cueing criteria for the cross-coupling motion responses. The fidelity boundaries of the current experiment should be used with caution when reducing the uncertainty of the initial fidelity boundaries developed in the previous experiment, as they do not fully overlap. Data collected in the current study will add to data from the next experiment, which aims to further refine and optimize the objective motion criteria found to date.