NASA Ames Vertical Motion Simulator Research Articles

Coaxial-Compound Helicopter Flight Control Design and High-Speed Handling Qualities Assessment

To provide the government with independent control-system design, handling qualities analysis, and simulation research capabilities in support of Future Vertical Lift, the U. S. Army Combat Capabilities Development Command Aviation & Missile Center has developed generic high-fidelity flight-dynamics models of several advanced high-speed rotorcraft configurations. One of the configurations modeled is a lift offset coaxial-compound helicopter with a pusher propeller. Full flight envelope explicit model following control laws were designed for the generic coaxial-compound helicopter using a multiobjective optimization approach to meet a comprehensive set of stability, handling qualities, and performance specifications. Helicopter response types were used for hover/low-speed, while typical fixed-wing response types (normal acceleration and sideslip command) were used at high speed. The control laws were evaluated in a piloted simulation experiment at the NASA Ames Vertical Motion Simulator using a series of previously developed high-speed handling qualities demonstration maneuvers. This paper discusses the control laws and the results of the piloted handling qualities assessment, which showed assigned Level 1 handling qualities for six of the seven maneuvers evaluated.

Tiltrotor Flight Control Design and High-Speed Handling Qualities Assessment

To provide the government with independent control-system design, handling qualities analysis, and simulation research capabilities in support of Future Vertical Lift, the U. S. Army Combat Capabilities Development Command Aviation & Missile Center has developed generic high-fidelity flight-dynamics models of several advanced high-speed rotorcraft configurations including a tiltrotor. Full flight envelope explicit model following control laws were designed for the generic tiltrotor using a multiobjective optimization approach to meet a comprehensive set of stability, handling qualities, and performance specifications. Helicopter response types were used for hover/low-speed, while typical fixed-wing response types (normal acceleration and sideslip command) were used at high speed. The control laws were evaluated in a piloted simulation experiment at the NASA Ames Vertical Motion Simulator using a series of previously developed high-speed handling qualities demonstration maneuvers. This paper discusses the control laws and the results of the piloted handling qualities assessment which show overall assigned Level 1 handling qualities in high-speed and Level 2 in transition.

Transfer of Training on the Vertical Motion Simulator

This paper describes a quasi-transfer-of-training study in the NASA Ames Vertical Motion Simulator. Sixty-one general aviation pilots trained on four challenging commercial transport tasks under one of four different motion conditions: no motion, small hexapod, large hexapod, and Vertical Motion Simulator motion. Then, every pilot repeated the tasks in a check with Vertical Motion Simulator motion to determine if training with different motion conditions had an effect on task performance. New objective motion criteria guided the selection of the motion parameters for the small and large hexapod conditions. Considering results 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 recovery, 3) pilot ratings of motion utility and maximum load factor obtained in an overbanked upset recovery, and 4) pilot ratings of motion utility and pedal input reaction time in an engine-out-on-takeoff task. Because the training motion conditions revealed statistical differences on objective measures in all the tasks performed in the Vertical Motion Simulator 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 offer valid standardization benefits because 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.

Human Spatial Orientation Perception During Simulated Lunar Landing Motions

Safe and precise piloted lunar landings require control inputs that depend on an accurate perception of vehicle orientation and motion. However, the unique environment and motions experienced during a lunar landing trajectory may lead to misperceptions in vehicle state. Eight subjects participated in a human subject experiment in the NASA Ames vertical motion simulator, where self-reports of perceptions of vehicle tilt angle and horizontal velocity were made during lunar-landing-like motions. Three cases of sensory cues were studied: Subjects were blindfolded and given no visual cues; subjects were provided a simulated dynamic view of the lunar terrain out a forward-looking window; and subjects were provided dynamic instrument displays showing current vehicle states. Subjects’ perception indications differed substantially from the motions being simulated in the blindfolded and out-the-window conditions, but were better matched when viewing instrument displays. Subject perceptions were also compared with predictions from a numerical model of orientation perception, and qualitatively matched in the blindfolded case, but were less well aligned in the out-the-window case. These types of misperceptions may impact astronaut control inputs and degrade vehicle performance and safety.

Evaluation of Simulation Motion Fidelity Criteria in the Vertical and Directional Axes

An evaluation of existing motion fidelity criteria was conducted on the NASA Ames Vertical Motion Simulator. Experienced test pilots flew single-axis repositioning tasks in both the vertical and the directional axes. Using a first-order approximation of a hovering helicopter, tasks were flown with variations only in the filters that attenuate the commands to the simulator motion system. These filters had second-order high-pass characteristics, and the variations were made in the filter gain and natural frequency. The variations spanned motion response characteristics from nearly full math-model motion to fixed-base. Between configurations, pilots recalibrated their motion response perception by flying the task with full motion. Pilots subjectively rated the motion fidelity of subsequent configurations relative to this full motion case, which was considered the standard for comparison. The results suggested that the existing vertical-axis criterion was accurate for combinations of gain and natural frequency changes. However, if only the gain or the natural frequency was changed, the rated motion fidelity was better than the criterion predicted. In the vertical axis, the objective and subjective results indicated that a larger gain reduction was tolerated than the existing criterion allowed. The limited data collected in the yaw axis revealed that pilots had difficulty in distinguishing among the variations in the pure yaw motion cues.

Simulation and flight test evaluation of head-up display guidance for Harrier approach transitions

Position and speed guidance displays for STOVL aircraft curved, decelerating approaches to hover and vertical landing have been evaluated for their effectiveness in reducing pilot workload and improving performance. The NASA V/STOL Systems Research Aircraft, a modified YAV-8B Harrier prototype, was used to evaluate the displays in flight, whereas the NASA Ames Vertical Motion Simulator was used to extend the flight test results to instrument meteorological conditions (IMC) and to examine performance in various conditions of wind and turbulence. The simulation data showed close correlation with the flight test data, and both demonstrated the feasibility of the displays. With the exception of the hover task in zero visibility, which was level-3, averaged Copper-Harper handling qualities ratings given during simulation were level-2 for both the approach task and the hover task in all conditions. During flight tests in calm and clear conditions, the displays also gave rise to level-2 handling qualities ratings. Pilot opinion showed that the guidance displays would be useful in visual flight, especially at night, as well as in IMC.

Investigation of the Effects of Bandwidth and Time Delay on Helicopter Roll‐Axis Handling Qualities

Several years of cooperative research conducted under the U.S./German Memorandum of Understanding (MOU) in helicopter aeromechanics have recently resulted in a successful handling qualities study. The focus of this cooperative research has been the effect of time delays in a high bandwidth vehicle on handling qualities. The jointly performed study included the use of U.S. ground-based simulation and German in-flight simulation facilities. The NASA-Ames Vertical Motion Simulator (VMS) was used to develop a high bandwidth slalom tracking task which took into consideration the constraints of the facilities. The VMS was used to define a range of the test parameters and to perform initial handling qualities evaluations. The flight tests were conducted using DLR's variable-stability BO 105 S3 Advanced Technology Testing Helicopter System (ATTHeS). Configurations included a rate command and an attitude command response system with added time delays of up to 160 milliseconds over the baseline and band width values between 1.5 and 4.5 rad/sec. Sixty-six evaluations were performed in about 25 hours of flight time during ten days of testing. The results indicate a need to more tightly constrain the allowable roll axis phase delay for the Level 1 and Level 2 requirements in the U.S. Army's specification for helicopter handling qualities Aeronautical Design Standard (ADS)-33C.

Investigation of the Effects of Bandwidth and Time Delay on Helicopter Roll-Axis Handling Qualities

Several years of cooperative research conducted under the U.S./German Memorandum of Understanding (MOU) in helicopter flight control has recently resulted in a successful handling qualities study. The focus of this cooperative research has been the effects on handling qualities due to time delays in combination with a high bandwidth vehicle. The jointly performed study included the use of U.S. ground-based simulation and German in-flight simulation facilities. The NASA-Ames Vertical Motion Simulator (VMS) was used to develop a high bandwidth slalom tracking task which took into consideration the constraints of the facilities. The VMS was also used to define a range of the test parameters and to perform initial handling qualities evaluations. The flight tests were conducted using DLR's variable-stability BO 105 S3 Advanced Technology Testing Helicopter System (ATTHeS). Configurations included a rate command and an attitude command response system with added time delays up to 160 milliseconds over the baseline and bandwidth values between 1.5 and 4.5 rad/sec. Sixty-six evaluations were performed in about 25 hours of flight time during ten days of testing. The results indicate a need to more tightly constrain the allowable roll axis phase delay for the Level 1 and Level 2 requirements in the U.S. Army's specification for helicopter handling qualities, ADS-33C.

Improvements in Hover Display Dynamics for a Combat Helicopter

This paper describes a piloted simulation conducted on the NASA Ames Vertical Motion Simulator. The objective of the experiment was to investigate the handling qualities benefits attainable using new display law design methods for hover displays. The new display laws provide improved methods to specify the behavior of the display symbol that predicts the vehicle's ground velocity in the horizontal plane; it is the primary symbol that the pilot uses to control aircraft horizontal position. The display law design was applied to the Apache helmet-mounted display format, using the Apache vehicle dynamics to tailor the dynamics of the velocity predictor symbol. The representations of the Apache vehicle used in the display design process and in the simulation were derived from flight data. During the simulation, the new symbol dynamics were seen to improve the pilots' ability to maneuver about hover in poor visual cuing environments. The improvements were manifested in pilot handling qualities ratings and in measured task performance. The paper details the display design techniques, the experiment design and conduct, and the results.

Game theory for automated maneuvering during air-to-air combat

A game-matrix approach has been developed to generate intelligent maneuvering decisions for low-flying aircraft during one-on-one air combat over hilly terrain. The decisions are made by comparing scores based on the predicted orientation, range, velocity, and terrain clearance for various maneuver combinations of both aircraft. A computer program implements the decision process in real time and computes the state of the aircraft employing the selected maneuvers. Predicted states are obtained by numerically integrating the dynamic equations. The program has been installed and demonstrated at the NASA Ames vertical motion simulator to provide an automated adversary for manned helicopter combat simulations. A stand-alone version of the program, in which the decisions of both combatants are generated by the computer, has also been prepared for nonpiloted simulations. Sample trajectories show that this new automated maneuvering logic generates some of the tactics employed by experienced pilots in combat flight tests. Whereas the current application applies to helicopter combat, the program can be used for fixed-wing aircraft by replacing those subroutines that provide the aircraft capabilities.

Helmet Mounted Display Systems for Helicopter Simulation

Simulation scientists continually pursue improved flight simulation technology with the goal of closely replicating the “real world” physical environment. The presentation/display of visual information for flight simulation is one such area enjoying recent technical improvements that are fundamental for conducting simulated operations close to the terrain. Detailed and appropriate visual information is especially critical for Nap-Of-the-Earth (NOE) helicopter flight simulation where the pilot maintains an “eyes-out” orientation to avoid obstructions and terrain. This paper elaborates on the visually-coupled Wide Field Of View Helmet Mounted Display (WFOVHMD) system technology as a viable visual display system for helicopter simulation. In addition the paper discusses research conducted on the NASA-Ames Vertical Motion Simulator that examined one critical research issue for helmet mounted displays.