Simulation, whether in-flight or ground-based, is an invaluable tool for testing and evaluating aircraft. Classically, a simulation model is specific to a single particular airframe, only able to model those flying characteristics. Vast information can be gained from a simulation that is able to model a wide range of aircraft, through a comparison of the performance of these aircraft. Such a variable stability simulation model was created based on 46 stability parameters, including natural frequencies, damping ratios, time constants, and gains. The simulation was obtained using transfer functions representing the aircraft state responses to control inputs. These transfer functions were converted into state space systems used to create the linear equations for the model. The model was first developed as a desktop simulation and then converted for use with the Virginia Tech's 2F122A flight simulator. This conversion required a simple dynamic inversion of the body axis force and moment terms. To reduce the error in these terms, a model following scheme was incorporated. A series of canned inputs and real-time pilot-in-the-loop tests were flown to evaluate the variable stability model. Results in this paper have demonstrated the successful creation of a variable stability simulation model. / Master of Science

The linear variable stability Transfer Function Simulation Model (TFSM), inspired by the United States Air Force's NF-16D Variable stability In-flight Simulator Test Aircraft (VISTA) and created by Henrik Pettersson, can simulate any desired aircraft. The TFSM represents a non-linear aircraft model with its stability parameters - a collection of gain constants, time constants, damping ratios, and natural frequencies. Stability parameters for aircraft generally fall into two uncoupled modes: longitudinal and lateral-directional. Unfortunately, flight tests using the TFSM exhibited undesired lateral-directional coupling in the longitudinal responses. An S-turn maneuver, formation flight test, and an uncontrolled simulation with an initial bank angle of 60 degrees were the foundation for the investigation to pinpoint the TFSM's errors. The flight tests and subsequent analysis showed that although this model is highly versatile, it has three fundamental problems. First, the original creation of the TFSM incorrectly assumed that the time rate of change for the pitch angle (in the local-horizontal reference frame) is equal to the body-axis pitch-rate for all flight conditions. Second, the TFSM's dynamics do not contain gravity terms. Third, the TFSM cannot generate the angular rates needed in a turn. Integrating the aircraft's pitch, roll, and yaw angles with the equations of motion for aircraft fixed the first problem. Unfortunately, resolving this issue only intensified the second two problems. The results from this thesis show that the last two problems are part of the TFSM and cannot be fixed explicitly. / Master of Science

During the period 1980 to 2008 there were 359 fatal accidents involving UK registered light aeroplanes of which 36% occurred in visual meteorological conditions. In all, 216 lives were lost with accidents being attributed to the pilot 'failing to maintain proper control resulting in a stall or spin'. Dissimilar fatal stallrelated accident rates are evident for aeroplane makes & models of similar design. During the course of this programme of research, flight testing of two similar aeroplane models using a case study method showed marked differences in the variation of stick force with airspeed or stick force gradient in all flight conditions. This suggested that 'control feel' was a contributory factor towards the pilot’s failure to maintain proper control. Current certification standards for light aeroplanes rely upon the subjective assessment of stick force gradients by test pilots, requiring that substantial changes in airspeed are accompanied by clearly perceptible changes in stick force with no specified minimum gradient. This programme of research has been carried out to determine acceptable criteria for stick force gradients of a light aeroplane in all flight conditions. Criteria has been determined from flight tests of aeroplanes with different in-service safety records and subjective pilot workload assessment using simulated flying tasks with different stick force gradients performed by twenty GA pilots. Simulation tests indicated that pilot mental demand increased significantly (p > 0.05) when stick force gradient was reduced to ‘zero’, representing an aeroplane with neutral longitudinal static stability. A predictive model has been developed to estimate stick force gradients for a light aeroplane in any flight condition under quasi-static, longitudinal, non-manoeuvring flight and 1-g loading conditions. The model builds upon previous published work limited to cruising flight, and enables the estimation of stick forces and gradients due to high lift devices in the climb and landing condition by consideration of the combined effects of wing loading, CG, elevator gearing, flaps and elevator trim setting. Implemented using MATLAB, the model has been validated by comparing with flight test results for the case study aeroplanes and showed mean differences of ±0.025 daN/kt. The predictive model should be used in preliminary aeroplane design to assess tendencies towards neutral stability in high workload, safety critical flight conditions such as the take-off and landing. In addition, the model should be used to analyse existing aeroplanes with comparatively low or neutral stick force gradients in safety critical flight phases and to predict the effects of changing CG and/or flap limits to increase stick force gradient and improve control feel. The combined results of these studies suggest that a minimum acceptable stick force gradient for a non-aerobatic light aeroplane in all flight conditions should be nonzero and between 0.10~0.13 daN/kt. A stable and predictable stick force variation with airspeed will ensure that any substantial deviation from trimmed airspeed is accompanied by a stick force change clearly perceptible to the pilot and also provide additional warning of the proximity to the stall. The use of specific criteria to complement qualitative test pilot opinion, will assist in confirming compliance and provide consistency with current standards for sailplanes/powered sailplanes and large commercial aeroplanes, both of which already have defined minimum acceptable gradients.

The purpose of this thesis was to evaluate currently commercially available head mounted virtual reality displays for potential use in pilot training simulators. For this purpose acommercial simulator was modified to display the virtual environment in an Oculus RiftDK2 headset. A typical monitor based setup was used to provide a set of hardware requirements which the VR implementation had to meet or exceed to be considered potentially usable for pilot training simulators. User tests were then performed with a group of users representative of those normally using pilot training simulators, including both pilots and engineers working with simulator development. The main focus of the user tests was to evaluate some potential weaknesses found in the technical comparison (such as when a measured parameter was close to the lower limit defined by the monitor based setup) and to make a measurement of the usability of the VR implementation. The results from the technical comparison showed that the technical requirements were met and in most cases also exceeded. There were however some potential weaknesses revealed during the user tests, which included screen resolution and the field of view. There was one main critical deficiency found during the user tests. This was the lack of interaction with the aircraft as users were only able to interact with the flight stick and throttle lever. While this enabled the users to control many aspects of the aircraft (by using buttons and other controls fitted on the flight stick/throttle) in a training scenario a user also has to be able to interact with other switches and/or monitors in the cockpit. This was however a known limitation of the implementation and thus didn’t affect the tested parts of the simulator. The user tests also confirmed that the resolution was a potential problem, but that the overall usability was high. Thus the VR implementation had potential for use in a pilot training simulator, if the critical issues found during the user tests were solved.

In-flight simulation allows one aircraft to simulate the dynamic response of another aircraft. A control system designed to give RASCAL, a JUH-60A Black Hawk helicopter based at Moffett Field, CA, in-flight simulation capabilities has been designed, optimized and validated in this research. A classical explicit model following control system with a frequency dependent feedback controller was used. The frequency dependent controller allows model following of the attitude in the short term and the velocity in the long term. Controller gains were optimized using a high order, linearized model of UH-60 dynamics. Non-linear simulations of the control laws were performed, first on a desktop computer based simulation, then in the RASCAL development facility, a hardware-in-the-loop simulator. Comparing quantitative results of the non-linear simulations with the results of the optimization using the linearized model ensured that the control system designed with the linearized model was valid in non-linear environments. Finally, a piloted evaluation in the hardware-in-the-loop simulator was performed to obtain qualitative information on the behavior of the control laws.

Currently, it is uncertain how well a typical ground-based simulator's hexapod motion system can simulate the aggressive motion during airplane upset. To address this issue, this thesis attempts to improve simulator motion for upset recovery simulation by defining new motion fidelity criteria, implementing body frame filtering, and improving an existing adaptive motion drive algorithm. The successfully improved adaptive algorithm was used to conduct a paired comparison experiment to study the effects of trade-offs between translational and rotational motion cues on pilot subjective fidelity and upset recovery performance. Analysis of the experimental data found that pilots generally rejected motion with false lateral cues and they preferred the presence of rotational cues for moderate roll angles. Also, performance analysis suggested that roll cues helped improve lateral control. Overall, pilots preferred to have simulator motion during upset simulation and significant improvements in performance were observed when simulator motion was present.

A helicopter rotor in descent flight encounters its own wake, resulting in a doughnut-shaped ring around the rotor disk, known as the Vortex Ring State (VRS). Flight in VRS condition can be dangerous as it may cause uncommanded drop in descent rate, loss of control effectiveness, power settling, excessive thrust and torque fluctuations, and vibration. As simple momentum theory is no longer valid for a rotor in VRS, modeling of rotor inflow in VRS continues to challenge researchers, especially for flight simulation applications. In this dissertation, a simplified inflow model, called the ring vortex model, is developed for a helicopter rotor operating in descent condition. By creating a series of vortex rings near the rotor disk, the ring vortex model addresses the strong flow interaction between the rotor wake and the surrounding airflow in descent flight. In addition, the total mass flow parameter in the existing inflow models is augmented to create a steady state transition between the helicopter and the windmill branches. With the ring vortex model, rotor inflow can now be adequately predicted over a wide range of descent rates. Validations of the ring vortex model for helicopter rotors are conducted extensively in axial and inclined descent. Effects from blade taper, blade twist, and rotor thrust are also investigated with further application of the finite-state inflow model. The ring vortex model is applied to a single main-rotor helicopter. The main effort is to establish VRS boundary based on heave stability criterion. In addition, two important phenomena observed in the descent flight tests are addressed in the dynamic simulation, including uncommanded drop in descent rate and loss of collective control effectiveness. The ring vortex model is further applied to a side-by-side rotor configuration. Lateral thrust asymmetry on the side-by-side rotor configuration can be reproduced through uneven distribution of vortex rings at the two rotors. Two important issues are investigated, including the impact of vortex rings on lateral thrust deficit and on lateral AFCS limit.

Image generator host is the interface of the host computer systemof a flight simulator to its image generator. Image generator host, updates positions of the entities by sending operational codes to the image generator. Positional data of the entities is pipelined by tactic interface of the simulator at host update rate. A network jitter, latency, packet loss or inadequate bandwidth may disturb the smoothness of this pipelined entity information packets. This study presents an algorithm for the host system of a flight simulator, intending to minimize model flickering in the image generator display output.

The problem of real-time simulation of ocean surface waves, ship movement and the coupling in between is tackled, and a number of different methods are covered and discussed. Among these methods, the finite volume method has been implemented in an attempt to solve the problem, along with the compressible Euler equations, an octree based staggered grid which allows for easy adaptive mesh refinement, the volume of fluid method and a variant of the Hyper-C advection scheme for compressible flows for advection of the phase fraction field. The process of implementing the methods that were chosen proved to be tricky in many ways, as they involve a large number of advanced topics, and the implementation that was implemented in this thesis work suffered from numerous issues. There were for example problems with keeping the interface intact, as well as a harsh restriction on the time step size due to the CFL condition. Improvements required to make the method sustainable for real-time applications are discussed, and a few suggestions on alternative approaches that are already in use for similar purposes are also given and discussed. Furthermore, a method for compensating for gain/loss of mass when solving the incompressible flow equations with an inaccurately solved pressure Poisson equation is presented and discussed. A momentum conservative method for transporting the velocity field on staggered grids without introducing unnecessary smearing is also presented and implemented. A simple, physically based illumination model for sea surfaces is derived, discussed and compared to the Blinn–Phong shading model, although it is never implemented. Finally, a two-dimensional partial differential equation in the spatial domain for simulating water surface waves for mildly varying bottom topography is derived and discussed, although it is deemed to be too slow for real-time purposes and is therefore never implemented. / <p>This publication differs from the printed version of the report in the sense that links are blue in this version and black in the printed version.</p>

Currently, it is uncertain how well a typical ground-based simulator's hexapod motion system can simulate the aggressive motion during airplane upset. To address this issue, this thesis attempts to improve simulator motion for upset recovery simulation by defining new motion fidelity criteria, implementing body frame filtering, and improving an existing adaptive motion drive algorithm. The successfully improved adaptive algorithm was used to conduct a paired comparison experiment to study the effects of trade-offs between translational and rotational motion cues on pilot subjective fidelity and upset recovery performance. Analysis of the experimental data found that pilots generally rejected motion with false lateral cues and they preferred the presence of rotational cues for moderate roll angles. Also, performance analysis suggested that roll cues helped improve lateral control. Overall, pilots preferred to have simulator motion during upset simulation and significant improvements in performance were observed when simulator motion was present.