Characterization of Pilot Technique

Skilled pilots often use pulse control when controlling higher order (i.e. acceleration-command) vehicle dynamics. Pulsing does not produce a stick response that resembles what the human Crossover Model predicts. The Crossover Model (CM) assumes the pilot provides compensation necessary (lead or lag) such that the suite of display-human-vehicle approximates an integrator in the region of crossover frequency. However, it is shown that the CM does appear to drive the pilots pulsing behavior in a very predictable manner. Roughly speaking, the pilot generates pulses such that the area under the pulse (pulse amplitude multiplied by pulse width) is approximately equal to area under the hypothetical CM output. This can allow a pilot to employ constant amplitude pulsing so that only the pulse duration (width) is modulated a drastic simplification over the demands of continuous tracking. A pilot pulse model is developed, with which the parameters of the pilots internally-generated CM can be computed in real time for pilot monitoring and display compensation. It is also demonstrated that pursuit tracking may be activated when pulse control is employed

Autorotation flight control system

The present invention provides computer implemented methodology that permits the safe landing and recovery of rotorcraft following engine failure. With this invention successful autorotations may be performed from well within the unsafe operating area of the height-velocity profile of a helicopter by employing the fast and robust real-time trajectory optimization algorithm that commands control motion through an intuitive pilot display, or directly in the case of autonomous rotorcraft. The algorithm generates optimal trajectories and control commands via the direct-collocation optimization method, solved using a nonlinear programming problem solver. The control inputs computed are collective pitch and aircraft pitch, which are easily tracked and manipulated by the pilot or converted to control actuator commands for automated operation during autorotation in the case of an autonomous rotorcraft. The formulation of the optimal control problem has been carefully tailored so the solutions resemble those of an expert pilot, accounting for the performance limitations of the rotorcraft and safety concerns

Modeling Pilot Pulse Control

In this study, behavioral models are developed that closely reproduced pulsive control response of two pilots from the experimental pool using markedly different control techniques (styles) while conducting a tracking task. An intriguing find was that the pilots appeared to: 1) produce a continuous, internally-generated stick signal that they integrated in time; 2) integrate the actual stick position; and 3) compare the two integrations to issue and cease pulse commands. This suggests that the pilots utilized kinesthetic feedback in order to perceive and integrate stick position, supporting the hypothesis that pilots can access and employ the proprioceptive inner feedback loop proposed by Hess' pilot Structural Model. The Pulse Models used in conjunction with the pilot Structural Model closely recreated the pilot data both in the frequency and time domains during closed-loop simulation. This indicates that for the range of tasks and control styles encountered, the models captured the fundamental mechanisms governing pulsive and control processes. The pilot Pulse Models give important insight for the amount of remnant (stick output uncorrelated with the forcing function) that arises from nonlinear pilot technique, and for the remaining remnant arising from different sources unrelated to tracking control (i.e. neuromuscular tremor, reallocation of cognitive resources, etc.)

Linking the Pilot Structural Model and Pilot Workload

Behavioral models are developed that closely reproduced pulsive control response of two pilots using markedly different control techniques while conducting a tracking task. An intriguing find was that the pilots appeared to: 1) produce a continuous, internally-generated stick signal that they integrated in time; 2) integrate the actual stick position; and 3) compare the two integrations to either issue or cease a pulse command. This suggests that the pilots utilized kinesthetic feedback in order to sense and integrate stick position, supporting the hypothesis that pilots can access and employ the proprioceptive inner feedback loop proposed by Hess's pilot Structural Model. A Pilot Cost Index was developed, whose elements include estimated workload, performance, and the degree to which the pilot employs kinesthetic feedback. Preliminary results suggest that a pilot's operating point (parameter values) may be based on control style and index minimization

On-Line Loss of Control Detection Using Wavelets

Wavelet transforms are used for on-line detection of aircraft loss of control. Wavelet transforms are compared with Fourier transform methods and shown to more rapidly detect changes in the vehicle dynamics. This faster response is due to a time window that decreases in length as the frequency increases. New wavelets are defined that further decrease the detection time by skewing the shape of the envelope. The wavelets are used for power spectrum and transfer function estimation. Smoothing is used to tradeoff the variance of the estimate with detection time. Wavelets are also used as front-end to the eigensystem reconstruction algorithm. Stability metrics are estimated from the frequency response and models, and it is these metrics that are used for loss of control detection. A Matlab toolbox was developed for post-processing simulation and flight data using the wavelet analysis methods. A subset of these methods was implemented in real time and named the Loss of Control Analysis Tool Set or LOCATS. A manual control experiment was conducted using a hardware-in-the-loop simulator for a large transport aircraft, in which the real time performance of LOCATS was demonstrated. The next step is to use these wavelet analysis tools for flight test support

Perception-based synthetic cueing for NVD rotorcraft hover operations

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000.Includes bibliographical references (p. 144-146).Helicopter flight using night-vision devices (NVDs) is difficult to perform, given evidence by the high accident rate associated with NVD flight compared to day operation. A mishap analysis of NVD-related helicopter accidents was conducted which found approximately 70% of the accidents attributable to pilot misperception of the flight environment, with the most frequently misperceived states being spatial in nature and in the hover regime. While hardware changes such as increasing the field of view or image resolution may alleviate some of the problems, it is unlikely that they will address all of the perceptual issues. The approach proposed in this thesis is to augment the NVD image with synthetic cueing, whereby the cues would emulate position and motion in an ecological fashion and appear to be actually occurring in physical space on which they are overlaid. Synthetic cues allow for selective enhancement of perceptual state gains to match the task requirements. The perceptual gains examined were aircraft positional error along the three translational axes. A hover cue set was developed based on an analogue of a physical target used in a flight handling qualities tracking task, a perceptual task analysis for hover, and fundamentals of human spatial perception. The display was implemented on a simulation environment, constructed using a virtual reality device, an ultrasound head-tracker, and a fixed-base helicopter simulator. Seven highly trained helicopter pilots were used as experimental subjects and tasked to maintain hover in the presence of aircraft positional disturbances while viewing a synthesized NVD environment and the experimental hover cues. The simulation employed a number of unique techniques that enabled identification of visual perception and division-of-attention effects. Measures of hover performance and subjective ratings were collected, and frequency analysis was used to measure system (i.e., pilot/display/vehicle suite) stability and bandwidth. Significant performance improvements in NVD flight were observed when using synthetic cue augmentation. Subjective ratings showed longitudinal control to be more difficult than in the other axes for both single and multi-axis control. This thesis demonstrates that artificial magnification of perceptual states through synthetic cueing can be an effective method of improving night-vision helicopter hover operations.by Edward N. Bachelder.Ph.D

Empirical Comparison of Data Structures for Line-Of-Sight Computation

Line-of-sight (LOS) computation is important for interrogation of heightfield grids in the context of geo information and many simulation tasks like electromagnetic wave propagation and flight surveillance. Compared to searching the regular grid directly, more advanced data structures like a 2.5 d kd-tree offer better performance. We describe the definition of a 2.5 d kd-tree from the digital elevation model and its use for LOS computation on a point-reconstructed or bilinear-reconstructed terrain surface. For compact storage, we use a wavelet-like storage scheme which saves one half of the storage space without considerably compromising the runtime performance. We give an empirical comparison of both approaches on practical data sets which show the method of choice for CPU computation of LOS

Terrain and Model Queries Using Scalar Representations with Wavelet Compression

In this paper, we present efficient height/distance field data structures for line-of-sight (LOS) queries on terrains and collision queries on arbitrary 3-D models. The data structure uses a pyramid of quad-shaped regions with the original height/distance field at the highest level and an overall minimum/maximum value at the lower levels. The pyramid can compactly be stored in a wavelet-like decomposition but using max and plus operations. Additionally, we show how to get minimum/maximum values for regions in a wavelet decomposition using real algebra. For LOS calculations, we compare with a kd-tree representation containing the maximum height values. Furthermore, we show that the LOS calculation is a special case of a collision detection query. Using our wavelet-like approach, even general and arbitrary collision detection queries can efficiently be answered

Empirical comparison of data structures for line-of-sight computation

Line-of-sight (LOS) computation is important for interrogation of heightfield grids in the context of geo information and many simulation tasks like electromagnetic wave propagation and flight surveillance. Compared to searching the regular grid directly, more advanced data structures like a 2.5 d kd-tree offer better performance. We describe the definition of a 2.5 d kd-tree from the digital elevation model and its use for LOS computation on a point-reconstructed or bilinear-reconstructed terrain surface. For compact storage, we use a wavelet-like storage scheme which saves one half of the storage space without considerably compromising the runtime performance. We give an empirical comparison of both approaches on practical data sets which show the method of choice for CPU computation of LOS

The use of surface modified poly(glycerol-co-sebacic acid) in retinal transplantation

Retinal transplantation experiments have advanced considerably during recent years, but remaining diseased photoreceptor cells in the host retina and inner retinal cells in the transplant physically obstruct the development of graft-host neuronal contacts which are required for vision. Recently, we developed methods for the isolation of donor photoreceptor layers in vitro, and the selective removal of host photoreceptors in vivo using biodegradable elastomeric membranes composed of poly(glycerol-co-sebacic acid) (PGS). Here, we report the surface modification of PGS membranes to promote the attachment of photoreceptor layers, allowing the resulting composite to be handled surgically as a single entity. PGS membranes were chemically modified with peptides containing an arginine-glycine-aspartic acid (RGD) extracellular matrix ligand sequence. PGS membranes were also coated with electrospun nanofiber meshes, containing laminin and poly(epsilon-caprolactone) (PCL). Following in vitro co-culture of biomaterial membranes with isolated embryonic retinal tissue, composites were tested for surgical handling and examined with hematoxylin and eosin staining and immunohistochemical markers. Electrospun nanofibers composed of laminin and PCL promoted sufficient cell adhesion for simultaneous transplantation of isolated photoreceptor layers and PGS membranes. Composites developed large populations of recoverin and rhodopsin labeled photoreceptors. Furthermore, ganglion cells, rod bipolar cells and All amacrine cells were absent in co-cultured retinas as observed by neurofilament, PKC and parvalbumin labeling respectively. These results facilitate retinal transplantation experiments in which a composite graft composed of a biodegradable membrane adhered to an immature retina dominated by photoreceptor cells may be delivered in a single surgery, with the possibility of improving graft-host neuronal connections. (C) 2009 Elsevier Ltd. All rights reserved