Stefan Schuet

A Model-Based Probabilistic Inversion Framework for Characterizing Wire Fault Detection Using TDR

Time-domain reflectometry (TDR) is one of the standard methods for diagnosing faults in electrical wiring and interconnect systems, with a long-standing history focused mainly on hardware development of both high-fidelity systems for laboratory use and portable handheld devices for field deployment. While these devices can easily assess distance to hard faults such as sustained opens or shorts, their ability to assess subtle but important degradation such as chafing remains an open question. This paper presents a unified framework for TDR-based chafing fault detection in lossy coaxial cables by combining an S -parameter-based forward-modeling approach with a probabilistic (Bayesian) inference algorithm. Results are presented for the estimation of nominal and faulty cable parameters from laboratory data.

An Adaptive Nonlinear Aircraft Maneuvering Envelope Estimation Approach for Online Applications

A nonlinear aircraft model is presented and used to develop an overall unified approach to online trim and maneuverability envelope estimation with uncertainty quantification without any requirement for active input excitation. The concept of time scale separation makes this method suitable for the adaptive characterization of altered safe maneuvering limitations based on aircraft performance after impairment. The results can be used to provide pilot feedback and/or be combined with flight planning, trajectory generation, and guidance algorithms to help maintain safe aircraft operations in both nominal and off-nominal scenarios.

Safe maneuvering envelope estimation based on a physical approach

This paper discusses a computationally efficient algorithm for estimating the safe maneuvering envelope of damaged aircraft. The algorithm performs a robust reachability analysis through an optimal control formulation while making use of time scale separation and taking into account uncertainties in the aerodynamic derivatives. This approach differs from others since it is physically inspired. This more transparent approach allows interpreting data in each step, and it is assumed that these physical models based upon flight dynamics theory will therefore facilitate certification for future real life applications.

Piloted Simulator Evaluation of Maneuvering Envelope Information for Flight Crew Awareness

This paper discusses the implementation and evaluation of an efficient method for estimating safe aircraft maneuvering envelopes. A Bayesian approach is used to produce a deterministic algorithm for estimating aerodynamic system parameters from existing noisy sensor measurements, which are then used to estimate the trim envelope through efficient high-fidelity model-based computations of attainable equilibrium sets. The safe maneuverability limitations are extended beyond the trim envelope through a robust reachability analysis derived from an optimal control formulation. The trim and maneuvering envelope limits are then conveyed to pilots through three axes on the primary flight display. These display features were evaluated in the Advanced Concepts Flight Simulator at NASA Ames Research Center, as part of a larger research initiative, to investigate the impact on aircraft energy state awareness of the crew. Commercial airline crews flew multiple challenging approach and landing scenarios in a relevant environment. Results show that the additional display features have the potential to significantly improve cautiousness of the flight crew.

High-speed 3D scanner with real-time 3D processing

A novel 3D sensing system with real-time 3D processing has been developed which is capable of scanning an object at very high speeds (greater than 500,000 3D points/second) and creating high-resolution 3D surface maps. Laser triangulation is used in conjunction with a high-resolution camera, a laser diode, and processing electronics all incorporated into a small sensor package that traverses linearly or rotates from a fixed position to scan an object. Processing is done on board the instrument and the resultant 3D data is transmitted to a PC. This results in rapid scans, with 3D images produced as the instrument is scanning. The sensing system was developed for the NASA Mars rover program and for the inspection of Shuttle Thermal Protection System (tiles), radiator, and structures.

Trajectory Prediction and Alerting for Aircraft Mode and Energy State Awareness

This paper describes the implementation and evaluation of technologies that predict and assess the future aircraft energy state and autoflight configuration, and provide appropriate alerting to better inform pilots of the effect of problematic autoflight inputs or conditions. Prediction algorithms are used to extrapolate the current state of the aircraft based on flight management, autopilot and autothrottle system control laws and knowledge of mode transition logic. The resulting predicted trajectory represents the future four-dimensional flight path of the aircraft if the current course of action is continued. Probabilistic methods are used to estimate the trim envelope through high-fidelity model-based computation of attainable equilibrium sets. The corresponding maneuverability limitations of the aircraft are determined through a robust reachability analysis (relative to the trim envelope) through an optimal control formulation. The combination of prediction and assessment technologies are used to trigger timely alerts to avoid loss of control situations. The maneuvering envelope limits are also indicated on the primary flight display, and the predicted trajectory is displayed on navigation and vertical situation displays. The display features and alerts were evaluated in the Advanced Concepts Flight Simulator at NASA Ames Research Center, where commercial airline crews flew multiple problematic approach and landings scenarios to investigate the impact on current and future aircraft energy state awareness. Results show that the display features and alerts have the potential to improve situational awareness of what the automation is doing now and what it will do in the future.

Aircraft Mode and Energy-State Prediction, Assessment, and Alerting

This paper describes the implementation and evaluation of technologies that predict and assess the future aircraft energy state and autoflight configuration and provide appropriate alerting to better inform pilots of the effect of problematic autoflight inputs or conditions. Prediction algorithms are used to extrapolate the current state of the aircraft based on flight management, autopilot and autothrottle system control laws, and mode transition logic. Probabilistic estimates of aerodynamic coefficients are used in a high-fidelity model-based computation of the trim envelope. The maneuverability limitations of the aircraft are determined through a robust reachability analysis (relative to the trim envelope). These prediction and assessment technologies are used to trigger timely alerts to detect and avoid loss-of-control situations. Maneuvering envelope limits and the predicted trajectory are indicated on existing flight displays. These display features and alerts were evaluated in the Advanced Concepts...

On-Line Safe Flight Envelope Determination for Impaired Aircraft

The design and simulation of an on-line algorithm which estimates the safe maneuvering envelope of aircraft is discussed in this paper. The trim envelope is estimated using probabilistic methods and efficient high-fidelity model based computations of attainable equilibriumsets. From this trim envelope, a robust reachability analysis provides the maneuverability limitations of the aircraft through an optimal control formulation. Both envelope limits are presented to the flight crew on the primary flight display. In the results section, scenarios are considered where this adaptive algorithm is capable of computing online changes to the maneuvering envelope due to impairment. Furthermore, corresponding updates to display features on the primary flight display are provided to potentially inform the flight crew of safety critical envelope alterations caused by the impairment.

A model-based probabilistic inversion framework for wire fault detection using TDR

Time-domain reflectometry (TDR) is one of the standard methods for diagnosing faults in electrical wiring and interconnect systems, with a long-standing history focused mainly on hardware development of both high-fidelity systems for laboratory use and portable hand-held devices for field deployment. While these devices can easily assess distance to hard faults such as sustained opens or shorts, their ability to assess subtle but important degradation such as chafing remains an open question. This paper presents a unified framework for TDR-based chafing fault detection in lossy coaxial cables by combining an S-parameter based forward modeling approach with a probabilistic (Bayesian) inference algorithm. Results are presented for the estimation of nominal and faulty cable parameters from laboratory data.

Piloted Simulator Evaluation of Safe Flight Envelope Display Indicators for Loss of Control Avoidance

In recent studies, it has been observed that loss of control in flight is the most frequent primary cause of accidents. One of the technologies that will significantly reduce the risk of loss of control accidents is onboard safe flight envelope estimation. An efficient method for estimating the safe flight envelope for impaired aircraft has been implemented and evaluated in piloted simulations. This modular method is based on a physical approach. The aerodynamic system parameters are estimated from realistic noisy sensor measurements based on a probabilistic approach. These parameters are then used for efficient model-based computations of the trim envelope as a set of equilibrium points that can be attained by means of admissible inputs. The safe maneuverability limitations are extended beyond the trim envelope through a robust reachability analysis derived from an optimal control formulation. These trim and maneuvering envelope limits can be used for multiple purposes. For example, they can be conveyed ...