Piloted Flight Simulation Research Articles

Evaluation of a Sliding Mode Fault-Tolerant Controller for the El Al Incident

This paper presents piloted flight simulator results associated with the EL-AL flight 1862 scenario using a model reference–based sliding mode control allocation scheme for fault tolerant control. The proposed controller design was carried out without any knowledge of the type of failure, and in the absence of any fault detection and isolation strategy. This is motivated by the fact that the flight crew were unaware of the loss of the right engines. For this reason, the control allocation scheme which is proposed uses (fixed) equal distribution of the control signals to all actuators (for both nominal situations and when a fault or failure occurs). The paper analyzes the scheme and determines the conditions under which closed-loop stability is retained. The results represent the successful real-time implementation of the proposed controller on the SIMONA motion flight simulator configured to represent a B747 aircraft. The evaluation results from the experienced pilots show that the proposed controller has the ability to position the aircraft for landing in both a nominal and the EL-AL failure scenario. It is also shown that actuator faults and failures which occured during the EL-AL incident can be handled directly without reconfiguring the controller.

Fault tolerant flight control: from theory to piloted flight simulator experiments

Loss of control accounts for over 25% of aircraft accidents worldwide. This study presents a fault tolerant flight control strategy for increasing aircraft safety. The work has been undertaken within the Action Group on fault tolerant control (FTC) of the European GARTEUR programme, which develops collaborative efforts in Europe to create new FTC technologies that could significantly advance the goals of the aviation safety. After the fault detection and confirmation by the in-flight dedicated systems, a compensation loop is activated to ensure safe recovery. The design of the FTC loop is achieved without any changes in the nominal (and certificated) flight control system (FCS). The FTC scheme design is formulated as an H∞ strong stabilisation problem. Fault compensability is subsequently discussed and formulated as a trim-deficiency analysis problem. The proposed technique is implemented on the SIMONA flight simulator and evaluated through a pilot experiment. The tested scenario corresponds to the landing approach of a large transport aircraft (B747-100/200). The faulty situation is related to trimmable horizontal stabiliser (THS) failures. Piloted flight simulator experiments show that fault tolerance can be achieved under the condition that there exists sufficient remaining control authority.

A turbulence criterion for safe helicopter operations to offshore installations

AbstractThis paper describes the development of a wind turbulence criterion for the safe operation of helicopters to offshore installations. The development of the criterion was recommended following a review of the environmental effects around offshore platform helidecks.Currently, criteria exist for ambient temperature and for vertical wind component in the vicinity of helidecks, but a questionnaire-based survey of helicopter pilots revealed that the principal safety hazard and source of highest workload is turbulence around offshore installations. The new turbulence criterion will plug a long-standing gap in the guidance on offshore helideck design.The paper describes how the criterion has been developed using piloted flight simulation in a research flight simulator together with data from wind tunnel tests on offshore platforms. Initial validation has been successfully performed, and extended to include correlation with the large database of helicopter operational flight data records being collected through the UK North Sea Helicopter Operations Monitoring Programme (HOMP).The turbulence criterion will be used, together with existing criteria on vertical wind component and temperature, in the assessment of new offshore installation designs, or proposed modifications to existing designs, to determine wind conditions where turbulence is likely to be excessive for safe helicopter operations. These will be used to estimate helideck operability and thereby inform the installation topsides design process, and will provide input to the setting and maintenance of helicopter operational limitations for individual installations.The work will lead to improved safety through better prediction of safe operating envelopes and helideck operability at the design stage. In addition, development of the work is expected to enable the wind environment around offshore installations to be mapped and monitored in-service using helicopter flight data records.The new turbulence criterion has been included in updated guidance on helideck design, and offshore installation designers are now required to inform helicopter operators about wind conditions which result in violations of the turbulence criterion on their offshore installations (as is currently the case for the temperature and vertical wind component criteria).

Hazard criteria for wake vortex encounters during approach

Airbus has prepared a methodology to assess the severity of a Wake Vortex Encounter (WVE). This methodology is called Vortex Encounter Severity Assessment (VESA). VESA makes it possible to compare the effect of wake vortices generated by different aircraft on an aircraft that encounters such a vortex. Important elements of VESA are the hazard criteria that rate particular aircraft reactions during WVEs. Hazard criteria are necessary to compare WVEs in batch simulations. This paper describes how piloted flight simulations for WVE investigations during landing approach were prepared and how the results were used for hazard criteria development. This work was part of the European S-WAKE program.

AV‐8B Flight Hazard Awareness Analysis and Training Using Flight Simulation

ABSTRACT The V/STOL capability of the AV‐8B Harrier is provided through a sophisticated combination of vectored thrust and aerodynamic technology. The proper interaction of the nozzle thrust and flap system is of extreme importance. Specific combinations of nozzle angle and flap position are employed to optimize both jet lift and aerodynamic lift. However, if the proper flap‐nozzle position schedule is violated, the resulting thrust and flap impingement may cause a severe nose‐down pitching moment sufficient to override the pilot control. Depending upon ground proximity, this condition creates a hazard which causes great potential for loss of aircraft and/or pilot.Flap impingement hazard was identified on the AV‐8B aircraft as a potential catastrophic flight hazard. In response, a requirement was established to 1) study the severity of the flap impingement hazard on the AV‐8B, 2) devise flight operational procedures which would minimize pilot exposure to the hazard potential and the resulting pilot control problems during flight, and 3) devise a training capability to familiarize pilots with flap impingement hazard characteristics and recovery procedures. This paper comprises the results of a study which utilized piloted flight simulation and fleet simulation trainers to meet these requirements.

Closed-loop assessment of flight simulator fidelity

An analytical methodology is presented for the preliminary assessment of piloted flight simulator fidelity. The hypothesis that forms the central theme of the methodology is that many major simulator fidelity problems stem from simulator limitations that adversely affect the pilot's innermost feedback control loop, referred to here as the primary control loop. This loop is the most critical in terms of task performance and the pilot's evaluation of vehicle handling qualities. The proposed methodology, based on a pilot/vehicle analysis of the vehicle and tasks being simulated, has the potential for serving as a tool for the rapid diagnosis of simulator fidelity problems. Selected results from experiments involving both flight test and piloted simulation of a UH-60A rotorcraft in a pair of demanding vertical and lateral hover tasks are used to exercise the methodology and indicate its potential.

Management of Computer-Aided Control System Design from Concept to Flight Test

Active control technology (ACT) has brought a dramatic change to the way aircraft can be designed and flown. The challenge for flight control research is, given the potential of ACT, to define what is required. The problem is that to answer this question a 'flyable' implementation is needed, whether for a piloted flight simulator or for full-scale flight. The need for an implementation introduces issues of software design and management and a possible 'conflict' with the needs of research. This paper describes an environment for flight control law research being developed in Flight Management Department at RAE Bedford, to provide a rigorous yet flexible framework. A comprehensive life cycle is defined for the evolution of flight control laws from concept via piloted simulation to flight test. In its current fonm, the life cycle has four major phases: conceptual design, engineering design, flight clearance and flight test. Conceptual design covers off-line simulation - modelling, design anc dnalysis - and some pilot-in-the-loop simulation using RAE's Advanced Flight Simulator. The outputs from this stage include infonmation on the response types and system characteristics required. Engineering design is the process of full control law design and includes further refinement of control system architectures via modelling and more detailed piloted simulation. Flight clearance consolidates results from earlier stages and achieves a verified implementation for the target flight control computer. Flight test evaluates the control system in full scale flight and appropriate operational conditions, with further comprehensive data collection. A structured description of all these phases is presented, with emphasis on the conceptual phase; some examples of the control law life cycle are given with particular application to helicopter flight control. The verification and validation issues associated with the attendant software development are also addressed.

Improvement of helicopter handling qualities using H∞-optimisation

In the paper, we present the results of a study into the use of H∞-optimisation for the design of robust feedback control laws for improving the handling qualities of high-performance helicopters. A low-speed controller was designed to give accurate control of pitch and roll attitude, yaw rate and heave velocity for a typical combat helicopter. The design was based on a linearised model obtained from a six-degree-of-freedom nonlinear model of a helicopter provided by the Royal Aerospace Establishment (RAE), Bedford, UK. Robustness was a major issue because rotor dynamics were not included in the design model. Numerical compliance of the design with handling qualities requirements was assessed by testing simulated responses against specifications from a proposed airworthiness design standard. Robust stability was assessed from singular-value plots. In addition, the qualitative features of the design were assessed in a piloted flight simulation trial held at RAE, Bedford.

General Aviation Application of Separate Surface Stability Augmentation

A design and development project undertaken to provide the benefits of full-time stability augmentation at a cost low enough to encourage application in general aviation aircraft is described. The stability augmentation investigated was attitude command mechanized through separate control surfaces. With attitude command, the automatic control system maintains aircraft attitude proportional to pilot control deflection, despite disturbances such as atmospheric turbulence. Piloted flight simulation indicates that significant improvements in aircraft flying qualities may be provided by attitude command. The separate surface attitude command concept will be investigated and demonstrated in a flight test program on a Beech Model 99 modified for this purpose.