CERES :: Browsing by Author "Padfield, Gareth D."

Browsing by Author "Padfield, Gareth D."

Now showing 1 - 13 of 13

Open Access
The application of perturbation methods to nonlinear problems in flight mechanics
(Cranfield University, 1976-09) Padfield, Gareth D.; Christopher, P. A. T.
Analytical-techniques are developed for deriving approximate solutions to a class of problems that arise in nonlinear flight mechanics typically when an aeroplane is flying close to a stability boundary. The techniques are based on pertoz-bation methods and the method of multiple scales is used to correct for_nonuriformities otherwise present in the asymptotic expai!,. 3ions. Applications are mainly concerned with the lateral dynamics of slender aircraft flying at high incidence. Approximations are derived for both linear and nonlinear lateral motions that serve to illustrate the importance of particular parameters in the problem. For the linear theory the approximations are achieved by reducing the fourth order system to two. weakly coupled second order systems. The nonlinear theory is mainly concerned with the effect of aerodynamic nonlinearity on the lateral oscillation when the latter has marginal stability or instability, as predicted by the linear theory. The analytic approximations are extended for use in the problem of estimating damping moments on aircraft in oscillatory motion. For this purpose approximations are constructed for the logarithmic decrement of a nonlinear oscillation that can be used to fit experimental measurements. Some thoughtis given to-the issue of memory effects in the representation of aerodynamic forces and moments.
Open Access
Appraisal of handling qualities standards for rotorcraft lateral-directional dynamics
(European Rotorcraft Forum, 2021-01-04) Cameron, Neil; White, Mark D.; Padfield, Gareth D.; Lu, Linghai
The coupled vehicle roll-yaw-sway motion of Lateral-Directional Oscillations is often a contributor to rotorcraft Handling Qualities deficiencies. The extent of the deficiencies, and the required pilot control compensation to mitigate their effects, depend critically on the LDO damping and frequency and relative contributions from the roll, yaw and sway motions. Current rotorcraft performance/certification standards (e.g. ADS-33E-PRF/CS-29) for LDO stability have been developed from standards that date from the 1950s or from fixed-wing requirements; there has been limited flight test to support their validation. This paper builds on previous work examining the suitability of these LDO stability criteria to modern rotorcraft operations through ground-based simulation assessment covering a range of HQs, selected based on a frequency of 2.5 rad/s with varying damping and roll-yaw ratio. The underlying simulation model is a FLIGHTLAB Bell 412 model, augmented to ensure that the non-LDO HQs are Level 1. The LDO test configurations have been developed with delta-derivatives added to the nonlinear model to change the LDO frequency, damping and the magnitude ratio of the roll/yaw motion, whilst preserving yaw control sensitivity. The preliminary results demonstrate Handling Qualities generally degrade as the amount of roll in the LDO increased with a p/r = 1.5 giving a reasonable match with the military standards. If the ratio is reduced, Level 1 ratings were awarded with a lower damping. Conversely, no Level 1 ratings were returned for p/r = 2 when the LDO was triggered in the closed loop task.
Open Access
The development of a pilot control adaptation metric for simulation perceptual fidelity assessment
(Vertical Flight Society, 2021-09-09) Memon, Wajih A.; Cameron, Neil; White, Mark D.; Padfield, Gareth D.; Lu, Linghai
This paper reports the use of a control compensation metric to examine pilot adaptation in the objective assessment of simulation perceptual fidelity. The utility of the proposed metric to quantify different levels of pilot control compensation, hence adaptation, whilst flying low and high aggression tasks is explored. The tasks were conducted by different test pilots using the Heliflight-R simulator to examine the effect of additional transport delays on overall simulation perceptual fidelity. A weighted adaptive control compensation metric shows strong correlation with (Cooper-Harper) Handling Qualities and Simulation Fidelity Ratings awarded for each of the tasks. Moreover, in combination with a time-varying frequency-domain exposure, the metric is shown to be insightful for understanding variations in the pilots’ assessment of simulation perceptual fidelity.
Open Access
Helicopter handling qualities: a study in pilot control compensation
(Cambridge University Press, 2021-11-16) Memon, W. A.; White, Mark D.; Padfield, Gareth D.; Cameron, N.; Lu, Linghai
The research reported in this paper is aimed at the development of a metric to quantify and predict the extent of pilot control compensation required to fly a wide range of mission task elements. To do this, the utility of a range of time- and frequency-domain measures to examine pilot control activity whilst flying hover/low-speed and forward flight tasks are explored. The tasks were performed by two test pilots using both the National Research Council (Canada)’s Bell 412 Advanced Systems Research Aircraft and the University of Liverpool’s HELIFLIGHT-R simulator. Handling qualities ratings were awarded for each of the tasks and compared with a newly developed weighted adaptive control compensation metric based on discrete pilot inputs, showing good correlation. Moreover, in combination with a time-varying frequency-domain exposure, the proposed metric is shown to be useful for understanding the relationship between the pilot’s subjective assessment, measured control activity and task performance. By collating the results from the subjective and objective metrics for a range of different mission task elements, compensation boundaries are proposed to predict and verify the subjective assessments from the Cooper-Harper Handling Qualities Rating scale.
Open Access
A new heuristic approach to rotorcraft system identification
(Vertical Flight Society, 2022-11-03) Lu, Linghai; Agarwal, Dheeraj; Padfield, Gareth D.; White, Mark D.; Cameron, Neil
High-fidelity rotorcraft flight simulation relies on the availability of a quality flight model that further demands a good level of understanding of the complexities arising from aerodynamic couplings and interference effects. This paper explores rotorcraft flight dynamics in the low-speed regime where such complexities abound and presents a new heuristic approach in the time domain to aid identification of nonlinear dynamics and fidelity assessment. The approach identifies flight model parameters “additively,” based on their contribution to the local dynamic response of the system, in contrast with conventional approaches where parameter values are identified to minimize errors over a whole maneuver. In these early investigations, identified low-order, rigid-body, linear models show good comparison with flight-test data. The approach is extended to explore nonlinearities attributed to the so-called maneuver wake distortion and wake skew effects emerging in larger maneuvers. The results show a good correlation for the proposed nonlinear model structure, demonstrated by its capability to capture the time response and variations of the stability and control derivatives with response magnitude.
Open Access
On the use of approximate solutions for non linear oscillations
(Cranfield College of Aeronautics, 1974-08) Padfield, Gareth D.
Open Access
The potential impact of adverse aircraft-pilot couplings on the safety of tilt-rotor operations
(Cambridge University Press, 2022-03-17) Padfield, Gareth D.; Lu, Linghai
This paper addresses the potential impact of adverse aircraft-pilot couplings on tiltrotor safety, when a pilot or autopilot attempts to constrain flight dynamics with strong control. The work builds on previously published research on the theory and application of constrained flight to fixed- and rotary-wing aircraft. Tiltrotor aircraft feature characteristics from both types of aircraft and how these determine behaviour in a unique manner is investigated using a FLIGHTLAB simulation model of the XV-15 aircraft. Two different scenarios are explored in detail, using linearised models that reflect the flight-physics of stability for small deviations from trim. First, the control of vertical flight path with longitudinal cyclic pitch and elevator, and the consequences for the stability of the aircraft surge mode and short-period pitch-heave mode. The classical surge-mode instability for flight at speeds below minimum power is shown to apply to the tiltrotor in helicopter mode but alleviated in conversion and airplane modes. The impact on the short–period mode is seen to be a trade-off between the stabilising pitch attitude and destabilising incidence (angle-of-attack) contributions to the flight-path angle. The second example concerns strong control of roll attitude in the presence of adverse aileron-yaw. Here, the yaw-sway motion can be driven unstable, a problem encountered on fixed-wing aircraft with weak weathercock stability, but rare in the rotorcraft world. For both examples, the loss of stability is expressed as the change in sign of effective damping or stiffness stability derivatives. The explanatory theory for these non-oscillatory or low-frequency aircraft-pilot couplings is presented, along with interpretations in terms of handling qualities criteria. The paper also addresses the question of how to translate the findings into a form of aeronautical knowledge useful for the pilot training community.
Open Access
Preliminary guidelines for a requirements-based approach to certification by simulation for rotorcraft
(2022-09-08) van ’t Hoff, Stefan; Lu, Linghai; Padfield, Gareth D.; Podzus, Philipp; White, Mark D.; Quaranta, Giuseppe
The paper presents an introduction to the preliminary guidelines for rotorcraft certification by simulation developed by the partners of the Clean Sky 2 project Rotorcraft Certification by Simulation – RoCS . The guidelines are primarily aimed at the application of (rotorcraft) flight modelling and simulation in support of certification for compliance with standards CS-27 and CS-29, PART B (Flight) and other Flight-related aspects (e.g. CS-29, Appendix B, Airworthiness Criteria for Helicopter Instrument Flight). However, the guidelines are also applicable, in principle, to the certification of other types of rotorcraft, including tilt-rotors and e-VTOL configurations. A requirements-based approach is advocated and outlined, acknowledging the profound importance of assembling preliminary requirements, as complete as possible, before embarking on simulation development processes. The proposed approach presents examples of metrics for quantifying the fidelity that is ‘sufficient’ for application to relevant Applicable Certification Requirements (ACRs). The concept of ‘adaptive fidelity’ is introduced in this Guidance to emphasise that what might be sufficient is task-specific, and therefore ACR-specific. The paper introduces the structure of the proposed Rotorcraft Certification by Simulation process, together with the main concepts that guide applicants to the development of simulations that can be effectively employed to reduce the cost, timescales, complexity and risks that may be associated with certification performed solely though flight tests.
Open Access
Preliminary guidelines for the rotorcraft certification by simulation process: update no. 1, March 2023
(Rotorcraft Certification by Simulation (RoCS), 2023-03) Padfield, Gareth D.; vant' Hoff, Stefan; Lu, Linghai; Podzus, Philip; White, Mark; Quaranta, Giuseppe
This document presents preliminary Guidance for the application of (rotorcraft) flight modelling and simulation in support of certification for compliance with standards CS-27 and CS-29, PART B (Flight) and other Flight related aspects (e.g. CS-29, Appendix B, Airworthiness Criteria for Helicopter Instrument Flight). The Guidance is presented in the form of a structured process, starting from the relevant paragraphs in the Certification Specifications, through a comprehensive description of the assembly of flight simulation requirements, informed by judgements on Influence, Predictability and Credibility, and on into the detailed building of the three major elements of the process: • the flight simulation model (FSM), • the flight simulator (FS), and • the flight test measurement system (FTMS). The FTMS feeds both the flight model and simulator development with real-world test data to support validation and fidelity assessment. A structured and systematic approach to data/configuration management and documentation is recommended, aided by the creation of the Rotorcraft Certification by Simulation (RCbS) project management plan. This is the first update of the RCbS Guidelines and includes modifications based on the first round of feedback received before and after the European Rotors RoCS workshop held in Cologne on November 9th 2022. The Guidelines will continue to be updated, as appropriate, with the next major revision to include exercising the process in case studies based on applicable certification requirements from EASA CS-27 and CS-29 (to appear in Section 10). In the current update, the RoCS team have also addressed the issue of resourcing the RCbS process (within Section 9) and suggested potential next steps for aspiring applicants (new Section 11).
Open Access
Review of flight simulation fidelity requirements to help reduce ‘rotorcraft loss of control in‑flight’ accident rates
(Springer, 2021-08-21) White, Mark D.; Padfield, Gareth D.; Lu, Linghai; Advani, Sunjoo; Potter, Mario
This paper examines the fidelity requirements for flight simulators to improve training and address the problems associated with rotorcraft loss of control in-flight (LOC-I). To set the context, trends in rotorcraft accident statistics are presented. The data show that, despite recent safety initiatives, LOC-I rotorcraft accidents have been identified as a significant and growing contribution to accident rates. In the late 1990s, the fixed-wing commercial aircraft community faced a similar situation relating to upset prevention and recovery, and through a coordinated international effort, developed a focussed training programme to reduce accident rates. Lessons learned from the fixed-wing programme are presented to highlight how improved rotorcraft modelling and simulation tools are required to reduce rotorcraft accidents through higher quality, simulator-based training programmes. Relevant flight simulator certification standards are reviewed, with an emphasis on flight-model fidelity and vestibular motion cueing requirements. The findings from rotorcraft modelling and motion cueing research, that highlight relevant fidelity issues, are presented to identify areas for further activities to enhance the fidelity of simulators standards for use in LOC-I prevention training.
Open Access
Rotorcraft lateral-directional oscillations: the anatomy of a nuisance mode
(Vertical Flight Society, 2021-07-22) Agarwal, Dheeraj; Lu, Linghai; Padfield, Gareth D.; White, Mark D.; Cameron, Neil
High-fidelity rotorcraft flight simulation relies on the availability of a quality flight model that further demands a good level of understanding of the complexities arising from aerodynamic couplings and interference effects. One such example is the difficulty in the prediction of the characteristics of the rotorcraft lateral-directional oscillation (LDO) mode in simulation. Achieving an acceptable level of the damping of this mode is a design challenge requiring simulation models with sufficient fidelity that reveal sources of destabilizing effects. This paper is focused on using System Identification to highlight such fidelity issues using Liverpool's FLIGHTLAB Bell 412 simulation model and in-flight LDO measurements from the bare airframe National Research Council's (Canada) Advanced Systems Research Aircraft. The simulation model was renovated to improve the fidelity of the model. The results show a close match between the identified models and flight test for the LDO mode frequency and damping. Comparison of identified stability and control derivatives with those predicted by the simulation model highlight areas of good and poor fidelity
Open Access
Rotorcraft simulation fidelity improvements through augmented rotor inflow
(Vertical Flight Society, 2021-09-09) Agarwal, Dheeraj; Lu, Linghai; Padfield, Gareth D.; White, Mark D.; Cameron, Neil
In rotorcraft research, the prediction of correct off-axis response using a simulation model is a challenging task, particularly for hover and low-speed flight. This can be attributed to the complex aeromechanical behaviour exhibited by a rotorcraft, including the unsteady and hysteretic nature of the main rotor wake and its coupling with the fuselage and empennage in manoeuvring flight. A traditional approach to improve the off-axis response prediction is to include the manoeuvre wake distortion effect arising from the variation of the induced inflow through the rotor disc. Various approaches have been developed to deal with this phenomenon but usually demand prerequisites of high levels of expertise and profound aerodynamic knowledge. This paper presents a new and practical approach to capturing this wake distortion through an augmented rotor inflow model. The proposed model is integrated into a nonlinear simulation using the FLIGHTLAB environment. The response comparisons between the simulation and flight test in hover indicate the good quality of the proposed model. The results reported are part of ongoing research at Liverpool and its partner Institutions into rotorcraft simulation fidelity for predicting dynamic behaviour for operationally-relevant mission-task-elements.
Open Access
The use of augmented rotor inflow to predict rotorcraft responses in hover and low-speed manoeuvres
(Cambridge University Press, 2022-01-28) Agarwal, Dheeraj; Lu, Linghai; Padfield, Gareth D.; White, Mark D.; Cameron, Neil
The rotorcraft is a complex dynamical system that demands specialist modelling skills, and a high level of understanding of the aeromechanics arising from the main rotor wake and aerodynamic couplings. One such example is the difficulty predicting off-axis responses, particularly in hover and low-speed flight, associated with induced velocity variation through the rotor disk resulting from the rotor wake distortions. Various approaches have been developed to deal with this phenomenon but usually demand prerequisites of high levels of expertise and profound aerodynamic knowledge. This paper presents a new and practical approach to capturing this wake distortion through an augmented rotor inflow model. The proposed model is coupled with a nonlinear simulation using the FLIGHTLAB environment, and comparisons are made between the simulation results and flight test data from the National Research Council of Canada’s Advanced System Research Aircraft in hover and low speed. Results show good predictability of the proposed nonlinear model structure, demonstrated by its capability to closely match the time responses to multi-step control inputs from flight test. The results reported are part of ongoing research at Liverpool and Cranfield University into rotorcraft simulation fidelity.

Browsing by Author "Padfield, Gareth D."

Results Per Page

Sort Options