In-flight simulation of high agility through active control: Taming complexity by design

The motivation for research into helicopter agility stems from the realization that marked improvements relative to current operational types are possible, yet there is a dearth of useful criteria for flying qualities at high performance levels. Several research laboratories are currently investing resources in developing second generation airborne rotorcraft simulators. The UK's focus has been the exploitation of agility through active control technology (ACT); this paper reviews the results of studies conducted to date. The conflict between safety and performance in flight research is highlighted and the various forms of safety net to protect against system failures are described. The role of the safety pilot, and the use of actuator and flight envelope limiting are discussed. It is argued that the deep complexity of a research ACT system can only be tamed through a requirement specification assembled using design principles and cast in an operational simulation form. Work along these lines conducted at DRA is described, including the use of the Jackson System Development method and associated Ada simulation

Role of endothelial progenitor cells in acute vascular injury in man

Percutaneous coronary intervention (PCI) acutely improves coronary blood flow and myocardial perfusion but at the expense of endovascular laceration and endothelial denudation. PCI associated vascular injury is associated with intense inflammation and a loss of vascular function that may lead to significant in-stent restenosis (ISR), and the potentially catastrophic, acute stent thrombosis. Reendothelialisation is essential to the restoration of normal homeostasis and facilitating vascular healing. Attention has recently focused on a novel mechanism of reendothelialisation mediated by bone marrow-derived precursor or stem cells: endothelial progenitor cells (EPC). EPC are thought to home to, and reendothelialise sites of endothelial denudation, and therefore offer the potential to provide exciting new developments in the management of cardiovascular disease. Understanding the role of EPC following vascular injury may help us to enhance vascular repair following PCI. The following studies were performed to clarify the relationships between putative EPC and vascular injury associated with PCI. In studies of patients undergoing elective PCI for stable anginal symptoms I found that concentrations of traditional circulating phenotypic EPC expressing CD34+VEGFR-2+ were unaffected, unlike CD34+CD45- cell concentrations, which were transiently increased six hours following PCI, subsequently returning to normal by 24 hours, notably without an increase in CD34+ adhesion molecule expression or VEGF-A production. However, the purported progeny of CD34+VEGFR-2+ cells, endothelial cell-colony forming units (EC-CFU), were mobilised at 24 hours, commensurate with a systemic inflammatory response. Interestingly the concentration of circulating CD34+VEGFR-2+ cells and EC-CFU were unrelated to each other, emphasising the distinction between these two cell populations. Although EC-CFU contained proliferating cells and exhibited some endothelial characteristics, EC-CFU predominantly expressed the leukocyte antigen CD45 in addition to the lymphocyte markers CD4 and CD8, and most intensely, the surface markers CD68 and CD105, epitopes commonly expressed on macrophages. Notably, EC-CFU were a potent stimulus for the migration of mononuclear cells. However, despite being mobilised in the context of an acute systemic inflammatory response and being composed of leukocytes, isolated systemic inflammation in healthy volunteers (induced by Salmonella Typhus vaccination) in the absence of vascular injury did not cause selective mobilisation of EC-CFU or indeed of putative phenotypic EPC. It is therefore likely that EC-CFU mobilisation is a relatively specific inflammatory response to cardiovascular injury. In a cohort of 201 patients undergoing coronary angiography, traditional circulating phenotypic EPC (CD34+VEGFR-2+ and CD34+VEGFR-2+CD133+) were very rare indeed and were not increased in response to an acute coronary syndrome (ACS). Furthermore traditional EPC concentrations bore no relation to atheroma burden or clinical outcome. In contrast, concentrations of CD34+CD45- cells were increased in patients with coronary artery disease compared to those with normal coronary arteries and were increased in association with more severe coronary disease. Increased concentrations of circulating CD34+CD45- cells were also associated with a shorter cumulative event-free survival. Both EC-CFU and angiogenic monocytes expressing Tie-2 and VEGFR-2 were increased following acute myocardial infarction but did not relate to coronary atheroma or clinical outcome. These studies examine the behavior of putative EPC in response to both discrete vascular injury and myocardial infarction, and isolated inflammation in the absence of vascular injury. I have identified novel characteristics of the EC-CFU assay and determined that specific factors associated with cardiovascular injury likely trigger EC-CFU mobilisation. The clinical relevance of the traditional phenotypic EPC population is uncertain, but a novel CD34+CD45- population is mobilised acutely following discrete vascular injury and is significantly associated with coronary atheroma and clinical events. It is probable that the circulating CD34+CD45- concentration reflects vascular injury and atheroma burden, and I suggest that CD34+CD45- cells are released directly from the vessel wall following PCI, and do not reflect a reparatory response. In order to determine the impact of EPC populations on vascular healing, prospective studies examining the impact of periprocedural EPC concentrations on vascular healing following PCI are required

Three coronary arteries arising from the right coronary cusp with a malignant sub-pulmonary course of the left anterior descending artery

AbstractWe describe a case of a 45-year-old man presenting with acute myocardial infarction investigated by computed tomography coronary angiography. Interestingly all three coronary arteries arose from the right coronary cusp. The left anterior descending artery (LAD) subtended an acute angle from the aortic root, associated with significant kinking and stenosis at the ostium, before passing anteriorly, taking a sub-pulmonic course and descending in the anterior interventricular groove. The distal vessel was small with an atrophic appearance. The circumflex artery followed a retro-aortic route, before trifurcating to supply the lateral and posterior walls of the left ventricle. The right coronary artery was normal. Given his unstable presentation and the potentially lethal course of the LAD, he was referred for grafting of the LAD vessel which successfully ameliorated his symptoms and has thus far prevented recurrent myocardial infarction.<Learning objective: Computed tomography coronary angiography is becoming increasingly accessible to physicians for the investigation of patients with suspected coronary disease and the planning of surgery. As such, coronary anomalies are likely to be encountered more frequently, and it is important to appreciate their clinical significance.

Rotorcraft Loss of Control In-Flight – The need for research to support increased fidelity in flight training devices, including analogies with upset recovery for fixed-wing aircraft

A review of the worldwide commercial jet fleet accident data, 2001 – 2010, showed that the largest single factor leading to fatalities was Loss of Control In-Flight (LOC-I). 20 such accidents occurred during this timeframe with over 1800 fatalities [1], highlighting the need for research to investigate the causes of this problem and to develop new regulations and training programmes to improve flight safety. For civil helicopter operations, the need to significantly reduce accident rates has been the focus of the International Helicopter Safety Team (IHST), which was formed in 2005 to address factors affecting the “unacceptable” helicopter accident rate. The Team’s mission was to facilitate an 80% reduction in accident rates by 2016. From 2006 to 2011, a team completed a review of 523 U.S. helicopter accidents, from which LOC-I was cited as the main factor in accidents; LOC-I was evident in 217 (41%) of the accidents [2]. Addressing LOC-I for fixed-wing aircraft, the Royal Aeronautical Society’s Flight Simulation Group (FSG) 2009 Spring Conference was entitled: ‘Flight Simulation: Towards the Edge of the Envelope’, during which Upset Prevention and Recovery Training (UPRT) was highlighted as a major potential contributor to enhanced aviation safety. During the FSG conference, the International Committee for Aviation Training in Extended Envelopes (ICATEE) was formed to deliver a long-term strategy for reducing the rate of LOC-I accidents and incidents through enhanced UPRT [3]. To achieve this, ICATEE created two streams: the Training and Regulations Stream addressing the development of a UPRT training requirements matrix, and the Research and Technology Stream performing a thorough analysis of the technological requirements for UPRT. Key recommendations from the ICATEE work included better use of existing simulators for training, and aerodynamic enhancements to simulators to include stall characteristics. The impact of the ICATEE work is that their recommendations resulted in a new ICAO publication, “Manual on Aeroplane Upset Prevention and Recovery Training” [4]. National Authority regulations have also been impacted, with EASA UPRT requirements expected to be complete by May 2019 and the FAA requiring all Part 121 pilots to be UPRT-trained by March 2020. For the rotorcraft community, an equivalent safety initiative has recently been established. In 2016, the US Helicopter Safety Team (USHST) began the analysis of 104 fatal helicopter accidents (2009–2013) to develop intervention strategies and produce Helicopter Safety Enhancements (H-SE) that would further reduce rotorcraft accident rates. The USHST analysed accidents where LOC-I occurred during basic manoeuvres (e.g., hover, quick stop) and during unsuccessful attempted recoveries from potentially unsafe conditions (e.g., loss of tail rotor effectiveness, settling with insufficient power). Helicopter Safety Enhancement (H-SE) 81 titled, “Improve Simulator Modeling for Outside-the-Envelope Flight Conditions” [5] was established to “improve the accuracy of full flight simulators (FFS)/flight training devices by providing recommendations for developing better mathematical/physics-based models for helicopter flight dynamics”. The goal is to “achieve more realistic, higher-fidelity simulations of outside-the-envelope flight conditions” and to examine the “possible use of simulation for purposes of preventing, recognizing, and recovering from spatial disorientation”. Complementing the H-SE 81 initiative, a rotorcraft simulation fidelity research activity is underway at the University of Liverpool and Liverpool John Moores University [6]. The goal of this work is to establish a rational and systematic engineering approach to flight simulation fidelity enhancement, using physics-based models, linking in with goals of H-SE 81. Whilst rotorcraft operations pose different challenges to fixed-wing operations, drawing on the best practices developed by the fixed-wing safety community could benefit the rotorcraft community by reducing the time to implement new safety regulations and develop new training programmes. The presentation will provide an overview of the critical success factors of the ICATEE work, will report on the rotorcraft fidelity research ongoing in Liverpool, highlighting challenges and opportunities involved in developing simulator-based training for rotorcraft LOC-I scenarios

Appraisal of handling qualities standards for rotorcraft lateral-directional dynamics

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

A New Heuristic Approach to Rotorcraft System Identification

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. </jats:p

The use of augmented rotor inflow to predict rotorcraft responses in hover and low-speed manoeuvres

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