Rotorcraft flight control for improved handling, loads reduction and envelope protection

The advent of fly-by-wire control systems has made it possible to design elaborate automatic flight control systems that can provide a whole range of functions from basic stabilisation to advanced envelope protection systems and autopilots. The research presented in this thesis is focused on the design of novel control systems for rotorcraft with the aim to improve handling' qualities, provide structural load alleviation and to provide envelope protection. The application of the control theory used for the design is considered to be novel. Methods used include nonlinear control and H:o control. Seven control laws are designed for three different rotorcraft types. They are designed first of all for the Bell 412 Advanced Systems Research Aircraft, a fly-by-wire research helicopter of the National Research Council in Canada. This aircraft is equipped with a full-authority simplex control architecture with single nonredundant set of fly-by-wire actuators, sensors and flight control computer and software. Inherent to the design philosophy of the Advanced Systems Research Aircraft's simplex architecture is a reliance on automated safety monitoring systems and a safety pilot to guard against system failure or operational flight envelope exceedance. Novel control laws can actually be flight tested on this aircraft. A highfidelity nonlinear simulation model of this aircraft was developed in the project for control law design. The other two aircraft for which control laws are designed are the XV-I5 tilt-rotor and the FLIGHTLAB Generic Rotorcraft, a nonlinear simulation model representative of the UH-60 Black Hawk. Nonlinear simulation models of the latter two were available at the start of the project. One of the key outcomes presented in this thesis is the design and flight test of a nonlinear control law for the Bell 412. The attitude quickness could be specified within a nonlinear element. High bandwidths were achieved in flight, which correlated very closely to the simulationbased predictions. Also, describing function analysis was successfully applied to analyse the stability of the control law. Other important results are the presentation of a new design method for structural load alleviation control laws, in combination with a newly proposed structural load severity scale that can be used for the analysis of these types of control laws. Flight envelope protection was investigated as well. A heave axis control law providing mast torque envelope protection was designed for the Bell 412. The design method used was the Boo loop shaping procedure in combination with a nonlinear outer loop. Stability problems with the inner loop were encountered during the first flight test with this control law. The control law was therefore automatically disengaged by the safety systems of the Advanced Systems. Research Aircraft. Piloted simulation suggested that the structure of the control law is useful, provided the inner loop tracks torque. Finally, a complete flight control system was built with additional outer loops in order to take on a challenging problem: the automatic landing of a helicopter on a ship using ''t-theory'. The variable 't is commonly used in optical flow theory ofvisual perception. It is essentially the time to contact given a certain speed and distance. Theory suggests that pilots use this variable for manual flight control. The height rate reference signal generated by the automatic landing system was based on the variable 't during the final landing phase (from hover above the deck until touch down). A successful automatic .landing was simulated in zero wind conditions. The height control in the final phase of the automatic landing seemed natural, as if a human pilot performed it. The 't-based height control loop is essentially a proportional controller with a time dependent proportional gain. This application of't-theory in control is considered to be novel. Keywords: Flight control, Flight test, Hoo control, Nonlinear control, Rotorcraft Modelling and Simulation, Envelope protection, Structural Load Alleviation, Handling Qualities, Shipboard landing, Bell 412 ASRA, FGR, XV-15

Streamlining Cross-Organizational Aircraft Development: Results from the AGILE Project

The research and innovation AGILE project developed the next generation of aircraft Multidisciplinary Design and Optimization processes, which target significant reductions in aircraft development costs and time to market, leading to more cost-effective and greener aircraft solutions. The high level objective is the reduction of the lead time of 40% with respect to the current state-of-the-art. 19 industry, research and academia partners from Europe, Canada and Russia developed solutions to cope with the challenges of collaborative design and optimization of complex products. In order to accelerate the deployment of large-scale, collaborative multidisciplinary design and optimization (MDO), a novel methodology, the so-called AGILE Paradigm, has been developed. Furthermore, the AGILE project has developed and released a set of open technologies enabling the implementation of the AGILE Paradigm approach. The collection of all the technologies constitutes AGILE Framework, which has been deployed for the design and the optimization of multiple aircraft configurations. This paper focuses on the application of the AGILE Paradigm on seven novel aircraft configurations, proving the achievement of the project’s objectives

In-Hospital outcomes after hemiarthroplasty versus total hip arthroplasty for isolated femoral neck fractures

BACKGROUND: Previous studies suggest total hip arthroplasty may have some benefits compared to hemi-arthroplasty for displaced intracapsular femoral neck fractures in patients more than 60 years of age. The primary research question of our study was whether in-hospital adverse events, post-operative length of stay (LOS) and mortality in patients 60 year of age or older differed between total hip and hemi-arthroplasty for femoral neck fracture. METHODS: We obtained data on 82951 patients more than 60 years of age with an isolated femoral neck fracture treated with either hemi-arthroplasty or total hip arthroplasty in 2009 or 2010 from the National Hospital Discharge Survey (NHDS) database. The International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9, CM) was used to code diagnoses, comorbidities, complications, and procedures. RESULTS: Controlling for demographics and comorbidities, patients treated with hemi-arthroplasty had a 40% (95% CI 1.4-1.5) higher risk of adverse events compared to patients treated with a total hip arthroplasty. Length of stay and in-hospital mortality did not differ between these groups. CONCLUSIONS: The observed advantage for total hip arthroplasty might reflect greater infirmity in hemi-arthroplasty patients that was not accounted for by ICD-9 codes alone

Implementation of a Heterogeneous, Variable-Fidelity Framework for Flight Mechanics Analysis in Preliminary Aircraft Design

This paper presents the implementation of a framework for flight mechanical analysis with adaptable aerodynamics methods in the preliminary stage of aircraft design. Basis to the framework are software modules for the disciplines conceptual design, flight mechanics and aerodynamics which have been developed within different design frameworks and which contain heterogeneous interfaces. The focus is placed on the technique for the integration of the different analysis components and the realization of the variable-fidelity capability. Backbone of the framework is the XML-based 'Common Parametric Aircraft Configuration Schema' (CPACS) which was extended in course of this study. The paper introduces the utilized analysis codes and software modules, presents their integration into the framework and discusses the faced challenges and developed solutions. Exemplary results are shown as illustrative use cases. Analogies of linked design systems lead to a standardized integration process. In a next step the homogenization of different design systems by a unified parameterization appears to be feasible

Data-driven maintenance of military systems: Potential and challenges

The success of military missions is largely dependent on the reliability and availability of the systems that are used. In modern warfare, data is considered as an important weapon, both in offence and defence. However, collection and analysis of the proper data can also play a crucial role in reducing the number of system failures, and thus increase the system availability and military performance considerably. In this chapter, the concept of data-driven maintenance will be introduced. First, the various maturity levels, ranging from detection of failures and automated diagnostics to advanced condition monitoring and predictive maintenance are introduced. Then, the different types of data and associated decisions are discussed. And finally, six practical cases from the Dutch MoD will be used to demonstrate the benefits of this concept and discuss the challenges that are encountered in applying this in military practice

Metabolomic Changes in Serum of Children with Different Clinical Diagnoses of Malnutrition

Mortality in children with severe acute malnutrition (SAM) remains high despite standardized rehabilitation protocols. Two forms of SAM are classically distinguished: kwashiorkor and marasmus. Children with kwashiorkor have nutritional edema and metabolic disturbances, including hypoalbuminemia and hepatic steatosis, whereas marasmus is characterized by severe wasting. The metabolic changes underlying these phenotypes have been poorly characterized, and whether homeostasis is achieved during hospital stay is unclear. We aimed to characterize metabolic differences between children with marasmus and kwashiorkor at hospital admission and after clinical stabilization and to compare them with stunted and nonstunted community controls. We studied children aged 9-59 mo from Malawi who were hospitalized with SAM (n = 40; 21 with kwashiorkor and 19 with marasmus) or living in the community (n = 157; 78 stunted and 79 nonstunted). Serum from patients with SAM was obtained at hospital admission and 3 d after nutritional stabilization and from community controls. With the use of targeted metabolomics, 141 metabolites, including amino acids, biogenic amines, acylcarnitines, sphingomyelins, and phosphatidylcholines, were measured. At admission, most metabolites (128 of 141; 91%) were lower in children with kwashiorkor than in those with marasmus, with significant differences in several amino acids and biogenic amines, including those of the kynurenine-tryptophan pathway. Several phosphatidylcholines and some acylcarnitines also differed. Patients with SAM had profiles that were profoundly different from those of stunted and nonstunted controls, even after clinical stabilization. Amino acids and biogenic amines generally improved with nutritional rehabilitation, but most sphingomyelins and phosphatidylcholines did not. Children with kwashiorkor were metabolically distinct from those with marasmus, and were more prone to severe metabolic disruptions. Children with SAM showed metabolic profiles that were profoundly different from stunted and nonstunted controls, even after clinical stabilization. Therefore, metabolic recovery in children with SAM likely extends beyond discharge, which may explain the poor long-term outcomes in these children. This trial was registered at isrctn.org as ISRCTN1391695