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Higher augmented control of a utility helicopter using model following controllers
No full textHigher augmented control of a medium sized utility helicopter with fly-by-wire controls is accomplished by implementing translational rate command position hold (TRCPH) type controllers. These control algorithms complements previously designed attitude command attitude hold (ACAH) type inner loops in a cascaded manner. ACAH controllers are based on two different design approach: explicit model following (EMF) and optimal model following (OMF). TRCPH mode is optimized for pilot workload alleviation based on ADS-33E-PRF specifications. Four sample mission task elements (MTEs) are performed in a desktop simulation environment with both EMF and OMF. A modified pilot model and power frequency metric are used to get some sense about qualitative pilot opinion
Fatigue of rotorcraft gears: overview and prospects of improvement
Get PDFThe helicopter transmission design is a critical aspect due to the complexity of the components and the potential severity of a failure. A Rotorcraft Transmission Safety Working Group (RTSWG) has been set up in 2017 with the major Helicopter Manufacturers and EASA, addressing some recommendations to improve design and increase safety. During the years, Leonardo Helicopters has promoted some research activities in collaboration with Politecnico di Milano focused on the determination of the tooth strength under bending load. Following an extended test campaign, Wohler curves have been produced for the main materials used for transmission gears. The Safe Life analysis is now based on specific Wohler curves implemented on dedicated software which elaborates the flight data in a full fatigue spectrum, as for the rotor components. Flaw Tolerance requirements are complied with Flaw Tolerance Safe Life/No Growth analyses, performed in accordance with the Threat Assessment. Damage tolerance tests have been carried out on LH planet gears with simulated spalling, demonstrating adequate performance and robustness of design. Future research activities will be focused on the characterization of the contact fatigue on a back-to-back gear test rig for the definition of the endurance limits for pitting failure mode
A new approach for finite state dynamic rotor inflow modelling
Get PDFWe present a new method to model the induced velocities generated by a rotor. A spectral Galerkin method is applied to the incompressible non linear Euler equations, and 1lters are added to improve stability, while maintaining the accuracy of the scheme. We then compare it to other induced velocity models with satisfying results, while underlying some further work
Simulation of trimmed flight of a helicopter using the URANS solver ANSYS fluent
Get PDFThe methodology of simulation of a fully trimmed flight of rotorcraft has been developed and applied to simulate a helicopter flight within a range of flight velocities from a hover to fast flight at advance ratio 0.34. The presented approach is based on a solution of Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. In contrast to typical solutions of such problem, in the newly developed methodology, the flight controls corresponding to the trimmed-flight conditions are also determined based on the solution of URANS equations. The methodology is based on coupling of several computational models of Computational Fluid Dynamics and Flight Dynamic. The URANS equations are solved in a three-dimensional region surrounding the flying helicopter, using the ANSYS FLUENT code. The approach is truly three-dimensional, with truly modelled geometry and kinematics of main and tail rotor blades. This applies to modelling of blade flapping, too. The trimming procedure uses six independent parameters (i.e. collective and cyclic pitch of main rotor blades, collective pitch of tail rotor blades, pitch and bank angles of a helicopter) that should be adjusted so as to balance all forces and moments acting on the helicopter. The detailed description of the developed methodology as well as the results of simulation of trimmed hover of the helicopter are presented
GNSS solutions for increased ga and rotorcraft airport accessibility demonstration
No full textWithin the framework of the SESAR programme concepts were developed to integrate general aviation aircraft and rotorcraft into the airspace and airports without influencing the main traffic flow. On the one hand this paper discusses the idea of a low-level route network to allow IFR operations separately from the regular routing. On the other hand the concept of simultaneous non-interfering approaches is presented to guide these aircraft to or from a point in space located at a final approach and take-off area from which it can continue visually to land. Both concepts have been evaluated in real-time simulations by DLR in preparation for a flight trial. The exercise will be explained in detail and the results show that operational concepts should work. It is concluded to continue the process of implementing these concepts and advised to enable safer flight by further promoting advanced point-in-space procedures
Development of integrated avionics functions for external situation awareness in civil helicopter missions
Get PDFProviding a consistent perception about the external situation to the helicopter flight crew can greatly enhance awareness, simplify mission and contribute to a safer operating environment. This paper focuses on the HELIONIX® external situation awareness functions including SVS, HTAWS, DMAP integrated in the HELIONIX® avionics suite of Airbus light and medium helicopter platforms. First, a background of CFIT incidents that motivated the development of the external awareness functions is presented. The context of civil helicopter mission is then described to identify the needs regarding external awareness under different operations. Thereafter the main capabilities of the SVS, HTAWS and DMAP functions along with their HMI concept are explained. Finally, some aspects about a standardised common development and certification approach are highlighted. Due to the awareness functions being fully embedded in the cockpit multi-function displays, a coherent and consistent HMI concept as well as cost, weight and space savings are achieved while answering the needs of civilian helicopter missions
Master minimum equipment list (MMEL) / engine time limited dispatch (TLD) on helicopter
Get PDFThe certification regulations published by Joint Airworthiness Authorities (JAA), European Aviation Safety Agency (EASA) or Federal Aviation Administration (FAA) require that all equipment installed on a helicopter must be operative in compliance with the airworthiness standards and the operating rules. However, the rules (e.g. in JAR-MMEL/MEL or CS-MMEL) permit the publication of a Minimum Equipment List (MEL) where compliance with certain equipment requirements is not necessary in the interests of safety under all operating conditions. Experience has shown that with the various levels of redundancy designed into helicopter, operation of every system or installed component may not be necessary when the remaining operative equipment can provide an acceptable level of safety. Hence helicopter utilization is improved and more convenient and economic air transportation for the public is provided thereby. In order to enable the aircraft operators to establish their individual MELs, the Master Minimum Equipment List (MMEL) is developed as a basis for the MEL by the type certificate holder of the respective aircraft as part of the Operational Suitability Data (OSD) and approved by the competent authority. The MMEL includes those items of equipment related to airworthiness and operating regulations and other items of equipment which the competent authority finds may be inoperative and yet maintain an acceptable level of safety by appropriate conditions and limitations. Special attention has to be paid if engine related items shall be implemented in the MMEL. As engines have their own type certificate (TC), engine related parts cannot be directly implemented in the aircraft MMEL by the aircraft manufacturer. To implement these items, a �permission� given by the engine manufacturer is needed. To have this permission officialised, the competent airworthiness authority has to approve it in the TC. To obtain the approval, a �Time Limited Dispatch� (TLD) approach needs to be performed for failures leading to redundancy failures in the engine control system. For failures not leading to redundancy failures, the �classical� MMEL approach can be conducted. The compliance demonstration is based on the list of relevant failures leading to redundancy failures in the engine control system. These failures have to be justified by appropriate means, e.g. fault tree analyses, taking into account that one failure has already occurred. For the TLD approach also new analysis methods need to be applied taking into account the requirements of the certification specification for engines (CS-E). Airbus Helicopters performed this approach as the first helicopter manufacturer in the world successfully in a joined approach together with the engine manufacturer
A rugged fiber optics monitoring system for helicopter rotor blades
Get PDFHealth and Usage Monitoring (HUM) and Structural Health Monitoring (SHM) technologies play an increasingly important role in aerospace applications, for example in support to 2eet maintenance and for test and development purposes. We describe the design, manufacture and integration of an advanced blade strain monitoring system for the tail rotor of the AW139 helicopter. The goal was two-fold: to demonstrate the feasibility of a rugged rotor-based interrogation system and the practical embedding of Fiber Bragg Gratings (FBG) sensors within composite rotor blades. This task required careful study of the optimal 1ber path within the constraints of the blade composite structure and the ply stacking sequence. A temperature compensation method was developed to decouple thermal strain. An integrated interrogation-communication system housed in a dedicated beanie was developed with the capability to withstand the harsh high-g environment of a rotor hub. In order to avoid the need for slip rings for power and data transfer between 1xed and rotating frames, the interrogator was designed as a self-contained unit equipped with batteries and wireless data transmission capability. This rugged monitoring system offers cleaner aerodynamics and longer sensor life compared to traditional strain gauges and represents a stepping stone towards the development of future 1ber-based HUM with photonics chip interrogators
Complementary use of black-box and physics-based techniques in rotorcraft system identification
No full textAccurate linear helicopter models are needed for control system development and simulation and can be determined by system identi1cation when appropriate test data are available. Standard methods for rotorcraft system identi1cation are the frequency domain maximum likelihood method and the frequency response method that are used to derive physics-based linear state-space models. But also the optimized predictor-based subspace identi1cation method (PBSIDopt), a time domain system identi1cation method that yields linear black-box state-space models, has been successfully applied to rotorcraft data. As both methods have their respective strengths and weaknesses, it was tried to combine both techniques. The paper demonstrates the successful complementary use of physics-based frequency domain methods and the black-box PBSIDopt method in the areas of database requirements, accuracy metrics, and model structure development using 2ight test data of DLR's ACT/FHS research rotorcraft
Investigation of optic flow, time-to-intercept, and pilot workload during aggressive approach to hover maneuvers
No full textThis work proposes a novel relationship between pilot workload and optic flow during visual approach-to-land maneuvers. A simulation experiment was conducted at NASA Ames Vertical Motion Simulator (VMS) to evaluate the workload associated with operating two candidate Army Future Vertical Lift (FVL) vehicles: a compound (coaxial-rotor and push-prop) vehicle, and a tilt-rotor vehicle. The UH-60 was included in the evaluation as a baseline reference. Sixteen experienced military pilots flew aggressive visual approaches terminating in a hover while providing Bedford workload ratings in real time. No approach or hover guidance was displayed to the pilot. The out-the-window (OTW) environment (front and chin monitors) was digitally recorded and the optical flow of each video frame computed. Prior work identified a mathematical relationship between pilot workload and the combination of display error rate and stick rate during compensatory tracking tasks. The current work extends this relationship to visual landing approaches, where the pilot is hypothesized to track key optical variables that are available from the OTW scene. Via correlation analysis a set of candidate tracking variables which appears to drive pilot workload is identified: the rate of change of optical flow, and the angle formed between the cockpit glareshield and the intended landing spot. Combined with stick rate these variables are used to generate a Bedford estimate. Actual and modeled Bedford ratings are compared for the compound aircraft (video for the other aircraft will be processed and presented in a future paper. Innovative contributions of this research include: 1) Optical flow from high resolution, high frame rate flight video is computed and analyzed for workload analysis; 2) A modelling technique is developed that produces workload estimates that closely matches actual pilot ratings; 3) A technique based on visual perceptual requirements allows optical flow to be employed in a very simplistic, tractable, yet effective manner; 4) While tau motion theory (i.e. rate of instantaneous time-to-arrive is approximately constant) was roughly observed during the approaches, it appears that tau motion was a result of the pilot adhering to a strategy of minimizing deviation in optic flow rather than being the source of pilot behavior. This preliminary, significant conclusion proceeds from the observation that workload correlated well and was causal with minimizing change in optic flow, but correlated poorly and was often non-causal with changes in tau motion; 5) Using a novel method, Bedford workload ratings were collected in real time without impinging on the flight task, enabling in-situ workload analysis. Potential applications include: a) If a pilot has transferred control to automation during an approach in an Optionally Piloted Vehicle (OPV), pilot trust may be higher if he/she observes system behavior that resembles what a skilled operator would produce, i.e., optic flow control; b) Control of optic flow may be an effective, robust method for autonomously executing power-off (autorotative) flight to the groun