Papers

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    The feel system is an extension of both the vehicle and neuromuscular systems
    ( 2021) Bachelder, E. ; Aponso, B.
    In an aircraft with powered controls, a manual tracking task employs limb neuromuscular (NM) control of an inceptor, which can then provide input to a control system through an artificial feel system. Traditionally inceptors have been passive and hand-gripped, and the resulting inceptor-limb dynamics allowed the open-loop NM element to be represented as a self-contained second-order transfer function with a fixed damping ratio and natural frequency. However, active inceptors and gaming devices present themselves as candidate human-vehicle interfaces, and it is shown through elementary mechanical modeling how limb-inceptor interaction can influence the NM system. A physical example of this is provided. It is well-established that inceptor force feedback is an important NM cue to the pilot. An experiment using a passive joystick with and without spring restoring force investigated the effect of force feedback on tracking performance and NM response. The preliminary results suggest the role of NM equalization changes depending on whether force feedback is present, and that the presence or absence of force feedback influences the role of visual equalization. When it is available, force (rather than stick deflection) appears to be the signal employed to close the loop around the NM element. Neurophysiological research and this work’s observations suggest that muscle tension arising from limb co-contraction drives operator gain, which in turn governs crossover frequency. This muscle tension affects the mechanical NM response by changing the muscle stiffness and damping. This work proposes a NM model that first integrates both limb and inceptor dynamics, from which the open-loop NM system can then be isolated using the feel system dynamics and loop closure made with the force output. The location of the NM mode can have a key influence on the extent that an operator can generate frequency compensation, and the degree to which the Crossover Model is adhered to.
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    Rotor power savings with active camber actuation varying baseline rotor properties and operating conditions
    ( 2021) Komp, D. ; Hajek, M. ; Rauleder, J.
    A variation of helicopter main rotor properties was investigated with regard to their effects on active camber induced power savings using a comprehensive analysis model including elastic blade modeling and free vortex wake analysis. A Bo 105 main rotor was used as the baseline rotor in this work. This study was aimed at analyzing the transferability of results on active camber induced power savings to other rotor systems, while also identifying design targets for a rotor designated to be operated with an active camber system. A range of advance ratios from 0 to 0.35 was investigated. Active camber actuation on the modified baseline rotors was examined with regard to the absolute power variation compared to the original baseline rotor, and the relative power variation compared to the modified baseline rotor. The rotor blade torsional stiffness did not prove to be an important design parameter to optimize rotor power at high-speed flight using active camber. Only the relative rotor power savings from active camber notably depended on the blade torsional stiffness. The built-in twist of the baseline Bo 105 rotor was identified to be below the optimum. This lack of efficiency was compensated by active camber. Therefore, active camber yielded a reduced capability to improve rotor power for higher geometric built-in blade twist, especially for low advance ratios. Increased efficiency of the baseline rotor, however, did not necessarily reduce the efficiency gain from active camber. This was shown in case of varying the number of rotor blades and the blade taper ratio, where greater baseline rotor efficiency still resulted in an increase of relative power savings from active camber. A reduction in rotational speed resulted in significant rotor total power savings, but had a negative effect on the power savings from active camber. However, active camber was able to ameliorate detrimental effects from a reduced rotor rotational speed on thrust and stall margins.
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    Challenges and opportunities offered by flight certification of rotorcraft by simulation
    ( 2021) Quaranta, G. ; Hoff, S. van 't ; Jones, M. ; Lu, L. ; White, M.
    Newly developed aircraft must obtain a type certificate from the responsible aviation regulatory authority. This certificate testifies that the type of aircraft meets the safety requirements set by the authority. The compliance demonstration itself is the lengthiest and most expensive part of the certification process. The driving factor for the cost and duration of the compliance demonstration is the amount of ground and flight testing required. Moreover, certain certification flight test activities, particularly those involving demonstrations of control system or engine failures, can be classified as high-risk in terms of flight safety. The ROtorcraft Certification by Simulation (RoCS) project aims to explore the possibilities, limitations, and guidelines for best practices for the application of flight simulation to demonstrate compliance to the airworthiness regulations related to helicopters and tiltrotors. The paper presents the main objectives of the project and then introduces to some of the approaches that will be employed to achieve these goals.
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    Drone strike on a helicopter canopy demonstrator
    ( 2021) Ritt, S.A. ; Hofer, F. ; Oswald,J. ; Schile, D.
    The evaluation of structures under impact where large-scale projectiles like birds or drones are involved needs analyses at full-scale. The reason is that size effects can yet not be scaled from smaller samples. Hence, a canopy demonstrator with representative dimensions of a medium sized helicopter was developed. The two objectives for the demonstrator were the design development of a purely bonded windshield concept and the sizing of the windshield. For the windshield, polycarbonate (PC) was used while the carbon fibre reinforced plastics (CFRP) composite frame was adhesively bond by polyurethane. The experimental results of bird impact tests at different temperatures were used to validate the modelling and simulation approach for the final component design in the real 3d design. For the drone strike analysis, drone configurations and sizes were analysed. The work was then focused on the widely applied quadcopter configuration. Several steps were taken to validate the material and structural behaviour of the selected drone. With the generated quadcopter model, several loading conditions on a fast compound helicopter were modelled and the impact of the drone was applied. For the first experiment of a quadcopter drone strike on a plastics windshield a critical impact load case was selected. To further improve modelling and simulation, there was applied a path for the correlation by means of an instrumentation by force measurement.
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    Simulation and testing of helicopter-ship aerodynamic interaction
    ( 2021) Taymourtash, N. ; Zanotti, A. ; Gibertini, G. ; Quaranta, G.
    Development of a high-fidelity simulation environment, suitable for Helicopter-Ship Dynamic Interface testing has shown numerous advantages with respect to at-sea test campaigns. To correctly replicate the workload of the pilot, it is crucial to model the unsteady loads caused by complex aerodynamic interaction between airwake of the ship and inflow of the rotor. This paper aims to investigate the behaviour of the unsteady aerodynamic loads on a scaled-helicopter operating in the airwake of a generic frigate model. A series of wind tunnel tests have been conducted to characterise the unsteady loading for a wide range of wind speeds, directions and positions of the helicopter over the deck. A stern landing trajectory was simulated by trimming the rotor at different positions along an oblique path towards the landing spot. The unsteady measurements have been used to evaluate a numerical model developed by integrating the time-accurate CFD airwake of the isolated ship into the simulation environment. The numerical and experimental results show similar behaviour, as moving towards the landing spot the unsteadiness is increased. However, the numerical model underestimates the unsteadiness in most of the test points and the difference becomes more significant when testing with a 60_ wind-angle. Furthermore, a fully dynamic landing maneuver was tested in the wind tunnel to evaluate the effect of the approach velocity of the helicopter on the unsteady loads. In comparison to the measurements at fixed positions, the effect of approach velocity was found to be more significant when testing with the wind from the port side compare to the headwind condition.