MULTIBODY ANALYSIS OF THE M-346 PILOTS INCEPTORS MECHANICAL CIRCUITS INTRODUCTION

Transcription

1 MULTIBODY ANALYSIS OF THE M-346 PILOTS INCEPTORS MECHANICAL CIRCUITS Emanuele LEONI AERMACCHI Italy SAMCEF environment has been used to model and analyse the Pilots Inceptors (Stick/Pedals) mechanical circuits of the AERMACCHI M-346 Aircraft, a twin engine, two seats, fly-by-wire transonic advanced trainer and light fighter. The main purpose of the analysis was to assist the design of the circuits from a kinematic/dynamic point of view and to tune all the parameters apt to provide the pilots with the required Artificial Feel effectiveness. INTRODUCTION The necessity to provide the instructor pilot and the pupil with a suitable interconnected flight control mechanism (i.e. linked sticks & pedals) has always represented a requirement for trainer aircrafts. This had obviously represented a must for conventional trainers but concept still holds for flyby-wire architectures. The AERMACCHI M-346 aircraft, a twin engine, two seats, fly-by-wire transonic advanced trainer and light fighter is provided with interconnected circuits between the pilot and the copilot. SAMCEF environment has been widely utilised to model and analyse the pilots inceptors mechanical circuits now installed on the first two prototypes of the M-346 which successfully underwent the first flight on July, the 15 th, 24 and already logged more than 3 flights by the end of 24. Photo 1 Photo 2 M-346 in flight M-346 Mock-up cockpit layout 1

2 PROBLEM DEFINITION AERMACCHI needed to develop mechanical circuits interconnecting the sticks / pedals of the instructor pilot and the pupil. A concurrent design process utilising CATIA for what concerns the shape modelling, SAMCEF Field V4.2 and SAMCEF Mecano V1.1 for the kinematic / dynamic requirements verification has been adopted. Moreover, the potentialities of BOSS quattro V4.3 have been used in order to identify the parameters apt to provide the pilots with the required Artificial Feel effectiveness. Since Pitch/Roll mechanical controls were independent from the Yaw one, two different SAMCEF models have been created. The layout of the model used for Pitch/Roll controls is shown in Figure 1; Yaw control layout is instead represented in Figure 2. Basically each pilots mechanical circuit permits to synchronise the inputs coming from the front and the rear seat and to provide the pertinent position sensor with an angular displacement (each time generating a redundant electrical output signal) proportional to the sticks/pedals travel. Position sensors signals are continuously transmitted to the 4 Flight Control Computers and suitably implemented in the FCC embedded Control Laws to provide to the Aircraft the required Command and Stability Augmentation. Figure 1 Pitch and Roll controls layout 2

3 Figure 2 Yaw control layout SAMCEF MODELS GOVERNING HYPOTHESIS AND LIMITATIONS The following simplifying assumptions have been considered as basic for the Pitch/Roll and Yaw SAMCEF models: All mechanical details such as bolts, nuts, washers etc... have not been introduced in the models. All constraints (both relative and fixed) have been modelled as being ideal (i.e. no backlash and friction) and having no mass. All bodies have been considered as rigid with the exception of those for which the effects of the flexibility was predicted to be non-negligible (control sticks, torsion tubes, etc...). The three position sensors and the three dampers have been considered as ideal components (i.e. not affected by the effects of friction and backlash). Structural ground interfaces used to constrain the mechanical linkages have been considered infinitely rigid. The mechanical characteristics of the springs used as part of the Artificial Feel have been considered as ideal (i.e. described only by elastic constant K and pre-load F o ). The mechanical characteristics of the dampers used as part of the Artificial Feel have been considered as ideal (i.e. described only by damping coefficient C). 3

4 KINEMATIC BEHAVIOUR OF M-346 MECHANICAL LINK The starting point in the design of the M-346 mechanical circuits was to define the requirements in terms of pilot workload vs. inceptor displacement (i.e. pilot force vs. stick/pedal displacement), stiffness and dynamical behaviour (i.e. basically damping and balancing) of the linkages. SAMCEF Field has been massively used in the design stage permitting a step-by-step verification of the implementation of each requirement. Any effect of the flexibility was disregarded at this stage. In Figure 3 the required upper and lower (thus constituting a boundary for the actual behaviour) normalised force vs. displacement characteristics of the Pitch command path are presented together with the results of the predictive analysis carried out using SAMCEF. Dedicated rigging tests conducted on the aircraft showed an excellent accordance with the analysis results. Besides, in Figure 4 and 5 the relevant behaviours of the Roll and Yaw command paths are reported. 1.8 STICK FORCE [N] STICK DISPLACEMENT [mm] -.2 Upper Requirement Lower Requirement SAMCEF Analysis Figure 3 Pitch pilots circuit Stick force vs. Stick displacement normalised characteristic 4

5 STICK FORCE [N] STICK DISPLACEMENT [mm] Upper Requirement Lower Requirement SAMCEF Analysis Figure 4 Roll pilots circuit Stick force vs. Stick displacement normalised characteristic Any SAMCEF predicted requirement marginal compliance was confirmed during dedicated aircraft tests permitting an advance evaluation of impact and acceptability PEDAL FORCE [N] PEDAL DISPLACEMENT [mm] Upper Limit Lower Limit SAMCEF Analysis Figure 5 Yaw pilots circuit Pedal force vs. Pedal displacement normalised characteristic 5

6 DYNAMIC BEHAVIOUR OF M-346 MECHANICAL LINK SAMCEF models have been also widely used to study the dynamic behaviours of the mechanical circuits and to identify the parameters that enabled the design to satisfy Flight Control System (FCS) requirements. The main topic that have been investigated where: Damping Inertial balancing Mechanical jam case M346 Pilot controls were required to provide a minimum overshoot during self-centering form end travel and an adequate inertial balancing. The effects of damping can be mainly split in two contributes, basically; a structural non-linear damping, due to the friction that every element in the link introduces and the linear one provided by a suitable device (damper) introducing an amount of damping directly proportional to the inceptor actuation speed. The aim of the analysis was to identify the damping coefficient value (or better range, since friction is not easy to determine during the design phase) to be allocated to the damper and which enables the mechanical circuits to comply with the requirements. A BOSS quattro case study has been carried out in order to determine a relationship between inceptor overshoot during self-centering and the damping coefficient; the analysis has been performed for each command path and the achieved results for the Yaw control are represented in Figure PEDAL INCEPTOR 1 st OVERSHOOT [%] DAMPING COEFFICIENT [Nms/rad] Figure 6 Yaw pilots circuit Pedal Inceptor 1 st Overshoot vs. Damping coefficient characteristic 6

7 The second objective of the dynamic analysis was to assess the compliance to the inertial balancing requirements. During manouvres, all aircraft parts are subjected to inertial forces that could be anyhow directed along the three coordinate axes. Usually these parts are somehow restrained but each mechanical circuit has one degree of freedom thus allowing the inceptor, if not suitably balanced, to unintentionally move during the manouvres. In other words, a mechanical circuit could be said perfectly balanced only if, during a manouvre, the inertial forces on each part counterbalance at inceptor level. Aircraft maximum acceleration limits (along X, Y and Z axes) have been imparted to the models and the inceptors extra-displacement (i.e. due to the manouvre induced acceleration field) monitored. The normalised X direction inceptor extra-displacement resulting from an application of +8g (1g equals 9.81 m/s 2 ) in the pilot-normal direction, is reported in Figure 7. Extra-displacement, where not zero, are negligible and deemed acceptable. STICK EXTRA-DISPLACEMENT [mm] TIME [s] Figure 7 Stick longitudinal normalised extra-displacement due to a +8g manouvre Any mechanical link could be affected by jamming thus preventing the pilot to control the aircraft. Particular attention has to be put in choosing elements that foresees a de-coupling capability in the case of jam occurrence or at least a dual load path. M-346 mechanical link design foresees the use of position sensors and dampers featuring this disconnect capability. In particular, each internal quadruple redundant position sensor is required to comply with a fail operative / fail operative / fail safe concept. 7

8 For what concerns the dampers, which have not been categorised as safetycritical components, a simple disconnecting device (shear pin) has been incorporated in the design. Details of dampers installation for the pitch and roll commands are shown in Figure 8 and Figure 9. Damper Roll Damper installation Figure 9 Roll Damper installation re 8 Figure 8 Pitch Damper installation Figure 9 Damper A damper jam (both for pitch and roll commands) was simulated by means of SAMCEF models in order to assess if the pilot forces, to be applied to the stick and needed to disconnect the locked devices, were within acceptable limits. Figure 1 and Figure 11 show the relationship between pilot force (normalised to the operational value) and damper input shaft torque in the case of a mechanical jam inside the unit. The forces that the pilot needs to apply to the stick were deemed adequate and within the force ranges easily achievable SHEAR PIN BREAK STICK FORCE [N] DAMPER SHAFT TORQUE [Nm] Figure 1 8

9 Pitch Damper jamming case analysis STICK FORCE [N] SHEAR PIN BREAK.25. DAMPER SHAFT TORQUE [Nm] Figure 11 Roll Damper jamming case analysis CONCLUSIONS AND FUTURE DEVELOPMENTS SAMCEF environment has been widely used to model and analyse the Pilots Inceptors (Stick/Pedals) mechanical circuits of the AERMACCHI M-346 Aircraft. The main purposes of the analyses were to assess the kinematics of the linkages and to tune all the parameters apt to provide the pilots with the required Artificial Feel effectiveness. Deep investigations have been conducted to simulate the behaviour of the subsystem in an airborne environment also in order to verify its balancing properties and compliance to Design Requirements. SAMCEF as a risk reduction and concurrent engineering design tool. AERMACCHI will optimise, on the basis of Flight Test Results and the use of SAMCEF, the mechanical circuits for the 3 rd Prototype which is to be considered a pre-series design configuration of the M-346 Aircraft. A particular thanks to SAMTECH Italia (Mr. Eros Gabellini and Mrs. Anna Selvi) that provided a continuous, timely and valuable support to AERMACCHI activities. SAMCEF models have been satisfactory validated through dedicated aircraft tests performed before and during the initial flight test campaign of the M-346, thus reinforcing AERMACCHI winning choice of 9