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Numerical investigation of aerodynamics of a helicopter articulated main rotor in hovering and horizontal flight
Get PDFThe paper is devoted to the numerical study of aerodynamic characteristics of a four-bladed articulated main rotor of a helicopter with cyclic pitch control and flapping motions of the blades and to the comparative analysis of the results against the similar case of rigid rotor with the fixed pitch angle and precone angle. The numerical investigation is carried out for the following working conditions: hover mode without cyclic control; forward flight without cyclic control; forward flight with cyclic control. The computations are performed on unstructured hybrid meshes using the in-house CFD code NOISEtte
Drone strike on a helicopter canopy demonstrator
Get PDFThe 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
Helicopter data science - From concepts to applications
Get PDFThis paper presents three application use cases of Machine Learning (ML) - under different forms: classification, regression and clustering - in order to improve the exploitation of helicopter data in different business problems. In each use case a real data is used and promising results are highlighted. After presenting the use cases and obtained results, conclusions address the perspectives as well as the challenges that ML and data science in general open in terms of learning from experience for helicopter continuous improvement
The development of a pilot control adaptation metric for simulation perceptual fidelity assessment
No full textThis paper reports the use of a control compensation metric to examine pilot adaptation in the objective assessment of simulation perceptual fidelity. The utility of the proposed metric to quantify different levels of pilot control compensation, hence adaptation, whilst flying low and high aggression tasks is explored. The tasks were conducted by different test pilots using the Heliflight-R simulator to examine the effect of additional transport delays on overall simulation perceptual fidelity. A weighted adaptive control compensation metric shows strong correlation with (Cooper-Harper) Handling Qualities and Simulation Fidelity Ratings awarded for each of the tasks. Moreover, in combination with a time-varying frequency-domain exposure, the metric is shown to be insightful for understanding variations in the pilots’ assessment of simulation perceptual fidelity
Estimation of rotor mast moments using a data-driven observer tuning
Get PDFIncorporating main rotor-states like the tip-path-plane flapping angles into the flight control system of a rotorcraft allows for enhanced handling and ride qualities as well as reduced pilot workload. Still, measuring rotor-states in the rotating frame is cost-intensive and more complex than fixed-frame measurements. In this paper, an observer is proposed to estimate the rotor mast bending moments using only fixed-frame measurements. Therefore, linear models of the research rotorcraft ACT/FHS are identified from an extensive flight test campaign. On this basis, different linear observers are designed and optimized using flight data. Two promising observers of different complexity are then selected using a cross-validation. Finally, these observers are analyzed in the time and frequency domain using a variety of different flight maneuvers like sweeps, stable forward flight and flight in turbulenc
Performance improvement of tail rotors by dynamically extendable chord
No full textIn order to study the performance improvement of variable speed tail rotors by dynamically extendable chord, a flight performance model is established, which includes a rotor model, a tail rotor model, a fuselage model, and a propulsive trim method. The flight data of the UH-60A helicopter is utilized to validate this model. The results show that the extendable chord has little effect on the power at hover. At cruise, some extra power is needed. At high speed flight, the power can be reduced significantly. The extendable chord is best placed inboard and close to the blade tip region to efficiently shift the lift and/or the drag inboard. The optimal azimuth angles for the deployment of extendable chord are 40°~50° and 130°~140°. The dynamically extendable chord with non-harmonic motion can obtain more power savings than the other strategies. The extendable chord is suitable for deployment on variable speed tail rotors. When the tail rotor speed is reduced by 20%, the maximum power reduction is 20.3%. The extendable chord increases the maximum thrust, which can compensate for the decrease in the maximum thrust by the reduction of the tail rotor speed
Design of a haptic obstacle avoidance for low speed helicopter operations using active sidesticks
No full textHelicopter collisions with obstacles are one of the most frequent and most devastating causes of accidents. To avoid these collisions in low speed operations a “haptic ticker” cue in form of repetitive impulses as a force feedback was designed for an active sidestick. Various design questions were examined in pilot campaigns using a full flight simulator and four test scenarios. As a result, the pilots always knew which distance-based hazard area (green, yellow, red) they were in. Furthermore, the ticker is disruptive and roughly reduces the handling qualities from Level 1 to Level 2. It is therefore primarily activated as a hazard warning and not as a main input to control the distance. As a warning cue the ticker was evaluated as non-disturbing. The force threshold to detect the direction of a tick was determined. With tick strengths above this threshold, the direction is not recognized at all in around 2% of the ticks. For the remaining ticks, the accuracy with which the direction is recognized is about 15°. In the fourth scenario, obstacles were moved towards the hovering helicopter, potentially forcing a collision. However, with the ticker a collision occurred in less than 4% of the cases, instead of 84% without the ticker. The ticker was rated as very intuitive and worth recommending. When asked how many accidents of this kind could be prevented with this ticker, all five pilots independently estimated 75%
The feel system is an extension of both the vehicle and neuromuscular systems
Get PDFIn 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
Numerical investigation of quad rotors in ground effect
Get PDFFlowfield and performance of quad rotors hovering in ground effect (IGE) are investigated through numerical simulations. A variable pitch-controlled quadrotor drone developed for applications in severe gusty circumstances is modeled in the simulations. Compared with a single rotor, the flowfields around the quad rotors are highly complex. The change of rotor performance with the height from the ground is noticeably different comparing to the single rotor case. The required power for a constant thrust does not monotonically decrease with the rotor height, which adds difficulties to the stable flight control near the ground. Comparisons to the quadrotor drone with a central fuselage are also performed. Remarkable differences in the flowfield and rotor performance are found