ERF European Rotorcraft Forum
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A surrogate-based approach for uncertainty analysis of the ONERA 7A rotor
Get PDFAn uncertainty quantification framework for rotorcraft applications is introduced. The capabilities of the developed approach are demonstrated using the ONERA 7A rotor at high-speed to model the uncertainties in blade properties including torsion, flap, and lag stiffness on rotor power and loads including torsion, flap bending, and chord bending moments. To support large-scale simulations which are needed to establish statistical convergence, a surrogate-based framework is introduced using an artificial neural network that is conceptualized, trained, and validated using data derived from rotorcraft comprehensive analysis code. The analysis characterizes the input uncertainties as aleatory, hence are normally distributed. Through propagation it is established that the uncertainties in rotor power are limited; moderate for peak torsion moment; and significant for peak flap bending and chord bending moments. The analysis further quantified that uncertainties in spanwise flap bending moment are present and are influenced by the variability in flap and torsion stiffness. The results demonstrate the integration of a probabilistic-based framework to a surrogate-based approach for the quantification of system uncertainties to facilitate informed decision making based on model-based predictions
Autorotation design and simulation for a small-scale helicopter
Get PDFSafety of manned and unmanned aircraft is strictly related to the capability of managing emergency situations. In the case of helicopter engine failure, the autorotation manoeuvre represents a valid possibility for a safe emergency landing. Such manoeuvre is made of two different main phases: 1) the steady descent, where the rotor angular rate is kept in a proper range and the helicopter descends with constant velocity, and 2) the final flare, where the kinetic energy stored in the main rotor is used to generate a braking force, so to reduce the vertical velocity to a minimum value. For a manned piloted helicopter, experience and piloting skills of the pilot are mandatory for performing a safe emergency landing. For unmanned rotorcraft, since the remote pilot does not have the direct perception of linear accelerations and attitude motion, the remote autorotation is indeed an extremely hazardous task. For this reason, there is a significant interest in the design of a control algorithms allowing a remotely piloted helicopter to automatically perform the autorotation manoeuvre, which is a crucial feature for all missions over populated areas and/or for all aircraft carrying expensive payloads. In this paper, a preliminary investigation on steady descent conditions in autorotation, and a first design of a complete autorotation maneuver has been made through a model-based design approach. Also, a closed loop control system has been developed, to perform the two main phases of autorotation. Simulations results show the suitability of the proposed approach for a wide range of initial conditions (altitude and advancing velocity)
The influence of rotor/wing aerodynamic interaction of compound helicopter in forward flights on wing-body
Get PDFThis paper investigates the influence on aerodynamic characteristics of a winged-body of a rotor/winged-body configuration due to changes of the advance ratio through numerical simulations. A winged compound helicopter has a single main rotor and a fixed-wing located under the rotor. Due to the configuration, an aerodynamic interaction occurs between the rotor and the wing. In high advance ratio flight, the aerodynamic interaction produces asymmetrical aerodynamic characteristics on the left and right sides of the wing. This phenomenon is dependent on the rotor flow field and is presumed to be changed by the advance ratio. Therefore, in this paper, the asymmetrical aerodynamic characteristics of the wing were investigated for advance ratio from 0.1 to 0.7. A computational model is constituted by the UH-60A main rotor only the blades and the winged-body. The winged-body combines a rectangle wing and a fuselage designed by JAXA. The wing has span length that of 0.7 times of the rotor diameter and an aspect ratio of 10. The rotor speed was scheduled to decrease along with increasing flight speed. The combination for this simulation was selected from the schedule in order to correspond to the advance ratio from 0.1 to 0.7. As a result, the lift coefficient, drag coefficient and lift-to-drag ratio of both sides on the wing of the rotor/winged-body configuration becomes closer to that of the isolated winged-body as the advance ratio increases, but that of the right side, witch is under the advancing side of the rotor, remains different to that of the isolated winged-body. The influences on the lift and drag coefficient are stronger at the root than the tip on the wing, at the right side more than the left side and at low advance ratio than at high advance ratio
A theoretical basis for adverse aircraft-pilot coupling
Get PDFCurrently there is no reliable quantitative method for definitively predicting the likelihood for encountering Adverse Pilot Coupling (APC) during human-in-loop operation. This work examines APC characterized by oscillations near the: 1) rigid body dynamic mode frequency, and 2) closed loop neuromuscular (NM) mode frequency. The influence of pilot control input noise (pilot response that is not linearly correlated with the forcing function) on APC was also examined. The source of data for the work was a human-in-the-loop simulation experiment using an active sidestick where the independent variables were stick force gradient, stick sensitivity, and roll lag frequency. A specific combination of the experimental variables was observed to significantly influence the occurrence and repeatability of APC. The study developed a novel method to predict the propensity for APC that incorporates pilot noise estimation as part of pilot parameter estimation. Departing from the traditional method of using a high-frequency sum-of-sines forcing function to identify a pilot’s NM frequency response, a less intrusive approach leveraging internal noise as the NM forcing function is employed instead. Preliminary results indicate that pilot internal noise originates primarily from the pilot visual equalization element. An adaptive pilot model incorporating a simple objective function and the observed relationship between noise and visual equalization and is shown to produce behavior that closely matches the experimental data. Based on APC occurrence observed in the study a new metric, Relative Margin Proximity (RMP), is proposed for assessing APC propensity. The adaptive pilot model was used to investigate vehicle configurations from an experimental data base that had been rated for APC severity. The RMP values produced by the pilot model for these configurations were consistent with their APC ratings
Helicopter Augmented Control Laws for Ship deck landing: HACLAS ONERA/DLR joint team
No full textDifferent types of control laws are implemented, tested and compared for maritime operations particularly ship deck landing maneuvers at the flight simulation facilities at both DLR (German Aerospace Center) and ONERA (The French Aerospace Lab). At DLR, ”classical” cyclic and collective stick flight controls were used during the piloted simulator trials while active side-sticks were operated at ONERA. A joint maritime scenario for ship deck landing in the simulation environments of both institutes is presented. Test methodologies and assessment techniques to evaluate the ship deck landings are harmonized based on different criteria such as quantitative measures and handling qualities (HQ) ratings in order to analyze the developed control laws. Simulation results based on pilot studies for an EC135 in the DLR simulator and an EC225 at ONERA are presented
Automatic landing on unprepared zone
No full textLanding is arguably the most complex and most dangerous phase of flight for an aircraft. As a consequence, automatic landing on unprepared zone is a fundamental function and a key challenge for unmanned aerial vehicles. Many obstacles such as a pylon or any object on the helipad can hinder the descent. Cameras and lidars can be disturbed or deceived by a smoke cloud, low luminosity or obstacles with low reflectance. Therefore, using a combination of different types of sensors for the landing zone clearance diagnosis improves the robustness of the system. Although trajectory generation and optimal control are already widely spread, fewer methods deal with Automatic Decision Making. At Airbus Helicopters we have designed a demonstrator to prove our ability to enable a drone to make its own decision. A drone equipped with an autopilot will be given an order to find the closest helipad and land on it only if it is safe. Otherwise, the drone will fly to the next helipad
JAXA-ONERA-DLR cooperation: results from rotor optimization in forward flight
No full textThis paper presents the results of a cooperative study by JAXA, DLR, and ONERA on the optimal design of helicopter blades for high-speed forward flight. Optimizations and simulations are carried out by each agency with their own analysis codes using both blade element theory-based methods and computational fluid dynamics. These results are cross-compared and show common trends identified for optimum rotor blades obtained by each agency and the mechanism for improving forward flight performance are discussed. From the effective drag distributions, it is confirmed that, in order to improve forward flight performance, it is first important to reduce drag on the advancing side, and that a blade with a relatively small twist angle and planforms with a smaller chord length at the root and tip compared to the mid-span section is generally a suitable blade
Multi-physics modelling and simulation of a distributed electric propulsion system for helicopter anti-torque
No full textThe flexibility offered by Distributed Electric Propulsion (DEP) has triggered in the recent years a variety of new aircraft demonstrators, showing a way to improve the overall efficiency, capabilities and robustness of the future air-vehicles [1]. In comparison, the conventional helicopter tail rotor, with its vulnerable and complex installation, looks like an example of system application ready to take advantage of DEP, both in terms of redundancy and simplification of the flight control chain. This paper investigates the behavior of a distributed electric anti-torque system, starting from a reference usage spectrum and a fixed-pitch/variable-speed rotor design. The goal is to optimize the key electrical components for steady state operation and to verify the dynamic behavior of the system in healthy as well as in degraded conditions. Following an introduction to the safety requirements and the electrical technology state-of-the-art, all the main components are modelled and combined into a single dynamic network. Simulation results from different testing scenarios are then reviewed (in the mechanical, thermal and electrical domain) to show compliance with the minimum acceptance criteria. Finally, the article discusses the advantages and disadvantages of a distributed versus concentrated electrical solution
Pseudo-inverse simulation of pull-up maneuvers at low and high speeds by means of optimization
Get PDFIn the course of the certification process of a helicopter, applying EASA certification specifications and means of compliance, a loads survey is required which is then used for the design process or the stresses verification. Reasonable load cases can be derived from typical maneuvers, e.g. pull-ups, characterized by a phase of positive pitch rate and increased load factor. The paper at hand presents how an optimization of pull-up maneuvers simulated with the flight mechanics code Flightlab can be utilized to acquire desired load cases. The maneuvers are “flown” by prescribing control inputs for longitudinal cyclic and collective, whereas lateral cyclic and pedal a handled by a control system. The simplified input signals for longitudinal and collective controls are parameterized and then altered by an optimization framework, called Maneuver Optimization Tool (MOPT) and written in Python, in order to achieve given maneuver characteristics, e.g. a target pitch rate and main rotor torque. The simulation framework, consisting of Flightlab and the mentioned Python optimization, is introduced, and results are shown for low-speed flight at vl = 70 kts indicated and at never-exceed speed vNE. In addition, four different combinations of low/high helicopter mass, and front/aft center of gravity location are considered
