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Development of a civil light helicopter flight simulator for pilot training
Get PDFThis paper aims at defining the necessary characteristics to develop a reliable and cheap helicopter flight simulator that could be used in flight schools for pilot training. The main contribution is the definition of helicopter dynamics and model parameters that are necessary to reproduce those characteristics perceivable by a pilot in a simulated environment. From this analysis, a physical-based nonlinear helicopter model is implemented. The proposed model description allows helicopter flight characteristics to be modified by changing only few physical parameters, which are readily accessible. The helicopter model is integrated with commercially available off-the-shelf helicopter controls and a Virtual Reality headset to create a cheap fixed-based simulator. The helicopter simulator is then validated through a pilot in-the-loop experiment with five licensed helicopter pilots. Subjective as well as objective metrics are considered for the evaluation. Results suggest that the proposed flight simulator can be effectively used in flight schools to save flight hours for the training of novice pilots. However, for training expert pilots a more complex setup would be necessary, able to provide additional features like the motion cueing
Low order multidisciplinary optimisation of counter-rotating open rotors
Get PDFA recent renewed interest in CROR propulsion demands the need for suitable design and analysis tools. As an unconventional propulsion system, a multidisciplinary analysis should be made at the preliminary design stage in order to fully evaluate a designs suitability across a number of domains. To address this, this contribution presents a number of low order models ideally suited for the preliminary design stage. Low order models for the evaluation of aerodynamic, acoustic and structural performance are presented. Following this, a multi-objective optimisation is carried out. Suitable objective functions are presented to evaluate the performance over a number of flight phases. Using these, a number of designs are presented for take-off only, cruise only, and combined take-off and cruise. These designs are shown to be of greater performance with respect to a baseline design. The work presented highlights the potential of the low order models and optimisation routine as a preliminary design and analysis tool for CROR propulsion
Experimental investigation of the effects of different helicopter rotor tip geometries on aerodynamic performance and tip vortex characteristics
Get PDFIn this study, the effects of different tip geometries (rectangular, anhedral, swept-tapered and swept-tapered-anhedral) on the rotor hover performance and tip vortex characteristics are investigated experimentally. A scaled rotor model set-up, instrumented with thrust and torque sensors, is used for aerodynamic performance measurements in hover and a two-dimensional (2D) particle image velocimetry (PIV) is used to obtain the tip vortex characteristics such as vortex trajectory, maximum tangential velocity, and circulation. Although taper+swept and taper+swept+anhedral configurations have the best ????/???? values at lower blade loadings, at higher blade loadings anhedral case has the best performance and an increase of 0.03 figure of merit compared to the baseline. It is observed that different tip shapes change the vortex trajectory, in addition, reduces maximum tangential velocity and circulation significantly. The PIV measurements which were performed at a high blade loading show that there is a correlation between the aerodynamic performance and the vortex strength
Numerical simulation of different rotor designs in hover and forward flight
Get PDFThis paper presents numerical simulations of different rotor designs using the HMB3 solver of Glasgow University. The PSP blade with a swept-tapered tip, the Langley Baseline blade with a rectangular planform and the Langley BERP blade with an advanced tip shape were studied. Firstly, the three blades were examined in hover. The integrated loads were compared with experiments and show very good agreement for each of the blade designs. The effect of anhedral in hover was investigated and was found to be more beneficial for the BERP-like design, than the other blades. The PSP blade was also simulated in forward flight at three thrust coefficients. The advancing and retreating blade surface pressures were extracted and found to follow experimental data obtained using pressure transducers. The predictions for the simulated cases demonstrate the ability of the CFD method to accurately predict the performance of rotors regardless of planform geometry, or design complexit
Some results of GARTEUR Action Group HC-AG 19 on methods for improvement of structural dynamic finite element models
No full textThe issue of vibration in helicopters is of major concern to operators. This requires close attention to the vehicle dynamics. The ability to faithfully simulate and optimise vehicle response, structural modifications, vehicle updates, the addition of stores and equipment is the key to producing a low vibration helicopter. GARTEUR Action Group, HC-AG14, concluded that helicopter dynamic models are still deficient in their capability to predict airframe vibration. The AG looked at the methods for improving the model correlation with modal test data along with the suitability of existing shake test methods. The helicopter structure tested in AG14 was suspended in the laboratory. However, this is not the operational environment where there are very significant mass, inertia and gyroscopic effects from the rotor systems. Nowadays, modal analysis consists of two principal approaches: experimental modal analysis (EMA) and operational modal analysis (OMA). The EMA evaluates the modal parameters by considering that the excitation and the response of the system are both measurable. The OMA evaluates the modal parameters using only the measured response. The lack of knowledge of the input is replaced by the assumption that the input is a distributed stochastic load, constant in a broad frequency band, e.g. white noise, and uncorrelated in space. This hypothesis, nevertheless, is restrictive in rotorcraft applications, because in these cases the load is characterized by harmonic components, i.e. deterministic signals, originating from the rotating parts. A new action group HCAG19 was formed to study the benefit of using in-flight dynamic data for improving finite element models. Methodologies were assessed to evaluate vibration measurements from flight tests. The objective is to extract modal parameters and demonstrate that the dynamic model can be updated using this data. This paper presents one of the approaches developed by the University of Rome �La Sapienza"
Rotorcraft-pilot couplings: analysis and detection in a safety enhancement framework
No full textNowadays, the complexity of high speed civil transport and highly-augmented rotorcraft, has led to an increase in the chances of encountering unwanted unstable phenomena, such as the so called Aircraft/Rotorcraft-Pilot Couplings (A/RPCs) or Pilot-Induced Oscillations (PIOs), whose unpredictability has given rise to a serious problem concerning the safety of a mission. When talking about PIOs, McRuer defined them as "inadvertent, sustained aircraft oscillations which are a consequence of an abnormal joint enterprise between the aircraft and the pilot". However, A/RPCs, these undesirable events associated with the interaction between pilot and aircraft, have become diverse and more complex than those encountered in the past. At the moment, there are different methods available to prevent and detect Cat. I/II A/RPC, but particular interest has recently arisen in this topic for flight simulation applications as any enhancement of these tools in order to accurately and objectively predict, detect (in real-time) and alleviate RPCs will be greatly welcomed. One of the main questions to be answered through the efforts carried out within this work is related to the better detection in real-time of embedded tendencies to RPCs in modern aircraft. To answer this question, initially an assessment of the efficacy of the Phase-Aggression Criterion (PAC), which has been designed a few years ago at the University of Liverpool, will be undertaken either: as a means of alerting the pilot to conditions likely to lead to the onset of a PIO; or, given that the time available for the pilot to counteract may be extremely limited, as a means to assist him/her in alleviating (automatically) the PIO condition itself. Preliminary results from flight simulation trials to explore how best to achieve this will be reported. Moreover, this work will report on the development of PAC boundaries for more highly augmented response types. Furthermore, as classified by McRuer, Cat. III PIO, which is nonlinear in essence, is the most complex one. However, the researches on Cat. III PIO are rare. This paper will reveal some elementary results of Cat. III PIO. Since there is no existing method used for predicting and detecting Cat. III PIO, this paper utilized the characteristics of PIO, such as the amplitude, the oscillation frequency and ultimate tendency of key aircraft response states to judge Cat. III PIO preliminarily. By using this elementary judgment of PIO, we studied the following factors: time delay of pilot input and helicopter main body, actuator position saturation, actuator rate limit and SCAS control authority in triggering PIO. Results show that PIO induced by actuator position saturation, actuator rate limit and SCAS control authority can be regarded as Cat. III PIO as the variation of these factors can be viewed as a kind of transition of effective controlled vehicle dynamics. These kinds of transition can cause a mismatch between the effective controlled vehicle dynamics and pilot control strategy, which is the main cause of Cat. III PIO
Detecting planetary gear bore crack
No full textSince 2009 there have been two fatal crashes of the Super Puma helicopter caused by fatigue cracks propagated from the bore of the planetary gear in the main transmission gearbox. The bore crack propagated through the gear rim causing the planet gear to breakup, which consequently destroyed the integrity of the transmission gearbox. For helicopter safety, it is imperative to develop methodologies for detecting such faults and to implement this capability into helicopter Health and Usage Monitoring Systems (HUMS). In this paper, a method is proposed to detect and track the propagation of a planetary gear bore-crack based on planet gear Synchronous Signal Averaging (SSA) and residual signal enveloping. The method has been initially validated using the vibration data generated from a small industrial planetary gearbox test rig with a notch inserted in the bore of one of its planetary gears. Results from this test show that the planetary gear bore notch is detectable with two different notch sizes using the residual signal of the composite planet SSA signal under three different load conditions. Furthermore, the diagnostic capability may be achievable using the squared envelope of the SSA residual signal, where the respective meshing of the defective section in the planet gear with the ring and sun gears are individually identifiable. Further bench testing will be conducted in the small test gearbox and in a full-scale Bell-206B helicopter main rotor gearbox with a very fine spark-eroded initial notch defect inserted in the bore of the planetary gear. The objective is to initiate a real fatigue crack from the bore notch and propagate the crack. The vibration data generated in this test will be used to further validate the proposed method
Twist morphing of a hingeless rotor blade using a moving mass
Get PDFThis paper presents a new concept of morphing by changing the twist of a composite blade through the movement of a mass near the tip of the blade. The mass is moved in the chordwise direction which then modifies the centrifugal force near the tip of the blade. The blade is tailored with composite materials and hence coupling is introduced. By moving the mass in the chordwise direction, a variable bending moment is produced which is the result of the offset between the point mass centrifugal force and the shear centre of the blade section. This bending moment will be transferred to the composite spar, and then through the bend-twist coupling of the composite layup, a variable torsional moment will be induced. This variable torsional moment changes the twist distribution of the blade. The dynamics of the rotating composite blade is modelled by using the geometrically exact fully intrinsic beam equations and the point mass is considered as a non-structural concentrated mass which has offsets with respect to the beam reference line. It is found that by moving the mass in the chordwise direction, the twist distribution of the blade changes. The rate of twist change completely depends on the bend-twist coupling and also the point mass magnitude and location. Finally, the effect of sensitive morphing parameters on the rotating frequencies of the Bo105 main rotor blade is determined
Correlation of finite state multi-rotor dynamic inflow models with a high fidelity viscous vortex particle method
Get PDFFinite state inflow models have been developed from potential flow theory to predict inflow distributions for single rotor con1gurations. Superposition of velocity or pressure potentials associated with individual rotors has been proposed for arriving at inflow models for multi-rotor configurations. In this study, fidelity assessment of finite state inflow models arrived at using pressure and velocity potential superposition methods for two tandem rotor configurations is considered. Physical wake effects, such as wake contraction and viscous wake dissipation, that are not inherently included in potential flow theory are added to both Pressure Potential Superposition Inflow Model (PPSIM) and Velocity Potential Superposition Inflow Model (VPSIM). In addition, new mass flow parameter formulation for VPSIM is proposed to match with one used in PPSIM. Using this formulation, it is shown that PPSIM and VPSIM have similar steady-state inflow distributions. For model fidelity assessment, the developed finite state inflow models are compared against a high fidelity numerical model known as Viscous Vortex Particle Method (VVPM). Differences in rotors uniform, fore-to-aft and side-to-side inflow components between the models are quantitatively analysed in hover and forward flight. Contour plots of inflow distributions are also provided for qualitative comparison. In addition, effects of inflow distribution and interference velocities on flapping angle predictions are discussed
Wind turbine wakes and helicopter operations - An overview of the GARTEUR HC-AG23 activities
Get PDFThe effects of a wind turbine wake on General Aviation and the behaviour of helicopters in the tip vortex of large fixed-wing aircraft has been topic of research in the past years, but less is known about the interactions of helicopters operating in a wind turbine wake. A dedicated GARTEUR Action Group, HC-AG23, consisting of European universities and research institutes was formed to investigate helicopter behaviour in a wind turbine wake and to study the consequences for helicopter handling and safety of flight. The activities are structured in work packages addressing wind turbine wake identification, wake experiments and computations, offline and piloted simulations and management and dissemination activities. This paper presents an overview of the partners� activities and provides a short overview of the results that have been achieved in the past three years