• Journal of the Korean Society for Aviation and Aeronautics
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• v.18 no.1
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• pp.51-57
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• 2010

This study was to analyze the difference in pilot error by using the Signal Detection Theory. The task was to detect the targeted aircraft(signal) which is different shape from many other aircraft(noise). From the two experiments, we differentiated the task difficulty followed by change in noise stimuli. Experiment 1 was to search the signal stimuli(fighter plane) while the noise stimuli(cargo plane) were increasing. The results from the Experiment 1 showed the tendency to decrease the hit rate by increasing the number of noise stimuli. However, the false alarm rate was not increased. The sensitivity(d') showed quite high. In Experiment 2, a disturbance stimulus(helicopter) was added to noise stimuli. The result was generally similar to those of Experiment 1. However, the hit rate was lower than that of Experiment 1.

• Advances in aircraft and spacecraft science
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• v.9 no.4
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• pp.319-333
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• 2022

This work presents a numerical investigation of the aerodynamics and aero acoustics of the HVAB rotor in hover conditions. Two fully turbulent models are employed, the one-equation Spalart-Allmaras model and the two-equation k-ω SST model. Transition effects are investigated as well using the Langtry-Menter γ-Re θt transition transport model. The noise generation and propagation are being investigated using the Ffows-Williams Hawking model for far-field noise and the broadband model for near-field noise. Comparisons with other numerical solvers and with the PSP rotor test data are presented. The results are presented in terms of thrust and power coefficients, the figure of merit, surface pressure distribution, and Sound pressure level. Velocity, pressure, and vortex structures generated by the rotor are also shown in this work. In addition, this work investigates the contribution of different blade regions to the overall noise levels and emphasizes the importance of considering specific areas for future improvements.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.140-143
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• 2008

Experiments are performed to consider the ground effects on unsteady loading and acoustic generation. Partially inclined plate is used to maximize the unsteadiness of the rotor. Indirect method to recognize the unsteady effect is used by measuring the noise in the normal direction from the rotor plane. The experiment is conducted with a square plate of about $9m^2$ and one half of the plate is placed parallel with the rotor plane and the other half is inclined. The height of the plate and the angle of the inclined plate can be changed. Helicopter noise is also measured at the 4 different positions to study the directivity of the rotor noise. The distance between microphone and rotor hub is 1.3m. Tonal noise and broad band noise are measured and analyzed. Thickness noise, steady loading noise and unsteady loading noise are investigated from the rotor noise measurement.

• Journal of KSNVE
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• v.7 no.5
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• pp.819-826
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• 1997

The finite element analyses of a composite hingeless rotor blade in forward flight have been performed to investigate the influence of blade design parameters on the blade stability. The blade structure is represented by a single cell composite box-beam and its nonclassical effects such as transverse shear and torsion-related warping are considered. The nonlinear periodic differential equations of motion are obtained by moderate deflection beam theory and finite element method based on Hamilton principle. Aerodynamic forces are calculated using the quasi-steady strip theiry with compressibility and reverse flow effects. The coupling effects between the rotor blade and the fuselage are included in a free flight propulsive trim analysis. Damping values are calculated by using the Floquet transition matrix theory from the linearized equations perturbed at equilibrium position of the blade. The aeroelastic results were compared with an alternative analytic approch, and they showed good correlation with each other. Some parametric investigations for the helicopter design variables, such as pretwist and precone angles are carried out to know the aeroelastic behavior of the rotor.

• Journal of computational fluids engineering
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• v.19 no.3
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• pp.62-68
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• 2014

The aerodynamic and noise calculations were performed through the CFD-CSD loose coupling methodology. In the loose coupling process, the trimmed rotor airloads were predicted by the in-house CFD code based on unstructured overset meshes, and the trim of the rotorcraft and the aeroelastic deformation of rotor blades were accounted with the CAMRAD II rotorcraft comprehensive code. The set of codes was used to analyze the HART-II baseline test condition. The effect of grid resolution and time step was examined and the loose coupling approach was found to be stable and convergent for the case. Comparison of the resulting sectional airloads, structural deformations, the noise carpets and the wake geometry with experimentally measured data was presented and showed the good agreement.

• Journal of Preventive Medicine and Public Health
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• v.41 no.5
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• pp.307-314
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• 2008

Objectives : We conducted an epidemiologic survey to evaluate the effect of the aircraft noise exposure on the health of the residents near the military airbases in Pyeongtaek City. Methods : The evaluation of environmental noise level, questionnaire survey, and health examination were performed for 917 residents. The study population consisted of four groups: subjects who lived in the village close to the fighter airbase (high exposure), subjects who lived along the course of fighters (intermediate exposure), and subjects near a helicopter airbase, and the control group. Results : The prevalence of the aircraft noise related accident and irritable bowel syndrome in the exposure groups were higher than that of the control group. The risks of noise induced hearing loss, hypertension and diabetes mellitus were higher in the exposed groups than in the control group. The prevalence of anxiety disorder and primary insomnia were higher in the exposed groups than in the control group. Prevalence odd ratios of the risk for primary insomnia after adjusting age, sex, agricultural noise, and occupation were 4.03 [95% confidence interval (95% Cl) 1.56-10.47] for the subject near the helicopter airbase, 1.23 (95% Cl 0.40-3.76) for those intermediately exposed to fighter noise, and 4.99 (95% Cl 2.14-11.64) for those highly exposed to fighter noise. Conclusions : The results of the present study suggest that the aircraft noise may have adverse effects on hearing function, cardiovascular health and mental health. Therefore, it seems to be needed to take proper measures including the control of the aircraft noise and the management of the exposed people's health.

• International Journal of Aeronautical and Space Sciences
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• v.4 no.1
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• pp.88-98
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• 2003

Compared to the noise limits (CAN7) specified in ICAO Annex 16 for civil helicopters, the Lynx helicopter equipped with BERP blades has only 0.2 EPNdB margin in the approach case although it has more than 4 EPNdB margin in fly-over and take-off conditions. The objectives of the study described in this paper were to devise a low noise main rotor blade for the Lynx using UEAF combined with the high resolution airload model ACROT. A design requirement is that the new blade, KBERP (Korean BERP) blade should achieve a significant reduction in noise during approach(at least 6EPNdB margin) without any noise penalty in fly-over and take-off conditions and minimal performance penalty. It was decided to investigate a tip modification to the BERP blade, employing the twin vortex concept to reduce the BVI noise and to retain the excellent high speed performance characteristics of BERP. Through the parametric study, the KBERP blade with optimized twin vortices has at least a 9 EPNdB noise margin in approach flight condition with only a small penalty in fly-over and take-off conditions. The KBERP tip is thus a very cost effective wav to reduce BVI noise during approach.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.492-497
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• 2011

Helicopter uses a rotor system to generate lift, thrust and forces, and its aerodynamic environment is generally complex. Unsteady aerodynamic environment arises such as blade vortex interaction. This unsteady aerodynamic environment induces vibratory aerodynamic loads and high aeroacoustic noise. Those are at N times the rotor blade revolutions (N/rev). But conventional rotor control system composed of pitch links and swash plate is not capable of adjusting such vibratory loads because its control is restricted to 1/rev. Many active control methodologies have been examined to alleviate the problem. The blade using active control device manipulates the blade pitch angle at arbitrary frequencies. In this paper, Active Trailing-edge Flap blade, which is one of the active control methods, is designed to modify the unsteady aerodynamic loads. Active Trailing-edge Flap blade uses a trailing edge flap manipulated by an actuator to change camber of the airfoil. Piezoelectric actuators are installed inside the blade to manipulate the trailing edge flap.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.680-685
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• 2006

This paper describes the aeroelastic stability test of the small-scaled 'Next-Generation Blade(NRSB)' with NRSH (Next-Generation Hub System) and HCTH hingeless hub system in hover and forward flight conditions. Excitation tests of rotor system installed in GSRTS(General Small-scale Rotor Test System) at KARI(Korea Aerospace Research Institute) were tarried out to get lead-lag damping ratio of blades with flexures as hub flexure. MBA(Moving Block Analysis) technique was used for the estimation of lead-lag damping ratio. First, NRSB-1F blades with HCTH hub system, Then NRSB-1F with NRSH hub system were tested. Second, NRSB-2F blades with NRSH hub system were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Non-rotating natural frequencies, non-rotating damping ratios and rotating natural frequencies were showed similar level fir each cases. Estimated damping ratios of NRSB-1F, NRSB-2F with HCTH and NRSH were above 0.5%, and damping ratio increased by collective pitch angle increasement. Furthermore damping ratios of NRSB-2F were higher than damping ratios of NRSB-1F in high pitch angle. It was confirmed that the blade design for noise reduction would give observable improvement in aeroelastic stability compared to paddle blade and NRSB-1F design.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.8 s.113
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• pp.848-856
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• 2006

This paper describes the aeroelastic stability test of the small-scaled 'Next-generation Blade(NRSB)' with NRSH (next-generation hub system) and HCTH hingeless hub system in hover and forward flight conditions. Excitation tests of rotor system installed in GSRTS (general small-scale rotor test system) at KARI (Korea Aerospace Research Institute) were carried out to get lead-lag damping ratio of blades with flexures as hub flexure. MBA(moving block analysis) technique was used for the estimation of lead-lag damping ratio. First, NRSB-1F blades with HCTH hub system, then NRSB- 1F with NRSH hub system were tested. Second, NRSB-2F blades with NRSH hub system were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Non-rotating natural frequencies, non-rotating damping ratios and rotating natural frequencies were showed similar level for each cases. Estimated damping ratios of NRSB-1F, NRSB-2F with HCTH and NRSH were above 0.5%, and damping ratio increased by collective pitch angle increasement. Furthermore damping ratios of NRSB-2F were higher than damping ratios of NRSB-1F in high Pitch angle. It was confirmed that the blade design for noise reduction would give observable improvement in aeroelastic stability compared to paddle blade and NRSB-1F design.