• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.6
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• pp.487-497
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• 2011

Numerical analysis has been performed to investigate the rotor speed and pitch range variations when the airspeed is increased in autorotation. Transient Simulation Method(TSM) was used to obtain the steady states of autorotation. The rotor blade was analyzed by the two-dimensional compressible Navier-Stokes solver in order to adapt to the airspeed increase and the results were used in the transient simulation method. Meanwhile, the Pitt/Peters inflow theory was used to supply the induced velocity fields. For the prescribed torque equilibrium state, the combinations of velocity, shaft angle, and pitch angle were produced to investigate the rotor speeds and variable ranges. The rotor tip Mach number and rotor speed were correlated and the trim range of pitch angle was observed with respect to the shaft angle decrease.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.889-893
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• 1991

This paper describe the mathematical model of helicopter rotor, which is suitable for the calculation of trim condition to develop the stability and control. The mathematical model is a nonlinear, total force and moment model of a single main rotor helicopter. The effects of fuselage, tail rotor, horizontal tail, and vertical tail are included. The phase angle and stick displacement are obtained and compared at the trim condition.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.2
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• pp.186-196
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• 2017

In order to resolve the trimming difficulty in rotor CFD calculations, a high-efficiency and improved "delta trim method" is established to compute the blade control settings that are necessary to identify the blade motion. In this method, a simplified model which combines the blade element theory and different inflow models is employed to calculate the control settings according to the target aerodynamic forces, then it is coupled into a CFD solver with unsteady Navier-Stokes equations by the delta methodology, which makes the control settings and aerodynamics calculated and updated in the meantime at every trim cycle. Different from the previous work, the current research combines the inflow model based on prescribed wake theory. Using the method established, the control settings and aerodynamic characteristics of Helishape 7A, AH-1G and Caradonna-Tung rotors are calculated. The influence of different inflow models on trimming calculations is analyzed and the computational efficiency of the current "delta trim method" is compared with that of the "CFD-based trim method". Furthermore, for the sake of improving the calculation efficiency, a novel acceleration factor method is introduced to accelerate the trimming process. From the numerical cases, it is demonstrated that the current "delta trim method" has higher computational efficiency than "CFD-based trim method" in both hover and forward flight, and up to 70% of the amount of calculation can be saved by current "delta trim method" which turns out to be satisfactory for engineering applications. In addition, the proposed acceleration factor shows a good ability to accelerate the trim procedure, and the prescribed wake inflow model is always of better stability than other simple inflow models whether the acceleration factor is utilized in trimming calculations.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.153-158
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• 1992

The purpose of this paper is to calculate the dynamic derivatives of single rotor Helicopter in forward flight. From trim condition, the equation of motion is derived, and we can calculate the dynamic dervatives. The results were compared with flight test data. The phase angle and stick displacement are obtained and compared at the trim condition.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.115-121
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• 2007

The aeroelastic analysis of rotor blades with trailing edge flaps, focused on reducing vibration while minimizing control effort, are investigated using large deflection-type beam theory in forward flight. The rotor blade aerodynamic forces are calculated using two-dimensional quasi-steady strip theory. For the analysis of forward flight, the nonlinear periodic blade steady response is obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim. The objective function, which includes vibratory hub loads and active flap control inputs, is minimized by an optimal control process. Numerical simulations are performed for the steady-state forward flight of various advance ratios. Also, numerical results of the steady blade and flap deflections, and the vibratory hub loads are presented for various advance ratios and are compared with the previously published analysis results obtained from modal analysis based on a moderate deflection-type beam theory.

• International Journal of Naval Architecture and Ocean Engineering
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• v.2 no.2
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• pp.57-67
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• 2010

Experimental investigations were carried out on an Axi-symmetric Body Model fitted with Pump-jet Propulsor (PJP) in the Cavitation Tunnel at Naval Science and Technological Laboratory (NSTL). The tests were intended for evaluating the propulsion characteristics of the body and propulsor. The self propulsion point of the model for two configurations was determined after finding the corrections for tunnel blockage effects and differences in model length at zero trim. The results were found to match closely with the towing tank results. The rotor and stator torques also matched closely over full range of experiment. Further experiments were carried out on the body at $4.5^{\circ}$ angle of trim to investigate the propulsive performance and assess the operational difficulties in the sea. The results indicated an increase in resistance and decrease in rotor thrust; but the balance of torques between the rotor and stator was undisturbed, causing no concern to vehicle roll.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.12
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• pp.1011-1018
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• 2021

This numerical study conducts the modeling and the hover performance analyses of coaxial co-rotating rotor(or stacked rotor), using a rotorcraft comprehensive analysis code, CAMRAD II. The important design parameters such as the index angle and axial spacing for the coaxial co-rotating rotor are varied in this simulation study. The coaxial co-rotating rotor is trimmed using the torque value of the upper rotor of the previous coaxial counter-rotating rotor or the total thrust value of the previous coaxial counter-rotating rotor in hover. The maximum increases in the rotor thrust is 1.84% for the index angle of -10° when using the torque trim approach. In addition, the maximum decreases in the rotor power is 4.53% for the index angle of 20° with the thrust trim method. Thus, the present study shows that the hover performance of the coaxial co-rotating rotor for e-VTOL aircraft can be changed by the index angle.

• International Journal of Aeronautical and Space Sciences
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• v.6 no.2
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• pp.23-32
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• 2005

An experimental control system is proposed for the attitude control of a simplified 2-DOF helicopter model. The main rotor is a rigid one, and the fuselage is simply supported by a fixed hinge point where the longitudinal motion is decoupled from the lateral one since the translations and the rolling rotation are completely removed. The yaw trim of the helicopter is performed with a tail rotor, by which the azimuthal attitude can be adjusted on the rotatable post in the yaw direction. The robust sliding mode control tracking a given attitude angle is proposed based on the flight dynamics. A pitch damper is inserted for the control of pitching angle while the compensator to reaction torque is used for the control of azimuth angle. Several parameters of the system are selected through experiments. The results shows that the proposed control method effectively counteracts nonlinear perturbations such as main rotor disturbance, undesirable chattering, and high frequency dynamics.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.192-195
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• 2008

A sensor fault detection method for small turbo shaft engine considering multiple trim conditions is proposed. This engine is used in a helicopter. Firstly, under multiple trim conditions, we derive the linearized models from a nonlinear model which includes engine, rotor and feedback control loop. As a fault detection method, we adopt the Kalman filter based method. To keep continuity of estimates between the changes of trim conditions, we reconfigure the initial values of state variables at trim changes. We detect the faults with two steps that when the first filter does not alarm the faults for some sensors, the second filter is runned for other sensor. Via some simulations we show that the proposed method works well under multiple trim conditions.

• 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.