• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.4
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• pp.311-318
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• 2020

This study investigates the performance and blade airloads for a rigid coaxial rotor of high-speed compound unmanned rotorcrafts. The present compound unmanned rotorcraft uses not only a rigid coaxial rotor, but also wings and propellers for high-speed flights. For the rigid coaxial rotor in this work, CAMRAD II, a rotorcraft comprehensive analysis code, is used to study the performance at a flight speed of up to 250 knots and blade section lift forces at 230 knots. As the flight speed increases, the rotor power decreases; however, the power of propellers increases to overcome the drag force of a rotorcraft in high-speed flight. The effective lift-to-drag ratio of a rotor has the maximum value of about 11.6 which is much higher than the value of the conventional helicopter. The blade section lift forces of the upper and lower rotors at 230 knots show the similar variation trends for one rotor revolution, and the impulses because of the aerodynamic interaction between both rotors are observed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.3
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• pp.224-231
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• 2009

In this study, an aerodynamic performance analysis code has been developed as a part of rotorcraft comprehensive program. Airloads on rotor blades are calculated based on the blade element theory with look-up tables of aerodynamic coefficients of 2-D airfoils. In order to calculate rotor induced inflow, various inflow prediction methods such as linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot's inflow distribution and sectional normal force coefficients of AH-1G.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.9
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• pp.21-27
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• 2022

The rotorcraft engine gearbox transmits the power generated by the turboshaft engine to the rotor by reducing the rotational speed and increasing the torque. The core of the rotorcraft engine gearbox is lightweight performance, which requires maximum weight reduction within the range that meets various requirements and constraints. Therefore, lightweight design through gear macro geometry optimization is necessary. In this study, gear macro geometry optimization was performed to reduce the weight of a rotorcraft engine gearbox. NSGA-III was used for the optimization, resulting in a combination of the gear ratio and macro geometry that minimizes the weight of the total gear. In addition, the safety factor of the gears satisfied the given conditions.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.30-36
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• 2018

In this study, a small-scaled test system for a tip jet rotor was developed to contribute to the research on unmanned compound rotorcraft. The performance and dynamic characteristics of the tip jet rotor were investigated using the test system. The diameter of the tip jet rotor was set to 2m in consideration of the size of the test site and the pneumatic supply capacity of the. The rotating speed of the rotor was controlled by the pressure of the compressed air. The thrust and forces during the rotor rotation were measured using a load measuring device. A hydraulic actuator was installed for the dynamic test and full-bridge strain gages were attached to the root of each blade to measure the flap, lag, and torsion-wise responses generated when the rotor is excited by the actuator. The performance and dynamic characteristic tests were conducted at various rotor speeds and blade pitches. In order to check the validity of the test results, the results were also compared with the CAMRAD II analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.5
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• pp.364-370
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• 2019

In this paper, an individual blade control (IBC) methodology is applied to find the best input scenario for vibratory hub loads reduction of XH-59A co-axial rotorcraft in high speed flight. A comprehensive aeromechanics analysis code CAMRAD II is employed to analyze the aircraft. A parametric study is conducted for optimum IBC inputs leading to the maximum vibration reduction. Numerical results demonstrate that up to 50% reduction in the hub vibration index is obtained for an IBC input at 3/rev frequency with the amplitude and phase angle of 0.5 deg. and 300 deg., respectively. The upper rotor exhibits as much as 6% more vibration reduction as compared to that of the lower rotor due to a clean inflow characteristic of the rotor. It is found that further vibration reduction gain is reached for IBC inputs with advancing-side only control. The hub vibration becomes reduced by up to 17% in reference to that with full rotor disk control. It is noted that the additional gain is obtained with significantly less power input with the advancing-side only control.

• ICROS
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• v.7 no.6
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• pp.10-17
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• 2001

본 논문에서는 훈련용과 연구용 시뮬레이터들에서 차량조종 및 자동조종(autopilot) 시스템들을 시뮬레이션하기 위하여 공통적으로 사용되는 기술들을 소개한다. 여기서 언급하는 차량 조종 시스템들은 고정익기와 회전익기의 비행제어시스템은 물론 지상차량의 조종 시스템들을 모두 포함한다. 본 논문은 다양한 유형의 비행 및 지상차량 조종 시스템들에 대한 검토로 시작된다. 다음으로 차량조종 및 자동조종 시스템들의 시뮬레이션과 모델링, 조정 부하(control loading)라 통상 일컫는 조종감(control feel)의 시뮬레이션, 조종계통 모델링툴 시스템 통함 및 시스템 성능 비준 등의 주요 주제들이 이어진다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.5
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• pp.415-422
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• 2014

There has been a lot of discussion to revise military helicopter crashworthiness design criteria. In this paper, newly revised crashworthiness criteria is analyzed centering around the Crashworthiness Index which is the core content of revised criteria. The Crashworthiness Index(CI) was conceived as an adequate method to quantify the crashworthiness capabilities of a rotorcraft design. The index can rate how well a new or derivative design complies with design requirements. The CI rating is made up of seven assessment areas. While the Basic Airframe Crashworthiness(BAC) area tends to be an objective calculation, other areas of the CI tend to be more subjective. Therefore, in this paper, detail CI calculation process for the BAC area is analyzed to inspect the effectiveness of revised criteria.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.2
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• pp.95-105
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• 2018

Increasing cruise speed is an important issue for the development of the next generation rotorcraft. Among several concepts proposed by previous research, the rotorcraft with ducted fan demonstrates its possibility of high-speed flight. In this study, numerical simulations are conducted to investigate the aerodynamic and flow characteristics of multi-ducted fan in forward flight. The aerodynamic efficiency around front ducted fan is determined by interaction between free-stream velocity and the induced velocity. While flow characteristics of rear ducted fan are dominantly influenced by the front ducted fan. Separation in the front ducted fan occurs faster than that of rear ducted fan, and the separation at duct inlet induces an increase of fan thrust. As a result of interaction effect between each ducted fan, relatively aligned inflow enters to the rear ducted fan. Therefore, thrust of the rear fan is decreased steadily before separation, and sudden changes of thrust in fans occur simultaneously. Due to the pressure decrease on lower surface, the normal force of rotorcraft is reduced with forward speed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.2
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• pp.124-129
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• 2007

Prediction methods for a rotor averaged inflow in forward flight are investigated in this study. The investigated methods are Drees linear inflow model, Mangler & Squire model and free vortex wake(FVW) method. Predictions have been performed for a four-blade rotor operating at three different advance ratios i.e. 0.15, 0.23 and 0.30, at which experimental data are available. According to results, Drees model has a limitation for the inflow non-uniformity prediction due to an inherent linear characteristics. Mangler & Squire model has a reasonable accuracy except the disk edge region. KARI FVW method has very good accuracy and has better accuracy than the other FVW method especially in inboard region. However, there are some discrepancies in retreating side due to the dynamic stall effect and in near hub region due to the fuselage upwash effect.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.4
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• pp.297-305
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• 2011

In this study, the aeroelastic analysis of rotorcraft in forward flight has been performed using dynamic inflow model to handle unsteady aerodynamics. The quasi-steady airload model based on the blade element method has been coupled with dynamic inflow model developed by Peters and He. The nonlinear steady response to periodic motion is obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim for stability analysis. The aerodynamic and structural characteristics of dynamic inflow model are validated against other numerical analysis results by comparing induced inflow and blade tip deflections(flap, lag). In order to validate aeroelastic stability of dynamic inflow model, lag damping are also compared with those of linear inflow model.