• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.7
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• pp.497-505
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• 2022

Performance and hub vibratory load analyses for a lift-offset coaxial rotor are conducted using a rotorcraft comprehensive analysis code, CAMRAD II. The lift-offset coaxial rotor is trimmed to match the total rotor thrust(lift-offset coaxial rotor's thrust) or the individual rotor thrust(upper and lower rotor thrusts, respectively) in this study. The individual rotor's lift and torque, and effective rotor lift to drag ratio for the total rotor are investigated for various advance ratios and lift-offset values. The two result sets with different trim methods are similar to each other and they are correlated well with the wind-tunnel test results. Therefore, the present study using CAMRAD II validates successfully the aeromechanics modeling and analysis techniques for the lift-offset coaxial rotor.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.3
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• pp.255-263
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• 2021

This paper investigates numerically the effect of rotor hub vibratory load components on the airframe vibration responses of high-speed compound unmanned rotorcraft (HCUR) using a lift-offset coaxial rotor, wings, and two propellers. The rotor hub vibratory loads are predicted using a rotorcraft comprehensive analysis code, CAMRAD II, and the airframe vibration responses are calculated by a finite element analysis software, MSC.NASTRAN. It is shown that the vibratory hub pitch moment of a lift-offset coaxial rotor is the most dominant component for both the longitudinal and vertical vibration responses at four specified locations of the airframe.

• 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.