Investigation of Lift Offset on Flight Dynamics Characteristics for Coaxial Compound Helicopters

Abstract

The coaxial compound helicopters adopt the Lift-Offset (LOS) strategy to improve the rotor performance in high speed flight, which influences the flight dynamics characteristics of the vehicle. Thus, a flight dynamics model and an inverse simulation method are developed to assess the effect of LOS on this helicopter. The trim results demonstrate that LOS reduces the collective and the longitudinal cyclic pitch across the flight range, and it also adds the control input of the propeller collective in hover and lower speed forward flight. LOS control strategy reduces the power consumption and increases the maximum flight speed. Also, LOS control strategy is affected by the gross weight. Furthermore, the stability is dependent on LOS due to its effect on the rotor efficiency and flapping motion. From the controllability results, LOS brings about severe coupling between the rolling moment and the collective differential input. Lastly, the Pull-up & Pushover and the Transient Turn Mission-Task-Elements (MTEs) with different LOS control strategies are assessed with inverse simulation. The results show that a reasonable LOS control strategy could not only reduce the power consumption but also have a positive influence on the oscillation in control inputs during the manoeuvre.

A novel solution methodology for longitudinal flight characterization of a Flying-Wing Micro Aerial Vehicle

“…7,8 It is well established that rotary wings have problems of stability at low speeds whereas flying-wing microaerial vehicles (FWMAVs) are longitudinally stable and have high endurance but lack hovering capability. 9,10 This research is focused on FWMAVs only which is of fixed-wing type and, therefore, other types of MAVs will not be discussed. The flying-wing microaerial vehicle is a small-sized flying-wing aircraft.…”

“…Aerodynamic derivatives were plugged into equations ( 16) to (21) to get aerodynamic forces, moments coefficients in the wind axes (forces), and stability axes (moment equations). These coefficients were multiplied with dynamic pressure, characteristics length, and reference surface area to get aerodynamic forces, and moments which were inserted into equations of motion, equations ( 6), (8), and (10). For trimmed flight conditions, three longitudinal equations were equated to zero ð _ U ¼ _ W ¼ _ Q ¼ 0Þ and were solved analytically for three unknown parameters (trimmed elevator deflection δ etrim , trimmed advance ratio required J trim , and trimmed angle of attack α trim ).…”

“…7,8 It is well established that rotary wings have problems of stability at low speeds whereas flying-wing microaerial vehicles (FWMAVs) are longitudinally stable and have high endurance but lack hovering capability. 9,10…”

A hybrid trim strategy for coaxial compound helicopter

“…This LOS strategy is designed to improve the flight dynamics characteristics and performance across the flight range and is also employed in the literature. 5,6,8,14,9,21,22 For the trim problem, the rudder deflection angle could be set to 0. The aerodynamic efficiency of the rudder begins to be predominant at medium and high speeds to control the yaw moment and replace the main rotor differential.…”

High-efficiency hybrid trim method for CFD simulation of rigid coaxial rotor

“…Rigid coaxial rotor compound helicopter shows substantial advantages in high-speed flight and aerodynamic performance. 1 The representative is the X2 Technology TM Demonstrator aircraft 2 developed by Sikorsky Aircraft. This configuration has two coaxial and contra-rotating rotors, and the torque can be balanced.…”