Chul Yong Yun

DESIGN AND PERFORMANCE TESTS OF CYCLOIDAL PROPULSION SYSTEMS

The cycloidal propeller, which can be described as a horizontal rotary wing, offers powerful thrust levels, and a unique ability to change the direction of the thrust almost instantly. In this work, cycloidal propulsion system was designed and implemented with sinusoidal low pitch system to investigate the fundamental characteristics of hovering states. Before experimental study, computational analysis was made in commercial CFD tool, CD Adopco/StarCD. This work gives schematic view of flow field around rotor. And it predicts the load variation on a blade with respect to revolution and the total thrust from cycloidal rotor, at specific condition. CFD analysis also makes it possible to check the camber effect. The propulsion system was built up with sinusoidal low pitch control mechanism. Thrust, power and efficiency were measured for various conditions of parameter setting. It was accomplished by designing the equipment which can change the rotational radius, number of blade, phase angle of eccentricity and amplitude of eccentricity.

Improvement of aeroelastic stability of hingeless helicopter rotor blade by passive piezoelectric damping

To augment weakly damped lag mode stability of a hingeless helicopter rotor blade in hover, piezoelectric shunt with a resistor and an inductor circuits for passive damping has been studied. A shunted piezoceramics bonded to a flexure of rotor blade converts mechanical strain energy to electrical charge energy which is dissipated through the resistor in the R-L series shunt circuit. Because the fundamental lag mode frequency of a soft-in-plane hingeless helicopter rotor blade is generally about 0.7/rev, the design frequency of the blade system with flexure sets to be so. Experimentally, the measured lag mode frequency is 0.7227/rev under the short circuit condition. Therefore the suppression mode of this passive damping vibration absorber is adjusted to 0.7227/rev. As a result of damping enhancement using passive control, the passive damper which consists of a piezoelectric material and shunt circuits has a stabilizing effect on inherently weakly damped lag mode of the rotor blades, at the optimum tuning and resistor condition.

Thrust Control Mechanism of VTOL UAV Cyclocopter with Cycloidal Blades System

This study describes the control mechanism of a VTOL UAV cyclocopter. The cycloidal blades system (CBS), which is a thrust system of cyclocopter is composed of several blades rotating about a horizontal axis. To generate the required thrust, the pitch angles of the blades are periodically oscillated by a pitch control mechanism. And it can change both the magnitude and the direction of the thrust almost instantly. For the thrust control mechanism of the cyclocopter, the mathematical model is derived, and the control forces to control the magnitude and direction of the thrust are determined. In addition, it is designed and developed by radio-controlled actuators.

Stability augmentation of helicopter rotor blades using passive damping of shape memory alloys

In this study, shape memory alloy damper with characteristics of pseudoelastic hysteresis for helicopter rotor blades are investigated. SMAs can be available in damping augmentation of vibrating structures. SMAs show large hysteresis in the process of pseudoelastic austenite-martensite phase transformation which takes place while subjected to loading above the austenite finish temperature. Since SMAs display pseudoelastic hysteresis behavior over large strain ranges, a significant amount of energy dissipation is possible. A damper can be designed with SMA wires prestressed to a baseline level somewhere in the middle of the pseudoelastic stress range. An experimental study of the effects of pre-strain and cyclic strain amplitude as well as frequency on the damping behavior of pseudoelastic shape memory alloy wires are performed. The effects of the shape memory alloy damper on aeroelastic and ground resonance stability of helicopter are studied. In aeroelastic stability, the dynamic characteristics of blades related to pitch angle and the amplitude of lag motion for the rotor equipped with SMA damper were examined. The performance of SMA damper on ground resonance instability are presented through the frequencies and modal damping with respect to rotating speed.

Passive suppression of nonlinear panel flutter using piezoelectric materials with resonant circuit

In this study, a passive suppression scheme for nonlinear flutter problem of composite panel, which is believed to be more reliable than the active control methods in practical operations, is proposed. This scheme utilizes a piezoelectric inductor-resistor series shunt circuit. The finite element equations of motion for an electromechanically coupled system is derived by applying the Hamilton’s principle. The aerodynamic theory adopted for the present study is based on the quasi-steady piston theory, and von-Karrnan nonlinear strain-displacement relation is also applied. The passive suppression results for nonlinear panel flutter are obtained in the time domain using the Newmark-β method. To achieve the best damping effect, optimal share and location of the piezoceramic (PZT) patches are determined by using genetic algorithms. The effects of passive suppression are investigated by employing in turn one shunt circuit and two independent shunt circuits. Feasibility studies show that two independent inductor-resistor shunt circuits suppresses flutter more effectively than a single shunt circuit. The results clearly demonstrate that the passive damping scheme that uses piezoelectric shunt circuit can effectively attenuate the flutter.

Performance Comparison between Piezoelectric and Elastomeric Lag Dampers on Ground Resonance Stability of Helicopter

In this study, a piezoelectric lag damper using damping characteristics in piezoelectric ceramics is proposed to alleviate ground resonance instability. The piezoelectric passive damper consists of piezoelectric elements and electrical circuits such as resistors and inductors in a series. By bonding the piezoelectric ceramics to the rotor flexures, piezoelectric strain energy is converted to electrical energy and dissipated through an electrical network. To verify the effect of the piezoelectric damper on rotating blades, experiments for the aeroelastic stability of the rotor blades were carried out. The experiment results for rotor blades with the piezoelectric damper show that the piezoelectric damper has a strong stabilizing effect on the inherently weakly lag-mode damping of the blades. The performance of piezoelectric and elastomeric lag dampers on ground resonance instability are compared and modal frequency and modal damping with respect to rotating speed are shown.

Development of Smart Missile Fins with Active Spoiler

For conventional missiles, electric or hydraulic actuators are mounted inside the missile fuselage to activate the aerodynamic control surfaces. These internally mounted actuators occupy considerable volume which otherwise can be used for payload or additional fuel. Reducing the size of the internal actuators and hence lowering the total actuator weight may improve the overall performance of missile significantly. The goal of this research is to develop a light-weight, low cost smart missile fin capable of surviving the supersonic operating environment while providing necessary performance comparable to existing missile fins. In this study, in an alternative to facilitate realistic design concepts and to generate enough actuation forces required for missile controls, smart fins with trailing-edge-mounted retractable wedge are considered. The retractable wedge stretches in or out appropriately to decrease the applied pitching moment of the missile fin. For the theoretical calculation, a commercial CFD software package is used to obtain the forces and the moments generated by the fin with retractable wedge. The piezoelectric actuation mechanism that is applicable to the wedge type actuator is also investigated.

Comparisons of Rotor Performance and Noise between Candidate Light Civil Helicopters

The rotor blade of helicopter is the core component determining helicopter performance and requiring low noise and low vibration because the blade becomes the major source of noise during flight. The performance analysis of candidates rotor blades is very critical because LCH(Light Civil Helicopter) will be developed parallel with LAH(Light Armed Helicopter) as an international upgrade program based on the existing platform of foreign civil helicopter. This research was aimed to recognize the performance of the candidates rotor blades compared with the newly developed foreign rotor blades and to investigate the feasibility about developing korea unique shape rotor blades by analysis the rotor performance and noise. The result of this research can be used for the target performance index during negotiation with foreign helicopter company and developing korea unique shape rotor blades.

Optimal design of a piezoelectric passive damper for vibrating plates

In this paper, an efficient piezoelectric passive damper is newly devised to suppress the multi-mode vibration of plates. To construct the passive damper, the piezoelectric materials are utilized as energy transformer, which can transform the mechanical energy to electrical energy. To dissipate the electrical energy transformed from mechanical energy, multiple resonant shunted piezoelectric circuits are applied. The dynamic governing equations of a coupled electro-mechanical piezoelectric with multiple piezoelectric patches and multiple resonant shunted circuits is derived and solved for the one edge clamped plate. The equations of motion of the piezoelectrics and shunted circuits as well as the plate are discretized by finite element method to estimate more exactly the effectiveness of the piezoelectric passive damper. The method to find the optimal location of a piezoelectric is presented to maximize effectiveness for desired modes. The electro-mechanical coupling term becomes important parameter to select the optimal location.

Smart missile fins with active spoiler using a piezoelectric actuator

In this work, smart missile fins with trailing-edge-mounted retractable wedge are investigated. The wedge stretches back or forth in the chordwise direction in a means to reduce the applied pitching moment acting on the missile fins. An actuator system, which is composed of a one-way clutch bearing, driving shaft with thread and sliding nut and a piezo-bimorph beam, has been built and tested to verify the concept of the actuator. This actuator is designed to translate the rotational motion of the shaft into the linear motion of the sliding nut to generate a desired stroke. When a voltage signal is applied at a given frequency to the piezo-element, it will bend up and down. This bending action induces an angular input to the shaft, which is then rectified with the clutch bearing to the rotational output of the shaft. Preliminary tests showed that the proposed actuator system can be very effective in generating large stroke output with relatively small voltage inputs: Nearly 19mm of actuator displacement was obtained under an input voltage of 75 Vrms at a frequency level of 700 Hz. A series of experimental tests as well as CFD calculations for missile aerodynamics have been performed to investigate the effectiveness of the actuator.