• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.263-267
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• 2008

In this work the realistic install performance analysis of a helicopter was performed together with power extraction enabling to operate auxiliary system as well as intake pressure loss, loss due to bleed air, etc. which must be considered in practical propulsion system's performance modelling to be installed to the airframe. The pressure loss occurring in intake was estimated from the intake performance map with relationships of Mach Number and pressure loss. In order to evaluate the proposed installed performance model, the experimental data for comparison must be needed when mounted in propulsion system. However because of lack of accessibility to such real data at the moment, the alternative way was made through comparison that the analysis results by the proposed model were compared with a wellknown commercial program GASTURB's analysis results. The validity of the proposed installed performance model was consequently confirmed because its average deferences from the GASTURB's results were within 0.5%.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.1
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• pp.51-56
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• 2008

In this work the realistic install performance analysis of a helicopter was performed together with power extraction enabling to operate auxiliary system as well as intake pressure loss, loss due to bleed air, etc. which must be considered in practical propulsion system's performance modelling to be installed to the airframe. The pressure loss occurring in intake was estimated from the intake performance map with relationships of Mach Number and pressure loss. In order to evaluate the proposed installed performance model, the experimental data for comparison must be needed when mounted in propulsion system. However because of lack of accessibility to such real data at the moment, the alternative way was made through comparison that the analysis results by the proposed model were compared with a wellknown commercial program GASTURB's analysis results. The validity of the proposed installed performance model was consequently confirmed because its average deferences from the GASTURB's results were within 0.5%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.6
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• pp.981-987
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• 1997

Modern helicopter rotor blades with non-homogeneous cross section composed of anisotropic material rquire highly sophisticated structural analysis. Variation in cross section geometry makes this task of analysis more complicated. Since rotor blades generally are much longer than their lateral dimensions, one-dimensional models seem feasible, at least from a computational point of view. Therefore determination of the principal coordinate system is very important to remove the structural coupling for one-dimensional beam modelling. In this study, shear center, and principal direction. The method will be verified by comparing the results with confirmed experimental results.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.2
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• pp.23-33
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• 2009

The inherent aeromechanical complexity of a rotor system necessitated the comprehensive analysis code for helicopter rotor system. In the present study, an aerodynamic analysis module has been developed as a part of rotorcraft comprehensive program. Aerodynamic analysis module is largely classified into airload calculation routine and inflow analysis routine. For airload calculation, quasi-steady analysis model is employed based on the blade element method with the correction of unsteady aerodynamic effects. In order to take unsteady effects - body motion effects and dynamic stall - into account, aerodynamic coefficients are corrected by considering Leishman-Beddoes's unsteady model. Various inflow models and vortex wake models are implemented in the aerodynamic module to consider wake induced inflow. Specifically, 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 induced inflow distribution and sectional normal force coefficients of AH-1G. In order to validate unsteady aerodynamic model, 2-D unsteady model for NACA0012 airfoil is validated against aerodynamic coefficients of McAlister's experimental data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.6
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• pp.691-698
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• 2014

This paper describes the manufacturing processes for a flexbeam and torque tube made of composite materials, along with the procedures for testing their basic properties. A flexbeam and torque tube can be considered to be key structural components of a bearingless rotor hub system. A hinge offset effect can be realized by a large elastic deformation and twist of the flexbeam, and the blade pitch control forces are transferred by the rotation of the torque tube. The basic property tests included bending and twist tests to determine the flap stiffness, lag stiffness, and torsion stiffness of the flexbeam, torque tube, and blade, and these tests were performed prior to starting the whirl tower test. In addition, the estimated results were compared with experimental data, and the calculations were found to be a good match for the analysis results and had a similar tendency. Through these results, we could confirm that a flexbeam and torque tube made of composite materials satisfied the structural stiffness requirements.

• The KSFM Journal of Fluid Machinery
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• v.4 no.1 s.10
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• pp.7-13
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• 2001

In developing a multistage compressor, the stage matching is one of the critical design issues. The mismatching can be often observed even if each stage has been proven good and then used as part of a compression system. A good matching among the stages can be achieved by changing various design parameters (i.e., passage cross sectional areas, blades angles, stagger angles, curvature, solidity, etc.). Therefore, designers need to find out what parameters must be changed and how much. In this study, a method to search the design parameters for optimum stage matching has been used based on an 1-D mathematical model of a compressor, which uses the data obtained from the preliminary test to identify the design parameters. This methodology is applied with a two-stage axial compressor, which was originally designed for a helicopter gas turbine engine. After identifying design parameters using preliminary test data, an optimization process has been employed to achieve the best matching between the stages (i.e., maximum efficiency of the compressor at its operation modes within a given range of the rotor speed under given restrictions for required stall margins and mass flow). 3-D flow calculations have been performed to confirm the usefulness of the corrections based on the 1-D mathematical model. Calculational results agree well with the experimental data in view of the performance characteristics. Some promising results were produced through the methodology proposed in this paper in conjunction with flow calculations.

• Transactions of the KSME C: Technology and Education
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• v.2 no.2
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• pp.113-124
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• 2014

In developing an aircraft, configuration determination and requirement proofing depend on flight test results. Since the flight tests require much time and high cost, systematic flight test planning and analysis are needed to reduce cost and development time. This paper presents a desirability function approach to present an integrative measure of vibration levels at important positions and suggests a fractional factorial design which is one of the experimental design methods to help perform systematic flight tests. A method to perform flight tests in stages is also suggested to further reduce the number of flight tests.

• Journal of Advanced Navigation Technology
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• v.3 no.2
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• pp.108-119
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• 1999

In recent, there has been remarkable progress in the field of GPS applications. In a few years, an appreciable number of aircraft will adopt GPS as a landing guidance system because GPS is more economic, more reliable and more accurate than any other aviation systems. In this respect, we have performed several helicopter landing flight tests based on the real-time DGPS system made in SNUGL (Seoul National University GPS Laboratory). From the experimental results, we found several problems Which should be fixed to adopt DGPS as a aircraft landing guidance system. In this paper, we will introduce the problems found in tests and also suggest modifications to solve the problems. Our modifications can be classified into three parts. The first is about the attitude determination with single GPS antenna. The second deals with the cockpit display module. The display was devised to integrate the Instrument Landing System(ILS) with tunnel-the-sky using virtual reality. With the display, pilot can achieve more safe landings. The last part is the digital map. We inserted digital map into our system and put direction indicator on the map using position information from GPS. It is very useful for pilot to find airports even in bad weather. Using the newly designed DGPS landing system, we conducted flight test at Kimhae International Airport, Pusan, Korea. It was successful! Our system can also satisfy Category-I criterion for aircraft landing approach and determine attitude angle with a high level of reliability. It is supported by video materials.

• 제어로봇시스템학회:학술대회논문집
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• 1999.10a
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• pp.9-12
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• 1999

This paper presents the development of a control architecture for the autonomous underwater vehicle (AUV) with VARIVEC (variable vector) propeller. Moreover this paper also describes the new technique of controlling the servomotors using the Field Programmable Gate Array (FPGA). The AUVs are being currently used fur various work assignments. For the daily measuring task, conventional AUV are too large and too heavy. A small AUV will be necessary for efficient exploration and investigation of a wide range of a sea. AUVs are in the phase of research and development at present and there are still many problems to be solved such as power resources and underwater data transmission. Further, another important task is to make them smaller and lighter for excellent maneuverability and low power. Our goal is to develop a compact and light AUV having the intelligent capabilities. We employed the VARIVEC propeller system utilizing the radio control helicopter elements, which are swash plate and DC servomotors. The VARIVEC propeller can generate six components including thrust, lateral force and moment by changing periodically the blade angle of the propeller during one revolution. It is possible to reduce the number of propellers, mechanism and hence power sources. Our control tests were carried out in an anechoic tank which suppress the reflecting effects of the wall surface. We tested the developed AUV with required performance. Experimental results indicate the effectiveness of our approach. Control of VARIVEC propeller was realized without any difficulty.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.98-105
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• 2005

This paper presents the result of the aeroelastic stability test of the small-scaled hingeless hub system with composite paddle blades in hover and forward flight conditions. Excitation tests of hingeless hub system installed in GSRTS(General Small-scale Rotor Test System) at KARI(Korea Aerospace Research Institute) were carried out to get lead-lag damping ratio of blades with flexures as hub flexure. MBA(Moving Block Analysis) technique was used for the estimation of lead-lag damping ratio. First, blades with metal flexures, then with composite flexures of the same dynamic properties of rotor system as metal one were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Composite flexures were found to have better damping characteristics over metal ones in the non-rotating vibration test, and it was confirmed that the use of composite flexures would give observable improvement in aeroelastic stability compared to metal ones in all test conditions.