• Title/Summary/Keyword: high-angle-of-attack flight

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A Numerical Study on Unsteady Flowfield around a NACA 0021 Airfoil at High Angles of Attack (고영각 NACA 0021 익형 주위의 비정상 유동장에 대한 수치해석적 연구)

  • Kim, Sang Dug
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.28 no.2
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    • pp.12-17
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    • 2020
  • Even though the benefit of flight at high angle-of-attack is to be able to reduce the speed of flight and maneuvers in complex flight environment, the flight at high angle-of-attack, however, is easy to be in stall which is characterized by sever unsteady flow separation over an airfoil. Current unsteady numerical analysis using DES was conducted to predict the aerodynamic characteristics of a NACA 0021 airfoil at high angle-of-attack conditions. And this provides the comparison with the steady numerical one with the typical turbulence models. The unsteady calculation by DES is appropriate in terms of predicting the aerodynamic performance of NACA 0021 airfoil at high angle-of-attack conditions.

A Numerical Study on the Flowfield around a NACA 0021 Airfoil at Angles of Attack (NACA 0021 익형 유동장의 수치해석적 연구)

  • Kim, Sang-Dug
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.24 no.4
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    • pp.20-25
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    • 2016
  • A primary benefit of flight at high angle-of-attack conditions is to be able to reduce the speed of flight and maneuvers, which can enhance the capability of sensing and obstacle avoidance for a small UAV. The flight at high angle-of-attack conditions, however, is easy to be beyond stall which is characterized by substantial flow separation over an airfoil. Current numerical analysis was conducted on the capabilities of three representative turbulence models to predict the aerodynamic characteristics of a typical airfoil at angle-of-attack conditions. The investigation shows that these turbulence models provide good comparison with experimental data for attached flow at moderate angle-of-attack conditions. Calculation by current turbulence models are, however, not appropriate at high angle-of-attack conditions with flow separation.

A Design of Fuzzy Logic Controllers for High-Angle-of-Attack Flight Control of Aircraft Using Adaptive Evolutionary Algorithms (적응진화 알고리즘을 이용한 항공기의 고공격각 비행 제어를 위한 퍼지 제어기 설계)

  • Won, Taep-Hyun;Hwang, Gi-Hyun;Park, June-Ho;Lee, Man-Hyung
    • Journal of Institute of Control, Robotics and Systems
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    • v.6 no.11
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    • pp.995-1002
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    • 2000
  • In this paper, fuzzy logic controllers(FLC) are designed for control of flight. For tuning FLC, we used adaptive evolutionary algorithms(AEA) which uses a genetic algorithm(GA) and an evolution strategy (ES) in an adaptive manner in order to take merits of two different evolutionary computations. We used AEA to search for optimal settings of the membership functions shape and gains of the inputs and outputs of FLC. Finally, the proposed controller is applied to the high-angle-of-attack flight system for a supermaneuverable version of the f-18 aircraft and compares with other methods.

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Design of FLC for High-Angle-of-Attack Flight Using Adaptive Evolutionary Algorithm

  • Won, Tae-Hyun;Hwang, Gi-Hyun;Park, June-Ho;Lee, Man-Hyung
    • Journal of Mechanical Science and Technology
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    • v.17 no.2
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    • pp.187-196
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    • 2003
  • In this paper, a new methodology of evolutionary computations - An Adaptive Evolutionary Algorithm (AEA) is proposed. AEA uses a genetic algorithm (GA) and an evolution strategy (ES) in an adaptive manner in order to take merits of two different evolutionary computations : global search capability of GA and local search capability of ES. In the reproduction procedure, the proportions of the population by GA and ES are adaptively modulated according to the fitness. AEA is used to. designing fuzzy logic controller (FLC) for a high-angle-of-attack flight system for a super-maneuverable version of F-18 aircraft. AEA is used to determine the membership functions and scaling factors of an FLC. The computer simulation results show that the FLC has met both robustness and performance requirements.

Study on Aerodynamic Characteristics of a Launch Vehicle with Mach Number, Angle of Attack and Nozzle Effect at Initial Stage (발사초기 단계에서 발사체의 마하수, 받음각 및 노즐 효과에 따른 공력특성 연구)

  • Jeong, Taegeon;Kim, Sungcho;Choi, Jongwook
    • Journal of the Korean Society of Visualization
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    • v.17 no.1
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    • pp.34-42
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    • 2019
  • Aerodynamic characteristics for a launch vehicle are numerically analyzed with various conditions. The local drag coefficients are high at the nose of the launch vehicle in subsonic region and on the main body in supersonic region because of the induced drag and the wave drag, respectively. The drag coefficients show the similar trend with the angle of attack except zero degree. However, the more the angle of attack increases, the more dependent on the Mach number the lift coefficient is. The body rotation for the flight stability destroys the vortex pair formed above the body opposite to the flight direction, so the flow fields are more or less complicated. The drag coefficient of the launch vehicle at sea level is about three times larger than that at altitude 7.2 km. And the thrust jet at the nozzle causes to reduce the drag coefficient compared with the jetless transonic flight.

A Study on Longitudinal Phugoid Mode Affected by Application of Nonlinear Control Laws

  • Kim, Chong-Sup;Hur, Gi-Bong;Kim, Seung-Jun
    • International Journal of Aeronautical and Space Sciences
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    • v.8 no.1
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    • pp.21-31
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    • 2007
  • Relaxed Static Stability (RSS) concept has been applied to improve aerodynamic performance of modern version supersonic jet fighter aircraft. The T-50 advanced supersonic trainer employs the RSS concept in order to improve the aerodynamic performance. And the flight control system stabilizes the unstable aircraft and provides adequate handling qualities. The T-50 longitudinal control laws employ a proportional-plus-integral type controller based on a dynamic inversion method. The longitudinal dynamic modes consist of short period with high frequency and phugoid mode with low frequency. The design goal of longitudinal control law is optimization of short period damping ratio and frequency using Lower Order Equivalent System (LOES) complying the requirement of MIL-F-8785C. This paper addresses phugoid mode characteristics such as damping ratio and natural frequency that is affected by the nonlinear control laws such as angle of attack limiter, auto pitch attitude command system and autopilot of pitch attitude hold.

Calculating Dynamic Derivatives of Flight Vehicle with New Engineering Strategies

  • Mi, Baigang;Zhan, Hao;Chen, Baibing
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.2
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    • pp.175-185
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    • 2017
  • This paper presents new differential methods for computing the combined and single dynamic stability derivatives of flight vehicle. Based on rigid dynamic mesh technique, the combined dynamic stability derivative can be achieved by imposing the aircraft pitching to the same angle of attack with two different pitching angular velocities and also translating it to the same additional angle of attack with two different rates of angle of attack. As a result, the acceleration derivative is identified. Moreover, the rotating reference frame is adopted to calculate the rotary derivatives when simulating the steady pull-up with different pitching angular velocities. Two configurations, the Hyper Ballistic Shape (HBS) and Finner missile model, are considered as evaluations and results of all the cases agree well with reference or experiment data. Compared to traditional ones, the new differential methods are of high efficiency and accuracy, and potential to be extended to the simulation of combined and single stability derivatives of directional and lateral.

The Numerical Analysis of Asymmetric Vortices around the Slender body at High Angle of Attack Supersonic Flow (고받음각 초음속 유동에서의 세장형 몸체 주변에 발생하는 비대칭와류에 대한 수치적 연구)

  • Jeon, Young-Jin;Ji, Young-Moo;Kim, Ki-Su;Seo, Hyung-Seok;Byun, Yung-Hwan;Lee, Jae-Woo
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2007.04a
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    • pp.335-338
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    • 2007
  • In the case of an antiaircraft missile, high angle of attack flight capability is required to get the agile maneuverability in a supersonic flow. Even through a symmetric slender body does not have side slip, asymmetric vortex is generated at high angle of attack conditions. This asymmetric vortex produces unnecessary side force and yawing moment; hence, these effects deteriorate directional stability. In this study, the numerical analysis of asymmetric vortices around the slender body was conducted at high angle of attack supersonic flow. In order to simulate the vortices, a bump is installed on the nose of the slender body. As a result of the numerical analysis, the asymmetric vortices around the slender body could be simulated.

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FUZZY CONTROL LAW OF HIGHLY MANEUVERABLE HIGH PERFORMANCE AIRCRAFT

  • Sul Cho;Park, Rai-Woong;Nam, Sae-Kyu;Lee, Man-Hyung
    • 제어로봇시스템학회:학술대회논문집
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    • 1998.10a
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    • pp.205-209
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    • 1998
  • A synthesis of fuzzy variable structure control is proposed to design a high-angle-of-attack flight system for a modification version of the F-18 aircraft. The knowledge of the proportional, integral, and derivative control is combined into the fuzzy control that addresses both the highly nonlinear aerodynamic characteristics of elevators and the control limit of thrust vectoring nozzles. A simple gain scheduling method with multi-layered fuzzy rules is adopted to obtain an appropriate blend of elevator and thrust vectoring commands in the wide operating range. Improving the computational efficiency, an accelerated kernel for on-line fuzzy reasoning is also proposed. The resulting control system achieves the good flying quantities during a high-angle-of- attack excursion. Thus the fuzzy logic can afford the control engineer a flexible means of deriving effective control laws in the nonlinear flight regime.

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A Study on Control Law Augmentation in order to Improve Aircraft Controllability and Stability in High Angle of Attack (고받음각에서 조종성능 및 안정성 증강을 위한 제어법칙에 관한 연구)

  • Kim, Chong-Sup;Hwang, Byung-Moon;Lee, Dong-Gyu
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.10
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    • pp.60-67
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    • 2005
  • Modern version of supersonic jet fighter aircraft must have guaranteed appropriate controllability and stability in HAoA(high angle of attack). Limit value of aircraft entering into the deep stall in HAoA is related to aircraft configuration design. But, In order to guarantee the aircraft's safety in HAoA, control law for HAoA region implemented in digital Fly-By-Wire flight control system of supersonic jet fighter. The AoA limiter is designed for positive HAoA in longitudinal control law. But, aircraft departure during aggressive negative pitch maneuver such as push over in departure resistance flight test. Therefore negative AoA limiter is needed in longitudinal control law. Result of T-50 flight test show that the AoA is exceed the limit value during aggressive positive pitch maneuver in pull up of power approach mode. In this paper, the AoA limit control law in positive and negative AoA was proposed in order to improve aircraft controllability and stability.