Hwan-Kee Cho

Store Separation Analysis of a Fighter Aircraft\'s External Fuel Tank

The repetitive vibrating action of an aerodynamic load causes an external fuel tank’s horizontal fin to experience a shorter life cycle than its originally predicted one. Store separation analysis is needed to redesign the fin of an external fuel tank. In this research, free-drop tests were conducted using 15% scaled models in a subsonic wind tunnel in order to analyze the store separation characteristics of an external fuel tank. The store separation trajectory based on grid tests was also obtained to verify the results of the free-drop tests. The results acquired from the free-drop tests correlated well with the grid tests in regards to the trajectories and behavior of the stores separated from the aircraft. This agreement was especially noted in the early stages of the store separation.

Experimental Study for the Safety Analysis of an External Store Separation from Fighter Aircraft

The prediction of the separation trajectories of external stores carried by military aircraft is an important task in the area of aircraft design having the objective to define the operational, release envelopes. This paper presents the results obtained for safe store separation from a fighter aircraft by experimental methods in the subsonic wind tunnel. The problems associated with separation of external stores can be studied by the use of several wind-tunnel test techniques. Attention is given the two most useful techniques: 1) dynamically scaled drop-model testing, 2) grid testing. A description of each method is given and data obtained are shown to validate the similarity within acceptable limits.

A Wind Tunnel Study on the Static Stability Characteristics of Light Sport Aircraft

During the conceptual design phase of a light sport aircraft, the wind tunnel tests were conducted to investigate the static stability of newly-designed configuration. The 1/5 scale-down wind tunnel model consisted of fuselage, main wing, vertical tail and horizontal tail. The main wing and tails were able to be attached or detached from the fuselage. The aerodynamic forces and moments acting on the 6 different configurations compounding each component were measured by using the internal balance system and their static stability derivatives were derived. With these experimental data, the baseline lift and drag characteristics as well as the effects of each component to the longitudinal, directional and lateral static stability were quantitatively analyzed.

Analysis of the Longitudinal Static Stability and the Drop Trajectory of a Fighter Aircraft`s External Fuel Tank

The present work is to analyze the longitudinal static stability and the drop trajectory of fighter aircrafts external fuel tank, of which horizontal fin is modified as the 20% scale down size compared with the original one. The analytical results to the pitching stability of external fuel tank using a thin airfoils aerodynamic force data show the corresponding tendency to results of wind tunnel experiment. Results of trajectory simulation by the 6 degree of freedom equations of motion, comparing with drop trajectories of wind tunnel experiment, are shown that aircrafts attitude affects strongly on horizontal movement but not on the vertical movement. Those results give the reliability to aircraft safety when the external fuel tank with the 20% reduced horizontal fins is released from aircraft based on the flight manual.

Aerodynamic Interference Effect of Aircraft Wing Tip Vortex in Formation Flight

Experimental study was conducted to investigate aerodynamic interference effect of wing tip vortex in formation flight of high speed aircraft. In formation flight, wing tip vortex produced by leading aircraft can affect on the aerodynamic characteristics of trailing aircraft. The interference effect of flow is varied with distances between wing tips of leading and trailing aircraft. It is confirmed, in this study, that the interference of wing tip vortex generated from the leading aircraft makes the aerodynamic forces and moments of the trailing aircraft with the vertical or horizontal positions of the trailing aircraft. Especially, the lift coefficients of trailing aircraft were highly increased at y/b

Application of Wind Tunnel Testing on the Dynamic Stability Derivatives of a Rocket Model

This paper described the wind tunnel testing apparatus and technique to acquire the dynamic stability derivatives of large slenderness ratio air vehicle such as the guided missiles or rockets. There have been few difficulties in conducting wind tunnel testing for slender long rocket due to the size limitation of the test section size and the installation of oscillation equipments. In this study, the dynamic stability balance was used as the wind tunnel technique for obtaining the dynamic stability derivatives. Through the wind tunnel testing, the experimental apparatus for slender air vehicle`s oscillation is established. The measured data showed that it is possible to acquire the dynamic stability derivatives of large slenderness ratio rocket, properly.

Changing Effect in Aerodynamic Characteristics of a Captive Body Separated from Aircraft

The aerodynamic characteristics of a separated captive body in flow field around aircraft are studied to observe aerodynamic stability for safe separation from aircraft. Since the captive body separated from aircraft is initially exposed to unsteady flow pattern, the change of aerodynamic forces and moments should be measured to analyze how the flow pattern affects on the captive body at the vicinity of aircraft. Aerodynamic forces and moments of the separated captive body are measured at selected positions along predictable dropping trajectories. The measuring trajectories, generated by the free drop test of the dropping model in the wind tunnel, are consisted of 9 possible lines by free dropped trajectories. Experimental results show that the aerodynamic forces and moments are significantly varied with the distance between the captive body and aircraft. In conclusion, the change of aerodynamic characteristics within flow field around aircraft should be considered to simulate trajectories of the separated captive body from aircraft.

Experimental Study on the Static Stability of a Sounding Rocket Model in the Supersonic Wind Tunnel

ABSTRACT In this work, experiments on hybrid sounding rocket were conducted to investigate the aerodynamic characteristics and analyze longitudinal static stability. Tests were performed on 1/10 scale models of sounding rocket through Mach number ranging from 1.75 to 2.5 and for angle of attack from 0° to 6°. Aerodynamic forces and moments were measured by means of a 4component internal balance. With measured forces and moments, static stability characteristics of rocket were calculated. Tests were made for three models with different length to determine the effect of body length. The visualization of shock waves was carried out by Schlieren optical system to observe variations of shock waves with Mach number and angle of attack. 초 록 본 연구에서는 하이브리드 과학로켓의 공력특성을 파악하고 정적 세로 안정성에 대한 판단을 하기 위해서 초음속 풍동실험을 하였다. 과학로켓의 10% 축소모델에 대해서 마하수 1.75~2.5, 받음각 0°~6°의 조건에서 실험을 수행하였으며, 4분력 내장형 밸런스를 사용하여 실험모델의 공력과 모멘트를 측정하였다. 측정된 자료를 바탕으로 로켓의 안정성을 판단하였으며, 로켓의 길이효과를 분석하기 위하여 길이가 다른 3개의 모델에 대하여 실험을 수행하였다. 또한, 쉴리렌 광학장치를 이용하여 초음속 비행 시 발생하는 충격파를 가시화하고 속도 및 받음각 변화에 따른 충격파의 변화를 관찰하였다.Key Words : Hybrid Sounding Rocket(하이브리드 과학로켓), 4Component Internal Balance(4분력 내장형 밸런스), Shock Wave(충격파), Schlieren Optical System(쉴리렌 광학장치)

Measurements of the Pitch Dynamic Stability Derivatives of a Standard Dynamics Model Using a Forced Vibration Technique

An experimental study was carried out in order to measure the pitch dynamic stability derivatives of a standard dynamics model in a low-speed wind tunnel. When a trigger signal is generated, the aircraft model starts oscillation with constant amplitudes and frequencies provided by DC electrical servomotor. The measured data are simultaneously recorded on a data recorder for 25 cycles of the model oscillation. The Phase shift needed to compute the dynamic stability derivatives is determined by calculating differences between the peak values of the input and output signals from the dynamic stability balance. Stabilator effects on the stability derivatives were also investigated with deflection angles. Although the driving apparatus and experimental equipments manufactured creatively for this study are different from other experiments, the variational trend of dynamic stability derivatives with the angle of attack is in a good accordance with the results of TPI, NAE, and FFA.