Soo Hyung Park

In supersonic and hypersonic wind tunnels, large transient loads generated during tunnel start-up and shut-down can significantly exceed steady-flow loads, leading to balance failure and degradation of measurement accuracy. Under such conditions, reliable force measurement requires a balance that combines high structural stiffness with sufficient sensing capability. This paper presents an experimental investigation of the feasibility of an internal axial-force balance employing semiconductor strain gauges in an impulse-type Ludwieg tube. Three axial-force balances with flexure thicknesses of 1.0, 1.5, and 2.0 mm were fabricated using metal-foil strain gauges, and an additional balance with a 2.0 mm flexure was instrumented with semiconductor strain gauges to enable micro-strain measurement in a high-stiffness structure. To reduce zero-offset drift associated with the high temperature sensitivity of semiconductor strain gauges, a full Wheatstone bridge with an additional voltage-divider circuit was implemented. The balances were calibrated and tested using the HB-2 (Hemispherical Body 2) standard model at Mach 6 with total pressures of 30, 40, and 50 bar, and the measured axial-force coefficients were compared with Missile DATCOM (Missile Data Compendium) predictions. The metal-foil strain-gauge balances exhibited increased measurement scatter and deviation from the predictions with increasing total pressure, particularly for the thickest flexure configuration, for which stable repeatability was not achieved. In contrast, the semiconductor strain-gauge balance demonstrated consistent agreement with the Missile DATCOM predictions and stable repeatability across all test conditions, despite its high structural stiffness. The experimental results obtained in this study indicate that balance accuracy in impulse-type hypersonic wind tunnel testing is governed not solely by static sensitivity, but by the dynamic compatibility between balance stiffness, flow-induced excitation, and sensor resolution. By enabling accurate force measurements in high-stiffness flexures, semiconductor strain gauges offer a feasible approach for improving the robustness and reliability of internal balance designs in hypersonic impulse-type facilities.

틸트로터형 항공기(Tiltrotor Aircraft)는 고정익기(Fixed Wing Aircraft)의 동체 형 상을 가지면서 비행 모드에 따라 회전축의 각도(Shaft Angle)를 조절할 수 있는 프롭 로터(Proprotor

서 론 일반적인 회전익기 로터에서도 복잡한 유동 현상이 발생하고 후류의 거동으로 인 한 블레이드, 동체 간섭 현상이 성능에 중요하게

The air and structural loads of a 5-ton class light helicopter (LH) rotor in a 2.24 g pull-up maneuver are investigated using a coupling between the computational structural dynamics (CSD) and computational fluid dynamics (CFD) methods. The LH rotor is characterized by a five-bladed system with elastomeric bearings and inter-bladed dampers. The periodic trim solution along with the converged CFD/CSD delta airloads obtained in steady-level flight (advance ratio of 0.287) are used to perform the transient CSD maneuver analysis. The resulting vehicle attitude angles and velocity profiles of the aircraft are then prescribed in the quasi-static (QS) CFD maneuver analysis. It is demonstrated that the present QS approach provides an effective means for the maneuver loads’ analysis. The important flow behaviors such as BVI (blade–vortex interaction)-induced oscillations and the negative pitching moment peaks met in maneuver flight are captured nicely with the proposed method. Either the vortex trajectories or the surface pressure distributions are examined to identify the sources of the oscillations. A loose CFD/CSD coupling (LC) is used to predict the blade elastic motions, structural moments, and pitch link loads at the specified maneuver revolution of the rotor and also to correlate these with the transient CSD-based predictions. A reasonable correlation is obtained. The LC results show more pronounced 5P (five per revolution) oscillations on the structural response than those of the CSD-based methods.