Pitching moment

About: Pitching moment is a research topic. Over the lifetime, 3213 publications have been published within this topic receiving 38721 citations.

Experimental Investigation of Annular Wing Aerodynamics

Abstract: A low-speed wind-tunnel investigation was conducted to explore the behavior of annular (ring) wings. Effects of aspect ratio as well as gap were investigated. Ring wings using a low Reynolds number Eppler section and a NACA 0012 profile were manufactured and tested. Measurements were recorded using a six-component sting balance. Experimental and theoretical trend comparisons were effected using a vortex-lattice code. The experimental results indicate wing efficiency factors well above 1 are achievable. The effect of gap was to increase the wing lift-curve slope as well as efficiency. The large increases in aerodynamic efficiency were generally mitigated by the significant minimum drag coefficient. Pitching moment characteristics were unfavorable and were dominated by dissimilar stall behavior between the upper and lower wing sections.

Aerodynamics of a Flapping and Pitching Wing Using Simulations and Experiments

Abstract: Computational fluid dynamics simulation results for a thin cambered plate airfoil, and flow visualization and force measurements from experiments conducted in water on a flapping-and-pitching thin flat-plate wing of semi-elliptic planform at low Reynolds numbers are reported. Time-varying force data, measured using a force transducer, provide a means to understand the mechanisms that lead to enhanced performance observed in insect flight compared with fixed-wing aerodynamics. Experimental uncertainties associated with low-level (∼1 N) fluid dynamic force measurements on flapping-and-pitching wings, including inertia effects, are addressed. A previously proposed pitching mode in which the leading-edge and trailing-edge switch roles to allow using cambered airfoils is shown to be feasible. A vortex-trapping model is proposed to explain the aerodynamic advantages of switching. The present results also support the authors' proposed idea that an optimum reduced flapping frequency might exist. The study has applications in micro air vehicle development.

Bifurcation Analysis of Aircraft Pitching Motions About Large Mean Angles of Attack

Abstract: Bifurcation theory is used to analyze the nonlinear dynamic stability characteristics of an aircraft'subject to single-degree-of-freedom pitching-motion perturbations about a large mean angle of attack. The requisite aerodynamic information in the equations of motion can be represented in a form equivalent to the response to finite-amplitude pitching oscillations about the mean angle of attack. It is shown how this information can be deduced from the case of infinitesimal -amplitude oscillations. The bifurcation theory analysis reveals that when the mean angle of attack is increased beyond a critical value at which the aerodynamic damping vanishes, new solutions representing finite-amplitude periodic motions bifurcate from the previously stable steady motion. The sign of a simple criterion, cast in terms of aerodynamic properties, determines whether the bifurcating solutions are stable (supercritical) or unstable (subcritical). For flat-plate airfoils flying at supersonic/hypersonic speed, the bifurcation is subcritical, implying either that exchanges of stability between steady and periodic motion are accompanied by hysteresis phenomena, or that potentially large aperiodic departures from steady motion may develop.

Experimental investigation of trailing-edge devices at transonic speeds

Abstract: The influence of trailing-edge devices such as Gurney flaps and divergent trailing edges of different height on the aerodynamic performance of an airfoil at transonic speeds has been investigated experimentally. The investigation has been carried out in the Transonic Wind Tunnel Gottingen (TWG) using the two-dimensional airfoil model VC-Opt at freestream Mach numbers of M element of [0.755, 0.775, 0.790] and a Reynolds number of Re = 5.0 · 10 6. The results have shown that the trailing-edge devices increase the circulation of the airfoil leading to a lift enhancement and pitching-moment decrease as well as an increase in minimum drag compared to the baseline configuration. The maximum lift-to-drag ratio is considerably improved and the onset of trailing-edge flow separation is shifted to higher lift. Besides the increased rear-loading, a downstream displacement of the shock provides the main lift enhancement in transonic flow. The simple Gurney flap provides the largest additional circulation of all geometries tested. The smoother turning of the flow due to the additional ramp of the divergent trailing edge leads to a smaller increase of circulation. Slightly less lift but considerably less viscous (pressure) drag is generated enhancing the maximum lift-to-drag ratio compared to the Gurney flap. The negative affect of the Gurney flap on the pitching moment is also reduced. For the high divergent trailing edges, different ramp slopes have a significant influence on the aerodynamic performance whereas at low device heights the influence is considerably diminished. The results show that the divergent trailing edge proves to be the better trailing-edge device at transonic speeds. The application as an element for an adaptive wing is generally possible.