Topic
Pitching moment
About: Pitching moment is a research topic. Over the lifetime, 3213 publications have been published within this topic receiving 38721 citations.
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TL;DR: In this paper, the effects of amplitude of vibration, incident angle and Reynolds number on the spanwise correlation of aerodynamic loading are studied and it is shown that aerodynamic forces along the span are not fully correlated, which indicates that the application of the strip assumption may overestimate the overall aerodynamic load on large span structures, and consequently may result in a large error margin in evaluation of flutter and aeroelastic response.
23 citations
TL;DR: In this article, a quasi-steady theory for the flight of windborne plate debris is proposed, and the effects of the rotational lift, drag, and pitching moment are included in the model.
Abstract: This paper analyzes models based on the quasi-steady theory for the flight of windborne plate debris. It is shown that the effects of the rotational lift, drag, and pitching moment are important and are included in the model. The model was used with success to predict the behavior of thin, square plates in a uniform stream, based on comparisons with existing experimental data. In fact, some of the scatter in the existing experimental data was explained by the numerical results. It was also shown that the buoyancy parameter was the key parameter in determining initial flight speeds and normalization of spatial coordinates with this parameter collapsed the data well.
23 citations
10 May 1967
TL;DR: Several conclusions were drawn with respect to stall flutter and airload prediction of high speed and/or highly loaded helicopter rotor blades with associated airloads of the type described by classical unsteady airfoil theory.
Abstract: : Several conclusions were drawn with respect to stall flutter and airload prediction of high speed and/or highly loaded helicopter rotor blades. The stall of an airfoil section during rapid transient high angle of attack changes is delayed well above the static stall angle and results in a large transient negative pressure disturbance leading to large transient lift and nose down pitching moment. The magnitude of the pitching moment is such as to generate substantial nose down pitching displacements of the blade. These pitching displacements can substantially alter the angle of attack distribution of the rotor blade. The dynamic stall phenomenon of a helicopter rotor blade can be separated into three major phases: (1) A delay in the loss of blade leading edge suction to an angle of attack far above the static stall angle, with associated airloads of the type described by classical unsteady airfoil theory. (2) A subsequent loss of leading edge suction accompanied by the formation of large negative pressure disturbance (due to the shedding of vorticity from the vicinity of the blade leading edge) which moves aft over the upper surface of the blade. Associated with this phase are high transient lift, drag, and nose-down pitching moment associated with the greatly altered pressure distribution on the airfoil. (3) Complete upper surface separation of the classic static type, characterized by low lift, high drag, and moderate nose- down pitching moment.
23 citations
TL;DR: In this paper, an aeroelastic analysis is conducted on a two-degree-of-freedom airfoil in transonic flow using a generalized state-space approximation for the unsteady aerodynamics.
Abstract: An aeroelastic analysis is conducted on a two-degree-of-freedom airfoil in transonic flow using a generalized state-space approximation for the unsteady aerodynamics. The aerodynamic representation is validated against computational fluid dynamic solutions for angle of attack oscillations up to Mach numbers of 0.875 and at reduced frequencies up to 1.0. Despite the inherent nonlinear nature of transonic flow, it is shown that a linear finite-state model with as few as eight states can provide a good approximation to the unsteady lift and moment behavior if appropriate allowance is made for Mach number effects on the airfoil's static lift curve slope and mean aerodynamic center. It is shown how the aerodynamic representation can be coupled to the structural equations of a typical airfoil section with bending and torsional degrees of freedom. The stability of the resulting aeroelastic system is determined by eigenanalysis. This aeroelastic analysis is shown to be in excellent agreement with calculations performed using more sophisticated unsteady aerodynamic theories.
23 citations
TL;DR: In this paper, the simulation of a two-rotor aircraft in different geometric configurations during hover flight was performed using an implementation of the unsteady vortex-lattice method (UVLM).
Abstract: This paper presents the simulation of a two-rotor aircraft in different geometric configurations during hover flight. The analysis was performed using an implementation of the unsteady vortex-lattice method (UVLM). A description of the UVLM is presented as well as the techniques used to enhance the stability of results for rotors in hover flight. The model is validated for an isolated rotor in hover, comparing numerical results to experimental data (high-Reynolds, low-Mach conditions). Results show that an exclusion of the root vortex generates a more stable wake, without affecting results. Results for the two-rotor aircraft show an important influence of the number of blades on the vertical thrust. Furthermore, the geometric configuration has a considerable influence on the pitching moment.
23 citations