Pitching moment

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

Unsteady Force Measurements in Pitching-Plunging Airfoils

Abstract: A new sensor for unsteady force measurements of pitching and plunging airfoils using Fiber Bragg Gratings (FBG) in a water channel facility has been the developed. Load cells having four or five FBG sensors written in a single optical fiber have been developed to measure the strain at flexures designed and determine the normal and axial forces, the pitching moment and the temperature. The main advantage of the present approach compared to other designs using electrical strain gages is the simplicity of a single optical fiber carrying all the sensor information, and low noise. The design, compensation, calibration and application to force measurement on an airfoil at steady and unsteady flow conditions are described. The measurement results show the unsteady large lift coefficients produced during mild and deep stall in a pitching and plunging SD 7003 airfoil.

Application of circulation control for three-axis control of a tailless flight vehicle

Abstract: The application of circulation control (CC) manoeuvre effectors to a tailless flight vehicle enables the possibility of providing control moments about three axes without the use of conventional control surfaces. Strong similarities exist between the use of split flap elevons and CC units used as trailing edge devices for the provision of three-axis control. Both control types can produce independent roll and pitching moments by lateral symmetric operation. Yawing moments can also be produced by simultaneous blowing from upper and lower CC slots increasing the local section axial force. An existing datasheet method for predicting the lift and pitching moment increments for plain flaps is modified to support some aspects of sizing CC devices; however, there are some significant gaps such as high fidelity models for the prediction of Coanda jet separation from the curved trailing edge, which require further research. A case study is presented in which the provision of three-axis control moments using CC is evaluated for a tailless 20 kg class gas-turbine-powered model aircraft. Wind tunnel experiments are used to demonstrate the validity of the aerodynamic design of the vehicle and the ability to produce control moments from CC sufficient to meet basic trim and manoeuvre requirements. The peak values of CC control gains achieved for ? CL/ ? C? is 20 and the control gain for ? CD/ ? C? for use as part of a ?thrust?-based yaw control scheme from blowing from both upper and lower slots is low (?0.5); however this is sufficient to trim the case study aircraft at 8� of sideslip at cruise conditions with 10 per cent mass flow bleed from the engine. For lateral symmetric operation of CC controls, the change in pitching moment with control lift increment has been shown to be similar for both CC and flaperon devices

Short duration force measurements in impulse facilities

Abstract: A new multiple component stress wave force balance has been designed, calibrated and tested in the High Enthalpy Shock Tunnel Gottingen (HEG) of the German Aerospace Center (DLR). The balance is able to measure forces of short duration (milliseconds) on instrumented models from angles of attack from -40 to 20 degrees. Two models, a blunt cone 303mm long and a standard force reference model (HB-2) of 70mm diameter, are used to establish the accuracy of the force balance. The blunt cone tests were conducted at two different test conditions with a constant Mach number of 7.8 and total enthalpies of 3.0 and 3.5MJ/kg. At 0 degrees angle of attack and an enthalpy of 3.0MJ/kg, the measured axial coefficient was recovered to within 6% when compared to computational fluid dynamic (CFD) simulations. At –10 degrees, the axial and normal coefficients were within 6% and 9% respectively of CFD predictions while the center of pressure (based on chord length) was within 2%. Tests with the HB-2 standard force reference model were conducted at enthalpies ranging from 12 to 22 MJ/kg at an angle of attack of 0 degrees. A linear variation of the axial coefficient with the viscous similarity parameter was predicted with non-equilibrium CFD simulations assuming a laminar boundary layer. The recovered axial force coefficient remained within 6% of the CFD predictions and compared well with experimental results from other wind tunnel facilities. Reasonable comparison of pressure and heat flux measurements along longitudinal symmetry lines of the model was obtained. The accuracy of the force balance is estimated at approximately 5% for the axial component and 4% for the normal and pitching moment components.

Wind Tunnel Tests on Aerodynamic Characteristics of Ice-Coated 4-Bundled Conductors

Abstract: Wind tunnel tests were carried out to obtain the static aerodynamic characteristics of crescent iced 4-bundled conductors with different ice thicknesses, initial ice accretion angles, bundle spaces, and wind attack angles. The test models were made of the actual conductors and have a real rough surface. Test results show that the influence of wake interference on the drag coefficients of leeward subconductors is obvious. The interference angle range is larger than 20° and the drag coefficient curves of leeward subconductors have a sudden decrease phenomenon at some certain wind attack angles. The absolute value of the lift and moment coefficient increases with the increase of the ice thickness. In addition, the galloping of the iced subconductor may occur at the angle of wind attack near ±20° and the wake increases the moment coefficient. The variation of initial ice accretion angle has a significant influence on the aerodynamic coefficients. The aerodynamic coefficient curves exhibit a “moving” phenomenon at different initial ice accretion angles. The bundle spaces have a great influence on the moment coefficient of leeward thin ice-coated conductors. With the increase of ice thickness, the bundle spaces generally have little influence on the aerodynamic coefficients.