Showing papers on "Pitching moment published in 1968"

Aerodynamic loading on a two-dimensional airfoil during dynamic stall.

Abstract: A general theory is developed for the unsteady aerodynamic loading on an airfoil during dynamic stall. The dynamic stall process is represented by the shedding of vorticity from the vicinity of the airfoil leading edge. The theory is subsequently applied to the prediction of the stall-induced airloading on an airfoil experiencing a sudden onset of flow and on an airfoil performing oscillatory pitching motion. Satisfactory agreement between theoretical and experimental pressure distributions, forces and moments, and vortex trajectories is demonstrated.

An Experimental Investigation of a Low-Speed Circulation-Controlled Aerofoil

Abstract: Experiments performed on a low-speed circulation-controlled aerofoil are described. The aerofoil was of elliptic section with the circulation controlled by means of a jet blowing around the blunt trailing edge. Results for the lift, drag and pitching moment on the aerofoil are presented as functions of the blowing momentum coefficient and the angle of incidence. The results are for a two-dimensional aerofoil. Possible applications of this type of aerofoil are briefly discussed.

Comparison of Three Methods for the Evaluation of Subsonic Lifting-Surface Theory

Abstract: Independent numerical methods for obtaining the subsonic load distribution on a thin wing of arbitrary twist and camber have been developed at NPL, NLR (Netherlands) and BAC (Warton), The three methods have been studied jointly and their novel features have been reviewed critically. The best solutions by each method show excellent agreement for wings, at uniform incidence, having smooth leading and trailing edges. Spanwise loading, local aerodynamic centres, lift, pitching moment, vortex drag and chordwise loadings are tabulated for circular and rectangular planforms, for a wing of constant chord with hyperbolic leading and trailing edges, and for a tapered sweptback wing. The convergence of the solutions is examined in detail with respect to separate parameters representing the numbers of spanwise integration points and spanwise and chordwise collocation points. The tapered sweptback planform is considered with different amounts and types of artificial central rounding, but the crucial problem of a central kink under lifting conditions remains a subject for research.

Two-dimensional tests of airfoils oscillating near stall. volume 1. summary and evaluation of results

Abstract: : An experimental investigation into rotor blade dynamic stall was conducted Two typical airfoils, the NACA 0012 (modified) and the Vertol 23010- 158, were tested by measuring the differential pressures acting during pitching and translatory oscillations over a range of angles of attack covering the stall regime There were two main objectives The first was to determine the influence of stall on the aerodynamic pitching moment of an airfoil executing pitching motions corresponding to the elastic torsional oscillations of a rotor blade The second was to determine the extent to which time-varying angle of attack could affect the maximum aerodynamic lift that a rotor blade can develop The cambered profile remained free of negative damping for 3 to 6 degrees beyond the point where the symmetrical section encountered negative damping in the Mach 02 to 04 range The cambered section exhibited higher attainable C sub N's than the symmetrical section under all conditions of motion, except for the highest frequency tested at Mach 06

Aerodynamic characteristics of a five jet VTOL configuration in the transition speed range

Abstract: Wind tunnel tests of a VTOL jet fighter to determine aerodynamic characteristics including stability

An experimental investigation of ground effect on a four-propeller tilt- wing v/stol model

Abstract: : Tests were conducted on a one-tenth scale model of a tilt-wing V/STOL at specified points simulating flight conditions at various heights above the ground. The model was moved at selected velocities through still air; and lift, drag, and pitching moment were measured at various heights above the ground. Investigations included combinations of 30, 40, and 60 deg wing incidence angle with 30, 40, and 60 deg flap deflection, and thrust coefficients ranging from 0. 80 to 0.95. Model ground clearances of 3.5 to 36 inches were investigated both at constant altitude and with the altitude continuously varying during the run. The data are presented as plots of lift, drag, and pitching moment coefficients. Also included are data from wind tunnel tests on similar models. A brief analysis is made of ground effect phenomena and an understanding of the general data trends is obtained. The magnitude and direction of the force change in ground effect are predictable. However, the pitching moment change is strongly influenced by factors such as the flow field beneath the fuselage, the change in downwash at the horizontal tail, the other effects.

Static aerodynamic force measurements of bodies in tubes

Abstract: Experiments were performed in a water tunnel to measure the lift, drag, and pitching moment on models intended to simulate a vehicle traveling in a tube. Bodies of three different thickness ratios were tested, and the heave displacement and angle of incidence was varied. In one series of tests the body alone was tested in a tube. In another series a propeller was placed near the rear of the body in the tube and the thrust of the propeller was made equal to the drag of the body, thereby simulating the condition of self-propulsion. The slopes of the measured lift-displacement and moment-displacement curves at zero displacement, for both heave and incidence displacements, were found to give good agreement with a theory previously derived by one of the authors. These curves remained virtually unaltered when self-propulsion was simulated. (Author)

Wind-tunnel measurement at M equal 4.28 of some static and dynamic aerodynamic characteristics of finned missiles suspended magnetically.

Abstract: The lift, drag, pitching moment, and rolling moment due to roll velocity have been measured at M — 4.28 for two slender finned missile models by means of a magnetic suspension and balance system. Comparisons of the results with data measured by conventional balances show substantial agreement. The trend for damping in roll due to roll velocity to increase gradually with increasing angle of attack is more clearly shown than in earlier data because the scatter in the data is reduced by a factor of J.

Experimental Investigation of a High-lift Low-drag Aerofoil. Report no. 6802

Abstract: One of a series of low-drag aerofoils (1) Designated GU 25-5(11) 8 was selected for low speed wind tunnel testing at Reynolds numbers around half a million. Coefficients of lift, drag and pitching moment were obtained for a range of incidence. The maximum section lift coefficient obtained was 1.93 and the minimum profile drag coefficient was 0.0112. Results compared favourably with those deduced theoretically. The addition of a boundary layer trip to the upper surface caused the profile drag to decrease at some incidences. At the design lift coefficient of 1.4, the ratio of lift to profile drag was 108 at a Reynolds number of 0.63 million. The addition of an extended, sealed, flat-plate flap (with a chord one tenth that of the aerofoil) at the trailing edge of the aerofoil gave favourable results. A maximum ratio of lift to profile drag of 116 was obtained at a lift coefficient of 1.8 with a flap deflection of 17.8 degrees, while the maximum lift coefficient achieved was 2.30.

The Slender Wing with a Half Body of Revolution Mounted Beneath

Abstract: The slender-body theory of Ward is applied to a configuration consisting of a slender, pointed wing, carrying directly beneath it a pointed half-body of revolution divided along a meridian plane. Expressions for lift and drag due to incidence are found which are valid in both subsonic and supersonic flow if the flow is attached. The lift result can be used to find pitching moment. For the supersonic case the drag at zero incidence is also found and the expressions for a conical configuration are developed so that a limiting form of these can be compared with the results of ref. 3.

Aerodynamic Features of the Flap-Balanced Swivel Airfoil

Abstract: coefficients, Eqs. (1) and (2) positive quadratic root coefficients, Eqs. (5) and (6) airfoil chord chord of corresponding, fixed airfoil moment coefficient about the main hinge and flap hinge, respectively lift coefficient pitching-moment coefficient coefficients, Eq. (11) negative quadratic root chord of flap as a proportion of airfoil chord floating ratio, Eq. (15) main-hinge moment per unit span and flap-hinge moment per unit span, respectively moment of inertia of flap about the main hinge and abovit the flap hinge, respectively moment of inertia of airfoil airfoil span lift per unit span mass per unit area of airfoil airfoil pitching moment coefficients, Eqs. (3) and (4) gearing ratio, Eq. (8) ra2 = (mi + Xai)/#62 E= 1 + 2P/[P 4Q] , 1 + r 2 mi + Xai + Ebi V = velocity of flow a, df, as = angle of flow to frame, flap to airfoil, and airfoil surface to frame, respectively oif,

Effects of flexibility on lift and pitching- moment characteristics of a series of low- aspect-ratio wing-body combinations at transonic speeds

Abstract: Flexibility effects on lift and pitching moments of low aspect ratio delta wing-conical- cylindrical body combinations at transonic speeds