Showing papers on "Pitching moment published in 1974"

A Quasi-Vortex-Lattice Method in Thin Wing Theory

Abstract: A quasi-continuous method is developed for solving thin-wing problems. For the purpose of satisfying the wing boundary conditions, the spanwise vortex distribution is assumed to be stepwise-constant, while the chordwise vortex integral is reduced to a finite sum through a modified trapezoidal rule and the theory of Chebyshev polynomials. Wing-edge and Cauchy singularities are acounted for. The total aerodynamic characteristics are obtained by an appropriate quadrature integration. The two-dimensional results for airfoils without flap deflection reproduce the exact solutions in lift and pitching moment coefficients, the leading edge suction, and the pressure difference at a finite number of points. For a flapped airfoil, the present results are more accurate than those given by the vortex-lattice method. The three-dimensional results also show an improvement over the results of the vortex-lattice method. Extension to nonplanar applications is discussed.

Extension of leading-edge-suction analogy to wings with separated flow around the side edges at subsonic speeds

Abstract: A method for determining the lift, drag, and pitching moment for wings which have separated flow at the leading and side edges with subsequently reattached flow downstream and inboard is presented. Limiting values of the contribution to lift of the side-edge reattached flow are determined for rectangular wings. The general behavior of this contribution is computed for rectangular, cropped-delta, cropped-diamond, and cropped-arrow wings. Comparisons of the results of the method and experiment indicate reasonably good correlation of the lift, drag, and pitching moment for a wide planform range. The agreement of the method with experiment was as good as, or better than, that obtained by other methods. The procedure is computerized and is available from COSMIC as NASA Langley computer program A0313.

Variable area, variable camber wing for aircraft

Abstract: A mechanism is provided for both extending the chord of a wing by more than seventy percent and for increasing the camber of the wing without creating the high pitching moment characteristics of conventional high lift wing systems. These advantageous capabilities are accomplished by constructing forward and aft wing sections which cover the wing box beam and form a high wing loading cruise flight wing. The sections can be extended and deflected to uncover the wing box beam and form a greatly increased area to lower the wing loading and an increased camber with low pitching moment to provide high lift for short take-off and landing.

Some Measurements on Dynamic Stall

Abstract: Details of a flow oscillation device and of force and moment measurements on a 2 ft chord twodimensional NACA 0012-64 airfoil in the oscillating flow and oscillated in pitch in a steady flow through stall are presented. Results indicate that both methods give essentially the same description of the dynamic stall process. It is apparent from peaks in the pressure distributions and in the pitching moment traces that more than one vortex is shed from the leading edge during the stall process. This, coupled with the very rapid changes that occur during stall, requires very close scrutiny of force and moment data that has not been recorded continuously. Understanding of dynamic stall overshoot will not be complete until detailed measurements are obtained in the region of the laminar separation bubble near the nose.

Comparison of three methods for calculation of helicopter rotor blade loading and stresses due to stall

Abstract: A comparison is made of the results of three methods for calculating the effects of dynamic stall on the performance, airloads, and blade stresses of a helicopter rotor at high loading. The three dynamic-stall methods considered predict essentially the same performance and trim for the rotor. They give roughly the same mean bending moments, but the peak-to-peak torsion and bending moments differ by 25 to 40 percent, and there are differences in the details of the predicted blade motion and stresses. The latter are due to significant differences in the dynamic stall aerodynamic loads, particularly the aerodynamic pitch moment, predicted by the three methods.

Coupled Pitch and Heave Porpoising Instability in Hydrodynamic Planing

Abstract: "Porpoising" is a form of longitudinal instability characterized by an unstable coupling between heave and pitch degrees of freedom. In connection with flying boat stability, it was first analyzed by Perring and Glauert.2 In this paper, a simple theoretical description is first presented, based on quasistatic forces and moments, to show that stability is a function of center of gravity (c.g) location with respect to the center of pressure; and to a lesser extent, on the longitudinal radius of gyration. It is found that there are two stable zones; one where the c.g. is well forward of the center of pressure (analogous to a longitudinally stable aeroplane), and a second with the c.g. close to the trailing edge, which has no parallel in aircraft stability theory. Buoyancy terms are found to have a favorable effect for all c.g. positions, so that porpoising is essentially a high speed phenomenon, when most of the weight is supported by dynamic forces. Expressions are then developed for the transient hydrodynamic forces due to heave and pitch rates and accelerations, and the complete pitch and heave equations of motion are studied in some detail. It is concluded that there are several different ways of achieving stability, only one of which (moving the c.g. forward) is intuitively obvious. Other solutions include moving the c.g. right aft, the use of a very large radius of gyration in relation to the length of the planing surface, and the use of a high aspect ratio planing surface. All of these solutions can be identified in successful high-speed boats and hydroplanes. The calculations in the main body of the report assume that the fluid is inviscid. It can be shown (the calculations are omitted for brevity) that skin friction on the planing bottom results in additional terms in the stability equations, but that these are an order of magnitude less than the inviscid terms for a typical planing hull. But at very high speeds, coupled with a high c.g. position, the skin friction term in the pitching moment equation can become important, and may then have a dominant effect on stability. Generally, skin friction terms increase static stability and degrade dynamic stability. Despite the many porpoising tests made in the past with specific flying boat designs, there is very little experimental data available for simple planing surfaces alone; in fact, only the work of Day and Haag12 is known to the writer. A comparison between the theory and their experimental data gives reasonable agreement under the circumstances, but also points to the need for more experimental work.

Helicopter rotor blade balancing method

Abstract: A helicopter rotor blade having at least one ramp tab of selected span and chord dimensions, weight and shaped to define an outer surface of selected angularity with respect to the blade chord and being selectively positioned along the blade trailing edge and bonded to its upper or lower surface so as to be totally within the blade chord profile and be effective to eliminate or reduce to within acceptable limits blade pitching moment dynamic unbalance.

Stability and control characteristics at Mach numbers from 0.20 to 4.63 of a cruciform air-to-air missile with triangular canard controls and a trapezoidal wing

Abstract: Investigations have been conducted in the Langley 8-foot transonic pressure tunnel and the Langley Unitary Plan wind tunnel at Mach numbers from 0.20 to 4.63 to determine the stability and control characteristics of a cruciform air-to-air missile with triangular canard controls and a trapezoidal wing. The results indicate that canards are effective in producing pitching moment throughout most of the test angle-of-attack and Mach number range and that the variations of pitching moment with lift for trim conditions are relatively linear. There is a decrease in canard effectiveness with an increase in angle of attack up to about Mach 2.50 as evidenced by the beginning of coalescence of the pitching-moment curves. At a Mach number above 2.50, there is an increase in effectiveness at moderate to high angles of attack. Simulated launch straps have little effect on the lift and pitch characteristics but do cause an increase in drag, and this increase in drag induces a rolling moment at a zero roll attitude where the straps cause an asymmetric geometric shape. The canards are not suitable devices for roll control and, at some Mach numbers and roll attitudes, are not effective in producing pure yawing moments.

Two-Dimensional Subsonic Evaluation of a 15-Percent Thick Circulation Control Airfoil with Slots at Leading and Trailing Edges,

Abstract: : A 15-percent-thick circulation control elliptical airfoil section with slots at both leading and trailing edges for tangential blowing was evaluated in a subsonic wind tunnel to determine its potential for high-speed (300-400 knot) helicopter rotor systems. Fore-and-aft slot utilization were determined by local flow direction over the blade as it revolved around the azimuth. Aerodynamic performance was not affected by the addition of an unblown leading edge slot except beyond the usable positive angle of attack range where some loss in lift and increase in drag were noted. At equal plenum pressures, simultaneous blowing from the leading and trailing edges resulted in a decrease in lift, an increase in drag, and a more positive pitching moment than for trailing edge blowing alone. (Modified author abstract)

Optimal angle of release for the competition javelin as determined by its aerodynamic and ballistic characteristics

Abstract: The purpose of this study was to determine the optimal angle of release for the competition javelin as determined by its aerodynamic and ballistic characteristics. In particular, aerodynamic measurements included lift, drag, and the pitching moment, while ballistic tests consisted of horizontal flight distances of the javelin at various angles of release combined with various velocities.

Calculation of the longitudinal aerodynamic characteristics of STOL aircraft with externally-blown jet-augmented flaps

Abstract: A theoretical investigation was made to develop methods for predicting the longitudinal aerodynamic characteristics of externally-blown, jet-augmented wing-flap combinations. A potential flow analysis was used to develop two models: a wing-flap lifting surface model and a high-bypass-ratio turbofan engine wake model. Use of these two models in sequence provides for calculation of the wing-flap load distribution including the influence of the engine wake. The method can accommodate multiple engines per wing panel and part-span flaps but is limited to the case where the flow and geometry of the configuration are symmetric about a vertical plane containing the wing root chord. Comparisons of predicted and measured lift and pitching moment on unswept and swept wings with one and two engines per panel and with various flap deflection angles indicate satisfactory prediction of lift and moment for flap deflections up to 30 to 40 degrees. At higher flap angles with and without power, the method begins to overpredict lift, due probably to the appearance of flow separation on the flaps.

Analysis of the wind tunnel test of a tilt rotor power force model

Abstract: Two series of wind tunnel tests were made to determine performance, stability and control, and rotor wake interaction on the airframe, using a one-tenth scale powered force model of a tilt rotor aircraft. Testing covered hover (IGE/OCE), helicopter, conversion, and airplane flight configurations. Forces and moments were recorded for the model from predetermined trim attitudes. Control positions were adjusted to trim flight (one-g lift, pitching moment and drag zero) within the uncorrected test data balance accuracy. Pitch and yaw sweeps were made about the trim attitudes with the control held at the trimmed settings to determine the static stability characteristics. Tail on, tail off, rotors on, and rotors off configurations were testes to determine the rotor wake effects on the empennage. Results are presented and discussed.

Unsteady lift forces on highly cambered airfoils moving through a gust

Abstract: An unsteady airfoil theory in which the flow is linearized about the steady potential flow of the airfoil is presented. The theory is applied to an airfoil entering a gust. After transformation to the W-plane, the problem is formulated in terms of a Poisson's equation. The solutions are expanded in a Fourier-Bessel series. The theory is applied to a circular arc with arbitrary camber. Closed form expressions for the velocity and pressure on the surface of the airfoil are obtained. The unsteady aerodynamic forces are then calculated and shown to contain two terms. One in an explicit closed analytical form represents the contribution of the oncoming vortical disturbance, the other depends on a single quadrature and accounts for the effect of the wake.

A study of the nonlinear aerodynamics of bodies in nonplanar motion

Abstract: Concepts from the theory of functionals are used to develop nonlinear formulations of the aerodynamic force and moment systems acting on bodies in large-amplitude, arbitrary motions. The analysis, which proceeds formally once the functional dependence of the aerodynamic reactions upon the motion variables is established, ensures the inclusion, within the resulting formulation, of pertinent aerodynamic terms that normally are excluded in the classical treatment. Applied to the large-amplitude, slowly varying, nonplanar motion of a body, the formulation suggests that the aerodynamic moment can be compounded of the moments acting on the body in four basic motions: steady angle of attack, pitch oscillations, either roll or yaw oscillations, and coning motion. Coning, where the nose of the body describes a circle around the velocity vector, characterizes the nonplanar nature of the general motion.

Experiments on rudders with small flaps in free-stream and behind a propeller

Abstract: Water tunnel experiments were performed to determine the characteristics of rudders with small flaps both in the free stream and behind a propeller The results include plots of lift, drag, rudder moment, and flap moment coefficient for a complete range of angles of attack and flap deflection

Effect of ground proximity on the longitudinal aerodynamic characteristics of an aspect-ratio-1 wing with and without wing-tip blowing

Abstract: An investigation has been conducted to determine the effect of ground proximity on the aerodynamic characteristics of an aspect-ratio-1 wing with and without wing-tip blowing. This investigation was conducted in the Langley towing tank no. 1 with the model towed over the water to eliminate the effects of walls and of wind-tunnel ground-board boundary layers. The results indicate that the model is stable with height and pitch at positive angles of attack and that the lift-drag ratio is improved at small ground heights with some blowing at the wing tips.

Low-speed aerodynamic characteristics of airfoil sections with rounded trailing edges in forward and reverse flow

Abstract: Low-speed wind-tunnel tests were conducted to determine the two-dimensional aerodynamic characteristics of 6-, 12-, and 18-percent-thick airfoil sections with rounded trailing edges in both forward and reverse flow. The shapes incorporated camber with both the leading and trailing edges rounded to provide reasonable aerodynamic performance with either edge directed toward the free-stream flow. The tests were conducted with the airfoils in both normal and reverse orientations relative to the free stream. The Mach number was varied from 0.16 to 0.36 and the angle of attack was varied from minus 10 to 24 million. Reynolds number, based on the airfoil chord, was varied from about 1.0 to 12.0 million.

Wind tunnel tests of a full-scale model of a light twin-engine airplane with fixed auxiliary airfoil or leading-edge slot

Abstract: An investigation has been conducted by means of wind-tunnel tests of a full-scale mockup of a light twin-engine airplane configuration to determine the effects of outboard partial-span slots and of auxiliary airfoils ahead of the leading edge of the wing in improving aerodynamic characteristics at high angles of attack. Both of the stall-control devices gave considerable improvement in high angle-of-attack characteristics with the auxiliary airfoil giving the more favorable results, but neither device performed as well as might have been expected.

On the use of thick-airfoil theory to design airfoil families in which thickness and lift are varied independently

Abstract: A method has been developed for designing families of airfoils in which the members of a family have the same basic type of pressure distribution but vary in thickness ratio or lift, or both. Thickness ratio and lift may be prescribed independently. The method which is based on the Theodorsen thick-airfoil theory permits moderate variations from the basic shape on which the family is based.

Low speed aerodynamic characteristics of NACA 6716 and NACA 4416 airfoils with 35 percent-chord single-slotted flaps. [low turbulence pressure tunnel tests to determine two dimensional lift and pitching moment characteristics

Abstract: An investigation was conducted in a low-turbulence pressure tunnel to determine the two-dimensional lift and pitching-moment characteristics of an NACA 6716 and an NACA 4416 airfoil with 35-percent-chord single-slotted flaps. Both models were tested with flaps deflected from 0 deg to 45 deg, at angles of attack from minus 6 deg to several degrees past stall, at Reynolds numbers from 3.0 million to 13.8 million, and primarily at a Mach number of 0.23. Tests were also made to determine the effect of several slot entry shapes on performance.

Effect of gaseous and solid simulated jet plumes on an 040A space shuttle launch configuration at m=1.6 to 2.2

Abstract: The effect of plume-induced flow separation and aspiration effects due to operation of both orbiter and the solid rocket motors on a 0.019-scale model of the launch configuration of the Space Shuttle Vehicle is determined. Longitudinal and lateral-directional stability data were obtained at Mach numbers of 1.6, 2.0, and 2.2 with and without the engines operating. The plumes exiting from the engines were simulated by a cold-gas jet supplied by an auxiliary 200-atm air supply system and solid-body plume simulators. The aerodynamic effects produced by these two simulation procedures are compared. The parameters most significantly affected by the jet plumes are pitching moment, elevon control effectiveness, axial force, and orbiter wing loads. The solid rocket motor (SRM) plumes have the largest effect on the aerodynamic characteristics. The effect of the orbiter plumes in combination with the SRM plumes is also significant. Variations in the nozzle design parameters and configuration changes can reduce the jet plume-induced aerodynamic effects.

Theoretical prediction of thick wing and pylon-fuselage-fanpod-nacelle aerodynamic characteristics at subcritical speeds. Part 2: Computer program description

Abstract: The procedures required to operate the thick wing and pylon-fuselage-fanpod-nacelle computer program are presented. The program computes surface velocities and pressure, section loads, and total configuration loads and pitching moment. Potential flow theory is used to compute the surface pressures and the associated lift, moment, and vortex drag. The skin friction drag is also computed.

Calculation of Nonlinear Lift and Pitching Moment Coefficients forSlender Wing-Body Combinations

Abstract: Becker, J. V., "Prospects for Actively Cooled Hypersonic Transports," Aeronautics and Astronautics, Vol. 9, No. 8, Aug. 1971, pp. 32-39. Helenbrook, R. G. and Anthony, F. M., "Design of a Convective Cooling System for a Mach 6 Hypersonic Transport Airframe," CR-1918, Dec. 1971, NASA. Anderson, E. C. and Lewis, C. H., "Laminar or Turbulent Boundary Layer Flows of Perfect Gases or Reacting Gas Mixtures in Chemical Equilibrium," CR-1893, Oct. 1971, NASA. Price, J. M. and Harris, J. E., "Computer Program for Solving Compressible Nonsimilar-Boundary-Layer Equations for Laminar, Transitional, or Turbulent Flows of a Perfect Gas," TM X2458, April 1972, NASA

Magnetohydrodynamical Unsteady Flow past a Slender Body of an Arbitrary Cross-Section

Abstract: By using the slender body approximation, the linearized equation for unsteady flow past a slender body in the presence of an applied alligned magnetic field is introduced. The transient problem of the slender body which executes an oscillation is considered. The velocity, the magnetic potential and the electric stream function are obtained in the case of small conductivity of the fluid. For an example, the lift and pitching moment of a body of revolution are calculated.