Showing papers on "Flapping published in 1988"

Dynamic pressure loads associated with twin supersonic plume resonance

Abstract: The phenomenon of twin supersonic plume resonance is defined and studied as it pertains to high level dynamic loads in the inter-nozzle region of aircraft like the F-15 and B1-A. Using a 1/40th scale model twin jet nacelle with powered choked nozzles, it is found that intense internozzle dynamic pressures are associated with the synchrophased coupling of each plume's jet flapping mode. This condition is found most prevalent when each plume's jet flapping mode has constituent elements composed of the B-type helical instability. Suppression of these fatigue bearing loads was accomplished by simple geometric modifications to only one plume's nozzle. These modifications disrupt the natural selection of the B-type mode and thereby decouple the plumes.

Forward flapping flight from flexible fins

Abstract: The mechanics and energetics of aquatic flight by the clearnose skate (Raja eglanteria) are examined with cinefilm and a new theoretical approach toward flight mechanics. Film analyses show that these animals move with a flapping, flexing wing that has a propulsive wave travelling rearward at twice the forward speed of the animal. A combination of blade-element theory and unsteady airfoil theory is used to examine the mechanics and energetics of this mode of locomotion. The theoretical analysis shows that (i) unsteady effects determine the overall performance of the wings, and (ii) there exist wing shapes that minimize the cost of transport or maximize the thrust. The theory indicates that the wings of swimming skates closely approach the minimum cost of transport. The results are extended to explore other modes of flapping wing propulsion, including those in animals whose wings deform passively in response to hydro- or aero-dynamic loads.

Bird decoy with motor drive wings

Abstract: A bird decoy including a body and a flapping mechanism mounted therein is disclosed. The flapping mechanism moves a pair of wings, which oscillate with respect to the body. The flapping mechanism includes a battery-operated motor, which creats a rotary motion, which rotary motion is transformed into reciprocal motion and which is in turn transformed into pivotal or oscillatory motion about a pair of pivot points. A method of the invention shows how a bird decoy body can be modified to include the flapping mechanism.

Wake model for helicopter rotors in high speed flight

Abstract: Two alternative approaches are developed to calculate blade-vortex interaction airloads on helicopter rotors: second order lifting-line theory, and a lifting surface theory correction. The common approach of using a larger vortex core radius to account for lifting-surface effects is quantified. The second order lifting-line theory also improves the modeling of yawed flow and swept tips. Calculated results are compared with wind tunnel measurements of lateral flapping, and with flight test measurements of blade section lift on SA349/2 and H-34 helicopter rotors. The tip vortex core radius required for good correlation with the flight test data is about 20 percent chord, which is within the range of measured viscous core sizes for helicopter rotors.

On the Pairing Process in an Excited, Plane, Turbulent Mixing Layer.

Abstract: The flow field in a plane, turbulent mixing layer which was disturbed by a small oscillating flap was investigated. Three experiments were carried out: one in which the flap oscillated sinusoidally at a single frequency Ff; a second in which the flap oscillated at two frequencies, a fundamental and a subharmonic, but the ensuing motion was dominated by the fundamental perturbation; and a third in which the amplitude of the subharmonic perturbation was increased until a distortion in the mean flow was noticeable. Two velocity components were measured at all phase angles relative to the subharmonic oscillation of the flap at densely spaced intervals. The data were used to map vorticity fields and the streak-line patterns for the purpose of assessing the relevance of the latter to the understanding of the dynamical process involved.

Return air barrier for motor vehicles

Abstract: A return air barrier for a system for venitilation of the passenger compartment of a motor vehicle has a closure flap made of a flexible low-density material suspended, and resting by its own weight against an inclined grid in the housing of the return air barrier, and during air flow moves against the direction of outflow into the closed position. Above the closure flap within its range of travel thereof, there are several hook-like webs mounted in such a way that at the height at which flapping begins, the flap touches the free end of at least one web and, with increasing air velocity, buckles in the lower edge region, adheres snugly to the webs and is held in an angular form.

Flapping wing inertia control

Abstract: A flapping wing propulsion system having a flapping wing inertia control for producing an effective "coupled parallel/rotating flapping movement", the lift force P acting virtually on the leading edge of the wing on the flapping surfaces which are mounted at the cross-sectional centre of gravity such that they can rotate to a limited extent and are held in an unstable manner in the basic position by springs, and the wing thus rotates into the respective flapping direction, which is carried out by inertia forces, remaining in this state during the parallel flapping movement. In addition, at the end of each upward stroke and downward stroke, the mass of the wing arrangement is absorbed by low-damping springs which store the excess flapping energy and feed it back into the drive process.

Flapping-wing drive system

Abstract: A flapping-wing drive system has been developed further in the specific direction of muscle-power drive and hybrid drive with a pressure drive. The flapping-wing movement device has been improved and has been designed in a more effective manner by means of a traction movement transmission. In addition, a double-acting fluid-oscillating motor has been permanently coupled to a muscle-power drive arrangement. The fluid-oscillating motor can be used on the one hand as an external pressure drive and on the other hand as a pressure pump (operating as a coupling element which is dependent on the flapping direction and has a pulse transmitter function) by means of a changeover device.

Helicopter stability and control modeling improvements and verification on two helicopters

Abstract: A linearized model of helicopter flight dynamics is developed which includes the flapping, lead-lag, and dynamic inflow degrees of freedom (DOF). The model is a combination of analytical terms and numerically determined stability derivatives, and is used to investigate the importance of the rotor DOF to stability and control modeling. The results show that the rotor DOF can have a significant impact on some of the natural modes in a linear model. The flap and dynamic inflow DOF show the greatest influence. Flapping exhibits strong coupling to the body, dynamic inflow, and to lead-lag to a lesser extent. Dynamic inflow tends to damp the high-frequency flapping modes, and reduces the damping on coupled body-flap motion. Dynamic inflow also couples to the flapping motion to produce complex roots. With body-flap and lag regressing modes as exceptions, the results show essentially similar behavior for most modes of articulated and hingeless rotor helicopters.

Prediction of stochastic blade responses using measured wind-speed data as input to the FLAP code

Abstract: Accurately predicting wind turbine blade loads and response is important in predicting the fatigue life of wind turbines. The necessity of including turbulent wind effects in structural dynamics models has long been recognized. At SERI, the structural dynamics model, or FLAP (Force and Loads Analysis Program), is being modified to include turbulent wind fluctuations in predicting rotor blade forces and moments. The objective of this paper is to show FLAP code predictions compared to measured blade loads using actual anemometer array data and a curve-fitting routine to form series expansion coefficients as the turbulence input to FLAP. The predictions are performed for a three-bladed upwind field test turbine. An array of nine anemometers was located 0.8 rotor diameters (D) upwind of the turbine, and data from each anemometer are used in a least-squares curve-fitting routine to obtain a series expansion of the turbulence field over the rotor disk. Three 10-min data cases are used to compare FLAP predictions to measured results. Each case represents a different mean wind speed and turbulence intensity. The time series of coefficients in the expansion of the turbulent velocity field are input to the FLAP code. Time series of predicted flap-bending moments at two blademore » radial stations are obtained, and power spectra of the predictions are then compared to power spectra of the measured blade bending moments. Conclusions are then drawn about the FLAP codes' ability to predict the blade loads for these three data cases. Recommendations for future work are also made.« less

Flapping-wing glider

Abstract: The invention relates to a flapping-wing glider which is preferably assisted in gliding flight by means of muscle power and also allows running starts and climbing flights to be carried out. While conventional flapping-wing aircraft remain unsuccessful because they have transmissions to flapping wings which greatly reduce the power and also disadvantageous vibration resonances and, above all, height losses during the phase in which the wing is flapping up, the flapping-wing glider operates with separate surfaces for continuous support and discontinuous flapping, these surfaces being dimensioned to be in each case approximately of equal size overall in order to optimise their respective function, as a result of which an aircraft is produced which is equipped with an area that is approximately twice as large as that required for the overall weight and on which aircraft, however, the flapping surface remains essentially ineffective in terms of lift during gliding. The continuous gliding state of the flapping-wing glider reduces the force which has to be applied for flapping down and to a large extent prevents dropping while the wing is flapping up. Furthermore, inter alia, the use of a lifting flapping wing which flaps down over its entire span width and utilises the forces without any significant transmission losses, and vibration-resonance damping (which operates via the production of a rotational pulse) and a flapping-up aid also act in a power-saving manner.