Showing papers on "Flapping published in 1999"

The novel aerodynamics of insect flight: applications to micro-air vehicles.

Abstract: The wing motion in free flight has been described for insects ranging from 1 to 100 mm in wingspan. To support the body weight, the wings typically produce 2–3 times more lift than can be accounted for by conventional aerodynamics. Some insects use the fling mechanism: the wings are clapped together and then flung open before the start of the downstroke, creating a lift-enhancing vortex around each wing. Most insects, however, rely on a leading-edge vortex (LEV) created by dynamic stall during flapping; a strong spanwise flow is also generated by the pressure gradients on the flapping wing, causing the LEV to spiral out to the wingtip. Technical applications of the fling are limited by the mechanical damage that accompanies repeated clapping of the wings, but the spiral LEV can be used to augment the lift production of propellers, rotors and micro-air vehicles (MAVs). Design characteristics of insect-based flying machines are presented, along with estimates of the mass supported, the mechanical power requirement and maximum flight speeds over a wide range of sizes and frequencies. To support a given mass, larger machines need less power, but smaller ones operating at higher frequencies will reach faster speeds.

Kinematics of flap-bounding flight in the zebra finch over a wide range of speeds

Abstract: It has been proposed elsewhere that flap-bounding, an intermittent flight style consisting of flapping phases interspersed with flexed-wing bounds, should offer no savings in average mechanical power relative to continuous flapping unless a bird flies 1.2 times faster than its maximum range speed (Vmr). Why do some species use intermittent bounds at speeds slower than 1.2Vmr? The 'fixed-gear hypothesis' suggests that flap-bounding is used to vary mean power output in small birds that are otherwise constrained by muscle physiology and wing anatomy to use a fixed muscle shortening velocity and pattern of wing motion at all flight speeds; the 'body-lift hypothesis' suggests that some weight support during bounds could make flap-bounding flight aerodynamically advantageous in comparison with continuous flapping over most forward flight speeds. To test these predictions, we studied high-speed film recordings (300 Hz) of wing and body motion in zebra finches (Taenopygia guttata, mean mass 13.2 g, N=4) taken as the birds flew in a variable-speed wind tunnel (0-14 m s-1). The zebra finches used flap-bounding flight at all speeds, so their flight style was unique compared with that of birds that facultatively shift from continuous flapping or flap-gliding at slow speeds to flap-bounding at fast speeds. There was a significant effect of flight speed on all measured aspects of wing motion except percentage of the wingbeat spent in downstroke. Changes in angular velocity of the wing indicated that contractile velocity in the pectoralis muscle changed with flight speed, which is not consistent with the fixed-gear hypothesis. Although variation in stroke-plane angle relative to the body, pronation angle of the wing and wing span at mid-upstroke showed that the zebra finch changed within-wingbeat geometries according to speed, a vortex-ring gait with a feathered upstroke appeared to be the only gait used during flapping. In contrast, two small species that use continuous flapping during slow flight (0-4 m s-1) either change wingbeat gait according to flight speed or exhibit more variation in stroke-plane and pronation angles relative to the body. Differences in kinematics among species appear to be related to wing design (aspect ratio, skeletal proportions) rather than to pectoralis muscle fiber composition, indicating that the fixed-gear hypothesis should perhaps be modified to exclude muscle physiology and to emphasize constraints due to wing anatomy. Body lift was produced during bounds at speeds from 4 to 14 m s-1. Maximum body lift was 0.0206 N (15.9 % of body weight) at 10 m s-1; body lift:drag ratio declined with increasing air speed. The aerodynamic function of bounds differed with increasing speed from an emphasis on lift production (4-10 m s-1) to an emphasis on drag reduction with a slight loss in lift (12 and 14 m s-1). From a mathematical model of aerodynamic costs, it appeared that flap-bounding offered the zebra finch an aerodynamic advantage relative to continuous flapping at moderate and fast flight speeds (6-14 m s-1), with body lift augmenting any savings offered solely by flap-bounding at speeds faster than 7.1 m s-1. The percentage of time spent flapping during an intermittent flight cycle decreased with increasing speed, so the mechanical cost of transport was likely to be lowest at faster flight speeds (10-14 m s-1).

Biologically-Inspired Bodies Under Surface Waves Part 2: Theoretical Control of Maneuvering

Abstract: The theoretical control of low-speed maneuvering of small underwater vehicles in the dive plane using dorsal and caudal fin-based control surfaces is considered. The two dorsal fins are long and are actually mounted in the horizontal plane. The caudal fin is also horizontal and is akin to the fluke of a whale. Dorsal-like fins mounted on a flow aligned vehicle produce a normal force when they are cambered. Using such a device, depth control can be accomplished. A flapping foil device mounted at the end of the tailcone of the vehicle produces vehicle motion that is somewhat similar to the motion produced by the caudal fins offish. The moment produced by the flapping foils is used here for pitch angle control. A continuous adaptive sliding mode control law is derived for depth control via the dorsal flns in the presence of surface waves. The flapping foils have periodic motion and they can produce only periodic forces. A discrete adaptive predictive control law is designed for varying the maximum tip excursion of the foils in each cycle for the pitch angle control and for the attenuation of disturbance caused by waves. Strouhal number of the foils is the key control variable. The derivation of control laws requires only imprecise knowledge of the hydrodynamic parameters and large uncertainty in system parameters is allowed. In the closed-loop system, depth trajectory tracking and pitch angle control are accomplished using caudal and dorsal fin-based control surfaces in the presence of system parameter uncertainty and surface waves. A control law for the trajectory control of depth and regulation of the pitch angle is also presented, which uses only the dorsal fins and simulation results are presented to show the controller perfor­ mance.

Development of piezoelectrically actuated micro-aerial vehicles

Abstract: A discussion of the principles involved in small-scale flight is presented here. In addition, several novel mechanisms have been developed in an attempt to mechanically emulate flapping flight on the meso-scale. Wings are being developed which will exploit particular material properties to emulate the dynamic characteristics of insect wings. The flapping mechanisms developed in this paper use piezoelectric unimorph actuators integrated with compliant, solid-state flexure based mechanisms. Four and five bar linkages are used to convert the linear unimorph output into a single degree-of-freedom rotational flapping motion. Due to their capacitive nature, piezoelectric actuators generally dissipate less power than traditional actuation methods such as electromagnetic mirrors. Piezoelectric actuators possess a high power density and are capable of high force output. They are frequently used to induce structural resonances, making them suitable for use in these devices. The dynamics of these systems rely on the mechanics of flexure mechanisms, the mechanical and electrical behavior of the piezoelectric elements, and the aerodynamic interaction of the wing and the air, resulting in a complex, nonlinear problem.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Periodic Flap Control of a Helicopter Blade in Forward Flight

Abstract: The primary objective of this paper is to present new periodic control strategies for the control of flapping motion of an individual helicopter rotor blade in forward flight, which is represented ...

Aerodynamic Characteristics and Control Effectiveness of the HL-20 Lifting Body Configuration at Mach 10 in Air

Abstract: A 0.0196-scale model of the HL-20 lifting-body, one of several configurations proposed for future crewed spacecraft, was tested in the Langley 31-Inch Mach 10 Tunnel. The purpose of the tests was to determine the effectiveness of fin-mounted elevons, a lower surface flush-mounted body flap, and a flush-mounted yaw controller at hypersonic speeds. The nominal angle-of-attack range, representative of hypersonic entry, was 2 deg to 41 deg, the sideslip angles were 0 deg, 2 deg, and -2 deg, and the test Reynolds number was 1.06 x 10 E6 based on model reference length. The aerodynamic, longitudinal, and lateral control effectiveness along with surface oil flow visualizations are presented and discussed. The configuration was longitudinally and laterally stable at the nominal center of gravity. The primary longitudinal control, the fin-mounted elevons, could not trim the model to the desired entry angle of attack of 30 deg. The lower surface body flaps were effective for roll control and the associated adverse yawing moment was eliminated by skewing the body flap hinge lines. A yaw controller, flush-mounted on the lower surface, was also effective, and the associated small rolling moment was favorable.

Swim fin and monofin with flapping foil

Abstract: A swim fin for each foot or a monofin for both feet of a swimmer has an elastic flapping foil that bends away from the ball of the foot on the kicking stroke in which the instep is advanced first, and that is forced against the sole of the of the foot on the opposite stroke. this greatly enhances the efficiency of the kicking action. The free edge of the flapping foil may be curled upward to further enhance the flapping action.

Foot rest flap for tying shoe laces

Abstract: The height adjustable tread-board (2) slopes at 30 deg when folded out and can be lowered to the ground. The flapping movement is dampened and after use the tread board automatically folds up by time control. The flap operates by a self-locking slide, or by an electric motor.

Design of Supersonic Transport Flap Systems for Thrust Recovery at Subsonic Speeds

Abstract: A study of the subsonic aerodynamics of hinged flap systems for supersonic cruise commercial aircraft has been conducted using linear attached-flow theory that has been modified to include an estimate of attainable leading edge thrust and an approximate representation of vortex forces. Comparisons of theoretical predictions with experimental results show that the theory gives a reasonably good and generally conservative estimate of the performance of an efficient flap system and provides a good estimate of the leading and trailing-edge deflection angles necessary for optimum performance. A substantial reduction in the area of the inboard region of the leading edge flap has only a minor effect on the performance and the optimum deflection angles. Changes in the size of the outboard leading-edge flap show that performance is greatest when this flap has a chord equal to approximately 30 percent of the wing chord. A study was also made of the performance of various combinations of individual leading and trailing-edge flaps, and the results show that aerodynamic efficiencies as high as 85 percent of full suction are predicted.

Double-wing flapping airplane

Abstract: PROBLEM TO BE SOLVED: To provide a flapping airplane sufficiently enjoyable outdoors as well as indoors, securing larger thrust and direct advancing ability by adopting two pairs of flapping wings and one driving tail assembly SOLUTION: Front and rear pairs of flapping wings 17, 18, and one driving tail assembly 16 are adopted in this airplane In order to drive them, two slider cranks 4a, 4b are mounted on one power shaft 4, and a balance arm 15 is mounted as a transmission device of the output power In addition, a 'power shaft stopper device' for holding all the wings at the most appropriate angles for gliding is mounted at the nose of the airplane in order to improve the gliding ability

Shear layer flapping and interface convolution in a separated supersonic flow

Abstract: The steadiness and convolution of the interface between the freestream and recirculating/wake core regions in an axisymmetric, separated supersonic flow were studied using planar imaging. Five regions along the shear layer/wake boundary were investigated in detail to quantify the effects that key phenomena, such as the recompression and reattachment processes, have on the development of large-scale unsteady motions and interfacial convolution. These studies show that flapping motions, when viewed from the side, generally increase in magnitude, in relation to the local shear layer thickness, with downstream distance, except at the mean reattachment point, where they are slightly suppressed. When viewed from the end, the area-based (pulsing) fluctuations increase monotonically downstream as a percentage of the local area, whereas the position-based (flapping) motions show pronounced peaks in magnitude in the recompression region and in the developing wake. The interface convolution increases monotonically with downstream distance in both the side- and end-view orientations

Experimental and Numerical Optimization of a High-Lift System To Improve Low-Speed Performance, Stability, and Control of an Arrow-Wing Supersonic Transport

Abstract: An investigation was performed to evaluate leading-and trailing-edge flap deflections for optimal aerodynamic performance of a High-Speed Civil Transport concept during takeoff and approach-to-landing conditions. The configuration used for this study was designed by the Douglas Aircraft Company during the 1970's. A 0.1-scale model of this configuration was tested in the Langley 30- by 60-Foot Tunnel with both the original leading-edge flap system and a new leading-edge flap system, which was designed with modem computational flow analysis and optimization tools. Leading-and trailing-edge flap deflections were generated for the original and modified leading-edge flap systems with the computational flow analysis and optimization tools. Although wind tunnel data indicated improvements in aerodynamic performance for the analytically derived flap deflections for both leading-edge flap systems, perturbations of the analytically derived leading-edge flap deflections yielded significant additional improvements in aerodynamic performance. In addition to the aerodynamic performance optimization testing, stability and control data were also obtained. An evaluation of the crosswind landing capability of the aircraft configuration revealed that insufficient lateral control existed as a result of high levels of lateral stability. Deflection of the leading-and trailing-edge flaps improved the crosswind landing capability of the vehicle considerably; however, additional improvements are required.

Flapping-wing mechanism of artificial bird

Abstract: The utility model relates to a flapping-wing mechanism for artificial birds, comprising a bird casing whose center is provided with a DC electric magnet and a wing casing. The position which is corresponding to the DC electric magnet and is on the wing casing is provided with a permanent magnetic block. A connecting piece on the upper end of shells of an artificial bird and swings is an elastic sheet to replace a soft cloth strip in the prior patent of CN2177981Y applied by Shuhongqi. The elastic sheet can make artificial birds complete the action of wing flapping naturally, vividly, and livingly. The amplitude of the wing flapping can be larger, and any mechanical trace can not be exposed on the external of the artificial birds. The utility model can reach a spurious process effect nearly.

Stabilization of Periodic Flap-Lag Dynamics in Rotorcraft

Abstract: An approach developed to stabilize periodic orbits in chaotic attractors is generalized and applied to non-chaotic flap-lag instability in helicopter rotor blades Periodic flapping and lead-lag oscillations occur in rotor blades during forward flight; the governing equations are nonlinear with periodic coefficients Oscillations become unstable as the advance ratio of the helicopter increases Stabilization may be achieved by control of the mean pitch angle of the blade once per period according to a discrete control law The control law is applied to the Poincare map which governs samples of the system obtained once per period The controller stabilizes but does not attempt to change underlying periodic orbits This approach is particularly well-suited to systems with periodic coefficients (such as rotorcraft) since the discrete version of the system is time-invariant

Studies on a horizontal axis wind turbine with passive pitch-flap mechanism (performance and flow analysis around wind turbine)

Abstract: We describe the development of a passive system to control the output power of a horizontal axis wind turbine. This pitch-flap coupling mechanism can reduce rotor power above rated wind speed. This mechanism has two kinds of blade motions: the flapping and the pitching motions. Braking effects are investigated experimentally

Free Flight of Dragonfly and Flow

Abstract: The flapping styles of dragonflies in horizontal free flight and at take-off from a vertical wall surface were observed and analyzed with a high-speed video camera. Also, a dragonfly was set in a wind tunnel and flow states generated by flapping of wings were visualized by smoke flow. The results represented the facts that when the wings were flapping with amplitude of about 50-80 degrees, the flow upstream of the body was sucked into the lower pressure region around the body, and in the wake, convex protuberance and concave depressions are brought about on its boundary of the wake. Moreover, when the wings are flapping with amplitude of 3-5 degrees, a mushroom type of vortex was brought forth behind the wings.