Keiji Kawachi

Airfoil section characteristics at a low Reynolds number

The aerodynamic characteristics of airfoils operating at Re = 4 X 10 3 were examined, varying the parameters related to the airfoil shape such as thickness, camber, and roughness. Airfoils with good aerodynamic performance at this Re have the following shape characteristics : (1) they are thinner than airfoils for higher Re numbers, (2) they have a sharp leading edge, and (3) they have a camber of about five percent with its maximum camber at about mid-chord. The characteristics of airfoils are strongly affected by leading edge vortices. The measured two-dimensional airfoil characteristics indicate that the planform, which greatly affects the flight performance of the three-dimensional wing at high Reynolds numbers, has little effect on the flight performance at this Reynolds number.

Comparison of Wing Characteristics at an Ultralow Reynolds Number

The hydrodynamic characteristics of 20 wings of different airfoil shape were measured at Re = 4 X 103. Each wing had an aspect ratio At of 7.25. Comparison of the measured wing characteristics showed that hydrodynamic characteristics of a wing with a rectangular airfoil can be improved by either a camber of 5%, a sharp leading edge, or proper corrugation

A fringe shadow method for measuring flapping angle and torsional angle of a dragonfly wing

A fringe shadow (FS) method was developed for measuring the flapping angle and torsional angle of a dragonfly wing during beating motion. This new method involves two sets of fringe patterns projected onto the wing from orthogonal directions. The torsional angle is determined using the length of the shadow of the wing chord that is cast by the two sets of fringe patterns. The flapping angle is determined using the shadowgraph of the wing projected by a laser. The advantages of the FS method are its capability (i) to measure the flapping angle and torsional angle of a dragonfly wing simultaneously using only one high-speed camera and (ii) to recognize the spanwise position of a section from the number of fringes, without having to use diffuse marks that are common in current methods. The resolution of the FS method can be changed easily by adjusting the fringe spacing. The measurement results for the torsional angle and flapping angle of a dragonfly wing prove the effectiveness of the FS method in studying the flight performance of dragonflies.

A scanning projected line method for measuring a beating bumblebee wing

A scanning projected line method was developed for measuring the flapping angle, lag angle, torsional angle and torsional deformation of a bumblebee wing during beating motion. The method uses an acousto optic deflector (AOD) with high diffraction efficiency to generate projected lines, allowing us to adjust the interbeam angle easily, and to measure the wing with low reflectivity. Combining AOD with a grating, we can measure a beating bumblebee wing with a large measurement range.

ANALYTICAL PREDICTION OF HEIGHT-VELOCITY DIAGRAM OF A HELICOPTER USING OPTIMAL CONTROL THEORY

The autorotative landing of a single-engine helicopter following power failure is analyzed using optimal control theory. The optimization problems are formulated to minimize the unsafe region in the height-velocity diagram under the condition that the touchdown speed is within the capability of the landing gear. Nonlinear equations of motion are described using a rigid-body dynamic model with longitudinal three degrees of freedom. The aerodynamic model of the rotor takes account of the effects of blade stall during descent and increased induced flow in the vortex ring state. The present method gives a good estimation of the height-velocity boundary in comparison with the existing flight test data. It is pointed out that the test pilot started the collective flare earlier than that occurred in the optimal solution.

Optimal Takeoff of a Helicopter for Category A V/STOL Operations

Two applications of a nonlinear optimal control theory are used to calculate the optimal control procedures for a helicopter following one engine failure during takeoff. One application is concerning the problem of optimization of the takeoff procedure for category A short-takeoff-and-Ianding (STOL) operation so that the required heliport size is minimized. The results show that the required takeoff distance using the normal takeoff procedure can be reduced by 30-60% if the takeoff path and the critical decision point are specifically optimized for a given set of the operating conditions, e.g., takeoff weight, ambient conditions, and heliport configuration. The second application concerns the problem of evaluation of the takeoff performance for category A verticaltakeoff-and-landing (VTOL) operation. The calculated maximum weight for the normal takeoff path shows good agreement with the certificated takeoff weight. Additionally, optimization of the takeoff path is shown to allow increasing the payload by 10%.

Response characteristics of visual altitude control system in Bombus terrestris

SUMMARY Frequency response characteristics of bumblebees to vertical visual oscillations were measured and analyzed. We measured the vertical force of the bees at four oscillation frequencies (0.9, 1.8, 3.6 and 7.4 Hz), and summarized their response characteristics in terms of amplitude and phase differences. The amplitude was almost constant throughout the examined frequency domain, whereas the phase gradually lagged with increasing frequency. In order to view the relationship between the input (visual oscillation) and output (response of the bee) more clearly as a control system, we compared them in the same dimension; we calculated hypothetical positions of the tethered bees on the basis of the measured variation in the vertical force, and compared them with the visual stripe positions. The resultant gain and phase data were plotted on a Bode plot. A transfer function was identified from the Bode plot, revealing that the response characteristics of the measured system could be represented as a simple expression. The dynamic control characteristics of the bumblebees were analyzed on the basis of the frequency response data. First, we showed that the measured system possesses a substantial stability margin. This means that the control system has substantial damping characteristics, and was suitable for stable flight control. In addition, our results showed that the measured bumblebee system possesses superior steady state and quick-response characteristics in comparison with a human pilot-vehicle system. Such excellence in both the steady state and transient characteristics (i.e. damping and quick response characteristics) provide the evidence that bumblebees can effectively control their flight with stability and maneuverability.

Two-directional scanning method for reducing the shadow effects in laser triangulation

A two-directional scanning method has been developed to reduce the shadow effects in laser triangulation probes. This method, which we call 2DS, uses an acousto-optic deflector (AOD) as a scanner to allow a diffracted beam to scan an object from two directions, and a position sensor to detect the shift of a spot projected from these two directions alternately by a time-sharing technique. The shadow effects are thereby reduced by this two-direction projection. First we determined the accuracy of the 2DS method by measuring the displacement of a plastic plate along the x- and y-axes and then comparing the results with those obtained using a linear gauge. Then we confirmed the capability of the method by using it to measure the cross sectional shape of a half-ball button, and then comparing the results with those obtained using a conventional one-directional scanning laser triangulation method. A relative uncertainty of 0.8% was obtained.

High-speed voltage-sensitive dye imaging of an in vivo insect brain

We have developed an improved optical recording technique with high spatio-temporal resolution to investigate neural activity from an in vivo insect brain. Optical images were acquired from hawk moth antennal lobe (AL) neurons. When activity was elicited by electrical stimulation of the antennal nerve using a stereoscopic microscope, depolarization followed by hyperpolarization was consistently recorded in the AL. When gamma-aminobutyric acid (GABA)-mediated synaptic transmission was blocked by the picrotoxin, the typical hyperpolarization was greatly reduced while no changes were observed in the depolarization. This suggests that the hyperpolarization results from inhibitory postsynaptic potentials (IPSPs) originating from GABA-sensitive chloride channels on the AL neurons.

Two-dimensional, noncontact measurement of the natural frequencies of dragonfly wings using a quadrant position sensor

A new method for measuring vibrations using a quadrant position sensor has been developed. It allows noncontact measurement of natural frequencies of objects that are transparent and small or lightweight, such as dragonfly wings. It simultaneously measures natural frequencies in two dimensions without any reflective mark having to be placed on the object. The system consists of a laser light source, a quadrant position sensor, and a spectrum analyzer. The object is illuminated by divergent laser rays coming from a microscope objective lens. The vibration amplitudes of the object are magnified and detected by the position sensor. By adjusting the distance between the object and either the lens or the sensor, the sensitivity and linearity of the system can be changed to measure objects of different size. We measured the natural frequencies of a dragonfly wing along the chord and the span, using a vein as a mark to measure displacement during vibration. This allowed us to determine the natural frequencies of bending and torsional deformation. Our results show that this two-dimensional, noncontact method can be effectively applied to the field of millibioflight.