Shigeru Sunada

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

Unsteady Forces on a Two-Dimensional Wing in Plunging and Pitching Motions

Unsteady e uid dynamic forces acting on a two-dimensional wing in sinusoidal plunging and pitching motions in still water were measured. The measured e uid dynamic forces were larger than those estimated by quasi-steady analysis, where the effect of unsteady separated vortices on the e uid dynamic forces is not considered. Vortex capture is a phenomenon related to the larger e uid dynamic forces in wing motion that is similar to wing motion of real insects. By using the measured e uid dynamic forces, we identie ed combinations of plunging and pitching motions for maximum time-averaged thrust and for maximum efe ciency. Nomenclature a = dimensionless position of the rotational axis of the pitching motion b = span length of the wing immersed in water C`;Cd = lift and drag coefe cients Cn;Ct = normal and tangential force coefe cients CX;CZ = force coefe cients in X and Z directions c = chord length c = chord vector Fn; Ft = e uid dynamic forces normal and tangential to airfoil chord FX; FZ = e uid dynamic forces in X and Z directions Fx; Fz = forces in x and z directions f = frequency of both pitching and plunging motions

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.

Pitch, Roll, and Yaw Damping of a Flapping Wing

a = lift slope C = damping coefficient Cd = drag coefficient c = chord length of the wing c = mean chord length F = tension of the thread f = flapping frequency g = gravitational acceleration h = distance between the tip path plane and the center of gravity I = moment of inertia of the total system (i.e., the flapping-wing aircraft, suspension bar, and counterbalancing weights) K = a constant in Eq. (2) L = rolling moment Lp = roll damping of the flapping-wing aircraft l = distance between the two threads used to suspend a bar attached to the X-flapping-wing aircraft ls = length of each of two threads used to suspend a bar attached to the flapping-wing aircraft M = pitching moment Mq = pitch damping of the flapping-wing aircraft m = total mass of the flapping-wing aircraft, suspension bar, and counterbalancing weight ma = mass of the flapping-wing aircraft mw = mass of one wing N = yawing moment N r = yaw damping of the flapping-wing aircraft P = cycle period of rotation p = roll rate q = pitch rate R = wing length r = spanwise position r = yaw rate Sw = area of one wing t = time T = thrust vi = induced velocity = flapping angle 0 = mean flapping angle = amplitude of flapping motion = rotational angle 0 = initial rotational angle = amplitude of the rotational motion = feathering angle = amplitude of feathering motion = density of air = angle of the thread measured from the vertical direction of the gravitational force

High-resolution method for measuring the torsional deformation of a dragonfly wing by combining a displacement probe with an acousto-optic deflector

To better understand the passive torsional motion and to quantify the torsional motion of an insect, we developed a new scanning beam method that can measure with high resolution the variation in both the torsion angle and shape of an insect wing during pure flapping motion. This new method is based on the conventional principle used in a laser beam displacement probe with a position detector, but introduces the use of an acousto-optic deflector, which enables us to pass the scanning laser beam over the wing. Therefore, by measuring the relative displacement between the beam spots on the wing, we can determine the passive variation in both the torsion angle and shape of an insect wing with high resolution. According to the waveform supplied to the acousto-optic deflector, we define both a two-point scanning method, which we use to measure the variation in torsion angle, and a multipoint scanning method, which we use to measure the variation in shape. We apply these methods to a dragonfly wing at different flapping frequencies, and compare the results with those determined using a high-speed video camera. The good agreement between the two methods shows that the scanning beam method can be effectively applied in the field of biomechanics to study the torsion angle variation and shape variation of an insect wing.

Flutter of an Aircraft Flying on Mars

R ECENTLY, a Mars airplane was proposed that can explore a wider range than the Rover type explorer and with a higher image dissection than a satellite-type explorer. The atmospheric density, sound speed, and gravitational acceleration on Mars are different from those on Earth (Table 1). These differences cause differences in the design of an airplane between Mars and Earth. In this Note, we compared the wing flutter speeds on Mars and Earth. We considered the identical airplane flying on Mars and Earth and assumed the following. 1) The lift coefficient is the same on Earth and Mars. 2) The effect of compressibility is neglected. The equilibrium in the vertical direction is given by

Flow Control with Pitching Motion of UAV using MEMS Flow Sensors

This paper presents separation control using a MEMS flow sensor. The MEMS flow sensor measures flow field characteristics from which the separation position is estimated. An airplane’s attitude is then controlled by the elevons so that separation occurs at the desired position, resulting in a maximum lift coefficient. The fluid dynamics around the wing is modeled by dynamic wind tunnel experiments. The dynamic fluid model and direct measurements help to maintain separation control. A controller is designed using the H∞ control method with sufficient robust stability. Numerical simulations and actual flight tests were conducted, and the performance of the flow control was investigated.

A study of autorotating plant seeds.

A leading edge vortex exists on the upper surface of an autorotating plant seed. The vortex enhances the vertical aerodynamic force acting on the seed and decreases the rate of descent. We analyzed the flight data of rotary seeds and revealed that the lift-drag ratio affects the descent factor more strongly than the vertical force coefficient. This has also been confirmed by falling tests of model rotors, which have various aspect ratios, airfoil shapes and total masses.

Stability of Gliding Flight of a Swallowtail Butterfly

aD = coefficient of 2 for CD bW = wing length 2 c = chord length at yW c = mean aerodynamic chord CD = drag coefficient of a wing element CL = lift coefficient of a wing element CL0 = lift coefficient when W is zero CL0; 0 = CL0 when is zero CM = pitching moment coefficient of a wing element CD = @CD=@ W CD0 = drag coefficient when W is zero CD0, CD = CD0 and CD of swallowtail dD = drag acting on a wing element dFxW , dFyW , dFzW = forces acting on a wing element in xW , yW , and zW directions dL = lift acting on a wing element dM = pitching moment acting on a wing element dMxW , dMyW , dMzW = moments acting on a wing element about xW , yW , and zW axes FxS, FyS, FzS = forces acting on a right wing in xS, yS, and zS directions FxS;L, FzS;L = forces acting on a load cell in xS and zS directions g = acceleration of gravity h = distance between centers of gravity and a load cell IxxS, IyyS, IzzS = moments of inertia about xS, yS, and zS axes L0 , L 0 p, L 0 r, N0 , N 0 p, N 0 r = primed derivatives