1. In other models of insect wings such as drosophila (Table 4, VI; Vogel53), cranefly (Nachtigall54) andlocust (Jensen52),the maximumlift coefficient is scatteredoverawiderange(0.6-1.3).AtverylowReynoldsnumbers(Re < 2,Table 4, VIII), Thorn and Swart55obtained the result that the steady aerodynamic forces actingonawing (spanbandchordc)movingwithaverylowspeed V aregivenby L = (3/2)iJib sin(2ct) andD = 6p.bV. Hence,theaerodynamicforces areproportionaltothe fluid viscosity //, wingspanb,and speed V butareindependentof the chord c.The coefficients are, as shown inTable 4, givenby CL= (3/Re) sin(2a) and CD - 12/Re and are inverselyproportionalto the Reynoldsnumberbased on the chord (Re= Vc/v). 358 A. AZUMA ET AL.
2. By making force measurement of tethered dragonflies, Somps and Luttges82reported that the simple large lift peaks of 15-20 times body weight or 15-20G occurred once in each stroke period and suggested that the lift generation was dominated by integrated interactions between wings rather than by the unsteady effects elicitedindependentlyby eachofthefour wings.Theresultofthe abovelift generation has sometimes been quoted in papers by Wakeling and Ellington95"97andEllingtonetal.98whostressthefavorableeffect oftheunsteadyseparatedflow. However, this extraordinary large lift is considered to be unrealistic for the flight of living creatures, except when rapidly maneuvering (Azuma and Watanabe50). Reavis and Luttges99presented later that the maximum lift obtained from the tethered dragonfly was 5.5G in escape mode and 3.7G in hovering mode.
3. It is awell-knownfact that asthe Reynolds number increases,the aerodynamic characteristicsof awing flying atlow Reynolds number (below the critical value) is improved (Okamoto105) and the surface roughness also improves the aerodynamic characteristics as if the Reynolds number increases equivalently. Many examples exist: the seeds of plants or samara (Azuma and Okuno106) and insect wings (Rees,107'108Okamotoet al.47).Yasuda andAzuma109demonstrated that 1) samarasareautorotatingwithahighlift coefficient, whichisclosetothemaximum coefficient of Q)17iax= 1.2-1.5, 2) by smoothing the surface irregularities on the samarawingofamaple,therateof spinwasreducedandthefalling rateincreased, and 3) by attaching thin columns near the leading edge of a model samara made of balsa wood, the falling rate was remarkably reduced. Some changes in performance are shown in Table 5.