Wing rotation and the aerodynamic basis of insect right

Science

Volumn 284, Issue 5422, 1999, Pages 1954-1960

  Dickinson, Michael H ^a   Lehmann, Fritz Olaf ^b   Sane, Sanjay P ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

^b UNIVERSITY OF WÜRZBURG   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; DYNAMICS; FLIGHT; FORELIMB; INSECT; MATHEMATICAL ANALYSIS; PRIORITY JOURNAL; ROTATION; STEADY STATE;

ANIMALIA; HEXAPODA; INSECTA;

EID: 0033580976     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.284.5422.1954     Document Type: Article

References (39)

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18. M. Cloupeau, J. F. Devillers, D. Devezeaux, J. Exp. Biol. 80, 1 (1979); M. H. Dickinson and K. G. Götz, ibid. 199, 2085 (1996); P. J. Wilkin and M. H. Williams, Physiol. Zool. 66, 1015 (1993).
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21. J. M. Zanker, Philos. Trans. R. Soc. London Ser. B 327, 1 (1990); C. P. Ellington, ibid. 305, 41 (1984); A. R. Ennos, J. Exp. Biol. 142, 49 (1989); F.-O. Lehmann, thesis, Eberhad-Karls-Universität Tübingen, Germany (1994).
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24. J. M. Zanker, Philos. Trans. R. Soc. London Ser. B 327, 1 (1990); C. P. Ellington, ibid. 305, 41 (1984); A. R. Ennos, J. Exp. Biol. 142, 49 (1989); F.-O. Lehmann, thesis, Eberhad-Karls-Universität Tübingen, Germany (1994).
25. D, was calculated by similar means. The same formulae were used in reverse to predict the translational component of flight force for a given set of kinematics.
26. K. C. Götz and U. Wandel, Biol. Cybernetics 51, 135 (1984).
27. To visualize the pattern of flow in the mineral oil, we forced air through a series of aquarium stones at the bottom of the tank. After a few large bubbles quickly rose, the remaining small, slowly rising bubbles generated a stable seed for both qualitative and quantitative analysis of the flow. To visualize a select section, we used fiber-optic pipes and pairs of black shutters to create thin slices of white light. For particle image velocimetry, images of bubble motion through a light slice were captured at 30 frames per second using a 0.5-inch diagonal chip CCD (charge-coupled device) camera. Flow fields were generated by finding maxima in 2D spatial cross-correlations of 40 pixel by 40 pixel windows from successive images. To reduce noise, adjacent windows overlapped by 50%. All software was written using MATLAB, version 5.2 (Mathworks, Inc.).
28. H. Wagner, Z. Angew. Math. Mech. 5, 17 (1925).
29. Our calibration procedure using a dummy inertial wing automatically eliminates any contribution of wing mass acceleration and gravity from our measurements. However, the mass of fluid attached to the wing ("added mass") is a dynamic quantity that may change with speed and angle of attack and is thus difficult to model either physically or mathematically. In order to test whether rotational transients might be caused by the translational inertia of added mass, we repeated our experiments using a modified kinematic pattern in which the translation of the wing was limited to a flat stroke plane (Fig. 3). Under these conditions, added mass acceleration might contribute to an error in the measurement of drag, but it should not contaminate the measurement of the lift. As indicated in Fig. 3A, the two large lift transients are still present during stroke reversal when the wing is flapped using the simplified kinematic pattern, indicating that added mass accelerations cannot explain the rotational forces. In order to test whether our results were contaminated by rotational inertia, we rotated the model wing according to the same kinematic pattern used in the other experiments, but in the absence of translation. The forces generated by this purely rotational motion were negligible.
30. Y. C. Fung, An Introduction to the Theory of Aeroelasticity (Dover, New York, 1993).
31. R. K. Adair, The Physics of Baseball (Harper and Row, New York, 1990).
32. To better study rotational effects, we used a simplified kinematics pattern in which translational motion was limited to a flat stroke plane and the upstroke and downstroke angles were equal (18).
33. M. H. Dickinson, F.-O. Lehmann, K. G. Götz, J. Exp. Biol. 182, 173 (1993).
34. R. M. May, in Diversity of Insect Faunas, L. A. Mound and N. Waloff, Eds., no. 9 of the Symposia of the Royal entomological Society of London Series (Blackwell, New York, 1978), chap. 12, pp. 188-204.
35. Drosophila are known to use the clap and fling at the start of the downstroke [K. G. Götz, J. Exp. Biol. 128, 35 (1987)]. Using the model fly, we measured a small (5 to 10%) increase in the mean lift produced during each cycle caused by this effect, which though significant, is small relative the effects of delayed stall, rotational circulation, and wake capture.
36. -12.8x). Thus, the forces generated by the wing at the center location fell within 1% of asymptotic values in all dimensions, indicating that the experimental conditions well approximate an infinite volume. It should be noted that in shortening the distance to the bottom of the tank, force production passed through a global minimum at a depth of 8 cm. The augmentation of lift at extremely low altitude is a manifestation of the ground effect, an interaction of a downward-directed wake with a solid boundary [J. M. V. Rayner, Philos. Trans. R. Soc. London Ser. B 334, 119 (1991)].
37. High-speed video films indicate that Drosophila wings do not twist extensively during flight. However, to test for effects of wing flexion, we repeated experiments using a flexible composite wing consisting of a Plexiglas leading edge and a thin metal foil blade. The thickness of the foil was chosen to produce deformations comparable to those observed in real flies. The use of flexible wings did not significantly alter any of the findings, although forces measured with rigid wings were typically higher than those measured with flexible wings.
38. The sensor was a miniaturized version of a design used in a previous 2D study (7). One sensor measured total force normal to the surface of the wing, while the other measured the force parallel to the surface in the chordwise direction. Preliminary experiments indicated that lengthwise parallel forces were negligible compared to the other components and have been ignored. Lift and drag forces, defined conventionally with respect to wing motion, were constructed trigonometrically from the normal and parallel channels. We deliberately designed the sensor to measure shear deflection and not cantilever bending so that measurements would not be sensitive to the loading distribution on the wing. Forces measured with calibration weights placed at the base, tip, trailing edge, and leading edge of the wing differed by <5%. The final calibration was based on static loading at the wing's center of area. During data collection, we used a low-pass four-pole Bessel filter with a cut-off frequency of 10 Hz, roughly 50 times the flapping frequency. Spectral analysis indicated that this filter introduced no appreciable phase lag within the range of relevant frequencies. During subsequent offline analysis, we conditioned each signal using an 8-pole recursive digital filter (Butterworth) with a cut-off of 5 Hz and zero phase delay (implemented in MATLAB, Mathworks, Inc.). Each trial consisted of a burst of four continuous wing strokes; four such bursts were averaged for each experimental condition. Force measurements during the first cycle of each burst were slightly different due to transient effects and have been excluded from the present analysis. Each experiment was repeated using an inertial model, consisting of a short brass cylinder machined to have an equal mass and center of mass to that of the wing. The data from the inertial model were subtracted from the raw wing data to remove the contributions of wing inertia and gravity.
39. Supported by grants from NSF (IBN-9723424), Defense Advanced Research Projects Agency, and the U.S. Office of Naval Research (M.H.D.).