Aerodynamic characteristics of feathered dinosaur shapes measured using physical models: a comparative study of maneuvering

<p>Cite as:  Cam, Chun, Huynh, Mehrabani, Tse, and Evangelista 2011.  Journal of Vertebrate Paleontology 31(Supplement 2):129-130. </p> <p> </p> <p>Society of Vertebrate Paleontology Annual Meeting 2011, Las Vegas NV. </p> <p> </p> <p>Related manuscript submitted and in review. </p

Dataset for Evangelista et al (2014), Aerodynamic characteristics of a feathered dinosaur measured using physical models: effects of form on static stability and control effectiveness, accepted to PLoS

<p>Dataset for Evangelista et al (2014) PLoS ONE 9(1):e85203 - the DOI for the main paper is 10.1371/journal.pone.0085203; a preprint has been deposited at bioRxiv at the URL listed below. The data are also hosted on Bitbucket; for the latest bleeding-edge repository copy:</p> <p>hg clone ssh://[email protected]/devangel77b/microraptor-data</p

Aerodynamic Characteristics of a Feathered Dinosaur Measured Using Physical Models. Effects of Form on Static Stability and Control Effectiveness

<div><p>We report the effects of posture and morphology on the static aerodynamic stability and control effectiveness of physical models based on the feathered dinosaur, <i>Microraptor gui</i>, from the Cretaceous of China. Postures had similar lift and drag coefficients and were broadly similar when simplified metrics of gliding were considered, but they exhibited different stability characteristics depending on the position of the legs and the presence of feathers on the legs and the tail. Both stability and the function of appendages in generating maneuvering forces and torques changed as the glide angle or angle of attack were changed. These are significant because they represent an aerial environment that may have shifted during the evolution of directed aerial descent and other aerial behaviors. Certain movements were particularly effective (symmetric movements of the wings and tail in pitch, asymmetric wing movements, some tail movements). Other appendages altered their function from creating yaws at high angle of attack to rolls at low angle of attack, or reversed their function entirely. While <i>M. gui</i> lived after <i>Archaeopteryx</i> and likely represents a side experiment with feathered morphology, the general patterns of stability and control effectiveness suggested from the manipulations of forelimb, hindlimb and tail morphology here may help understand the evolution of flight control aerodynamics in vertebrates. Though these results rest on a single specimen, as further fossils with different morphologies are tested, the findings here could be applied in a phylogenetic context to reveal biomechanical constraints on extinct flyers arising from the need to maneuver.</p></div

<i>Microraptor gui</i> from [2], a dromaeosaur from the Cretaceous Jiufotang Formation of Liaoning, China; physical models, and sign conventions.

<p>A, Holotype specimen IVPP V13352, scale bar 5 cm. Notable features include semilunate carpal bones, a boomerang-shaped furcula, a shield-shaped sternum without a keel, uncinate processes on the ribs, unfused digits, an intermediate angle of the scapulocoracoid, and a long tail of roughly snout-vent length. In addition, there are impressions of feathers on the forelimbs, hindlimbs, and tail. B-J, Physical models of <i>M. gui</i>, scale model wingspan 20 cm, snout-vent-length 8 cm. Reconstruction postures, B-I, used for constructing physical models: B, sprawled, after <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-Xu1" target="_blank">[2]</a>; C, tent, after <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-Davis1" target="_blank">[34]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-Xu6" target="_blank">[58]</a>; D, legs-down, after <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-Davis1" target="_blank">[34]</a>; E, biplane, after <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-Chatterjee1" target="_blank">[32]</a>. F-I additional manipulations: F, asymmetric leg posture with 9090 leg mismatch ( <i>arabesque</i> ); G, example asymmetric leg posture with 45 dihedral on one leg ( <i>dégagé</i> ), H, sprawled without leg or tail feathers; I, tent without leg or tail feathers. J, test setup; K, sign conventions, rotation angles, and definitions for model testing, after <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-McCay1" target="_blank">[10]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-McCay3" target="_blank">[30]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-McCormick1" target="_blank">[31]</a>.</p

Presence or absence of leg and tail feathers can substantially alter longitudinal plane aerodynamics.

<p>Sprawled and tent postures with and without feathers, all coefficients shown versus angle of attack, solid squares with leg and tail feathers, open squares without leg or tail feathers. A, Lift coefficient. Stall occurs at higher angle of attack when leg feathers are present. B, Drag coefficient. Leg feathers increase drag at high angle of attack, improving parachuting performance. C, Lift coefficient versus drag coefficient. D, Lift to drag ratio. Lift to drag ratio is improved slightly without the additional drag and less-efficient lift generation of hind wings. E, Pitching moment coefficient. Without leg feathers, stability is not achieved in either posture. F, Pitching stability coefficient.</p

Asymmetric tail movement (lateral bending) effect on yaw, tent posture.

<p>Baseline tent position (solid square), tail 10 left (open square), tail 20 left (open triangle), tail 30 left (open diamond). The tail is effective at creating yawing moments but at low angles of attack it is shadowed by the body and larger movements are needed (yellow versus red lines).</p

Asymmetric wing tucking control effectiveness for tent posture; both wings out (solid square), no right wing (open square) and no wings (open diamond).

<p>Tucking one wing produces large roll moments but at the expense of one quarter of the lift. Large yaw moments are not generated except at higher angles of attack where the leg and tail positions become more important. Rolling moments generated in the two-wing symmetric position illustrates the senstivity of symmetry, model positioning, and sting placement; in addition, yawing moments at extreme angle of attack further illustrate sensitivity to position which could be exploited as a control mechanism during high angle of attack flight.</p

Asymmetric leg dihedral (leg <i>dégagé</i>, see inset) effect on yaw.

<p>Baseline down position (solid square) versus one leg at 45 dihedral (down arrow). Placing one leg at a dihedral is destabilizing in yaw and produces side force and rolling and yawing moments due to the asymmetry.</p

The differences in yaw stability at different angles of attack also depend on the presence or absence of leg feathers.

<p>A, At 0, some feathered-leg postures are more stable in yaw than others. B, At 60, postures that were stable at 0 may go unstable, such as tent posture with leg feathers. C, At 90, all postures are marginally stable due to symmetry. Color represents the base posture: red for sprawled, blue for tent, green for biplane, and purple for down.</p

Asymmetric wing pronation (e.g. left and right wings pitched in opposite directions) control effectiveness for tent posture for wing pronation angles of –30 (large down triangle), –15 (down triangle), 0 (square), +15 (up triangle) and +30 (large up triangle).

<p>At low angles of attack, asymmetric wing pronation generates large rolling moments. At high angles of attack, there is a shift in function and asymmetric wing pronation tends to generate yawing moments instead of rolling moments. Function at high angle of attack is similar to what is observed in human skydivers <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-Cardona1" target="_blank">[37]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085203#pone.0085203-Evangelista1" target="_blank">[38]</a>. Organisms may have navigated this transition from high angle of attack to low.</p