RESULTSPosture and leg & tail feathers have important effects on gliding performance and longitudinal (pitch) stability

but...leg & tail feathers drastically alter which AOA can be stably adopted.Leg & tail feathers increase parachuting performance at high AOA.

Leg & tail feathers appear to alter L/D...Leg & tail feathers affect lift by delaying stall.

Effects of leg and tail feathers on the gliding performance and aerodynamic stability of a small dinosaurAdrian Tisbe, Eric Guenther-Gleason, Dennis Evangelista, M. A. R. Koehl; University Of California, Berkeley

Abstract: Discoveries during the last decade of a diversity of feathered dinosaurs from the Cretaceous of China have led to considerable speculation about the roles that the feathers played on these extinct animals. The aerodynamic hypotheses can be tested empirically by measuring defined aspects of the gliding performance of physical models of the fossils in a wind tunnel. Feathers can be added or removed from the models to quantify their effects on aspects of performance such as glide distance, and also the stability and maneuverability that affect a falling animalʼs ability to navigate through complex habitats. We focused on Microraptor gui, a cat-sized dromaeosaur from the Cretaceous of China that had flight feathers on both its fore and hind limbs. We compared the lift, drag, and side forces, and the pitch, roll, and yaw moments on models with vs. without leg and tail feathers, and we tested the models in different symmetric and asymmetric postures that have been proposed by various researchers. In some cases leg and tail feathers had no effect, and in others they did (e.g. leg & tail feathers reduced drag for some postures at some angles of attack). Therefore, whether or not leg and tail feathers affected gliding, parachuting, or maneuvering performance depended on the posture and orientation of the dinosaur. These results will contribute to our understanding of the role of aerodynamic surfaces aft of a gliding animalʼs center of mass.

METHODSScale models of M. gui based on holotype specimen IVPP V13352 (Xu et al. 2003)were constructed using polymer clay, wire, and paper.

Models were mounted on a 6-degree of freedom force sensor and flown in a wind tunnel at 6 m/s.

Angle of attack (AOA) was varied with an adjustable sting.

DISCUSSIONFor the morphologies tested here, leg and tail feathers are essential for pitch stability.

Leg and tail feathers do not impede gliding performance at lower angles of attack, possibly because they are within the wake of the body. Leg feathers delay the onset of stall, allowing generation of lift at higher AOA, and improve parachuting performance at higher AOA by virtue of larger areas.

Feathered surfaces have higher control authority than those without feathers.

Some postures exhibit shifts in yaw stability when AOA is changed.

INTRODUCTIONMicroraptor gui was a small, forest-dwelling dinosaur with flight feathers on its arms and legs. The postures that M. gui could have adopted and the aerodynamic effects of leg & tail feathers are debated. Aspects of aerodynamic performance that might have affected M. guiʼs survival:

Parachuting performance - High drag (force parallel to air movement relative to a body) slows a falling animal so it hits the ground with lower force.Gliding performance - The ratio of lift (force normal to air movement relative to a body) to drag determines the horizontal distance an animal can travel per distance it falls.Static aerodynamic stability - An airborne animal is stable if the aerodynamic moments on its body when deflected tend to return it to its original orientation. Stable bodies also resist maneuvers. Control effectiveness - Altering the position of a control surface (wing, leg, tail) generates aerodynamic forces and moments for maneuvers.

RESEARCH QUESTIONSDoes posture alter basic parachuting or glide performance?Does the presence or absence of leg & tail feathers alter stability or control effectiveness?

FUTURE WORKExamine if other morphologies indicate greater aerodynamic stability or control effectiveness

Apply these methods to other species, within a phylogenetic context, to further our understanding of the evolution of early flying species

Further investigate effects of diverse aerodynamic surfaces aft of a bodyʼs center of mass

Acknowledgements: We thank the following students, who also participated in the M. gui project: Griselda Cardona, Chang Chun, Michael Cohen, Vincent Howard, Tony Huynh, Shyam Jaini, Austin Kwong, Felicia Linn, Alex Lowenstein, Divya Manohara, Dylan Marks, Neil Ray, Kyle Tse, Francis Wong, Karen Yang, Olivia Yu, and Richard Zhu.  This research was done through the Berkeley Undergraduate Research Apprentice Program (URAP) and was funded by the Virginia and Robert Gill Fund (to M. Koehl).  We also thank Robert Dudley for occasional use of his wind tunnel, Tom Libby and the Berkeley Center for Integrative Biomechanics in Education and Research (CIBER) for use of a force sensor.

Leg & tail feathers and angle of attack (or glide angle)can have a large impact on yaw stability

Stalling occurs at higher AOA when leg & tail feathers are present

AOA 0° AOA 60° AOA 90°

yaw angle, deg

yaw

mom

ent c

oeffi

cien

t

−0.02

0.00

0.02

0.04

−30 −20 −10 0 10 20 30

yaw angle, deg

yaw

mom

ent c

oeffi

cien

t

−0.01

0.00

0.01

0.02

0.03

0.04

−30 −20 −10 0 10 20 30

yaw angle, deg

yaw

mom

ent c

oeffi

cien

t

−0.02

−0.01

0.00

0.01

0.02

0.03

0.04

−30 −20 −10 0 10 20 30

angle of attack, deg

lift c

oeffi

cien

t

−0.4

−0.2

0.0

0.2

0.4

0.6

0 20 40 60 80

angle of attack, deg

drag

coe

ffici

ent

0.2

0.4

0.6

0.8

1.0

1.2

0 20 40 60 80

angle of attack, deg

pitc

hing

mom

ent c

oeffi

cien

t

−0.5

−0.4

−0.3

−0.2

−0.1

0.0

0.1

0 20 40 60 80

angle of attack, deg

lift t

o dr

ag ra

tio

−2

0

2

4

0 20 40 60 80

High lift-to-drag ratio indicates better gliding performance.

Leg & tail feathers have greater effect on drag at higher angles of attack

M. gui is stable when pitching moment is zero and the derivative is negative.

Neither tent nor sprawled positions are stable without hind feathers.

Without hind or tail feathers, higher L/D is not achievable due to instability.

with leg& tail feathers

without legor tail feathers

sprawled(Xu et al. 2003)

tent(Xu proposed)

20 cm

At 0° AOA, feathered legs & tail improve yaw stability in tent posture.

At higher AOA, tent posture with feathered legs & tail is unstable.

All postures are marginally stable when falling straight down.

feathered

not feathered

feathered

not feathered

feathered(STABLE)

not feathered(UNSTABLE)

delayed stall

up

down

right

left

Feathers alter the aerodynamic control authority of the appendages to which they are attached

without leg or tail featherswith leg & tail feathers

Control authority is smaller without leg or tail feathers for low to medium angles of attack.

Control authority is observed by moving the tail up 15° (upward triangle) or down 15° (downward triangle). Negative pitch is nose-down. Tail at 0° is shown with squares.

angle of attack, deg

pitc

hing

mom

ent c

oeffi

cien

t

−0.6

−0.4

−0.2

0.0

0.2

0 20 40 60 80

tail up

tail down

angle of attack, deg

pitc

hing

mom

ent c

oeffi

cien

t

−0.6

−0.4

−0.2

0.0

0.2

0 20 40 60 80

38 cm

angle of attack

air flow

open-jet wind tunnel

adjustable sting

Photo: Evangelista, Tisbe, Guenther-Gleason