Abstract
An extant bird resorts to flapping and running along its take-off run to generate lift and thrust in order to reach the minimum required wing velocity speed required for lift-off. This paper introduces the replication hypothesis that posits that the variation of lift relative to the thrust generated by the flapping wings of an extant bird, along its take-off run, replicates the variation of lift relative to the thrust by the flapping wings of a protobird as it evolves towards sustained flight. The replication hypothesis combines experimental data from extant birds with evidence from the paleontological record of protobirds to come up with a physics-based model of its evolution towards sustained flight while scaling down the time span from millions of years to a few seconds. A second hypothesis states that the vertical and horizontal forces acting on a protobird when it first encounters lift-off are in equilibrium as the protobird exerts its maximum available power for flapping, equaling its lift with its weight, and its thrust with its drag.
Highlights
Lift is often considered the primordial force leading the primitive, evolving bird, referred to here as a protobird, towards sustained flight, a pervasive concept in the field of flight biomechanics.A protobird is a non-flying, non-descript animal capable of running while generating thrust by flapping its wings
The limited flapping kinematics of a protobird is assumed to involve a low level of specific kinetic energy available at its wings, that increases along evolution, until reaching a critical level
This paper presents: (i) the replication hypothesis, applicable along the take-off run of a protobird, and (ii) a hypothesis that proposes the protobird to be in equilibrium when first encountering lift-off, a condition defined by two simultaneous equations
Summary
Lift is often considered the primordial force leading the primitive, evolving bird, referred to here as a protobird, towards sustained flight, a pervasive concept in the field of flight biomechanics. This paper presents: (i) the replication hypothesis, applicable along the take-off run of a protobird, and (ii) a hypothesis that proposes the protobird to be in equilibrium when first encountering lift-off, a condition defined by two simultaneous equations. Both of these hypotheses make use of the normalized lift, η L , normalized thrust, η T and the normalized drag, η D (counterparts to the lift coefficient CL , the thrust coefficient CT , and the drag coefficient, CD ), nondimensional numbers that have a physical meaning, and can be applied directly.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
