Bio-aerial Locomotion (EK131/132)

Professor Robert Dudley, from UC Berkeley, is the world's leading expert in the evolutionary origins of flight, and flight maneuverability and flight performance in birds and insects. He answers students' questions on these and other subjects. (Audio only)

Explanation of aircraft wing tip vortices, and example observations. Bird wakes, continuous vortex and vortex ring type wakes, not really different 'gaits' but a continuum. Excursion to vortex rings in nature.

Flapping flight, continued. Engineering inspiration: SmartBird. History of ornithopter studies and Erich von Holst.

Yonatan Munk's dissertation focuses on how posture and morphology determine the stability and control in gliding ants. He approached the problem by means of field work and dynamical simulations in the lab. In his conversation with the students, he explains the new understanding in gliding behavior of ants and other wingless insects, how he worked on this problem for the past four years, and what some implications are for both evolutionary questions and engineering applications.

Prof. Full answers questions from the students on the active tails of geckos, and how this and other discoveries have been used by engineers. He describes the crazy cockroaches crashing onto a wall to start climbing, where "crashing is not a failure". He talks about the mysteries around the evolution of flight, and the difficulties of interdisciplinary collaboration. He also encouraged students to consider graduate study, and to get involved in undergraduate research as soon as possible.

In reptiles, gliding adaptations include webbed feet, like in flying frogs, and skin membranes between long ribs, in the case of flying lizards. A fossil record exists of a lizard that had this membrane, called patagium, and lived 125 million years ago. Flying (rather gliding) snakes can do amazing maneuvers in the air while falling, while flying fish have elongated fins that serve as a parasail. Gliding mammals also use a patagium, in this case, a skin membrane joining their limbs; examples are the gliding squirrel and the colugo.

Parachuting and gliding is very diverse in nature. There are some wingless insects can "skydive" in a control fashion, the gliding ants were the first insects discovered to perform "directed aerial descent". We discuss the amazing behavior of canopy ants, discovered by Prof. Steve Yanoviak.

Summary of results presented by the recent publications of the Berkeley group that discovered the fastest air-righting response ever measured. Zero-angular momentum air-righting model.

Flapping flight: a flapping flyer overcomes the cost of generating lift (drag) by producing thrust. To understand thrust production in flapping flight, which is quite complicated, we start by analyzing a simpler case: the thrust generation in airplane propellers. The analogy between a helicopter rotor and flapping wings is also discussed.

Guest speaker Prof. Jake Socha answers student questions about the gliding snakes (the first portion of his video conference was unfortunately not recorded, and the microphone used by the students is also not being captured, so only Prof. Socha's answers can be heard).

Continues the discussion of the aerodynamics of the gliding snake, from both wind tunnel experiments and computational simulations, as published by Prof. Jake Socha and collaborators. Motivation of next topic: Flapping Flight, by some slow motion videos of birds flying.

Discussion: What do you know about lift? Chrysopelea: the gliding snake. Its rib action causes the body to flatten, becoming a fairly good airfoil. The research of Prof. Jake Socha and collaborators is contributing to understanding the aerodynamics of the gliding snake, from both wind tunnel experiments and computational simulations. Excursion: flow around a circular cylinder and the von Kármán vortex street.

Deviations from the trend on the Great Flight Diagram (and explanation): Boeing 737, Gossamer Condor, the swifts. How birds change their wing area to fly at different speeds. The fastest animal in the planet: the peregrine falcon. On landing, birds open their wings as wide as possible to reduce speed.

In swifts, extended wings provide the best glide performance, but swept wings offer higher performance at high speeds. They also can bear higher loads for safety while executing fast turns. Turning back to The Great Flight Diagram, we note the continuity between the smallest bird and the largest insect.

The swallow, martin and swift lie to the left of the trend line on the Great Flight Diagram: they have large wings for their weight. But they do not fly slow in general; they fold their wings to fly fast! Most birds do this: they change wing geometry according to the flight conditions. Swifts are specially good at it: they fly while roosting, with their wings fully extended, at a speed of about 20 mph; with swept wings, they fly at speeds up to 60 mph. The engineering inspiration, called RoboSwift, was built by a Dutch team in 2008. We describe the studies of swift wing performance that led to an understanding of their morphing wings.

Ardian Jusufi takes some time off his busy schedule attending a conference on robotics, to answer some of the students' questions via video conference. How the knowledge about the gecko's air-righting response could be used for robots in search and rescue missions; the importance of asking simple and specific question to an experimental system; how the air-righting response was discovered almost by chance; some of the remaining questions about how flapping flight might have evolved, and more.

Wing loading is a function of velocity only: the higher the wing loading, the faster a bird must fly. Detour into some history of the science of flight: Sir George Cayley, the father of aerodynamics, introduced the fundamental idea of sustentation accomplished by moving a fixed surface through the air, and the separation of sustentation and propulsion. 19th Century flight theories: centred on the question of the power required for flight: a simple analysis leads to the relationship between power loading and wing loading. Scaling arguments leading to the relationship between wing loading and weight. The Great Flight Diagram, including ever creature or machine that flies on a wing loading / speed vs. weight logarithmic plot.

The live course posed a challenge question to students: what size tail would you need to perform the gecko's righting manoeuvre? Students' answers were posted as comments on a course blog post. One student only (and the winner) pointed to the use of the moment of inertia to solve this problem. We review in class the calculation of the moment of inertia of the gecko's tail. The next topic is the "Basic science of flight"— starting by a careful explanation of lift (including clarifying that the "equal transit time" version is wrong!).

We review the different morphologies of gliding animals, and discuss the colugo in particular. The wingsuit is presented as an imitation of nature, and we see an exciting demonstration on video. An introduction to the science of flight - wing "carrying capacity", the force of lift, the lift coefficient, stall, wing loading.

Prof. Steve Yanoviak, who discovered the gliding behaviour of canopy ants, joins the class via video conference and answers questions from the students: how he made his discovery, other interesting things ants do, and more.

When falling, geckos are able to right themselves turning their body in mid-air, and always land safely on their feet. Includes videos from research group of Prof Robert Full in UC Berkeley. Prof Full's TED talk of Feb. 2009 was shown in class, but is not in this video---see it at http://www.ted.com/talks/robert_full_learning_from_the_gecko_s_tail.html

What is the course about? We will discuss a selection of interesting cases of bio-aerial locomotion of increasing sophistication: falling, parachuting, gliding, flying & soaring. Nature is inspiring engineers today to design new devices such as micro-air vehicles and robots. We get a glimpse of the modern activity of bio-inspired engineering, in relation to the fields of aeronautics and robotics. (The course makes use of the Blackboard(TM) online learning environment, and a course blog.)