Professor and Students Create Bird Flight Simulator
By: Rungun Nathan, Associate Professor of Engineering
It is Spring, and you are sitting by your window watching the birds pecking away at worms and seeds on the ground, and then suddenly they perform a squat-like motion, pull their wings out, flap hard, and fly away. Even raptors and other bigger, heavier birds do this with so much ease. They do not need a long runway nor do they need to run, accelerate, or gain high speed to take off. Watch the same birds land and that is an amazing feat too. They can land on an electric wire up in the air and never crash. Somehow in aping the flight of nature, we humans missed something.
The success of the Wright Brothers with their fixed wings brought an early demise to flapping flight. Not many know, but Otto Lilienthal had some preliminary success with flapping flight after studying the subject extensively. It is said that the Wright brothers and Lilienthal had exchanged several notes on flying machines.
In recent years, there has been a great interest in flapping flight, but most of it is focused on the smaller end of the scale, namely insects and other tiny flying creatures. The flights of these creatures are characterized by thin membrane wings that flap at a very high frequency.
My research with undergraduate students in the Mechatronics and Intelligent Systems (MeIS) lab at Penn State Berks focuses specifically on birds and more closely on how they generate lift and thrust from the flapping motion of their non-membrane wings. The research is not looking at gliding flight as seen in soaring raptors and other larger birds that use thermal eddies to soar, but at flapping flight at lower altitudes with a several types of disturbances such as wind gusts.
We need to overcome weight due to gravity by an opposing force called “Lift.” To move forward we need “Thrust.” Whenever there is thrust we have the necessary and evil force of “Drag.” The idea behind flight is to generate enough lift to overcome weight including any payload and focus the rest of the energy in generating thrust to move forward and maneuver in the air.
In our pursuit of the bio-mimicry of birds, we are working towards reducing the weight, while emulating the bird as closely as possible in the wing motion. You might notice that a bird’s flap is slower and takes longer on its path from the top to the bottom. Then on the return path, the wing is folded and goes to the top ready for the next flap in a quicker time.
The key focus of my research begins with the development of a quick return mechanism emulating the bird closely. In the mechanism, the flapping down motion, which generates lift, takes a longer time and the flapping up motion, which reduces the lift, is completed in a shorter time. The mechanism also replicates the wing fold on the motion of the wing to the top.
The group is experimenting with other types of quick return mechanisms. We have developed wings that replicate bird wing motion but with two joints rather than the three joints that are in an actual bird. Typically these joints would be powered by motors and would need batteries, which in turn would increase the weight. After several iterations, we have developed a wing which holds flat during the flap down and folds when flapping up. This was achieved by a custom developed passive mechanisms with springs.
Based on the simulations, membrane wings were built and tested It has been our groups’ belief that wind tunnels are excellent tools to study fixed wing flights, but are poor tools for studying flapping wing flight due to the disturbances caused to the air flow due to the moving wing. To overcome this, the MeIS team is developing an alternate test bed that is not wind tunnel based.
Our immediate goal is to be able to obtain a mathematical model for the flapping flight that can be used for the control of the flying bird we will build. The next step is to make the bird fly autonomously.