Despite being one of the most profuse and successful forms of vehicular transport ever, the airplane’s ability to fly remains a mystery to many people. The fact that an ungainly multi-ton object like a Boeing 747 can roll down a mile of paved surface and lift inexplicably into the air is both amazing and yet ordinary. How can such a thing happen? The answer: aerodynamics. On March 6, as part of the Engineering Saturdays lecture series, graduate student and PhD candidate Serhiy Yarusevych presented answers to the above and many other questions.
Most vehicles are acted upon by the forces of weight, thrust and drag. Weight drags a vehicle towards the earth’s centre, thrust propels it forward and drag is friction fighting against thrust’s force. Sometimes vehicles like Indy cars will inadvertently generate a fourth force called lift, which pulls upwards; in land-based vehicles this usually happens with disastrous results. An airplane uses its wings to intentionally generate lift and carry it aloft in a more controlled manner. A wing’s shape viewed from the side (called an airfoil) separates the airflow around it into a dense, fast moving stream underneath and a slower, less dense mass over top. Because dense air masses tend to move towards less dense masses, the air underneath pushes its way up against the wing, thereby lifting the aircraft into the air.
Airflow may seem a mild force-certainly not powerful enough to send a 747 thousands of feet into the atmosphere, but doubters may (very carefully) try putting their hands outside the window of a car moving at 60km/h and remember that the speeds aircraft travel at are sometimes easily ten times this rate. When dealing with such velocity the forces of drag and lift carry a great deal of effect.
Aircraft and other vehicular designs depend heavily upon aerodynamic considerations, not merely because of the desire to generate a maximum of lift and thrust but to minimize weight and especially drag. Sometimes, as is the case with the above-mentioned accidents where cars generate lift and loose stability, an inverted wing called a spoiler is used to push the car back onto the driving surface. Alternatively, “ground effects” are designed into a car’s shape-a concave space is left underneath the vehicle’s body that generates a vacuum during driving, and the suction created by the vacuum pulls the car towards the ground. Other types of spoilers force air down into the vacuum space created behind flat backed vehicles like station wagons to reduce drag and increase fuel economy.
Yarusevych’s lecture covered much of the above material in addition to aircraft testing procedures, present and future aviation projects and a brief overview of the history of human flight. Scientific aerodynamic testing has been around since at least the dawn of aviation itself, with one of the first wind tunnels ever built constructed by the Wright brothers themselves. Prior to their historical first flight the Wrights built a number of kites and gliders to test their theories in experimentation; today wind tunnel and flight testing are done in a similar fashion. Scale and full-size models are tested for their aerodynamic properties, then prototypes are built and flight tested, a process which can take years.
The engineering Saturdays lecture series is designed with prospective students in mind and will continue until the middle of April with coverage of the architecture of materials and AutoCAD design software.
