Airplanes | How Do They Fly?
“I can state flatly that heavier than air flying machines are impossible.” Baron William Thomson Kelvin told this quote in 1895. By 1917, Albert Einstein had explained the relationship between space and time. But that same year, he designed a flawed airplane wing. His attempt was based on an incomplete theory of flight. Insufficient and inaccurate explanations still circulate today. So, where did Einstein go wrong? And how do planes fly?
Understanding Lift:
Although we don’t usually think of it this way, air is a fluid medium, it’s just less dense than liquids like water. Objects that are less dense than air float in it, while denser objects need an upward force, known as lift, to keep them airborne. For aircraft, this force is primarily created by the wings.
The “Longer Path” or “Equal Transit Time” explanation is an especially common false explanation of lift. It claims that air molecules passing over the top of a curved wing travel further than those traveling underneath. For the air molecules above to reach the wing’s trailing edge in the same instance as those that split off and went below, air must travel faster above, creating a pocket of lower pressure that lifts the plane. This explanation has been thoroughly debunked. Air molecules above and below a wing do not need to reform into each other. In the real world, air moving on top reaches that trailing edge considerably sooner than the moving air below.
How Lift Develops:
Imagine a wing motion as if replicating an actual airplane wing movement. As that wing moves forward in the air surrounding it, it’s actually altering or influencing the stream of air. As air meets the wing’s solid surface, a thin layer sticks to the wing. This layer pulls the surrounding air with it. The air splits into pathways above and below the wing, following the wing’s contour. As the air routed above makes its way around the nose of the wing, it experiences centripetal acceleration, the force you also feel in a sharply turning car. Therefore, above, the air gathers more speed than the air traveling below. Coupled with this increased speed is a decrease in pressure above the wing, which pulls even more air across the upper surface of the wing. The air flowing across the lower surface has less change in direction and speed. The pressure across the wing’s lower surface must therefore be higher than that above the upper surface. This pressure difference leads to the force that lifts upwards. The more rapidly the plane moves, the more pressure difference it creates and thus the stronger the force is. When this upward force surpasses the downward force of gravity, the plane is off and running.
The smooth flow of air past curved wings. But curve shape is not the reason for a wing’s lift. Indeed, a flat wing angled upward deflected airflow creates lifting the air curves to follow it, building and sustaining the pressure difference. On the other hand, a curve that is too sharp or too steep angles is disastrous in this case, the airflow above breaks away from the wing and becomes turbulent.
Einstein’s Wing Design:
This is probably what happened with Einstein’s wing design, nicknamed “the cat’s back.” By increasing the wing’s curvature, Einstein thought it would generate more lift. But one test pilot reported that the plane wobbled like “a pregnant duck” in flight.
More Factors Affecting Lift:
Our explanation is still a simplified description of this nuanced, complex process. Other factors, such as the air sweeping meters beyond the wing’s surface, being carried up, then down, or air vortices formed at the wing tips, all impact lift. Even though experts may agree that a pressure difference produces lift, how they explain can differ. One might focus on the behavior of the air at the wing surface; another might draw attention to the upward force as the air is deflected downwards. But the math itself is not in dispute. Engineers use a particular set of formulas, known as the Navier-Stokes equations, to accurately model airflow around a wing and provide detailed descriptions of how lift is created.
Conclusion:
More than a century after Einstein’s experiment in aeronautics, the mystery of lift still continues. But when it feels like everything is about to come crashing down, remember, it’s just the physics of fluid in motion. It’s understanding lift and the factors that make it possible for engineers and pilots to design and operate aircraft in safety and efficiency. Next time you see a plane soaring through the sky, you’ll know it’s not magic, but science at work.
FAQs:
1. What is a lift in aviation?
Lift is an upward force that allows planes to stay aloft.
2. How is lift generated?
Lift is generated by the wings through pressure differences.
3. What was the flawed theory of lift?
The “Longer Path” explanation, which has been debunked.
4. How does wing curvature affect lift?
Wing curvature influences airflow and pressure differences.
5. What happened with Einstein’s wing design?
It was too curved, causing unstable flight.
6. What equations model lift?
The Navier-Stokes equations model airflow and lift generation.