What is lift?
Understanding what makes an airplane fly (i.e., what gives an airplane lift) and how lift is generated is more important than you think. Unfortunately, it is common in the hobby of radio control to bypass or even outright ignore flight dynamics all for the sake of the desire to just get flying. So what is lift exactly? Well, it is what it sounds like. When you hear the word lift, usually you’ll think of an object being picked up and off of a surface. Be it weight in the gym or an elevator going up. Both imply an object leaving the ground where it once stood still. But how do you lift an airplane off the ground? Nobody is physically lifting the airplane, so how is it done?
Your airplane flies because you are pulling it through the air at a fast enough rate to cause the phenomenon of lift.
How does an airplane wing provide lift?
The atmosphere around us is made of many elements. For this discussion visualize the air we will be flying in as being packed with small particles or objects. These particles create the physical presence of our air.
Now zoom in on a section of our air and place a wing inside that space.
You can see our particles are not moving and neither is our wing. Therefore nothing is really happening short of lazy particles floating around doing a whole lot of nothing. Not very exciting. So let’s turn it up a notch and make our wing start moving forward through the air with the help of an engine.
Airflow and pressure create lift
With the wing in motion take note of its shape. The bottom of the wing is flat while the top of the wing has a curve. When we move relatively slow through the air the particles zip by unaffected and also not affecting the wing. However, if we speed up the rate at which the wing is passing through our air, the particles start acting very differently and begin to interact with our wing and its surface. Think of the particles zipping by our fast-moving wing like a traffic jam. Traffic will bottleneck to one point if 4 lanes of a highway are closed down to 1 lane. Now what you have are the same 4 lanes of traffic trying to get through a single lane. When our wing moves forward through the air, our particles begin acting much the same way as traffic and begin to bottleneck.
It’s the curved shape of our wing that causes this bottle-neck. Now the same amount of air, which had 4 lanes, must now use 1 lane to pass. And this decrease in space for all the air to pass through causes a dramatic increase in the speed of the airflow. Because of this faster airflow, there aren’t as many particles able to hit the wing. They don’t have time because they need to get moving over the wing and to the other side. This causes an area of Low Pressure to be created over the top of the wing (not many particles hitting the wing).
The differences in pressure on the wing, high vs. low, together cause lift.
Adversely, since there is not a curve on the bottom of the wing and the particles don’t have to squeeze into a smaller area to pass by, more particles can hit the wing surface. And this causes an area of High Pressure (lots of particles hitting the wing) below the wing. It’s these differences in pressure, high vs. low, that together cause lift. These forces independently do not cause lift, let’s be clear about that. The high pressure alone does not ‘push’ the wing up, just as the low pressure above the wing doesn’t ‘suck’ the wing into the air. They work as a team.
The reason your airplane flies is because you are pulling it through the air at a fast enough rate to cause the phenomenon of lift to occur on your wing. But keep in mind, speed does not always mean you’ll have lift. You can actually be moving quite fast in the air and suddenly lose altitude because you completely lost your lift. This loss of lift is called a stall.