Planes being able to fly is all based on 4 forces:
- Drag: the force that acts in the opposite direction of the plane and slows the plane down
- Lift: the upward force that allows an airplane to stay in the air
- Thrust: the forward force that propels the plane forward
- Weight: the downward force of gravity that pulls the plane toward the ground
(thank-you English engineer, inventor, and aviator George Cayley, who officially identified the four forces back in 1799)
The way planes are able to do this can be complicated for people who don’t study aviation. So decades ago, NASA gave a great example of these forces in simpler terms:
Have you ever thrown a Frisbee®? It flies because of four forces. These same four forces help an airplane fly. The four forces are lift, thrust, drag, and weight. As a Frisbee flies through the air, lift holds it up. You gave the Frisbee thrust with your arm. Drag from the air made the Frisbee slow down. Its weight brings the Frisbee back to Earth again.
And then, when applied to a plane, it goes this way:
- Thrust is a force that moves an aircraft in the direction of the motion. It is created with a propeller, jet engine, or rocket. Air is pulled in and then pushed out in an opposite direction. One example is a household fan.
- Drag is the force that acts opposite to the direction of motion. It tends to slow an object. Drag is caused by friction and differences in air pressure. An example is putting your hand out of a moving car window and feeling it pull back.
- Weight is the force caused by gravity.
- Lift is the force that holds an airplane in the air. The wings create most of the lift used by airplanes.
More from NASA:
The way the four forces act on the airplane make the plane do different things. Each force has an opposite force that works against it. Lift works opposite of weight. Thrust works opposite of drag. When the forces are balanced, a plane flies in a level direction. The plane goes up if the forces of lift and thrust are more than gravity and drag. If gravity and drag are bigger than lift and thrust, the plane goes down. Just as drag holds something back as a response to wind flow, lift pushes something up. The air pressure is higher on the bottom side of a wing, so it is pushed upward.
Companies that build planes are constantly looking at ways to have better control of those forces wherever possible. The addition of wingtips, for example (where the tip of the wing flips up), help increase lift.
You can also increase lift by increasing the thrust (read: use more powerful engines. When the plane begins to move faster, more air is forced over the wing, which produces more lift [think of how high that Frisbee went, depending on how hard you threw it]. But more powerful engines means more weight, which means gravity gets involved).
The weight of the plane is the force that airlines have the most control over. The weight of the actual plane is a constant. But airlines do a bunch of things to control what’s INSIDE the plane (here are a bunch of them. Some are really creative!). Controlling how heavy checked luggage is a way to keep the weight of the plane relatively constant. And knowing how heavy passengers are, is another.
Most airlines don’t weigh every passenger every time they fly; instead they have an idea of same, based on weight standards that get updated every few years.
It’s apparently “get new weight standards in South Korea” time. According to the country’s Ministry of Land, Infrastructure and Transport’s “Aircraft Weight and Balance Management Standards,” airlines must measure passenger standard weights at least every five years or as needed and calculate average values.
The last time they did weight measurements was 2018, so to be in compliance with these aviation laws, for the next few weeks, Korean Air will weigh passengers and their carry-on bags when they board domestic and international flights. Here’s the schedule:
- Domestic passengers at Gimpo International Airport will be weighed from Aug. 28 to Sept. 6
- International passengers at Incheon International Airport will be weighed from Sept. 8 to Sept. 19
The airline will weigh the passengers at the gates, before boarding. The airline says that the collected data will be anonymous and used for safety operations. Passengers who prefer to not participate in the measurements can inform the staff at the time of boarding. The airline specified that there are no plans to charge overweight passengers more, according to newspaper Korea JoongAng Daily (that was in response to a Korean Air passenger had. Another wanted to know they weigh less, can they bring more carry on baggage. [No, they can’t]).
Other airlines in South Korea will conduct their own weighing on their own schedules.
The United States also requires airlines to update their weight measurements; the last time was in 2021. At the time, the Federal Aviation Authority (FAA) allowed airlines to ask passengers to volunteer their weight and “make a reasonable estimate” if their numbers seemed to be too low.
Feature image: Raw Pixel
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