My flight just announced that it will be pretty empty, and that it is important for everyone to sit in their assigned seats to keep the weight balanced. What would happen if everyone, on a full flight, moved to one side of the plane?

Question

My flight just announced that it will be pretty empty, and that it is important for everyone to sit in their assigned seats to keep the weight balanced. What would happen if everyone, on a full flight, moved to one side of the plane?

In: 8623

Answer 1

If you fly model RC planes or paper airplanes you get to learn this lesson hands on but without all the crashing and dying. You want a plane that has a *center of gravity* located very close to the *center of lift* or the plane will be hard to control.

Center of what, now?

Planes like anything have a *center of gravity* (CG or CoG) basically the average location of all weight—the force pulling the aircraft toward the earth. For example, the CG of a uniform sphere is the center. With a lollipop, CG is closer to the middle of the sweet part because it’s heavier than the stick.

Similar to the concept of CG is the *center of lift* (CL), which is the average location of all upward (aka lift) forces of the wings.

Planes are symmetrical left to right. And cargo/people are located in the middle, left to right. So what matters then is matching the CG and CL along the long axis of the aircraft.

Imagine you balance a [wood yardstick](https://www.didax.com/pub/media/catalog/product/cache/541f549daeb5bdd8bd77b8568b2d1c3a/2/1/211553.jpg), which represents the plane, on your index finger. To do that it has to be located in the middle. Your finger/arm/muscles provide the lift forces. Gravity represents gravity (:)).

Pretend the 0″ mark is the nose and the 36″ mark is the tail.

Now tape a roll of quarters at the 24″ mark. Try to lift the yardstick from the middle and what happens? The heavier end rotates down around the lift point. The plane is tail heavy and wants to pitch up. Because the CG is behind the CL.

Likewise, a roll of quarters at the 12″ mark rotates down on that end. The plane is nose heavy and wants to pitch down.

Flying RC planes I find that a slightly nose heavy plane is easier to control than a slightly tail heavy plane. A very nose heavy plane is very hard to control and I’ll likely crash and a very tail heavy plane is impossible to control and I’ll definitely crash.