Okay, so where should the center of gravity (CG) be? We know we can’t change the neutral point without changing our aircraft, so we can only adjust our CG.
Let’s try putting it behind the neutral point. We have our lift pulling the nose and wing up, and our weight pulling the aircraft down. This seems great, because we generally like having our airplanes go up.
But if we increase our angle of attack, like if we get hit by a wind gust, our lift also increases…which pivots the nose and wing even higher…which increases the angle of attack more…and we have a harmful feedback loop. This is an unstable aircraft, like a ball at the top of a hill: any small push in one direction will send it careening down the hill.
We don’t really like that. (Except in fighter planes—but those are special.)
So let’s try putting our CG in front of the neutral point, so our weight pulls the aircraft down and the lift pushes it up. Now we’re flying along and we get hit by that same wind gust, so our nose gets pushed to a higher angle of attack.
But this time it’s different—the lift increase from that wind gust is acting behind the CG, so it actually rotates the aircraft and pushes the nose back down. We avoid that harmful feedback loop entirely, our nose drops back to where it originally was, and we putter along like nothing ever happened.
This is exactly what we want. We call this a stable aircraft—just like a pendulum, a push in one direction or another will always return to the center equilibrium.
Okay, but how close or far to the neutral point should the CG be? How do we control our center of gravity location? And why are fighter planes so special, anyways?
Let’s talk about that tomorrow.