How can I simulate a nose-heavy airplane in three.js? [closed]

I'm building a simple flight simulator in three.js and I want my plane's nose to constantly pull towards the ground, no matter how it is oriented. I tried plane.rotateX, but that will make it pull down relative to the plane, consequently, if you are flying upside down, it will pull up relative to the ground. I tried having it increase the plane.rotation.X value, but that rotates it relative to the world X axis, so if you turn 90 degrees to either side, it tries to make you roll, and if you turn 180 degrees, it will make you pitch up instead of down. I'm guessing it's some sort of complex vector math, which is not one of my strong points, so if you know how, please explain in somewhat simple terms.