 Today, we're going to discuss aircraft principle axes, and we're going to use a simple paper airplane to help orient ourselves. If you'd like to follow along, construct a paper airplane, and you'll probably also want a pencil to serve as an axis. The first axis we would like to discuss is the one extending from the front of the plane, running from the back of the plane, forward to the front of the plane. This axis has a particular name. You can help remember it by thinking that it runs along the longest part of the plane, and this is known as the longitudinal axis. The second principle axis runs out the side of the plane, out the right side of the plane, as you're looking at it from the top. This axis you might be able to remember if you can recall from American football the lateral pass, which goes sideways. It runs out the side of the plane, and it is called the lateral axis. You might also recall latitude and longitude. So if you remember longitudinal, you can also remember the lateral from the latitude and longitude. The third axis runs up and down, extending either from above or down below the plane. Obviously, they're running up and down. We use the word for up and down, which is vertical. So this axis is going to be known as the vertical axis. If you recall, many of our systems, our perpendicular systems in three dimensions, are oriented using the right hand rule. In order to know whether or not we want to go up or down with the vertical axis, let's go ahead and use our right hand and apply the right hand rule. The first axis we talked about is the longitudinal axis. So I'll begin by running my right hand along the longitudinal axis. I'm running my right hand axis with the lateral axis. And with this case, it's extending away from us. So if I bend my fingers toward the screen, that's the wrong direction. I need to turn around, bend my fingers in the direction of the lateral axis. Now that I've done that, if I extend my thumb, my thumb is now pointing in a direction that creates a right-handed system. So if I want a right-handed system with longitude first, lateral second, I'm going to be going down. And that is indeed the system that we are going to use for our aircraft principal axes. Once again, this downward axis is known as the vertical axis. Each of these axes serve a purpose when I'm attempting to describe the orientation of my airplane. The first axis, the longitudinal axis, if I take that axis, I wrap my right hand around the axis. And I think about the spin or the twist of that axis. So if I take my right hand and I bend my fingers, some of you might recall lefty, loosey, righty, tidy. If I tighten my fingers around my thumb, as I do that, if I turn the plane in that direction, you'll notice the plane will rotate in a clockwise direction. That is considered a positive spin. Well, there's a name for that positive spin that's turned around that axis. That is known as the roll. This is a positive roll and unwrapping my fingers would be a negative roll. Positive, negative. We will use the same convention for the lateral axis. If I turn my plane, so the lateral axis is horizontal, and then use my right hand, twist it around the axis, pointing my thumb in the direction, the positive direction of the axis. If I twist my fingers, you'll notice the nose of the plane will tend to go up, and if I release my fingers, the nose will go down. Positive, negative. This axis is called the pitch axis. Positive pitch, negative pitch. Similarly, if we consider our vertical axis, we can use the same convention. Now I'm going to look down at the top of the plane, extending the vertical axis out of the bottom of the plane, grab it with my right hand, and as I do so, as I twist my fingers around, the nose of the plane will turn clockwise, and as I unwrap them, counterclockwise. Positive, clockwise. Negative, counterclockwise. Positive, negative. This is known as the yaw axis, and if you're from the south, yaw better remember this one. Those three principal axes taken together help us to orient our airplane. Again, if we rotate around the longitudinal axis, this is our roll axis, if we rotate around the lateral axis, also known as our pitch axis, and if we rotate around the vertical axis, that's called our yaw, and we call that the yaw axis. You should practice a little bit with your airplane. Hold it in between your fingers, do something along this, and then practice the wave that's associated with each axis. You can do a little roll. You can wave with your pitch, and you can twist side to side with your yaw. Roll, pitch, yaw.