 Well, hello. Today we're going to spend a little bit of time talking about some different terminology that we use to refer to the geometry of wings. And we're going to annotate a three-dimensional orthographic view of an airplane here to help illustrate where these different pieces and parts are. So if you want to follow along, you might want to pause the video for a second and sketch something similar to this so that you can also annotate your own notes. So there's a few terms that we're going to use here. The first term we're going to use is, we're going to refer to the wings and we're going to talk about the front of the wing, the part of the wing that actually meets the air when the airplane is moving first. This edge here, I will draw it here on this view. This is the plan view of the airplane. And there's that first line they're making in green. That is going to be called the leading edge, leading edge of the wing or the airfoil. Okay, notice we can also see that leading edge here. If we look at this side view of the plane, there's actually two leading edges, the one that's on the upper airfoil and the one that's on the lower airfoil. So if we have a leading edge, we're also interested in another term known as the trailing edge, the edge that comes behind. I'm going to draw that here in purple. There we go. There's the trailing edge of our top airfoil and also you'll see that there's actually a trailing edge here of the lower wing as well. Okay, and so let me go ahead and label that our trailing edge. So once we've identified the leading edge and the trailing edge, one very common measurement we make is the distance between those two things. And that distance will be parallel to the longitudinal axis. Remember, the longitudinal axis is this line along the length of the plane. Well, if we go parallel to that and we go from the leading edge perpendicular from that edge back to the trailing edge, that's a measurement. I'm not sure if I drew that exactly parallel there, but that measurement there going from the front to the back is a term called the cord. Now, notice the cord isn't always the same in all contexts. In this case, the cord is pretty consistent until we get toward the edge of the wing and that cord can vary as the shape of the wing changes. For a completely rectangular wing, the cord will stay the same, but that cord can vary depending on where you are in the wing. Now, when we're measuring this cord, because it can vary at different places in the wing, we will talk about different parts of the wing, the part of the wing that's close to the airplane where effectively the wing attaches to the airplane. In this case, it looks like there's one big wing going across the top of the entire airplane, but often other airplanes have separate wings one on each side of the airplane. So the place where it attaches to the plane is called the root, and so that distance from front to back at that place where it attaches to the plane is the root cord. In the case of a single wing, that root is considered to be the middle of the wing, and that might not be exactly where it attaches to the airplane, but we're treating this as an entire wing, so we'll stop the wing that there there's the root for the wing on the left and the wing on the right, and then on the other end, we have something called the tip. So we have the wing tip, which makes sense, and the wing root, which you may not have heard of before, but that's the terminology for those two parts. And notice if we're talking about the measurement at each of those places, the root cord is the measurement here at the root, and then the tip cord would be the measurement at the tip. Now, if it rounds off like that, it's hard to know exactly what that measurement is. It effectively goes to zero when it rounds off or if it comes to a point, but often if it ends abruptly like in a rectangle or something like that, that is a measurement that's of value. Okay, so we also have measurements just like we have a measurement from the leading edge to the trailing edge. We have a measurement along the wing from the tip to the root. Let me label that in red here from the tip to the root. Okay, we can also label it over here on this side along the wing, and that measure is known as the SPAN. Now notice it's going to be important that you discuss the context in which you're referring to the wing SPAN. Often the wing SPAN might be the context of the entirety of two wings from tip to tip, and that might be the reference of the span of the wing where it goes from tip to tip. Very often that's the context that's being used, but if you're also talking about just a single wing on one side, it might be from the tip to the root. So the term SPAN needs to be used in a context that's understood by whoever's communicating about it. All right, well now that we have that various terminology, one of the things that we might be interested in is the area of the wing. Now there's a couple of ways of talking about what the area of the wing is. All right, so one of the ways we're going to look about it here is I'm going to use a term called the wing planform area. And that area, the area of the wing planform is the area you see when you're looking at the planform or the shape of the plan of the airplane. In other words, it's the area you see here as we look down on the wing. That would be the wing planform area. Now notice that isn't necessarily the area of the top of the wing or the surface area of the wing, because if the wing is curved, which often it is, it will have a slightly different area that takes into account that curve. Just like if you look at an orange or a globe or a ball, the area that you see of the circle is different than the area of the hemisphere that you would see if you were trying to paint it, for example. So we will often refer to the wing of planform area as being the area that you see here. And that wing planform area will be roughly approximated by being the span times the cord. But I'm going to put a little dash above the cord here, where that cord is some sort of average cord. If it's a rectangle, then that average is the same, and it's just the cord. But that area is roughly the span times the cord. Later on in another video, we'll talk about ways that we can calculate area for more complicated shapes. But that's roughly an estimate for that area. What's also very useful is a measure known as the aspect ratio. Aspect ratio. An aspect ratio is a relationship in a shape between its length and its width or its length and its height. It basically will be a relationship in two, sometimes three dimensions, but in this case we're talking about two dimensions. Our aspect ratio in this case is going to be the relationship between the span of the wing, which is typically longer than the cord of the wing. So the simplest measure of aspect ratio is the span divided by the cord. In other words, if you have an aspect ratio of something like four, that means that the span of the wing, the wing is four times longer along that span than it is thick along the cord. So that has a pretty standard measurement for aspect ratio. Of course, that aspect ratio just works for a simple rectangular shape. There is another way of estimating the aspect ratio, which is to, instead of taking the span times the cord, you take the span squared and you divide it by the area. Now, notice if the area is rectangular, span times cord, then spans will cancel out and you'll get span over cord. It's the simple aspect ratio. But for a wing that varies quite a bit, maybe a wing that's triangular or a swept wing that we can see at another point in time, when you have different shapes of wings, sometimes that cord is not very consistent. So a better way of estimating the aspect ratio of the wing is to take the span squared and then divide that by the area, which defaults for into span over cord in the case of a simple rectangular wing. All right. So we have a number of different terms here now that we've discussed that we'll use when we talk about wing geometry. Let's now consider the wing geometry instead of looking just down this top view. Let's also consider that wing geometry from this view here on the, from the front view of the plane. Okay. You'll notice in this airplane that wing there is pretty level. All right. It doesn't change its angle. However, that's not always true about all airplanes. In fact, many airplane designs you'll see here on this airplane design, there is a very slight upward angle of the wing. It's very slight. If I try to draw a straight line here and then I draw an angle at the wing is there's a little bit of an angle there. Okay. That angle has a name we'll talk about in just a second. I will also point out that similarly, we might have a case where, and this is a little bit more pronounced in this particular picture, you'll see that that wing instead of being up off of the horizontal, it's actually down off of the horizontal. Okay. So that particular term, the term for those particular things are as follows. If it's up, it's called a dihedral angle. Oops. Angle. And if it's down, it's called an anhydral angle. Tips up and tips down. Notice that's a little different than normal angles where the angle is rotating in one direction or another. Well, on one side, it rotates one way. On the other side, it rotates the other way for them to both be up. One of the ways that's helpful in the, that's sort of helpful in the 2010s or so, is there is sort of a move known as a dab with something like this. And that's one of the ways I try to encourage my students to remember which one is up and which one's down. Okay, you can kind of remember the women's name, Diane. And when the which one's up and which one's down, well, the dihedral dab is up, die and so die is up and an is down, dihedral and hydral angles. So that's some terminology for the orientation of the wings, whether they're level or whether there is an angle involved with each of them. Now we're also going to go and take a look at the wing from the side. If you take a wing here and if I look at this wings, maybe down here at the bottom, you'll see that sort of side view of the wing. We looked at it from the top from the plan view. We've looked at it from the front, but now we're going to look at it from the side view and consider this wing and you'll see there's a shape of the wing there. And that shape will often change. Okay, but that shape is known as an airfoil. And here I've sort of sketched a shape that roughly represents an airfoil. You can think about it as if I took the wing and took a scissors and went slice, I would see the shape of the wing there. And notice that will likely vary. For most modern airplanes, that shape will vary as you move along the span of the wing. Okay, but there's a couple of pieces of information there that we want to identify. First of all, we've already used the information where we have our leading edge. Okay, and now I'm assuming that the air is coming from that direction and that the airplane is traveling in that direction. So we have our leading edge and our trailing edge. And then remember, we have a measurement from the leading to the trailing edge. And that measurement will go here. I'll draw that across there. Okay, and there is our cord. Now notice this cord, even the way I've drawn it, is not perfectly horizontal. Alright, and so that cord might change, it might lift up or down. In fact, it will lift up and down as you sort of adjust your airplane. And we'll see that there's a measurement there off of that horizontal. Okay, that's known as the angle of attack. There's an angle in there that's between the cord and the horizontal. But often when we're first looking at just at airfoils, we'll often have that cord be perfectly horizontal. In this case, I didn't draw it that way. So hopefully now you could look at an airfoil and see where's the leading edge, where's the trailing edge. Usually the trailing edge is pointed, the leading edge is rounded to help with the flow of air around the airfoil. And in addition, there's also a description that we can use where if we look carefully at this, if we look carefully at this airfoil, we can start that leading edge. And we move along the leading edge. And what I'm going to do is I'm going to approximate where the middle of the airfoil is at each point. Where's about halfway in between? Where's the halfway point as I move down and try to draw a line that's through the middle? Whoops, I got attached there at the leading edge. And then we'll meet it back down there at the trailing edge. Okay, that line is halfway between the top and the bottom. Okay, this line has a name. It's known as the mean, basically being the middle between the top and the bottom. Camber line. Now camber is a term that's also used for basically the curvature of the wing. And you'll notice if that line runs through the middle, there's a tendency for it to curve right now. Okay, and so we find that mean camber line is sort of a measurement of how much that wing is bent and how much that wing is likely to deflect air in the curve pattern and deflect it down. And what we will often do is we will determine a place where that mean camber line is furthest from the cord. And that measure there is the maximum camber. Is that distance from that mean camber line? Where is the center of the airfoil the furthest from that direct line from that cord? So there's some terminology there, our cord, our mean camber line, our maximum camber. And then there's one more piece that we want to look at here. That piece there, as we find the place where the airfoil is the thickest, and we call this the thickness. Actually, we could say that thickness is anywhere from the top to the bottom. But then the thickest part is generally the measurement of the thickness of the airfoil. So hopefully now you have some sketches within your notebook that indicate some of the terminology that we use when describing the parts of a wing.