Introduction to Aerodynamics

 

Aerodynamics

 

Aerodynamics is probably the first subject that comes to mind when most people think of Aeronautical or Aerospace Engineering.

Subscribe here to our Youtube Channel ... And you will have the advantage of asking questions specific to you and you get quick answers to your situations ....

Click here for the previous lessons, to learn about: Principle of Airframe; Principles of Aerodynamics; Airfoil Characteristics; Primary Flight Control Surfaces; Description and Operation of Helicopter; Miscellaneous Components of an Aircraft…

 Aerodynamics is essentially the application of classical theories of “fluid mechanics” to external flows or flows around bodies, and the main application which comes to mind for most aero engineers is flow around wings.

The wing is the most important part of an airplane because without it there would be no lift and no aircraft. Most people have some idea of how a wing works; that is, by making the flow over the top of the wing go faster than the flow over the bottom we get a lower pressure on the top than on the bottom and, as a result, get lift. The aero engineer needs to know something more than this. The aero engineer needs to know how to shape the wing to get the optimum combination of lift and drag and pitching moment for a particular airplane mission. In addition he or she needs to understand how the vehicle’s aerodynamics interacts with other aspects of its design and performance. It would also be nice if the forces on the wing did not exceed the load limit of the wing structure.

If one looks at enough airplanes, past and present, he or she will find a wide variety of wing shapes. Some aircraft have short, stubby wings (small wing span), while others have long, narrow wings. Some wings are swept and others are straight. Wings may have odd shapes at their tips or even attachments and extensio
ns such as winglets. All of these shapes are related to the purpose and design of the aircraft.

In order to look at why wings are shaped like they are we need to start by looking at the terms that are used to define the shape of a wing.

 Here is the viedo about the  Primary Flight Control Surfaces

Figure 1.1: Airfoil Terminology

A two dimensional slice of a wing cut parallel to the centerline of the aircraft fuselage or body is called the airfoil section. A straight line from the airfoil section leading edge to its trailing edge is called the chord line. The length of the

chord line is referred to as the chord. A line drawn half way between the airfoil section’s upper and lower surfaces is called the camber line. The maximum distance between the camber line and chord line is referred to as the airfoil’s camber and is usually enumerated as a percent of chord. We will see that the amount of airfoil camber and the location of the point of maximum camber are important numbers in defining the shape of an airfoil and predicting its performance. For most airfoils the maximum camber is on the order of zero to five percent and the location of the point of maximum camber is between 25% and 50% of the chord from the airfoil leading edge.

When viewed from above the aircraft the wing shape or planform is defined by other terms.

 

 

Figure 1.2: Wing Planform Terminology

 

 

 

Note that the planform area is not the actual surface area of the wing but is “projected area” or the area of the wing’s shadow. Also note that some of the abbreviations used are not intuitive; the span, the distance from wing tip to wing tip (including any fuselage width) is denoted by b and the planform area is given a symbol of “S” rather than perhaps “A”. Sweep angles are usually given a symbol of lambda (λ).

Another definition that is based on the planform shape of a wing is the Aspect Ratio (AR).

 

AR = b²/S.

Aspect ratio is also the span divided by the “mean” or average chord. We will later find that aspect ratio is a measure of the wing’s efficiency in long range flight.

Wing planform shapes may vary considerably from one type of aircraft to another. Fighter aircraft tend to have low aspect ratio or short, stubby wings, while long range transport aircraft have higher aspect ratio wing shapes, and sailplanes have yet higher wing spans. Some wings are swept while others are not. Some wings have triangular or “delta” planforms. If one looks at the past 100 years of wing design he or she will see an almost infinite variety of shapes. Some of the shapes come from aerodynamic optimization while others are shaped for structural benefit. Some are shaped the way they are for stealth, others for maneuverability in aerobatic flight, and yet others just to satisfy their designer’s desire for a good looking airplane.

Figure 1.3: Some Wing Planform Shapes

 

 

 

In general, high aspect ratio wings are desirable for long range aircraft while lower aspect ratio wings allow more rapid roll response when maneuverability is a requirement. Sweeping a wing either forward or aft will reduce its drag as the plane’s speed approaches the speed of sound but will also reduce its efficiency at lower speeds. Delta wings represent a way to get a combination of high sweep and a large area. Tapering a wing to give it lower chord at the wing tips usually gives somewhat better performance than an untapered wing and a non-linear taper which gives a “parabolic” planform will theoretically give the best performance.

In the following material we will take a closer look at some of the things mentioned above and at their consequences related to the flight capability of an airplane.

Before we take a more detailed look at wing aerodynamics we will first examine the atmosphere in which aircraft must operate and look at a few of the basic relationships we encounter in “doing” aerodynamics.