SKY AIR TECHNOLOGY

Why a Golf Ball Has Dimples? While few among us can deny that golf is one of the least exciting of all spectator sports, we aerospace engineers are fascinated by its aerodynamics! Even the non golfers of the world are familiar with the shape of a golf ball, like that pictured below, and have probably wondered why its surface is covered with small indentations called dimples. The dimples of a typical golf ball Before explaining the purpose of dimples, we first need to understand the aerodynamic properties of a sphere. Let us start by looking at a smooth sphere without any dimples, like a ping-pong ball. If we lived in an ideal world without any friction, the air flowing around a smooth sphere would behave like that shown in the following diagram. In this figure, the angle  represents position along the surface of the sphere. The leading edge of the sphere that first encounters the incoming airflow is at =0° while the trailing edge is at =180°. A position of =90° is the top of th...

What is Area Rule and What Aircraft were developed? The area rule is an important concept related to the drag on an aircraft or other body in  transonic and supersonic flight. The area rule came into being in the early 1950s when  production fighter designs began pushing ever closer to the sound barrier. Designers  had found that the drag on these aircraft increased substantially when the planes  traveled near Mach 1, a phenomenon known as the transonic drag rise illustrated  below. This increase in drag is due to the formation of shock waves over portions of the  vehicle, which typically begins around Mach 0.8, and this drag increase reaches a  maximum near Mach 1. Because of its source, this type of drag is referred to as wave  drag. Increase in wave drag at transonic Mach numbers Since the physics of supersonic flight were still largely a mystery to manufacturers,  designers had no idea how to address this problem except to provide their a...

Why do aircraft have only three landing gear? Why not four? Most aircraft today have three landing gear. Two main landing gear struts located near the middle of the aircraft usually support about 90% of the plane's weight while a smaller nose strut supports the rest. This layout is most often referred to as the "tricycle" landing gear arrangement. However, there are numerous other designs that have also been used over the years, and each has its own advantages and disadvantages. Let's take a closer look at the various undercarriage options available to engineers. Tail-wheel or Tail-dragger :  Gear Though the tricycle arrangement may be most popular today, that was not always the case. The tail-wheel undercarriage dominated aircraft design for the first four decades of flight and is still widely used on many small piston-engine planes. The tail-dragger arrangement consists of two main gear units located near the center of gravity (CG) that support the majority of the p...

Airflow Around a Bullet in a Wind Tunnel Based on this photo, we can get some idea of the basic phenomenon that occur on a body traveling at supersonic speeds. Most notable is the strong shock wave that is created off of the nose of the bullet. This sort of shock wave is referred to as a bow SUPERSONIC BULLET shock, and it is so strong because the nose creates such a sudden discontinuity as the supersonic air flow encounters it. We also see a series of lines similar to shock waves that emanate from different regions along the body. These are compression and expansion waves.   A compression wave is created when the cross-sectional area of the body increases, because the flow is squeezed into a smaller area and "compressed." If the compression is strong enough, this squeezing of the flow will result in a shock wave. For example, a series of compression waves can be seen near the middle of the above bullet. They form a large blurred region close to the bullet's surface but m...

What is the difference between two dimensional and axisymmetric nozzles? The vast majority of jet-powered aircraft have used what are known as axisymmetric  nozzles. These nozzles, like those illustrated below, direct thrust purely along the axis of the engine, hence the name axisymmetric. Comparison of axisymmetric (top)  and 2D (bottom) nozzles Two-dimensional nozzles, on the other hand, are capable of not only directing the thrust along the axis of the engine, but can deflect to vector the thrust and produce a force that points the nose of the plane in a different direction. This type of nozzle is at the heart of what is known as thrust vectoring.  The nozzles depicted above are capable of vectoring the thrust up or down to produce an up force or down force. Down force will force the aircraft nose to pitch upward while up force has the opposite effect. The two nozzles can also be deflected deferentially (one producing up force, the other down forc...

Do you know what adverse yaw is and how to solve it? To understand what adverse yaw is, we need to first explain the axes of motion for an  airplane. An aircraft in flight can rotate around three different axes, as illustrated below. Aircraft control surfaces However, the effect of one control surface is not always limited to just pitch, roll, or yaw  alone. When the deflection of one control surface affects more than one of these  orientations, we say that the orientations are coupled. The most important of these  coupled interactions is adverse yaw. To better understand the concept, let's study a  picture of what happens when the pilot deflects the ailerons to roll the aircraft. As you can see, the aircraft rolls because one aileron is deflected downward while the other is deflected upward. Lift increases on the wing with the downward-deflected aileron because the deflection effectively increases the camber of that portion of the wing. Conversely, lift decreas...