Sample Aviation Essay Paper on Aerodynamics of Supersonic Flight

Aerodynamics of Supersonic Flight

Theory of Supersonic Flight

Supersonic flights are among one of the four types of fastest flights that exist.  The other regime of flight includes subsonic, transonic, and hypersonic (Anderson, 2005). Movement at such speeds is much greater than four times the movement of a car. In normal cases, movements happen in the presence of a particular medium. Different variables are always present in this medium and would change considerably depending on how different supersonic planes move. When planes move at supersonic speeds, they create a difference in the medium in which they are passing through. Both front and back parts of the plane change considerably when the plane is moving (Anderson, 2005). The formation of shock waves which force the plane to move in a characteristic one direction. All of the other variables such as temperature and pressure would affect the movement of the plane. The aerodynamics of supersonic flights is greatly based on several important variables, which include shock waves, compressible flow, sonic booms, and compression. All of the above factors play a critical role in determining the movement of planes at supersonic speeds.

Figure one. Link between the wave drag and Mach number in relation to the sound barrier

Shock Wave

 A shock wave is considered to be any form of disturbance that is propagated.  A shock wave is formed when the wave movement is faster to the local speed of sound. Normally, waves carry a certain amount of energy which can be propagated through a variety of mediums.  However, any abrupt changes in the medium create the shock. Most of the changes are due to variable factors such as the amount of pressure, the level of temperature and density of the medium in which the fluid is moving through (Anderson, 2005). In supersonic airflow shock waves occur due to abrupt changes in the features of different mediums. These features can be stated to be in phase transitions. A good example is in the diagrams below where changes in the amount of time and pressure of any supersonic object are characterized by a shock wave induced transition that is similar to the dynamic phase transition.

https://upload.wikimedia.org/wikipedia/commons/thumb/4/40/Pressure_plot.png/200px-Pressure_plot.png

Figure 2.   Pressure versus time diagram illustrating the case of a supersonic object moving past an observer. The leading edge that causes the shock wave is illustrated in red while trailing edges associated with the expansion is illustrated in blue.

Any object moving faster than the amount of information that is being propagated in any surrounding fluid makes the fluid closer to the point of disturbance not to react before the disturbance arrives.  In shock waves, the properties of different fluids such as density, temperature, pressure, flow velocity and Mach number instantaneously change (Lagerstrom, 2012). The measurement thickness of shock waves in the air is c of the same magnitude as a molecule of free gas. This means that any form of shock wave will either exist in a line or a plane especially if the flow field is either two or three dimensional (Von Karman, 2012). Shock waves normally form when the speed of fluid changes much faster compared to the speed of sound. In the region where these changes occur, the sound waves travel against the flow until they reach a certain point where it becomes impossible to travel upstream. As a result,  all of the pressure that had accumulated builds up and a shock wave of high pressure is formed in the process.  Shock waves are not classified as normal sound waves because they mostly take sharp changes that are closely associated with gas properties (Von Karman, 2012).  In the air, they produce different sounds and over long distances, they change theirs from being non- linear to linear degenerating into different sounds as they lose energy. The sound wave that is characteristically associated with the thud or thump sounds of a sonic boom is normally associated with the movement of supersonic flight or aircraft.

Figure 3. Shock waves created during supersonic speeds

Shock waves represent one of the different ways that gases are moving in the supersonic flow can be compressed. Some of the common methods used include isentropic compression which covers methods linked to the Prandtl- Meyer compression.  Compression of gases results in different temperatures which represent that are linked to pressure ratios. A shock wave compression would result in loss of the total pressure.  This is an efficient method of compressing gases. The appearance of any form of pressure drag in most of the supersonic aircraft is linked with compression of flow

Sonic Boom

Sonic boom refers to the sound that is created with shock waves when they travel at a speed that is much faster compared to normal sound. It generates enormous amounts of sound energy associated with explosions.  When an aircraft passes any medium in the air, it creates a region of pressure waves from behind and in front.  The effects is similar to the  movement of a boat under water which creates forces  in front and backwards (Von Karman, 2012). As the velocity of sound increases, the speed of the object increases and in turn waves are forced to compress or come together since they cannot get out of the way of each other. At the final stages, waves normally merge and travel at a  critical speed.

Flight in Transonic Region

Transonic conditions refer to flight conditions in which the different ranges of velocities exist surrounding and moving across air that is below the speed of sound. The Mach ranges are between 0.8 to 1.0 at sea level. The transonic region depends on several outcomes. They include the speed at which the aircraft is moving, the temperature of airflow and pressure surrounding the moving object. Speeds in the transonic regions are commonly classified depending on the Mach number scale (Cole & Cook, 2012). Movement past the 1.2 value indicates that flying in the supersonic section or speed.

Figure 4. Relation between Transonic region and mach number

Transonic speeds increase the drag effect from the normal range that is 0.8.  Drag, in turn, limits the speed of the plane. Most attempts have been focused on reducing the drag wave so that swept wings can be included in planes that are supposed to move much faster. The transonic speed causes a lot of instability to most planes. Shock waves are present in the air and move at faster speeds than sound (Von Karman, 2012).  When an object such as a plane is moving very first more than sound, sound waves normally build up resulting in the formation of one strong large shock wave.  The plane has to go through the large shock wave during transonic flight.  It also has to contend with the numerous difficulties associated with instability especially when it comes to moving faster in air

Supersonic Wing Designs

Wingspan present in supersonic aircraft must be limited to keep the drag effect as low as possible.  This reduces the aerodynamic efficiency especially when flying of the aircraft is concerned.  Since the airplane must take off and land at low speeds, it is necessary that the wings are designed in a manner that ensures  that the planes can effectively land and take off. Therefore, it is important the designed that is used takes all of the above factors into consideration (Cole & Cook, 2012). One of the commonly used approaches by most plane makers involves the use of variable but geometric wings that are commonly known as swing wings. In this case, the wings spread very wide to ensure that there is enough room for low-speed flights. The wings are also sharp to ensure that there is enough movement for backward movement, especially for supersonic flights (Cole & Cook, 2012). The swinging of the plane affects longitudinal trim and adds the extra weight On most planes and is commonly not used in most of the planes.

Another technique that is commonly used s the delta wing design. This is more common in the plane known as Concorde. This method had certain advantages over others. It can obtain high angles of attack at very low speeds in the process generating features that are similar to a vortex.  These features ensure that the upper surface of the plane greatly increases the lift and provides enough room that is required for landing purposes. The other kinds of wings that are commonly used are the short wing, swept forward wing and sweep back wing

Commercial Airlift with Supersonic Wings Design

There are several supersonic aircraft that have been classified for commercial uses. The prominent example of those forms of aircraft includes Concorde and Tupolev- 144. The former was the last driven in 2003 while the former was driven in 1999. Both designs are subject to ongoing studies with the major problem. The total number of Concordes that were built were twenty and were majorly composed of the prototype. Sixteen of the twenty aircraft were successful in entering the commercial service till 2003. Similarly, Tupolev- 144 was completed and successfully tested as one of the main launchers in commercial service

Effect on Engines

            The position in which wings are located has an effect on the wings of any plane. When the wing is mounted on the root, it has low asymmetric yaw and may cause the engine to fail. It is also associated with less drag and less rudder. The effects of parasitic drag would also be limited, and there will be little space for the bypass ratio. When the mountain pods is placed in the wing of the aircraft, there is high asymmetric yaw on the engines which results in engine failure due to the effects of drag.  In this form, wings provide bending relief and less drag. The angle at pods have the ability to prevent spanwise flow and fewer drag characteristics.

The engine that are deeply buried in the root of the wings reduces the effects of parasite drag and in essence reduces the minimum weight of all products that have been carried.  Inboard locations present minimizes the yawing movement that are caused by the asymmetric thrust due to engine failure. Nevertheless, they still pose a threat to the basic wing structure in case the blade or turbine present in the disk fail (Kuchemann, 2014). This is because it becomes difficult to maximize fully the inlet efficiency in the process making accessibility options to the above two sections harder than before. In case, a larger engine diameter is utilized the entire wing must be redesigned.  Such kinds of installations would effectively remove the flap region present in the engine exhaust in the process reducing the maximum speed of the craft.

References

Anderson, J. D. (2005). Introduction to flight (Vol. 199). Boston: McGraw-Hill.

Cole, J. D., & Cook, L. P. (2012). Transonic aerodynamics. Elsevier.

Kuchemann, D. (2014). Aircraft shapes and their aerodynamics for flight at supersonic speeds.     Advances in Aeronautical Sciences, 3, 221-252.

Lagerstrom, P. A. (2012). Linearized Theory of Supersonic Control Surfaces. Journal of the          Aeronautical Sciences.

Von Karman, T. (2012). Supersonic Aerodynamics-Principles and Applications The Tenth Wright Brothers Lecture. Journal of the Aeronautical Sciences.