Explain the theory of supersonic aircraft?

Answer 1

please be more detailed with your question. What do you want me to explain about it?

Answer 2

Hi Arun,

Maybe you mean,..How do planes fly?

It's less about speed and more about lift and drag.

Supersonic? Well, sonic relates to sound, super has been adopted to mean fast. In this case the two words mean Faster than Sound. Super Sonic!

SuperSonic has nothing to do with flight theory directly but it does describe the fact of an item travelling faster than the speed of sound.

A Sonic Boom is created by anything moving through the air so fast that it is gone before the air can fill the space it occupied, the air rushing in to the empty space creates the noise.

Forget the concept of Aircraft, a metior or comet both travel faster than the speed of sound, thus being supersonic. Heck, the Earth is travelling way past Supersonic speeds around the Solar system.

All the best, Rod

Answer 3

The great majority of supersonic aircraft today are military or experimental aircraft. Most of them, including many military fighter aircraft, are designed to exceed the speed of sound only in certain exceptional flight regimes; a handful of aircraft, such as the SR-71 Blackbird military reconnaissance aircraft and the Concorde supersonic civilian transport, are designed to cruise continuously at speeds above the speed of sound.

Supersonic flight brings with it substantial technical challenges, as the aerodynamics of supersonic flight are dramatically different from those of subsonic flight (i.e., flight at speeds slower than that of sound). These challenges have largely been met. However, political, environmental, and economic obstacles of greater magnitude continue to severely limit the actual deployment of supersonic aircraft, particularly in the civilian world. Additionally, the need and demand for supersonic flight have often been insufficient to justify development or deployment of supersonic aircraft, particularly in the domain of civilian transport. The aforementioned SR-71 and Concorde aircraft are no longer flying today because of multiple problems and impracticalities associated with supersonic flight...

Answer 4

As an aircraft moves through the air, the air molecules near the aircraft are disturbed and move around the aircraft. Exactly how the air re-acts to the aircraft depends upon the ratio of the speed of the aircraft to the speed of sound through the air. Because of the importance of this speed ratio, aerodynamicists have designated it with a special parameter called the Mach number in honor of Ernst Mach, a late 19th century physicist who studied gas dynamics.

For aircraft speeds which are greater than the speed of sound, the aircraft is said to be supersonic. Typical speeds for supersonic aircraft are greater than 750 mph but less than 1500 mph, and the Mach number M is greater than one, 1 < M < 3. In supersonic flight, we encounter compressibility effects and the local air density varies because of shock waves, expansions, and flow choking.
An F-14 which is powered by two afterburning turbofan engines. The wings of supersonic fighters are swept in planform to reduce drag. The F-14 is unique because the amount of sweep can be varied by the pilot; low sweep for good low speed performance, high sweep for supersonic flight. For Mach numbers less than 2.5, the frictional heating of the airframe by the air is low enough that light weight aluminum is used for the structure.

Answer 5

The great majority of supersonic aircraft today are military or experimental aircraft. Most of them, including many military fighter aircraft, are designed to exceed the speed of sound only in certain exceptional flight regimes; a handful of aircraft, such as the SR-71 Blackbird military reconnaissance aircraft and the Concorde supersonic civilian transport, are designed to cruise continuously at speeds above the speed of sound.

Supersonic flight brings with it substantial technical challenges, as the aerodynamics of supersonic flight are dramatically different from those of subsonic flight (i.e., flight at speeds slower than that of sound). These challenges have largely been met. However, political, environmental, and economic obstacles of greater magnitude continue to severely limit the actual deployment of supersonic aircraft, particularly in the civilian world. Additionally, the need and demand for supersonic flight have often been insufficient to justify development or deployment of supersonic aircraft, particularly in the domain of civilian transport. The aforementioned SR-71 and Concorde aircraft are no longer flying today because of multiple problems and impracticalities associated with supersonic flight.

Answer 6

I would say Ludwig is the father of supersonic theories.


The Work of Ludwig Prandtl

In the early decades of the 20th century, Ludwig Prandtl formulated several important aerodynamic theories. The most notable of these were his boundary layer, thin-airfoil, and lifting-line theories. He was also a teacher of many prominent aerodynamicists.

Ludwig Prandtl was born in Freising, Bavaria, in 1874. His father was a professor of engineering. His mother suffered from a lengthy illness and, as a result, the young Ludwig spent more time with his father, becoming interested in his father's physics and machinery books. His father also encouraged him to observe nature and think about his observations. This upbringing fostered the young Prandtl's interest in science and experimentation.

Prandtl began his formal scientific studies at the age of 20 in Munich, Germany, and graduated with a Ph.D. from the University of Munich within six years. His work at Munich had been in solid mechanics and his first job was as an engineer designing factory equipment. There, he entered the field of fluid mechanics when he had to design a suction device. After carrying out some experiments, he came up with a original device that worked well and used less power than the device that had been used.

Prandtl became a professor of mechanics at a technical school in Hannover, Germany, I 1901. There he developed his boundary layer theory and studied supersonic fluid flows through nozzles.

In 1904, he delivered a revolutionary paper to the Third International Mathematical Congress at Heidelberg, Germany. Titled “Ueber Flussigkeitsbewegung Bei Sehr Kleiner Reibung” (Fluid Flow in Very Little Friction), the paper described his boundary layer theory.

Prandtl's boundary layer theory contributed to an understanding of skin friction drag and how streamlining reduces the drag experienced by airplane wings and other moving bodies. Prandtl examined the drag that resulted from the friction that was created when a fluid such as air passed over an object's surface.

Prandtl determined that there was an extremely thin layer of fluid around a wing or airfoil that stuck to it because of friction. The friction caused this thin layer of fluid, called the boundary layer, to move, or flow, around the wing very slowly as if it were being dragged or pulled over the surface. The farther away from the wing's surface the layer of air was, the less it was affected by friction and the faster it moved until it reached the outer edges of the boundary layer, where the airflow was normal and the fluid moved at normal speed.

Prandtl also observed that flow separation was another possible result of friction. When a certain type of flow occurred, the boundary layer separated from the surface of the wing. This resulted in a region of slow-moving air behind the wing. This slow-moving air had lower pressure than the air flowing over the front of the wing. This change in pressure distribution around the wing resulted in a pressure drag toward the rear of the aircraft that much exceeded friction drag.

His 1904 paper raised Prandtl's prestige as an aerodynamicist. He became director of the Institute for Technical Physics at the University of Göttingen later in the year, where he worked with many outstanding students, creating the greatest aerodynamics research center of his time.

In the years that followed, Prandtl began work on calculating the effect of induced drag on lift. Induced drag is the drag created by the vortices that trail an aircraft from the tips of its wings. These vortices, or whirling motions of fluid, affect the pressure distribution over the wings and result in a force in the direction of drag. Hence, induced drag is a kind of pressure drag. He worked with Albert Betz and Max Munk for almost ten years to solve this problem. The result was his lifting line theory, which was published in 1918-1919. It enabled accurate calculations of induced drag and its effect on lift.

In England, Prandtl's lifting line theory is referred to as the Lanchester-Prandtl theory. This is because the English scientist Frederick Lanchester published the foundation for Prandtl's theory years earlier. In his 1907 book Aerodynamics, Lanchester had described his model for the vortices that occur behind wings during flight. Prandtl's model for his theory was similar to Lanchester's, although Prandtl claimed that he had not considered Lanchester's model when he had begun his work in 1911.

During World War I, Prandtl created his thin-airfoil theory that enabled the calculation of lift for thin, cambered airfoils. It is still used today. He later contributed to the Prandtl-Glauert rule for subsonic airflow that describes the compressibility effects of air at high speeds. Prandtl also made important advances in developing theories of supersonic flow and turbulence.

Prandtl worked with his student, Theodor Meyer, to develop the first theory for calculating the properties of shock and expansion waves in supersonic flow in 1908. In 1929, he worked with Adolf Busemann and created a method for designing a supersonic nozzle. Today, all supersonic wind-tunnel nozzles and rocket-engine nozzles are designed using the same method. Prandtl also developed a rule for correcting low-speed airfoil lift calculations that accounted for the way air compressed at high speeds. This became very useful during World War II as aircraft began approaching supersonic speeds.

In 1925 Prandtl became director of the Kaiser Wilhelm Institute for Flow Investigation at Göttingen. By the 1930s, he was known worldwide as the leader in the science of fluid dynamics, the study of the effect of fluid motion on objects. He continued his research in many areas, such as meteorology and structural mechanics. Prandtl also taught famous aerodynamicists such as Theodor von Kármán and Klaus Oswatitsch.

Ludwig Prandtl was a likeable man and an accomplished pianist. He worked at Göttingen until his death on August 15, 1953. His work and achievements in fluid dynamics resulted in equations that were easier to understand than others and are still used today in many areas of aerodynamics. It is for this reason that he is referred to as the father of modern aerodynamics

Answer 7

no brainer they just go fast

Answer 8

Supersonic aircraft design-

Planes designed for supersonic flight usually have a narrow fuselage and swept-back delta wings to limit the effects of turbulence at supersonic speeds. Some aircraft have a "coke bottle" fuselage, based on the 'Whitcomb area rule', which means that they taper in the middle slightly. This can reduce transonic drag.

Challenges of supersonic flight-

Poor range-
Supersonic aircraft tend to have a relatively limited range (~6000 km). The reason is their high fuel consumption, which in turn results from the high power needed for supersonic flight, combined with the practical limits on how much fuel an aircraft can carry. This makes them a difficult choice for airlines to purchase since many routes cannot be travelled.

Operation costs-

High fuel costs and low passenger capacity (due to the aerodynamic requirement for a narrow fuselage) have combined to make SSTs an expensive form of transportation compared with subsonic flight.

Reaching supersonic speeds requires considerable engine power to overcome wave drag, a powerful form of drag that starts at about Mach 0.8 and ends around Mach 1.2, the transonic speed range. Between these speeds the Cd factor is approximately tripled. Above the transonic range the Cd factor drops dramatically again, although it remains 30 to 50% higher than at subsonic speeds. In addition, drag increases in proportion to the square of the speed. However, this drag can be reduced back to near normal amounts by simply flying at a higher altitude where the air is far less dense.

Another significant design problem is the inefficiency of wings at speeds considerably above the speed of sound. At about Mach 2 a typical wing design will cut its lift-to-drag ratio in half (e.g., Concorde manages a ratio of 7.4 whereas the subsonic Boeing 747 is 17.)[1] Since the aircraft has to hold its own weight up, this means that the aircraft has to provide twice the thrust to maintain airspeed and altitude, so there is little or no overall gain in fuel efficiency. For this reason a considerable amount of research was put into designing a planform for sustained supersonic cruise.

Another problem for SSTs is that they require a much stronger (and therefore heavier) structure than subsonic aircraft, due to aeroelasticity problems, and also the fact that their fuselages are pressurized to a greater pressure differential (due to the ratio of cabin air pressure to the lower outside pressure at the high altitudes at which SSTs fly). These factors meant that the empty weight per seat of a Concorde is more than three times that of a Boeing 747. Both aircraft use approximately the same amount of fuel to cover the same distance, but the 747 can carry more than four times as many passengers.

Jet engine design differs significantly between supersonic and subsonic aircraft. Jets can supply increased fuel efficiency at supersonic speeds because, even though the specific impulse efficiency drops off somewhat at higher speeds, the distance traveled is greater, and the dropoff is less than proportional to speed until well above Mach 2. However, the same time as Concorde was being built, high bypass jet engines started to be deployed on subsonic aircraft. This meant that subsonic jet engines became much more efficient; but high bypass is a way of reducing the jet exhaust speed to better match the aircraft speed that could not be employed on supersonic jet engines, which need high exhaust speed.

Sonic booms-

The annoyance can be reduced by waiting to reach supersonic speeds until the aircraft is at high altitude over water; this is the technique used by Concorde. However, it precludes supersonic flights on transcontinental flights over populated areas. Supersonic aircraft seemingly inevitably have poor lift/drag ratios at subsonic speeds compared to subsonic aircraft and hence burn more fuel, and are economically disadvantageous for use over such flight paths.

Additionally, during the original SST efforts in the 1960s it was suggested that careful shaping of the fuselage of the aircraft could reduce the intensity of the shock waves that reach the ground. One way is to cause the shock waves to interfere with each other, greatly reducing sonic boom. This was difficult to test at that time due to the careful design it required, but the increasing power of computer-aided design has since made this considerably easier. In 2003 such a testbed aircraft was flown, the Shaped Sonic Boom Demonstration which proved the soundness of the design and demonstrated the capability of reducing the boom by about half. Even lengthening the vehicle (without significantly increasing the weight) would seem to reduce the boom intensity.

If the intensity of the boom can be reduced then this may make even very large designs of supersonic aircraft acceptable for overland flight (see sonic boom).

Damage to the ozone layer-

The high altitude flight makes such damage theoretically more likely than with traditional aircraft. However, research showed that the comparatively tiny quantity of nitric oxides generated in the exhaust actually boosts the ozone layer. [citation needed]

Need to operate aircraft over a wide range of speeds-

The design for aircraft needs to change with its speed for optimal performance. Thus, an SST would ideally change shape during flight to maintain optimal performance at both subsonic and supersonic speeds. Such a design would introduce complexity which increases maintenance needs, operations costs, and safety concerns.

In practice all supersonic transports have used essentially the same shape for subsonic and supersonic flight, and a compromise in performance is chosen, often to the detriment of low speed flight. For example Concorde had very high drag (lift to drag ratio of about 4) at slow speed, but it spent most of the flight at high speed.

Some designs of supersonic transports possessed swing wings, to give higher efficiency at low speeds.

North American Aviation solved this problem with the XB-70 Valkyrie. By lowering the outer panels of the wings at high Mach numbers, they were able to take advantage of compression lift on the underside of the aircraft. This gave the Valkyrie the best lift:drag ratio of any powered manned aircraft ever built and allowed a much better aspect ratio on take-off and landing. Some recent SST designs are considering this as an option.

Higher landing/takeoff speeds-

This requires longer runways and raises safety concerns.

Takeoff noise-

One of the main problems with Concorde and the Tu-144 operations was the high engine noise levels, associated with very high jet velocities used during take-off. SST engines need a fairly high specific thrust (net thrust/airflow) during supersonic cruise, to minimize engine cross-sectional area and, thereby, nacelle drag. Unfortunately this implies a high jet velocity, which makes the engines noisy which causes problems particularly at low speeds/altitudes and at take-off.

Therefore, a future SST might well benefit from a Variable Cycle Engine, where the specific thrust (and therefore jet velocity and noise) is low at take-off, but is forced high during Supersonic Cruise. Transition between the two modes would occur at some point during the Climb and back again during the Descent (to minimize jet noise upon Approach). The difficulty is devising a Variable Cycle Engine configuration that meets the requirement for a low cross-sectional area during Supersonic Cruise.

Several concepts show promise:-

In the Tandem Fan, the engine has two fans, both mounted on the LP shaft, with a significant axial gap between the units. In normal flight, the engine is in the Series Mode, with the flow leaving the front fan passing directly into the second fan, the engine behaving much like a normal turbofan. However, for take-off, climb-out, final-descent and approach, the front fan is allowed to discharge directly through an auxiliary nozzle on the underside of the powerplant nacelle. Auxiliary intakes are opened on each side of the powerplant, allowing air to enter the rear fan and progress through the rest of the engine. Operating the fans in this Parallel Mode, substantially increases the total airflow of the engine at a thrust, resulting in a lower jet velocity and a quieter engine. Back in the 1970s, Boeing modified a P&W JT8D to a Tandem Fan configuration and successfully demonstrated the switch from Series to Parallel operation (and vice-versa) with the engine running, albeit at part power.

In the Mid Tandem Fan concept a high specific flow single stage fan is located between the HP and LP compressors of a turbojet core. Only bypass air is allowed to pass through the fan, the LP compressor exit flow passing through special passages within the fan disc, directly underneath the fan rotor blades. Some of the bypass air enters the engine via an auxiliary intake. During take-off and Approach the engine behaves much like a normal civil turbofan, with an acceptable jet noise level (i.e., low specific thrust). However, for Supersonic Cruise, the fan variable inlet guide vanes and auxiliary intake close-off to minimize bypass flow and increase specific thrust. In this mode the engine acts more like a 'leaky' turbojet (e.g. the F404).

In the Mixed-Flow Turbofan with Ejector concept, a low-bypass ratio engine is mounted in front of a long tube, called an ejector. This silencer device is deployed during take-off and approach. Turbofan exhaust gases induce additional air into the ejector via an auxiliary air intake, thereby reducing the specific thrust/mean jet velocity of the final exhaust. The mixed-flow design does not have the advantages of the mid-tandem fan design in terms of low-speed efficiency, but is considerably simpler..