Abstract
The understanding of the performance of an aircraft is one of the most important issues that many stakeholders in the aviation sector aspire to understand comprehensively. A significant number of aircrafts experience challenges in the process of take-offs or when they are landing. However, through research, engineers have discovered that the climb performance of many aircrafts is affected by several factors including incidences of collision with various obstacles. It is also crucial to acknowledge that an aircraft is characterized by performances in different speed conditions. Through the performance at each speed condition, engineers are able to predict that manner at which various features of the aircraft would perform. Some of the speed conditions that could used to predict that performance of an aircraft include best angle speed and the rate of best climb among others. This paper presents a discussion concerning the difference in climb performance with regard to altitude and between proper driven aircraft and turbofan aircraft. Other issues that shall be discussed in this paper include the difference between Vy climb and Mach Intercept and Mach the relationship between IAS, TAS altitude increases and Mach. Consequently, this paper will provide a description of the impact of excess power and excess thrust as well as their relationship with climb performance in a turbofan aircraft.
Response to Question One
The climb rate off all aircrafts primarily depends on the excess power that is available. In turbojet propelled aircrafts, the excess power and power needed for climb increases as the aircraft flies at a higher speed with the excess power reducing at extremely high speed resulting in a buildup of drag as the power required for the aircraft climb increases (Anderson Jr, 34). Thus unlike propeller powered aircraft; jets climb at extremely high speeds that are typically at, and in some instances above the normal cruising speed. On the other hand, the climb speed for propeller powered aircraft is usually below cruising speed. Another difference between the two is that unlike turbojet powered aircrafts, propeller powered aircraft's are generally associated with superior take off performance due to their high low speed thrust and modest cruise performance (Anderson Jr, 37). Turbojet powered aircraft's on the other hand are characteristic with inferior takeoff performance and superior cruise performance.
Another difference between turbojet driven engines and propeller powered engines is that unlike propeller powered engines, turbojet driven engines are able to gain altitude quicker. This is because as mentioned forehand, turbojet powered aircraft's have considerably more thrust than propeller driven aircraft's.
In turbojet powered aircrafts, the maximum angle of climb is obtained at the maximum Specific Excess Thrust (Anderson Jr, 45). Unlike turbojet powered aircrafts, all the optimum points for aircraft's that are propeller driven are generally at lower speeds than those associated with turbojet powered aircraft's. This phenomenon is due to the variation that exists between thrust and speed. In propeller driven aircraft, the thrust is inversely proportional to the speed, while in turbojets, the thrust is constant over speed while in the subsonic range. Therefore, based on the information provided above, the mathematical relationship between velocity, and thrust in propeller aircraft is Vγmax < VminTR. The mathematical equation representing the relationship between velocity and thrust in turbojet powered aircraft's is VminTR = Vγmax (Kim et al, 383). These two equations showcase the difference that exists between the two methods of propulsion.
Response to Question Two
The primary difference between a Vy climb and a mach intercept climb performance lies in their description. A Vy climb also referred to as the Best Rate of Climb is a type of climb where the aircraft obtains the most altitude per unit of time (McCormick, 23). This form of climb enables an aircraft to get to its cruising altitude expeditiously thus providing for maximum efficiency. This is made possible due to its attribute of enabling the aircraft spend the least amount of time possible at lower altitudes that are usually less efficient.
On the other hand, a mach intercept climb is a type of climb that enables the aircraft to obtain the greatest altitude it can for every unit of ground distance it covers. Mach Intercept climb is regarded as the type of climb where the aircraft has the most excess thrust and excess force thus it is able to reach high altitudes faster. In this type of climb, the aircraft experiences two types of drag namely induced drag and parasite drag. Induced drag is the drag that is generated by the aircraft's lifts where as parasite drag is the drag that results from friction between the aircraft and the air. Thus while an aircraft is at slow speeds it experiences more induced drag and therefore flies at a higher angle at is able to climb much rapidly. At higher speeds the aircraft experience more parasite drag thus flies on a lower angle of attack and gains altitude much slower. By adding the two drags together, one obtains the total drag which represents the total amount of thrust needed in a Mach intercept Climb for the aircraft to stay level and also indicates the position where the aircraft is most efficient. Unlike the Mach intercept climb, a VY climb is predominantly about the power available to the aircraft. In a VY climb, increase in the amount of power, leads to an increase in the rate of climb which in turn results in an increase in the aircraft altitude. On the other hand decrease in the amount of power results in a decrease in the rate of climb which in turn contributes to a decrease in the altitude and planes angle of attack.
Response to Question Three
As an aircraft increases in altitude, the local sound speed decreases because of the resulting lower air density. This leads to an increase in the Mach number with the increase in altitude. Increase in an aircrafts altitude results in decreasing air density which in turn causes TAS to increase. Contrary to common perception, it is not decreasing pressure but decreasing temperature that causes the LSS to decrease due to an increase in altitude. This phenomenon is due to the fact that the gradient of temperature slopes to colder temperatures across the stratosphere and changes towards warmer temperatures up until the mesosphere. Therefore, it is logical to conclude that the LSS is dependent only on temperature and thus the formula LSS = square root (Absolute Temp). This explains the reason there is an increase in Mach number with increasing altitude (McCormick, 23).
Secondly TAS increases with constant IAS as one increase in altitude because the difference that exists between TAS and IAS is based on their density relationship. As one increases in altitude, the resulting decrease in pressure causes the air to become less dense. This causes the actual speed of the aircraft to become greater. This condition is made possible to the fact that density is inversely proportional to temperature and directly proportional to pressure b and the decrease in pressure is considered to be the overriding factor.
IAS increases with increase in altitude because as one starts to increase in altitude at Mach number that is constant. The aircraft changeover to climbing at a Mach number that is constant at around 25000ft (Kim et al, 380). This is due to each reaching MMO sooner than it reaches it VMO. Increase in altitude past over 25000ft still causes the temperature to decrease thus the equation TAS = Mach No. x LSS, where Mach No. is constant (Kim et al, 383). Based on the information provided above it is logical to conclude that TAS decreases due to the fact that LSS decreases as altitude increases. As TAS decreases so must IAS, this is because pressure continues to decrease with increase in altitude. This phenomenon also occurs as one passes the troposphere.
Response to Question Four
An aircraft's rate of climb is the vertical component of velocity. The higher the thrust of an aircraft, the lower its resulting drug as well as the lower its weight the better the aircraft's climbing performance. Whereas excess thrust determines the aircrafts angle of climb, excess power determines its rate of climb. Turbojet powered aircraft's impart much greater acceleration to a minimal amount of air. This is due to their ability to run the air through the turbine and compressor. A significant percentage of the thrust that is generated by turbojet engine originates from heating the air. The air enters the engine at atmospheric pressure but leaves at a pressure that is slightly higher and thus based on the equation PV = NRT, one can conclude that the air is leaving the engine at a velocity that is faster and in proportion to the degree by which it has been heated. Turbojet engines like piston engines also deliver no power to the aircraft (McCormick, 23). However, as one accelerates, the thrust that is delivered by the engines does not fall of rapidly do the fact that the engines exhaust velocity is significantly high.
Works Cited
Anderson Jr, John David. Fundamentals of aerodynamics. Tata McGraw-Hill Education, 2010.
Kim, Yong-Kyun, et al. "En-Route Trajectory calculation using Flight Plan Information for Effective Air Traffic Management." Journal of Information Processing Systems 6.3 (2010): 375-384.
McCormick, Barnes Warnock. Aerodynamics, aeronautics, and flight mechanics. Vol. 2. New York: Wiley, 2013.
