When designing an aircraft, the aircraft design engineers normally take into consideration many factors. These include the manufacturer's and customers' requirements, physical and economic constraints and safety measures among many other factors. For certain aircraft, the design process is regulated by the country's airworthiness authorities. However the design process usually begins by identifying the intended purpose and use of the aircraft. Considering this, the fighter jets, which are light in weight, are designed to perform high speed manoeuvres Commercial airliners on the other hand are mainly designed to carry cargo, payload or passengers. This demonstrates the level to which the two aerodynamic designs may differ. While the two types of designs differ in numerous ways, certain design features are quite similar. My essay will compare and contrast the aerodynamic design features of a typical light aircraft and a large commercial jet.
The P2006 T-Light Aircraft
Pascale and Nicolosi (2006, p.2-4) states that in the past decade, Tecnam Aircraft Industries has been deeply engaged in the development, design and manufacturing of more than 10 light and ultra light 2-seat aircrafts characterized by high or low wing configurations. One such light aircraft is the P2006 VELT (Very Light Twin), manufactured by the company in 2006. This is a 4-seat aircraft with two engines (Rotax Aircraft Engines 912 are normally used for ultra light aircrafts such as this one). This light aircraft has very unique aerodynamic design features to assure its stability and good control. One such feature of this aircraft is its low propeller revolution speed as well as low engine drag. The combination of the two aspects coupled with streamlined fuselage give the aircraft a good aerodynamic efficiency.
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(Picture 1 above showing P2006T in flight)
Engine Design and Position
The weight to power ratio of the P2006 VELT engine is favourable according to Pascale and Nicolosi (2006, p.4). This is due to the fact that the weight of the engine is lower than that of Lycoming Engines in comparison. In addition, Pascale and Nicolosi note that the engine frontal is lower to allow wing-mounted streamlined nacelle, thereby reducing drag penalty (wave drag) arising from the twin engines. This also ensures that the stability is maintained during take-off and landing. The lower revolution speed provides higher propeller thrust at low flight speed, which improves the stability of the aircraft during take-off and the climb performance.
The wing of the P2006 VELT aircraft is designed taking into consideration the need to have good flight performance and low structural weight according to Pascale and Nicolosi (2006, p.4-8). The wing span of the aircraft is set at a value of 11.2 metres to allow for easy control and stability. The interior part of this aircraft's wing is rectangular to simplify flap contraction. The wings of this aircraft are also made of aluminium material to enable the aircraft to be as light as possible.
Fuselage, Nacelle and Tail Design
The fuselage of this aircraft is designed so as to have low parasite drag. Its shape is characterized by a favourable low value of fuselage wetted area over fuselage volume. The aircraft's nacelle is very small and well streamlined due to the compact engine design and size. The aircraft is also fitted with an all manoeuvre stabilizer-elevator (aircraft control surface) to increase the aircraft's longitudinal control (higher tail efficiency) and for stick-free stability. The aircraft also has a vertical tail designed for minimum control speed (VMC) in One Engine Inoperative (OEI) conditions. Pascale and Nicolosi (2006) argue that a slightly higher value of minimum control speed with respect to all stall speed had been chosen for the aircraft to guarantee good and safe takeoff characteristics.
The weight of an aircraft is a key component that needs much attention during the design process according to Nicolosi and Pascale (2003). For the P2006, the body of the aircraft is made of aluminium alloy. The aluminium alloy is used to make the body of this aircraft because it is very light in weight for easy control and operation.
Boeing 777-commercial aircraft
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(Picture 2 above showing The Boeing 777 in flight)
The Boeing 777 is one of the most famously designed commercial aircraft used for transporting passengers and cargo. The aircraft has special aerodynamic design features to enable it to lift all the weight without any control or stability problems meaning that its design incorporates the latest technology.
The engine of the Boeing 777 is very large and heavy and it is mounted under the wing. Its machine is powered by a Rolls-Royce Trent 800 engine which weighs around 8.2 tonnes after the installation. Cupsty (2003, p. 7) notes that since most lifts are generated by wings, hanging the engine under the wings where they can easily be carried is a noble idea. The reason for putting the engine below the wing is to reduce the wing root bending moment thereby making it possible to reduce the essential strength and weight of the aircraft. This helps build stability and makes the aircraft easy to control.
Considering the number of passengers a Boeing 777 can carry, it measures approximately 246 ft with a wing span of 222 ft at a height of approximately 65 ft. The aircraft also has a total of 24 wheels out of which 24 are used as landing gear. It is also known that the fuselage of the aircraft is designed in such a manner that it helps to reduce fuselage over fuselage volume. The Boeing 777 also has a streamlined nacelle. The tail is vertically designed for minimum control speed. Also the aircraft is fitted with stabilizer-elevators to increase its longitudinal control.
Differences in Design between the Boeing 777 and the P2006
It is apparent that the commercial aircrafts differ slightly from the light aircrafts in terms of aerodynamic features. This is mainly due to the different purposes for which they are designed. For example, it is seen that the lighter aircrafts have lighter engines which are not placed below the wings as this is the case with the commercial aircrafts as seen with the Boeing 777 (Fielding 1999, p.17-26). For the Boeing 777, the wing engine which is also large and heavy is positioned below the wing to enable the aircraft to lift the heavy weight without any control or stability problems.
It is also clear that the Boeing 777 is much larger and longer compared to the P2006. It is also known that since Boeing is meant to carry many more passengers than the P2006, its base area has to be wide to increase the stability. In addition, commercial aircrafts have more wheels than the lighter aircrafts. This is meant to help maintain stability and improve the landing gear because of the weight according to Kundu (2010, p47-53). Unlike the lighter aircrafts like the P2006, commercial aircrafts have a relatively large fuselage to enable them have low parasite drag. The nacelle of larger aircrafts like Boeing is also relatively larger and less streamlined compared to those of lighter aircrafts.
Design Similarities between the Boeing 777 and the P2006
Many similarities can be seen with the two categories of aircrafts, one such being the weight characteristics. It is apparent that in both the aircrafts, the body is made of aluminium alloy to make the aircrafts lighter. This feature makes the aircrafts easy to fly and control. Furthermore, in both the aircrafts, the wing spans are all low, placed at a figure of about 11.2 m and again are both made of aluminium alloy. In both cases, the wings are rectangular to simplify flap contraction according to Kundu (2010, p47-53). On the other hand, the wings of the commercial aircrafts like the Boeing 777 are long, about 222 ft to increase the aircraft's stability when in flight and when changing direction. It is also clear that both aircrafts are fitted with stabilizer-elevators to increase longitudinal control. Both aircrafts also have vertical tails designed for minimum control speed. This enables the aircraft to have safe take-off characteristics. The only difference is that the Boeing 777 has a larger and longer tail due to the weight it lifts and controls.
It is now well known that aircrafts are designed taking into consideration the purposes for which they are intended. My essay has brought out these elements with regard to the aerodynamic design features of the two aircrafts that have been discussed in brief. Lighter aircrafts, for example, have lighter, less powerful engines compared to commercial aircrafts. In addition, the positions of these engines also differ because of the weight that they are supposed to lift. Differences have also been seen with the wing-size and length, nacelle, tail and fuselage. Similarities also exist mainly in stabilizer-elevators, wing spans and weight characteristics.
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