The Advantages and Disadvantages of Piston Engine in the Aircraft - Essay Example

Advantages and Disadvantages of Piston Engine in Aircrafts Name: Lecturer: Course: Date: Introduction Piston engines consist of one or more cylinders that contain solid cylinders (or pistons), which move up-and-down (or reciprocating motion) inside the cylinder. The pistons are attached to a crankshaft, through a connecting rod called piston rod (Ward 2010, p.178). In conventional 4- or 6-cylinder piston engine, the piston rods are linked to the crankshaft at offseting interval to balance the firing of the pistions. In most aircraft piston engines, a flywheel serves to minimise the vibration further and to facilitate smooth operation of the propeller (Ward 2010, p.183-185). Once the fuel is launched and ignited inside the cylinder, hot gases (fuel-air mixture) are generated, which expand at a tremendous force (Torenbeek & Wittenberg 2009, p.216). These drive the respective piston forward insider the cylinder. In turn, the piston rod moves forward, causing the crankshaft to turn (Asselin 1997, 37). Complete rotation of the crankshaft thrusts the piston back into the cylinder (Torenbeek & Wittenberg 2009, p.210-211). The power cycle continues. Ultimately, the crankshaft transforms the piston’s reciprocating and linear force into a rotating motion, which drives the propeller (Ward 2010, p.178). This paper examines the advantages and disadvantages of piston engines in aircrafts. Advantages Piston aircraft engines withstand high temperatures because of their cylinder designs. According to Ward (2010 p.181), a piston engine’s cylinder design is among the most critical factors that determine their effective performance. Almost all cylinders are manufactured from aluminium or alloys of aluminium and steel liners. The liners serve to endure the wear from friction, in addition to the high temperatures resulting from the sliding piston rings. Piston aircraft engines are also inexpensive to build, maintain and to operate since they burn fuel at a comparatively lower rate than conventional gas turbine engines. This has made them more preferable in the manufacture and application of engines for general aviation helicopters and airplanes (Torenbeek & Wittenberg 2009, p.209). The piston aircraft engines have also found extensive use in fire suppression, agricultural and acrobatic aircrafts. The piston engines generally have simple designs, which make building them relatively easy. For instance, reciprocating engines, such as the inline engine, has simple design where the cylinders lined up in a row. Common cylinder arrangements are made of two, four or six cylinders arranged in horizontally opposed formation (Ward 2010, p.179-182. Because of their simplistic formation, designing the aircraft to have a low-frontal area to reduce drag is easy. At this stage, the engine crankshaft can be positioned over the cylinders to create inverted inline engine. This enables the propeller to be fixed at an elevated level to create more ground clearance, as a result enabling more diminutive landing gear (Torenbeek & Wittenberg 2009, p.209). Piston engines have greater efficiency with superchargers. They can be supercharged to increase their performance at higher altitudes, and to attain higher compressor speed. At particular thermal and composition efficiency, the power of the shaft is relative to the mass of air drawn into the engine, for each unit of time, hence the air density is critical (Ward (2010, p.191-194). Correspondingly, the power reduces proportionally to the air density. For instance, at an altitude of 6000m to 7500m, supercharging can boost the performance of piston engines (Torenbeek & Wittenberg 2009, p.212). A supercharger (which consists of a separate compressor) can increase the boost pressure of the engine and the cylinder's intake air density. Additionally, the superchargers maintain the engine's maximum power at greater altitudes (Torenbeek & Wittenberg 2009, p.212). Moreover, because many aviation industries have much experience with this engine type, it makes the piston engines cheaper, reliable and easy to maintain (Torenbeek & Wittenberg 2009, p.209). The piston engines (especially spark-ignited internal-combustion engines) run on aviation gasoline (Avgas) that contain higher octane, allowing occurrence of higher compression ratios, in addition to increased power outputs and improved efficiency at high altitudes. Typical fuel has low lead content and octane rating of 100 (Ward 2010, p.205). The fuel consumption describes the rate of fuel efficiency of the reciprocating engines. It is referred to as brake specific fuel consumption (BSFC). Higher compression engine have low BSFR. Adding the superchargers also raises the BSFC at low shaft speeds (Ward 2010, p.205). Disadvantages The altitude and thrust capabilities of aerodynamic of piston engines are considerably limited compared to the gas turbine engines. This implies that piston aircraft engines are not suited for travelling at very high altitudes. According to Ward (2010, p.173), the maximum power output of piston aircraft engine is nearly 745W. On the other hand, the gas turbine engines such as turboprop can attain much higher power. This also indicates that the piston aircraft engines tend to have lower performance and travel at a lower speed as compared to the turboprop air craft engines. This is because of the “heat release per pound of air”. The horsepower created by the internal combustion engines (or piston prop engines) is relative to the heat released in the pistons. Once the heat released within the pistons rises, the corresponding mixture pressure (MEP) rises due to the increased temperature. At this rate, the heat release per pound depends on the fuel-air ratio (f/A) and fuel HV. Hence, if the fuel-air ratio rises, the mixture becomes denser. Ultimately, the combustion may become incomplete. On the other hand, if it is too small, the heat released decreases. In return, the existing power becomes lower (Asselin 1997, 42). Most contemporary piston aircraft engines have relatively low power, which often do not exceed 225kW. Despite this, high performing engines may go beyond 450kW Ward (2010 p.180). On the other hand, turboprop engines have higher power and travel at greater speeds. This is since the mass of air that injects into the cylinders of internal combustion engines (or piston prop engines) engines determines the quantity of heat released. For the fuel to burn completely, there has to be adequate air quantity. However, the air is less dense at higher altitudes. In which case, for any given throttle setting, the power output reduces (Asselin 1997, 42). On the other hand, given their efficiency, the turboprops tend to be more efficient at higher altitudes of between 20,000 and 30,000 feet, in addition to average speeds of 300ktas. Piston aircraft engines are less efficient since they are not pressurised. This implies that they fly at limited altitudes of averagely 12,000 feet and below. At the same time, since they have less power, their speed is limited to 200ktas (Torenbeek & Wittenberg 2009, p.215). Despite the fact that supercharging can increase the efficiency of piston engines at high altitudes of 6000m to 7500m, they still have a critical mechanical setback. This is since at higher altitudes, the power required to drive the supercharger substantially reduces the shaft power. This is worsened when the engine is throttled abruptly (Torenbeek & Wittenberg 2009, p.212) Since the aircraft piston engines are relatively heavy, they are more likely to witness in-flight failure, as compared to the gas turbine aircraft engines, such as turboprops. For instance, the inline piston engines have been cited to have a shortcoming of power-to-weight ratio, since it has long crankshaft and crankcase, which are heavy. Additionally, the compression-ignition engines are heavier, since they have to be constructed from stronger material, given the high compression ration (Ward 2010, p.178-179). Additionaly, they require large cylinder volume due to the low rpm. In respect to the permissible rpm, the horsepower that the internal combustion engines (or piston prop engines) generates directly corresponds to the engine's rpm. On the other hand, rpm of the engine is often vulnerable to the reliability of the engine, the tip speed of the properller, or the engine desined life (Asselin 1997, 36-42). Hence, the piston engines are not efficient. Within the engineering and manufacturing perspective, the reciprocating piston engines are less complex as compared to the turboprops. Essentially, this is because of the high forces and temperatures associated with engine operation of the turboprops. For instance, both have to be accommodated in the design of the engine and the material it is made from. However, these come at a higher price, meaning that the piston engine aircrafts comes at a relatively low cost. In general, the piston aircraft engines are intended for the smaller aircraft and suitable for relatively short distances of up to 300 miles. On the other hand, the turboprops are generally intended for larger aircrafts, and with more fuel on board, can travel for up to 1000 miles. The piston engines also produce a lot of noise. For instance, the piston aircraft engines have a maximum speed ranging from 2,500 to 3,000 rpm. The propeller may, however, be inefficient and generate much noise at this rotational speed. Due to this drawback, piston engines typically have step-down ration of between 0.5 and 0.7 (Torenbeek & Wittenberg 2009, p.215). According to Torenbeek and Wittenberg (2009, p.208-209), since the thermal efficiency of piston aircraft engine is not subjective to the flight speed, the variation of the efficiency is determined by the efficiency of the propulsion. Torenbeek and Wittenberg (2009, p.208-209) pointed out that the turboprops have higher efficiency compared to the piston aircraft engines with propellers, since the efficiency of the propeller reduces due to the effects of compressibility. Because of the scarcity of Avgas, fuel prices for piston engines are relatively expensive. On the other hand, gas turbine engines such as turboprops can use inexpensive kerosene-based fuel, or jet fuel. Ward (2010, p.173) stated that use of jet fuel is a basic reason why modern military and commercial propeller-driven aircrafts are mostly powered by turboprop engines rather than piston engines. Conclusion Piston engines have several advantages that have made them preferable for aircrafts. They can withstand high temperatures because of their cylinder designs. They are also inexpensive to build, maintain and to operate, since they burn fuel at a comparatively lower rate than conventional gas turbine engines. Piston engines have greater efficiency with superchargers. They can be supercharged for increased performance at higher altitudes, and to attain higher compressor speed. They also run on aviation gasoline (Avgas) that contain higher octane, allowing occurrence of higher compression ratios, in addition to increased power outputs and improved efficiency at high altitudes. Maintenance of piston engines is relatively easy due to their simple design. Within the engineering and manufacturing perspective, the reciprocating piston engines are less complex as compared to the turboprops. On the other hand, several disadvantages have made them less preferable as compared to the gas turbine engines. The altitude and thrust capabilities of aerodynamic of piston engines are considerably limited compared to the gas turbine engines. Most contemporary piston aircraft engines also have relatively low power, which often do not exceed 225kW. Despite the fact that supercharging can increase the efficiency of piston engines at high altitudes of 6000m to 7500m, they still have a critical mechanical setback. This is since at higher altitudes, the power required to drive the supercharger substantially reduces the shaft power. Since the aircraft piston engines are relatively heavy, they are more likely to witness in-flight failure, as compared to the gas turbine aircraft engines such as turboprops. Reference List Asselin, M 1997, An Introduction to Aircraft Performance, American Institude of Aeronatics and Astronautics, Reston, Virginia Torenbeek, E & Wittenberg, H 2009, Flight Physics: Essentials of Aeronautical Disciplines and Technology, with Historical Notes, Springer Science & Business Media, Delft, The Netherlands Ward, T 2010, Aerospace Propulsion Systems, John Wiley & Sons, Clementi Loop, Singapore Read More

The piston aircraft engines have also found extensive use in fire suppression, agricultural and acrobatic aircrafts. The piston engines generally have simple designs, which make building them relatively easy. For instance, reciprocating engines, such as the inline engine, has simple design where the cylinders lined up in a row. Common cylinder arrangements are made of two, four or six cylinders arranged in horizontally opposed formation (Ward 2010, p.179-182. Because of their simplistic formation, designing the aircraft to have a low-frontal area to reduce drag is easy.

At this stage, the engine crankshaft can be positioned over the cylinders to create inverted inline engine. This enables the propeller to be fixed at an elevated level to create more ground clearance, as a result enabling more diminutive landing gear (Torenbeek & Wittenberg 2009, p.209). Piston engines have greater efficiency with superchargers. They can be supercharged to increase their performance at higher altitudes, and to attain higher compressor speed. At particular thermal and composition efficiency, the power of the shaft is relative to the mass of air drawn into the engine, for each unit of time, hence the air density is critical (Ward (2010, p.191-194). Correspondingly, the power reduces proportionally to the air density.

For instance, at an altitude of 6000m to 7500m, supercharging can boost the performance of piston engines (Torenbeek & Wittenberg 2009, p.212). A supercharger (which consists of a separate compressor) can increase the boost pressure of the engine and the cylinder's intake air density. Additionally, the superchargers maintain the engine's maximum power at greater altitudes (Torenbeek & Wittenberg 2009, p.212). Moreover, because many aviation industries have much experience with this engine type, it makes the piston engines cheaper, reliable and easy to maintain (Torenbeek & Wittenberg 2009, p.209). The piston engines (especially spark-ignited internal-combustion engines) run on aviation gasoline (Avgas) that contain higher octane, allowing occurrence of higher compression ratios, in addition to increased power outputs and improved efficiency at high altitudes.

Typical fuel has low lead content and octane rating of 100 (Ward 2010, p.205). The fuel consumption describes the rate of fuel efficiency of the reciprocating engines. It is referred to as brake specific fuel consumption (BSFC). Higher compression engine have low BSFR. Adding the superchargers also raises the BSFC at low shaft speeds (Ward 2010, p.205). Disadvantages The altitude and thrust capabilities of aerodynamic of piston engines are considerably limited compared to the gas turbine engines.

This implies that piston aircraft engines are not suited for travelling at very high altitudes. According to Ward (2010, p.173), the maximum power output of piston aircraft engine is nearly 745W. On the other hand, the gas turbine engines such as turboprop can attain much higher power. This also indicates that the piston aircraft engines tend to have lower performance and travel at a lower speed as compared to the turboprop air craft engines. This is because of the “heat release per pound of air”.

The horsepower created by the internal combustion engines (or piston prop engines) is relative to the heat released in the pistons. Once the heat released within the pistons rises, the corresponding mixture pressure (MEP) rises due to the increased temperature. At this rate, the heat release per pound depends on the fuel-air ratio (f/A) and fuel HV. Hence, if the fuel-air ratio rises, the mixture becomes denser. Ultimately, the combustion may become incomplete. On the other hand, if it is too small, the heat released decreases.

In return, the existing power becomes lower (Asselin 1997, 42). Most contemporary piston aircraft engines have relatively low power, which often do not exceed 225kW. Despite this, high performing engines may go beyond 450kW Ward (2010 p.180). On the other hand, turboprop engines have higher power and travel at greater speeds.

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