Lecture 3b: Aircraft Engines

1903- 1940s: Propeller + Piston Engines Era From 1903 (Wright bros.) until the Early 1940s, all aircraft used the piston engine combined with propeller as their propulsion system. Piston engine is just similar with car engine except with several different. A propeller is essentially a type of fan which transmits power by converting rotational motion into thrust to propel the aircraft (move forward). The purpose of a propeller is to convert the power produced by an engine into propulsive thrust in order to propel the aircraft. The propeller blade has an aerofoil shape and like a wing produces lift, but in a horizontal direction. This lift is the thrust that causes forward motion. A propeller consists of two or more aerodynamically shaped blades attached to a central hub. This hub is mounted onto propeller shaft driven by the engine. Let’s take a closer simplified look to a propeller blade, its terminology and principal of operation. Piston engine uses the energy produced by burning a mixture of air and fuel to drive the propeller.

Piston engine Main parts IANS / ATC Training / Courses / Basic / ACFT ACFT 3 PISTON Piston engine Main parts The main parts of a piston engine are shown on the following drawing. Only one cylinder is cross-sectioned here, however aircraft engines usually contain more cylinders assembled in various configurations, as already explained. Describe the main parts: Cylinder Piston Cylinder head Inlet valve Exhaust valve Spark plug Combustion chamber Crankcase Crankshaft Connection rod Edition 1.2 20-02-2006

Piston engine Different configurations of piston engines IANS / ATC Training / Courses / Basic / ACFT ACFT 3 PISTON Piston engine Different configurations of piston engines Aircraft piston engines usually contain more cylinders assembled in various configurations. The in-line and "V" engines are very similar to those used in automobiles. Horizontally opposed engines are the third major configuration. These can be considered an extreme example of a "V" engine, in which the angle between the pistons is 180 degrees. The cylinders lie on a plane roughly parallel to the wings. The radial engine configuration is unique to aviation. Here the crankshaft is in the circular centerpiece of the engine and the cylinders radiate out from it in a plane perpendicular to the crankshaft. An interesting early design is the rotary engine, in which the engine block rotates about a fixed crankshaft. Edition 1.2 20-02-2006

Piston engine Examples IANS / ATC Training / Courses / Basic / ACFT ACFT 3 PISTON Piston engine Examples Piper PA-28 Cherokee Engine(s): Lycoming piston engine 4 cylinders 110 hp Propeller(s): 2 blades fixed pitch Performance: Max. speed 127kt Operational ceiling 11000 feet Information presented on the slide. Edition 1.2 20-02-2006

Piston engine Examples IANS / ATC Training / Courses / Basic / ACFT ACFT 3 PISTON Piston engine Examples Antonov AN-2 Engine(s): PZL piston engine, RADIAL 9 cylinders 1000 hp Propeller(s): 4 blades variable pitch Performance: Max. speed 139kt Operational ceiling 13000 feet (approx.) Information presented on the slide. Edition 1.2 20-02-2006

The differences between piston aircraft engines and car engines Crankshaft – The crankshaft in an piston aircraft engine turns a propeller, crankshaft in car engine is used to move the wheels of the car. Weight – the piston aircraft engine must be lightweight compare to car engine. Power demand to run the engines- the piston aircraft engine demands high power for very long times compare to car engines Numbers of engine parts - an aircraft engine has at least two sets for every parts, including ignition system (spark plugs and magnetos) and fuel pumps compare to car engine that only have one set. Operating environment different- an aircraft engine no need radiator for air-cooling compare to the car. First, an aircraft engine is designed with weight as a primary consideration. Thus, the weight-to-power ration is generally lower for an aircraft engine when compared with an automobile engine of comparable size. An airplane engine has two spark plugs on each cylinder that are fired independently from engine-driven magnetos. Before taking off, a pilot checks to see that the engine will run smoothly on either “mag” alone. Many airplane engine systems also incorporate an additional fuel pump that is electrically driven, independent of the engine. Since it must operate over a range of density altitudes, an airplane engine has a manual mixture control. At low altitude, the mixture is set relatively rich and is leaned at the higher altitudes, where the air is less dense. During a continuous climb, where a large amount of power is required, the pilot will also set the mixture on the rich side in order to provide better cooling. The richer the mixture, the cooler the exhaust gases will be. Running too rich, however, can result in a loss of power and premature spark plug fouling. Therefore, many airplanes are equipped with an exhaust temperature (EGT) gage that allows the pilot to set the mixture control more accurately. Carbureted aircraft engines, as opposed to fuel-injected engines, have a carburetor heat control. In the “on” position, this control provides heated air to the carburetor in order to avoid the build up of ice in venture. Since the air expands in the carburetor throat, the temperature in this region can be below freezing even when the outside air temperature is above freezing. If a pilot is flying through rain or heavy clouds at temperature close to freezing, the pilot can experience carburetor icing with an attendant loss of power unless the pilot pulls on the carburetor heat. An aircraft engine is operated with primary reference to two gages: the tachometer (which indicates the engine rpm), and the manifold pressure gage (which measures the absolute pressure within the intake manifold). These two quantities, at a given density altitude, determine the engine power. Aircraft spend the vast majority of their time travelling at high speed. This allows an aircraft engine to be air cooled, as opposed to requiring a radiator. With the absence of a radiator, aircraft engines can boast lower weight and less complexity. The amount of air flow an engine receives is usually carefully designed according to expected speed and altitude of the aircraft in order to maintain the engine at the optimal temperature. Aircraft operate at higher altitudes where the air is less dense than at ground level. As engines need oxygen to burn fuel, a forced induction system such as turbocharger or supercharger is especially appropriate for aircraft use. This does bring along the usual drawbacks of additional cost, weight and complexity.

Propeller + Piston Engine Aircraft Very efficient for low speed flight. Lower load capacity compared to similar sized jet powered aircraft. Consumes less fuel, thus cheaper and much more economic than jets. Quiet, but fly at lower speeds. The best option for people who need to transport a few passengers and/or small amounts of cargo. Best choice for pilots who wish to own their own aircraft. Propellers are not used on high speed aircraft.

Jet Engine History 1931: 1st turbojet engine designed 1930 by Sir Frank Whittle 1939: The 1st jet aircraft (Heinkel He 178) was developed in England and Germany 1943: The first jet fighter aircraft, Messerschmitt Me 262 went into service in the German Luftwaffe.

History of Aircraft Propulsion 1944 (After World War 2)-Today : Airplanes used jet engines to generate thrust. Jet engines also referred to as Gas Turbine Engines. Various types (turbo-jet, turbo-prop, turbo-shaft, turbo-fan , ramjet, scramjet) Messerschmitt Me-262 : 1st operational jet-powered aircraft German V-1 bomb (pulse jet engine): 1st application for military purposes. Bell P-59: 1st American aircraft MiG-15: 1st Soviet jet aircraft.

Jet Engines Jet aircraft make use of turbines for the creation of thrust. Consumes more fuel but provide much more thrust than a piston engine. Fly faster than propeller driven aircraft. Greater weight capacity Example: Airbus A340 and Boeing 777, can carry hundreds of passengers and several tons of cargo, and are able to travel for distances up to 13 thousand kilometers. Noisy, this makes jet aircraft a source of noise pollution. A turbojet is a type of gas turbine engine that was originally developed for military fighters during World War II. A turbojet is the simplest of all aircraft gas turbines.

Newton's 3rd law The theory of jet propulsion is based on the Newton’s third Law, which state that For every action there is an equal and opposite reaction. When the jet engine is operating, it draws a lot of air from the front and after air-fuel burns the gas ejects at high speed. During this process, the engine applies force to the gas and lets the gas accelerate in the backward direction and in the meantime, the gas also gives the engine a reactive force to push the aircraft to move forward.

Turbo-jet Engine Thrust Newton's 3rd law: For every action there is an equal and opposite reaction. This is called thrust. Inlet- inlet is the opening at the front of engine, it allows the outside air to enter the engine. Compressor – compressor is made up of fans with many blades, it compress the air and raises the pressure & temperature of the air, the compressed air then is delivered to the burner. Burner – Burning process occur here. Fuel is sprayed to the compressed air .The mixture of the fuel + air will be burned. The results is heated gas with high energy, high pressure and high temperature. Turbine- turbine used some of the heated gas energy to turn the compressor . This energy is transferred through the shaft. Nozzle- The balance of heated gas energy exits through the nozzle at very high speed. This causes thrust. As the jets of gas shoot backward, the engine and the aircraft are thrust forward. (Newton 3rd Law)

Turbo-prop Engine The propeller located at the front of engine The propeller converts the power developed by the engine into thrust as efficiently as possible under all operating conditions. These aircraft are popular with regional airlines, as they tend to be more economical on shorter journeys. Hercules-1 C130

Turbo-fan Engine Similar to the turboprop, except a fan replaces the turboprop propeller. Larger fan at the front provides thrust in the same way as a propeller. The turbofan engine has a front fan, which runs at the same speed as the compressor and fan turbine located at the back to drive the fan. Most modern airliners use turbofan engines because of they can produce high thrust, lower fuel consumption and low engine-noise. located to the rear of the compressor drive turbine may also drive the fan. The fan draws in more air than the compressor of a turbojet engine because of the larger area of the inlet. Because the larger amount of air is compressed and accelerated by the fan, the air completely bypasses the burner and turbine sections of the engine and exits through the fan exit ducts. Since the air is not heated by burning fuel to obtain thrust, the turbofan engine has The difference between the two engines is the airflow. The fan is inside a cowling, and as a result the airflow through the fan is unaffected by the aircraft's speed. This increase the efficiency. lower fuel consumption. To develop thrust, the turbofan engine accelerates a large amount of air at a relatively lowvelocity, which improves its propulsion efficiency. Compared to the turbojet, the turbofan engine has a low engine noise level. The low noise level results from the lower gas velocity as it exits the engine tailpipe. One reason for the decreased velocity is an additional turbine stage in the engine. This additional turbine stage extracts power from the exhaust gases to drive the fan. The aircraft powered by a turbofan engine has a shorter takeoff distance and produces more thrust during climb than a turbojet of approximately the same size. This extra thrust allows the turbofan aircraft to take off at a much higher gross weight.

Rocket Engine A rocket engine produces thrust by burning a fuel at high pressure and exhausting the gas through a nozzle. The oxygen for combustion is carried with the propulsion system. High temperatures and pressures is built up, the are used to accelerate the exhaust gases through a rocket nozzle to produce thrust. The heavier the rocket , the greater thrust needed to get it off the ground. Newton 3rd Law: “To every action there is an equal and opposite reaction." 17

Differences between Jet engine and Rocket engine Thrust direction Jet engine is an engine using jet propulsion for forward thrust . Rocket engine is an engine using jet propulsion for upward thrust. Source of oxygen Jet engines do not have their own source of oxygen. Outside air is sucked into the engine to act as an oxidizer There is no air in space. Rockets have their own oxygen source, either a liquid tank, or mixed in with the solid fuel for combustion. jet engine require a forced intake of air and compress ot to provide thrust. *very efficient. there is no air in space. any air for a jet engine would have to be brought from earth and used. *inefficient rockets burn fuel fuel and its directed thrust is immense. * not very efficient Jet engines require oxygen for combustion, there is no air in space therefore combustion cannot occur. Rockets carry all their own fuel with them and the combustion happens without oxygen which is why they can provide thrust outside of the atmosphere.

Rocket vs Missile Purpose Rocket mission is to send the satellite to outer space. Missile mission is as a weapon to attack high value target. Guidance Rocket no guidance system. Missile has a guidance system.