A&P Technician Powerplant Textbook (Jeppesen) PDF

DESIGN AND CONSTRUCTION Newton's third law of motion states that for every action there is an equal and opposite reaction. Jet propulsion applies this law by accelerating a quan- tity of air through an orifice (or nozzle). The accel- eration of the air is the action and forward move- ment is the re...

DESIGN AND CONSTRUCTION Newton's third law of motion states that for every action there is an equal and opposite reaction. Jet propulsion applies this law by accelerating a quan- tity of air through an orifice (or nozzle). The accel- eration of the air is the action and forward move- ment is the reaction. In nature, a squid propels itself through the water using a form of jet propulsion. A squid takes sea water into its body and uses its mus- cles to add energy to the water, then expels the water in the form of a jet. This action produces a reaction that propels the squid forward. [Figure 3-1] Figure 3-1. Many technological developments are made by observations of the natural world. A squid propels itself through the water by jet reaction. Figure 3-2. Hero's aeoiipile, invented long before Newton As early as 250 B.C., a writer and mathematician postulated his laws of Motion, proved that power by reaction named Hero devised a toy using this reaction prin- was possible. ciple. The toy, called the aeolipile, consisted of a covered kettle of water that was heated to produce HISTORY OF JET PROPULSION steam. The steam was routed through two vertical The history of mechanical jet propulsion began in tubes into a spherical container. Attached to the 1900, when Dr. Sanford Moss submitted a thesis on spherical container were several discharge tubes gas turbines. Later, Dr. Moss became an engineer for arranged radially around the container. As steam the General Electric Company in England. While filled the container, it would escape through the there, he applied some of his concepts in the devel- discharge tubes causing the sphere to rotate. [Figure 3-2] opment of the turbo-supercharger. His design used a small turbine wheel, driven by exhaust gases, to turn a supercharger. A modern example of Newton's reaction principle is observed when the end of an inflated balloon is Dr. Moss's research influenced the development released. As the air in the balloon rushes out the of what became the first successful turbojet opening, the balloon flies wildly around a room. engine. Dr. Frank Whittle of England was granted In spite of the everyday examples, scientific his first patent for a jet engine in 1930. Eleven efforts to apply Newton's reaction principle to years later, the engine completed its first flight in mechanical designs were largely unsuccessful a Gloster model E28/39 aircraft. The engine pro- until the 20th century. duced about one thousand pounds of thrust and Turbine Engines 3-3 produced approximately 1,650 pounds of thrust. Two of these engines were used to power a Bell XP- 59 "Airacomet." The Airacomet flew for the first time in October 1942 and proved the concept of jet- powered flight. However, it was never used in com- bat due to a limited flight time of 30 minutes. [Figure 3-5] Figure 3-5. First flown in 1942, the Bell XP-59 was the first American jet-powered aircraft. JET PROPULSION TODAY Today, the majority of commercial aircraft use some form of jet propulsion. Currently, several manufacturers produce entire lines of jet-powered Figure 3-3. Dr. Frank Whittle of England patented the first aircraft that cruise in excess of 600 miles per hour turbojet engine, the Whittle W1, in 1930. Its first flight and carry up to five hundred passengers or several occurred in a Gloster E28/39 aircraft in 1941. tons of cargo. propelled the aircraft at speeds over 400 miles per Another step in the progression of commercial and hour. [Figure 3-3] military aviation was the ability to produce an engine that would propel an aircraft faster than the While Whittle was developing the gas turbine speed of sound. Today, several military aircraft engine in England, Hans Von Ohain, a German engi- travel at speeds in excess of Mach one. Supersonic neer, designed and built a jet engine that produced aircraft are presently in use in military and research 1,100 pounds of thrust. This engine was installed in applications. The Concorde, a supersonic commer- a Heinkel He-178 aircraft and made a successful cial aircraft built collaboratively by a British and flight on August 27, 1939. As a result, it is recog- French consortium, was in service from 1976 nized as the first practical flight of a jet-propelled through 2003. The Concorde was capable of flying aircraft. [Figure 3-4] at 2.2 times the speed of sound. In the United States , research in the field of jet In addition to military and commercial aviation, jet propulsion lagged. Because of its extensive experi- propulsion is widely used in business jets. The use ence in building electrical generating turbines and of twin-engine aircraft has grown in part due to the turbo-superchargers the General Electric Company efficiency and reliability of the jet engines. received a contract to research and develop a gas turbine engine in 1941. The result was the GE-lA TYPES OF JET PROPULSION engine , a centrifugal-compressor type engine that Newton 's reaction principle has been applied to several propulsive devices used in aviation. All pro- duce thrust in the same manner; they accelerate a mass of gases within the engine. The most common types of propulsive engines are the rocket, the ram- jet, the pulsejet, and the gas turbine. ROCKET A rocket is a non-air-breathing engine that carries its own fuel and the oxygen needed for the fuel to burn. Figure 3-4. German engineer Hans Von Ohain designed and The two types of rockets in use are solid-propellant built the turbojet engine that powered the Heinkel He-178 rockets and liquid-propellant rockets. Solid-propel- in the world's first jet-powered flight in 1939. lant rockets use a solid fuel formed into a specific  3-4 Turbine Engines shape that promotes an optimum burning rate when mixed with an oxidizer. After the fuel is ignited, it FUEL NOZZLES produces an extremely high-velo city discharge of COMBUSTION CH AMBER gas through a nozzle at the rear of the rocket body. The reaction to the rapid dis charge is forward motion of the rocket body. Solid fuel rockets are used primarily to propel some military weapons and occasionally to provide additional thrust for takeoff of heavily loaded aircraft. In the latter case, booster rockets attached to an aircraft structure pro- vide the additional thrust needed for special-condi- tion takeoffs. [Figure 3-6] The second type of rocket is a liquid-fuel rocket, Figure 3 -7. As a ramjet m oves forwa rd , air enters the intake which uses fuel and an oxidizing agent such as liq- and proceeds t o a com bustion ch amber w here f uel is add ed uid oxygen. The two liquids are carried in tanks and ignit ed. T he heat fro m the bu rnin g fu el accelerat es the aboard the rocket. When the liquids are mixed , a f low of air t hrough a venturi t o prod uce t hru st. violent reaction occurs , which generates a tremen- dous amount of heat. The resulting high-velocity combustion chamber where it is heated by burning gas jet behind the rocket provides enough thrust to fuel. As the air within the combustion chamber propel it. expands, the increased air pressure increases to force the shutter valves closed. After it is enclosed RAMJET aft of the shutters, the expanding air in the chamber A ramjet is an athodyd (or aero-therm odynamic- is forced rearward to produce thrust. A pulsejet is duct), an air-breathing engine with no moving parts. typically considered more useful than a ramjet With no rotating compressor to draw air into the because pulsejets can produce thrust prior to engine, a ramjet must be moving forward at high achieving a high forward speed. [Figure 3-8] velocity before it can produce thrust. After air enters the engine, fuel is injected and ignited to provide GAS TURBINE ENGINE the heat needed to accelerate the air and produce The gas turbine engine is the most practical form of thrust. Because ramjets must be moving forward to jet engine in use today. In fact, the turbine engine produce thrust, their use is limited. Ramjets are has become the standard on nearly all commercial used in some military weapons delivery systems in (transport category), business, and military aircraft. which the vehicle is accelerated to a high enough The remainder of this section will focus on the gas velocity for the ramjet to take over power for sus- turbine engine. The four most common types of gas tained flight. [Figure 3-7] turbine engines are the turbojet, turbopropeller (tur- boprop), turboshaft, and turbofan. PULSEJET Pulsejet engines are similar to ramjets except that TURBOJET ENGINES the air intake duct is equipped with a series of shut- The basic operating principles of a turbojet engine ter valves that are spring-loaded to the open posi- are straightforward. Air enters through an inlet duct tion. Air drawn through the open valves enters a and proceeds to the compressor. After the air is compressed, it flows to a combustor section where fuel is added and ignited. The h eat generated by the burning fuel causes the compressed air to expand and flow toward the rear of the engine. As the air moves rearward, it passes through a set of turbine wheels connected to the compressor blades. The expanding air spins the turbines , which in turn drive the compressor. After it moves past the tur- bines, the air exits the engine at a much higher velocity than the incoming air. The difference in velocity between the air entering and the air exiting Figure 3 -6. Rocket assisted takeoff (RATO) devices are small, the engine produces thrust. solid propellant rocket motors attached t o an airplane t o pro vide additional takeoff thrust at high-alt itude airports or for lifting One of the most important aspects of turbojet engine extremely hea vy loads. operation that you must be familiar with is the Turbine Engines 3 -5 eG ~---- : --;-- --:- ~ r'·~~~""-- (B).r/'--.........~-.....::::::- -- - ~ -.: (. ,,::::,. _::::; --_.,..-- ---===--- t ~,, ~ r - _ - - ' -----;..... Figure 3 -9. Turboprop powerplants are common on corporate and commuter twin-engine aircraft. TURBOSHAFT ENGINES A gas turbine engine that delivers power to a shaft !AIR INTAKE FUEL \ _ COMBUSTION CHAMBER that can drive something else is referred to as a tur- boshaft engine. The biggest difference between a Figure 3-8. (A) In a pulsejet engine, air is drawn into the turbojet and turbosh aft engine is that on a turboshaft combustion chamber and mixed with fuel when the shutter engine, most of the energy produ ced by the expand- valve is open. (Bl As the fuel burns, air pressure within the ing gases is used to drive a turbine rath er th an pro- chamber increases and forces the shutter valves to close. duce thrust. Many h elicopters use a turboshaft gas After the shutter closes , the expanding air within the engine turbin e engine. In addition, turbosh aft engines are accelerates through the exhaust nozzle to produce thrust. widely used as auxiliary power units and , in indus- trial app lications, to drive electrical gen erators and surface trans portation systems. The output of a tur- engine pressure ratio , or EPR. An engine's EPR is boprop or turboshaft engine is measured by shaft th e ratio of the turbin e discharge pressure to the horsepower rather than thrust. engine inlet air pressure. EPR gauge readings are an indication of th e amount of th rust being produced TURBOFAN ENGINES for a given power lever setting. Total pressure pick- ups, or EPR probes , measure the air pressure at two A turbofan engin e consists of a multibladed, points in the engine; one EPR probe is located at th e du ct ed prope ller driven by a gas turbine engin e. compressor in let and a secon d just aft of the last Turbofans were develop ed to p rovide a co mpro - stage turbine in the exhau st section. EPR readings mi se b etween the b est fea tures of the turbojet and are often u sed to verify power settings for takeoff, th e turb op rop. Turb ofan engines have turb ojet- climb, and cruise. EPR readings are affected by and type cruise sp eed capability, yet retain some of are dependent on pressure altitude and outside air th e sh ort-field takeoff capability of a turb oprop. temperature (OAT). Nearly all present day airlin er s are powere d by turbofan en gines for these reason s as well as because turb ofans are relatively fuel-efficie n t. TURBOPROPELLER ENGINES A gas turbine engine that delivers power to a pro- A turbofan engin e can have the fan mounted either p eller is referred to as a turbopropeller, or turbo- in the front or back of the engine. Engines th at h ave prop , engin e. Turboprop engines are similar in the fan mounted in fro nt of the compressor are design to turbo jet engines except that the power called forward-fan engines , an d turbofan engines produced by a turboprop engine is delivered to a that have the fan mounted to the turbine section are reduction gear syst em th at spins a propeller. called aft-fan engines. [Figure 3-10] Reduction gearing is necessary because optimum propeller performance is achieved at mu ch slower Inlet air passing through a turbofan engine is usu- speeds than the engine operating speed. Turboprop ally divided into two separate streams of air. One engines are used extensively in business and com- stream passes through the engine core, and a second muter aircraft because the combin ation of jet power stream coaxially bypasses the engine core. From and propeller efficiency provides good p erformance th is bypass stream of air, this powerplant is referred characteristics at speeds between 300 and 400 miles to as a bypass engine. To discuss bypass engines , per h our. Additionally, most turboprop engines you must be familiar with three terms-thrust ratio , operate with th e best specific fuel consumption of bypass ratio , and fan pressure ratio. A turbofan any gas turbine engine. [Figure 3-9] engine 's thrust ratio is a comparison of the thrust 3- 6 Turbine Engines INLET HOT DUCT EXHAUST (A) FAN DISCHARGE --- Figure 3-1 0. (A) A forward-fan turbofan engine uses a relatively large-diameter, ducted fan that produces thrust and provides intake air to the compressor. (B) An aft-fan turbofan engine has a fan mounted on the aft turbine. This arrangement is rarely used because an aft fan does not contribute to air compression at the inlet. produced by the fan to the thrust produced by the the engine. Full fan ducts reduce aerodynamic drag engine core exhaust. On the oth er hand , a turbofan's and noise emissions. In either case, the end of the bypass ratio refers to the ratio of incoming air that duct u sually has a converging discharge nozzle that bypasses the core to the amount of air that passes increases velocity and produces reactive thrust. through the engine core. Turbofans in civil aircraft [Figure 3-11] are generally divided into three classifications based on bypass ratio: low bypass (1:1); medium Medium- or intermediate-bypass engines have air- bypass (2:1 or 3:1); and high bypass (4:1 or greater). flow bypass ratios ranging from 2:1 to 3:1. These Fan diameter determines a fan 's bypass ratio and engines have thrust ratios similar to their bypass thrust ratio. ratios. The fans used on these engines have a larger diameter than the fans used on low-bypass engines Generally, airflo w mass in the fan section of a low- of comparable power. bypass engine is the same as airflow mass in the compressor. The fan discharge could be slightly High bypass turbofan engines have bypass ratios of higher or lower depending on the engine model , but 4:1 or greater and use the largest diameter fan of any bypass ratios are approximate ly 1:1. In some of the bypass engines. High bypass turbines offer engines , the bypass air is vented directly overboard higher propulsive efficiencies and better fuel econ- through a short fan duct. However, in a ducted fan , omy than low or medium bypass turbines. the bypass air is ducted along the entire length of Consequently, they are the engines of choice on Turbine Engines 3-7 (A) DUCT ~~ x-- ~ FAN EXHAUST