AIRCRAFT ENGINES Chapter 01

1-28 AMP056How many of the following are factors in establishing the maximum compression ratio limitations of an aircraft engine? 1. Detonation characteristics of the fuel used. 2. Design limitations of the engine. 3. Degree of supercharging. 4. Spark plug reach.

1-28 Answer C. C. 3 Manifold pressure is the average absolute pressure ofthe air or fuel air charge supplying the engine. Combined with the compression ratio, the total pressure inside the combustion chamber of the engine is determined. Design limitations prevent unlimited pressure inside the engine. Since supercharging affects manifold pressure and fuels have various characteristics which affect their ability to be compressed without exploding, these three factors limit the maximum compression ratio that can be developed by an engine. The reach of the spark plug will affect the ignition of the compressed charge in an engine that has already been designed with the other three factors taken into consideration, however it does not affect maximum compression ratio.

1-29 AMP056 The horsepower developed in the cylinders of a reciprocating engine is known as the

1-29 Answer B. The indicated horsepower produced by an engine is the horsepower calculated from the indicated mean effective pressure and other factors which affect the power output of an engine. Indicated horsepower is the power developed in the combustion chambers without reference to frictional losses of the engine. This horsepower is calculated as a function of the actual cylinder pressure recorded during engine operation.

1-3 AMP008 The crankcase of an aircraft engine

1-3 Answer C. is the foundation of the engine containing crankshaft bearings and cylinder pads. The cast or forged crankcase is the foundation of the aircraft engine. It contains the bearings which support the crankshaft. Cylinders are bolted to the crankcase and the crankcase provides the attach points for the engine to be secured to the airframe. As such it must be very strong to receive the many variations of mechanical loads and forces from these components while keeping the crankshaft stable. The crankcase does act as a reservoir for the engine oil,but with all of its other functions and relatively heavyweight construction, this is not the crankcase's primary function.

1-30 AMP008 Friction horsepower

1-30 Answer C. may be as high as 10-15% of the indicated horsepower on a modern aircraft engine. Friction horsepower is the indicated horsepower minus brake horsepower. It is the horsepower used by an engine in overcoming friction of moving parts, drawing in fuel, expelling exhaust, driving oil and fuel pumps, and other engine accessories. On modern engines, this power loss through friction may be as high as 10 to 15 percent of the indicated horsepower.

1-31 AMP056 The type of horsepower that determines the performance of the engine - propeller combination is

1-31 Answer B. B. thrust horsepower. Thrust horsepower can be considered the result of the engine and propeller working together. Efficiency of a propeller varies with engine speed, attitude, altitude, temperature, and airspeed. It is not 100 percent and must be applied to the brake horsepower figure to calculate horsepower.

1-32 AMP008 The thermal efficiency of an engine

1-32 Answer A. A. affects the fuel consumption of an engine. Each quantity of fuel contains a finite amount of heat energy which can be extracted by the engine for mechanical work. The ratio of useful work done by an engine to the heat energy of the fuel it uses, expressed in work or heat units, is called the thermal efficiency of the engine. High thermal efficiency results in an engine producing the greatest amount of power with minimal excess heat reaching the valves, cylinders, pistons and cooling system of the engine. It also means low specific fuel consumption, therefore less fuel for a flight of a given distance at a given power setting.

1-33 AMP056Which of the following will decrease volumetric efficiency in a reciprocating engine? 1. Full throttle operation. 2. Low cylinder head temperature. 3. Improper valve timing. 4. Sharp bends in the induction system. 5. High carburetor air temperatures.

1-33 Answer B. B. 3, 4, and 5 Volumetric efficiency is a ratio expressed in terms of percentages. It is a comparison of the volume of the fuel/air charge inducted into the cylinder to the total piston displacement of the engine. Since piston displacement is unaffected by external factors, volumetric efficiency is a measure of external factors that reduce the total volume of the fuel/air charge inducted into the engine. Some of these factors are: part throttle operation, long intake pipes of narrow diameter, sharp bends in the induction system, high carburetor air temperature, high cylinder head temperature, incomplete scavenging, and improper valve timing. Full throttle operation and low cylinder head temperatures would increase the volume of the induction charge.

1-34 AMP053 Propulsive efficiency

1-34 Answer C. is maximized through the use of a constant-speed prop. Propeller efficiency affects propulsive efficiency which is defined as the ratio of thrust horsepower to brake horsepower. A constant-speed propeller maximizes propeller efficiency by changing the propeller blade angle to the most efficient angle for the power produced by the engine. This increases thrust horsepower which, by definition, increases propulsive efficiency.

1-35 AMP068 Most modern airliners that fly in the .8 mach speed range are fitted with

1-35 Answer A. A. turbofan engines. Differently constructed turbine engines are suited for various aircraft and flying conditions. Most modern airliners use turbofan engines that have at the front of the engine a relatively large diameter fan section. This accounts for the name - turbofan. This type of engine is relatively quiet and has better fuel consumption at the average cruising speed of airline flight. Turboprop engines have greater efficiency at 300-400mph. Turboshaft engine are found on helicopters and auxiliary power units (APUs).

1-36 AMP068 Looking at the diagram below (Figure 1-43 in FAA-H-8083-32), if this engine had 100 pps of airflow through the fan and 20 pps airflow through the core engine, the Bypass Ratio would be

1-36 Answer A. A. 5:1. The bypass ratio of a turbine engine compares the amount of air flow (in pounds per second) from the fan bypass tothe amount of air passing through the core of the engine. In the figure, most of the air from the fan passes around the core of the engine making it a high bypass engine. A low bypass engine would send more air through the engine core. A turboprop engine channels all inlet air through the core to develop power to rotate the propeller.

1-37 AMP011 Accessories such as electric generators and hydraulic pumps on turbine powered aircraft are

1-37 Answer C. driven at reduced speed from the high pressure compressor via a reduction gear box. The accessory section of a gas turbine aircraft has various functions. One of these includes driving accessories concerned with the operation of the aircraft such as electrical generators and hydraulic pumps. The rotational speeds of a turbine engine and its shafts are much greater than the optimum speed for driving rotating accessories. Therefore, turbine engine accessory sections incorporate a series of gears to reduce the speed of the various drives provided for accessories. The gear train is driven by the engine's high pressure compressor through an accessory drive shaft gear coupling.

1-38 AMP068 The primary function of the compressor on a gas turbine engine is to

1-38 Answer B. B. supply air in sufficient quantity for combustion. The compressor section of a gas turbine engine has many functions. Its primary function is to supply air in sufficient quantities to satisfy the requirements of the combustion burners. Specifically, to fulfill its purpose, the compressor must increase the pressure of the mass of air received from the air inlet duct, and then discharge it to the burner section in the quantities and pressures required. Cooling the engine and supplying air for cabin environmental functions are secondary purposes of the compressor.

1-39 AMP068 What are the two functional elements of the centrifugal flow compressor?

1-39 Answer C. C. impeller and diffuser A gas turbine engine may use a centrifugal-flow compressor which consists of an impeller (rotor), a diffuser (stator) anda compressor manifold. Although the diffuser is a separate unit from the compressor manifold, it is bolted inside the manifold and the two-piece assembly is referred to as the diffuser (diffuser + manifold). Therefore, the two functional elements are the impeller and the diffuser.

1-4 AMP008 The cylinders of an aircraft engine are mounted on cylinder pads that are machined onto the crankcase. The common method of attachment of the cylinders to the crankcase is

1-4 Answer A. A. by studs mounted in threaded holes in the crankcase. Several studs are installed into the crankcase around the circumference of each machined cylinder pad.These are used to mount the cylinders securely to the crankcase with nuts. The inner portion of a cylinder pad may be chamfered or tapered to permit the installation of a large rubber O-ring around the cylinder skirt. This seals the joint between the cylinder and the crankcase pad against oil leakage.

1-40 AMP068 What is meant by a double entry centrifugal compressor?

1-40 Answer C. A compressor with vanes on both sides of the impeller. The impeller in an engine with a centrifugal compressor may be of two types - single entry or double entry. The principal differences between the two types of impellers are size and ducting arrangement. The double entry type has a smaller diameter and is usually operated at higher rotational speed to ensure sufficient airflow. Its impeller has vanes on both sides (i.e. front and back) but requires more complex ducting to have intake air reach both sides. The single entry impeller has simple, conventional inlet ducting but the impeller is of a larger diameter, which increases the overall dimensions of the engine.

1-41 AMP019 Stator blades in the compressor of an axial-flow turbine engine

1-41 Answer C. C. decrease air velocity and prevent swirling. In an axial-flow engine, air flows along an axial path and is compressed at a ratio of approximately 1.25:1 per stage.The action of the rotor increases compression of the air at each stage and accelerates it rearward through several stages. The stator blades act as diffusers at each stage; they partially convert the high velocity to an increase in pressure while ensuring the air is directed smoothly to the next stage without swirling.

1-42 AMP019 What is the function of the inlet guide vane assembly on an axial-flow compressor?

1-42 Answer A. A. Directs air onto the first stage rotor blades at the proper angle. The first stage rotor blades on an axial-flow compressor can be preceded by an inlet guide vane assembly that can be either fixed or variable. The guide vanes help direct the airflow into the first stage rotor blades at the proper angle and establish a swirling motion for the air entering the compressor. This pre-swirl, in the direction of engine rotation, improves the aerodynamic characteristics of the compressor by reducing drag on the first stage rotor blades. The inlet guide vanes are curved steel vanes usually welded to steel inner and outer shrouds.

1-43 AMP019 The non-rotating axial-flow compressor airfoils in an aircraft gas turbine engine, are called

1-43 Answer B. B. stator vanes. The stator has rows of vanes which are attached inside an enclosing case. The stator vanes, which are stationary, project radially toward the rotor axis and fit closely on either side of each stage of the rotor blades.

1-44 AMP019 The compression ratio of an axial flow compressor is a function of the

1-44 Answer A. A. number of compressor stages. In an axial flow compressor, each consecutive pair of rotor and stator blades constitutes a pressure stage. The number of rows of blades (stages) is determined by the amount of air and total pressure rise required. The compressor pressure ratio increases with the number of compression stages. Most large engines use 16 stages or more.

1-45 AMP068 What is referred to as blade profile of a turbine engine compressor blade?

1-45 Answer B. B. a cutout that reduces blade tip thickness Compressor blade tips are reduced in thickness by cutouts, referred to as blade profiles. These profiles prevent serious damage to the blades or housing should the blades contact the compressor housing. Profiling also allows tighter clearances between the blade tips and the compressor case and requires the case interior surface to be lined with a relatively soft material to allow the blades to rub the surface without blade damage.

1-46 AMP019 What is the primary advantage of an axial-flow compressor over a centrifugal flow compressor?

1-46 Answer C. C. greater pressure ratio In an axial flow engine, at each stage of compression, the air is compressed at a ratio of approximately 1.25 to 1. Each consecutive pair of rotor and stator blades constitutes a pressure stage. The compressor pressure ratio increases with the number of compression stages. Large engines utilize up to 16 stages of compression (or more), and at each stage compression is increased by a ratio of 1.25 to1 above the previous stage. This gives an axial flow engine the ability to have a much higher overall compression ratio than a centrifugal engine which typically has one stage of compression at approximately an 8 to 1 pressure increase.

1-47 AMP019 In the dual axial flow or twin spool compressor system, the first stage turbine drives the

1-47 Answer B. B. N2 compressor. A spool in a split spool or twin spool engine refers toa turbine section, the compressor it drives, and the interconnecting shaft between the two. Each spool is independent of the other. The first stage turbine wheel is located immediately downstream of the combustion section of the engine--it receives the most energy from the combusted gases and, therefore, drives the high pressure compressor which is known as the N2 compressor. The second stage turbine is behind or downstream of the first stage turbine--it receives less energy from the combusted gases since the gases have already passed through the first stage turbine. The second stage turbine drives the low pressure compressor, which is known as the N1 compressor.

1-48 AMP068 What is the purpose of the diffuser section in a turbine engine?

1-48 Answer A. A. to increase pressure and reduce velocity The diffuser is the divergent section of the engine after the compressor but before the combustion section. Its function is to increase air pressure at a slower velocity. This prepares the air for the combustion section of the engine where it is mixed with fuel and burned. A continuous burn is desired and the slower velocity air allows the flame to persist without being extinguished and prevents the combustion process from moving forward into the compressor.

1-49 AMP068 What turbine engine section provides for proper mixing of the fuel and air?

1-49 Answer A. A. combustion section The primary function of the combustion section of a gas turbine engine is to burn the fuel/air mixture, thereby adding heat energy to the air. To do this efficiently, the combustion chamber must provide the means for proper mixing of the fuel and air to ensure good combustion.

1-5 AMP008 The crankpin is

1-5 Answer C. C. hardened by nitriding and is hollow to reduce weight. Crankpins are the machined journals on the crankshaft to which the piston connecting rods are attached. They are off center from the main journal. The two crank cheeks and the crankpin together make a "throw". When the force of combustion is applied to the crankpin, it causes the crankshaft to rotate. Crankpins are hardened by nitriding to resist wear and are hollow to keep the total weight of the crankshaft as light as possible. The hollow crankpin also permits the passage of oil as it turns in the crankcase.

1-50 AMP068 The air passing through the combustion chamber of a turbine engine is

1-50 Answer A. A. used to support combustion and to cool the engine. The air entering the combustion chamber is divided into two main streams - the primary and the secondary. The primary or combustion air is directed inside the liner at the front end, where it mixes with the fuel and is burned. Secondary or cooling air passes between the outer casing and the liner and joins the combustion air gases through larger holes toward the rear of the liner, cooling the combustion gases from about 3500 ̊F to below what the turbine section can withstand (near 1500 ̊F on earlier engines).

1-51 AMP068 The highest heat to metal contacts in a jet engine are the

1-51 Answer B. B. turbine inlet nozzle vanes. The turbine inlet nozzle vanes are located directly aft of the combustion chamber and immediately forward of the turbine wheel. This is the highest or hottest temperature that comes in contact with metal components in the engine. The turbine inlet temperature must be controlled or damage will occur to the turbine inlet nozzle vanes.

1-52 AMP068 Turbine inlet nozzle assembly located on the upstream side of each turbine wheel are used in the gas turbine engine to

1-52 Answer C. increase the velocity of the gases flowing past this point. After the combustion chamber has introduced the heat energy into the mass airflow and delivered it evenly to the turbine inlet nozzles, the nozzles must prepare the mass air flow to drive the turbine rotor. The stationary vanes of the turbine inlet nozzles are contoured and set at such an angle that they form a number of small nozzles discharging gas at extremely high speed; thus, the nozzles convert a varying portion of heat and pressure energy into velocity energy that can then be converted into mechanical energy through the rotation of the turbine blades. The second purpose of the turbine inlet nozzle is to direct the gases in the direction of turbine wheel rotation. This would be closer to perpendicular to the vertical line of the turbine blades than parallel to them.

1-53 AMP068 Reduced blade vibration and improved airflow characteristics in a gas turbine engine are brought about by

1-53 Answer C. C. shrouded turbine rotor blades. 'Most turbines are open at the outer perimeter of the blades. However, a second type, called the shrouded turbine, is sometimes used. The shrouded turbine blades effectively form a band around the outer perimeter of the turbine wheel. This improves efficiency by keeping the air from spilling over the blade tips and reduces vibration by holding the blade tips in place. Lighter turbine stage weights are possible with shrouded turbine rotor blades, but turbine speeds are somewhat limited by their use and more blades are required.

1-54 AMP068 The function of the exhaust cone assembly of a turbine engine is to

1-54 Answer C. The exhaust cone collects the exhaust gases discharged from the turbine section and gradually converts them into a solid flow of gases. In performing this, the velocity of the gases is decreased slightly and the pressure is increased.

1-55 AMP068 The oil dampened also known as hydraulic main bearing utilized in some turbine engines is used to

1-55 Answer B. B. provide an oil film between the outer race and the bearing housing in order to reduce vibration tendencies in the rotor system, and to allow for slight misalignment. The gas turbine rotors are supported by ball and roller bearings, which are antifriction bearings. Many newer engines use hydraulic bearings, in which the outside raceis surrounded by a thin film of oil. This reduces vibrations transmitted to the engine and allows for slight misalignment.

1-56 AMP068 Main bearing oil seals used in turbine engines are usually what type?

1-56 Answer A. A. labyrinth and/or carbon rubbing The oil seals for turbine engines are generally labyrinth or carbon rubbing-type seals. Labyrinth type seals are pressurized to minimize oil leakage along the compressor shaft. Carbon seals are usually spring loaded and are similar in material and application to the carbon brushes found in electric motors.

1-57 AMP068 The energy to turn the propeller on a turboprop engine is typically produced by

1-57 Answer B. B. additional turbine stages Turboprops are, fundamentally, gas turbine engines that have a compressor, combustion section, turbine, and exhaust nozzle (gas generator), all of which operate in the same manner as any other gas engine turbine engine. However, the difference is that the turbine in the turboprop engine usually has extra stages to extract energy to drive the propeller.

1-58 AMP068A turboshaft engine can be defined as

1-58 Answer A. a gas turbine engine that delivers power through a shaft to operate something other than a propeller. A gas turbine engine that delivers power through a shaft to operate something other than a propeller is referred to as a turboshaft engine. The output shaft may be coupled directly to the engine turbine, or the shaft may be driven by a turbine of its own (free turbine). The turboshaft engine's output is measured in horsepower instead of thrust because the power output is turning a shaft.

1-59 AMP068 Turbofan engines

1-59 Answer B. B. have either a mixed or separate exhaust nozzle. In a turbofan engine, the large, axial flow fan in front of the engine is driven by extra turbine stages similar to a turboprop engine. The fan air can be exhausted through its own nozzle or it can be mixed in a common nozzle with the core engine's exhaust. The large area of the common exhaust nozzle results in the fan producing around ~80% of the total thrust on some engines. Turbofan engines are the most widely used gas turbine engines on transport category aircraft.

1-6 AMP054 Which statement is correct about radial engine crankshafts?

1-6 Answer B. B. Moveable counterweights serve to reduce the dynamic vibrations in an aircraft reciprocating engine. Vibration occurs as the crankshaft rotates due to the forces of combustion acting on the pistons, connecting rods, and crankpins. These power impulses cause even a statically balanced crankshaft to vibrate. Moveable counterweights are dynamic dampeners are located in the counterweight lobes of the crankshaft. Using pendulum motion, the dampeners oscillate out of time with the crankshaft vibration thus reducing overall vibration.

1-60 AMP020 Newton`s Third Law of Motion states that

1-60 Answer B. B. for every action there is an equal and opposite reaction. The principle used by a gas turbine engine as it provides force to move an airplane is based on Newton's law of reaction. The law states that for every action, there isan equal and opposite reaction. Therefore, if the engine accelerates a mass of air (action) it applies a force on the aircraft (reaction) which moves the aircraft in the direction opposite to the accelerated mass of air.

1-61 AMP068 The Brayton cycle is known as the

1-61 Answer A. A. constant pressure cycle. The Brayton cycle is the name given to the thermodynamic cycle of a gas turbine engine to produce thrust. This is a variable-volume, constant- pressure cycle of events and is commonly called the constant pressure cycle. A more recent term is continuous combustion cycle. The four continuous and constant events are: intake, compression, expansion (which includes power) and exhaust.

1-62 AMP068 The most important factors affecting thermal efficiency in a turbine engine are

1-62 Answer C. turbine inlet temperature, compression ratio, and the component efficiencies of the compressor and turbine. Thermal efficiency is a prime factor in gas turbine performance; it's the ratio of net work produced by the engine to the chemical energy supplied in the form of fuel. The three most important factors affecting the thermal efficiency are turbine inlet temperature, compression ratio, and the component efficiencies of the compressor and turbine. Other factors that affect thermal efficiency are compressor inlet temperature and combustion efficiency.

1-63 AMP068 An engine's thrust output temporarily decreases as aircraft speed increases from static. This is overcome at higher speeds by

1-63 Answer B. B. ram air effect A rise in pressure above ambient pressure at the engine inlet as a result of forward velocity of an aircraft is referred toas ram pressure. Since any ram effect causes an increasein compressor entrance pressure over atmospheric, the resulting pressure rise causes an increase in the mass airflow and gas velocity, both of which tend to increase thrust.An engine's thrust output temporarily deceases as aircraft speed increases from static, but soon ceases to decrease. Moving toward higher speeds, thrust output increases again due to the increases pressure of ram recovery.

1-64 AMP061 Which of the following is true in reference to a split spool turbofan? 1. The rotors are independent with no physical connection. 2. Many dual rotor systems have rotors turning in opposite directions. 3. Most large turbofan engines use a large fan with a few stages of compression called the low-pressure spool.

1-64 Answer C. C. 1, 2 and 3 Most turbofan engines are of the split-spool compressor type. Most large turbofan engines use a large fan with a few stages of compression called the low-pressure spool. These turbofans incorporate two compressors with their respective turbines and interconnecting shafts, which form two physically independent rotor systems. Many dual rotor systems have rotors turning in opposite directions and with no mechanical connection to each other.

1-7 AMP054 Master rod bearings are generally what type of bearing?

1-7 Answer A. A. plain The master rod bearings refer to the bearing located on the crankpin end and the piston end of the master connecting rod commonly found in radial engines. Whether of solid or split design, plain bearings are used to mate with the crankpin journal of the crankshaft. The piston pin end of the master rod uses a plain bearing usually called a bushing to mate with the piston pin.

1-8 AMP049 Cam ground pistons are installed in some aircraft engines to

1-8 Answer A. provide a better fit at operating temperatures. Modern engines use cam ground pistons that have a larger diameter perpendicular to the piston pin. This larger diameter keeps the piston straight in the cylinder as the engine warms up from initial start. As the piston heats up during warm up, the part of the piston in line with the piston pin has more mass. It expands more than the piston area perpendicular to the piston pin making the piston completely round at operating temperature.

1-9 AMP049 Full-floating piston pins are those which allow motion between the pin and

1-9 Answer C. C. the piston and the small end of the connecting rod. The piston pins used in modern aircraft engines are the full- floating type, so called because the pin is free to rotate in both the piston and in the connecting rod piston pin bearing which is the small end of the connecting rod. As such, full floating piston pins must be held in place to prevent the pin ends from scoring the cylinder walls. This is accomplished with soft aluminum plugs on each end of the piston pin.

1-1 AMP008 The general requirements for an aircraft engine include efficiency, reliability, and a low weight-to-horsepower ratio. It also must

B. have good fuel economy, high durability, and be capable of sustained high power output.

1-10 AMP049 How is oil collected by the piston oil ring returned to the crankcase?

1-10 Answer B. B. through holes drilled in the piston oil ring groove Oil control rings are located just below the compression rings but above the piston pin on the typical aircraft piston. They regulate the thickness of the oil film on the cylinder wall. This keeps excessive oil from entering the combustion chamber past the compression rings. To allow the surplus oil to return to the crankcase, holes are drilled in the bottom of the oil control piston ring grooves or in the lands next to these grooves.

1-11 AMP050 Some cylinder barrels are hardened by

1-11 Answer A. A. nitriding. A cylinder barrel in an aircraft engine is made from a steel alloy forging with the inner surface, hardened to resist wear caused by the piston and piston rings which bear against it. The hardening is usually done by exposing the steel to ammonia or cyanide gas while the steel is very hot. The steel soaks up the nitrogen from the gas, forming iron nitride on the exposed surface of the barrel. Thus, the steel is said to be nitrided. This nitriding only penetrates into the cylinder barrel surface a few thousandths of an inch.

1-12 AMP056 The primary concern in establishing the firing order for an opposed engine is to

1-12 Answer A . A. provide for balance and eliminate vibration to the greatest extent possible. The firing order of an engine is the sequence in which the power event occurs in the different cylinders. The firing order is designed to provide balance and to eliminate vibration to the greatest extent possible.

1-13 AMP056 What is an advantage of using metallic sodium filled exhaust valves in aircraft reciprocating engines?

1-13 Answer B. reduced valve operating temperature Some intake and exhaust valves are hollow and partially filled with metallic sodium. This material is used because it is an excellent heat conductor. The sodium melts at 208 ̊F. The reciprocating motion of the valve circulates the liquid sodium, allowing it to carry heat away from the valve head and into the stem, where the heat is dissipated through the valve guide to the cylinder head and the cooling fins. Operating temperature of a sodium filled valve may be reduced as much as 300 ̊F to 400 ̊F.

1-14 AMP056What is the purpose of the stem keys installed on the valve stems?

1-14 Answer B. to hold the valve spring retaining washer in position The valve stem acts as a pilot for the valve head and rides the valve guide installed in the cylinder head. The stem is surface-hardened to resist wear. A machined groove near the tip of the valve stem opposite the valve head receives the split-ring stem keys. These stem keys form a lock ring to hold the valve spring retaining washer in place.

1-15 AMP056 The purpose of two or more valve springs in aircraft engines is to

1-15 Answer B. eliminate valve spring surge. Valve springs which slip over the stem of the valves are held in place by the valve spring retaining washer and stem key. The springs hold the valves closed when not forced open via the valve operating mechanism. Any single spring will surge at certain engine speeds, allowing a less that tight seating of the closed valve. By using two or more valve springs on each valve stem, while one spring may be surging at a certain engine RPM, the other(s) will not, due to variation in mass and construction. Thus oscillations are dampened with the added protection of one or more extra springs should one of the springs break.

1-16 AMP056 The tappet assembly

1-16 Answer B. converts rotational movement of the cam lob into reciprocating motion. The tappet assembly is located in the crankcase and typically contains a cylindrical tappet, a tappet guide, and with some newer engines a tappet roller or face that follows the contour of the cam lobes and a tappet spring. The function of the tappet assembly is to convert the rotational movement of the cam lobe into reciprocating motion and to transmit this motion to the push rod, rocker arm, and then to the valve tip, thus opening the valve at the proper time.

1-17 AMP056Excessive valve clearance in a piston engine

1-17 Answer C. C. decreases valve overlap. Reciprocating aircraft engines that use solid lifters or tappets generally require that the clearance between the rocker arm and the valve tip is adjusted to ensure that the valve canfully close. If the clearance is too great, the valve operating mechanism must span this distance which causes the valve timing to be late. The valve will open late and close early. Valve overlap refers to the time period when both the intake and exhaust valve are open. Late opening and early closing of the valves reduces valve overlap.

1-18 AMP057 Valve clearance changes on opposed-type engines using hydraulic lifters are accomplished by

1-18 Answer C. C. replacing the push rod. Hydraulic lifters are normally adjusted at the time of overhaul. They are assembled dry (no lubrication), clearances checked, and adjustments made by using pushrods of different lengths. A minimum and maximum valve clearance is established in this dry condition. Any measurement between these extremes is acceptable, but a pushrod that creates a clearance halfway between the minimum and maximum extremes is desired. Once assembled with the engine running, the hydraulic lifters are filled with oil; this removes the clearance and provides a quiet, lubricated, low maintenance valve operating mechanism.

1-19 AMP054 Which of the following is a characteristic of a thrust bearing used in most radial engines?

1-19 Answer C. C. deep-grooved ball Special deep-grooved ball bearings are used to transmit propeller thrust and radial loads to the engine nose section of radial engines. This type of bearing can accept both radial and thrust loads with minimal friction.

1-2 AMP056 The heat engine used predominantly in aviation is the

1-2 Answer B. B. O-type engine. There are many methods of aircraft engine classification, and classification of engines by cylinder arrangement is common. The "O"-type or Opposed engine has cylinders arrange-don opposite sides of the crankshaft, 180 ̊ opposed to each other. This compact shaped, low vibration engine is found on most light aircraft.

1-20 AMP053What is the primary advantage of using propeller reduction gears?

1-20 Answer B. to enable the engine RPM to be increased with an accompanying increase in power and allow the propeller shaft to remain at a lower RPM Increased brake horsepower of an engine results partially from increased crankshaft RPM. However, increasing crankshaft RPM without regard to propeller speed can cause propeller inefficiency--as propeller tip speed approaches the speed of sound, the prop becomes less efficient. Reduction gearing allows the engine RPM to be increased to extract maximum power while rotating the propeller at a slower speed than the crankshaft.

1-21 AMP053 Which type of propeller shaft is used on most modern reciprocating and turboprop engines

1-21 Answer C. C. flanged Fro A the propeller shaft of most low power output engines is forged as part of the engine crankshaft-- the propeller shaft is a tapered shaft with a milled slot for keying the prop hub to the shaft and the end of the shaft is threaded to accept a nut that secures the prop to the shaft. For B, high output radial engine propeller shafts are generally splined to receive the prop hub, and they also have a threadedend to accept a retaining nut. The answer is C: flanged propeller shafts are used on most modern reciprocating and turboprop engines. One end of the shaft is flanged with drilled holes to accept propeller mounting bolts.

1-22 AMP056 The five events of a four stroke cycle engine, in the order of their occurrence, are

1-22 Answer C. C. intake, compression, ignition, power, exhaust. The four-strokes plus the ignition event are the five events of a four-stroke cycle engine. In order of occurrence, the 5 events are: The Intake Stroke, The Compression Stroke, Ignition,The Power Stroke and The Exhaust Stroke. During the intake stroke, the crankshaft rotates and the piston moves down away from the top of the cylinder. As it does, it draws in a gaseous fuel/air charge through an open intake valve. As the piston nears the bottom of the cylinder, the intake valve closes and the piston reverses direction to begin the compression stroke. The fuel/air charge, trapped between the piston and the cylinder walls, compresses as the piston moves upward toward the cylinder head. Just before top center of the stroke, the spark plug fires which lights off the compressed charge. The energy released by the burning of the fuel air mixture forces the piston down toward the bottom of the cylinder during the power stroke--the heat energy is thus transferred to the crankshaft. The exhaust valve opens and the burnt gases are forced out of the cylinder as the piston returns to the top of the cylinder during the exhaust stroke.

1-23 AMP056On which stroke are both valves on a four-stroke cycle reciprocating engine open?

1-23 Answer C. C. intake and exhaust The valve timing chart in Figure 1-37 of FAA-H-8083- 32 illustrates when the valves open during the four stroke of the engine and upon what strokes both valves are open at the same time, which is known as valve overlap. On a typical reciprocating engine, the intake valve opens just beforethe piston reaches TDC (Top Dead Center) on the exhaust stroke. The exhaust valve opens just before the exhaust stroke begins and stays open until a little after the exhaust stroke is complete. This means the exhaust valve is open as the intake stroke begins, so both valves are open during a part of the exhaust stroke and a part of the intake stroke.

1-24 AMP056 If fuel/air ratio is proper and ignition timing is correct, the combustion process should be completed

1-24 Answer C. just after top center at the beginning of the power stroke. The time of ignition varies from 20 ̊ to 30 ̊ before TDC (depending upon the requirements of the specific engine) to ensure complete combustion of the charge by the time the piston is slightly past the TDC position.

1-25 AMP056The actual power delivered to the propeller of an aircraft engine is called

1-25 Answer B. B. brake horsepower. Indicated horsepower is the term used to describe the theoretical output of an engine. The total horsepower lost in overcoming friction (friction horsepower) must be subtracted from the indicated horsepower to arrive at the actual horsepower delivered to the propeller by the engine. This is known as brake horsepower.

1-26 AMP056 The compression ratio of an engine is equal to

1-26 Answer C. C. the volume of the cylinder with the piston at BDC divided by the volume of the cylinder at TDC. All internal combustion engines must compress the fuel/air mixture to receive a reasonable amount of work from each power stroke. The fuel/air charge in the cylinder can be compared to a coil spring. The more it is compressed, the more work it is potentially capable of doing. A comparison of the volume of the cylinder at bottom dead center (BDC) and at top dead center (TDC) of a stroke describes the amount of compression developed. Compression ratio is a controlling factor in the maximum horsepower developed by an engine.

1-27 AMP056The volume of a cylinder equals 70 cubic inches when the piston is at bottom center. When the piston is at the top of the cylinder, the volume equals 10 cubic inches. What is the compression ratio?

1-27 Answer C. C. 7:1 By definition, compression ratio is expressed as a ratio. The first number in the ratio is the total volume of the cylinder with the piston at BDC - the larger number. The second number is the total volume of the cylinder with the pistonat TDC - the smaller number. The small number is divided into the larger number to reduce the ratio into the smallest integers possible.