WWII PISTON AIRCRAFT ENGINE TYPES, MECHANISM & OILING SYSTEMS TRAINING FILM 59294

of all the means for transforming heat energy into mechanical power the internal combustion engine is the only type at present available suitable for aircraft this engine burns a fuel air mixture directly behind the piston all aircraft engines at present operate on a four-stroke performance cycle consisting of intake of the charge compression combustion and expansion of gases exhaust intake compression expansion exhaust at the beginning of the intake stroke the intake valve opens and remains open the piston moves toward the crank drawing in the charge of combustible mixture through the open intake valve which does not closed completely until after the end of this stroke during the second or compression stroke the piston moves toward the cylinder head compressing the charge near the end of this stroke the spark ignites the charge both valves remain closed and the power stroke follows the hot expanding gases of combustion exert a high pressure on the piston delivering the only power generated during the cycle the exhaust valve now opens and the fourth stroke expels the burnt gases the cycle then repeats beginning with admission of the next charge aircraft engines are classified as air-cooled in which fins are provided to increase cooling by convection and liquid cooled in which cylinders and belt ports are surrounded by a jacket which contains the cooling liquid various cylinder arrangements have been used this in-line engine is an obsolete model the inline type is still in use this is an obsolete model of double in-line in this modern form of the opposed type the two rows of cylinders are on opposite sides of the crankshaft its reduced height makes it specially adaptable for wing installation it has high power per unit weight aw type similar arrangement in an obsolete model an obsolete model of the X type a rotary engine an obsolete model of a V type of engine this is a modern liquid-cooled B type this engine has the cylinders arranged on the crankcase in two rows or banks forming a V with an angle of 60 degrees between them with cylinder blocks removed from the crankcase we see that in each Bank the cylinders are placed opposite each other this permits two connecting rods to operate on the same crank pin thereby reducing the weight for horsepower as compared to the vertical type with very little increase in the head resistance of the aircraft one efficient form of connecting rod designed to operate in pairs and the same crank pin consists of the fork rod is shown on the right and the blade rod on the left the fork ride carries a bronze sleeve or shell which rides on the crank pin the blade rod bearing rides on the bronze sleeve of the fork rod the single row radial engine is extensively used in modern military aircraft in this type the cylinders are evenly arranged around the crankcase in the same plane it utilizes three to nine cylinders in odd numbers all connecting rods are attached to a single crank pin resulting in very low weight for horsepower present types of double-row radial engines have a total of 14 to 18 cylinders arranged in two rows each row being distributed evenly around the crankshaft the i' head or valve in head cylinder is universally used in aircraft engines its construction facilitates the passage of gas into and out of the cylinders and reduces to a minimum losses due to cooling it has the disadvantage of requiring a complicated system of cams tappets push rod then rocker arms to effect the valve motion this is simplified on some engines by locating the camshaft above the cylinder instead of in the base poppet valves are the conventional means for controlling intake of the fresh charge and exhaust of the burnt gases they are superior to sliding valves in lightness simplicity and speed of operation valve guide stem seat and face are the important parts exhaust valves are subjected to temperatures as high as 1600 degrees they are therefore constructed of heat resisting material with hollow stems chemically cooled Inlet valves are cooled by the incoming charge and present no cooling problem multiple poppet valves are used on some engines to increase the area of opening and prevent the distortion of large valve heads by the extreme temperatures adjustment of valve timing depends on engine speed adjustment for maximum power must be such as to admit the maximum charge and expel the maximum amount of exhaust gas by leaving the intake valve open until bottom dead center is past the high velocity in the intake manifold is used to force more charge into the cylinder at a certain optimum speed the charge admitted will be maximum at low speeds with the intake valve remaining slightly open until after dead center is passed the piston will push some of the charge out of the cylinder before the valve closes resulting in poor idling the exhaust valve always opens before bottom dead center in order to secure most defective scavenging of burn gas as well as better cylinder cooling the higher the speed the earlier the opening for similar reasons the intake valve opens before top dead center and the exhaust valve closes after top dead center valve springs are used to close the valves and are duplicated on each valves to increase safety factor reduce side play and obtain increased spring tension in small space common practice provides two Springs of small pitch diameter one inside the other valve lift is effected by means of a cam which activates a system of linkages including cam followers tappets push rods and rocker arms in a V type aircraft engine the cams are mounted on the camshaft and the camshaft is located on a cylinder head in a radial type aircraft engine the cams are mounted on the cam drum each cam drum has two rings of cams one for intake valves and one for exhaust valves a cam drum is required for each row of cylinders in a two row radial engine cam drums taffet's and push rods are here indicated to permit expansion of Pistons with temperature modern Pistons are tapered and has the greatest clearance at the head and the least at the skirt to prevent loss of compression and leakage of gas through this clearance the piston is provided with grooves into which split elastic piston rings are sprung these rings provide an elastic fit they expand and fit the cylinder at all points notwithstanding slight variations in bores these upper rings are compression rings this is an oil control ring whose function is to prevent pumping oil into the combustion chamber its groove is drilled at several points to allow surplus oil to be drained into the crankcase the oil control ring is assisted by this additional ring in the piston skirt in preventing excessive oil consumption the piston pin or wrist pin is mounted in these wrist pin bosses it transmits the full thrust of the piston to the connecting rod owing to the high stresses to which it is subjected it is constructed of a tough steel case hardened this hard pin must be kept from contact with the cylinder walls to prevent wearing grooves in them the connecting rod is the member that transmits the force from the wrist pin to the crankshaft in radial engines connecting rods are of two types main or master rod and articulated or linked rod the crankshaft received the power developed on the piston through the connecting rod and delivers it to the propeller in rotary motion the crank case forms the foundation upon which the entire engine and the accessories are assembled crank cases are made up of a number of parts or sections usually five in a radial engine bolted together into one unit as a general rule each section is constructed of a light aluminum alloy forged or diecast for strength this nose section has seen from the other side in a sectionalized view carries the reduction gear in the geared engine the propeller shaft or crankshaft thrust bearing and the drilled oil passages for lubrication of the various parts and for operation of the propeller control valve which controls the pitch of the propeller blades it also contains the kam drum and Cam's the can followers and their guide behind the no section in this single row radial engine is the power or main section it is made of two symmetrical parts joined in the plane of the centerline of the cylinder by long through both the power section carries the crankshaft bearings and connecting rod assemblies the cylinders are bolted to this section in this pratt & whitney engine the accessory drive gears are housed in a section immediately behind the power section this section also carries the intake pipes and the passages leading from the blower to the intake ports the supercharger impeller is mounted on the rear wall of the same section it forces the charge through the tangential passages into the intake pipes the lower ends of which are fastened in the intake ports with rubber rings and locking nuts so as to permit movement of the pipes with contraction and expansion of the cylinder the upper ends of the intake pipes are curved to reduce the friction of the entering fuel charge in this right engine the mounting section located immediately behind the main section carries the mounting lugs which provide for the attachment of the engine to the mounting ring of the aircraft this section carries the tangential intake pipes leading to the cylinders and forms the front wall of the supercharger or blower chamber the supercharger provides the air pressure necessary for intake of adequate charge at high altitudes it receives the charge from the carburetor and delivers it under increased pressure through the intake pipe to the cylinders the blower section in this engine also houses the accessory drive gears again viewing the other side of this same right engine we see from left to right the mounting section with is tangential intake pipes the supercharger or blower section and the accessory section which forms the rear crankcase cover to which are attached the Magneto's starter generator and most of the other accessories in a hasty review of the arrangement of the major elements of a twin row radial engine we see first the nose section including valve operating mechanism and ignition cables for the first row of cylinders inside the nose section is the 3 to 2 reduction gear the 6 pinions of which are visible here removing the nose section we see the front crankcase bearing support governor and cam Drive we now see the front row of cylinders with push rods remove the cam drum drive cam followers and belt Abbott's the power section Pistons connecting rods and crankshaft with balancing counterweight a rear view of the front power section showing intake and exhaust ports the Pistons connecting rods and crankshaft of the rear power section the rear crankcase with valve lift mechanism and cam drum drive for the rear row of cylinders the blower section from the rear showing supercharger impeller and intake pipes for both rows of cylinders by means of which the charge is carried to the cylinders from the diffuser section the diffuser section seen from the front the spiral passages receive the charge from the impeller and distribute it to the intake pipes accessory and supercharger drive gears a rear view of the accessory section showing carburetor mounting and drives for starter generator Magneto's and other accessories the lubricating system in aircraft engines is designed to function under difficult conditions such as high operating temperatures high bearing stresses and operation in all possible flight attitudes of the aircraft in the pressure dry sump type of lubrication system a pressure pump forces the oil through the pipes and passages leading to the parts to be lubricated oil is removed from the crankcase by one or more scavenging pumps which draw the oil from one or more sump located at low points in the crankcase this is the scavenging pump in a single row radial engine and this is the pressure pump the internal portion of the oiling system built into the engine usually includes the following features a strainer located on the discharge side of the pressure pump which removes sediment or foreign matter before it reaches the bearing surfaces a pressure relief valve designed to open at a fixed oil pressure and shunt the surplus into the scavenging system or back to the intake side of the pressure pump a pressure gauge connection provides for a line to the oil pressure indicator screens are provided in the oil sump to collect sediment and fallen particles and prevent further circulation through the system oil return lines or passages connect the sump chambers to the intake side of the scavenging pump which returns the oil to the supply tank for recirculation to the pressure part of the system in this simplified diagram of the internal oiling system in an air-cooled radial engine oil leads the discharge side of the pressure pump passing a pressure release valve which in this type shunt surplus oil back into the scavenging system the rest of the oil continues through the strainer to the passages drilled in front and rear crankshaft journals oil is forced into these passages and is fed to cranked in master connecting rod bearings and the short rod knuckle pins one or more lines or passages branch from the rear crankshaft journal and lead the oil to various rear section drive shaft bearings such as this one the line branching up from the front crankshaft journal leads the oil under pressure to evolve which controls the oil feed to a variable pitch propeller in one type of installation engine oil pressure is stepped up in a booster pump from which it is fed through a control valve to a cylinder and there actuates a piston which in turn by cam arrangement rotates a bevel gear and changes the propeller pitch the oil which is forced out at these various points in the pressure system lubricates by splash and spray such parts as pistons rings cylinder walls valve accessory and accessory drive gears before draining into the scavenging system of sums from which it is removed by the scavenging pump this crankcase breather is installed at some point on the upper part of the crankcase to relieve the internal pressure resulting from high temperatures the internal baffles from it reduction of pressure without loss of oil in some breathers a gravity operated valve remains open in normal attitudes of the engine and closes when the engine is inverted to prevent loss of oil in the V type liquid cooled engine the pressure pump forces oil through or past the air pressure relief valve which shunts the surplus oil to the intake side of the pressure pump it then flows through the screen or strainer and is distributed to each of the crankshaft journals from the rear crankshaft journal oil is forced to the hollow camshaft and furnishes lubrication to the overhead valve mechanism from the front crankshaft journal the pressure line leads to the oil control valve which operates the controllable pitch propeller centrifugal force assists in forcing oil from the crankshaft journal to the crank pins and connecting rod bearings oil escapes from the pressure system at all these various points and after lubricating by splash Pistons rings cylinder walls valves taffet's and accessory drive gears drains into scavenging system stumps to scavenging pumps are utilized in this particular engine one of which drains the front engine some through a screen and the other drains the oil from the rear sump forcing it back into the external tank the breeder serves the same function as in the air-cooled radial engine the external oiling system comprises a storage tank necessary piping and connections the thermometer well the oil cooler thermometer and pressure gauge assuming the supply tank has been serviced to the proper level oil flows by gravity through large tubing to the inlet side of the oil pressure pump which forces the oil under pressure through the internal system oil discharged by the scavenging pump in the engine is returned to the top of the supply tank as a rule to vent lines connect the crankcase to the top and bottom of the supply tank so that at least one vent is open in all flight attitude the oil pressure gauge in the cockpit is connected to the pressure line in the engine the thermometer well is located at a tangent in the oil piping system between the outlet of the oil tank and the oil pressure engine pump the temperature of the oil entering the engine is therefore indicated by the reading of the meter in the cockpit this temperature must be kept within certain limits in order to maintain the proper viscosity or thickness oil of proper viscosity flows readily and adheres to the surface forming a protective film if the viscosity is too high it will not flow properly if it is too low it will not maintain the protective film for example if the oil in the wrist spin bearing on the right is of too low viscosity the proper oil film is not maintained and the pin rides lower in the bearing with greater resulting friction while the oil in the left bearing being of proper viscosity maintains the film and oil temperature regulator or cooler is provided between the engine oil outlet and the inlet to the oil supply tank the functioning of this cooler is controlled by a thermostatic valve which automatically controls the passage of oil through the cooler when the oil is sufficiently cool the valve opens and permits the oil to flow through an unobstructed passage which answer'd away from the cooling tube when the oil becomes hotter than normal the thermostatic valve closes and forces the oil to pass through a core in which it is in contact with air tubes for cooling purposes for cold weather starting a decrease of viscosity of oil is needed this is accomplished by adding gasoline from the fuel pressure line temporarily diluting the oil supplied to the engine the oil to be diluted for starting is segregated from the oil supply is the main oil tank by means of a relatively small hopper so located within the tank that the oil circulating through the engine is most readily drawn from the hopper and is returned from the engine to the hopper oil from the main supply is however always available and is drawn into the oil stream circulating through the hopper when the hopper oil level is lower the illusion of the oil is accomplished through this connection line leading from the fuel pressure line to the oil line entering the engine a metering unit in this connection line and a shutoff valve operated from the cockpit control the addition of engine fuel to the circulating oil thereby regulating the dilution the system is placed in operation when a start at low temperature is anticipated by holding this valve open for three or four minutes before the engine is shut down this fills the hopper with a diluted oil when this is done the engine can be turned over in sub-zero weather as freely as in summer in view of the small volume of the hopper approximately one to one and one half gallons and the high rate of flow air entrained in the oil during scavenging from the crank case might be carried on through the hopper and back into the engine resulting in faulty lubrication this is presented by tangential entry of the oil into the hopper then physical action forces the oil against this surface squeezing the air out of the oil stream and allowing it to escape this must be done without introducing turbulence which might interfere with the centripetal separation of the entrained air the eluted oil is provided only during starting as the engine warms up it consumes the oil from the hopper and heat distilled off the gasoline fresh undiluted oil from the main tank then flows in through this package fifteen to thirty minutes of operation will eliminate all the effects of dilution and return lubrication to normal most of the delusion is eliminated in the first five or ten minutes

Channel: PeriscopeFilm

Views: 596,378

Keywords: Periscope Film, Stock Footage, 4K, HD, 2K

Id: 4vBPlcquAD8

Length: 35min 19sec (2119 seconds)

Published: Mon Dec 09 2019