Airframe df Powerplant
MECHANICS
POWERPLANT HANDBOOK US. DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION 4
AIRFRAME AND POWERPLANT
MECHANICS
POWERPLANT HANDBOOK
DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION Flight Standards Service First Edition 1971 First Revision 1976 For sale by the Superintendent of Documents. U.S.Government Printing O5ce Washington. D.C. 20402
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PREFACE This advisory circular is printed for persons preparing for a mechanics certificate with a powerplant rating. It is intended to provide basic information on principles, fundamentals, and technical procedures in the areas relating to the powerplant rating. This is designed to serve as a guide for students enrolled in a formal course of instruction, as well as the individual who is studying on his own.
This volume is devoted to an explanation of the units which make up each of the systems that bring fuel, air, and ignition together in an aircraft engine for combustion. It also contains information on engine construction features, lubrication systems, exhaust systems, cooling systems, cylinder removal and replacement, compression checks, and valve adjustments.
Because there are so many different types of aircraft engines in use today, it is reasonable to expect minor differences to exist in like system components. To avoid undue repetition, the practice of using representative systems and units is carried out throughout the advisory circular. Subject-matter treatment throughout the text is from a generalized point of view and its use can be supplemented by reference to manufacturer's manuals and other textbooks if more detail is desired. This advisory circular is not intended to replace, substitute for, or supersede official regulations or manufacturer's instructions which should be consulted for final authority.
Grateful acknowledgement is extendei to the manufacturers of engine, propellers, and powerplant accessories for their cooperation in making material available for inclusion in this handbook.
This handbook contains material for which a copyright has been issued. Copyright material is used by special permission of United Aircraft Corporation, Pratt and Whitney Aircraft Division, and may not be extracted or reproduced without permission 'of the copyright owner.
The advancements in aerdnautical technology dictate that this advisory circular be brought up-to-date periodically. It has been updated, errors have been corrected, new material has been added, and some material has been rearranged to improve the usefulness of the handbook. We would appreciate, however, having errors brought to our attention, as well as suggestions for improving its usefulness. Your comments and suggestions will be retained in our files until such time as the next revision is completed.
A,ddress all correspondence relating to this handbook to:
Department of Transportation Federal Aviation Administration Flight Standards National Field Office P.O. Box 25082 Oklahoma City, Oklahoma 73125 The companion advisory circulars to AC 65-12A are the Airframc and Fowerplant Mechanics General Handbook, AC 65-9A, and the Airframc and Powerplant llechanics Airframe Handbook, AC 65-15A.
CONTENTS PREFACE ........................................................
CONTENTS .......................................................
CHAPTER 1.THEORY AND CONSTRUCTION OF AIRCRAFT ENGINES General .....................................................
Comparison of Aircraft Powerplants .............................
Types of Reciprocating Engines .................................
Reciprocating Engine Design and Construction ....................
Crankshafts ..................................................
Connecting Rods .............................................
Pistons .....................................................
Piston Rings ................................................
Cylinders ....................................................
Cylinder Numbering ..........................................
Firing Order ................................................
Valves ......................................................
Valve-Operating Mechanism ....................................
Bearings ....................................................
Propeller Reduction Gearing ...................................
Propeller Shafts ..............................................
Reciprocating Engine Operating Principles .......................
Operating Cycles .............................................
Four-Stroke Cycle ............................................
Reciprocating Engine Power and Efficiencies ......................
Efficiencies ..................................................
Turbine Engine Construction ...................................
Air Entrance ................................................
Accessory Section ............................................
Compressor Section ...........................................
Combustion Section ...........................................
Major Subassemblies ..........................................
Turboprop En, mines ...........................................
' Turboshaft En, u~nes ...........................................
' Turbofan En, mines ............................................
' Turbine Engine Operating Principles ............................
Thrust ......................................................
Gas Turbine Engine Performance ...............................
CHAPTER 2.-INDUCTION AND EXHAUST SYSTEMS Reciprocating Engine Induction Systems ..........................
Induction System Icing ........................................
Internally Driven Superchargers .................................
Externally Driven Superchargers ................................
Turbosupercharger System for Large Reciprocating Engines .........
Turbocharger ................................................
CHAPTER 2.-(Cont.)
Sea Level Boosted Turbocharger System86
Turbocompound Systems for Reciprocating Engines89
Turbojet Engine Inlet Duct Systems90
Turboprop Compressor Inlets94
Reciprocating Engine Exhaust Systems95
Reciprocating Engine Exhaust System Maintenance Practices98
Turbine Engine Exhaust Ducts101
Turboprop Exhaust System102
Thrust Reversers103
Engine Air-Inlet Vortex Destroyer106
CHAPTER 3.-ENGINE FUEL AND FUEL METERING SYSTEMS
Fuel System Requirements109
Turbine Engine Fuel System-General Requirements ............... 1.19 Fuel Quantity Indicating Units .................................. 174'
Basic Fuel System110
Fuel Metering Devices for Reciprocating Engines110
Carburetion Principles113
Carburetor Systems115
Carburetor Types116
Carburetor Icing116
Float-Type Carburetors117
Pressure Injection Carburetors122
Stromberg PS Series Carburetor134
Direct Fuel-Injection Systems136
Carburetor Maintenance142
Fuel System Inspection and Maintenance146
Water Injection System for Reciprocating Engines147
Jet Fuel Controls149
Coordinator153
Fuel Control153
Speed-Sensitive Control154
Fuel Manifold Drain Valve15-1
System Operation154
Hydromechanical Fuel Control156
Fuel Control Description156
Fuel Scheduling System163
Water Injection Re-Set System167
Jet Fuel Control Maintenance167
Engine Fuel System Components169
Water or Coolant Injection174
CHAPTER 4.-ENGINE IGNITION AND ELECTRICAL SYSTEMS
Reciprocating Engine Ignition Systems177
Battery Ignition System177
Magneto Ignition System Operating Principles177
Auxiliary Ignition Units190
Spark Plugs195
Reciprocating Engine Ignition System Maintenance and Inspection196
Magneto Ignition Timing Devices197
Checking the Internal Timing of a Magneto201
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CHAPTER 7.-(Cont. )
Feathering335
Hamilton Standard Hydromatic Propellers338
Hydraulic Governors344
Propeller Synchronization347
Propeller Ice Control Systems347
Propeller Inspection and Maintenance349
Propeller Vibration350
Blade Tracking350
Checking and Adjusting Propeller Blade Angles350
Propeller Balancing352
Servicing Propellers353
Turboprop Propeller354
Blade Cuffs358
CHAPTER 8.-ENGINE REMOVAL AND REPLACEMENT
General359
Reasons for Removal of Reciprocating Engines359
Preparation of Reciprocating Engines for Installation361
QECA Buildup of Radial Engines361
Inspection and Replacement of Powerplant External Units and Systems 364
Preparing the Engine for Removal365
Removing the Engine368
Hoisting and Mounting the Engine for Installation369
Preparation of Engine for Ground and Flight Testing372
Propeller Check373
Checks and Adjustments after Engine Run-up and Operation ........ 37%
Removal and Installation of an Opposed-Type Engine374
Engine Installation375
Turbojet Powerplant Removal and Installation375
Installation of Turbojet Engines377
Rigging. Inspections. and Adjustments378
Turboprop Powerplant Removal and Installation380
Helicopter Engine Removal and Installation381
Rigging and Adjustment of Helicopter QECA382
Engine Mounts382
Preservation and Storage of Engines386
Corrosion Preventive Treatment387
Engine Shipping Containers388
Inspection of Stored Engines390
Preservation and De-preservation of Gas Turbine Engines390
CHAPTER 9.-ENGINE FIRE PROTECTION SYSTEMS
General391
Reciprocating Engine Fire Protection Systems391
Fire Zones394
Fire Extinguishing Agents ..................................... 391.
Turbine Engine Fire Protection Systems397
Typical Multi-Engine Fire Protection System399
Fire Detection System Maintenance Practices403
Fire Extinguisher System Maintenance Practices406
Turbojet Aircraft Fire Protection System (Saberliner)407
...
Vlll
CHAPTER 10.-ENGINE MAINTENANCE AND OPERATION Reciprocating Engine Overhaul ..................................
General Overhaul Procedures ...................................
Cylinder Assembly Reconditioning ...............................
Crankshaft Inspection .........................................
Connecting Rods .............................................
Block Testing of Reciprocating Engines ..........................
Reciprocating Engine Operation ................................
Basic Engint. Operatins Principals ..............................
Factors Affecting Engine Operation ..............................
Engine Troubleshooting .......................................
Cylinder Maintenance .........................................
Cylinder Compression Tests ....................................
Cylinder Removal ............................................
Cylinder Installation .........................................
Valve and Valve Mechanism ....................................
Cold Cylinder Check .........................................
Turbine Engine Maintenance ...................................
Combustion Section ..........................................
Inspection and Repair of Turbine Disc ..........................
Commercial Ratings ..........................................
Engine Instrumentation .......................................
Turbojet Engine Operation ....................................
Ground Operation ............................................
Engine Shutdown .............................................
Troubleshooting Turbojet Engines ...............................
Turboprop Operation .........................................
Troubleshooting Procedures for Turboprop Engines ................
Jet Calibration Test Unit ......................................
Troubleshooting Aircraft Tachometer System ......................
Spectrometric Oil Analysis Program .............................
CHAPTER 1
THEORY AND CONSTRUCTION OF AIRCRAFT ENGINES
GENERAL For an aircraft to remain in level unaccelerated flight, a thrust must be provided that is equal to and opposite in direction to the aircraft drag. This thrust, or propulsive force, is provided by. a suitable type of heat engine.
All heat engines have in common the ability to convert heat energy into mechanical energy, by the flow of some fluid mass through the engine. In all cases, the heat energy is released at a point in Engine Type Major Means of Compression Turbojet. Turbine-driven compressor.
Turboprop. Turbine-driven compressor.
Ramjet. Ram compression due to high flight speed.
Pulse-jet. Compression due to combustion.
Reciprocating. Reciprocating action of pistons.
Rocket. Compression due to combustion.
the cycle where the pressure is high, relative to atmospheric.
These engines are customarily divided into groups or types depending upon:
(1) The working fluid used in the engine cycle,
(2) the means by which the mechanical energy is transmitted into a propulsive force, and
(3) the method of compressing the engine working fluid.
The types of engines are illustrated in figure 1-1.
Engine Working Propulsive Fluid Working Fluid Fuel/air mixture. Same as engine working fluid.
Fuel/air mixture. Ambient air.
Fuel/air mixture. Same as engine working fluid.
Fuel/air mixture. Same as engine working fluid.
Fuel/air mixture. Ambient air.
Oxidizer/fuel Same as engine mixture. working fluid.
FIGURE1-1. Types of engines.
The propulsive force is obtained by the displacement of a working fluid (not necessarily the same fluid used within the engine) in a direction opposite to that in which the airplane is propelled. This is an application of Newton's third law of motion.
Air is the principal fluid used for propulsion in every type of powerplant except the rocket, in which only the byproducts of combustion are accelerated and displaced.
The propellers of aircraft powered by reciprocating or turboprop engines accelerate a large mass of air through a small velocity change. The fluid (air) used for the propulsive force is a different quantity than that used within the engine to produce the mechanical energy. Turbojets, ramjets, and pulse-jets accelerate a smaller quantity of air through a large velocity change. They use the same working fluid for propulsive force that is used within the engine. A rocket carries its own oxidizer rather than using ambient air for combustion. It discharges the gaseous byproducts of combustion through the exhaust nozzle at an extremely high velocity.
Engines are further characterized by the means of compressing the working fluid before the addition of heat. The basic methods of compression are :
(1)The turbine-driven compressor (turbine engine).
(2) The positive displacement, piston-type com-
pressor (reciprocating engine).
(3) Ram compression due to forward flight speed (ramjet).
(4) Pressure rise due to combustion (pulse-jet and rocket).
A more specific description of the major engine types used in commercial aviation is given later in this chapter.
COMPARISON OF AIRCRAFT POWERPLANTS In addition to the differences in the methods employed by the various types of powerplants for producing thrust, there are differences in their suitability for different types of aircraft. The following discussion points out some of the important characteristics which determine their suitability.
General Requirements All engines must meet certain general requirements of effkiency, economy, and reliability. Besides being economical in fuel consumption, an aircraft engine must be economical (the cost of original procurement and the cost of maintenance) and it must meet exacting requirements of efficiency and low weight per horsepower ratio. It must be capable of sustained high-power output with no sacrifice in reliability; it must also have the durability to operate for long periods of time between overhauls. It needs to be as compact as possible, yet have easy accessibility for maintenance. It is required to be as vibration free as possible and be able to cover a wide range of power output at various speeds and altitudes.
These requirements dictate the use of ignition systems that will deliver the firing impulse to the spark plugs or igniter plugs at the proper .time in all kinds of weather and under other adverse conditions. Fuel-metering devices are needed that will deliver fuel in the correct proportion to the air ingested by the engine regardless of the attitude, altitude, or type of weather in which the engine is operated. The engine needs a type of oil system that delivers oil under the proper pressure to all of the operating parts of the engine when it is running.
Also, it must have a system of damping units to damp out the vibrations of the engine when it is operating.
Power and Weight The useful output of all aircraft powerplants is thrust, the force which propels the aircraft. Since the reciprocating engine is rated in b.hp. (brake horsepower) and the gas turbine engine is rated in pounds of thrust, no direct comparison can be made.
However, since the reciprocating engine/propeller combination receives its thrust from the propeller, a comparison can be made by converting the horsepower developed by the reciprocating engine to thrust.
If desired, the thrust of a gas turbine engine can be converted into t.hp. (thrust horsepower). But it is necessary to consider the speed of the aircraft.
This conversion can be accomplished by using the formula :
thrust x aircraft speed (m.p.h.) t.hp. = 375 mile-pounds per hour The value 375 mile-pounds per hour is derived from the basic horsepower formula as follows:
1hp. =33,000 ft.-lb. per minute.
33,000 x 60 =1,980,000 ft.-lb. per hour.
1,980,000 =375 mile-pounds per hour.
5,280 One horsepower equals 33,000 ft.-lb. per minute or 375 mile-pounds per hour. Under static conditions, thrust is figured as equivalent to approximately 2.6 pounds per hour.
If a gas turbine is producing 4,000 pounds of thrust and the aircraft in which the engine is installed is traveling at 500 m.p.h., the t.hp. will be:
It is necessary to calculate the horsepower for each speed of an aircraft, since the horsepower varies with speed. Therefore, it is not practical to try to rate or compare the output of a turbine engine on a horsepower basis.
The aircraft engine operates at a relatively high percentage of its maximum power output throughout its service life. The aircraft engine is at full power output whenever a takeoff is made. It may hold this power for a period of time up to the limits set by the manufacturer. The engine is seldom held at a maximum power for more than 2 minutes, and usually not that long. Within a few seconds after lift-off, the power is reduced to a power that is used for climbing and that can be maintained for longer periods of time. After the aircraft has climbed to cruising altitude, the power of the engine (s) is further reduced to a cruise power which can be maintained for the duration of the flight.
If the weight of an engine per brake horsepower (called the specific weight of the engine) is decreased, the useful load that an aircraft can carry and the performance of the aircraft obviously are increased. Every excess pound of weight carried by
an aircraft engine reduces its performance. Tremendous gains in reducing the weight of the aircraft engine through improvement in design and metallurgy have resulted in reciprocating engines now producing approximately 1 hp. for each pound of weight.
Fuel Economy The basic parameter for describing the fuel economy of aircraft engines is usually specific fuel consumption. Specific fuel consumption for turbojets and ramjets is the fuel ffow (lbs./hr.) divided by thrust (lbs.), and for reciprocating engines the fuel flow (IbsJhr.) divided by brake horsepower.
These are called "thrust specific fuel consumption" and "brake specific fuel consumption," respectively.
Equivalent specific fuel consumption is used for the turboprop engine and is the fuel ffow in pounds per hour divided by a turboprop's equivalent shaft horsepower. Comparisons can be made between the various engines on a specific fuel consumption basis.
At low speed, the reciprocating and turbopropeller engines have better economy than the turbojet engines. However, at high speed, because of losses in propeller efficiency, the reciprocatihg or turbopropeller engine's efficiency becomes less than that of the turbojet. Figure 1-2 shows a comparison of average thrust specific fuel consumption of three types of engines at rated power at sea level.
Flight Mach number FIGURE1-2. Camparison of fuel consumption for three types of engines at rated power at sea level.
Durability and Reliability Durability and reliability are usually considered identical factors since it is difficult to mention one without including the other. An aircraft engine is reliable when it can perform at the specified ratings in widely varying flight attitudes and in extreme weather conditions. Standards of powerplant reliability are agreed upon by the FAA, the engine manufacturer, and the airframe manufacturer. The engine manufacturer ensures the reliability of his product by design, research, and testing. Close control of manufacturing and assembly procedures is maintained, and each engine is tested before it leaves the factory.
Durability is the amount of engine life obtained while maintaining the desired reliability. The fact that an engine has successfully completed its type or proof test indicates that it can be operated in a normal manner over a long period before requiring overhaul. However, no definite time interval between overhauls is specified or implied in the engine rating. The TBO (time between overhauls) varies with the operating conditions such as engine temperatures, amount of time the engine is operated at high-power settings, and the maintenance received.
Reliability and durability are thus built into the
engine by the manufacturer, but the continued reliability of the engine is determined by the maintenance, overhaul, and operating personnel. Careful maintenance and overhaul methods, thorough periodical and preflight inspections, and strict observance of the operating limits established by the engine manufacturer will make engine failure a rare occurrence.
Operating Flexibility Operating flexibility is the ability of an engine to run smoothly and give desired performance at all speeds from idling to full-power output. The aircraft engine must also function efficiently through all the variations in atmospheric conditions encountered in widespread operations.
Compactness To effect proper streamlining and balancing of an aircraft, the shape and size of the engine must be as compact as possible. In single-engine aircraft, the shape and size of the engine also affect the view of the pilot, making a smaller engine better from this standpoint, in addition to reducing the drag created by a large frontal area.
Weight limitations, naturally, are closely related to the compactness requirement. The more elongated and spreadout an engine is, the more difficult it becomes to keep the specific weight within the allowable limits.
Powerplant Selection Engine specific weight and specific fuel consumption were discussed in the previous paragraphs, but for certain design requirements, the final powerplant selection may be based on factors other than those which can be discussed from an analytical point of view. For that reason, a general discussion of powerplant selection is included here.
For aircraft whose cruising speeds will not exceed 250 m.p.h. the reciprocating engine is the usual choice. When economy is required in the low-speed range, the conventional reciprocating engine is chosen because of its excellent efficiency. When high-altitude performance is required, the turbosupercharged reciprocating engine may be chosen because it is capable of maintaining rated power to a high altitude (above 30,000 feet).
In the range of cruising speeds from 180 to 350
m.p.h. the turbopropeller engine performs better than other types of engines. It develops more power per pound of weight than does the reciprocating engine, thus allowing a greater fuel load or payload for engines of a given power. The maximum overall efficiency of a turboprop powerplant is less than that of a reciprocating engine at low speed. Turboprop engines operate most economically at high altitudes, but they have a slightly lower service ceiling than do turbosupercharged reciprocating engines. Economy of operation of turboprop engines, in terms of cargo-ton-miles per pound of fuel, will usually be poorer than that of reciprocating engines because cargo-type .aircraft are usually designed for lowspeed operation. On the other hand, coit of operation of the turboprop may approach that of the reciprocating engine because it burns cheaper fuel.
Aircraft intended to cruise from high subsonic speeds up to Mach 2.0 are powered by turbojet engines. Like the turboprop, the turbojet operates mo'st e~ciently at high altitudes. High-speed, turbo- *i jet-propelled aircraft fuel economy, in terms of miles per pound of fuel, is poorer than that attained at low speeds with reciprocating engines.
However, reciprocating engines are more complex in operation than other engines. Correct operation of reciprocating engines requires about twice the instrumentation required by turbojets or turboprops, and it requires several more controls. A change in power setting on some reciprocating engine installations may require the adjustment of five controls, but a change in power on a turbojet requires only a change in throttle setting. Furthermore, there are a greater number of critical temperatures and - pressures to be watched on reciprocating engine installations than on turbojet or turboprop installations.
TYPES OF REC~PROCAT~~ ENGINES Many types of reciprocating engines have been designed. However, manufacturers have developed some designs that are used more commonly than others and are therefore recognized as conventional.
Reciprocating engines may be classified according to cylinder arrangement with respect to the crankshaft (in-line, V-type, radial, and opposed) or according to the dethod of cooling (liquid cooled or air cooled). Actually, all engines are cooled by transferring excess heat to the surrounding air. In air-cooled engines, this heat transfer is direct from the cylinders to the air. In liquid-cooled engines, the heat is transferred from the cylinders to the coolant, which is then sent through tubing and cooled within-a radiator placed in the airstream.
The radiator must be large enough to cool the liquid efficiently. Heat is transferred to air more slowly than it is to a liquid. Therefore, it is necessary to