AC65-12A Airframe & Powerplant
MECHANICS
POWERPLANT HANDBOOK
• U.S. DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION
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 Office Washington. D.C. 20402
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.
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 extended 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 aeronautical 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.
Address 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 Airframe and Powerplant Mechanics General Handbook, AC 65-9A, and the Airframe and Powerplant iii
CONTENTS PREFACE jii
CONTENTS CHAPTER 1.-THEORY AND CONSTRUCTION OF AIRCRAFT ENGINES General ..
Comparison of Aircraft Powerplants 2 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 01 Turboprop Engines Turboshaft Engines 63 Turbofan Engines 64 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 System 86 Turbocompound Systems for Reciprocating Engines ... 89 Turbojet Engine Inlet Duct Systems . 90 Turboprop Compressor Inlets 94 Reciprocating Engine Exhaust Systems .. 95 Reciprocating Engine Exhaust System Maintenance Practices 98 Turbine Engine Exhaust Ducts 101 Turboprop Exhaust System . 102 Thrust Reversers 103 Engine Air-Inlet Vortex Destroyer 106 CHAPTER 3.-ENGINE FUEL AND FUEL METERING SYSTEMS Fuel System Requirements .. 109 Basic Fuel System 110 Fuel Metering Devices for Reciprocating Engines 110 Carburetion Principles 113 Carburetor Systems 115 Carburetor Types 116 Carburetor Icing 116 Float-Type Carburetors 117 Pressure Injection Carburetors 122 Stromberg PS Series Carburetor 134 Direct Fuel-Injection Systems 136 Carburetor Maintenance ... 142 Fuel System Inspection and Maintenance 146 Water Injection System for Reciprocating Engines 147 Turbine Engine Fuel System-General Requirements 149 Jet Fuel Controls 149 Coordinator 153 Fuel Control 153 Speed-Sensitive Control 154 Fuel Manifold Drain Valve 151 System Operation 154 Hydromechanical Fuel Control 156 Fuel Control Description .. 156 Fuel Scheduling System 163 Water Injection Re-Set System 167 Jet Fuel Control Maintenance 167 Engine Fuel System Components 169 Fuel Quantity Indicating Units 174 Water or Coolant Injection . 174 CHAPTER 4.-ENGINE IGNITION AND ELECTRICAL SYSTEMS Reciprocating Engine Ignition Systems 177
Battery Ignition System177
Magneto Ignition System Operating Principles . 177
Auxiliary Ignition Units190
Spark Plugs .. 195 Reciprocating Engine Ignition System Maintenance and Inspection . 196 Magneto Ignition Timing Devices 197 Checking the Internal Timing of a Magneto . 201 vi
CHAPTER 4.-(Cont.)
Timing High-Tension System Distributor Fingers 208 Spark Plug Inspection and Maintenance 213
The Engine Analyzer228
Turbine Engine Ignition Systems230
Ignition System Inspection and Maintenance 234 Removal, Maintenance, and Installation of Ignition System Components 235 Powerplant Electrical Systems .. 235 Lacing and Tying Wire Bundles . 246
Cutting Wire and Cable249
Stripping Wire and Cable250
Emergency Splicing Repairs 253 Connecting Terminal Lugs to Terminal Blocks .. 254 Bonding and Grounding ... 255 Connectors 257 Conduit . 260 Electrical Equipment Installation . 260 CHAPTER 5.-ENGINE STARTING SYSTEMS General 263 Reciprocating Engine Starting Systems 263 Starting System Using Combination Inertia Starter . 205 Direct-Cranking Electric Starting System for Large Reciprocating Engines 265 Direct-Cranking Electric Starting System for Small Aircraft 269 Gas Turbine Engine Starters 270
Air Turbine Starters276
Cartridge/Pneumatic Turbine Engine Starter .. 279 Fuel/Air Combustion Turbine Starter 283 CHAPTER 6.-LUBRICATION AND COOLING SYSTEMS Principles of Engine Lubrication 285 Requirements and Characteristics of Reciprocating Engine Lubricants. 285 Reciprocating Engine Lubrication Systems 286 Internal Lubrication of Reciprocating Engines 293 Lubrication System Maintenance Practices 294 Requirements for Turbine Engine Lubricants 301 Turbine Engine Lubrication Systems 302 Typical Dry Sump Lubrication System 308 Engine Cooling Systems .. 314 Inspection of Cowling ... 318 Engine Cylinder Cooling Fin Inspection 319 Turbine Engine Cooling ... 322 CHAPTER 7.-PROPELLERS General ... 325 Basic Propeller Principles .. 325 Propeller Operation 327 Types of Propellers . 329 Classification of Propellers . 331 Propellers Used on Light Aircraft 331 Constant Speed Propellers .. 333 vii
CHAPTER 7.—(Cont.)
Feathering • • Hamilton Standard Hydromatic Propellers Hydraulic Governors Propeller Synchronization .. 347 Propeller Ice Control Systems 347 Propeller Inspection and Maintenance 349 Propeller Vibration 350 Blade Tracking 350 Checking and Adjusting Propeller Blade Angles 350 Propeller Balancing .. 352 Servicing Propellers Turboprop Propeller ... 354 Blade Cuffs .. 358 CHAPTER 8.-ENGINE REMOVAL AND REPLACEMENT General . 359 Reasons for Removal of Reciprocating Engines 359 Preparation of Reciprocating Engines for Installation . 361 QECA Buildup of Radial Engines 361 Inspection and Replacement of Powerplant External Units and Systems 364 Preparing the Engine for Removal .. 365
Removing the Engine368
Hoisting and Mounting the Engine for Installation .. 369 Preparation of Engine for Ground and Flight Testing . 372 Propeller Check 373 Checks and Adjustments after Engine Run-up and Operation 371 Removal and Installation of an Opposed-Type Engine . 374 Engine Installation 375 Turbojet Powerplant Removal and Installation . 375 Installation of Turbojet Engines 377 Rigging, Inspections, and Adjustments 378 Turboprop Powerplant Removal and Installation . 380 Helicopter Engine Removal and Installation . 381 Rigging and Adjustment of Helicopter QECA 382 Engine Mounts . 382 Preservation and Storage of Engines . 386 Corrosion Preventive Treatment .. 387 Engine Shipping Containers .. 388 Inspection of Stored Engines . 390 Preservation and De-preservation of Gas Turbine Engines 390 CHAPTER 9.-ENGINE FIRE PROTECTION SYSTEMS General 391 Reciprocating Engine Fire Protection Systems . 391
Fire Zones394
Fire Extinguishing Agents 394 Turbine Engine Fire Protection Systems 397 Typical Multi-Engine Fire Protection System 399 Fire Detection System Maintenance Practices 403 Fire Extinguisher System Maintenance Practices .. 406 Turbojet Aircraft Fire Protection System (Saberliner) ... 407 viii
CHAPTER 10.-ENGINE MAINTENANCE AND OPERATION Reciprocating Engine Overhaul 411 General Overhaul Procedures . ·11 Cylinder Assembly Reconditioning .. 415
Crankshaft Inspection128
Connecting Rods428
Block Testing of Reciprocating Engines 429 Reciprocating Engine Operation 436 Basic Engine Operating Principals 412 Factors Affecting Engine Operation 446
Engine Troubleshooting453
Cylinder Maintenance ... 157 Cylinder Compression Tests . 159 Cylinder Removal 462 Cylinder Installation 463 Valve and Valve Mechanism . 465 Cold Cylinder Check 470 Turbine Engine Maintenance 472 Combustion Section 476 Inspection and Repair of Turbine Disc 179 Commercial Ratings 483 Engine Instrumentation 183 Turbojet Engine Operation . 486 Ground Operation • 488 Engine Shutdown . 489 Troubleshooting Turbojet Engines . 490 Turboprop Operation 190 Troubleshooting Procedures for Turboprop Engines 492 Jet Calibration Test Unit ... 493 Troubleshooting Aircraft Tachometer System 497 Spectrometric Oil Analysis Program 498 i×
CHAPTER 1
THEORY AND CONSTRUCTION OF AIRCRAFT ENGINES 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 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 Type Major Means Engine Working Propulsive of Compression Fluid Working Fluid Turbojet. Turbine-driven Fuel/air mixture. Same as engine compressor. working fluid.
Turboprop. Turbine-driven Fuel/air mixture. Ambient air.
compressor.
Ramjet. Ram compression due Fuel/air mixture. Same as engine to high flight speed. working fluid.
Pulse-jet. Compression due to Fuel/air mixture. Same as engine combustion. working fluid.
Reciprocating. Reciprocating action Fuel/air mixture. Ambient air.
of pistons.
Rocket. Compression due to Oxidizer/fuel Same as engine combustion. mixture. working fluid.
FIGURE 1-1. 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
(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 efficiency, 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 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 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:
t.hp. = thrust x aircraft speed (m.p.h.) 375 mile-pounds per hour The value 375 mile-pounds per hour is derived from the basic horsepower formula as follows:
1 hp. = 33,000 ft.-lb. per minute.
33,000 × 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:
4000 × 500 = 5,333.33 t.hp.
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 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 2
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 flow (lbs./hr.) divided by thrust (Ibs.), and for reciprocating engines the fuel flow (lbs./hr.) 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 flow 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 reciprocatirig 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.
1.8
1.6 Ibs. 1.4 Thrust specific fuel consumption Turbojet .8 Reciprocating Turboprop
o. .4 .2
0.2 0.4 0.6 0.8 1.0 1.2 1.4 Flight Mach number FIGURE 1-2. Comparison 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.
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 4011 specus 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 than on turbojet or installations.
TYPES OF RECIPROCATING ENGINES Many types of reciprocating engines have been 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 method 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