University of Central Missouri Fall 2024 / Professor Terry Hunt / Chapter 15 and 16 of …

Slides

Design and Construction

• Powered flight was made possible with the development of the internal combustion engine.

• A heat engine converts thermal energy into mechanical energy.

• A specific volume of air is compressed and then heat is added through the burning of a fuel.

• The air expands and creates a force that is used to produce torque to drive a propeller.

• The engines are said to “reciprocate” because of the start-stop/back and forth motion of the pistons.

The Wright Engine

• The engine the Wright brothers used to power the first heavier-than-air machine was a four-cylinder water cooled design.

• 12 HP for the first minute. ~8 HP thereafter.

• Weight—180lbs.

• No throttle.

• 200 CID.

• Make and break magneto ignition. (battery for start)

• “Automatic Intake Valves”.

• Built by Charles Taylor (the first aviation mechanic)

• 12 horsepower per 180 lbs

• Expected run time 1-5 mins

Rotary Radials

• Came onto the scene around 1909.

• Led technology until early 1920’s.

• Highest power to weight ratio of any engine at the time.

• Crankshaft was stationary and the crankcase rotated around it.

• The propeller was attached to the case.

• The Gnome and the Le Rhone are typical examples.

  • Rotary Radial engines have very high power to weight ratios.

  • Usually have port type intake valves (Monosoupape design)

  • No throttle. (Blip Switch)

  • Require Castor Oil

    • Really bad for people

  • Also made by Clerget and Oberursel.

The “V” Engines

• By the end of WWI (1914 to 1918) the “V” type engine had come of age.

• Cylinders arranged in a “V” arrangement around the crankshaft.

• Made the development of the carburetor/throttle possible.

• Solved many problems associated with ignition, lubrication and aircraft controllability. (No high rotational mass as found with the rotary radial).

• The “Liberty” and the Curtiss OX-5 are typical examples.

• The OX-5 coupled with the Curtiss JN-4 “Jenny” created “General Aviation” in the US.

  • Hundreds of these airplanes were sold surplus as the end of WWI, usually for $75 to $200. They were used by the “barnstormers” and were the beginning of GA—Airmail and Private Operators.

The “In-Line” Engines

• In-Line engines became popular in the 1930’s in low to medium performance aircraft.

• Cylinders are in a line.

• Cooling of rear cylinders is a problem.

• Visibility over the nose is a challenge. This led to inverted in-lines.

• Popular in Europe.

• The Menasco “Super Pirate” was popular in the Ryan STA.

• A new family of in-line diesel engines have recently been certified and in use

  • The Austro Engine Co. AE300  Diesel Engine Used in the Diamond DA-44 170 HP Turbo-Diesel

The Stationary (Static) Radial Engine

• Developed by the Wright Aeronautical Corporation.

• The J-5 “Whirlwind” was a 7 cylinder engine that powered the “Spirit of St. Louis”. It established itself as the height of reliability.

• May have as few as 3 and as many as 28 cylinders.

• High power-to-weight ratio.

• Pratt & Whitney R-985 “Wasp Jr.” 450 HP workhorse. Supercharged

• Pratt & Whitney R-4360 Largest radial engine.

  • 28 cylinders

  • 3,400 hp.

• Wright R-3350

  • 3,000 hp engine that powered aircraft such as the Douglas Skyraider, Lockheed Constellation and others.

The Big “V” Engines

• Developed in the 1930’s alongside radial technology.

• V-12’s with water cooling.

• Each nation approaching WWII developed their workhorses.

• England-The Rolls-Royce “Merlin” Built under license in the U.S. as the Packard “Merlin” for the P-51.

• Germany-The Junkers Jumo and Daimler DB 601.

• U.S. The Allison V-1710.

• Ingenious Radiator Designs.

• Gear-Reductions, Turbo-charged, Super-Charged, Fuel Injected.

• Some had provision for a cannon to fire from the center of the spinner

• The Rolls-Royce “Merlin”

  • The British engine that powered the hawker Hurricane and the famous Supermarine “Spitfire” and that saved the North American Apache” and made it the “MUSTANG”!

The Opposed Engines

• Designed for low horsepower GA aircraft designs of the 1930’s.

• One of the earliest was the McCulloch 36HP. Two Cylinder.

• Continental Engines produced the C-65 and applied it to the Piper J-3-C65 Cub.

• Initially viewed as a low-horsepower engine, but they have produced 400 horsepower in certificated applications.

• These are “the” GA powerplant.

  • Light

  • Strong

  • Reliable

  • Air-cooled (There have been water cooled variations- Voyager)

Engine Classification and Theory

Reciprocating Engine Destination

• Engines are categorized according to the arrangement of the cylinders:

  • R—Radial

  • V

  • O—Opposed

  • X

• Engines are then designated according to Cubic Inch Displacement (CID).

• There may be prefix letters that denote supercharging, turbocharging, gear reductions, aerobatic capability or fuel injection

  • TCM-O-200-A

  • Lycoming O-320

  • P & W R-985

  • Lycoming AIO-360

  • TCM GTSIO-520

  • Lycoming GO-435

• There will be suffix letters and numbers that denote particular engine models and characteristics

Engine Orientation

• The crankshaft end of the engine is always the “front”.

• The accessory end of the engine is always the “rear” or “back”.

• Left or right side is based on looking forward from the rear of the engine. (From the pilots seat in a conventional arrangement).

• Propeller rotation is always based on looking forward from the rear of the engine. (From the pilots seat in a conventional arrangement).

Cylinder Numbering- Opposed

• The two primary manufacturers of aircraft piston engines are:

  • Teledyne Continental (TCM)

  • Avco Lycoming

• Each manufacturer numbers their cylinders differently.

• TCM-#1 cylinder is on back/right of the engine

• Lycoming #1 cylinder is the front right.

• Both manufacturers have odd cylinders on right and even on the left.

Cylinder Numbering- Radials

• On Radials, cylinders are numbered clockwise as viewed from the rear or accessory end of the engine.

• The number 1 cylinder is the one centered on the top of the engine.

• Single row radials are numbered consecutively as viewed from the accessory end.

• Twin row radials are numbered the same as single row engines except all of the odd cylinders are on the back row and all of the even cylinders are on the front row

Engine Firing Order

• The firing order is the sequence in which each cylinder of the engine reaches its ignition/combustion event.

• Firing order is determined by the manufacturer to maintain optimum balance and minimum vibration.

• The more cylinders an engine has, the fewer degrees of rotation it has between power pulses and, therefore the smoother it is in operation.

• Radials are inherently smooth and relatively vibration free.

• Opposed engines are inherently more vibratory and oscillatory

• Opposed

  • Most four cylinder engines fire 1-3-2-4  or 1-4-2-3

  • 6 cylinder engines fire either 1-4-5-2-3-6 or 1-6-2-3-5-4

• Radial

  • The firing order of a radial allows the power pulses to follow the crank throw during rotation.

  • On single-row radials the odd numbered cylinders fire then the even numbered cylinders:

    • 7 cylinder---1-3-5-7-2-4-6

    • 9 cylinder---1-3-5-7-9-2-4-6-8

Reciprocating Engine Operating Cycles- 2 Stroke Cycle

• A reciprocating engine produces power through the following operations:

  • 1) The air-fuel mixture is introduced into the cylinder.

  • 2) The air-fuel mixture is compressed.

  • 3) The mixture is ignited.

  • 4) The gases expand with the application of heat and generate a force that acts on the piston.

  • 5) The combustion residue is scavenged and ejected from the cylinder.

• A two-stroke engine accomplishes these operations in two “strokes” of the piston or 360 degrees of crankshaft rotation.

• When the piston moves upward, two operations occur:

  • 1) The air/fuel mixture is compressed.

  • 2) A low pressure draws new air/fuel mixture into the crankcase.

• When the piston moves downward, two operations occur:

  • 1) The burnt air/fuel mixture is ejected.

  • 2) The low pressure in the cylinder draws in fresh air/fuel mixture.

• A two-stroke engine is lubricated as the air/fuel mixture circulates in the crankcase.

• The oil that is added to the fuel is centrifugally separated and coats the internal parts.

• NOTE—A leading advantage of a two-stroke engine is its light weight. This is because the engine has no lubrication system as such. (No sump, oil supply, pump, filters, galleries, etc.)

2 Stroke Engines

• Two stroke engines are simple and lightweight.

• They are commonly used as low cost power around the house such as weed eaters, small tillers, chain saws, go-carts, mini bikes.

• Used on some ultralights and LSA aircraft such as weight shift aircraft.  Rotax 582

• Disadvantages: inefficient use of fuel, require oil and/or oil premix, difficult to cool, make power at high RPM.

Reciprocating Engine Operating Cycles- 4 Stroke Cycle

• The 4 stroke cycle is also referred to as the “Otto Cycle” after August Otto, who developed it

• The “stroke” that is referred to is 180 degrees of crankshaft rotation and is piston movement from top dead center (TDC) to bottom dead center (BDC).

• The 4 stroke engine requires 720 degrees (or two complete rotations) of crankshaft rotation to accomplish the intake, compression, ignition, power and exhaust processes.

• 4 Stroke (5 Event) Cycle:

  • Intake

  • Compression

  • Power

  • Exhaust

• The intake and exhaust valves must be precisely timed to allow for maximum volumetric efficiency during the intake process and for maximum scavenging during the exhaust stroke.

• To accomplish this, the valves are timed to open as early as possible and  close as late as possible and allow for a period of time when both the intake and the exhaust valve are both open (valve overlap).

• The cam lobes must be precisely ground to created the geometry necessary to create the correct “lead”, “lag”, “overlap”, “lift” and “duration” of the valve train.

• The intake valve will open from 8-55 degrees BTDC on the exhaust stroke—to take advantage of the pressure drop created by the exhaust gases ejecting from the cylinder to help create additional intake force to increase volumetric efficiency.

• The ignition event takes place from 20-35 degrees BTDC on the compression stroke to allow more time for ignition and complete burning of the mixture for maximum power release. In addition, dual ignition assists in this.

• The exhaust valve opens a few degrees BBDC on the power stroke to enhance scavenging.

• There is a period of time where both the intake and the exhaust valve are open. This is called “Valve Overlap”.

• “Valve Overlap” increases volumetric efficiency and aids in cooling.

Aircraft Diesel Power Plants: The Diesel Engine

• Invented by German inventor Rudolph Diesel in 1893.

• Has high available power/torque.

• Lowest specific fuel consumption of all the reciprocating engines.

• The engine relies on “compression ignition”, therefore no ignition system is required.

• May be two stroke or 4 stroke designs.

• Use low cost “heavy fuels” that are readily available.

• Produce high torque at low RPM—ideal for aircraft applications.

• Diesel aircraft engines were common in Germany from the airship era of the 1930’s until the end of WWII in 1945.

• Diesel engines for aircraft applications were reliable and powerful but had the disadvantage of being very heavy.

• As gasoline engines were improved diesel aircraft powerplants faded into history.

• The aviation industry is in the middle of a fuel crisis that had it beginnings in the increase of EPA legislation in the late 1970’s with a ban in TEL for automotive fuels in the early 1980’s.

• New materials and technology coupled with the turbocharger have made a “new diesel” possible.

• In a gasoline engine, an ignition source must be timed to ignite the fuel/air charge at the proper time on the compression stroke.

• In a gasoline engine, compression ratios range from 6.5:1 to 9.5:1. The limitations being the structural integrity of  the cylinder and the threat of detonation.

• In a diesel engine, the fuel/air charge is ignited through the heat of compression, therefore no separate ignition system is required.

• A high pressure fuel injection pump is required to inject fuel into the cylinder at the proper time for combustion to occur.

• In a diesel engine, compression ratios range from 16:1 to 22:1. (Detonation is not a threat in a diesel engine in that the engine is in a continual state of detonation!)

• Diesel engines may be of a 2 stroke or a 4 stroke design.

• 2 stroke diesel engines are less efficient as compared to 4 stroke diesel engines as there is a period of time when both the intake and the exhaust ports are both open and no effective pressure is acting on the piston.

• Both 2 stroke and 4 stroke diesel engines may be supercharged or turbocharged for increased power and efficiency. (Higher levels of “charging” are possible as detonation  is not a factor).

• 2-Stroke Diesel Cycle

  • Exhaust and Intake

  • Compression

  • Power

• 4-Stroke Diesel Cycle

  • Induction

  • Compression

  • Ignition

  • Exhaust

• Jumo 205 2 Stroke Diesel Engine 600-1,000 HP The last variant of the engine produced 1,000HP at TO and maintained that output to 20,000FT! 6 cylinder 12 pistons 2 crankshafts

  • Junkers Ju.86 with Jumo 205 2-Stroke Diesel Engines

• Today the aviation industry operates on a “waiver” from the EPA allowing TEL in aviation gasoline.

• Currently there is an 11 year timeline to find a replacement for TEL. None currently exists. (80UL, MTBE)

• As the price of 100LL rises, there is a move to develop alternative power for GA.

• Small turbines are cost prohibitive.

• Aviation diesel engines can use readily available Jet-A

• There are now several diesel aircraft powerplants that are certified by the FAA for application in certificated aircraft.

• The Thielert company in Austria produced engines for the Diamond DA42.

• This company filed for bankruptcy and is now reorganized as Austro Engine Company.

• The engine is based on a Mercedes-Benz 1.7 liter automotive engine. There is now a 4.0 liter engine available.

• DeltaHawk DH200V is a V-4 2 stroke water cooled 200HP engine

• Societe de Motorisations Aeronautique (SMA) Is a 4 stroke diesel 230HP

• DB602 V16 has 1,320 HP

Diesel Aircraft Engine Advantages

• Diesel engines produce high power at low RPM’s. This lends itself well to propellers that are speed limited by the local speed of sound. (A 135HP diesel can replace a 180HP gasoline engine in an aircraft application).

• Modern aviation diesel engines are made of new generation materials that drastically reduce weight over old technology diesel engines.

• Diesel fuels are related to Jet-A and are simpler to refine.

• Although diesel fuel weighs more per gallon than gasoline, it has more Btu’s of heat energy per pound.

• A diesel engine has a lower BSFC than a comparable gasoline engine. Usually .32 to .38 lb. per HP (compared to .53 to .59 lb. per HP for a gasoline engine).

• Diesel engines experience reduced engine wear due to the lubricity of diesel fuel. This leads to higher TBO’s and TBR’s.

• Modern aviation diesel engines have FADEC that increases efficiency and provides single power lever technology.

Aircraft Reciprocating Engines

• Aircraft reciprocating engines are unique in several respects:

• They are constructed with a “crank case” rather than “en bloc”

• The crank case is usually made of aluminum alloy.

• Each cylinder assembly is a separate, removable unit.

• There are two sparkplugs per cylinder.

• The forward section of the crankshaft may be hollow to allow for a constant speed propeller.

• Air-Cooled

Reciprocating Engine Power and Efficiencies

• Work / Power Considerations

  • Aircraft engines are rated according to their ability to perform work and produce power.

  • WORK—When a force moves an object, work is produced.

  • When a force is applied to an object but the object does not move—No work is performed

  • WORK= FORCE X DISTANCE

    • Ex. If an object weighing 400 pounds is lifted 10 feet, then 4,000 ft/lbs of work is accomplished.

  • Time is not considered when work is calculated.

  • POWER is a measure of the amount of work accomplished per unit of time.

    • Power = (Force x Distance) /Time

      • (ft/lbs per second)

    • Note—POWER is the rate of doing work.

    • In engine applications, power is indicated in HORSEPOWER

• James Watt

• Horsepower

  • The horsepower was established by James Watt to equate the power of draft horses to the newly developed steam engine.

  • One horsepower is the amount of power required to perform 33,000 foot-pounds of work per minute.

  • This also equates to 550 foot- pounds of work per second.

• Indicated horsepower

  • IHP =The total amount of horsepower developed in the cylinders of the engine, Does not account for friction losses.

  • IHP = PLANK/ 33,000

    • P = IMEP on the power stroke.

    • L = Length of stroke (in ft.!).

    • A = Area of the piston in sq. inches. (𝜋∗𝑟^2)

    • N = # of power strokes/minute (RPM/2).

    • K = Number of cylinders.

    • Example: An 6 cylinder engine has a bore of 5 inches and a stroke of 5 inches. It is turning at 2,750 rpm and has an IMEP of 125 psi.

      P = 125

      L = 5/12 = .416”

      A = 3.1416 X 〖2.5〗^2 = 19.62 〖𝑖𝑛〗^2

      N = 2750/2 = 1,375

      K = 6

      PLANK = 8,421,270 8,421,270/33,000 = 255.19HP

• Friction Horsepower

  • IHP is a theoretical measurement of a frictionless engine.

  • In reality, the engine must overcome internal friction of pistons, gears and accessories and the work expended in the pumping of the air through the cycle. Not all of the horsepower produced in the engine can be used to turn the propeller, Some of it must be used to overcome these internal resistances.

  • FRICTION HORSEPOWER is measured in a laboratory by driving the engine with a calibrated motor and noting the power required.

• Brake Horsepower

  • BHP is the actual amount of horsepower delivered to the propeller.

  • IHP – FRICTION HP = BHP

  • Measured with a calibrated dynamometer that turns engine power into an electrical signal or a hydraulic pressure. In years past, it was measured with a Prony Brake. A device that put a calibrated load on the shaft and measured torque in ft/lbs.

  • Torque is then used to indicate horsepower at the shaft by using the formula BHP = (2 X 𝜋 𝑋 𝑡𝑜𝑟𝑞𝑢𝑒 𝑋 𝑅𝑃𝑀)/ 33,000

  • Example: An engine develops 600 ft/lb of torque at 2700 rpm.

    6.28 X 600 X 2700 = 10,173,600 = 308.3 BHP

    33,000 33,000

• Engine Displacement

  • Cylinder displacement is a measure of the volume of air moved through the engine as the crankshaft rotates through 720 degrees.

  • CID = Piston area x Length of stroke x # of cylinders.

  • Example

    • Piston diameter— 4”

    • Length of stroke—6

    • Number of cylinders—6

    • 3.1416 x 4= 12.56 x 6 x 6 = 452.39 CID

• Rare Bear - The fastest piston powered aircraft in the world at 528 mph

  • 3,350 cubic inches

  • 4000 @ 3,200rpm and 80”MAP

  • 4,500 with Nitrous oxide

• There is no replacement for displacement

• Engine Efficiency Considerations

  • Energy is the capacity for doing work and cannot be created or destroyed.

  • Energy can be transformed from potential (stored) to kinetic.

  • Aircraft engines transform the chemical energy stored in the fuel into heat energy through the combustion process. The heat energy is then transformed into kinetic energy through mechanical means.

  • Several factors such as engine design, fuel type and environmental conditions affect how efficiently an engine converts the energy into useful work.

  • The typical efficiency factors addressed for aircraft engines  are: thermal, volumetric and mechanical.

• Thermal Efficiency

  • Thermal efficiency is a percentage that indicates the amount of useful work produced by the engine compared to the amount of heat energy available in the fuel.

  • This is a useful value for comparing similar engines. If two engines that produce identical amounts of horsepower are being compared, the one that has the lower fuel consumption rate converts a greater portion of the available heat energy into work and, therefore, has a higher thermal efficiency.

  • Most reciprocating engines are 30-40% thermally efficient.

    • 15-20% lost in cooling.

    • 5-10% lost in overcoming friction.

    • 40-45% lost through the exhaust!

  • How does turbocharging increase Thermal Efficiency?

• Volumetric Efficiency

  • VE is the percentage of how much air/fuel mixture is taken in on the intake stroke compared to total cylinder displacement.

  • If an engine drew in a volume of air and fuel exactly equal to cylinder displacement, then the volumetric efficiency would be 100%.

  • If an engine has a total engine displacement of 320 cubic inches and it draws in 288 cubic inches then the volumetric efficiency would be 90%.

  • Formula for Volumetric Efficiency is: Volume of Mixture/Total Cylinder Displacement

• Volumetric Efficiency Considerations

  • A normally aspirated engine will never achieve 100 percent Volumetric Efficiency.

  • A supercharged or turbocharged engine compresses the incoming air so these engines will commonly have volumetric efficiencies that exceed 100%

  • Any factor that decreases the density or volume of the incoming air decreases volumetric efficiency.

• Factors that Decrease Volumetric Efficiency

  • Part throttle positions restrict airflow into the engine and reduce volumetric efficiency.

  • Even at full throttle, the presence of the throttle plate causes about a 1” Hg. drop in MAP.

  • Induction Friction—Surface roughness in the induction system restricts airflow and decreases volumetric efficiency. The amount of friction present is proportional to intake pipe length and inversely proportional to their cross-sectional area.

  • High Induction Air Temperatures- As air temperatures increase, air density decreases so that on each intake stroke, less air enters the cylinders.

  • Elevated Cylinder Head Temperatures- High temperatures decrease air density, thereby decreasing volumetric efficiency.

  • Increases in Altitude-The density of the air decreases with increases in altitude at the rate of 1”Hg/1,000 Ft. So as the aircraft ascends, the amount of air entering the cylinders decreases. Since fuel flow remains constant-the mixture becomes progressively richer and volumetric efficiency decreases. This is why the mixture is leaned at altitude. supercharging and turbocharging minimize this problem by increasing the density of the incoming air at altitude

• Mechanical Efficiency

  • Mechanical Efficiency found by dividing brake horsepower by indicated horsepower.

  • This represents the percentage of the power produced in the cylinders that actually reaches the propeller.

  • Most reciprocating engines are 85-95% mechanically efficient.

  • The most significant factor that reduces mechanical efficiency is internal friction.

• Factors Affecting Power Production

  • Manifold Air Pressure (MAP)- The absolute pressure measured in the induction system. Directly controlled by the throttle. When RPM is held constant by the propeller governor, the throttle directly controls engine  power output. (Refer to PLANK formula)

    • Operating at excessively high MAP settings may cause premature engine  wear and the possibility of detonation.

  • Compression Ratio- The air/fuel charge must be compressed so that when heat is released, it will create a significant amount of reactive work

  • Compression ratio is the relationship between cylinder volume with the piston at BDC and cylinder volume with the piston at TDC

  • Example: If the volume of a cylinder with the piston at BDC is 140 cubic inches and the volume of the cylinder with the piston at TDC is 20 cubic inches the compression ratio would be 140:20 or 7:1

• Compression Ratio Considerations

  • As compression ratio increases, power production increases.

  • The compression ratio is a characteristic built into the engine by the designers.

  • The maximum compression ratio is limited by:

    • 1) Structural Limitations

    • 2) Detonation Resistance of the Fuel

    • 3) Degree of “charging”

• Compression Ratio and Detonation

  • The air/fuel mixture can only be compressed so much (critical pressure) before it will spontaneously combust.

  • Detonation is a destructive phenomenon that is a real possibility in an aircraft engine.

  • Typically, the air/fuel mixture ignites normally and as the flame front moves across the combustion chamber it compresses the remaining air/fuel mixture in front of it until the critical pressure it  reached, and the remainder of the charge combusts

  • NOTE—Detonation is different from PRE-IGNITION—Know the difference between them.

• Compression Ratio and “Charging”

  • A supercharged or turbocharged engine has an additional limitation imposed upon it regarding compression ratio.

  • Since the compressor increases the pressure (and temperature) of the intake air, and both these factors reduce detonation resistance, the compression ratio on these engines must be carefully established by the designers.

  • “Charging” does not increase compression ratio but it does increase manifold pressure and mean effective pressure in the cylinder that does decrease anti-detonation margins.

• Factors Affecting Power Production

  • Ignition Timing- For complete combustion and maximum working pressures to be generated, the ignition event must be precisely timed. For most TCM and Lycoming engines, ignition occurs from 20° to 32° BTDC on the compression stroke.

  • If ignition occurs too early, the expanding gases push back against the work of the compression stroke.

  • If ignition occurs too late, the gases expand as the piston is moving away on the power stroke and minimal pressure is created. In addition, the exhaust valve will open as the air/fuel mixture is still burning and the face of the valve will be heated and damaged. This could cause pre-ignition.

  • Engine Speed- The faster an engine turns, the more power it produces. (PLANK formula)

  • There are several factors that limit the maximum RPM for a particular engine:

    • 1) ignition timing (point float)

    • 2) valve timing (valve float)

    • 3) inertial effects of reciprocation

    • 4) propeller tip speed limitations (Gear reductions)

  • Air/Fuel Ratio- The fuel must be vaporized and mixed with the proper amount of air for combustion to take place.

  • The perfect or “stoichiometric” mixture is 15:1. In reality the best power mixture is slightly richer than stoichiometric.

  • Burnable mixtures range from 8:1 (rich) to 18:1 (lean)

  • NOTE-It is not a “fuel/air” mixture it is an “AIR/FUEL” mixture. (air is referred to first in the ratio)

  • Why is the stoichiometric mixture important for leaning an engine?

Reciprocating Engine Combustion Basics

• The internal combustion engine is a “heat” engine in that it uses heat to cause a gas (air) to expand and generate a force that acts on the crown of a piston creates power.

• The combustion of the air/fuel mixture must be accurately controlled and the mixture ratio maintained across the power range of  the engine.

• There must be some means for the pilot to control engine power output.

• There must be a means for delivering a burnable mixture in the correct quantity to produce the desired amount of power across the designed power range of the engine. This is FUEL METERING.

• Mixture Ratio

  • Gasoline will not burn in the liquid state.

  • It must be vaporized and combined with the correct amount of oxygen to create a burnable mixture.

  • If there is excess air to fuel, the mixture is too “lean” and will not burn.

  • If there is too little air to fuel, the mixture too “rich” and will not burn.

  • Gasoline will burn in a cylinder with a mixture ratio ranging from 8:1 “rich” to 18:1 “lean” by weight.

    • NOTE—It is not uncommon to see mixture ratios expressed as a decimal equivalent.

    • Ex. 12:1 may be expressed as .083 (1/12).

  • The mixture ratio that provides perfect combustion is 15:1 (.067)

  • This provides 1lb of air for .067lbs of fuel by weight

  • With this mixture, all O2 molecules combine with available gasoline molecules with non left over

  • This mixture is called the “Stoichiometric Mixture”

  • The result of this “perfect combustion” process is heat+water vapor+CO2

  • 2C8H18+25O2=HEAT+16CO2+18H2O

  • In theory, the stoichiometric mixture would provide maximum heat release and, therefore, maximum power production with an exhaust made up of only carbon dioxide and water vapor

  • In reality, due to combustion inefficiencies, the mixture required to produce “best power” is substantially richer than stoichiometric.

  • Because of this, combustion is always somewhat incomplete. Therefore, the results of combustion are HEAT + C𝑂_2 + 𝐻_2 O + CO (Carbon Monoxide!)

• Mixture Terminology

  • Rich/Lean: Relative terms that indicate variations in mixture.

  • A lean mixture has more air added OR fuel removed from the mixture.

    • Ex.- A 10:1 mixture is leaner than an 8:1 mixture.

  • The air/fuel mixture is a pilot controllable variable. As such, the following terms are important to the concept:

  • Full Rich: In this position, the mixture control is full forward providing the most rich air/fuel mixture. This is the common mixture setting for ground operations EXCEPT for high altitude airport operations.

  • Idle Cut-Off (ICO): In this  position, the mixture control is in the full aft position. All flow through the metering device is cut off. This position is used to shut down an aircraft engine as the engine will continue to run until all residual fuel is consumed from the induction system. This reduces the chances for a prop-strike injury.

  • Lean Best Power/Rich Best Power: The best power mixture is the mixture ratio that results in the most heat energy being released and, therefore the most power being produced by the engine. Best power is created over a slight air/fuel mixture range with the bottom of the range being “lean best power” and the top of the range being “rich best power”. These values are determined by reference to the power chart and leaning procedures for a particular engine.

  • Best Economy Mixture: This is the mixture ratio that results in the greatest amount of engine power for the least amount of fuel consumption. This usually results from a particular MAP/RPM combination coupled with the manufacturers leaning procedure.

  • Leaning:  The process of adjusting the air/fuel mixture for the existing altitude or conditions. As altitude increases air density decreases but the amount of fuel being delivered into the induction airflow remains the same. The result is a mixture that enrichens as altitude increases. At power settings below 70%, the mixture can be leaned to reduced for economy and to adjust for the effects of altitude on the A/F mixture. In addition, the mixture can be leaned on the ground at high altitude airports to assure that full power is available on take-off. (It is an accepted practice to lean on the ground in all cases to reduce sparkplug fouling during ground operations. REMEMBER TO ENRICHEN THE MIXTURE FOR TAKEOFF!!).

• Leaning

  • Leaning is the process of reducing fuel flow in relation to airflow in order to maintain the ideal air/fuel mixture in the cylinder for a particular mode of flight.

  • Engines are typically leaned:

    • 1) On the ground to prevent sparkplug fouling.

    • 2) At high elevation airports to allow the engine to produce maximum power for TO

    • At cruise power at altitude to reduce fuel flow and compensate for the decrease in air density.

  • Leaning-Fixed Pitch Propeller-No EGT:

  • Leaning with an EGT:

  • Leaning with Fuel Injection/Fuel Flow Indicator:

  • Leaning with Turbocharging:

• Leaning- No EGT

  • Light aircraft with fixed-pitch propellers usually are leaned by setting recommended cruise power RPM as specified in the POH or AFM and them slowly leaning the mixture until the engine roughens and there is a drop in RPM.

  • At this point, the mixture is enrichened until  the engine operates smoothly.

• Exhaust Gas Temperature Indicators EGT

  • The exhaust gas temperature gauge was developed in the 1960’s and is a common instrument in certificated aircraft.

  • The EGT is a thermocouple system using probes made of iron and constantan.

  • Remember—A thermocouple system requires no external electrical power as it generates its own when heated.

  • EGT systems may be simple systems that indicate the temperature of a single cylinder or a multi-probe system that is part of an overall “graphic engine monitoring” system.

  • The basic system as designed by Alcor has a gauge with 25° increments but no indication of actual temperature.

  • There is usually an asterisk at the 80% point for reference.

  • There is a moveable reference needle that is pilot settable that is used to indicate “peak”.

• Multiple Cylinder EGT

  • Some EGT indication systems are coupled with a computing system that integrates EGT and CHT into a system that gives real-time indications of all cylinders simultaneously with the ability to lean with reference to the first cylinder to “peak”.

  • A very useful tool for overall engine performance monitoring. (Actual EGT temperature indications can be misleading and confusing for most pilots-Alcor 25° increment system may be better).

• Leaning with EGT

  • The recommended leaning procedure will be outlined in the POH or AFM.

  • Once cruise power is set, the mixture can be leaned slowly with reference to the EGT (and the Tach if you look close enough).

  • As the mixture is leaned, the EGT indication will increase. At some point movement of the mixture control aft will no longer produce an increase in EFT. This is “peak”.

  • Peak is the “stoichiometric” point and is an unchanging reference point that the pilot can locate each time.

  • The mixture is then enrichened until the recommended setting is reached. (25° to 100° ROP)

  • In some cases, there are aircraft with power settings that allow LOP mixtures.

• Leaning with Fuel Injection (Fuel Flow Indicator)

  • Aircraft with TCM or Bendix fuel injection will usually have a fuel flow gauge that indicates fuel flow in GPH.

  • It must be noted that the gauge is NOT a true flow meter. It is a pressure gauge that indicates the total pressure drop across the injector nozzles. (The pressure drop across an orifice is directly proportional to the flow through the orifice).

  • The mixture can be set to a particular fuel flow as specified in the POH or AFM.

• Leaning a Turbocharged Engine

  • Due to the high temperatures involved, great care must be exercised when leaning a turbocharged engine.

  • In addition to EGT and Fuel Flow, a Turbine Inlet Temperature (TIT) gauge is monitored as the temperature of the exhaust gases driving the turbine are directly affected by the air/fuel mixture.

  • The mixture control must be moved slowly to allow time for all variables to stabilize. Below critical altitude the process is fairly straight forward. Above critical altitude the waste gate is fully closed and all available exhaust gases are driving the turbine, therefore any change in air/fuel mixture affects the mass of the exhaust gases and, therefore, turbine speed which, in turn affects compressor output. So—movement of the mixture control will affect MAP!

• Combustion Anomalies

  • During normal combustion, the air/fuel mixture burns in a smooth and predictable way. Pressures rise smoothly in the cylinder and create a smooth force on the crown of the piston with an increase to maximum at the correct time during the power stroke.

  • Detonation: Detonation is the uncontrolled explosion of the air/fuel charge in the cylinder. The heat generated pressure “spikes” over a short period of time which focuses the heat and pressure on the crown of the piston in the form of an intense pressure wave.

  • This can cause power loss, engine roughness, overheat and eventually cylinder/engine destruction.

  • Typically caused by excessive air/fuel charge temps and pressures, lean mixture or operation with lower than specified octane rating.

  • Always occurs AFTER the normal ignition event.

  • Pre-Ignition: The ignition of the air/fuel charge prior to the normal ignition point. This causes power loss and engine heating that perpetuates the problem or can lead to detonation.

  • Caused by something in the combustion chamber acting as a “glow-plug” and acting as an ignition source. May be caused by carbon deposits, oil droplets, cracked ceramic on sparkplug or feather-edged valve.

  • Backfiring: The ignition of the air/fuel charge in the induction system that causes it to “blast” back through the induction system and fuel metering device. Caused by excessively lean mixtures that slow the flame speed so that the air/fuel charge is still burning when the intake valve opens.

  • May cause damage to fuel metering device or cause an air filter fire.

  • Afterfiring: The burning of the air/fuel mixture when the exhaust valve opens.

  • When the exhaust valve opens, the exposure of the charge to free oxygen in the exhaust manifold cause it to burn down the exhaust system and out the exhaust stack with a bright orange bushy flame.

Fuel Metering

• Aviation Carburetors

  • Early aircraft engines had no real fuel metering system.

  • They dripped fuel onto balsa wood balls contained in a metal box that was heated by exhaust heat to cause vaporization.

  • The vaporized fuel was drawn into the engine induction system through normal aspiration.

  • There was no throttle and the engine ran at full power all the time.

  • Power could be varied a few hundred RPM by advancing and retarding the timing and power could be interrupted with a “blip” switch on the stick.

  • In 1916, a carburetor very similar to the ones in use today was developed by the French.

  • “Hydrocarbon Burette”– “Carburetor”

  • Had a throttle to control power, a stable mixture across the power range and the ability to control mixture.

  • Used a float bowl to establish the fuel to air relationship and a venturi to created a proportional metering force.

  • Carburetors can be down draft, updraft and in some applications such as the Marvel-Schebler (Facet) HA-6, a side draft.

  • In a float type carburetor, the metering force is the pressure drop at the throat of a venturi.

  • Remember-A venturi is a specially shaped orifice that has a restriction that causes a transformation of energy when a gas or liquid flows through it.

  • The pressure drop at the throat of the venturi is directly proportional to the volume of air flowing through it. In turn, this low pressure can be used to draw fuel off of the discharge nozzle in the proper proportion.

  • A reciprocating engine is in essence a reciprocating air pump. For each two revolutions of the crankshaft, the engine attempts to “breathe” a volume of air equal to it’s displacement.

  • Because of this, the power output of the engine may be controlled by the pilot by installing a “throttle plate” in the induction system.

  • By combining the proportional metering capability of a venturi with the air-flow controlling throttle plate, a means of accurately controlling engine power is possible.

  • To meet all requirements for aviation applications, a functional carburetor (or any fuel metering system) must have the following systems:

    • Main Metering

    • Idle Metering

    • Accelerating

    • Power enrichment/economizer

    • Mixture (Manual/Automatic or both)

• Float Carburetors

  • The most common type of aviation carburetor is the “float” type.

  • A float bowl with a needle-valve and seat are used to control flow of fuel into the carburetor.

  • The “height” of the float level is set by the mechanic and proportions the air/fuel mixture across the engine power range. The distance from the fuel level to the fuel discharge nozzle opening is called the “Fuel Metering Head”.

• Air Bleed

  • Due to surface tension, the fuel has a tendency to stick to the walls of the discharge nozzle and flow into the airstream in a series of slugs or “blobs” rather than as a fine aerated mist.

  • To break the surface tension and increase the atomization tendency of the fuel, an air bleed is incorporated into the main metering system.

  • The air bleed system allows a controlled amount of ambient air to be drawn from an area behind the venturi and diffused into the fuel flow downstream of the main metering jet.

  • This aerates the fuel, breaks the surface tension and breaks the fuel into smaller particles that more readily atomize at the discharge nozzle.

• Power Enrichment/Economizer System

  • At higher power settings an air-cooled engine needs additional cooling to prevent overheating and the potential for detonation.

  • The power enrichment system enrichens the air/fuel mixture at power settings above 70% power.

  • The additional fuel cools the cylinder as it vaporizes.

  • The system may also be referred to as an “economizer” system as it allows for a leaner mixture to be used at lower power settings and only enriches at settings above 70% power. (Older applications had to run a mixture that was rich across the power range to assure a rich enough mixture at the higher power settings).

  • Two types of power enrichment systems may encountered; 1) the Needle type and 2) the Air Bleed type.

• Induction Icing

  • Engines equipped with carburetors are susceptible to three types of icing:

    • 1) Throttle Ice

    • 2) Fuel Evaporation Ice

    • 3) Impact Ice

• Induction Heating

  • Carbureted engines will be equipped with a carburetor heat system.

  • Fuel Injected engines will be equipped with an alternate air system. (FI engines are still susceptible to impact icing.)

• Introduction

  • The pressure carburetor is a completely pressurized system.

  • Fuel will be accurately metered regardless of attitude or G loading.

  • Fuel is pushed out the discharge nozzle under a positive head of pressure. No differential pressure causing fuel discharge is used.

  • Since there is no fuel evaporation within a venturi, the chance of carburetor icing is drastically reduced.

  • These carburetors were common on the Beech Bonanza and Travel Aire/Baron and the Navion in the 1950’s. (Bendix PS-5)

  • Aircraft fuel metering systems have evolved over many years.

  • Float carburetors have and continue to serve as highly effective fuel metering devices in a wide array of aircraft.

  • Although float carburetors are effective, they have several limitations that motivated innovation in the area of fuel metering systems.

  • Pressure Injection Carburetors were developed on the 1940’s to address carburetor limitations associated with g loading and flight attitude. (A huge issue in WWII). These carburetors prevented the occurrence of throttle ice and reduced the occurrence of fuel evaporation ice, although its occurrence was still possible.

  • Pressure Carburetors did not address the fuel distribution issues associated with induction manifolds.

• Float Carburetor Limitations

  • The float carburetor has the following limitations that have had to be addressed to some degree:

    • 1) Performance affected by g loading and flight attitude.

    • 2) Propensity to form throttle ice and fuel evaporation ice.

    • 3) Variation in air/fuel mixture for each cylinder due to induction manifold concept.

• Aviation Fuel Injection

  • Fuel injection addresses all limitations associated with previous fuel metering systems.

  • In addition, fuel injection improves fuel economy, smoothness of engine operation and increased horsepower production.

  • The earliest fuel injection systems used on aircraft were developed in Germany in the 1930’s and used throughout the war by them and the Japanese.

  • These systems were complex and were of the “Direct Injection Type” where fuel was injected directly into the cylinder in the form of a timed high pressure pulse similar to what is done in a diesel application today.

  • Daimler Benz DB601 Direct Injection Pump

  • By the time WWII ended in 1945, direct fuel injection was adopted the allies and used on a wide array of aircraft including the B-29.

  • When fuel injection was developed for light GA applications in the 1960’s, a simpler “Continuous Flow System” was used.

  • “Continuous Flow” fuel injection delivers fuel through an injection nozzle into the intake port just upstream of the intake valve.

  • These systems are must simpler in application although they do require an accurate metering system in order to deliver the correct amount of fuel to meet engine demand.

  • Today fuel injection is rapidly replacing carburetors in the GA fleet.

    There are two types of fuel injection systems the mechanic will encounter in the field:

    • 1) Bendix RSA (Precision Airmotive)

    • 2) Teledyne Continental Motors (TCM)

• Bendix (Precision) RSA Fuel Injection

  • The RSA system was developed by the Bendix corporation and is the system that will be encountered in Avco Lycoming engines.

  • The system is currently owned and supported by Precision Airmotive.

  • The system is an outgrowth of the Bendix PS series pressure injection carburetor.

  • The theory of operation is identical in most respects to the pressure carburetor. The exception is that instead of delivering the fuel to a central discharge nozzle, it is delivered to a flow divider and from there to each individual cylinder via an injector nozzle.

  • Bendix PS7 Pressure Carburetor

• RSA Fuel Injection

  • The central component of the system is the “venturi housing”.

  • This device is made of cast aluminum and has a venturi installed at one end and the throttle plate at the other. All engine induction air flows through this device.

  • In addition, the fuel metering unit and the fuel regulator are cast as one piece into this unit. (The components are illustrated in the text as separate units for clarity).

• Flow Divider

  • When the engine is operating above idle power, the pressure of the fuel off-seats the diaphragm valve and flows directly to each injector line with the injector nozzles themselves causing the back pressure that affects the fuel metering force.

  • At idle power settings, the flow through the injection nozzles is insufficient to create the back pressure required to produce the metered fuel pressure.

  • In this mode, the spring in the flow divider forces the valve to a closed position that offers a resistance to fuel flow. This creates a stable metered fuel pressure.

  • In addition, when the engine is shut down, the spring forces the valve closed creating a positive fuel shut off.

• Engine Starting with the RSA System

  • Starting an engine with the RSA system, the mixture will be in the ICO position.

  • Master Switch— “ON”

  • Boost Pump--- “ON”

  • Mixture to “FULL RICH”-monitor fuel flow indication to prime then back to ICO.

  • Magnetos “ON” –Starter Engaged

  • When engine catches---Mixture to FULL RICH

• Teledyne Continental Motors Fuel Injection

  • The TCM fuel injection system is simpler than the Bendix RSA system in that there are no diaphragms, no venturi, no air metering force, no ball valve etc.

  • The sensing element of the system is a positive displacement rotary-vane type pump.

  • The system is made up of:

    • 1) Injection Pump

    • 2) Fuel/Air Control Unit

    • 3) Manifold Valve

    • 4) Injection Nozzles

  • Cessna 185 Skywagon

Aircraft Reciprocating Engine Cooling and Lubrication

• Aircraft Engine Cooling

  • Even though water cooling has been used in aviation applications in the past, currently air cooling is the norm with a few exceptions.

  • The advantage of water cooling is uniform and effective cooling.

  • The disadvantage of water cooling is related to the weight of the associated components and the drag associated with the radiator.

  • Most modern piston powered aircraft utilize air cooling.

  • The system is configured to create a pressure differential that forces air to flow across the fins of the cylinders and into target areas to carry away heat.

  • Engine baffles, baffle seals and blast tubes direct cooling air to critical areas.

  • Fixed or moveable cowl flaps are used to control cooling.

  • Some older aircraft used “Augmenter Tubes” to “augment” or enhance the volume of air that flowed through the cowling, thereby allowing for tighter, more streamlined cowlings while maintaining effective cooling.

  • Makes airplane sound Great!

  • Very loud.

• Lubrication Systems

  • The lubrication system is extremely important to the life and continued reliability of the aircraft piston engine.

  • The oil truly is the “life blood” of the engine.

  • Any loss of the oil supply, oil pressure or flow will cause an imminent engine failure.

• Functions of Engine Oil

  • Lubrication

  • Cools

  • Seals

  • Cushions

  • Prevents Corrosion

  • Hydraulic Function

  • (Lifters, Constant Speed Prop, Wastegate)

• Aircraft Piston Engine Lubrication System

  • The lubrication systems used in piston powered aircraft may be:

    • 1) Dry Sump Configuration

    • 2) Wet Sump Configuration

• Dry Sump Lubrication System

  • Oil supply is contained in a reservoir separate from the engine.

  • A pressure pump pushes oil through the engine.

  • A scavenge pump returns oil to the reservoir via an oil cooler.

  • Common to radial engines and many older horizontally opposed engine installations.

• Wet Sump Lubrication Systems

  • Common to most modern piston powered aircraft.

  • Oil supply is contained in an enclosed area of the crankcase (sump).

  • Similar to an automotive application.

Propellers

• A propeller is a mechanical device that converts horsepower into thrust.

• Early propellers were merely paddles that pushed air backwards.

• The Wright brothers were among the earliest researchers to understand propeller airfoil theory.

• As stronger materials became possible, thinner, more efficient blade sections were possible.

• The modern propeller is a rotating airfoil.

• It makes thrust much like a wing makes lift.

• This also means that it will also have a critical angle of attack like a wing.

• The propeller can be hypothetically “sectioned” into an infinite number of slices, with each slice having a different blade angle and resultant angle of attack. (Dreiwycki theory)

• The propeller is formed with a “blade angle”. This is the angle formed between the blade chord line and the plane of rotation.

• The “resultant” angle-of-attack is created through the relationship of RPM and Airspeed.

  • RPM constant/Airspeed 0---Blade angle=AOA

  • RPM constant/Airspeed >---AOA decreases

  • RPM >/Airspeed constant---AOA Increases

• The most effective angle-of-attack for a propeller is between 2-4 degrees.

• Therefore, blade angles that produce a resultant angle of attack ranging from 2 to 4 degrees are ideal, but a challenge for engineers because the speed of the propeller varies from blade root to tip.

• Because the speed of the blade varies from root to tip, various airfoil sections and blade angles are required so the ideal resultant angle of attack will be created at the airspeed/RPM combination expected for that aircraft.

• The blade angle will be higher near the blade root and the airfoil selected for this area will be of the “low speed” variety.

• The blade angle will be flatter near the tip and the airfoil selected will be of the “high speed” variety.

• This gives the blade a “twist” when viewed from the tip. This is called blade twist or “PITCH DISTRIBUTION”.

• Notice that the resultant angle-of-attack is the product of RPM/Airspeed. So…a propeller will only be at max. efficiency at a particular RPM/Airspeed range.

  • (Either high RPM/Low Airspeed or Low RPM/High Airspeed)

• For fixed pitch propellers, you only have three choices:

  • Climb Propeller, Cruise Propeller, Standard or compromise

  • (Notice: A constant speed propeller will always be the optimum prop for any RPM/Airspeed combination)

• FORCES ACTING ON A PROPELLER:

  • Centrifugal Force: the greatest single force acting on the prop. Can be as high as 7,500 g!

  • Thrust Bending Force: The force that attempts to bend the blades forward at the tips.

  • Torque Bending Force: A force that attempts to bend the blades in the opposite direction of rotation.

  • Aerodynamic Twisting Moment: A by-product of thrust production that causes a force that attempts to increase blade angle.

  • Centrifugal Twisting Moment: Opposes Aerodynamic Twisting moment. Attempts to decrease blade angle.

• PROPELLER PITCH: Propeller pitch is the theoretical distance a propeller will advance in one revolution.

• GEOMETRIC PITCH: The distance in inches that a given propeller will move forward (through a solid medium). This is measured at the 75% blade station.

  • ex. A “51” propeller means it would travel 51” forward in one rotation.

• EFFECTIVE PITCH: The actual distance a propeller will move forward through the air in one revolution.

  • (This will range from 0 when the aircraft is not in motion to about 90% of the geometric pitch at optimum RPM/Airspeed.

• The difference between geometric and effective pitch is called “SLIP” and represents the efficiency of that particular propeller.

  • EXAMPLE: If a propeller has a geometric pitch of 50 inches, in theory it should move forward 50 inches in one revolution.

  • If, in reality, it moves forward only 35 inches in one revolution, the effective pitch of the propeller is 35 inches and the efficiency is 70%

  • (Slip represents 15 inches or a loss of 30%)

  • In reality, most propellers are 75-85 percent efficient

• FIXED PITCH PROPELLER CLASSIFICATIONS:

  • As previously stated, a fixed pitch propeller is only suited for one RPM/Airspeed combination. Out if this narrow range, the propeller will be operating at something less than optimum efficiency.

  • A prop with a fairly low blade angle will allow the engine to develop maximum RPM for aggressive take-off and climb. But at altitude, as airspeed increases to cruise levels, the prop will be making more drag than thrust. This would be known as a CLIMB PROP. .(Sometimes known as a SEAPLANE PROP)

  • A prop with a relatively high blade angle will create more engine load that will equate to a lower RPM for takeoff. This will cause a longer take-off roll and lower rates of climb. But, when the aircraft is at cruise airspeeds, the propeller will be at optimum efficiency and high cruise speeds will be produced. This would be known as a CRUISE PROP.

  • Some manufacturers will make a “STANDARD PROP available to customers. It is a compromise. It isn’t a great climb prop and it isn’t a great cruise prop, but it is a good compromise between these two extremes.

• ADJUSTABLE PITCH PROPELLERS

  • Very early on, the limitations of fixed pitch propellers became evident.

  • The early barnstormers usually carried two props. Not only for a spare, but one was usually a climb prop and the other a cruise prop.

  • Not very convenient, but necessary at times.

• GROUND ADJUSTABLE PROPELLER

  • (Late 1920’s-Early 1930’s)

  • A propeller that allowed each blade clamp to be loosened and blade angle adjusted between a low pitch and high pitch position.

  • A step in the right direction, but still not a perfect solution.

• CONTROLLABLE PITCH PROPELLER

  • (Mid-1930’s)

  • Developed by the Hamilton Standard Company

  • Propeller had a hydraulic pitch change mechanism that allowed the pilot to select low pitch and high pitch positions with a control in the cockpit.

• CONSTANT SPEED PROPELLER

  • (Mid-Late 1930’s)

  • An outgrowth of the two-position prop.

  • Perfected by Hamilton Standard.

  • A governor is installed in the systems that allows the pilot to select an infinite number of blade angles (RPM) from the low pitch to the high pitch stop and the engine will constantly fine tune the angle to maintain the selected RPM.

• CONSTANT SPEED PROPELLER

  • Primary advantage is that this propeller system will convert a high percentage of engine power into thrust across a wide RPM/Airspeed range.

  • Another advantage is that it will maintain the RPM selected by the pilot allowing for consistent power management and fuel consumption.

  • Engine power controlled by the throttle and monitored with a MAP gauge. RPM controlled by the Prop control and monitored with a tachometer.

  • On multi-engine installations the propellers will move through the high pitch stop and allow the blades to FEATHER. This stops rotation and drastically reduces drag.

  • The propeller governor allows the pilot to select the desired RPM and them will maintain that RPM should engine power or air load vary.

• The governor uses two sensing variables to control oil flow to/from the propeller pitch change mechanism.

  • Centrifugal Force on the flyweights (RPM)

  • Spring tension on the speeder spring

• When the pilot moves the prop control to select at desired RPM, they are actually varying the tension on the speeder spring.

• There are three modes of operation for the governor:

  • “ON-SPEED”-Spring tension is equal to centrifugal force.

  • “OVER-SPEED”-Centrifugal force is greater than Spring tension. (Generates corrective force that will increase blade angle)

  • “UNDER-SPEED”-Spring Tension is greater than centrifugal force. (Generates corrective force that will decrease blade angle.)

• In Single-Engine installations:

  • Oil pressure/Aerodynamic Twisting Moment---Increase Blade angle

  • Centrifugal twisting moment/counterweights/spring tension---Decrease Blade Angle

• In Multi-Engine installations:

  • Aerodynamic twisting moment/counterweights/spring tension/nitrogen charge---Increase Blade angle (and feather)

  • Oil pressure/centrifugal twisting moment---Decrease Blade Angle

• CONSTANT SPEED PROPELLER

  • By having the ability to control engine MAP and engine RPM individually, very accurate power management can be achieved.

  • Look at the formula for INDICATED HORSEPOWER:

    • INDICATED HORSEPOWER: (P x L x A x N x K) / 33,000 = IHP

    • Where:

      P= Pressure in cylinder on the power stroke.

      L= Length of stroke (in feet)

      A=Area of piston in square inches.

      N= Number of power strokes/minute.

      K= Number of cylinders

  • Notice that of all the variables that make up the “PLANK” formula, only two are “pilot controllable”.

    • Pressure in the cylinder---MAP (throttle)

    • Number of power strokes/minute---RPM (prop)

  • Example:

    • An engine produces 200 IHP at 23” and 2300rpm

    • If the prop control is advanced to 2400rpm, MAP must decrease to a lower value.

    • If the RPM is reduced to (say) 2200rpm, the MAP must increase to a higher value

    • (Remember the PLANK formula)

  • This is why the operation of the prop control affects MAP.

  • (It should be noted that it is possible to damage the engine if the manifold pressure is too high for a given RPM.

  • Remember:

    • When reducing power, reduce MAP and then RPM.

    • When increasing power, increase RPM and then MAP

    • “KEEP THE PROP MORE FORWARD THAN THE THROTTLE”

  • Power settings for airplanes with constant speed propellers are a MAP/RPM combination.

    • 23”/2300---Square Setting

    • 20”/2300---Under Square Setting

    • 23”/2100—Over Square Setting

Class

Mix some copper with aluminum alloy and aluminum gets strong as steel almost

Our plane 2024T3 something metal. Means copper main alloy in aluminum

32/1000 inch thick metal for our plane

Aluminum almost impossible to weld, that’s why riveted??

Used to use Elmer’s glue on planes…???

Then hide glue

Many crank case made out of cast iron

Aircraft engines have difficulty with fuel distribution and lubrication

2 stroke engine mix oil and gas???

Air show in NY state with old planes

Schneider Cup

…we have lead in avgas

P-51 not a mass produce-able plane since every piece is very specific and different

Radiator and cooling drag

Fins for cooing

European planes expect pilots to perform, American design expect engine to

“if you flew, you flew a J-3 cub”

I- Fuel injected

O- Opposed

A- Aerobatic

• Flange beefier

• Better oil system

• Fuel system pressurized

G- Gear reduction

T- Turbocharge

S- Supercharge

Pratt and Whitm

TCM- Teledyne Continental Motors (manufacturer like Lycoming)

LYCOMING IS LIKE LYCOMING COLLEGE I miss that place

Lycoming have valve issue??? Something like that cause oil upside-down

Resonant frequency of engine

Vibration frequency can kill structure

Know it’s a 2-stroke engine when you have to add oil to the fuel (Like the 4-wheelers)

4 stroke cycle called Otto cycle after August Otto

Our engine has dynafocal mount to help not shake

Anodizing

Sacrificial corrosion

Prop Wiggles

Rings made out of grate cast-iron

Piston Rings go on piston to make gas-tight seal

Oil rings go on piston to keep oil from going up into combustion chamber

Service window engines (basically within warranty), new engines, overhaul engines (taken apart and fixed)

Scraper ring & bevel upward or downward determine thickness of oil lubrication film

Our engines usually have choke cylinder which means top of cylinder just a teeny bit narrower which allows for expansion without messing with compression

Crankshafts hammer forged, looks like a key to me

VAR = Vacuum arc remelt

Camshaft has to be timed to crankshaft so both have timing gear that go together

Valve train

Max speed for prop is about 3000rpm (not actually practical)

Lycoming starter in front

Planetary gear reduction

Spur gear reduction

JAARS? Dad would be interested in the odd bible people

Turbonormalized engine has just enough boost to act like sea level normal conditions

Use a turbocharger to make up for that decrease in air density

centrifugal …peller

14 CFR Part 23

When you look at prop from inside plane, you see the face. When looking at from outside you see the back

Blade twist aka pitch distribution

Cruise prop or climb prob, Cessna uses standard which is like middle

Climb prop for flight school

Controllable pitch propeller =/= constant speed, but very similar. More like intermediary to constant speed

7 Purposes of Oil

• Lubricaion

• Cleaning

• Sealing

• Cooling

• Prevent corrosion

• ?

• ?

Exercises